CN118284992A - Composition for forming electrode active material layer for lithium ion secondary battery - Google Patents

Abstract

A composition for forming an electrode active material layer for a lithium ion secondary battery, which comprises an electrode active material and carbon nanotubes, wherein the content of carbon nanotubes is 0.01-1.4% by mass, and the content of electrode constituent materials other than the electrode active material and the carbon nanotubes is 0-10.0% by mass, based on 100% by mass of the total composition, and which enables the production of a battery having a longer life. After discharging from the state of SOC100% to the state of SOC90% at 25 ℃ and 2.5C or more, the rest is performed for 10 minutes, and the increase in voltage during the rest is measured, and the internal resistance is calculated by the following equation (2): internal resistance= (rise of voltage during rest (V)/current value at discharge (a)) ×opposing area of positive and negative electrodes (cm ²) (2), the non-uniformity of reaction in the battery, which is a factor of abrupt decrease in capacity (secondary degradation), can be evaluated.

Description

Composition for forming electrode active material layer for lithium ion secondary battery

Technical Field

The present invention relates to a composition for forming an electrode active material layer for lithium ion secondary batteries.

Background technique

The lithium-ion battery (LIB) industry has achieved rapid growth through continuous technological development aimed at miniaturization and lightness of portable devices and high functionality (pursuit of convenience) by effectively utilizing its high energy density, high voltage, and safety characteristics. At present, with global environmental and resource issues receiving attention, it is expected that policies such as the promotion of the popularization of eco-friendly cars and the conversion to renewable energy will continue to drive the growth of the lithium-ion battery market in the future. Thus, it is calculated that the application of lithium-ion batteries for personal electric vehicles (EV) and stationary power storage (balanced renewable energy, etc.) and the required lithium-ion batteries in 2030 will be about 10 times that of 2018. From the perspective of economic efficiency, such as the skyrocketing battery cost caused by the shortage of resources, it may happen that it is not preferred for users. Therefore, from the perspective of how to use a battery for a long time, from the perspective of reuse or resource recovery, the research and development of recycling has become active, and the extension of battery life is also effective from the perspective of life cycle assessment (LCA).

In addition, new proposals have been made about the existence of mobile bodies such as EVs. CASE and MaaS, which aim to further improve user convenience, are becoming a reality. There are signs that mobile bodies such as EVs will shift from personal ownership to sharing in the future. It is expected that in this process, the AIEV (Artificial Intelligence Electric Vehicle) that will be launched on the market in the future will be an EV equipped with AI, with automated driving and shared vehicles. The car is not owned by an individual but managed by a management company, which provides mobility services (CASE) and various services required by users in the vehicle (MaaS). In addition, driving control and charge and discharge control can also be implemented by the management company, so it is also possible to use it in consideration of battery life, safety, etc. Furthermore, by sharing the vehicle, the burden on the user can be reduced to about 1/5 compared to the case of personal ownership, so the economy is also excellent. That is, in the future, by replacing gasoline cars with AIEV (shared cars), private cars, which are the mainstream, can be expected to contribute to the global environment, reduce traffic accidents and traffic congestion, provide new means of transportation for aging and sparsely populated areas, reduce personal cost burdens, and effectively use travel time. Furthermore, AIEV can also function as a huge power storage system that automatically charges electricity generated by renewable energy with large fluctuations through the management system of the management company and discharges it as needed.

However, its realization requires reconsidering the development direction of the current mainstream lithium-ion batteries (Figure 1).

In particular, it is essential to dramatically extend the life of batteries installed in electric vehicles. In order to realize AIEV, unlike the situation of personal vehicle ownership, the total driving distance of the vehicle needs to be, for example, more than 500,000 km. If the battery life is at the current level, multiple battery replacements will be required, which will affect the economy and the resource problem will not be solved. Regarding the required battery performance, compared with the energy density (driving distance) and fast charging performance, which are the current mainstream requirements, more emphasis is placed on life. As a specific example, the energy density is ensured to be 400Wh/L in a single battery, and the vehicle driving distance is 200 to 300km when equipped with 20 to 30kWh, but as an actual service life, it is necessary to target more than 5 times the current life.

Summary of the invention

Technical problem to be solved by the invention

So far, various studies have been conducted on extending the life of batteries, but when the actual service life is targeted to be more than five times the current one, research from a new perspective is needed. The inventors have focused on the overvoltage factor in the present invention, compared with the degradation factors that have been widely studied in the past, such as degradation caused by oxidation and reduction of active materials and components, degradation accompanied by insertion and extraction of lithium ions into active materials, consumption of lithium ions caused by decomposition of electrolytes, and degradation caused by relaxation of electrodes.

The inventors and others were able to explain low-temperature degradation, secondary degradation, and other phenomena by defining a new degradation mechanism, "degradation caused by overvoltage factor (current × resistance)". Degradation caused by overvoltage factor is defined as a degradation factor affected by load current and battery resistance (DC resistance). For example, degradation during low-temperature cycling can be explained as being caused by an increase in resistance at low temperatures, and degradation caused by rapid charging can be explained as being caused by an increase in load current. In addition, when the battery deteriorates, the resistance increases, and further, when the capacity deteriorates, the load (apparent load) on the effective active material portion increases when the same current as the initial stage is applied. Furthermore, when gas or the like accumulates in the electrode group, since the gas does not permeate ions, a load is applied to the electrode portion and active material other than the gas accumulation. From this point of view, one factor that affects the life as an overvoltage factor is: there is a non-uniform reaction in the electrode. When the reaction occurs non-uniformly in the electrode, the active material used in the electrode, etc., accumulates a load in a part of the active material, etc. during the long-term use of the battery. For example, in the case of the negative electrode, it induces the consumption of lithium ions due to being placed in a local strong reduction. In the worst case, it induces lithium electrodeposition, etc. For example, in the case of the positive electrode, due to the induction of the degradation of the positive electrode active material caused by cracks, etc., when a certain number of charge and discharge cycles are repeated, a sharp decrease in capacity and a sharp increase in resistance (secondary degradation) almost always occur. By making the reaction of the electrode uniform and suppressing the non-uniformity of the reaction in the battery, the secondary degradation (sharp decrease in capacity) can be suppressed, and the life can be greatly extended. Therefore, it is important to make the reaction in the battery uniform, but the current situation is that there is almost no effort to make the reaction in the battery uniform.

In order to make the reaction in the battery uniform, it is important to make an electrode structure that can make the ion movement in the electrode uniform. As its means, so far, research has been carried out to increase the porosity of the electrode or reduce the weight per unit area of the electrode, but these methods are methods accompanied by a reduction in energy density (travel distance), so only by these methods, there is a limit from the above-mentioned point of view of ensuring the 400Wh/L level. In addition, although it is considered that from the point of view of making the ion movement in the electrode uniform, it is effective to exclude factors that can hinder the movement of ions in the electrode, the factors are generally used to give strength to the electrode. Adhesives, thickeners, dispersants, etc. are used to stabilize the electrode slurry. Electrode constituent materials, but when these constituent materials are reduced or eliminated, the strength of the electrode is significantly reduced, and the volume change of the electrode accompanying charge and discharge cannot be followed, and the current collection path is missing, etc., and the life characteristics are reduced instead.

The present invention is completed in order to solve the above-mentioned technical problems, and its purpose is to provide a composition for forming a negative electrode active material layer capable of manufacturing a further long-life battery. In addition, the present invention also aims to provide a method for evaluating the heterogeneity of the reaction in the battery which is the main cause of the rapid decrease in capacity (secondary degradation).

Technical solutions for solving technical problems

The inventors of the present invention have repeatedly conducted in-depth research in view of the above-mentioned technical problems. As a result, it was found that by setting the electrode constituent materials such as adhesives that can hinder the movement of ions in the electrode to be non-existent or extremely small, and using extremely small amounts of carbon nanotubes for current collection between active material particles, maintaining the shape of the electrode, etc., the electrode has a strength that can maintain the shape of the electrode, and it is not easy to hinder the movement of lithium ions, so that the reaction in the battery can be uniformed and the battery life can be extended. In addition, the inventors of the present invention also found that by calculating the internal resistance in the rest state after discharge under high load conditions, the non-uniformity of the battery reaction can be evaluated. The present invention is completed by further repeated research based on such insights. That is, the present invention includes the following structure.

Item 1. A composition for forming an electrode active material layer for a lithium ion secondary battery containing an electrode active material and carbon nanotubes, wherein:

When the total amount of the composition is set to 100% by mass,

The content of carbon nanotubes is 0.01 to 1.4% by mass.

The content of the electrode constituent materials other than the electrode active material and the carbon nanotubes is 0 to 10.0% by mass.

Item 2. The composition for forming an electrode active material layer for a lithium ion secondary battery according to Item 1, wherein

The content of the electrode active material is 96.6-99.9% by mass.

The content of the electrode constituent materials other than the electrode active material and the carbon nanotubes is 0 to 2.0% by mass, and

The composition is a composition for forming a negative electrode active material layer for a lithium ion secondary battery.

Item 3. The composition for forming an electrode active material layer for a lithium ion secondary battery according to Item 1, wherein

The content of the electrode active material is 97.4-99.9% by mass.

The content of the electrode constituent materials other than the electrode active material and the carbon nanotubes is 0 to 1.2% by mass.

Item 4. The composition for forming an electrode active material layer for a lithium ion secondary battery according to Item 3, wherein

The composition is a composition for forming a negative electrode active material layer for a lithium ion secondary battery.

Item 5. The composition for forming an electrode active material layer for a lithium ion secondary battery according to any one of Items 1 to 4, wherein

The content of the carbon nanotubes is 0.01 to 0.8% by mass.

The electrode active material contains an amorphous carbon material, and

The composition is a composition for forming a negative electrode active material layer for a lithium ion secondary battery.

Item 5-1. The composition for forming an electrode active material layer for a lithium ion secondary battery according to Item 5, wherein

The composition contains a conductive additive other than the carbon nanotubes,

When the total amount of the composition is 100% by mass, the content of the conductive additive other than the carbon nanotubes is 0.1 to 10.0% by mass.

Item 5-2. The composition for forming an electrode active material layer for a lithium ion secondary battery according to Item 5 or 5-1, wherein

When the total amount of the carbon nanotubes and the conductive additive other than the carbon nanotubes is 100% by mass, the content of the carbon nanotubes is 0.1 to 10.0% by mass.

Item 5-3. The composition for forming an electrode active material layer for a lithium ion secondary battery according to any one of Items 5 to 5-2, wherein

When the total amount of the composition is 100% by mass, the content of the electrode active material is 79.2 to 99.8% by mass.

Item 5-4. The composition for forming an electrode active material layer for a lithium ion secondary battery according to any one of Items 5 to 5-3, wherein

The composition contains electrode constituent materials other than the electrode active material, the carbon nanotubes, and a conductive auxiliary agent other than the carbon nanotubes.

When the total amount of the composition is 100% by mass, the content of the electrode constituent material is 0.1 to 10.0% by mass.

Item 6. A composition for forming an electrode active material layer for a lithium ion secondary battery containing an electrode active material and carbon nanotubes, wherein:

When the total volume of the composition is set to 100 volume %,

The volume ratio of the electrode active material is 75.06 to 99.97% by volume.

The volume ratio of carbon nanotubes is 0.02 to 4.55% by volume.

The volume ratio of the electrode constituent materials other than the electrode active material and the carbon nanotubes is 0 to 21.56 volume %.

Item 7. The composition for forming an electrode active material layer for a lithium ion secondary battery according to Item 6, wherein

When the total volume of the composition is set to 100 volume %,

The volume ratio of the electrode active material is 93.38-99.98% by volume.

The volume ratio of the carbon nanotubes is 0.02 to 2.18% by volume.

The volume ratio of the electrode constituent materials other than the negative electrode active material and the carbon nanotubes is 0 to 4.52 volume %, and

The composition is a composition for forming a negative electrode active material layer for a lithium ion secondary battery.

Item 8. The composition for forming an electrode active material layer for a lithium ion secondary battery according to Item 6, wherein

The volume ratio of the electrode active material is 96.19-99.98% by volume.

The volume ratio of the carbon nanotubes is 0.02 to 2.18% by volume.

The volume ratio of the electrode constituent materials other than the electrode active material and the carbon nanotubes is 0 to 1.63 volume %.

Item 9. The composition for forming an electrode active material layer for a lithium ion secondary battery according to Item 8, wherein

The composition is a composition for forming a negative electrode active material layer for a lithium ion secondary battery.

Item 10. The composition for forming an electrode active material layer for a lithium ion secondary battery according to any one of Items 1 to 9, wherein

The average particle size of the electrode active material is 0.1 to 13.0 μm.

Item 11. The composition for forming an electrode active material layer for a lithium ion secondary battery according to Item 10, wherein

The average particle size of the electrode active material is 0.1 to 13.0 μm, and the content thereof is 96.6 to 99.9% by mass.

The content of the carbon nanotubes is 0.01 to 1.4% by mass.

The content of the electrode constituent materials other than the electrode active material and the carbon nanotubes is 0 to 2.0% by mass, and

The composition is a composition for forming a negative electrode active material layer for a lithium ion secondary battery.

Item 12. The composition for forming an electrode active material layer for a lithium ion secondary battery according to Item 10, wherein

The average particle size of the electrode active material is 0.1 to 13.0 μm, and the volume ratio thereof is 93.38 to 99.98% by volume.

The volume ratio of the carbon nanotubes is 0.02 to 2.18% by volume.

The volume ratio of the electrode constituent materials other than the electrode active material and the carbon nanotubes is 0 to 4.52 volume %, and

The composition is a composition for forming a negative electrode active material layer for a lithium ion secondary battery.

Item 13. The composition for forming an electrode active material layer for a lithium ion secondary battery according to Item 1 or 10, wherein

The content of the electrode active material is 88.6-99.9% by mass.

The content of the conductive additive other than the carbon nanotubes is 0 to 10.0% by mass.

The composition does not contain electrode constituent materials other than the electrode active material, the carbon nanotubes, and a conductive auxiliary agent other than the carbon nanotubes.

The composition is a composition for forming a positive electrode active material layer for a lithium ion secondary battery.

Item 14. The composition for forming an electrode active material layer for a lithium ion secondary battery according to Item 6 or 10, wherein

The volume ratio of the electrode active material is 75.06 to 99.97% by volume.

The content of the carbon nanotubes is 0.03-4.55% by volume.

The content of the conductive additive other than the carbon nanotubes is 0 to 21.56% by volume.

The composition does not contain electrode constituent materials other than the electrode active material, the carbon nanotubes, and a conductive auxiliary agent other than the carbon nanotubes.

The composition is a composition for forming a positive electrode active material layer for a lithium ion secondary battery.

Item 14-1. The composition for forming an electrode active material layer for a lithium ion secondary battery according to Item 13 or 14, wherein

The conductive auxiliary agent other than the carbon nanotubes is carbon black.

Item 15. The composition for forming an electrode active material layer for a lithium ion secondary battery according to any one of Items 1 to 14-1, wherein

The electrode active material is a material that can absorb and release lithium ions.

Item 15-1. The composition for forming an electrode active material layer for a lithium ion secondary battery according to Item 15, wherein

The electrode active material is an amorphous layered carbon material, and the interlayer distance of the (002) plane is greater than 0.350 nm.

Item 15-2. The composition for forming an electrode active material layer for a lithium ion secondary battery according to Item 15 or 15-1, wherein

The electrode active material contains hard carbon.

Item 16. The composition for forming an electrode active material layer for a lithium ion secondary battery according to any one of Items 1 to 15-2, wherein

The carbon nanotubes are single-layer carbon nanotubes.

Item 17. The composition for forming an electrode active material layer for a lithium ion secondary battery according to any one of Items 1 to 16, wherein

The composition is used to reduce the non-uniformity of a reaction in a lithium ion secondary battery.

Item 18. The composition for forming an electrode active material layer for a lithium ion secondary battery according to any one of Items 1 to 17, wherein

The composition is used for a lithium ion secondary battery used in an electric car for car sharing.

Item 19. An electrode active material layer for a lithium ion secondary battery, wherein:

The electrode active material layer contains the composition for forming an electrode active material layer for a lithium ion secondary battery according to any one of items 1 to 18.

Item 20. The electrode active material layer for a lithium ion secondary battery according to Item 19, wherein

The electrode active material layer is used for a lithium ion secondary battery used in an electric car for car sharing.

Item 21. An electrode for a lithium ion secondary battery, wherein:

The electrode comprises the electrode active material layer for a lithium ion secondary battery according to item 19 or 20.

Item 22. The lithium ion secondary battery electrode according to Item 21, wherein

The electrode is used for a lithium ion secondary battery used in an electric car for car sharing.

Item 23. A lithium ion secondary battery, wherein:

The lithium ion secondary battery comprises the lithium ion secondary battery electrode according to item 21 or 22.

Item 24. The lithium ion secondary battery according to Item 23, wherein

The charge rate SOC is defined as the following formula (1):

SOC (%) = Remaining capacity (Ah) / Full charge capacity (Ah) × 100 (1)

Under the conditions of 25°C and 3.0C, the battery was discharged from a state of SOC 100% to a state of SOC 90%, and then rested for 10 minutes. The voltage rise during the rest period was measured.

The internal resistance calculated by the following formula (2) is 1.0 to 35.0 Ω·cm ² :

Internal resistance = (voltage rise during rest (V)/current value during discharge (A)) × facing area of positive and negative electrodes (cm ² ) (2).

Item 24-1. The lithium ion secondary battery according to Item 24, wherein

The internal resistance is 1.0 to 25.0 Ω·cm ² .

Item 24-2. The lithium ion secondary battery according to Item 24 or 24-1, wherein

The internal resistance is 1.0 to 19.0 Ω·cm ² .

Item 25. The lithium ion secondary battery according to any one of Items 23 to 24-2, wherein

The charge rate SOC is defined as the following formula (1):

SOC (%) = Remaining capacity (Ah) / Full charge capacity (Ah) × 100 (1)

At 0°C and 0.5C, the battery was discharged from SOC 100% to SOC 90%, and then rested for 1 minute. The voltage rise during the rest period was measured.

The internal resistance calculated by the following formula (2) is 1.0 to 45.0 Ω·cm ² :

Internal resistance = (voltage rise during rest (V)/current value during discharge (A)) × facing area of positive and negative electrodes (cm ² ) (2).

Item 26. The lithium ion secondary battery according to any one of Items 23 to 25, wherein

The lithium ion secondary battery is used in an electric car for car sharing.

Item 27. A method for evaluating the heterogeneity of a reaction in a lithium-ion secondary battery, wherein:

The method comprises the following steps:

The charge rate SOC is defined as the following formula (1):

SOC (%) = Remaining capacity (Ah) / Full charge capacity (Ah) × 100 (1)

After discharging from SOC 100% to SOC 90% at 25°C and 2.5C or higher, the battery rested for 10 minutes and the voltage rise during the rest period was measured.

The internal resistance is calculated using the following formula (2):

Internal resistance = (voltage rise during rest (V)/current value during discharge (A)) × facing area of positive and negative electrodes (cm ² ) (2).

Effects of the Invention

According to the present invention, by utilizing a very small amount of carbon nanotubes for current collection between active material particles, maintaining the shape of the electrode, etc., and by not containing a binder or making it a very small amount, the battery has a strength sufficient to maintain the shape of the electrode and is not easily hindered from moving lithium ions, thereby making the reaction within the battery uniform and extending the life of the battery.

Furthermore, according to the present invention, by calculating the internal resistance during rest after discharge under high load conditions, it is possible to evaluate the non-uniformity of the battery reaction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the direction of lithium-ion battery development in view of a world view in which the use and operation of automobiles have changed significantly.

FIG. 2 is a graph schematically showing an analysis method in the AC impedance measurement of Test Examples 2 and 6. FIG.

FIG. 3 is a graph showing the results of AC impedance measurement in Test Example 2. FIG.

FIG. 4 is a graph schematically showing an analysis method of the internal resistance in the high-load rest method of Test Examples 3, 7, 11, and 14. FIG.

FIG. 5 is a graph showing the results of internal resistance at room temperature (25° C.) in the high-load rest method of Test Example 3. FIG.

FIG. 6 is a graph showing the results of the life characteristics of Test Example 3. FIG.

FIG. 7 shows the results of estimating the life of the battery of Example 7 based on the results of Test Example 3. As shown in FIG.

FIG. 8 is a graph summarizing the results of the internal resistance of Test Example 3 and the life characteristics of Test Example 4. As shown in FIG.

FIG. 9 is a graph showing the results of AC impedance measurement in Test Example 6. FIG.

FIG. 10 is a graph showing the results of internal resistance at room temperature (25° C.) in the high-load rest method of Test Example 7. FIG.

FIG. 11 is a graph showing the results of internal resistance at a low temperature (0° C.) in the high-load rest method of Test Example 7. FIG.

FIG. 12 is a graph showing the capacity maintenance rate when the overvoltage load is gradually increased in the limit load test of Test Example 8. FIG.

FIG. 13 is a graph showing the capacity maintenance rate for 10 cycles of overvoltage load in the limit load test of Test Example 8. FIG.

FIG. 14 is a graph showing the results of the life characteristics of Test Example 9. FIG.

FIG. 15 is a graph showing the results of the life characteristics of Test Example 12. FIG.

FIG. 16 is a graph showing the results of the life characteristics of Test Example 15. FIG.

Detailed ways

In the present specification, “comprising” is a concept that includes any of “including”, “consisting essentially of” and “consisting only of”.

In addition, in this specification, the expression "A to B" means "A or more and B or less".

1. Composition for forming an electrode active material layer for lithium ion secondary battery

Usually, in the active material layer in the electrode, in addition to the active material, most of them contain a considerable amount of electrode constituent materials other than the electrode active material, such as a binder. Since these electrode constituent materials other than the electrode active material are substances that are not permeable to lithium ions, when a considerable amount of electrode constituent materials other than the electrode active material is contained, the movement of lithium ions will be hindered, and uniform charging and discharging cannot be performed. When the movement of lithium ions is hindered, the reaction is concentrated in the part where the movement of lithium ions is less hindered. As a result, in the case of the negative electrode, lithium electrodeposition is induced, and in the case of the positive electrode, due to the induction of the degradation of the positive electrode active material caused by cracks, when a certain number of charge and discharge cycles are repeated, a sharp decrease in capacity and a sharp increase in resistance (secondary degradation) occur. On the other hand, even if the amount of electrode constituent materials other than the electrode active material is simply reduced, the strength to the extent that the electrode shape can be maintained cannot be maintained. Therefore, during charging and discharging, due to expansion and contraction, damage to the electrode structure, and reduced conductivity in the electrode, the current collection deteriorates, thereby reducing the life characteristics of the battery. Therefore, simply reducing the amount of electrode constituent materials other than the electrode active material cannot take into account both the mitigation of reaction inhomogeneity and the improvement of life characteristics. In the case of the negative electrode, as described above, the life characteristics of the battery are reduced due to the deterioration of the current collection such as damage to the electrode structure and reduced conductivity in the electrode. In the case of the positive electrode, as described above, due to the induction of deterioration of the positive electrode active material caused by cracks, etc., it is technical common sense that the amount of electrode constituent materials other than the electrode active material cannot be significantly reduced. This trend is particularly significant in the negative electrode with damaged electrode structure.

In contrast, the composition for forming an electrode active material layer for a lithium ion secondary battery of the present invention (1) is a composition for forming an electrode active material layer for a lithium ion secondary battery containing an electrode active material and carbon nanotubes, wherein the content of the carbon nanotubes is 0.01 to 1.4% by mass, and the content of the electrode constituent materials other than the electrode active material and the carbon nanotubes is 0 to 10.0% by mass. It should be noted that in the composition for forming an electrode active material layer for a lithium ion secondary battery of the present invention (1), the total amount (total amount of the composition) of the electrode active material, the carbon nanotubes, and the electrode constituent materials other than the electrode active material and the carbon nanotubes is 100% by mass.

In addition, in the composition for forming a negative electrode active material layer for a lithium ion secondary battery of the present invention (the 2), the volume ratio of the electrode active material is 75.06 to 99.97% by volume, the volume ratio of the carbon nanotubes is 0.02 to 4.55% by volume, and the content of the negative electrode constituent material other than the electrode active material and the carbon nanotubes is 0 to 21.56% by volume. It should be noted that in the composition for forming an electrode active material layer for a lithium ion secondary battery of the present invention (the 2), the total amount of the electrode active material, the carbon nanotubes, and the electrode constituent materials other than the electrode active material and the carbon nanotubes (the total volume of the composition) is 100% by volume.

By adopting such a structure, it is possible to reduce the mass of lithium ion obstacles while maintaining the strength to the extent that the electrode shape can be maintained, thereby suppressing the movement of lithium ions, and as a result, the reaction of the battery can be made uniform and the battery life can be extended. That is, the composition for forming an electrode active material layer for a lithium ion secondary battery of the present invention can be used to reduce the non-uniformity of the reaction in a lithium ion secondary battery.

In addition, as mentioned above, in the past, when the movement of lithium ions was hindered, the reaction was concentrated on the part where the movement of lithium ions was less hindered. As a result, in the case of the negative electrode, lithium electrodeposition was induced, and the life characteristics of the battery were reduced due to the damage of the electrode structure, the reduction of the conductivity in the electrode, and the deterioration of the current collection, so the amount of the negative electrode constituent materials other than the negative electrode active material could not be significantly reduced. This is technical common sense. Therefore, the composition for forming an electrode active material layer for a lithium ion secondary battery of the present invention is used to homogenize the reaction of the battery, and it is particularly useful to apply it in the negative electrode. Therefore, in the composition for forming an electrode active material layer for a lithium ion secondary battery of the present invention (1), it is preferably a composition for forming an electrode active material layer for a lithium ion secondary battery containing an electrode active material and carbon nanotubes, wherein the content of the electrode active material is 96.6-99.9% by mass, the content of the carbon nanotubes is 0.01-1.4% by mass, and the content of the electrode constituent materials other than the electrode active material and the carbon nanotubes is 0-2.0% by mass, and the composition is a composition for forming a negative electrode active material layer for a lithium ion secondary battery. Similarly, among the composition for forming an electrode active material layer for lithium ion secondary batteries of the present invention (part 2), preferably it is a composition for forming an electrode active material layer for lithium ion secondary batteries containing an electrode active material and carbon nanotubes, wherein the volume ratio of the electrode active material is 93.38 to 99.98 volume %, the volume ratio of the carbon nanotubes is 0.02 to 2.18 volume %, the volume ratio of the electrode constituent materials other than the electrode active material and the carbon nanotubes is 0 to 4.52 volume %, and the composition is a composition for forming a negative electrode active material layer for lithium ion secondary batteries.

On the other hand, in the present invention, by setting the electrode constituent materials such as the binder that can hinder the movement of ions in the electrode to be free or extremely small, using an extremely small amount of carbon nanotubes to collect current between active material particles, maintain the shape of the electrode, etc., so as to have a strength that can maintain the shape of the electrode, and it is not easy to hinder the movement of lithium ions, so that the reaction in the battery can be uniformed and the battery life can be extended. Therefore, it is preferred to minimize the electrode constituent materials other than the electrode active material and the carbon nanotubes. From this viewpoint, the composition for forming an electrode active material layer for lithium ion secondary batteries of the present invention (the 1) is preferably a composition for forming an electrode active material layer for lithium ion secondary batteries containing an electrode active material and carbon nanotubes, wherein the content of the electrode active material is 97.4-99.9% by mass, the content of the carbon nanotubes is 0.01-1.4% by mass, and the content of the electrode constituent materials other than the electrode active material and the carbon nanotubes is 0-1.2% by mass. Similarly, the composition for forming an electrode active material layer for lithium ion secondary batteries of the present invention (2) is preferably a composition for forming an electrode active material layer for lithium ion secondary batteries containing an electrode active material and carbon nanotubes, wherein the volume ratio of the electrode active material is 96.19 to 99.98% by volume, the volume ratio of the carbon nanotubes is 0.02 to 2.18% by volume, and the volume ratio of the electrode constituent materials other than the electrode active material and the carbon nanotubes is 0 to 1.63% by volume. As described above, these compositions are particularly useful for use in negative electrodes, and therefore are further preferably compositions for forming negative electrode active material layers for lithium ion secondary batteries.

Hereinafter, four preferred aspects of the composition for forming an electrode active material layer for a lithium ion secondary battery of the present invention will be described in order.

(1-1) Composition for forming an electrode active material layer for lithium ion secondary battery (first aspect)

The first embodiment of the present invention involves a composition for forming an electrode active material layer for a lithium ion secondary battery (the 1 thereof), which is a composition for forming an electrode active material layer for a lithium ion secondary battery containing an electrode active material and carbon nanotubes, wherein the content of the electrode active material is 97.4 to 99.9% by mass, the content of the carbon nanotubes is 0.01 to 1.4% by mass, and the content of electrode constituent materials other than the electrode active material and the carbon nanotubes is 0 to 1.2% by mass. The composition is a composition for forming a negative electrode active material layer for a lithium ion secondary battery. In addition, similarly, the first embodiment of the present invention involves a composition for forming an electrode active material layer for a lithium ion secondary battery (the 2), which is a composition for forming an electrode active material layer for a lithium ion secondary battery containing an electrode active material and carbon nanotubes, wherein the volume ratio of the electrode active material is 96.19 to 99.98 volume %, the volume ratio of the carbon nanotubes is 0.02 to 2.18 volume %, and the volume ratio of electrode constituent materials other than the electrode active material and the carbon nanotubes is 0 to 1.63 volume %, and the composition is a composition for forming a negative electrode active material layer for a lithium ion secondary battery.

[1-1-1] Electrode Active Materials

The electrode active material (negative electrode active material) is not particularly limited, and materials that can be used as negative electrode active materials in lithium ion secondary batteries, that is, materials that can absorb and release lithium ions, can be used, including: carbon materials such as natural graphite, artificial graphite, and amorphous carbon; metal materials that can alloy with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Si alloys, Sn alloys, and Al alloys; metal oxides that can absorb and release lithium ions such as _SiOx (0<x<2), _SnOx (0<x<2), Si, _Li2TiO3 , and _vanadium oxides; composite materials containing metal materials and carbon materials such as Si-C composites and Sn-C composites. It should be noted that as amorphous carbon, non-crystalline carbon materials described later can also be used. These electrode active materials (negative electrode active materials) can be used alone or in combination of two or more. From the viewpoint of suppressing the volume change of the electrode active material (negative electrode active material) during charge and discharge and improving the charge and discharge cycle characteristics, it is also possible to use a material not containing silicon, namely: a carbon material; a metal material not containing silicon, such as Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Sn alloy, Al alloy, etc., which can alloy with lithium; a metal oxide not containing silicon, such as _SnOx (0<x<2), Si, _{Li2TiO3 ,} vanadium oxide, etc., which can absorb and release lithium ions; a composite material not containing silicon, such as Sn-C composite, etc., which contains a metal material and a carbon material. Among them, when a conductive material such as a carbon material is used as an electrode active material (negative electrode active material), the electrode active material (negative electrode active material) can also function as a conductive material, and the content of a substance that hinders the movement of lithium ions can be particularly easily reduced.

As the electrode active material (negative electrode active material) as described above, from the viewpoint of particularly suppressing the volume change of the electrode active material (negative electrode active material) during charge and discharge, easily suppressing the capacity reduction caused by the volume change, and particularly easily improving the charge and discharge cycle characteristics, the volume change of the electrode active material (negative electrode active material) during charge and discharge is preferably 50% or less, preferably 20% or less. It should be noted that the less the volume change, the better, and no lower limit is set, but if a lower limit is set, it is 0%. It should be noted that the numerical value of the volume change is set to 0% in the absence of any volume change, indicating the extent to which the electrode active material (negative electrode active material) expands when fully charged compared to the electrode active material (negative electrode active material) when fully discharged, by the following formula:

((Volume when fully charged) - (Volume when fully discharged)) / (Volume when fully discharged) × 100

calculate.

As electrode active materials (negative electrode active materials) that satisfy such volume changes, for example, carbon materials such as natural graphite, artificial graphite, and amorphous carbon; lithium composite titanium oxide ( _{Li2TiO3 ,} etc.) and the like can be cited. Their volume changes vary depending on the type of material and the depth of charge and discharge, but are about 10% in the case of graphite and several % in the case of amorphous carbon. In addition, when using a plurality of electrode active materials (negative electrode active materials), it is preferred that the average value of the volume changes of the electrode active materials (negative electrode active materials) is within the above range.

The shape of the electrode active material (negative electrode active material) is not particularly limited, and various shapes such as spherical, flaky, massive, fibrous, whisker-like, and broken shapes can be adopted. In addition, electrode active materials (negative electrode active materials) of various shapes can also be used in combination. It should be noted that the spherical shape can be a true spherical shape, and it can also be an elliptical shape, etc.

In addition, the particle size of the electrode active material (negative electrode active material) is not particularly limited. From the perspective of facilitating current collection between negative electrode active material particles through a small amount of carbon nanotubes and making it easier to extend the battery life, the average particle size is preferably 0.1 to 25 μm, and more preferably 1 to 20 μm. In addition, considering the uniformity of the reaction at low temperatures, the average particle size of the electrode active material (negative electrode active material) can also be 0.1 to 13.0 μm, preferably 0.5 to 10.0 μm, and more preferably 1.0 to 8.0 μm. It should be noted that the average particle size of the negative electrode active material is measured by a laser diffraction scattering method.

The first mode of the present invention is to form a composition for forming an electrode active material layer for lithium ion secondary batteries. It can collect current between active material particles, maintain the shape of the electrode, etc. through a very small amount of carbon nanotubes. As a result, it is also possible to reduce the amount of electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material). As a result, it has a strength that can maintain the shape of the electrode, and it is not easy to hinder the movement of lithium ions, so it is possible to make the reaction in the battery uniform and make the battery life longer. Therefore, compared with the existing electrode active material layer forming composition (negative electrode active material layer forming composition), the content of the electrode active material (negative electrode active material) is large. Therefore, the content of the negative electrode active material is 97.4-99.9% by mass, preferably 97.7-99.7% by mass, and more preferably 98.0-99.5% by mass. It should be noted that when using a variety of electrode active materials (negative electrode active materials), it is preferably adjusted in a manner such that its total amount becomes within the above range. It should be noted that in the composition for forming an electrode active material layer for a lithium-ion secondary battery involved in the first embodiment of the present invention (1), the total amount (total amount of the composition) of the electrode active material (negative electrode active material), carbon nanotubes, and electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) and carbon nanotubes is 100% by mass.

In addition, for the same reason, in the composition for forming an electrode active material layer for lithium ion secondary battery according to the first embodiment of the present invention (2), the volume ratio of the negative electrode active material is 96.19-99.98% by volume, preferably 97.00-99.70% by volume, and more preferably 97.50-99.50% by volume. It should be noted that when using a variety of electrode active materials (negative electrode active materials), it is preferably adjusted in such a way that the total volume thereof is within the above range. It should be noted that in the composition for forming an electrode active material layer for lithium ion secondary battery according to the first embodiment of the present invention (2), the total amount (total volume of the composition) of the electrode active material (negative electrode active material), carbon nanotubes, and electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) is 100% by volume.

[1-1-2] Carbon Nanotubes

The composition for forming an electrode active material layer for a lithium ion secondary battery according to the first embodiment of the present invention can collect current between active material particles, maintain the shape of the electrode, etc. through a very small amount of carbon nanotubes, and as a result, the amount of electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) can be reduced. As a result, it has a strength that can maintain the shape of the electrode, and is not easy to hinder the movement of lithium ions, so that the reaction in the battery can be uniform and the battery life can be extended. Carbon nanotubes are also a substance that hinders the movement of lithium ions, but if they are in a small amount, they will not hinder the movement of lithium ions, that is, they can have a strength that can maintain the shape of the electrode on the basis of maintaining the uniform reaction in the battery.

Carbon nanotubes are hollow carbon materials in which graphite sheets (i.e., carbon atom planes of graphite structure or single-layer graphene sheets) are closed into a tube, and the diameter is nanometer-level, and the wall structure has a graphite structure. Carbon nanotubes whose wall structure is a shape in which a piece of graphite sheet (single-layer graphene sheet) is closed into a tube are called single-layer carbon nanotubes. On the other hand, carbon nanotubes in which multiple graphite sheets are closed into a tube and become nested are called multilayer carbon nanotubes of nested structure. In the present invention, any one of single-layer carbon nanotubes and multilayer carbon nanotubes can be used. From the viewpoint of being easy to have a strength that can maintain the shape of the electrode, being easy to collect electricity between electrode active materials (negative electrode active materials), not being easy to hinder the movement of lithium ions, and therefore being easy to make the reaction in the battery uniform, and being easy to make the battery life longer, single-layer carbon nanotubes are preferred.

Such carbon nanotubes may be used alone or in combination of two or more.

From the viewpoint of increasing the number of carbon nanotubes per unit volume, reducing the content of carbon nanotubes used to maintain the shape of the electrode, and not hindering the movement of lithium ions, it is preferred that the average outer diameter of the carbon nanotubes is small. Therefore, the average outer diameter of the carbon nanotubes is preferably 0.43 to 20 nm, more preferably 0.43 to 10 nm. The average outer diameter of the carbon nanotubes is measured by electron microscope (TEM) observation. The average inner diameter of the carbon nanotubes having such an average outer diameter is set according to the average outer diameter.

The longer the average length of the carbon nanotubes, the easier it is to have a strength that can maintain the shape of the electrode, and the easier it is to collect current between the negative electrode active materials; on the other hand, from the perspective of easily improving dispersibility and not hindering the movement of lithium ions, it is preferred that the average length of the carbon nanotubes is short. Therefore, the average length of the carbon nanotubes is preferably 0.5 to 200 μm, and more preferably 1 to 50 μm. The average length of the carbon nanotubes is measured by electron microscopy (SEM) observation.

The higher the average aspect ratio of the carbon nanotubes, which is defined as the ratio of the average length of the carbon nanotubes to the average outer diameter, the easier it is to have a strength sufficient to maintain the shape of the electrode with a small content of carbon nanotubes, and the easier it is to collect current between the negative electrode active materials and not to hinder the movement of lithium ions. Therefore, it is easy to make the reaction in the battery uniform and to extend the life of the battery. From this point of view, the average aspect ratio of the carbon nanotubes is preferably 25 to 200,000, and more preferably 100 to 50,000.

In the present invention, the carbon nanotubes can be used individually or as a carbon nanotube aggregate formed by bundling a plurality of carbon nanotubes in order to easily show strength in the form of a bundle. In either case, current collection between active material particles and electrode shape maintenance can be performed by a very small amount of carbon nanotubes, and as a result, the amount of electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) can be reduced. As a result, the electrode has a strength that can maintain the shape of the electrode, and is not easily hindered from moving lithium ions, so that the reaction in the battery can be uniformed and the battery life can be extended.

In addition, from the viewpoint of suppressing the reactivity of carbon nanotubes with electrolyte, it is considered that carbon nanotubes with fewer defects in the graphene structure, that is, with a higher G/D ratio in Raman spectrum, are preferred. Therefore, in the present invention, the carbon nanotubes preferably have a G/D ratio of 1 to 200, more preferably 50 to 150 in Raman spectrum.

The composition for forming an electrode active material layer for lithium ion secondary batteries (composition for forming a negative electrode active material layer for lithium ion secondary batteries) according to the first embodiment of the present invention can collect current between active material particles, maintain the shape of the electrode, etc., and as a result, the amount of negative electrode constituent materials other than the electrode active material (negative electrode active material) can be reduced. As a result, it has a strength that can maintain the shape of the electrode, and it is not easy to hinder the movement of lithium ions, so the reaction in the battery can be uniformized and the battery life can be extended, so the content of carbon nanotubes is a small amount. Therefore, in the composition for forming an electrode active material layer for lithium ion secondary batteries according to the first embodiment of the present invention (1), the content of carbon nanotubes is 0.01 to 1.4% by mass, preferably 0.1 to 1.2% by mass, and more preferably 0.2 to 1.0% by mass. It should be noted that when using a variety of carbon nanotubes, it is preferably adjusted in a manner that the total amount thereof is within the above range. Carbon nanotubes are also substances that hinder the movement of lithium ions, but if it is about 1.2% by mass or less, it is not easy to hinder the movement of lithium ions, and it can have a strength that can maintain the shape of the electrode on the basis of maintaining the uniform reaction in the battery. It should be noted that in the composition for forming an electrode active material layer for a lithium ion secondary battery (one of the 1) involved in the first embodiment of the present invention, the total amount (total amount of the composition) of the electrode active material (negative electrode active material), carbon nanotubes, and electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) is 100% by mass.

In addition, for the same reason, in the composition for forming an electrode active material layer for lithium ion secondary batteries according to the first embodiment of the present invention (2), the volume ratio of carbon nanotubes is 0.02 to 2.18% by volume, preferably 0.20 to 2.00% by volume, and more preferably 0.40 to 1.75% by volume. It should be noted that when using a variety of carbon nanotubes, it is preferably adjusted in such a way that the total volume thereof is within the above range. It should be noted that in the composition for forming an electrode active material layer for lithium ion secondary batteries according to the first embodiment of the present invention (2), the total amount (total volume of the composition) of the electrode active material (negative electrode active material), carbon nanotubes, and the electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) is 100% by volume.

[1-1-3] Electrode constituent materials other than electrode active materials and carbon nanotubes

The first embodiment of the present invention involves a composition for forming an electrode active material layer for a lithium-ion secondary battery, which can collect current between active material particles, maintain the shape of the electrode, etc. through the above-mentioned extremely small amount of carbon nanotubes. As a result, the amount of electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) can be reduced. As a result, it has a strength sufficient to maintain the shape of the electrode and is not easily hindered from the movement of lithium ions. Therefore, the reaction in the battery can be uniformized, thereby extending the battery life.

It should be noted that in the present invention, electrode constituent materials (negative electrode constituent materials) other than electrode active materials (negative electrode active materials) and carbon nanotubes are a general term for substances (binders) having adhesion to electrode active materials (negative electrode active materials) and electrode current collectors (negative electrode current collectors), as well as conductive materials other than carbon nanotubes such as carbon black, dispersants, etc. other than carbon nanotubes that hinder the movement of lithium ions (lithium ion movement hindering substances).

As the electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) and the carbon nanotubes in the present invention, for example, as a conductive material, acetylene black, Ketjen black, carbon black, graphene, amorphous carbon obtained by heat-treating an organic substance, etc. can be cited; as a binder, a thickener or a dispersant, fluorine-based polymers (polyvinylidene fluoride resin, polytetrafluoroethylene resin, vinylidene fluoride-hexafluoropropylene copolymer, etc.), polyolefin-based resins (styrene butadiene copolymer resin, ethylene vinyl alcohol copolymer resin, etc.), synthetic rubbers (styrene butadiene rubber, acrylonitrile butadiene rubber, ethylene propylene diene rubber, etc.), polyacrylonitrile, polyamide, polyimide, polyacrylic acid, polyacrylate, polyvinyl ether, carboxymethyl cellulose, carboxymethyl cellulose sodium salt, carboxymethyl cellulose ammonium, polyurethane, hydroxypropyl cellulose, hydroxyethyl cellulose, methyl cellulose, etc. can be cited. It should be noted that as amorphous carbon, the non-crystalline carbon material described later can also be used. These electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) and the carbon nanotubes may be used alone or in combination of two or more.

The composition for forming an electrode active material layer for a lithium ion secondary battery according to the first embodiment of the present invention can collect current between active material particles, maintain the shape of the electrode, etc. through a very small amount of carbon nanotubes. As a result, the amount of electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) can also be reduced. As a result, it has a strength that can maintain the shape of the electrode, and it is not easy to hinder the movement of lithium ions, so the reaction in the battery can be uniformized and the battery life can be extended. Therefore, it does not contain electrode constituent materials (negative electrode constituent materials) other than electrode active materials (negative electrode active materials) and carbon nanotubes, or even if it is included, its content is a small amount. Therefore, in the composition for forming an electrode active material layer for a lithium ion secondary battery according to the first embodiment of the present invention (1), the content of electrode constituent materials (negative electrode constituent materials) other than electrode active materials (negative electrode active materials) and carbon nanotubes is 0 to 1.2% by mass, preferably 0.2 to 1.1% by mass, and more preferably 0.4 to 1.0% by mass. It should be noted that when using a variety of electrode constituent materials (negative electrode constituent materials) other than electrode active materials (negative electrode active materials) and carbon nanotubes, it is preferably adjusted in a manner such that the total amount thereof is within the above range. Electrode constituent materials (negative electrode constituent materials) other than electrode active materials (negative electrode active materials) and carbon nanotubes are substances that hinder the movement of lithium ions, but if it is about 1.2% by mass or less, it is not easy to hinder the movement of lithium ions, and it is possible to have a strength that can maintain the shape of the electrode on the basis of maintaining the uniform reaction in the battery. It should be noted that in the composition for forming a negative electrode active material layer for lithium ion secondary batteries (the 1) involved in the first embodiment of the present invention, the total amount (total amount of the composition) of electrode active materials (negative electrode active materials), carbon nanotubes, and electrode constituent materials (negative electrode constituent materials) other than electrode active materials (negative electrode active materials) is 100% by mass.

In addition, for the same reason, in the composition for forming an electrode active material layer for lithium ion secondary battery according to the first embodiment of the present invention (2), the volume ratio of the electrode active material (negative electrode active material) and the electrode constituent material (negative electrode constituent material) other than the carbon nanotube is 0 to 1.63% by volume, preferably 0.20 to 1.50% by volume, and more preferably 0.40 to 1.40% by volume. It should be noted that when using multiple electrode active materials (negative electrode active materials), it is preferably adjusted in such a way that the total volume thereof is within the above range. It should be noted that in the composition for forming an electrode active material layer for lithium ion secondary battery according to the first embodiment of the present invention (2), the total amount (total volume of the composition) of the electrode active material (negative electrode active material), carbon nanotubes, and the electrode constituent material (negative electrode active material) other than the carbon nanotube is 100% by volume.

[1-1-4] Composition for forming an electrode active material layer for lithium ion secondary battery

In the composition for forming an electrode active material layer for lithium ion secondary batteries (composition for forming a negative electrode active material layer for lithium ion secondary batteries) according to the first embodiment of the present invention, when the electrode active material (negative electrode active material), carbon nanotubes, and electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) and the carbon nanotubes are mixed to form a paste composition for forming an electrode active material layer for lithium ion secondary batteries, it is also possible to make a paste by including one or more of organic solvents such as water or alcohol (methanol, ethanol, n-propanol, isopropanol, etc.), acetone, N-methylpyrrolidone, dimethyl sulfoxide, dimethylformamide, etc. In this case, the content of each component is the total amount of the electrode active material (negative electrode active material), carbon nanotubes, and electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) and the carbon nanotubes, that is, the total amount of the solid content is set to 100% by mass or 100% by volume.

The manufacturing method of the composition for forming an electrode active material layer for a lithium ion secondary battery (composition for forming a negative electrode active material layer for a lithium ion secondary battery) involved in the first embodiment of the present invention is not particularly limited. For example, by mixing the above-mentioned components using a conventional method, the composition for forming an electrode active material layer for a lithium ion secondary battery of the present invention can be manufactured. With regard to mixing, all the components can be mixed simultaneously or one by one.

(1-2) Composition for forming an electrode active material layer for lithium ion secondary battery (second aspect)

The second embodiment of the present invention relates to a composition for forming an electrode active material layer for a lithium ion secondary battery (1), which is a composition for forming an electrode active material layer for a lithium ion secondary battery containing an electrode active material and carbon nanotubes, wherein the average particle size of the electrode active material is 0.1 to 13.0 μm, and its content is 96.6 to 99.9% by mass, the content of carbon nanotubes is 0.01 to 1.4% by mass, and the content of electrode constituent materials other than the electrode active material and the carbon nanotubes is 0 to 2.0% by mass, and the composition is a composition for forming a negative electrode active material layer for a lithium ion secondary battery. It should be noted that in the composition for forming an electrode active material layer for a lithium ion secondary battery (1) according to the second embodiment of the present invention, the total amount (total amount of the composition) of the electrode active material (negative electrode active material), carbon nanotubes, and electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) and the carbon nanotubes is 100% by mass. In addition, similarly, the composition for forming an electrode active material layer for lithium ion secondary batteries involved in the second embodiment of the present invention (2) is a composition for forming an electrode active material layer for lithium ion secondary batteries containing an electrode active material and carbon nanotubes, wherein the volume ratio of the electrode active material is 96.19-99.98% by volume, the volume ratio of the carbon nanotubes is 0.02-2.18% by volume, the volume ratio of the electrode constituent materials other than the electrode active material and the carbon nanotubes is 0-1.63% by volume, and the composition is a composition for forming a negative electrode active material layer for lithium ion secondary batteries. It should be noted that in the composition for forming an electrode active material layer for lithium ion secondary batteries involved in the second embodiment of the present invention (2), the total amount (total volume of the composition) of the electrode active material (negative electrode active material), the carbon nanotubes, and the electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) is 100% by volume.

When the electrode active material (negative electrode active material) is reduced in particle size, the number of interfaces between the electrode active material (negative electrode active material) particles increases, and thus the number of starting points for structural collapse increases. As a result, it has been more difficult to significantly reduce the amount of electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material). In the second embodiment of the present invention, by adopting the above-mentioned structure, although the number of interfaces between the electrode active material (negative electrode active material) particles increases due to the reduction in particle size of the electrode active material (negative electrode active material), and thus the number of starting points for structural collapse increases, even if the amount of electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) is significantly reduced, current collection between the electrode active material (negative electrode active material) particles, electrode shape maintenance, etc. can be performed by a very small amount of carbon nanotubes, and as a result, the strength to the extent that the electrode shape can be maintained can be maintained. In addition, in the present invention, since the electrode active material (negative electrode active material) is made small in particle size and the reaction area is increased, the lithium ion flux per unit area is reduced, especially under high load conditions and long-term use, the risk of lithium precipitation is reduced, and the amount of electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) is significantly reduced, so the life characteristics are significantly improved. That is, the composition for forming an electrode active material layer for a lithium ion secondary battery (composition for forming a negative electrode active material layer for a lithium ion secondary battery) involved in the second embodiment of the present invention can be used to reduce the heterogeneity of the reaction in a lithium ion secondary battery.

[1-2-1] Electrode active materials

The electrode active material (negative electrode active material) is not particularly limited, and materials that can be used as electrode active materials (negative electrode active materials) in lithium ion secondary batteries, that is, materials that can absorb and release lithium ions, can be used, including: carbon materials such as natural graphite, artificial graphite, and amorphous carbon; metal materials that can alloy with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Si alloys, Sn alloys, and Al alloys; metal oxides that can absorb and release lithium ions such as _SiOx (0<x<2), _SnOx ( ₀ <x<2), Si, _Li2TiO3 , and vanadium oxides; composite materials containing metal materials and carbon materials such as Si-C composites and Sn-C composites. It should be noted that as amorphous carbon, non-crystalline carbon materials described later can also be used. These electrode active materials (negative electrode active materials) can be used alone or in combination of two or more. Among them, when a conductive material such as a carbon material is used as an electrode active material (negative electrode active material), the electrode active material (negative electrode active material) can function as a conductive material, and the content of substances that hinder the movement of lithium ions can be particularly easily reduced.

The shape of the electrode active material (negative electrode active material) is not particularly limited, and various shapes such as spherical, flaky, massive, fibrous, whisker-like, and broken shapes can be adopted. In addition, electrode active materials (negative electrode active materials) of various shapes can also be used in combination. It should be noted that the spherical shape can be a true spherical shape, and it can also be an elliptical shape, etc.

In addition, the average particle size of the electrode active material (negative electrode active material) is 0.1 to 13.0 μm, preferably 0.5 to 10.0 μm, and more preferably 1.0 to 8.0 μm. When the average particle size of the electrode active material (negative electrode active material) is less than 0.1 μm, agglomeration cannot be avoided, the flux of lithium ions per unit area increases instead, and the life characteristics deteriorate. On the other hand, if the average particle size of the electrode active material (negative electrode active material) exceeds 13.0 μm, there is room for improvement in the homogenization of the reaction, especially at low temperatures. It should be noted that the average particle size of the negative electrode active material is measured by a laser diffraction and scattering method.

As the electrode active material (negative electrode active material) as described above, from the viewpoint of particularly suppressing the volume change of the electrode active material (negative electrode active material) during charge and discharge, easily suppressing the capacity reduction caused by the volume change, and particularly easily improving the charge and discharge cycle characteristics, the volume change of the electrode active material (negative electrode active material) during charge and discharge is preferably 50% or less, preferably 20% or less. It should be noted that the less the volume change, the better, and no lower limit is set, but if a lower limit is set, it is 0%. It should be noted that the numerical value of the volume change is set to 0% when there is no volume change at all, indicating the extent to which the electrode active material (negative electrode active material) expands when fully charged compared to the electrode active material (negative electrode active material) when fully discharged, by the following formula:

((Volume when fully charged) - (Volume when fully discharged)) / (Volume when fully discharged) × 100

calculate.

As electrode active materials (negative electrode active materials) that satisfy such volume changes, for example, carbon materials such as natural graphite, artificial graphite, and amorphous carbon; lithium composite _titanium oxide ( _Li2TiO3 , etc.) and the like can be cited. Their volume changes vary depending on the type of material and the depth of charge and discharge, but are about 10% in the case of graphite and several % in the case of amorphous carbon. In addition, when using a plurality of electrode active materials (negative electrode active materials), it is preferred that the average value of the volume changes of the electrode active materials (negative electrode active materials) is within the above range.

The second embodiment of the present invention relates to a composition for forming an electrode active material layer for lithium ion secondary batteries (composition for forming a negative electrode active material layer for lithium ion secondary batteries) that makes the electrode active material (negative electrode active material) small in particle size, thereby increasing the interface between the electrode active material (negative electrode active material) particles, and thus increasing the starting point of structural collapse. Nevertheless, even if the amount of electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) is significantly reduced, the current collection between the electrode active material (negative electrode active material) particles, the shape maintenance of the electrode, etc. can be performed by a very small amount of carbon nanotubes, and the strength of the degree that can maintain the shape of the electrode (negative electrode) can be maintained. In addition, in the present invention, since the electrode active material (negative electrode active material) is made small in particle size and the reaction area is increased, the lithium ion flux per unit area becomes smaller, especially under high load conditions and in long-term use, the risk of lithium precipitation decreases, and the amount of electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) is significantly reduced, so the life characteristics are significantly improved. Therefore, the composition for forming an electrode active material layer for lithium ion secondary battery (composition for forming a negative electrode active material layer for lithium ion secondary battery) according to the second embodiment of the present invention is compared with the existing composition for forming an electrode active material layer (composition for forming a negative electrode active material layer), and the content of the electrode active material (negative electrode active material) is large. Therefore, in the composition for forming an electrode active material layer for lithium ion secondary battery according to the second embodiment of the present invention (1), the content of the electrode active material (negative electrode active material) is 96.6-99.9% by mass, preferably 97.6-99.8% by mass, and more preferably 98.2-99.7% by mass. It should be noted that when using a variety of electrode active materials (negative electrode active materials), it is preferably adjusted in a manner such that the total amount thereof is within the above range. It should be noted that in the composition for forming an electrode active material layer for a lithium-ion secondary battery involved in the second embodiment of the present invention (one of them), the total amount (total amount of the composition) of the electrode active material (negative electrode active material), carbon nanotubes, and electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) and carbon nanotubes is 100% by mass.

In addition, for the same reason, in the composition (2) for forming an electrode active material layer for lithium ion secondary battery involved in the second embodiment of the present invention, the volume ratio of the electrode active material (negative electrode active material) is 93.38-99.98 volume%, preferably 95.00-99.70 volume%, and more preferably 96.00-99.50 volume%. It should be noted that when using a variety of electrode active materials (negative electrode active materials), it is preferably adjusted in a manner such that its total volume is within the above range. It should be noted that in the composition (2) for forming a negative electrode active material layer for lithium ion secondary battery involved in the second embodiment of the present invention, the total amount (total volume of the composition) of the electrode active material (negative electrode active material), carbon nanotubes, and electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) is 100 volume%.

[1-2-2] Carbon Nanotubes

The second embodiment of the present invention involves a composition for forming an electrode active material layer for a lithium ion secondary battery (a composition for forming a negative electrode active material layer for a lithium ion secondary battery) that can collect current between active material particles, maintain the shape of the electrode, etc. through a very small amount of carbon nanotubes. As a result, although the number of interfaces between the particles of the electrode active material (negative electrode active material) increases due to the small particle size of the electrode active material (negative electrode active material), thereby increasing the number of starting points for structural collapse, the strength is sufficient to maintain the shape of the electrode (negative electrode) even if the amount of electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) is reduced; and since the reaction area of the electrode active material (negative electrode active material) increases due to the small particle size, the lithium ion flux per unit area becomes smaller, and the risk of lithium precipitation is reduced, especially under high load conditions and long-term use; and the amount of electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) is significantly reduced, so the life characteristics are significantly improved. Carbon nanotubes also inhibit the movement of lithium ions, but if they are present in a small amount, they do not inhibit the movement of lithium ions, that is, they have a strength sufficient to maintain the shape of the electrode (negative electrode) while maintaining a uniform reaction in the battery.

As for the carbon nanotubes that can be used, the same carbon nanotubes as those described in the above-mentioned [1-1-2] can be used.

The second embodiment of the present invention involves a composition for forming an electrode active material layer for a lithium ion secondary battery (a composition for forming a negative electrode active material layer for a lithium ion secondary battery) that can collect current between electrode active material (negative electrode active material) particles, maintain the shape of the electrode, etc. through a very small amount of carbon nanotubes. As a result, although the number of interfaces between the electrode active material (negative electrode active material) particles increases due to the small particle size of the electrode active material (negative electrode active material), thereby increasing the number of starting points for structural collapse, the composition has a strength sufficient to maintain the shape of the electrode (negative electrode) even if the amount of electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) is reduced. In addition, the reaction area of the electrode active material (negative electrode active material) increases due to the small particle size, so the lithium ion flux per unit area becomes smaller, and the risk of lithium precipitation is reduced, especially under high load conditions and long-term use. In addition, the amount of electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) is significantly reduced, so the life characteristics are significantly improved. Therefore, in the composition for forming an electrode active material layer for lithium ion secondary batteries (composition for forming a negative electrode active material layer for lithium ion secondary batteries) according to the second embodiment of the present invention, the content of carbon nanotubes is a small amount. Therefore, in the composition for forming an electrode active material layer for lithium ion secondary batteries according to the second embodiment of the present invention (1), the content of carbon nanotubes is 0.01 to 1.4% by mass, preferably 0.1 to 1.2% by mass, and more preferably 0.2 to 1.0% by mass. It should be noted that when using a variety of carbon nanotubes, it is preferably adjusted in such a way that the total amount thereof becomes the above range. Carbon nanotubes are also substances that hinder the movement of lithium ions, but if it is about 1.4% by mass or less, it complements the situation that the particle size of the electrode active material (negative electrode active material) is small, and it is not easy to hinder the movement of lithium ions. In addition, although the particle size of the electrode active material (negative electrode active material) is small, it can also have a strength that can maintain the shape of the electrode (negative electrode) on the basis of maintaining the uniform reaction in the battery. It should be noted that in the composition for forming an electrode active material layer for a lithium-ion secondary battery involved in the second embodiment of the present invention (one of them), the total amount (total amount of the composition) of the electrode active material (negative electrode active material), carbon nanotubes, and electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) and carbon nanotubes is 100% by mass.

In addition, for the same reason, in the composition for forming an electrode active material layer for lithium ion secondary batteries according to the second embodiment of the present invention (2), the volume ratio of carbon nanotubes is 0.02 to 2.18% by volume, preferably 0.20 to 2.00% by volume, and more preferably 0.40 to 1.75% by volume. It should be noted that when using a variety of carbon nanotubes, it is preferably adjusted in such a way that the total volume thereof is within the above range. It should be noted that in the composition for forming an electrode active material layer for lithium ion secondary batteries according to the second embodiment of the present invention (2), the total amount (total volume of the composition) of the electrode active material (negative electrode active material), carbon nanotubes, and electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) is 100% by volume.

[1-2-3] Electrode constituent materials other than electrode active materials and carbon nanotubes

The second embodiment of the present invention involves a composition for forming an electrode active material layer for a lithium ion secondary battery (a composition for forming a negative electrode active material layer for a lithium ion secondary battery) that can collect current between active material particles, maintain the shape of the electrode, etc. through a very small amount of carbon nanotubes. As a result, although the electrode active material (negative electrode active material) has a smaller particle size, resulting in more interfaces between the electrode active material (negative electrode active material) particles, thereby increasing the number of starting points for structural collapse, even if the amount of electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) is reduced, the composition has a strength sufficient to maintain the shape of the electrode (negative electrode). In addition, the electrode active material (negative electrode active material) has a larger reaction area due to its smaller particle size, so the lithium ion flux per unit area becomes smaller, and the risk of lithium precipitation is reduced, especially under high load conditions and long-term use. In addition, the amount of electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) is significantly reduced, so the life characteristics are significantly improved.

In the present invention, the electrode constituent material (negative electrode constituent material) other than the electrode constituent material (negative electrode constituent material) and the carbon nanotubes can be the same materials as those described in the above [1-1-3].

The second embodiment of the present invention involves a composition for forming an electrode active material layer for a lithium ion secondary battery (a composition for forming a negative electrode active material layer for a lithium ion secondary battery) that can collect current between active material particles, maintain the shape of the electrode, etc. through a very small amount of carbon nanotubes. As a result, although the number of interfaces between the particles of the electrode active material (negative electrode active material) increases due to the small particle size of the electrode active material (negative electrode active material), thereby increasing the number of starting points for structural collapse, the strength is sufficient to maintain the shape of the electrode (negative electrode) even if the amount of electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) is reduced. In addition, the reaction area of the electrode active material (negative electrode active material) increases due to the small particle size, so the lithium ion flux per unit area becomes smaller, and the risk of lithium precipitation is reduced, especially under high load conditions and long-term use. In addition, the amount of electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) is significantly reduced, so the life characteristics are significantly improved. Therefore, the electrode constituent material (negative electrode constituent material) other than the electrode active material (negative electrode active material) and the carbon nanotube is not included, or even if it is included, its content is a small amount. Therefore, in the composition for forming an electrode active material layer for lithium ion secondary battery (1) according to the second embodiment of the present invention, the content of the electrode constituent material (negative electrode constituent material) other than the electrode active material (negative electrode active material) and the carbon nanotube is 0 to 2.0% by mass, preferably 0 to 1.2% by mass, and more preferably 0 to 0.8% by mass. It should be noted that when using a variety of electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) and the carbon nanotube, it is preferably adjusted in such a way that the total amount thereof is within the above range. The electrode constituent material (negative electrode constituent material) other than the electrode active material (negative electrode active material) and the carbon nanotubes is a material that hinders the movement of lithium ions, but if it is about 2.0% by mass or less, it complements the situation that the particle size of the electrode active material (negative electrode active material) is small, and it is not easy to hinder the movement of lithium ions. In addition, although the particle size of the electrode active material (negative electrode active material) is small, it can also have a strength that can maintain the shape of the electrode (negative electrode) on the basis of maintaining the uniform reaction in the battery. It should be noted that in the composition for forming an electrode active material layer for lithium ion secondary batteries involved in the second embodiment of the present invention (1), the total amount (total amount of the composition) of the electrode active material (negative electrode active material), carbon nanotubes, and the electrode constituent material (negative electrode constituent material) other than the electrode active material (negative electrode active material) is 100% by mass.

In addition, for the same reason, in the composition for forming an electrode active material layer for lithium ion secondary battery according to the second embodiment of the present invention (2), the volume ratio of the electrode constituent material (negative electrode constituent material) other than the electrode active material (negative electrode active material) and the carbon nanotube is 0 to 4.52% by volume, preferably 0 to 2.00% by volume, and more preferably 0 to 1.20% by volume. It should be noted that when using a variety of electrode active materials (negative electrode active materials), it is preferably adjusted in such a way that the total volume thereof is within the above range. It should be noted that in the composition for forming an electrode active material layer for lithium ion secondary battery according to the second embodiment of the present invention (2), the total amount (total volume of the composition) of the electrode active material (negative electrode active material), the carbon nanotube, and the electrode constituent material (negative electrode constituent material) other than the electrode active material (negative electrode active material) is 100% by volume.

[1-2-4] Composition for forming an electrode active material layer for lithium ion secondary battery

In the composition for forming an electrode active material layer for lithium ion secondary batteries (composition for forming a negative electrode active material layer for lithium ion secondary batteries) according to the second embodiment of the present invention, when the electrode active material (negative electrode active material), carbon nanotubes, and electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) and the carbon nanotubes are mixed to form a paste composition for forming an electrode active material layer for lithium ion secondary batteries (paste composition for forming a negative electrode active material layer for lithium ion secondary batteries), it is also possible to make a paste by including one or more of organic solvents such as water or alcohol (methanol, ethanol, n-propanol, isopropanol, etc.), acetone, N-methylpyrrolidone, dimethyl sulfoxide, dimethylformamide, etc. In this case, the content of each component is the value when the total amount of the electrode active material (negative electrode active material), carbon nanotubes, and electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) and the carbon nanotubes, that is, the total amount of the solid content is set to 100% by mass or 100% by volume.

The manufacturing method of the composition for forming an electrode active material layer for lithium ion secondary batteries (composition for forming a negative electrode active material layer for lithium ion secondary batteries) involved in the second embodiment of the present invention is not particularly limited. For example, by mixing the above-mentioned components using conventional methods, the composition for forming an electrode active material layer for lithium ion secondary batteries (composition for forming a negative electrode active material layer for lithium ion secondary batteries) involved in the second embodiment of the present invention can be manufactured. Regarding mixing, all components can be mixed simultaneously, and they can also be mixed one by one.

(1-3) Composition for forming an electrode active material layer for lithium ion secondary battery (third embodiment)

The composition for forming an electrode active material layer for a lithium ion secondary battery according to the third embodiment of the present invention (1) is a composition for forming an electrode active material layer for a lithium ion secondary battery containing an electrode active material and carbon nanotubes, wherein the content of the electrode active material is 88.6-99.9% by mass, the content of the carbon nanotubes is 0.01-1.4% by mass, the content of the conductive aid other than the carbon nanotubes is 0-10.0% by mass, and the electrode constituent materials other than the electrode active material, the carbon nanotubes and the conductive aid other than the carbon nanotubes are not contained, and the composition is a composition for forming a positive electrode active material layer for a lithium ion secondary battery. It should be noted that in the composition for forming an electrode active material layer for a lithium ion secondary battery according to the third embodiment of the present invention (1), the total amount (total amount of the composition) of the electrode active material (positive electrode active material), the carbon nanotubes, and the conductive aid other than the electrode active material (positive electrode active material) and the carbon nanotubes is 100% by mass. In addition, similarly, the composition for forming an electrode active material layer for lithium ion secondary batteries involved in the third embodiment of the present invention (2) is a composition for forming an electrode active material layer for lithium ion secondary batteries containing an electrode active material and carbon nanotubes, wherein the volume ratio of the electrode active material is 75.06 to 99.97% by volume, the volume ratio of the carbon nanotubes is 0.03 to 4.55% by volume, and the volume ratio of the conductive additive other than the carbon nanotubes is 0 to 21.56% by volume, and the composition is a composition for forming a positive electrode active material layer for lithium ion secondary batteries. It should be noted that in the composition for forming an electrode active material layer for lithium ion secondary batteries involved in the third embodiment of the present invention (2), the total amount of the electrode active material (positive electrode active material), carbon nanotubes, and the conductive additive other than the carbon nanotubes (the total volume of the composition) is 100% by volume.

By adopting such a structure, while maintaining the strength to the extent that the electrode (positive electrode) shape is maintained, the obstruction to the movement of lithium ions can be suppressed due to the reduction in the mass of lithium ion obstacles, and as a result, the reaction of the battery can be made uniform and the battery life can be extended. That is, the composition for forming an electrode active material layer for lithium ion secondary batteries (composition for forming a positive electrode active material layer for lithium ion secondary batteries) involved in the third embodiment of the present invention can be used to reduce the non-uniformity of the reaction in lithium ion secondary batteries.

[1-3-1] Electrode active materials

There are no particular restrictions on the electrode active material (positive electrode active material), and any material that can be used as an electrode active material (positive electrode active material) in a lithium-ion secondary battery, that is, a material that can absorb and release lithium ions, can be used. Examples include: lithium transition metal composite oxides having an α- _NaFeO2 type crystal structure, lithium transition metal oxides having a spinel crystal structure, polyanion compounds, chalcogenide compounds, sulfur, etc. Examples of lithium transition metal composite oxides having an α-NaFeO ₂ type crystal structure include Li[Li _x1 Ni _γ1 Mn _β1 Co _{(1-x1-γ1-β1)} ]O ₂ (0≤x1<0.5, 0≤γ1≤1, 0≤β1≤1, 0≤γ1+β1≤1), Li[Li _x2 Ni _γ2 Co _β2 Al _{(1-x2-γ2-β2)} ]O ₂ (0≤x2<0.5, 0≤γ2≤1, 0≤β2≤1, 0≤γ2+β2≤1), etc. Examples of lithium transition metal oxides having a spinel crystal structure include Li _x3 Mn ₂ O ₄ (0.9≤x3<1.5), Li _x4 Ni _γ4 Mn _(2-γ4) O ₄ (0.9≤x4<1.5, 0≤γ4≤2), etc. Examples of polyanionic compounds include LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ MnSiO ₄ , and Li ₂ CoPO ₄ F. Examples of chalcogenides include titanium disulfide, molybdenum disulfide, and molybdenum dioxide. A portion of the atoms or polyanions in these materials may be substituted with atoms or anion species containing other elements. These electrode active materials (positive electrode active materials) may be used alone or in combination of two or more. As the above-mentioned electrode active materials (positive electrode active materials), from the viewpoint of high energy density, the above-mentioned lithium transition metal composite oxides are preferred, and from the viewpoint of high safety, polyanionic compounds are preferred.

The morphology of the particles of the electrode active material (positive electrode active material) is not particularly limited, and various particles such as secondary particles and single particles can be used. The shape is not particularly limited, and various shapes such as spherical, flaky, massive, fibrous, whisker-like, and broken can be used. In addition, positive electrode active materials of various shapes can also be used in combination. It should be noted that the spherical shape can be a true sphere, or it can be an elliptical shape, etc.

In addition, the particle size of the electrode active material (positive electrode active material) is not particularly limited. From the perspective of facilitating the collection of current between the electrode active material (positive electrode active material) particles through a small amount of carbon nanotubes and making it easier to further extend the life of the battery, the average particle size is preferably 0.1 to 25 μm, and more preferably 1 to 20 μm. In addition, considering the uniformity of the reaction at low temperatures, the average particle size of the electrode active material (positive electrode active material) can also be 0.1 to 13.0 μm, preferably 0.5 to 10.0 μm, and more preferably 1.0 to 8.0 μm. It should be noted that the average particle size of the electrode active material (positive electrode active material) is measured by a laser diffraction scattering method.

The third embodiment of the present invention involves a composition for forming an electrode active material layer for a lithium ion secondary battery (a composition for forming a positive electrode active material layer for a lithium ion secondary battery) which can collect current between active material particles, maintain the shape of the electrode (positive electrode), etc. through a very small amount of carbon nanotubes. Therefore, by setting it to contain electrode constituent materials (positive electrode constituent materials) other than the conductive aid, the amount of electrode constituent materials (positive electrode constituent materials) other than the electrode active material (positive electrode active material) can be reduced. As a result, it has a strength sufficient to maintain the shape of the electrode (positive electrode) and is not easily hindered from the movement of lithium ions. Therefore, the reaction in the battery can be uniformized and the battery life can be extended. Therefore, compared with the existing composition for forming an electrode active material layer (a composition for forming a positive electrode active material layer), the content of the electrode active material (positive electrode active material) is large. Therefore, in the composition (1) for forming an electrode active material layer for lithium ion secondary batteries involved in the third embodiment of the present invention, the content of the electrode active material (positive electrode active material) is 88.6-99.9% by mass, preferably 90.8-98.4% by mass, and more preferably 93.0-97.8% by mass. It should be noted that when using a variety of electrode active materials (positive electrode active materials), it is preferably adjusted in a manner such that the total amount thereof is within the above range. It should be noted that in the composition (1) for forming a positive electrode active material layer for lithium ion secondary batteries involved in the third embodiment of the present invention, the total amount (total amount of the composition) of the electrode active material (positive electrode active material), carbon nanotubes, and conductive aids other than carbon nanotubes is 100% by mass.

In addition, for the same reason, in the composition (2) for forming a positive electrode active material layer for lithium ion secondary batteries involved in the third embodiment of the present invention, the volume ratio of the electrode active material (positive electrode active material) is 75.06-99.97% by volume, preferably 79.20-94.99% by volume, and more preferably 83.63-93.93% by volume. It should be noted that when using a variety of electrode active materials (positive electrode active materials), it is preferably adjusted in a manner such that its total volume is within the above range. It should be noted that in the composition (2) for forming an electrode active material layer for lithium ion secondary batteries involved in the second embodiment of the present invention, the total amount (total volume of the composition) of the electrode active material (positive electrode active material), carbon nanotubes, and conductive aids other than carbon nanotubes is 100% by volume.

[1-3-2] Carbon nanotubes

The composition for forming an electrode active material layer for a lithium ion secondary battery (composition for forming a positive electrode active material layer for a lithium ion secondary battery) of the present invention can collect current between active material particles, maintain the shape of the electrode (positive electrode), etc. through a very small amount of carbon nanotubes. Therefore, by setting it as an electrode constituent material (positive electrode constituent material) without containing an electrode constituent material other than a conductive auxiliary agent, the amount of electrode constituent materials (positive electrode constituent materials) other than the electrode active material (positive electrode active material) can also be reduced. As a result, it has a strength that can maintain the shape of the electrode (positive electrode) and is not easy to hinder the movement of lithium ions, so the reaction in the battery can be uniformed and the battery life can be extended. Carbon nanotubes are also a substance that hinders the movement of lithium ions, but if they are in a small amount, they will not hinder the movement of lithium ions, that is, they can have a strength that can maintain the shape of the electrode (positive electrode) on the basis of maintaining the uniformity of the reaction in the battery.

As for the carbon nanotubes that can be used, the same carbon nanotubes as those described in the above-mentioned [1-1-2] can be used.

The composition for forming an electrode active material layer for lithium ion secondary batteries (composition for forming a positive electrode active material layer for lithium ion secondary batteries) according to the third embodiment of the present invention can collect current between electrode active material (positive electrode active material) particles, maintain the shape of the electrode (positive electrode), etc. by using a very small amount of carbon nanotubes. Therefore, the electrode constituent material (positive electrode constituent material) other than the electrode active material (positive electrode active material) is set to be free of conductive additives. The amount of electrode constituent materials (positive electrode constituent materials) other than the electrode active material (positive electrode active material) can also be reduced. As a result, it has a strength that can maintain the shape of the electrode (positive electrode), and it is not easy to hinder the movement of lithium ions, so the reaction in the battery can be uniformized and the battery life can be extended. Therefore, the content of carbon nanotubes is a small amount. Therefore, in the composition for forming an electrode active material layer for lithium ion secondary batteries according to the third embodiment of the present invention (1), the content of carbon nanotubes is 0.01 to 1.4% by mass, preferably 0.1 to 1.2% by mass, and more preferably 0.2 to 1.0% by mass. It should be noted that when using a plurality of carbon nanotubes, it is preferably adjusted in a manner that the total amount thereof is within the above range. Carbon nanotubes are also substances that hinder the movement of lithium ions, but if it is about 1.4% by mass or less, it is not easy to hinder the movement of lithium ions, and it can have a strength that can maintain the shape of the electrode (positive electrode) on the basis of maintaining the uniform reaction in the battery. It should be noted that in the composition for forming an electrode active material layer for lithium ion secondary batteries (one of them) involved in the third embodiment of the present invention, the total amount of the electrode active material (positive electrode active material), carbon nanotubes, and the conductive auxiliary agent other than the carbon nanotubes (the total amount of the composition) is 100% by mass.

In addition, for the same reason, in the composition for forming an electrode active material layer for lithium ion secondary batteries according to the third embodiment of the present invention (2), the volume ratio of carbon nanotubes is 0.03 to 4.55% by volume, preferably 0.30 to 3.73% by volume, and more preferably 0.60 to 3.12% by volume. It should be noted that when using a variety of carbon nanotubes, it is preferably adjusted in such a way that the total volume thereof is within the above range. It should be noted that in the composition for forming an electrode active material layer for lithium ion secondary batteries according to the third embodiment of the present invention (2), the total amount of the electrode active material (positive electrode active material), carbon nanotubes, and the conductive aid other than the carbon nanotubes (total volume of the composition) is 100% by volume.

[1-3-3] Conductive additives other than carbon nanotubes

The third embodiment of the present invention involves a composition for forming an electrode active material layer for a lithium ion secondary battery (composition for forming a positive electrode active material layer for a lithium ion secondary battery) which can collect current between electrode active materials (positive electrode active materials) and maintain the shape of the electrode (positive electrode) through a very small amount of carbon nanotubes. Therefore, by setting it to contain electrode constituent materials (positive electrode constituent materials) other than the conductive aid, the amount of electrode constituent materials (positive electrode constituent materials) other than the electrode active material (positive electrode active material) can be reduced. As a result, it has a strength sufficient to maintain the shape of the electrode (positive electrode) and is not easily hindered by the movement of lithium ions. Therefore, the reaction in the battery can be made uniform, thereby extending the battery life.

However, in the composition for forming an electrode active material layer for lithium ion secondary batteries (composition for forming a positive electrode active material layer for lithium ion secondary batteries) according to the third embodiment of the present invention, according to the particle morphology, particle size, particle shape and electronic conductivity of the electrode active material (positive electrode active material), from the viewpoint of easily maintaining the current collection between particles of the electrode active material (positive electrode active material), in addition to a very small amount of carbon nanotubes, a certain amount of conductive additive can be included. For example, when using a lithium transition metal composite oxide having a particle morphology of secondary particles as an electrode active material (positive electrode active material), it is preferred to include a certain amount of conductive additive in addition to carbon nanotubes.

As the conductive aid other than carbon nanotubes in the composition for forming an electrode active material layer for lithium ion secondary batteries (composition for forming a positive electrode active material layer for lithium ion secondary batteries) involved in the third embodiment of the present invention, for example, carbon blacks such as acetylene black, furnace black, and Ketjen black; flaky graphite; graphene; amorphous carbon obtained by heat treating an organic substance, etc. These conductive aids other than carbon nanotubes can be used alone or in combination of two or more. Among them, carbon black is preferred from the viewpoint of not easily hindering the movement of lithium ions, making it easy to homogenize the reaction in the battery, and making it easy to prolong the life of the battery.

In the composition for forming an electrode active material layer for a lithium ion secondary battery according to the third embodiment of the present invention (1), from the viewpoint of not being easy to hinder the movement of lithium ions, making the reaction in the battery uniform, and making the battery life long, the content of the conductive aid other than carbon nanotubes is 0 to 10.0% by mass, preferably 1.0 to 8.0% by mass, and more preferably 2.0 to 6.0% by mass. It should be noted that when a plurality of conductive aids other than carbon nanotubes are used, it is preferably adjusted in a manner that their total amount is within the above range. It should be noted that in the composition for forming an electrode active material layer for a lithium ion secondary battery according to the third embodiment of the present invention (1), the total amount (total amount of the composition) of the electrode active material (positive electrode active material), carbon nanotubes, and the conductive aid other than carbon nanotubes is 100% by mass.

In addition, for the same reason, in the composition for forming an electrode active material layer for lithium ion secondary batteries according to the third embodiment of the present invention (2), the volume ratio of the conductive aid other than carbon nanotubes is 0 to 21.56% by volume, preferably 2.41 to 17.52% by volume, and more preferably 4.82 to 13.49% by volume. It should be noted that when using a plurality of conductive aids other than carbon nanotubes, it is preferably adjusted in such a way that the total amount thereof is within the above range. It should be noted that in the composition for forming an electrode active material layer for lithium ion secondary batteries according to the third embodiment of the present invention (2), the total amount of the electrode active material (positive electrode active material), carbon nanotubes, and the conductive aid other than carbon nanotubes (the total volume of the composition) is 100% by volume.

[1-3-4] Electrode constituent materials other than electrode active materials, carbon nanotubes, and conductive additives other than carbon nanotubes

The third embodiment of the present invention involves a composition for forming an electrode active material layer for a lithium ion secondary battery (composition for forming a positive electrode active material layer for a lithium ion secondary battery) which can collect current between electrode active material (positive electrode active material) particles, maintain the shape of the electrode (positive electrode), etc. through a very small amount of carbon nanotubes. Therefore, by setting it to not contain electrode constituent materials (positive electrode constituent materials) other than the electrode active material (positive electrode active material) and the conductive additive, the amount of electrode constituent materials (positive electrode constituent materials) other than the electrode active material (positive electrode active material) can also be reduced. As a result, it has a strength sufficient to maintain the shape of the electrode (positive electrode) and is not easily hindered by the movement of lithium ions. Therefore, the reaction in the battery can be made uniform, thereby extending the battery life.

In the previous compositions for forming electrode active material layers for lithium ion secondary batteries (compositions for forming positive electrode active material layers for lithium ion secondary batteries), in addition to the electrode active material (positive electrode active material) and the conductive aid, they usually also contain more or less substances that hinder the movement of lithium ions (lithium ion movement inhibiting substances) such as substances (binders) that have adhesion to the electrode active material (positive electrode active material) and the electrode current collector (positive electrode current collector), dispersants, etc.

In contrast, the third embodiment of the present invention involves a composition for forming an electrode active material layer for a lithium-ion secondary battery (composition for forming a positive electrode active material layer for a lithium-ion secondary battery) that can collect current between electrode active material (positive electrode active material) particles and maintain the shape of the electrode (positive electrode) through a very small amount of carbon nanotubes. Therefore, as described above, it can be configured to contain no electrode constituent materials (positive electrode constituent materials) other than a conductive aid.

It should be noted that other electrode constituent materials (positive electrode constituent materials) that are not included in the composition for forming an electrode active material layer for a lithium ion secondary battery (composition for forming a positive electrode active material layer for a lithium ion secondary battery) involved in the third embodiment of the present invention, for example, as a binder, a thickener or a dispersant, include: fluorine-based polymers (polyvinylidene fluoride resin, polytetrafluoroethylene resin, vinylidene fluoride-hexafluoropropylene copolymer, etc.), polyolefin-based resins (styrene butadiene copolymer resin, ethylene vinyl alcohol copolymer resin, etc.), synthetic rubbers (styrene butadiene rubber, acrylonitrile butadiene rubber, ethylene propylene diene rubber, etc.), polyacrylonitrile, polyamide, polyimide, polyacrylic acid, polyacrylate, polyvinyl ether, carboxymethyl cellulose, carboxymethyl cellulose sodium salt, carboxymethyl cellulose ammonium, polyurethane, hydroxypropyl cellulose, hydroxyethyl cellulose, methyl cellulose, etc.

[1-3-5] Composition for forming an electrode active material layer for lithium ion secondary battery

In the composition for forming an electrode active material layer for lithium ion secondary batteries (composition for forming a positive electrode active material layer for lithium ion secondary batteries) according to the third embodiment of the present invention, when the electrode active material (positive electrode active material), carbon nanotubes, and a conductive aid other than carbon nanotubes are mixed to form a paste composition for forming an electrode active material layer for lithium ion secondary batteries (paste composition for forming a positive electrode active material layer for lithium ion secondary batteries), it is also possible to make a paste by including one or more of organic solvents such as water or alcohol (methanol, ethanol, n-propanol, isopropanol, etc.), acetone, N-methylpyrrolidone, dimethyl sulfoxide, dimethylformamide, etc. In this case, the content of each component is the value when the total amount of the electrode active material (positive electrode active material), carbon nanotubes, and a conductive aid other than carbon nanotubes, that is, the total amount of the solid content is set to 100% by mass or 100% by volume.

The manufacturing method of the composition for forming an electrode active material layer for lithium ion secondary batteries (composition for forming a positive electrode active material layer for lithium ion secondary batteries) involved in the third embodiment of the present invention is not particularly limited. For example, by mixing the above-mentioned components using conventional methods, the composition for forming an electrode active material layer for lithium ion secondary batteries (composition for forming a positive electrode active material layer for lithium ion secondary batteries) involved in the third embodiment of the present invention can be manufactured. With regard to mixing, all components can be mixed simultaneously or one by one.

(1-4) Composition for forming an electrode active material layer for lithium ion secondary battery (fourth aspect)

The fourth embodiment of the present invention involves a composition for forming an electrode active material layer for a lithium ion secondary battery, which is a composition for forming an electrode active material layer for a lithium ion secondary battery containing an electrode active material and carbon nanotubes, wherein the electrode active material contains an amorphous carbon material, and when the total amount of the composition is set to 100 mass %, the content of carbon nanotubes is 0.01 to 0.8 mass %, and the composition is a composition for forming a negative electrode active material layer for a lithium ion secondary battery.

If the amorphous carbon material is a graphite material, the electronic conductivity is low, so in order to keep the reaction in the battery uniform, it is necessary to form a uniform electronic conduction path. On the one hand, when using a conductive aid with a small aspect ratio such as carbon black, the amount of conductive aid required to form the above-mentioned electronic conduction path becomes large, which may hinder the movement of lithium ions. On the other hand, carbon nanotubes with a high aspect ratio can form a uniform electronic conduction path in a small amount. In this way, by combining the use of amorphous carbon materials and carbon nanotubes, it is possible to form a uniform electronic conduction path while suppressing the obstruction of lithium ion movement, so that the reaction in the battery can be kept uniform. In addition, although carbon nanotubes are substances that can hinder the movement of lithium ions, in the present invention, the content of carbon nanotubes is extremely small, so the reaction in the battery can be kept uniform, and in addition, the battery can be made long-life by the synergistic effect with amorphous carbon materials. That is, the composition for forming an electrode active material layer for lithium ion secondary batteries (composition for forming a negative electrode active material layer for lithium ion secondary batteries) involved in the fourth embodiment of the present invention can be used to reduce the non-uniformity of the reaction in lithium ion secondary batteries.

[1-4-1] Electrode active materials

As the amorphous carbon material used as the electrode active material (negative electrode active material), an amorphous layered carbon material is preferred from the viewpoint of making the reaction in the battery uniform and prolonging the battery life.

From the viewpoint of making the reaction in the battery uniform and making the battery life long, the interlayer distance of the (002) surface of the amorphous layered carbon material is preferably 0.35 nm or more, more preferably 0.36 nm or more. The upper limit of the interlayer distance of the (002) surface of the amorphous layered carbon material is not particularly limited, and is usually 0.40 nm. It should be noted that the interlayer distance of the amorphous layered carbon material is measured by X-ray diffraction.

From the viewpoint of making the reaction in the battery uniform and prolonging the battery life, the average particle size of the amorphous layered carbon material is preferably 1 to 10 μm, more preferably 3 to 8 μm. The average particle size of the amorphous layered carbon material is measured by laser diffraction/scattering method.

As amorphous carbon materials that meet the above conditions, for example, hard carbon (difficult to graphitize carbon material), soft carbon (easy to graphitize carbon material), intermediate phase pitch carbide, etc. can be cited. These amorphous carbon materials can be used alone or in combination of two or more. Among them, hard carbon is preferred from the viewpoint of making the reaction in the battery uniform and making the battery life longer. It should be noted that in the present invention, hard carbon refers to an amorphous carbon material whose interlayer distance of the above-mentioned (002) plane is not less than 0.34nm when sintered at 3000°C. In addition, soft carbon refers to an amorphous carbon material whose interlayer distance of the above-mentioned (002) plane is less than 0.34nm when sintered at 3000°C.

The shape of the electrode active material (negative electrode active material) is not particularly limited, and various shapes such as spherical, flaky, massive, fibrous, whisker-like, and broken shapes can be adopted. In addition, electrode active materials (negative electrode active materials) of various shapes can also be used in combination. It should be noted that the spherical shape can be a true spherical shape, and it can also be an elliptical shape, etc.

The fourth embodiment of the present invention relates to a composition for forming an electrode active material layer for lithium ion secondary batteries (composition for forming a negative electrode active material layer for lithium ion secondary batteries) by using an amorphous carbon material as an electrode active material (negative electrode active material) and using a very small amount of carbon nanotubes, thereby suppressing the hindrance of the movement of lithium ions, and at the same time, forming a uniform electron conduction path, thereby making it possible to make the reaction in the battery uniform and prolong the battery life. In the present invention, the content of the electrode active material (negative electrode active material) is preferably 79.2 to 99.8% by mass, more preferably 83.5 to 96.4% by mass, and further preferably 77.8 to 94.9% by mass. It should be noted that when using multiple electrode active materials (negative electrode active materials), it is preferably adjusted in a manner that the total amount thereof is within the above range. It should be noted that in the composition for forming an electrode active material layer for a lithium ion secondary battery (composition for forming a negative electrode active material layer for a lithium ion secondary battery) involved in the fourth embodiment of the present invention, the total amount (total amount of the composition) of the electrode active material (negative electrode active material), carbon nanotubes, conductive aids other than carbon nanotubes, and electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material), carbon nanotubes and conductive aids other than carbon nanotubes (other electrode constituent materials (negative electrode constituent materials)) is 100% by mass.

[1-4-2] Carbon Nanotubes

The fourth embodiment of the present invention relates to a composition for forming an electrode active material layer for a lithium ion secondary battery (composition for forming a negative electrode active material layer for a lithium ion secondary battery) that uses an amorphous carbon material as an electrode active material (negative electrode active material) and uses a very small amount of carbon nanotubes, thereby suppressing the obstruction of the movement of lithium ions and forming a uniform electron conduction path, thereby making the reaction in the battery uniform and extending the battery life. Carbon nanotubes are also substances that hinder the movement of lithium ions, but if they are in a small amount, they will not hinder the movement of lithium ions, that is, the reaction in the battery can be made uniform and the battery life can be extended.

As for the carbon nanotubes that can be used, the same carbon nanotubes as those described in the above-mentioned [1-1-2] can be used.

The fourth embodiment of the present invention relates to a composition for forming an electrode active material layer for a lithium ion secondary battery (composition for forming a negative electrode active material layer for a lithium ion secondary battery) by using an amorphous carbon material as an electrode active material (negative electrode active material) and using a very small amount of carbon nanotubes, thereby suppressing the obstruction of the movement of lithium ions, and at the same time, forming a uniform electron conduction path, thereby making it possible to make the reaction in the battery uniform and prolong the battery life, so that the content of carbon nanotubes is a small amount. Therefore, in the present invention, the content of carbon nanotubes is 0.01 to 0.8% by mass, preferably 0.02 to 0.5% by mass, and more preferably 0.05 to 0.2% by mass. It should be noted that when using a variety of carbon nanotubes, it is preferably adjusted in a manner such that its total amount becomes within the above range. Carbon nanotubes are also substances that hinder the movement of lithium ions, but if it is about 0.8% by mass or less, it is not easy to hinder the movement of lithium ions, and the reaction in the battery can be kept uniform. It should be noted that in the composition for forming an electrode active material layer for a lithium ion secondary battery (composition for forming a negative electrode active material layer for a lithium ion secondary battery) involved in the fourth embodiment of the present invention, the total amount (total amount of the composition) of the electrode active material (negative electrode active material), carbon nanotubes, conductive aids other than carbon nanotubes, and electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material), carbon nanotubes and conductive aids other than carbon nanotubes (other electrode constituent materials (negative electrode constituent materials)) is 100% by mass.

[1-4-3] Conductive additives other than carbon nanotubes

The fourth embodiment of the present invention involves a composition for forming an electrode active material layer for a lithium ion secondary battery (composition for forming a negative electrode active material layer for a lithium ion secondary battery) which uses an amorphous carbon material as an electrode active material (negative electrode active material) and uses an extremely small amount of carbon nanotubes to suppress the obstruction of the movement of lithium ions and at the same time form a uniform electron conduction path, thereby making the reaction in the battery uniform and extending the battery life.

However, in the composition for forming an electrode active material layer for lithium ion secondary batteries (composition for forming a negative electrode active material layer for lithium ion secondary batteries) according to the fourth embodiment of the present invention, according to the particle morphology, particle size, particle shape and electronic conductivity of the amorphous carbon material, from the viewpoint of easily maintaining the current collection between particles of the electrode active material (negative electrode active material), it is also possible to include a certain amount of conductive additive in addition to a very small amount of carbon nanotubes. For example, when using a spherical amorphous carbon material as an electrode active material (negative electrode active material), it is preferred to include a certain amount of conductive additive in addition to carbon nanotubes.

As the conductive aid other than carbon nanotubes that can be used, the same conductive aid other than carbon nanotubes as described in the above [1-3-3] can be used.

In the present invention, in the case of containing a conductive aid other than carbon nanotubes, from the viewpoint of making the reaction in the battery uniform and making the battery life long, the content of the conductive aid other than carbon nanotubes is preferably 0.1 to 10.0% by mass, more preferably 1.0 to 8.0% by mass, and further preferably 2.0 to 6.0% by mass. It should be noted that when using a plurality of conductive aids other than carbon nanotubes, it is preferably adjusted in a manner that the total amount thereof is within the above range. It should be noted that in the composition for forming an electrode active material layer for lithium ion secondary batteries (composition for forming a negative electrode active material layer for lithium ion secondary batteries) according to the fourth embodiment of the present invention, the total amount (total amount of the composition) of the electrode active material (negative electrode active material), carbon nanotubes, conductive aids other than carbon nanotubes, and electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material), carbon nanotubes, and conductive aids other than carbon nanotubes is 100% by mass.

In addition, for the same reason, when the total amount of carbon nanotubes and conductive additives other than carbon nanotubes is 100% by mass, the content of carbon nanotubes is preferably 0.1 to 100.0% by mass, more preferably 0.5 to 50% by mass, and even more preferably 1.0 to 20.0% by mass. It should be noted that when a plurality of conductive additives other than carbon nanotubes are used, it is preferred to adjust the total amount thereof so as to be within the above range.

[1-4-4] Electrode constituent materials other than electrode active materials, carbon nanotubes, and conductive additives other than carbon nanotubes (other electrode constituent materials)

The fourth embodiment of the present invention involves a composition for forming an electrode active material layer for a lithium ion secondary battery (composition for forming a negative electrode active material layer for a lithium ion secondary battery) which uses an amorphous carbon material as an electrode active material (negative electrode active material) and uses an extremely small amount of carbon nanotubes to suppress the obstruction of the movement of lithium ions and at the same time form a uniform electron conduction path, thereby making the reaction in the battery uniform and extending the battery life.

It should be noted that in the present invention, electrode constituent materials (negative electrode constituent materials) other than electrode active materials (negative electrode active materials), carbon nanotubes and conductive aids other than carbon nanotubes (other electrode constituent materials (negative electrode constituent materials)) are a general term for substances (lithium ion movement inhibiting substances) other than carbon nanotubes and conductive aids other than carbon nanotubes, such as substances (binders) and dispersants that have adhesion to electrode active materials (negative electrode active materials) and electrode current collectors (negative electrode current collectors).

Regarding the electrode constituent materials (negative electrode constituent materials) (other electrode constituent materials (negative electrode constituent materials)) other than the electrode active material (negative electrode active material), carbon nanotubes, and the conductive aid other than the carbon nanotubes that can be used, the same materials as those described in [1-3-4] above can be used. The electrode constituent materials (negative electrode constituent materials) (other electrode constituent materials (negative electrode constituent materials)) other than the electrode active material (negative electrode active material), carbon nanotubes, and the conductive aid other than the carbon nanotubes can be used alone or in combination of two or more.

The fourth mode of the present invention relates to a composition for forming an electrode active material layer for a lithium ion secondary battery (composition for forming a negative electrode active material layer for a lithium ion secondary battery) by using an amorphous carbon material as an electrode active material (negative electrode active material), and using a very small amount of carbon nanotubes, thereby suppressing the obstruction of the movement of lithium ions, and at the same time, forming a uniform electron conduction path, thereby being able to make the reaction in the battery uniform, and making the battery long-life. From this viewpoint, the content of the electrode constituent material (negative electrode constituent material) (other electrode constituent materials (negative electrode constituent material)) other than the electrode active material (negative electrode active material), carbon nanotubes and conductive aids other than carbon nanotubes is preferably a small amount, and on the other hand, from the viewpoint of being easy to have a strength that can maintain the shape of the electrode, it is preferred that the content is a certain amount or more. Therefore, in the composition for forming an electrode active material layer for lithium ion secondary battery (composition for forming a negative electrode active material layer for lithium ion secondary battery) according to the fourth embodiment of the present invention, the content of the electrode constituent material (negative electrode constituent material) (other electrode constituent material (negative electrode constituent material)) other than the electrode active material (negative electrode active material), carbon nanotubes and the conductive auxiliary agent other than the carbon nanotubes is preferably 0.1 to 10.0% by mass, more preferably 1.0 to 8.0% by mass, and further preferably 2.0 to 6.0% by mass. It should be noted that when a plurality of electrode constituent materials (negative electrode constituent materials) (other electrode constituent materials (negative electrode constituent materials)) other than the electrode active material (negative electrode active material), carbon nanotubes and the conductive auxiliary agent other than the carbon nanotubes are used, it is preferred to adjust the total amount thereof to be within the above range. It should be noted that in the composition for forming an electrode active material layer for a lithium ion secondary battery (composition for forming a negative electrode active material layer for a lithium ion secondary battery) involved in the fourth embodiment of the present invention, the total amount (total amount of the composition) of the electrode active material (negative electrode active material), carbon nanotubes, conductive aids other than carbon nanotubes, and electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material), carbon nanotubes and conductive aids other than carbon nanotubes (other electrode constituent materials (negative electrode constituent materials)) is 100% by mass.

[1-4-5] Composition for forming an electrode active material layer for lithium ion secondary battery

In the composition for forming an electrode active material layer for a lithium ion secondary battery (composition for forming a negative electrode active material layer for a lithium ion secondary battery) involved in the fourth embodiment of the present invention, when the electrode active material (negative electrode active material), carbon nanotubes, a conductive aid other than carbon nanotubes as needed, and an electrode constituent material (negative electrode constituent material) other than the electrode active material (negative electrode active material), carbon nanotubes and a conductive aid other than carbon nanotubes as needed (other electrode constituent materials (negative electrode constituent materials)) are mixed to form a paste composition for forming an electrode active material layer for a lithium ion secondary battery (paste composition for forming a negative electrode active material layer for a lithium ion secondary battery), it can also be made into a paste by including one or more organic solvents such as water or alcohol (methanol, ethanol, n-propanol, isopropanol, etc.), acetone, N-methylpyrrolidone, dimethyl sulfoxide, dimethylformamide, etc. In this case, the content of each component is a value obtained when the total amount of the electrode active material (negative electrode active material), carbon nanotubes, conductive aids other than carbon nanotubes as needed, electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material), carbon nanotubes and conductive aids other than carbon nanotubes as needed (other electrode constituent materials (negative electrode constituent materials)), that is, the total amount of solid components is set to 100% by mass.

The manufacturing method of the composition for forming an electrode active material layer for lithium ion secondary batteries (composition for forming a negative electrode active material layer for lithium ion secondary batteries) involved in the fourth embodiment of the present invention is not particularly limited. For example, by mixing the above-mentioned components using conventional methods, the composition for forming an electrode active material layer for lithium ion secondary batteries (composition for forming a negative electrode active material layer for lithium ion secondary batteries) involved in the fourth embodiment of the present invention can be manufactured. With regard to mixing, all components can be mixed simultaneously or one by one.

2. Electrode active material layer for lithium ion secondary battery

The electrode active material layer for lithium ion secondary battery (negative electrode active material layer for lithium ion secondary battery or positive electrode active material layer for lithium ion secondary battery) of the present invention contains the composition for forming the electrode active material layer for lithium ion secondary battery (the composition for forming the negative electrode active material layer for lithium ion secondary battery or the composition for forming the positive electrode active material layer for lithium ion secondary battery) of the present invention.

The thickness of the electrode active material layer for lithium ion secondary battery (negative electrode active material layer for lithium ion secondary battery or positive electrode active material layer for lithium ion secondary battery) of the present invention is not particularly limited. From the perspective of ensuring the penetration and conductivity of lithium ions and making the reaction uniform, the thinner the better. On the other hand, the present invention aims to reduce the main causes that hinder the movement of lithium ions and make the battery reaction uniform to increase the life, so it can also be thickened for the energy density of each electrode. Therefore, the thickness of the electrode active material layer for lithium ion secondary battery (negative electrode active material layer for lithium ion secondary battery or positive electrode active material layer for lithium ion secondary battery) of the present invention is preferably 1 to 300 μm, more preferably 10 to 150 μm, and further preferably 50 to 100 μm.

Such an electrode active material layer for a lithium ion secondary battery of the present invention (a negative electrode active material layer for a lithium ion secondary battery or a positive electrode active material layer for a lithium ion secondary battery) can be manufactured by forming the above-mentioned composition for forming an electrode active material layer for a lithium ion secondary battery of the present invention (a negative electrode active material layer for a lithium ion secondary battery or a positive electrode active material layer for a lithium ion secondary battery) into a layer. For example, when the composition for forming an electrode active material layer for a lithium ion secondary battery of the present invention (a negative electrode active material layer for a lithium ion secondary battery or a positive electrode active material layer for a lithium ion secondary battery) is made into a paste composition for forming an electrode active material layer for a lithium ion secondary battery (a negative electrode active material layer for a lithium ion secondary battery or a positive electrode active material layer for a lithium ion secondary battery), the paste composition can be dried and formed into a layer by a conventional method.

3. Electrodes for lithium-ion secondary batteries

The electrode for a lithium ion secondary battery of the present invention (a negative electrode for a lithium ion secondary battery or a positive electrode for a lithium ion secondary battery) comprises the above-mentioned electrode active material layer for a lithium ion secondary battery of the present invention (a negative electrode active material layer for a lithium ion secondary battery or a positive electrode active material layer for a lithium ion secondary battery), specifically, preferably comprises an electrode current collector (a negative electrode current collector or a positive electrode current collector) and an electrode active material layer for a lithium ion secondary battery of the present invention (a negative electrode active material layer for a lithium ion secondary battery or a positive electrode active material layer for a lithium ion secondary battery) arranged on the electrode current collector (a negative electrode current collector or a positive electrode current collector).

The negative electrode current collector preferably includes a material that is electrochemically stable at the potential used and has high electronic conductivity, such as copper, stainless steel, nickel, or carbon material. The negative electrode current collector can be formed into a member such as a foil or a mesh.

The positive electrode current collector preferably includes a material that is electrochemically stable at the potential used and has high electronic conductivity, such as aluminum, stainless steel, or carbon material. The positive electrode current collector can be formed into a member such as a foil or a mesh.

When manufacturing such an electrode for a lithium ion secondary battery of the present invention (a negative electrode for a lithium ion secondary battery or a positive electrode for a lithium ion secondary battery), it can be manufactured by forming the above-mentioned composition for forming an electrode active material layer for a lithium ion secondary battery of the present invention (a composition for forming a negative electrode active material layer for a lithium ion secondary battery or a composition for forming a positive electrode active material layer for a lithium ion secondary battery) into a layer on an electrode current collector (a negative electrode current collector or a positive electrode current collector). For example, when the composition for forming an electrode active material layer for a lithium ion secondary battery of the present invention (a composition for forming a negative electrode active material layer for a lithium ion secondary battery or a composition for forming a positive electrode active material layer for a lithium ion secondary battery) is made into a paste composition for forming an electrode active material layer for a lithium ion secondary battery (a paste composition for forming a negative electrode active material layer for a lithium ion secondary battery or a paste composition for forming a positive electrode active material layer for a lithium ion secondary battery), for the electrode active material (negative electrode active material or positive electrode active material), the paste composition is dried and formed into a layer by a conventional method, and the electrode for a lithium ion secondary battery of the present invention (a negative electrode for a lithium ion secondary battery or a positive electrode for a lithium ion secondary battery) can be manufactured.

4. Lithium-ion secondary battery

The lithium ion secondary battery of the present invention is equipped with the above-mentioned lithium ion secondary battery electrode of the present invention (negative electrode for lithium ion secondary battery or positive electrode for lithium ion secondary battery). In addition, when the electrode for lithium ion secondary battery of the present invention is used as the negative electrode, as the positive electrode, the electrode for lithium ion secondary battery of the present invention can be used, and the known positive electrode suitable for lithium ion secondary battery can also be used. In addition, when the electrode for lithium ion secondary battery of the present invention is used as the positive electrode, as the negative electrode, the electrode for lithium ion secondary battery of the present invention can be used, and the known negative electrode suitable for lithium ion secondary battery can also be used. In addition, the lithium ion secondary battery of the present invention can also be equipped with a known electrolyte suitable for lithium ion secondary battery and a container for accommodating these electrode components.

When a known negative electrode suitable for lithium ion secondary batteries is used as the negative electrode, the negative electrode is not particularly limited, and a known negative electrode can be used. An example of a known negative electrode is shown below.

The negative electrode current collector constituting the negative electrode preferably includes a material that is electrochemically stable at the potential used and has high electronic conductivity, such as copper, stainless steel, nickel, or carbon material. The negative electrode current collector can be formed into a member such as a foil or a mesh.

In addition, as the negative electrode active material constituting the negative electrode, a material capable of absorbing and releasing lithium ions is generally used. For example, carbon materials such as natural graphite, artificial graphite, and amorphous carbon; metal materials capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Si alloys, Sn alloys, and Al alloys; metal oxides capable of absorbing and releasing lithium ions such as SiO _x (0＜x＜2), SnO _x (0＜x＜2), Si, Li ₂ TiO ₃ , and vanadium oxide; composite materials including metal materials and carbon materials such as Si-C complexes and Sn-C complexes, etc. These negative electrode active materials can be used alone or in combination of two or more. From the viewpoint of suppressing the volume change of the electrode active material (negative electrode active material) during charge and discharge and improving the charge and discharge cycle characteristics, it is also possible to use a material that does not contain silicon, namely: a carbon material; a metal material that does not contain silicon, such as Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Sn alloy, Al alloy, etc., which can alloy with lithium; a metal oxide that does not contain silicon and can absorb and release lithium ions, such as _SnOx (0<x<2), Si, _Li2TiO3 , _vanadium oxide, etc.; a composite material that does not contain silicon and contains a metal material and a carbon material, such as Sn-C composite, etc. Among them, when a conductive material such as a carbon material is used as the negative electrode active material, the negative electrode active material can also function as a conductive material, and the content of the substance that hinders the movement of lithium ions can be particularly easily reduced.

As the electrode active material (negative electrode active material) as described above, from the viewpoint of particularly suppressing the volume change of the electrode active material (negative electrode active material) during charge and discharge, easily suppressing the capacity reduction caused by the volume change, and particularly easily improving the charge and discharge cycle characteristics, the volume change of the electrode active material (negative electrode active material) during charge and discharge is preferably 150% or less, preferably 120% or less. It should be noted that the less the volume change, the better, and no lower limit is set, but if a lower limit is set, it is 0%. It should be noted that the numerical value of the volume change is set to 0% when there is no volume change at all, indicating the extent to which the electrode active material (negative electrode active material) expands when fully charged compared to the electrode active material (negative electrode active material) when fully discharged, by the following formula:

(Volume when fully charged) - (Volume when fully discharged) / (Volume when fully discharged) × 100

calculate.

As the negative electrode constituent materials other than the negative electrode active material constituting the negative electrode, the same materials as the conductive additive other than the carbon nanotubes and other positive electrode constituent materials in the above-mentioned lithium ion secondary battery electrode of the present invention can be used, and the content thereof can be set to a level commonly used.

When a known positive electrode suitable for lithium ion secondary batteries is used as the positive electrode, any known positive electrode can be used as long as it can supply lithium ions to the negative electrode. An example of a known positive electrode is shown below.

Examples of the positive electrode current collector constituting the positive electrode include materials that are electrochemically stable at a potential used and have high electronic conductivity, such as aluminum, stainless steel, and carbon materials.

In addition, as a positive electrode active material constituting the positive electrode, a material capable of absorbing and releasing lithium ions is generally used. For example, a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure, a lithium transition metal oxide having a spinel type crystal structure, a polyanion compound, a chalcogenide, sulfur, etc. can be cited. As a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure, for example, Li[Li _x1 Ni _γ1 Mn _β1 Co _{(1-x1-γ1-β1)} ]O ₂ (0≤x1<0.5, 0≤γ1≤1, 0≤β1≤1, 0≤γ1+β1≤1), Li[Li _x2 Ni _γ2 Co _β2 Al _{(1-x2-γ2-β2)} ]O ₂ (0≤x2<0.5, 0≤γ2≤1, 0≤β2≤1, 0≤γ2+β2≤1) and the like can be cited. As lithium transition metal oxides having a spinel crystal structure, Li _x3 Mn ₂ O ₄ (0.9≤x3<1.5), Li _x4 Ni _γ4 Mn _(2-γ4) O ₄ (0.9≤x4<1.5, 0≤γ4≤2) and the like can be cited. As polyanionic compounds, LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ MnSiO ₄ , Li ₂ CoPO ₄ F and the like can be cited. As chalcogenides, titanium disulfide, molybdenum disulfide, molybdenum dioxide and the like can be cited. A part of the atoms or polyanions in these materials can be substituted by atoms or anion species containing other elements. These positive electrode active materials can be used alone or in combination of two or more. As the above-mentioned positive electrode active material, from the viewpoint of high energy density, the above-mentioned lithium transition metal composite oxide is preferred.

As the positive electrode constituent material other than the positive electrode active material constituting the positive electrode, the same material as the electrode constituent material other than the electrode active material and the carbon nanotubes in the above-mentioned lithium ion secondary battery electrode of the present invention can be used, and its content can also be the same as the electrode constituent material other than the electrode active material and the carbon nanotubes in the lithium ion secondary battery electrode of the present invention.

The electrolyte is a salt dissolved in an aprotic organic solvent and is disposed between the positive electrode and the negative electrode, and is preferably impregnated and retained in a separator made of, for example, nonwoven fabric for preventing a short circuit between the positive electrode and the negative electrode.

It should be noted that, as the aprotic organic solvent constituting the above-mentioned electrolyte, for example, esters such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, methyl formate, and methyl acetate can be cited; furans such as tetrahydrofuran and 2-methyltetrahydrofuran; ethers such as dioxolane, diethyl ether, dimethoxyethane, diethoxyethane, and methoxyethoxyethane; dimethyl sulfoxide; sulfolanes such as sulfolane and methyl sulfolane; acetonitrile, etc. These aprotic organic solvents can be used alone or in combination of two or more.

On the other hand, the salts dissolved in such aprotic organic solvents include, for example, lithium salts such as lithium perchlorate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium halides, lithium chloroaluminate, and lithium bis(fluorosulfonyl)imide. These salts may be used alone or in combination of two or more.

Such a lithium-ion secondary battery of the present invention uses a composition for forming an electrode active material layer for a lithium-ion secondary battery of the present invention (a composition for forming a negative electrode active material layer for a lithium-ion secondary battery or a composition for forming a positive electrode active material layer for a lithium-ion secondary battery) in the negative electrode and/or the positive electrode, so it has a strength that can maintain the shape of the electrode, and is not easy to hinder the movement of lithium ions, so that the reaction in the battery can be uniformized and the battery life can be extended. Therefore, it is expected that the lithium-ion secondary battery will be promoted in the market in the future, and can be effectively used for electric vehicle applications for car sharing that require further extended life in the future, especially AIEV (Artificial Intelligence Electric Vehicle) applications.

5. Method for evaluating internal resistance and reaction heterogeneity of lithium-ion secondary batteries

Generally speaking, the reaction resistance of a battery is usually measured by an alternating current impedance measurement. However, according to the alternating current impedance measurement, whether the amount of binder is changed or the amount of carbon nanotubes is changed, the resistance of the battery reaction is almost the same value. That is, the reaction resistance measured by the alternating current impedance measurement is an index that does not include the influence caused by the uneven reaction, and the size of the unevenness of the reaction cannot be evaluated. In this way, even if the amount of binder is increased, the reaction resistance of the battery is almost the same value, and the unevenness of the reaction cannot be evaluated. Therefore, in the past, for the sake of electrode strength, the electrode active material (negative electrode active material, positive electrode active material, etc.) contained a considerable amount of binder, and there was no motivation to further reduce the amount of binder.

On the other hand, under high load conditions, non-uniform reaction is likely to occur. Therefore, by measuring the internal resistance under high load conditions, it is possible to evaluate the reaction hindrance and lithium ion movement hindrance caused by the binder.

However, under high load conditions during charging, lithium electrodeposition may occur at the negative electrode, making it difficult to accurately measure resistance. Therefore, it is necessary to measure the internal resistance under high load conditions during discharging.

Therefore, in the present invention, the charge rate SOC is defined as the following formula (1):

SOC (%) = Remaining capacity (Ah) / Full charge capacity (Ah) × 100 (1)

After discharging from SOC 100% to SOC 90% at 25°C and 2.5C or higher, the battery rested for 10 minutes and the voltage rise during the rest period was measured. Based on this, the internal resistance was calculated using the following formula (2):

Internal resistance = (voltage rise during rest (V)/current value during discharge (A)) × facing area of positive and negative electrodes (cm ² ) (2).

As described above, by setting the conditions under which uneven reactions are likely to occur, it is easy to evaluate the unevenness of the reactions. Therefore, the discharge rate is set to a high load condition, i.e., 2.5C or more (preferably 2.7 to 10.0C). At 0°C, it is set to a high load condition, i.e., 0.3C or more (preferably 0.4 to 4.0C).

The SOC at the start of discharge is set to 100% in order to make the state before measurement a state in which reaction non-uniformity occurs by sufficiently absorbing lithium ions in the negative electrode.

After discharge under this condition, the reaction stops, and the voltage rises. Usually, the voltage rise is saturated after 10 minutes, and a certain voltage is maintained. Therefore, the voltage rise during the stop can be measured after 10 minutes, and the internal resistance can be calculated by the following formula (2):

Internal resistance = (voltage rise during rest (V)/current value during discharge (A)) × facing area of positive and negative electrodes (cm ² ) (2).

It should be noted that the rest time varies depending on the temperature conditions and the discharge rate conditions, and the time until saturation occurs. For example, it can be set to 1 minute at a discharge rate of 0.5C and to 10 minutes at a discharge rate of 3.0C.

As a result, when the internal resistance value is large, it can be evaluated that the reaction non-uniformity is large and the life is short, and when the internal resistance value is small, it can be evaluated that the reaction non-uniformity is small and the life can be extended.

Specifically, when the composition for forming an electrode active material layer for a lithium ion secondary battery (a composition for forming a negative electrode active material layer for a lithium ion secondary battery or a composition for forming a positive electrode active material layer for a lithium ion secondary battery) of the present invention is used, the internal resistance calculated as described above at 25°C under the condition of 3.0C is preferably 1.0 to 35.0Ω·cm ² , more preferably 1.0 to 33.6Ω·cm ² , and further preferably 1.0 to 33.2Ω·cm ² . Among them, when an amorphous carbon material is used as an electrode active material (the case of the fourth embodiment described above), the internal resistance measured in the same manner is preferably 1.0 to 25.0Ω·cm ² , more preferably 1.0 to 24.0Ω·cm ² , and further preferably 1.0 to 23.0Ω·cm ² . When an electrode active material having an average particle size of 0.1 to 13.0 μm is used as the electrode active material (the case of the second embodiment described above), the internal resistance measured in the same manner is preferably 1.0 to 19.0 Ω·cm ² , more preferably 1.0 to 18.0 Ω·cm ² , and even more preferably 1.0 to 17.0 Ω·cm ² . The lower limit of the internal resistance is preferably 1.0 Ω·cm ² as described above, but may also be 2.0 Ω·cm ² , 3.0 Ω·cm ² or the like.

In addition, when an electrode active material having an average particle size of 0.1 to 13.0 μm is used as the electrode active material (the case of the second embodiment described above), the internal resistance calculated as described above at 0°C and 0.5°C is preferably 1.0 to 45.0 Ω·cm ² , more preferably 1.0 to 40.0 Ω·cm ² , and further preferably 1.0 to 38.0 Ω·cm ² . That is, according to the present invention, even under low temperature conditions where the internal resistance is likely to increase, the internal resistance can be sufficiently reduced to make the reaction uniform. It should be noted that the lower limit of the internal resistance is preferably 1.0 Ω·cm ² as described above, but 2.0 Ω·cm ² , 3.0 Ω·cm ² , etc. can also be used as the lower limit.

It should be noted that in the charging process for making the above-mentioned SOC 100%, as described above, when charging is performed at 3.0C as a high load condition, there is a concern that the electrodeposition of lithium in the negative electrode will occur, so it is preferred not to perform charging under high load conditions. In addition, the temperature condition is preferably set to 20°C or above at which the internal resistance decreases. In addition, since the purpose is to make the state before the measurement a state in which no uneven reaction occurs by fully absorbing lithium ions in the negative electrode, in the charging process for reaching the above-mentioned SOC 100%, it is preferred to charge with constant current low voltage charging (CCCV charging) until the upper limit voltage equivalent to SOC 100%. In addition, the charging rate is preferably 0.01 to 1.0C, and more preferably 0.01 to 0.75C. It should be noted that, as described above, the lower limit of the charging rate is preferably 0.01C, but 0.02C, 0.03C, etc. can also be used as the lower limit.

Example

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples.

It should be noted that in the following examples, the graphite particles and hard carbon used as negative electrode active materials are expressed by the following formula:

(Volume when fully charged) - (Volume when fully discharged) / (Volume when fully discharged)) × 100

The calculated volume changes were all 0%.

[First method]

Comparative Examples 1 to 7

The composition shown in Tables 1 and 2 was added with graphite particles (spherical coated natural graphite; average particle size 17 μm) as negative electrode active material, carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) as other negative electrode constituent materials, and an appropriate amount of water for kneading to form a slurry. The slurry was applied on a copper foil (thickness 10 μm) with a scraper in such a way that the weight per unit area of the negative electrode active material layer after drying became 10.3 to 10.9 mg/cm ² , dried at 60°C, rolled in such a way that the density of the negative electrode active material layer became 1.3 g/cm ³ , and dried under reduced pressure at 120°C to obtain a negative electrode.

However, in Comparative Example 7, the negative electrode could not be produced due to insufficient strength.

Examples 1 to 6 and Comparative Examples 8 to 9

The above-mentioned graphite particles, single-layer carbon nanotubes (bundled single-layer CNT aggregates; average outer diameter of each single-layer CNT is 2nm, average length is greater than 5μm, G/D: 80-150) as negative electrode active materials, the above-mentioned CMC and SBR as other negative electrode constituent materials, and an appropriate amount of water were added and kneaded to prepare slurry. The slurry was applied on the above-mentioned copper foil with a scraper in such a manner that the weight per unit area of the negative electrode active material layer after drying was 10.3-10.9mg/ ^cm2 , and after drying at 60°C, it was rolled in such a manner that the density of the negative electrode active material layer was 1.3g/ ^cm3 , and dried under reduced pressure at 120°C to obtain a negative electrode.

However, in Comparative Example 9, the amount of single-walled CNTs relative to the amount of CMC as a dispersant was large, resulting in poor dispersion of the single-walled CNTs, and thus, it was not possible to produce a negative electrode.

Example 7

The graphite particles, the single-layer CNT and an appropriate amount of N-methylpyrrolidone (NMP) were added to the composition shown in Tables 1 and 2 and kneaded to form a slurry. The slurry was applied to the copper foil with a scraper in such a way that the weight per unit area of the negative electrode active material layer after drying became 10.3 to 10.9 mg/cm ² , and after drying at 100° C., the negative electrode was rolled in such a way that the density of the negative electrode active material layer became 1.3 g/cm ³ , and dried under reduced pressure at 170° C. to obtain a negative electrode.

The compositions of the respective Examples and Comparative Examples are shown in Tables 1 and 2. Table 1 shows the mass ratio, and Table 2 shows the volume ratio.

[Table 1]

[Table 2]

Manufacturing Example: Manufacturing of Lithium Ion Secondary Battery

As the negative electrode, the negative electrodes obtained in Examples 1 to 7 and Comparative Examples 1 to 6 were used.

Relative to the total weight of the positive electrode composition, 93.0 wt% of LiNi1 _/ 3Mn1 _{/3Co1 / 3O2} (NMC111; average particle size 10 μm) as a positive electrode active material, 3.0 wt% of polyvinylidene fluoride (PVdF) and 4.0 wt% of acetylene black as other positive electrode constituent materials, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) were added and kneaded to prepare a slurry. The slurry was applied on an aluminum foil (thickness 15 μm) with a doctor blade in such a manner that the weight per unit area of the positive electrode active material layer after drying became 20.6 to 21.8 mg/ ^cm2. After drying at 100°C, the slurry was roll-pressed in such a manner that the density of the positive electrode active material layer became 2.55 g/ ^cm3 , and dried at 170°C under reduced pressure to obtain a positive electrode.

The electrolyte used was a solvent obtained by mixing ethylene carbonate (EC) and methyl ethyl carbonate (MEC) at a volume ratio of 3:7 and 1 mol/L lithium hexafluorophosphate (LiPF ₆ ) as a salt. The polyethylene porous membrane as a separator was impregnated with the electrolyte.

A lithium ion secondary battery composed of the negative electrode, positive electrode, electrolyte and separator was produced. The facing area of the positive and negative electrodes of the produced lithium ion secondary battery was set to 2.8 cm ² .

Test Example 1: Initial charge and discharge characteristics

For the purpose of confirming the initial charge and discharge capacity, a charge and discharge test was performed on the lithium ion secondary batteries of the prepared examples and comparative examples.

Regarding charge and discharge, the battery was charged at a constant current low voltage (CCCV) at a charge rate of 0.2C until the upper limit voltage reached 4.2V, and then the current value was 0.05C. After a 10-minute rest, the battery was discharged at a discharge rate of 0.2C until the lower limit voltage reached 2.7V, and then rested for 10 minutes. The results of the initial charge and discharge characteristics are shown in Table 3.

Even when the total amount excluding active materials and single-layer carbon nanotubes is as low as less than 1.2 mass % (less than 1.63 volume %), there is almost no effect on the initial characteristics compared to previous lithium-ion secondary batteries in which the total amount excluding active materials and single-layer carbon nanotubes is larger, and the initial charge and discharge characteristics are the same as those of the case without single-layer carbon nanotubes.

Test Example 2: Determination of reaction resistance

In the lithium ion secondary batteries of the embodiments and comparative examples, the charge and discharge reaction of the graphite negative electrode active material was measured:

[Chemistry 1]

For the purpose of measuring the resistance of the reaction, an AC impedance measurement was performed as a general method for measuring the reaction resistance.

Regarding the reaction resistance, the minimum intercept of the Z' axis in the Nyquist plot is taken as the bulk resistance, and the value obtained by subtracting the bulk resistance from the arc terminal resistance value is analyzed as the reaction resistance. As the measurement conditions, at 25°C, with the battery voltage as the reference, under the condition that the SOC (State of Charge) is 100%, the amplitude is set to 10mV, and the frequency is implemented from 500kHz to 0.1Hz. It should be noted that the outline of the analysis method in the AC impedance measurement is shown in Figure 2.

The results of the AC impedance measurement are shown in Table 3 and Figure 3. As a result, it is almost impossible to confirm the difference in reaction resistance caused by the difference in the amount of negative electrode constituent materials other than the negative electrode active material. Therefore, the generally evaluated reaction resistance is an indicator that does not include the influence caused by the uneven reaction, and it can be understood that it is impossible to evaluate the unevenness of the reaction by measuring the general electrode resistance.

Test Example 3: Internal resistance under high load conditions

In the lithium ion secondary batteries of the examples and comparative examples, internal resistance was measured by a high load rest method for the purpose of confirming the degree of reaction non-uniformity.

Specifically, for the lithium-ion secondary batteries of each embodiment and comparative example, at 25°C, under the condition of a charge rate of 0.5C, the cutoff current was set to 0.05C, and constant current low voltage charging (CCCV charging) was performed to an upper limit voltage of 4.2V equivalent to SOC100%. Then, after resting for 10 minutes, the battery was discharged (2 minutes) to SOC90% under the condition of a discharge rate of 3.0C, and then rested for 10 minutes. The electric rate SOC is defined as the following formula (1):

SOC (%) = remaining capacity (Ah) / full charge capacity (Ah) × 100 (1).

On this basis, through the following formula:

Internal resistance = (voltage rise during rest "ΔV (10 min)" / current value during discharge "3C current value") × facing area of positive and negative electrodes "2.8 cm ² "

The internal resistance is calculated. In addition, the outline of the analysis method in the high load rest method is shown in FIG4 .

The results of the high-load rest method are shown in Table 3 and FIG. 5 .

As a result, it was confirmed that: regardless of the total amount other than the active material and the single-walled carbon nanotubes, although the reaction resistance was the same, by reducing the total amount other than the active material and the single-walled carbon nanotubes to a small amount, the internal resistance under high load conditions was drastically reduced, that is, the reaction non-uniformity of the electrode was suppressed.

[table 3]

Test Example 4: Lifespan Characteristics

For the lithium ion secondary batteries of each embodiment and comparative example, a charge and discharge cycle test was performed at 45°C. The charge and discharge conditions are as follows: until the upper limit voltage is 4.2V, constant current low voltage charging (CCCV charging) is performed at a charging rate of 0.5C until the current value is 0.05C, after resting for 10 minutes, discharge at a discharge rate of 0.5C until the lower limit voltage is 2.7V, and then rest for 10 minutes. These charge and discharge processes are regarded as one cycle, and the charge and discharge cycle test is performed. In addition, the charge and discharge are performed every 25 cycles until 100 cycles, and every 100 cycles after 100 cycles to confirm the capacity of the lithium ion secondary batteries of each embodiment and comparative example. In order to confirm the charge and discharge of the capacity, until the upper limit voltage is 4.2V, constant current low voltage charging (CCCV charging) is performed at a charging rate of 0.2C until the current value is 0.05C, after resting for 10 minutes, discharge at a discharge rate of 0.2C until the lower limit voltage is 2.7V, and then rest for 10 minutes.

The results of the charge and discharge cycle characteristics are shown in FIG6 .

As a result, in the case where the total amount of negative electrode constituent materials other than the negative electrode active material and the carbon nanotubes was 2.5% by mass and 4.75% by volume (Comparative Example 1) without single-layer carbon nanotubes, secondary degradation was confirmed after 200 cycles, in which the rate of decrease of the capacity retention rate relative to the number of cycles became larger, and the capacity retention rate after 300 cycles was 73%. It is presumed that due to the large proportion of negative electrode constituent materials other than the negative electrode active material and the carbon nanotubes, the reaction in the electrode was uneven, resulting in secondary degradation. In addition, when the amount of negative electrode constituent materials other than the negative electrode active material and the carbon nanotubes was reduced to 1.0% by mass in order to suppress the uneven reaction in the electrode, the strength of the electrode was reduced, and due to the volume change of the active material layer of the electrode accompanying charge and discharge, a sharp decrease in capacity was confirmed from the initial stage of the cycle, which was believed to be caused by the isolation of the active material, and the life characteristics were further deteriorated. It can be seen from this that by reducing the total amount of negative electrode constituent materials other than the negative electrode active material and carbon nanotubes, even if the negative electrode shown in Test Example 3 with reduced internal resistance under high load, i.e., with suppressed reaction unevenness, is used for a lithium-ion secondary battery, good life characteristics cannot be obtained unless the electrode strength is sufficient to follow the volume changes accompanying charge and discharge.

On the other hand, it was confirmed that: in the case of containing a small amount (less than 1.4% by mass) of single-walled carbon nanotubes, even if the total amount of negative electrode constituent materials other than the negative electrode active material and the carbon nanotubes is small (less than 1.2% by mass) or does not contain (0% by mass), the above-mentioned rapid decrease in capacity, which is believed to be caused by the isolation of the active material, does not occur, and the electrode has a degree of strength that can follow the volume change accompanying charge and discharge. In addition, it can be understood that even after 200 cycles, secondary degradation is suppressed and the life characteristics are improved. For the battery of Example 7, the following formula is used

Capacity reduction = A × (number of cycles) ^β

The above-mentioned A and β were determined by the least square method from the measured data, and the life was estimated, and the results are shown in Figure 7. As described above, in Comparative Example 1, the capacity retention rate after 300 cycles was 73%, so the number of cycles at which the battery of Example 7 reached a capacity retention rate of 73% was calculated. As a result, it was estimated that the number of cycles at which the battery of Example 7 reached a capacity retention rate of 73% was 1300 cycles, and compared with 300 cycles in Comparative Example 1, it can be seen that the battery life was improved by about 4.3 times.

The results of the internal resistance of Test Example 3 and the life characteristics of Test Example 4 described above are summarized in FIG. 8 .

[Second method]

Comparative Examples 10 and 12

In the composition shown in Tables 4 and 5, graphite particles as negative electrode active materials, carboxymethyl cellulose (CMC) and styrene butadiene (SBR) as other negative electrode constituent materials, and an appropriate amount of water were added and kneaded to prepare slurry. The slurry was applied on a copper foil (10 μm) with a scraper in such a manner that the weight per unit area of the negative electrode active material layer after drying became 10.3 to 10.9 mg/cm ² , and after drying at 60°C, it was rolled in such a manner that the density of the negative electrode active material layer became 1.3 g/cm ³ , and dried under reduced pressure at 120°C to obtain a negative electrode. It should be noted that as graphite particles, coated natural graphite (average particle size 17.0 μm) or coated natural graphite (average particle size 5.0 μm) was used.

Examples 8 to 9 and Comparative Example 11

In the composition shown in Tables 4 and 5, graphite particles as negative electrode active materials, single-layer carbon nanotubes (bundled single-layer CNT aggregates; average outer diameter of each single-layer CNT is 2nm, average length>5μm, G/D: 80-150) and an appropriate amount of N-methylpyrrolidone (NMP) were added and kneaded to prepare slurry. The slurry was applied on the above copper foil with a scraper in such a way that the weight per unit area of the negative electrode active material layer after drying became 10.3-10.9mg/ ^cm2 , and after drying at 100°C, it was rolled in such a way that the density of the negative electrode active material layer became 1.3g/ ^cm3 , and dried under reduced pressure at 170°C to obtain a negative electrode. It should be noted that as graphite particles, coated natural graphite (average particle size 17.0μm), coated natural graphite (average particle size 12.0μm) or coated natural graphite (average particle size 5.0μm) was used.

Embodiments 10 to 12

The graphite particles as the negative electrode active material, the above-mentioned single-layer CNT, carboxymethyl cellulose (CMC) as other negative electrode constituent materials, and an appropriate amount of water were added to the composition shown in Tables 4 and 5 and kneaded to form a slurry. The slurry was applied to the above-mentioned copper foil with a scraper in such a way that the weight per unit area of the negative electrode active material layer after drying became 10.3 to 10.9 mg/cm ² , and after drying at 60°C, it was rolled in such a way that the density of the negative electrode active material layer became 1.3 g/cm ³ , and dried under reduced pressure at 120°C to obtain a negative electrode. It should be noted that as graphite particles, coated natural graphite (average particle size 5.0 μm) was used.

The compositions of the examples and comparative examples are shown in Tables 4 and 5. Table 4 shows the mass ratio, and Table 5 shows the volume ratio.

[Table 4]

[table 5]

Manufacturing Example: Manufacturing of Lithium Ion Secondary Battery

As the negative electrode, the negative electrodes obtained in Examples 8 to 12 and Comparative Examples 10 to 12 were used.

Relative to the total mass of the positive electrode composition, 92.0 mass % of LiNi _0.8 Co _0.15 Al _0.05 O ₂ (NCA; average particle size 6 μm) as a positive electrode active material, 4.0 mass % of polyvinylidene fluoride (PVdF) and 4.0 mass % of acetylene black as other positive electrode constituent materials, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) were added and kneaded to prepare a slurry. The slurry was applied on an aluminum foil (thickness 17 μm) with a scraper in such a manner that the mass per unit area of the positive electrode active material layer after drying became 20.05 to 21.29 mg/cm ^2. After drying at 100°C, the slurry was roll-pressed in such a manner that the density of the positive electrode active material layer became 3.0 g/cm ³ , and dried under reduced pressure at 170°C to obtain a positive electrode.

The electrolyte used was a solvent obtained by mixing ethylene carbonate (EC) and methyl ethyl carbonate (MEC) at a volume ratio of 3:7 and 1 mol/L lithium hexafluorophosphate (LiPF ₆ ) as a salt. The polyethylene porous membrane as a separator was impregnated with the electrolyte.

A lithium ion secondary battery composed of the negative electrode, positive electrode, electrolyte and separator was produced. The facing area of the positive and negative electrodes of the produced lithium ion secondary battery was 2.8 cm ² .

Test Example 5: Initial charge and discharge characteristics

For the purpose of confirming the initial charge and discharge capacity, a charge and discharge test was performed on the lithium ion secondary batteries of the prepared examples and comparative examples.

Regarding charge and discharge, constant current constant voltage charge (CCCV charge) was performed at a charge rate of 0.1C until the upper limit voltage reached 4.0V, until the current value reached 0.05C, and after a 10-minute rest, the battery was discharged at a discharge rate of 0.1C until the lower limit voltage reached 2.7V, and then rested for 10 minutes. The results of the initial charge and discharge characteristics are shown in Table 6.

Even in the case where the particle size of the negative electrode active material is reduced or the total amount excluding the negative electrode active material and the single-layer carbon nanotubes is reduced to less than 2.0 mass % (less than 4.52 volume %), there is almost no effect on the initial characteristics compared to the case where the negative electrode active material is large or the total amount excluding the negative electrode active material and the single-layer carbon nanotubes is large, and the initial charge and discharge characteristics have the same degree.

Test Example 6: Determination of reaction resistance

In the lithium ion secondary batteries of the embodiments and comparative examples, the charge and discharge reaction of the graphite negative electrode active material was measured:

[Chemistry 2]

For the purpose of measuring the resistance of the reaction, an AC impedance measurement was performed as a general method for measuring the reaction resistance.

Regarding the reaction resistance, the minimum intercept of the Z' axis in the Nyquist plot is taken as the bulk resistance, and the value obtained by subtracting the bulk resistance from the arc terminal resistance value is analyzed as the reaction resistance. As the measurement conditions, at 25°C, with the battery voltage as the reference, under the condition that the SOC (State of Charge) is 100%, the amplitude is set to 10mV, and the frequency is implemented from 500kHz to 0.1Hz. It should be noted that the outline of the analysis method in the AC impedance measurement is shown in Figure 2.

The results of the AC impedance measurement are shown in Table 6 and Figure 9. As a result, some differences in reaction resistance caused by the particle size of the negative electrode active material and the amount of negative electrode constituent materials other than the negative electrode active material were observed, and a trend of lowering the reaction resistance when the particle size of the negative electrode active material was reduced and the amount of negative electrode constituent materials other than the negative electrode active material was reduced was observed. However, the generally evaluated reaction resistance is an indicator that does not include the influence caused by the uneven reaction, and it can be assumed that it is difficult to evaluate the unevenness of the reaction by measuring the general electrode resistance.

Test Example 7: Internal resistance under high load conditions

In order to confirm the degree of reaction non-uniformity, the internal resistance of the lithium ion secondary batteries of Examples and Comparative Examples was measured by the high load rest method at room temperature (25° C.) and the high load rest method at low temperature (0° C.).

Regarding the determination of internal resistance based on the high-load rest method at room temperature (25°C), specifically, for the lithium-ion secondary batteries of each embodiment and comparative example, at room temperature (25°C), under the condition of a charge rate of 0.5C, the cutoff current is set to 0.05C, and constant current constant voltage charging (CCCV charging) is performed to an upper limit voltage of 4.0V corresponding to SOC100%. Then, after resting for 10 minutes, it is discharged to SOC90% (2 minutes) under the condition of a discharge rate of 3.0C, and then rested for 10 minutes. The charge rate SOC is defined as the following formula (1):

SOC (%) = remaining capacity (Ah) / full charge capacity (Ah) × 100 (1).

On this basis, through the following formula:

Internal resistance = (voltage rise during rest "ΔV (10 min)" / current value during discharge "3.0 C current value") × facing area of positive and negative electrodes "2.8 cm ² "

The internal resistance is calculated. In addition, the outline of the analysis method in the high load rest method is shown in FIG4 .

In addition, regarding the determination of internal resistance based on the high-load rest method at low temperature (0°C), specifically, for the lithium-ion secondary batteries of each embodiment and comparative example, at room temperature (25°C), under the condition of a charge rate of 0.5C, the cutoff current is set to 0.05C, and constant current constant voltage charging (CCCV charging) is performed to an upper limit voltage of 4.0V corresponding to SOC100%. Then, the temperature is changed to 0°C, and after resting for 180 minutes, it is discharged (12 minutes) to SOC90% under the condition of a discharge rate of 0.5C, and then rested for 1 minute. The charge rate SOC is defined as the following formula (1):

SOC (%) = remaining capacity (Ah) / full charge capacity (Ah) × 100 (1).

On this basis, through the following formula:

Internal resistance = (voltage rise during rest "ΔV (1 min)" / current value during discharge "0.5 C current value") × facing area of positive and negative electrodes "2.8 cm ² "

Calculate the internal resistance.

The results of these high-load rest methods are shown in Table 6 and FIGS. 10 and 11 .

As a result, it can be confirmed that although only some differences in reaction resistance caused by the difference in the particle size of the negative electrode active material and the amount of the negative electrode constituent material other than the negative electrode active material are observed, the internal resistance under high load conditions is reduced by reducing the particle size of the negative electrode active material and reducing the amount of the negative electrode constituent material other than the negative electrode active material, that is, the reaction non-uniformity of the electrode is suppressed. It can be understood that this trend is particularly significantly observed at low temperatures where the internal resistance is likely to increase, and the effect of the present invention is significantly observed under severe conditions where the internal resistance is likely to increase.

[Table 6]

Test Example 8: Extreme Load Characteristics

For the lithium ion secondary batteries of Example 9 and Comparative Examples 10 to 12, as shown in Table 5, the overvoltage load was gradually increased from Condition 1 to Condition 12 to perform a charge and discharge cycle test. It should be noted that 10 cycles were performed for each condition, and a total of 120 cycles of charge and discharge were performed. In addition, in each charging cycle, constant current charging (CC charging) was performed until the upper limit voltage was 4.0V, and after resting for 10 minutes, it was discharged until the lower limit voltage was 2.7V, and then rested for 10 minutes.

Then, by the following formula:

Overvoltage load (mV) = current value at 1C (mA) × charge and discharge rate (C) × DC resistance (Ω)

On this basis, the overvoltage load at which the capacity retention rate fell below 99.0% for the first time in 10 cycles of charge and discharge under each condition was evaluated as the limit overvoltage load.

The DC resistance at each temperature of the lithium ion secondary batteries of Example 9 and Comparative Examples 10 to 12 is shown in Table 7, the conditions of the charge and discharge cycle and the results of the overvoltage load at that time are shown in Table 8, the results of the limit overvoltage load are shown in Table 9, the results of the capacity maintenance rate during the charge and discharge cycle are shown in Figure 12, and the results of the capacity maintenance rate for 10 cycles of overvoltage load are shown in Figure 13.

[Table 7]

[Table 8]

[Table 9]

From the above results, it can be understood that, whether in the case of reducing the particle size of the negative electrode active material or in the case of adding a small amount of carbon nanotubes to reduce the amount of negative electrode constituent materials other than the negative electrode active material, the overvoltage load cannot be fully reduced at any temperature alone, and the charge-discharge cycle characteristics and rate characteristics are also insufficient. In contrast, it can be understood that in the present invention in which the particle size of the negative electrode active material is reduced, a small amount of carbon nanotubes is added, and the amount of negative electrode constituent materials other than the negative electrode active material is reduced, the overvoltage load can be fully reduced at any temperature, and the charge-discharge cycle characteristics and rate characteristics can be improved. It should be noted that it can be understood that in Example 9, even if the overvoltage load is increased to condition 12, the capacity retention rate of 10 cycles is not less than 99%, so the value of the limit overvoltage load in Table 10 is greater than the overvoltage load of condition 12, i.e., 195mV, and is therefore above 195.

Test Example 9: Lifespan Characteristics

For the lithium ion secondary batteries of Example 9, Comparative Example 10 and Comparative Example 12, a charge and discharge cycle test was performed at 25°C. The charge and discharge conditions were as follows: until the upper limit voltage was 4.0V, constant current constant voltage charging (CCCV charging) was performed at a charge rate of 0.5C until the current value was 0.05C, and after a rest of 10 minutes, the discharge was performed at a discharge rate of 0.5C until the lower limit voltage was 2.7V, and then rested for 10 minutes. These charge and discharge steps were regarded as 1 cycle, and the charge and discharge cycle test was performed.

The results of the charge and discharge cycle characteristics are shown in Table 10 and FIG. 13 .

[Table 10]

As a result, it can be understood that in the present invention, in which the particle size of the negative electrode active material is reduced and a small amount of carbon nanotubes is added to reduce the amount of negative electrode constituent materials other than the negative electrode active material, the overvoltage load can be sufficiently reduced and the charge and discharge cycle characteristics and rate characteristics can be improved.

[Third Method]

Comparative Example 13

93.0 mass % of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (NMC111; average particle size 10 μm) as a positive electrode active material, 4.0 mass % of acetylene black (AB) as a conductive aid other than carbon nanotubes, 3.0 mass % of polyvinylidene fluoride (PVdF) as another positive electrode constituent material, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) were added and kneaded to prepare a slurry. The slurry was applied on an aluminum foil (thickness 15 μm) with a doctor blade so that the weight per unit area of the positive electrode active material layer after drying was 21.2 mg/cm ² , dried at 100° C., and then rolled so that the density of the positive electrode active material layer was 2.55 g/cm ³ , and dried under reduced pressure at 170° C. to obtain a positive electrode.

Example 13

96.0 mass% of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (NMC111; average particle size 10 μm) as a positive electrode active material, 0.5 mass% of single-walled carbon nanotubes (bundled single-walled CNT aggregates; average outer diameter of each single-walled CNT 2 nm, average length>5 μm, G/D: 80-150), 3.5 mass% of acetylene black (AB) as a conductive aid other than carbon nanotubes, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) were added and kneaded to prepare a slurry. The slurry was applied on an aluminum foil (thickness 15 μm) with a doctor blade so that the weight per unit area of the positive electrode active material layer after drying was 20.6 mg/cm ² , dried at 100°C, and then rolled so that the density of the positive electrode active material layer was 2.55 g/cm ³ , and dried under reduced pressure at 170°C to obtain a positive electrode.

The compositions of the examples and comparative examples are shown in Table 11.

[Table 11]

Manufacturing Example: Manufacturing of Lithium Ion Secondary Battery

As the positive electrode, the positive electrodes obtained in Example 13 and Comparative Example 13 were used.

Relative to the total weight of the negative electrode composition, 97.5% by mass of graphite particles (spherical coated natural graphite; average particle size 17 μm) as a negative electrode active material, 1.0% by mass of carboxymethyl cellulose (CMC) and 1.5% by mass of styrene butadiene rubber (SBR) as other negative electrode constituent materials, and an appropriate amount of water are added and kneaded to form a slurry, and the slurry is applied on a copper foil (thickness 10 μm) with a scraper in such a way that the weight per unit area of the negative electrode active material layer after drying becomes 10.6 mg/ ^cm2 . After drying at 60°C, it is rolled in such a way that the density of the negative electrode active material layer becomes 1.3 g/ ^cm3 , and dried under reduced pressure at 120°C to obtain a negative electrode.

The electrolyte used was a solvent obtained by mixing ethylene carbonate (EC) and methyl ethyl carbonate (MEC) at a volume ratio of 3:7 and 1 mol/L lithium hexafluorophosphate (LiPF ₆ ) as a salt. The polyethylene porous membrane as a separator was impregnated with the electrolyte.

A lithium ion secondary battery composed of the positive electrode, negative electrode, electrolyte and separator was produced. The facing area of the positive and negative electrodes of the produced lithium ion secondary battery was 2.8 cm ² .

Test Example 10: Initial charge and discharge characteristics

In each of the manufactured lithium ion secondary batteries of Example 13 and Comparative Example 13, a charge and discharge test was performed for the purpose of confirming the initial charge and discharge capacity.

Regarding charging and discharging, constant current constant voltage charging (CCCV charging) was performed at a charging rate of 0.2C until the upper limit voltage was 4.2V, until the current value was 0.05C, and after a rest of 10 minutes, the battery was discharged at a discharge rate of 0.2C until the lower limit voltage was 2.7V, and then rested for 10 minutes. As a result, in Example 13, the charging capacity was 9.32mAh, the discharging capacity was 7.93mAh, and the coulombic efficiency was 85.09%, and in Comparative Example 13, the charging capacity was 9.53mAh, the discharging capacity was 8.24mAh, and the coulombic efficiency was 86.46%.

Even when the positive electrode constituent materials other than the positive electrode active material, carbon nanotubes, and the conductive additive other than the carbon nanotubes are not included, there is almost no influence on the initial characteristics, and the initial charge and discharge characteristics are equivalent to those when the positive electrode constituent materials are included.

Test Example 11: Internal resistance under high load conditions

In the lithium ion secondary batteries of Example 13 and Comparative Example 13, internal resistance was measured by a high load rest method for the purpose of confirming the degree of reaction non-uniformity.

Specifically, for the lithium ion secondary batteries of Example 13 and Comparative Example 13, at 25°C, under the condition of a charge rate of 0.5C, the cutoff current was set to 0.05C, and constant current constant voltage charging (CCCV charging) was performed to an upper limit voltage of 4.2V corresponding to SOC100%. Then, after resting for 10 minutes, the battery was discharged (2 minutes) to SOC90% under the condition of a discharge rate of 3.0C, and then rested for 10 minutes. The charge rate SOC is defined as the following formula (1):

SOC (%) = remaining capacity (Ah) / full charge capacity (Ah) × 100 (1).

On this basis, through the following formula:

Internal resistance = (voltage rise during rest "ΔV (10 min)" / current value during discharge "3C current value") × facing area of positive and negative electrodes "2.8 cm ² "

The internal resistance is calculated. In addition, the outline of the analysis method in the high load rest method is shown in FIG4 .

As a result of the high load rest method, the internal resistance of Example 13 was 25.90 Ω·cm ² , and the internal resistance of Comparative Example 13 was 36.46 Ω·cm ² .

As a result, it was confirmed that by adding a small amount of carbon nanotubes and not containing any positive electrode constituent materials other than the positive electrode active material, carbon nanotubes, and conductive additives other than carbon nanotubes, the internal resistance under high load conditions was significantly reduced, that is, the reaction non-uniformity of the electrode was suppressed.

Test Example 12: Lifespan Characteristics

For the lithium ion secondary batteries of Example 13 and Comparative Example 13, a charge and discharge cycle test was carried out at 45°C. The charge and discharge conditions are as follows: until the upper limit voltage is 4.2V, constant current constant voltage charging (CCCV charging) is performed at a charge rate of 0.5C until the current value is 0.05C, and after a rest of 10 minutes, the battery is discharged at a discharge rate of 0.5C until the lower limit voltage is 2.7V, and then rest for 10 minutes. These charge and discharge steps are regarded as 1 cycle, and 400 cycles of charge and discharge cycle tests are carried out. It should be noted that at 50 cycles, 100 cycles, 200 cycles and 300 cycles, charge and discharge are carried out to confirm the capacity of the lithium ion secondary batteries of Example 13 and Comparative Example 13. Regarding the charge and discharge to confirm the capacity, the upper limit voltage was 4.2V, and constant current low voltage charging (CCCV charging) was performed at a charging rate of 0.2C until the current value reached 0.05C. After a rest of 10 minutes, the battery was discharged at a discharge rate of 0.2C until the lower limit voltage reached 2.7V, and then rested for 10 minutes.

The results of the charge and discharge cycle characteristics are shown in FIG15 . The capacity retention rate (400 cycles) of Example 13 is 76.9%, and the capacity retention rate (400 cycles) of Comparative Example 13 is 53.5%. In addition, in Comparative Example 13, after 200 cycles, secondary degradation was confirmed in which the rate of decrease in the capacity retention rate relative to the number of cycles became larger. It is presumed that the secondary degradation is caused by the uneven reaction accompanying the charge and discharge cycle. On the other hand, it can be confirmed that in Example 13, which is configured to add a small amount of carbon nanotubes and does not contain a positive electrode constituent material other than a positive electrode active material, carbon nanotubes, and a conductive aid other than carbon nanotubes, secondary degradation is suppressed and the charge and discharge cycle characteristics are improved. It should be noted that in Comparative Example 13, the capacity increased sharply during the charge and discharge for capacity confirmation at 50 cycles, 100 cycles, 200 cycles, and 300 cycles, and it can be understood that in Comparative Example 13, the reaction non-uniformity was significant during the charge and discharge cycle, and the reaction non-uniformity was alleviated by the charge and discharge for capacity confirmation, and the capacity was restored. On the other hand, in Example 13, the capacity did not increase sharply during the charge and discharge for capacity confirmation, and it can be understood that the reaction non-uniformity was suppressed.

[Fourth Method]

Comparative Example 14

90.0% by mass of hard carbon (hard graphitizable carbon material; particle shape: spherical; average particle size 5 μm) as a negative electrode active material, 5.0% by mass of acetylene black (AB) as a conductive aid other than carbon nanotubes, 5.0% by mass of polyvinylidene fluoride (PVdF) as another negative electrode constituent material, and an appropriate amount of N-methylpyrrolidone (NMP) were added and kneaded to prepare a slurry. The slurry was applied on a copper foil (thickness 10 μm) with a doctor blade so that the weight per unit area of the negative electrode active material layer after drying was 10.6 mg/cm ² , dried at 100° C., and then rolled so that the density of the negative electrode active material layer was 1.0 g/cm ³ , and dried at 170° C. under reduced pressure to obtain a negative electrode.

Embodiment 14

90.0% by mass of hard carbon (hard graphitizable carbon material; particle shape: spherical: average particle diameter 5 μm) as negative electrode active material, 0.1% by mass of single-layer carbon nanotubes (bundled single-layer CNT aggregate; average outer diameter of each single-layer CNT 2 nm, average length>5 μm, G/D: 80-150) as carbon nanotubes, 4.9% by mass of acetylene black (AB) as a conductive aid other than carbon nanotubes, 5.0% by mass of polyvinylidene fluoride (PVdF) as other negative electrode constituent materials, and an appropriate amount of N-methylpyrrolidone (NMP) were added and kneaded to prepare slurry. The slurry was applied on the copper foil with a doctor blade so that the weight per unit area of the negative electrode active material layer after drying was 10.6 mg/ ^cm2 , dried at 100°C, rolled so that the density of the negative electrode active material layer was 1.0 g/ ^cm3 , and dried under reduced pressure at 170°C to obtain a negative electrode.

Table 12 shows the compositions of the examples and comparative examples.

[Table 12]

Manufacturing Example: Manufacturing of Lithium Ion Secondary Battery

As the negative electrode, the negative electrodes obtained in Example 14 and Comparative Example 14 were used.

Relative to the total weight of the positive electrode composition,

92.0 mass % of LiNi _0.8 Co _0.15 Al _0.05 O ₂ (NCA; average particle size 6 μm) as a positive electrode active material, 4.0 mass % of polyvinylidene fluoride (PVdF) as other positive electrode constituent materials, 4.0 mass % of acetylene black (AB), and an appropriate amount of N-methyl-2-pyrrolidone (NMP) were added and kneaded to prepare a slurry. The slurry was applied on an aluminum foil (thickness 17 μm) with a scraper in such a way that the mass per unit area of the positive electrode active material layer after drying became 16.2 mg/cm ^2. After drying at 100°C, the slurry was roll-pressed in such a way that the density of the positive electrode active material layer became 3.0 g/cm ³ , and dried under reduced pressure at 170°C to obtain a positive electrode.

The electrolyte used was a solvent obtained by mixing ethylene carbonate (EC) and methyl ethyl carbonate (MEC) at a volume ratio of 3:7 and 1 mol/L lithium hexafluorophosphate (LiPF ₆ ) as a salt. The polyethylene porous membrane as a separator was impregnated with the electrolyte.

A lithium ion secondary battery composed of the negative electrode, positive electrode, electrolyte and separator was produced. The facing area of the positive and negative electrodes of the produced lithium ion secondary battery was 2.8 cm ² .

Test Example 13: Initial charge and discharge characteristics

The lithium ion secondary batteries of Example 14 and Comparative Example 14 produced were subjected to a charge and discharge test for the purpose of confirming the initial charge and discharge capacity.

Regarding charging and discharging, constant current constant voltage charging (CCCV charging) was performed until the upper limit voltage was 4.05V and the charging rate was 0.1C until the current value was 0.05C, and after resting for 10 minutes, the battery was discharged at a discharge rate of 0.1C until the lower limit voltage was 2.0V, and then rested for 10 minutes. As a result, in Example 14, the charging capacity was 7.68mAh, the discharging capacity was 5.14mAh, and the coulombic efficiency was 66.9%, and in Comparative Example 14, the charging capacity was 7.76mAh, the discharging capacity was 4.90mAh, and the coulombic efficiency was 63.1%.

It was confirmed that the inclusion of a small amount of carbon nanotubes in order to form a uniform electron conduction path improves the initial coulombic efficiency and increases the discharge capacity.

Test Example 14: Internal resistance under high load conditions

In the lithium ion secondary batteries of Example 14 and Comparative Example 14, internal resistance was measured by a high load rest method for the purpose of confirming the degree of reaction non-uniformity.

Specifically, for the lithium ion secondary batteries of Example 14 and Comparative Example 14, at 25°C, under the condition of a charge rate of 0.5C, the cutoff current was set to 0.05C, and constant current constant voltage charging (CCCV charging) was performed to an upper limit voltage of 4.05V corresponding to SOC100%. Then, after resting for 10 minutes, the battery was discharged (2 minutes) to SOC90% under the condition of a discharge rate of 3.0C, and then rested for 10 minutes. The charge rate SOC is defined as the following formula (1):

SOC (%) = remaining capacity (Ah) / full charge capacity (Ah) × 100 (1).

On this basis, through the following formula:

Internal resistance = (voltage rise during rest "ΔV (10 min)" / current value during discharge "3C current value") × facing area of positive and negative electrodes "2.8 cm ² "

The internal resistance is calculated. In addition, the outline of the analysis method in the high load rest method is shown in FIG4 .

As a result of the high load rest method, the internal resistance of Example 14 was 21.67 Ω·cm ² , and the internal resistance of Comparative Example 14 was 28.25 Ω·cm ² .

As a result, it was confirmed that the internal resistance under high load conditions was significantly reduced, that is, the reaction non-uniformity of the electrode was suppressed, by using hard carbon and adding a small amount of carbon nanotubes.

Test Example 15: Lifespan Characteristics

The lithium ion secondary batteries of Example 14 and Comparative Example 14 were subjected to a charge and discharge cycle test at 25°C. The charge and discharge conditions were as follows: until the upper limit voltage was 4.05V, constant current constant voltage charging (CCCV charging) was performed at a charge rate of 0.5C until the current value was 0.05C, and after a rest of 10 minutes, the battery was discharged at a discharge rate of 0.5C until the lower limit voltage was 2.0V, and then rested for 10 minutes. The charge and discharge cycle test was performed with these charge and discharge steps as one cycle.

The results of the charge and discharge cycle characteristics are shown in FIG16 . The capacity retention rate (150 cycles) of Example 14 is 93.0%, and the capacity retention rate (150 cycles) of Comparative Example 14 is 79.7%.

As a result, it was confirmed that the charge-discharge cycle characteristics were improved by using hard carbon and adding a small amount of carbon nanotubes.

Claims (27)

1. A composition for forming an electrode active material layer for a lithium ion secondary battery, characterized in that: The composition contains an electrode active material and carbon nanotubes, When the total amount of the composition is set to 100% by mass, The content of carbon nanotubes is 0.01 to 1.4% by mass. The content of the electrode constituent materials other than the electrode active material and the carbon nanotubes is 0 to 10.0% by mass. 2. The composition for forming an electrode active material layer for a lithium ion secondary battery according to claim 1, wherein The content of the electrode active material is 96.6-99.9% by mass. The content of the electrode constituent materials other than the electrode active material and the carbon nanotubes is 0 to 2.0% by mass, and The composition is a composition for forming a negative electrode active material layer for a lithium ion secondary battery. 3. The composition for forming an electrode active material layer for a lithium ion secondary battery according to claim 1, wherein The content of the electrode active material is 97.4-99.9% by mass. The content of the electrode constituent materials other than the electrode active material and the carbon nanotubes is 0 to 1.2% by mass. 4. The composition for forming an electrode active material layer for a lithium ion secondary battery according to claim 3, wherein The composition is a composition for forming a negative electrode active material layer for a lithium ion secondary battery. 5. The composition for forming an electrode active material layer for a lithium ion secondary battery according to any one of claims 1 to 4, wherein The content of the carbon nanotubes is 0.01 to 0.8% by mass. The electrode active material contains an amorphous carbon material, and The composition is a composition for forming a negative electrode active material layer for a lithium ion secondary battery. 6. A composition for forming an electrode active material layer for a lithium ion secondary battery, characterized in that: The composition contains an electrode active material and carbon nanotubes, When the total volume of the composition is set to 100 volume %, The volume ratio of the electrode active material is 75.06 to 99.97% by volume. The volume ratio of carbon nanotubes is 0.02 to 4.55%. The volume ratio of the electrode constituent materials other than the electrode active material and the carbon nanotubes is 0 to 21.56 volume %. 7. The composition for forming an electrode active material layer for a lithium ion secondary battery according to claim 6, wherein: When the total volume of the composition is set to 100 volume %, The volume ratio of the electrode active material is 93.38-99.98% by volume. The volume ratio of the carbon nanotubes is 0.02 to 2.18% by volume. The volume ratio of the electrode constituent materials other than the negative electrode active material and the carbon nanotubes is 0 to 4.52 volume %, and The composition is a composition for forming a negative electrode active material layer for a lithium ion secondary battery. 8. The composition for forming an electrode active material layer for a lithium ion secondary battery according to claim 6, wherein The volume ratio of the electrode active material is 96.19-99.98% by volume. The volume ratio of the carbon nanotubes is 0.02 to 2.18% by volume. The volume ratio of the electrode constituent materials other than the electrode active material and the carbon nanotubes is 0 to 1.63 volume %. 9. The composition for forming an electrode active material layer for a lithium ion secondary battery according to claim 8, wherein: The composition is a composition for forming a negative electrode active material layer for a lithium ion secondary battery. 10. The composition for forming an electrode active material layer for a lithium ion secondary battery according to any one of claims 1 to 9, wherein The average particle size of the electrode active material is 0.1 to 13.0 μm. 11. The composition for forming an electrode active material layer for a lithium ion secondary battery according to claim 10, wherein The average particle size of the electrode active material is 0.1 to 13.0 μm, and the content thereof is 96.6 to 99.9% by mass. The content of the carbon nanotubes is 0.01 to 1.4% by mass. The content of the electrode constituent materials other than the electrode active material and the carbon nanotubes is 0 to 2.0 mass %, and The composition is a composition for forming a negative electrode active material layer for a lithium ion secondary battery. 12. The composition for forming an electrode active material layer for a lithium ion secondary battery according to claim 10, wherein The average particle size of the electrode active material is 0.1 to 13.0 μm, and the volume ratio thereof is 93.38 to 99.98% by volume. The volume ratio of the carbon nanotubes is 0.02 to 2.18% by volume. The volume ratio of the electrode constituent materials other than the electrode active material and the carbon nanotubes is 0 to 4.52 volume %, and The composition is a composition for forming a negative electrode active material layer for a lithium ion secondary battery. 13. The composition for forming an electrode active material layer for a lithium ion secondary battery according to claim 1 or 10, wherein The content of the electrode active material is 88.6-99.9% by mass. The content of the conductive additive other than the carbon nanotubes is 0 to 10.0% by mass. The composition does not contain electrode constituent materials other than the electrode active material, the carbon nanotubes, and a conductive auxiliary agent other than the carbon nanotubes. The composition is a composition for forming a positive electrode active material layer for a lithium ion secondary battery. 14. The composition for forming an electrode active material layer for a lithium ion secondary battery according to claim 6 or 10, wherein The volume ratio of the electrode active material is 75.06 to 99.97% by volume. The content of the carbon nanotubes is 0.03-4.55% by volume. The content of the conductive additive other than the carbon nanotubes is 0 to 21.56% by volume. The composition does not contain electrode constituent materials other than the electrode active material, the carbon nanotubes, and a conductive auxiliary agent other than the carbon nanotubes. The composition is a composition for forming a positive electrode active material layer for a lithium ion secondary battery. 15. The composition for forming an electrode active material layer for a lithium ion secondary battery according to any one of claims 1 to 14, wherein The electrode active material is a material that can absorb and release lithium ions. 16. The composition for forming an electrode active material layer for a lithium ion secondary battery according to any one of claims 1 to 15, wherein The carbon nanotubes are single-layer carbon nanotubes. 17. The composition for forming an electrode active material layer for a lithium ion secondary battery according to any one of claims 1 to 16, wherein The composition is used to reduce the non-uniformity of a reaction in a lithium ion secondary battery. 18. The composition for forming an electrode active material layer for a lithium ion secondary battery according to any one of claims 1 to 17, wherein A lithium ion secondary battery using the composition is used in an electric car for car sharing. 19 . An electrode active material layer for a lithium ion secondary battery, comprising the composition for forming an electrode active material layer for a lithium ion secondary battery according to claim 1 . 20. The electrode active material layer for lithium ion secondary battery according to claim 19, wherein A lithium ion secondary battery using the lithium ion secondary battery electrode active material layer is used in an electric car for car sharing. 21 . An electrode for a lithium ion secondary battery, comprising the electrode active material layer for a lithium ion secondary battery according to claim 19 or 20. 22. The electrode for lithium ion secondary battery according to claim 21, wherein A lithium ion secondary battery using the lithium ion secondary battery electrode is used in an electric car for car sharing. 23 . A lithium ion secondary battery, comprising the lithium ion secondary battery electrode according to claim 21 or 22 . 24. The lithium ion secondary battery according to claim 23, wherein: The charge rate SOC is defined as the following formula (1): SOC = Remaining capacity / Full charge capacity × 100 (1) In formula (1), the unit of SOC is %, and the units of remaining capacity and full charge capacity are both Ah. Under the conditions of 25°C and 3.0C, the battery was discharged from a state of SOC 100% to a state of SOC 90%, and then rested for 10 minutes. The voltage rise during the rest period was measured. The internal resistance calculated by the following formula (2) is 1.0 to 35.0 Ω·cm ² : Internal resistance = (voltage rise during rest/current value during discharge) × area of positive and negative electrodes facing each other (2) In the formula (2), the unit of the voltage increase during rest is V, the unit of the current value during discharge is A, and the unit of the facing area of the positive and negative electrodes is cm ² . 25. The lithium ion secondary battery according to claim 23 or 24, wherein: The charge rate SOC is defined as the following formula (1): SOC = Remaining capacity / Full charge capacity × 100 (1) In formula (1), the unit of SOC is %, and the units of remaining capacity and full charge capacity are both Ah. At 0°C and 0.5C, the battery was discharged from SOC 100% to SOC 90%, and then rested for 1 minute. The voltage rise during the rest period was measured. The internal resistance calculated by the following formula (2) is 1.0 to 45.0 Ω·cm ² : Internal resistance = (voltage rise during rest/current value during discharge) × area of positive and negative electrodes facing each other (2) In the formula (2), the unit of the voltage increase during rest is V, the unit of the current value during discharge is A, and the unit of the facing area of the positive and negative electrodes is cm ² . 26 . The lithium ion secondary battery according to claim 23 , which is used in an electric vehicle for car sharing. 27. A method for evaluating the heterogeneity of a reaction in a lithium ion secondary battery, characterized by comprising the following steps: The charge rate SOC is defined as the following formula (1): SOC = Remaining capacity / Full charge capacity × 100 (1) In formula (1), the unit of SOC is %, and the unit of remaining capacity and full charge capacity is Ah. After discharging from SOC 100% to SOC 90% at 25°C and 2.5C or higher, the battery rested for 10 minutes and the voltage rise during the rest period was measured. The internal resistance is calculated using the following formula (2): Internal resistance = (voltage rise during rest/current value during discharge) × area of positive and negative electrodes facing each other (2) In the formula (2), the unit of the voltage increase during rest is V, the unit of the current value during discharge is A, and the unit of the facing area of the positive and negative electrodes is cm ² .