CN118284992A - Composition for forming electrode active material layer for lithium ion secondary battery - Google Patents
Composition for forming electrode active material layer for lithium ion secondary battery Download PDFInfo
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- CN118284992A CN118284992A CN202280077333.7A CN202280077333A CN118284992A CN 118284992 A CN118284992 A CN 118284992A CN 202280077333 A CN202280077333 A CN 202280077333A CN 118284992 A CN118284992 A CN 118284992A
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- active material
- electrode active
- lithium ion
- ion secondary
- secondary battery
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Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Landscapes
- Battery Electrode And Active Subsutance (AREA)
- Secondary Cells (AREA)
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
Technical Field
The present invention relates to a composition for forming an electrode active material layer for a lithium ion secondary battery.
Background
The Lithium Ion Battery (LIB) industry has been developed by a continuous technology aiming at downsizing, weight saving, high functionality (pursuing convenience) of portable devices, and the like, by effectively utilizing high energy density, high voltage, safety characteristics, and the like thereof, and has been greatly increased. At present, attention is paid to global environmental problems and resource problems, and it is expected that policies such as popularization and promotion of environment-friendly automobiles and conversion to renewable energy sources will always lead to growth of the lithium ion battery market in the future. In this way, it was calculated that the lithium ion battery is applied to Electric Vehicles (EV) owned by individuals and stationary electric storage (equalization of renewable energy sources, etc.), and the lithium ion battery required is required to be 10 times as large as 2018 in year 2030, and that the situation that is not preferable to the user may occur from the viewpoint of economy such as an increase in battery cost due to shortage of resources, etc., and therefore, from the viewpoint of how long to use one battery, the research and development of recycling is also active from the viewpoint of recycling or resource recovery, and the long life of the battery is also effective from the viewpoint of life cycle evaluation (LCA).
In addition, as to the existence of a mobile object (mobility) such as an EV, a new proposal has been made, and CASEs, maaS and the like, aiming at further improving user convenience, are now becoming reality, and there are signs of transition from personal everywhere to sharing of a mobile object such as an EV in the future. In such a process, AIEV (ARTIFICIAL INTELLIGENCE ELECTRIC VEHICLE, artificial intelligent electric vehicle) developed in the market in the future is expected to be an EV on which AI is mounted, driving is automated, vehicles are shared, and vehicles are managed not by individuals but by management companies that provide mobile services (CASE) and various services (MaaS) required by users in the vehicles. Further, since the driving control and the charge/discharge control can be performed by the management company, the operation can be performed in consideration of the life of the battery, safety, and the like. Further, by sharing the vehicle, the burden on the user can be reduced to about 1/5 as compared with the case where the user is owned, and therefore, the economical efficiency is also excellent. That is, in the future, by replacing the gasoline vehicle with AIEV (shared automobile) which is the main stream of private vehicles, contribution to the global environment, reduction of traffic accidents and traffic jams, an aging and new traffic means in a sparsely populated area, reduction of personal cost burden, effective use of moving time, and the like can be expected. Further, AIEV can also function as a large power storage system that automatically charges and discharges electricity generated by using renewable energy sources with large fluctuation through a management system of a management company as needed.
But it is necessary to reconsider the development directivity of lithium ion batteries currently in main stream (fig. 1).
In particular, a significant lifetime of a battery mounted in an electric vehicle is indispensable. In order to realize AIEV, the total travel distance of the vehicle needs to be 50 km or more, for example, unlike the case where the individual owns the vehicle, and if the life of the battery is at the present level, multiple battery replacement is required, the economical efficiency is impaired, and the resource problem is not solved. Regarding the required battery performance, the lifetime is emphasized over the energy density (travel distance) and the quick charge performance, which are the main current demands, and as a specific example, the energy density is ensured at 400Wh/L level in a single cell, and the travel distance of a vehicle is 200 to 300km when 20 to 30kWh is mounted, but the actual service life is required to be 5 times or more of the current.
Disclosure of Invention
Technical problem to be solved by the invention
Various studies have been made so far on the long life of batteries, but in the case where the actual service life is 5 times or more of the current life, a new study is required. The inventors of the present invention paid attention to an overvoltage factor, which has been studied in many ways in the past for degradation factors such as degradation due to oxidation and reduction of an active material or a member, degradation due to intercalation and deintercalation of lithium ions into and from an active material, consumption of lithium ions due to decomposition of an electrolyte, and degradation due to relaxation of an electrode.
The inventors have defined a new degradation mechanism of "degradation due to an overvoltage factor (current×resistance)", and can explain phenomena such as low-temperature degradation and secondary degradation. The degradation due to the overvoltage factor is defined as a degradation factor affected by the load current and the battery resistance (direct current resistance), and for example, degradation at low temperature cycle can be explained as a rise in resistance due to low temperature and degradation due to rapid charge can be explained as a rise in load current. Further, when the battery is degraded, the resistance increases, and when the capacity is degraded, the load (apparent load) on the effective active material portion increases when the same current as in the initial stage is applied. Further, when gas or the like accumulates in the electrode group, the gas does not permeate ions, and thus a load is applied to the electrode portion and the active material other than the gas accumulation. From this point of view, 1 factor that affects lifetime as an overvoltage factor is: when the reaction in the electrode is not uniform, the active material used in the electrode or the like accumulates a load in a part of the active material or the like during long-term operation of the battery, for example, in the case of the negative electrode, consumption of lithium ions due to localized strong reduction is induced, and in the worst case, lithium electrodeposition or the like is induced, for example, in the case of the positive electrode, deterioration of the positive electrode active material due to cracks or the like is induced, and therefore, when charge and discharge cycles are repeated for a certain number of times, a rapid decrease in capacity and a rapid increase in resistance (secondary deterioration) occur in some cases. By uniformizing the reaction of the electrode, the unevenness of the reaction in the battery is suppressed, and this secondary degradation (abrupt decrease in capacity) can be suppressed, and the lifetime can be dramatically prolonged. Therefore, it is important to uniformize the reaction in the battery, but there is little effort to uniformize the reaction in the battery in the present situation.
In order to uniformize the reaction in the battery, it is important to make an electrode structure capable of uniformizing the movement of ions in the electrode. As means for this, studies have been made so far to increase the porosity of the electrode or reduce the weight per unit area of the electrode, but these methods are accompanied by a decrease in energy density (travel distance), and therefore there is a limit from the standpoint of ensuring the 400Wh/L level only by these methods. In addition, although it is considered that it is effective from the viewpoint of making the movement of ions in the electrode uniform to exclude factors that can inhibit the movement of ions in the electrode, specifically, electrode constituent materials such as binders used for imparting strength to the electrode, thickeners used for stabilizing the electrode slurry, dispersants, and the like, when these constituent materials are reduced or eliminated, the strength of the electrode is significantly reduced, and thus the electrode cannot follow the volume change accompanying charge and discharge, current collecting paths are lost, and the like, and the life characteristics are rather reduced.
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a composition for forming a negative electrode active material layer, which can produce a battery having a longer life. Further, another object of the present invention is to provide a method capable of evaluating the non-uniformity of a reaction in a battery, which is a factor of a rapid decrease in capacity (secondary degradation).
Technical scheme for solving technical problems
The present inventors have conducted intensive studies in view of the above-described problems. As a result, it has been found that by using an electrode constituent material such as a binder capable of blocking movement of ions in an electrode in a small amount or no amount, current collection between active material particles, shape maintenance of the electrode, and the like are performed by using a small amount of carbon nanotubes, and thus the electrode has strength at a level capable of maintaining the shape of the electrode, and movement of lithium ions is less likely to be blocked, and thus the reaction in a battery can be uniformized, and the battery can be made longer. The inventors have found that the nonuniformity of the battery reaction can be evaluated by calculating the internal resistance during the rest after discharge under high load conditions. The present invention has been completed based on such findings. That is, the present invention includes the following configurations.
Item 1. An electrode active material layer forming composition for a lithium ion secondary battery comprising an electrode active material and carbon nanotubes, wherein,
When the total amount of the composition is set to 100 mass%,
The content of the carbon nanotubes is 0.01 to 1.4 mass%,
The content of the electrode constituent material other than the electrode active material and the carbon nanotubes is 0 to 10.0 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 to 99.9 mass%,
The content of the electrode constituent material other than the electrode active material and the carbon nanotube 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.
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 to 99.9 mass%,
The content of the electrode constituent material other than the electrode active material and the carbon nanotubes is 0 to 1.2 mass%.
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.
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 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.
The composition for forming an electrode active material layer for a lithium ion secondary battery according to item 5-1, wherein,
The composition contains a conductive auxiliary agent other than the carbon nanotubes,
The content of the conductive auxiliary agent other than the carbon nanotubes is 0.1 to 10.0 mass% based on 100 mass% of the total composition.
The composition for forming an electrode active material layer for a lithium ion secondary battery according to item 5-2, wherein,
The content of the carbon nanotubes is 0.1 to 10.0 mass% when the total amount of the carbon nanotubes and the conductive auxiliary agent other than the carbon nanotubes is 100 mass%.
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,
The content of the electrode active material is 79.2 to 99.8 mass% based on 100 mass% of the total composition.
The composition for forming an electrode active material layer for a lithium ion secondary battery according to any one of items 5 to 3, wherein,
The composition contains an electrode constituent material other than the electrode active material, the carbon nanotubes and a conductive assistant other than the carbon nanotubes,
The content of the electrode constituent material is 0.1 to 10.0 mass% based on 100 mass% of the total amount of the composition.
Item 6. An electrode active material layer-forming composition for a lithium ion secondary battery comprising an electrode active material and carbon nanotubes, wherein,
When the total volume of the composition is set to 100% by volume,
The volume ratio of the electrode active material is 75.06 to 99.97% by volume,
The volume ratio of the carbon nano tube is 0.02-4.55% by volume,
The volume ratio of the electrode constituent materials excluding the electrode active material and the carbon nanotubes is 0 to 21.56% by volume.
Item 7. The electrode active material layer-forming composition for a lithium ion secondary battery according to item 6, wherein,
When the total volume of the composition is set to 100% by volume,
The volume ratio of the electrode active material is 93.38 to 99.98% by volume,
The volume ratio of the carbon nano tube is 0.02-2.18 volume percent,
The volume ratio of the electrode constituent materials other than the anode active material and the carbon nanotubes is 0 to 4.52% by volume, and
The composition is a composition for forming a negative electrode active material layer for a lithium ion secondary battery.
Item 8. The electrode active material layer-forming composition for a lithium ion secondary battery according to item 6, wherein,
The volume ratio of the electrode active material is 96.19 to 99.98% by volume,
The volume ratio of the carbon nano tube is 0.02-2.18 volume percent,
The volume ratio of the electrode constituent materials excluding the electrode active material and the carbon nanotubes is 0 to 1.63% by volume.
Item 9. The electrode active material layer-forming composition 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.
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 diameter of the electrode active material is 0.1-13.0 mu m.
Item 11. The composition for forming an electrode active material layer for a lithium ion secondary battery according to item 10, wherein,
The electrode active material has an average particle diameter of 0.1 to 13.0 [ mu ] m and a content of 96.6 to 99.9 mass%,
The content of the carbon nanotubes is 0.01 to 1.4 mass%,
The content of the electrode constituent material other than the electrode active material and the carbon nanotube 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.
Item 12. The electrode active material layer-forming composition for a lithium ion secondary battery according to item 10, wherein,
The electrode active material has an average particle diameter of 0.1 to 13.0 [ mu ] m and a volume ratio of 93.38 to 99.98% by volume,
The volume ratio of the carbon nano tube is 0.02-2.18 volume percent,
The volume ratio of the electrode constituent materials other than the electrode active material and the carbon nanotubes is 0 to 4.52% by volume, and
The composition is a composition for forming a negative electrode active material layer for a lithium ion secondary battery.
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 to 99.9 mass%,
The content of the conductive auxiliary agent other than the carbon nanotubes is 0 to 10.0 mass%,
The composition is free of electrode constituent materials other than the electrode active material, the carbon nanotubes and a conductive assistant other than the carbon nanotubes,
The composition is a composition for forming a positive electrode active material layer for a lithium ion secondary battery.
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 nano tube is 0.03-4.55% by volume,
The content of the conductive auxiliary agent other than the carbon nanotubes is 0 to 21.56% by volume,
The composition is free of electrode constituent materials other than the electrode active material, the carbon nanotubes and a conductive assistant other than the carbon nanotubes,
The composition is a composition for forming a positive electrode active material layer for a lithium ion secondary battery.
The composition for forming an electrode active material layer for a lithium ion secondary battery according to item 14-1, wherein,
The conductive auxiliary agent except the carbon nanotubes is carbon black.
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 capable of absorbing and releasing lithium ions.
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 0.350nm or more.
The composition for forming an electrode active material layer for a lithium ion secondary battery according to item 15-2, wherein,
The electrode active material contains hard carbon.
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.
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 for reducing reaction non-uniformity in a lithium ion secondary battery.
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 automobile for automobile 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 vehicle shared by automobiles.
Item 21. An electrode for a lithium ion secondary battery, wherein,
The electrode comprising the electrode active material layer for a lithium ion secondary battery according to item 19 or 20.
Item 22. The electrode for a lithium ion secondary battery according to item 21, wherein,
The electrode is used for a lithium ion secondary battery used in an electric vehicle shared by automobiles.
Item 23. A lithium ion secondary battery, wherein,
The lithium ion secondary battery includes the electrode for a lithium ion secondary battery according to item 21 or 22.
Item 24. The lithium-ion secondary battery of item 23, wherein,
The charge rate SOC is defined as the following equation (1):
SOC (%) =residual capacity (Ah)/full charge capacity (Ah) ×100 (1)
After discharging from the state of 100% SOC to the state of 90% SOC at 25℃and 3.0C, the test was stopped for 10 minutes, the voltage rise during the stop was measured,
The internal resistance calculated by the following formula (2) is 1.0 to 35.0 Ω·cm 2:
Internal resistance= (rise of voltage during rest (V)/current value at discharge (a)) ×opposing area of positive and negative electrodes (cm 2) (2).
Item 24-1. The lithium-ion secondary battery of 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.
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 equation (1):
SOC (%) =residual capacity (Ah)/full charge capacity (Ah) ×100 (1)
After discharging from the state of 100% SOC to the state of 90% SOC at 0℃and 0.5C, the test was stopped for 1 minute, and the voltage rise during the stop was measured,
The internal resistance calculated by the following formula (2) is 1.0 to 45.0 Ω·cm 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 lithium-ion secondary battery according to any one of items 23 to 25, wherein,
The lithium ion secondary battery is used for electric vehicles shared by automobiles.
Item 27. A method of evaluating non-uniformity 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 equation (1):
SOC (%) =residual capacity (Ah)/full charge capacity (Ah) ×100 (1)
After discharging from a state of 100% of SOC to a state of 90% of SOC at 25 ℃ and 2.5C or higher, the test was stopped for 10 minutes, and the rise of the voltage during the stop was measured,
The internal resistance was 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).
Effects of the invention
According to the present invention, the collector between active material particles, the shape maintenance of the electrode, and the like are performed using a very small amount of carbon nanotubes, and the binder is not contained or is made very small, so that the strength of the electrode shape can be maintained, and the movement of lithium ions is not easily blocked, and therefore, the reaction in the battery can be uniformed, and the battery can be made long-life.
Further, according to the present invention, the internal resistance during the rest after discharge under a high load condition is calculated, whereby the unevenness of the battery reaction can be evaluated.
Drawings
Fig. 1 is a schematic diagram showing the directionality of development of a lithium ion battery in consideration of the world view of the use and operation of automobiles.
Fig. 2 is a schematic diagram showing an analysis method in ac impedance measurement in test examples 2 and 6.
Fig. 3 is a graph showing the results of ac impedance measurement in test example 2.
Fig. 4 is a schematic diagram showing an analysis method of the internal resistance in the high load rest method of test examples 3, 7, 11 and 14.
FIG. 5 is a graph showing the results of internal resistance at room temperature (25 ℃) in the high-load resting method of test example 3.
Fig. 6 is a graph showing the results of the life characteristics of test example 3.
Fig. 7 shows the result of estimating the lifetime of the battery of example 7 from the result of test example 3.
Fig. 8 is a graph showing the results of summarizing the internal resistance of test example 3 and the life characteristics of test example 4.
Fig. 9 is a graph showing the results of ac impedance measurement in test example 6.
FIG. 10 is a graph showing the results of internal resistance at room temperature (25 ℃) in the high-load resting method of test example 7.
FIG. 11 is a graph showing the results of internal resistance at low temperature (0 ℃) in the high-load resting method of test example 7.
Fig. 12 is a graph showing the capacity retention rate when the overvoltage load is gradually increased in the limit load test of test example 8.
Fig. 13 is a graph showing a capacity retention rate of 10 cycles for an overvoltage load in the limit load test of test example 8.
Fig. 14 is a graph showing the results of the life characteristics of test example 9.
Fig. 15 is a graph showing the results of the life characteristics of test example 12.
Fig. 16 is a graph showing the results of the life characteristics of test example 15.
Detailed Description
In the present specification, the term "includes" and "consists essentially of … (consist essentially of) and" consists of … (consist of) "as well.
In the present specification, the expression "a to B" means "a or more and B or less".
1. Composition for forming electrode active material layer for lithium ion secondary battery
In general, in the active material layer in the electrode, a considerable amount of an electrode constituent material other than the electrode active material, such as a binder, is often contained in addition to the active material. Since these electrode constituent materials other than the electrode active material are materials that do not penetrate lithium ions, when they are contained in a considerable amount, movement of lithium ions is hindered, and uniform charge and discharge cannot be performed. When movement of lithium ions is blocked, the reaction concentrates in a portion where the movement of lithium ions is less blocked, and as a result, lithium electrodeposition or the like is induced in the case of the negative electrode, and in the case of the positive electrode, degradation of the positive electrode active material due to cracks or the like is induced, so that when charge and discharge cycles are repeated for a certain number of times, abrupt decrease in capacity and abrupt 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 such an extent that the electrode shape can be maintained cannot be maintained, and therefore, the electrode structure is damaged by expansion and contraction during charge and discharge, current collection deterioration such as reduction in the electrode internal conductivity, and the like, results in a reduction in the life characteristics of the battery. Therefore, it is not possible to reduce the amount of electrode constituent materials other than the electrode active material simply and to reduce the reaction unevenness and improve the life characteristics. In the case of the negative electrode, as described above, the life characteristics of the battery are reduced due to current collection degradation such as deterioration of the electrode structure and reduction of the conductivity in the electrode, and in the case of the positive electrode, as described above, degradation of the positive electrode active material due to cracks or the like is induced, and therefore, the amount of electrode constituent materials other than the electrode active material cannot be significantly reduced, which is common knowledge. This tendency is particularly remarkable in a negative electrode in which the electrode structure is damaged.
In contrast, the composition (1) for forming an electrode active material layer for a lithium ion secondary battery of the present invention contains an electrode active material and carbon nanotubes, and 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 10.0% by mass. In the composition (1) for forming an electrode active material layer for a lithium ion secondary battery of the present invention, 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 (total composition) is 100 mass%.
In the composition (2) for forming a negative electrode active material layer for a lithium ion secondary battery of the present invention, 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 excluding the electrode active material and the carbon nanotubes is 0 to 21.56% by volume. In the composition (2) for forming an electrode active material layer for a lithium ion secondary battery of the present invention, 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 (total volume of the composition) is 100% by volume.
By adopting such a configuration, the mass of the lithium ion inhibitor can be reduced while maintaining the strength of the electrode shape, and as a result, the inhibition of movement of lithium ions can be suppressed, and as a result, the reaction of the battery can be uniformized, and the battery can be made longer. 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 reaction non-uniformity in a lithium ion secondary battery.
As described above, conventionally, when movement of lithium ions is blocked, the reaction concentrates on a portion where the movement of lithium ions is less blocked, and as a result, in the case of the negative electrode, lithium electrodeposition or the like is induced, and the life characteristics of the battery are reduced due to deterioration of current collection such as deterioration of the electrode internal conductivity, due to damage of the electrode structure, and therefore, it is common knowledge that the amount of the negative electrode constituent material other than the negative electrode active material cannot be significantly reduced. Therefore, the composition for forming an electrode active material layer for a lithium ion secondary battery of the present invention is particularly useful for application to a negative electrode, by homogenizing the reaction of the battery. Therefore, in the composition (1) for forming an electrode active material layer for a lithium ion secondary battery of the present invention, it is preferable that the composition contains an electrode active material and carbon nanotubes, wherein the content of the electrode active material is 96.6 to 99.9 mass%, the content of the carbon nanotubes is 0.01 to 1.4 mass%, and the content of 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 an anode active material layer for a lithium ion secondary battery. Similarly, in the composition (2) for forming an electrode active material layer for a lithium ion secondary battery of the present invention, it is preferable that the composition contains an electrode active material and carbon nanotubes, wherein the volume ratio of the electrode active material is 93.38 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 electrode constituent materials other than the electrode active material and the carbon nanotubes is 0 to 4.52% by volume, and the composition is a composition for forming an anode active material layer for a lithium ion secondary battery.
On the other hand, in the present invention, since the electrode constituent material such as the binder capable of blocking the movement of ions in the electrode is not contained or is very small, and the collection of the active material particles and the shape maintenance of the electrode are performed by the very small amount of carbon nanotubes, the electrode constituent material is preferably reduced as much as possible, since the strength of the electrode shape can be maintained, and the movement of lithium ions is not easily blocked, the reaction in the battery can be uniformized, and the battery life can be prolonged. From this viewpoint, the composition (1) for forming an electrode active material layer for a lithium ion secondary battery of the present invention 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 97.4 to 99.9 mass%, the content of the carbon nanotubes is 0.01 to 1.4 mass%, and the content of electrode constituent materials other than the electrode active material and the carbon nanotubes is 0 to 1.2 mass%. Similarly, the composition (2) for forming an electrode active material layer for a lithium ion secondary battery of the present invention is preferably a composition for forming an electrode active material layer for a lithium ion secondary battery comprising 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 application to a negative electrode, and thus, a composition for forming a negative electrode active material layer for a lithium ion secondary battery is further preferable.
Hereinafter, preferred 4 modes of the composition for forming an electrode active material layer for a lithium ion secondary battery according to the present invention will be described in order.
(1-1) Composition for forming electrode active material layer for lithium ion secondary battery (first embodiment)
The composition (1) for forming an electrode active material layer for a lithium ion secondary battery according to the first aspect of the present invention is a composition for forming an electrode active material layer for a lithium ion secondary battery, which contains an electrode active material and carbon nanotubes, wherein the content of the electrode active material is 97.4 to 99.9 mass%, the content of the carbon nanotubes is 0.01 to 1.4 mass%, and the content of electrode constituent materials other than the electrode active material and the carbon nanotubes is 0 to 1.2 mass%, and the composition is a composition for forming a negative electrode active material layer for a lithium ion secondary battery. In the same manner, the composition (2) for forming an electrode active material layer for a lithium ion secondary battery according to the first aspect of the present invention is a composition for forming an electrode active material layer for a lithium ion secondary battery comprising 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 electrode constituent materials other than the electrode active material and the carbon nanotubes is 0 to 1.63% by volume.
[1-1-1] Electrode active material
The electrode active material (negative electrode active material) is not particularly limited, and materials that can be used as a negative electrode active material in a lithium ion secondary battery, that is, materials that can absorb and release lithium ions, can be used, and examples thereof include: carbon materials such as natural graphite, artificial graphite, amorphous carbon, and the like; a metal material capable of alloying with lithium, such as Si, al, sn, pb, zn, bi, in, mg, ga, si alloy, sn alloy, and Al alloy; siO x(0＜x＜2)、SnOx(0＜x＜2)、Si、Li2TiO3, vanadium oxide, and other metal oxides capable of absorbing and releasing lithium ions; and composite materials including a metal material and a carbon material such as si—c composite and sn—c composite. As the amorphous carbon, amorphous carbon materials described later can be used. These electrode active materials (negative electrode active materials) may be used alone or in combination of 2 or more. From the viewpoint of particularly suppressing the volume change of the electrode active material (negative electrode active material) at the time of charge and discharge and particularly easily improving the charge and discharge cycle characteristics, a silicon-free material, that is: a carbon material; silicon-free metal materials such as Al, sn, pb, zn, bi, in, mg, ga, sn alloy and Al alloy which can be alloyed with lithium; metal oxides such as SnO x(0＜x＜2)、Si、Li2TiO3 and vanadium oxides which do not contain silicon and can absorb and release lithium ions; and a composite material containing a metal material and a carbon material without containing silicon, such as a sn—c composite. In the case of using a conductive material such as a carbon material as an electrode active material (negative electrode active material), the content of a substance that inhibits lithium ion movement is particularly easily reduced by allowing the electrode active material (negative electrode active material) to function as a conductive material.
As the electrode active material (negative electrode active material) described above, the volume change of the electrode active material (negative electrode active material) at the time of charge and discharge is preferably 50% or less, more preferably 20% or less, from the viewpoints of particularly suppressing the volume change of the electrode active material (negative electrode active material) at the time of charge and discharge, easily suppressing the capacity decrease due to the volume change, and particularly easily improving the charge and discharge cycle characteristics. The smaller the volume change, the better, the lower limit value is not set, but the lower limit value is set to 0%. The value of the volume change was set to 0% when there was no volume change at all, and it was shown how much the electrode active material (negative electrode active material) swelled at the time of full charge compared with the electrode active material (negative electrode active material) at the time of full discharge by the following formula:
((volume at full charge) - (volume at full discharge))/(volume at full discharge) ×100
And (5) calculating.
Examples of the electrode active material (negative electrode active material) satisfying such volume change include carbon materials such as natural graphite, artificial graphite, and amorphous carbon; lithium composite titanium oxide (Li 2TiO3, etc.) and the like have a volume change that varies depending on the type of material and the depth of charge and discharge, but is about 10% in the case of graphite and about several% in the case of amorphous carbon. In the case where a plurality of electrode active materials (negative electrode active materials) are used, it is preferable that the average value of the volume change of the electrode active materials (negative electrode active materials) is within the above range.
The shape of the electrode active material (anode active material) is not particularly limited, and various shapes such as spherical, scaly, block, fibrous, whisker-like, and crushed can be used. In addition, electrode active materials (negative electrode active materials) of various shapes may be used in combination. The spherical shape may be a regular spherical shape, or may be an elliptical shape.
The particle size of the electrode active material (negative electrode active material) is not particularly limited, but the average particle size is preferably 0.1 to 25 μm, more preferably 1 to 20 μm, from the viewpoint that current collection between the negative electrode active material particles is easily performed by a small amount of carbon nanotubes and the battery is easily further prolonged in life. In addition, in view of homogenization of the reaction at low temperature, the average particle diameter of the electrode active material (anode active material) can be made to be 0.1 to 13.0 μm, preferably 0.5 to 10.0 μm, more preferably 1.0 to 8.0 μm. The average particle diameter of the negative electrode active material was measured by a laser diffraction/scattering method.
The composition for forming an electrode active material layer for a lithium ion secondary battery according to the first aspect of the present invention can collect electricity between active material particles, maintain the shape of an electrode, and the like by a very small amount of carbon nanotubes, and as a result, can reduce the amount of electrode constituent materials (negative electrode constituent materials) other than electrode active materials (negative electrode active materials), and as a result, has strength at such a level that the electrode shape can be maintained, and is less likely to inhibit movement of lithium ions, so that the reaction in the battery can be uniformed, the battery can have a longer life, and therefore, the content of an electrode active material (negative electrode active material) is larger than that of a conventional composition for forming an electrode active material layer (negative electrode active material layer-forming composition). Accordingly, the content of the negative electrode active material is 97.4 to 99.9 mass%, preferably 97.7 to 99.7 mass%, more preferably 98.0 to 99.5 mass%. When a plurality of electrode active materials (negative electrode active materials) are used, the total amount thereof is preferably adjusted so as to fall within the above-described range. In the composition (1) for forming an electrode active material layer for a lithium ion secondary battery according to the first aspect of the present invention, the total amount (total composition) of the electrode active material (negative electrode active material), the carbon nanotube, and the electrode constituent material (negative electrode constituent material) excluding the electrode active material (negative electrode active material) and the carbon nanotube is 100 mass%.
For the same reason, in the composition (2) for forming an electrode active material layer for a lithium ion secondary battery according to the first aspect of the present invention, the volume ratio of the negative electrode active material is 96.19 to 99.98% by volume, preferably 97.00 to 99.70% by volume, and more preferably 97.50 to 99.50% by volume. When a plurality of electrode active materials (negative electrode active materials) are used, the total volume is preferably adjusted so as to fall within the above-described range. In the composition (2) for forming an electrode active material layer for a lithium ion secondary battery according to the first aspect of the present invention, 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) excluding the electrode active material (negative electrode active material) and the carbon nanotube 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 aspect of the present invention can collect electricity between active material particles, maintain the shape of an electrode, and the like by a very small amount of carbon nanotubes, and as a result, can reduce the amount of electrode constituent materials (negative electrode constituent materials) other than electrode active materials (negative electrode active materials), and as a result, has strength at such a level that the shape of an electrode can be maintained, and lithium ions are less likely to be hindered from moving, so that the reaction in the battery can be uniformized, and the battery can be made longer in life. The carbon nanotubes are also substances that inhibit movement of lithium ions, but if the amount is small, movement of lithium ions is not inhibited, that is, the strength of the electrode shape can be maintained while keeping the reaction in the battery uniform.
The carbon nanotubes are hollow carbon materials in which graphite sheets (i.e., carbon atom faces of a graphite structure or single-layer graphene sheets) are closed into a tube shape, the diameter of the hollow carbon materials is nano-scale, and the wall structure has a graphite structure. Carbon nanotubes having a wall structure formed by closing a single sheet of graphite (single-layer graphene sheet) into a tubular shape are called single-layer carbon nanotubes. On the other hand, a plurality of carbon nanotubes in which graphite sheets are closed into a tube shape and are nested are called a multi-layered carbon nanotube having a nested structure. In the present invention, either a single-layer carbon nanotube or a multi-layer carbon nanotube can be used, and the single-layer carbon nanotube is preferable from the viewpoints of easy strength to maintain the electrode shape, easy current collection between electrode active materials (negative electrode active materials), less resistance to movement of lithium ions, easy homogenization of the reaction in the battery, and easy long life of the battery.
Such carbon nanotubes may be used alone or in combination of 2 or more.
The average outer diameter of the carbon nanotubes is preferably small from the viewpoints that the number of carbon nanotubes per unit volume can be easily increased, the content of carbon nanotubes for maintaining the shape of the electrode can be reduced, and movement of lithium ions is not easily inhibited. Therefore, the average outer diameter of the carbon nanotubes is preferably 0.43 to 20nm, more preferably 0.43 to 10nm. The average outer diameter of the carbon nanotubes was measured by observation with an electron microscope (TEM). The carbon nanotubes having such an average outer diameter have an average inner diameter set according to the average outer diameter.
The longer the average length of the carbon nanotubes is, the more easily the strength of the carbon nanotubes is enough to maintain the shape of the electrode, and the current collection between the negative electrode active materials is easily performed; on the other hand, the average length of the carbon nanotubes is preferably short, since the dispersibility is easily improved and the movement of lithium ions is not easily hindered. Therefore, the average length of the carbon nanotubes is preferably 0.5 to 200. Mu.m, more preferably 1 to 50. Mu.m. The average length of the carbon nanotubes was determined by electron microscope (SEM) observation.
The higher the average aspect ratio of the carbon nanotubes defined as the ratio of the average length to the average outer diameter of the carbon nanotubes, the more easily the strength of the electrode shape can be maintained by the small content of the carbon nanotubes, the easier the current collection between the negative electrode active materials is performed, and the movement of lithium ions is not easily hindered, so that the reaction in the battery is easily uniformed, and the longer the service life of the battery is easily achieved, and from this point of view, the average aspect ratio of the carbon nanotubes is preferably 25 to 200000, more preferably 100 to 50000.
In the present invention, carbon nanotubes may be used as individual carbon nanotubes, or may be used as a carbon nanotube aggregate in which a plurality of carbon nanotubes are bundled so as to easily exhibit strength in the form of bundles. In either case, the collection of the active material particles and the maintenance of the shape of the electrode can be performed by a very small amount of carbon nanotubes, and as a result, the amount of the electrode constituent material (negative electrode constituent material) other than the electrode active material (negative electrode active material) can be reduced, and as a result, the strength of the electrode shape can be maintained, and the movement of lithium ions is not easily inhibited, so that the reaction in the battery can be uniformized, and the battery life can be prolonged.
In addition, from the viewpoint of suppressing reactivity of the carbon nanotubes with the electrolyte, it is considered that the graphene structure of the carbon nanotubes has few defects, that is, a G/D ratio in the raman spectrum is preferable. Therefore, in the present invention, the G/D ratio of the carbon nanotubes in the Raman spectrum is preferably 1 to 200, more preferably 50 to 150.
The composition for forming an electrode active material layer for a lithium ion secondary battery according to the first aspect of the present invention (composition for forming a negative electrode active material layer for a lithium ion secondary battery) can collect current between active material particles, maintain the shape of an electrode, and the like by a very small amount of carbon nanotubes, and as a result, the amount of negative electrode constituent materials other than the electrode active material (negative electrode active material) can be reduced, and as a result, the composition has strength at a level at which the shape of the electrode can be maintained, and movement of lithium ions is less likely to be inhibited, so that the reaction in the battery can be uniformized, the battery can be prolonged, and the content of carbon nanotubes can be reduced. Accordingly, in the composition (1) for forming an electrode active material layer for a lithium ion secondary battery according to the first aspect of the present invention, the content of the 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. When a plurality of types of carbon nanotubes are used, the total amount is preferably adjusted so as to fall within the above range. Carbon nanotubes are also substances that inhibit movement of lithium ions, but if they are about 1.2 mass% or less, movement of lithium ions is not easily inhibited, and strength to such an extent that the electrode shape can be maintained while keeping the reaction in the battery uniform can be obtained. In the composition (1) for forming an electrode active material layer for a lithium ion secondary battery according to the first aspect of the present invention, the total amount (total composition) of the electrode active material (negative electrode active material), the carbon nanotube, and the electrode constituent material (negative electrode constituent material) excluding the electrode active material (negative electrode active material) and the carbon nanotube is 100 mass%.
For the same reason, in the composition (2) for forming an electrode active material layer for a lithium ion secondary battery according to the first aspect of the present invention, the volume ratio of the 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. When a plurality of types of carbon nanotubes are used, the total volume is preferably adjusted so as to fall within the above range. In the composition (2) for forming an electrode active material layer for a lithium ion secondary battery according to the first aspect of the present invention, 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) excluding the electrode active material (negative electrode active material) and the carbon nanotube is 100% by volume.
[1-1-3] Electrode constituent Material other than electrode active Material and carbon nanotube
The composition for forming an electrode active material layer for a lithium ion secondary battery according to the first aspect of the present invention can collect current between active material particles, maintain the shape of an electrode, and the like by the extremely small amount of carbon nanotubes, and as a result, can reduce the amount of electrode constituent materials (negative electrode constituent materials) other than electrode active materials (negative electrode active materials), and as a result, has strength at such a level that the shape of an electrode can be maintained, and movement of lithium ions is not easily blocked, so that the reaction in the battery can be uniformized, and the battery life can be prolonged.
In the present invention, the electrode constituent material (negative electrode constituent material) other than the electrode active material (negative electrode active material) and the carbon nanotube is a concept of a substance (binder) having adhesiveness to the electrode active material (negative electrode active material) and the electrode current collector (negative electrode current collector), and a substance (lithium ion movement blocking substance) other than the carbon nanotube such as a conductive material other than the carbon nanotube, a dispersant, or the like, which blocks movement of lithium ions.
Examples of the electrode constituent material (negative electrode constituent material) other than the electrode active material (negative electrode active material) and the carbon nanotube in the present invention include acetylene black, ketjen black, carbon black, graphene, amorphous carbon obtained by heat treatment of an organic substance, and the like as a conductive material; examples of the binder, thickener or dispersant include fluorine-based polymers (such as polyvinylidene fluoride resin, polytetrafluoroethylene resin, and vinylidene fluoride-hexafluoropropylene copolymer), polyolefin-based resins (such as styrene butadiene copolymer resin and ethylene vinyl alcohol copolymer resin), synthetic rubbers (such as styrene butadiene rubber, acrylonitrile butadiene rubber, and ethylene propylene diene rubber), polyacrylonitrile, polyamide, polyimide, polyacrylic acid, polyacrylate, polyvinyl ether, carboxymethyl cellulose, sodium carboxymethyl cellulose, ammonium carboxymethyl cellulose, polyurethane, hydroxypropyl cellulose, hydroxyethyl cellulose, and methyl cellulose. As the amorphous carbon, amorphous carbon materials described later can be used. These electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) and the carbon nanotube may be used alone or in combination of 2 or more.
The composition for forming an electrode active material layer for a lithium ion secondary battery according to the first aspect of the present invention can collect electricity between active material particles, maintain the shape of an electrode, and the like by a very small amount of carbon nanotubes, and as a result, can reduce the amount of electrode constituent materials (negative electrode constituent materials) other than electrode active materials (negative electrode active materials), and as a result, has strength at such a level that the electrode shape can be maintained, and is less likely to inhibit movement of lithium ions, so that the reaction in the battery can be uniformized, the battery life can be prolonged, and therefore, electrode constituent materials (negative electrode constituent materials) other than electrode active materials (negative electrode active materials) and carbon nanotubes are not contained, or even if contained, the content thereof is small. Therefore, in the composition (1) for forming an electrode active material layer for a lithium ion secondary battery according to the first aspect 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 1.2% by mass, preferably 0.2 to 1.1% by mass, and more preferably 0.4 to 1.0% by mass. In the case where a plurality of electrode constituent materials (anode constituent materials) other than the electrode active material (anode active material) and the carbon nanotube are used, the total amount thereof is preferably adjusted so as to fall within the above-described range. The electrode constituent material (negative electrode constituent material) other than the electrode active material (negative electrode active material) and the carbon nanotube is a substance that blocks movement of lithium ions, but if it is about 1.2 mass% or less, movement of lithium ions is not easily blocked, and strength to such an extent that the electrode shape can be maintained while keeping the reaction in the battery uniform can be obtained. In the composition (1) for forming a negative electrode active material layer for a lithium ion secondary battery according to the first aspect of the present invention, the total amount (total composition) of the electrode active material (negative electrode active material), the carbon nanotube, and the electrode constituent material (negative electrode constituent material) excluding the electrode active material (negative electrode active material) and the carbon nanotube is 100 mass%.
For the same reason, in the composition (2) for forming an electrode active material layer for a lithium ion secondary battery according to the first aspect of the present invention, the volume ratio of the electrode active material (negative electrode active material) to the electrode constituent material (negative electrode constituent material) other than carbon nanotubes 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. When a plurality of electrode active materials (negative electrode active materials) are used, the total volume is preferably adjusted so as to fall within the above-described range. In the composition (2) for forming an electrode active material layer for a lithium ion secondary battery according to the first aspect of the present invention, the total amount (total volume of the composition) of the electrode active material (negative electrode active material), the carbon nanotube, and the electrode active material (negative electrode active material) and the electrode constituent material (negative electrode constituent material) other than the carbon nanotube is 100% by volume.
[1-1-4] Composition for forming 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 according to the first aspect of the present invention (composition for forming an electrode active material layer for a lithium ion secondary battery), when an electrode active material (anode active material), carbon nanotubes, and an electrode constituent material (anode constituent material) other than the electrode active material (anode active material) and the carbon nanotubes are mixed to prepare a paste composition for forming an electrode active material layer for a lithium ion secondary battery, the paste composition may be prepared by containing 1 or 2 or more organic solvents such as water or alcohol (methanol, ethanol, N-propanol, isopropanol, etc.), acetone, N-methylpyrrolidone, dimethylsulfoxide, 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), the carbon nanotube, and the electrode constituent material (negative electrode constituent material) other than the electrode active material (negative electrode active material) and the carbon nanotube, that is, the total amount of the solid components is 100 mass% or 100 volume%.
The method for producing 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) according to the first embodiment of the present invention is not particularly limited. For example, the electrode active material layer forming composition for a lithium ion secondary battery of the present invention can be produced by mixing the above-described components by a conventional method. The mixing may be performed by mixing all the components simultaneously or sequentially.
(1-2) Composition for Forming electrode active Material layer for lithium ion Secondary Battery (second embodiment)
The composition (1) for forming an electrode active material layer for a lithium ion secondary battery according to the second aspect of the present invention is a composition for forming an electrode active material layer for a lithium ion secondary battery comprising an electrode active material and carbon nanotubes, wherein the average particle diameter of the electrode active material is 0.1 to 13.0 [ mu ] m, the content of the electrode active material is 96.6 to 99.9 mass%, the content of the carbon nanotubes is 0.01 to 1.4 mass%, and the content of 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 an anode active material layer for a lithium ion secondary battery. In the composition (1) for forming an electrode active material layer for a lithium ion secondary battery according to the second aspect of the present invention, the total amount (total composition) of the electrode active material (negative electrode active material), the carbon nanotube, and the electrode constituent material (negative electrode constituent material) excluding the electrode active material (negative electrode active material) and the carbon nanotube is 100 mass%. In the same manner, the composition (2) for forming an electrode active material layer for a lithium ion secondary battery according to the second aspect of the present invention is a composition for forming an electrode active material layer for a lithium ion secondary battery comprising 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 electrode constituent materials other than the electrode active material and the carbon nanotubes is 0 to 1.63% by volume. In the composition (2) for forming an electrode active material layer for a lithium ion secondary battery according to the second aspect of the present invention, 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) excluding the electrode active material (negative electrode active material) and the carbon nanotube is 100% by volume.
When the electrode active material (negative electrode active material) is made smaller in particle size, the number of interfaces between the electrode active material (negative electrode active material) particles increases, and therefore the number of starting points of structural collapse increases, and thus, 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 past. In the second aspect of the present invention, by adopting the above-described configuration, although the electrode active material (negative electrode active material) is reduced in particle size and the number of interfaces between the electrode active material (negative electrode active material) particles increases, the starting points of structural collapse increase, 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, shape maintenance of the electrode, and the like can be performed by a very small amount of carbon nanotubes, and as a result, strength to such an extent that the electrode shape can be maintained. In the present invention, since the electrode active material (negative electrode active material) is reduced in particle size and the reaction area is increased, the lithium ion flux per unit area is reduced, and particularly, the risk of lithium deposition during long-term use under high-load conditions 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 that the lifetime characteristics are significantly improved. That is, the composition for forming an electrode active material layer for a lithium ion secondary battery according to the second aspect of the present invention (composition for forming a negative electrode active material layer for a lithium ion secondary battery) can be used to reduce reaction non-uniformity in a lithium ion secondary battery.
[1-2-1] Electrode active material
The electrode active material (negative electrode active material) is not particularly limited, and materials that can be used as the electrode active material (negative electrode active material) in the lithium ion secondary battery, that is, materials that can absorb and release lithium ions, can be used, and examples thereof include: carbon materials such as natural graphite, artificial graphite, amorphous carbon, and the like; a metal material capable of alloying with lithium, such as Si, al, sn, pb, zn, bi, in, mg, ga, si alloy, sn alloy, and Al alloy; siO x(0＜x＜2)、SnOx(0＜x＜2)、Si、Li2TiO3, vanadium oxide, and other metal oxides capable of absorbing and releasing lithium ions; and composite materials including a metal material and a carbon material such as si—c composite and sn—c composite. As the amorphous carbon, amorphous carbon materials described later can be used. These electrode active materials (negative electrode active materials) may be used alone or in combination of 2 or more. In the case of using a conductive material such as a carbon material as an electrode active material (negative electrode active material), the content of a substance that inhibits lithium ion movement is particularly easily reduced by allowing the electrode active material (negative electrode active material) to function as a conductive material.
The shape of the electrode active material (anode active material) is not particularly limited, and various shapes such as spherical, scaly, block, fibrous, whisker-like, and crushed can be used. In addition, electrode active materials (negative electrode active materials) of various shapes may be used in combination. The spherical shape may be a regular spherical shape, or may be an elliptical shape.
The average particle diameter of the electrode active material (negative electrode active material) is 0.1 to 13.0. Mu.m, preferably 0.5 to 10.0. Mu.m, more preferably 1.0 to 8.0. Mu.m. When the average particle diameter of the electrode active material (negative electrode active material) is smaller than 0.1 μm, aggregation is unavoidable, and the flux of lithium ions per unit area is rather increased, and the life characteristics are deteriorated. On the other hand, if the average particle diameter of the electrode active material (negative electrode active material) exceeds 13.0 μm, there is room for improvement in particular for homogenization of the reaction at low temperatures. The average particle diameter of the negative electrode active material was measured by a laser diffraction/scattering method.
As the electrode active material (negative electrode active material) described above, the volume change of the electrode active material (negative electrode active material) at the time of charge and discharge is preferably 50% or less, more preferably 20% or less, from the viewpoints of particularly suppressing the volume change of the electrode active material (negative electrode active material) at the time of charge and discharge, easily suppressing the decrease in capacity due to the volume change, and particularly easily improving the charge and discharge cycle characteristics. The smaller the volume change, the better, the lower limit value is not set, but the lower limit value is set to 0%. The value of the volume change was set to 0% when there was no volume change at all, and it was shown how much the electrode active material (negative electrode active material) swelled at the time of full charge compared with the electrode active material (negative electrode active material) at the time of full discharge by the following formula:
((volume at full charge) - (volume at full discharge))/(volume at full discharge) ×100
And (5) calculating.
Examples of the electrode active material (negative electrode active material) satisfying such volume change include carbon materials such as natural graphite, artificial graphite, and amorphous carbon; lithium composite titanium oxide (Li 2TiO3, etc.) and the like have a volume change that varies depending on the type of material and the depth of charge and discharge, but is about 10% in the case of graphite and about several% in the case of amorphous carbon. In the case where a plurality of electrode active materials (negative electrode active materials) are used, it is preferable that the average value of the volume change of the electrode active materials (negative electrode active materials) is within the above range.
The composition for forming an electrode active material layer for a lithium ion secondary battery according to the second aspect of the present invention is a composition for forming an electrode active material layer for a lithium ion secondary battery, which is capable of reducing the particle size of an electrode active material (negative electrode active material) and thereby increasing the number of interfaces between electrode active material (negative electrode active material) particles, and thus increasing the starting points of structural collapse, and even though the amount of an electrode constituent material (negative electrode constituent material) other than the electrode active material (negative electrode active material) is significantly reduced, it is possible to perform current collection between electrode active material (negative electrode active material) particles, maintenance of the shape of an electrode, and the like by a very small amount of carbon nanotubes, and as a result, it is possible to maintain the strength to such an extent that the shape of an electrode (negative electrode) can be maintained. In the present invention, since the electrode active material (negative electrode active material) is reduced in particle size and the reaction area is increased, the lithium ion flux per unit area is reduced, and particularly, the risk of lithium deposition during long-term use under high-load conditions 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 that the lifetime characteristics are significantly improved. Therefore, the composition for forming an electrode active material layer for a lithium ion secondary battery according to the second aspect of the present invention (composition for forming a negative electrode active material layer for a lithium ion secondary battery) has a larger content of an electrode active material (negative electrode active material) than the conventional composition for forming an electrode active material layer (composition for forming a negative electrode active material). Accordingly, in the composition (1) for forming an electrode active material layer for a lithium ion secondary battery according to the second aspect of the present invention, the content of the electrode active material (negative electrode active material) is 96.6 to 99.9% by mass, preferably 97.6 to 99.8% by mass, and more preferably 98.2 to 99.7% by mass. When a plurality of electrode active materials (negative electrode active materials) are used, the total amount thereof is preferably adjusted so as to fall within the above-described range. In the composition (1) for forming an electrode active material layer for a lithium ion secondary battery according to the second aspect of the present invention, the total amount (total composition) of the electrode active material (negative electrode active material), the carbon nanotube, and the electrode constituent material (negative electrode constituent material) excluding the electrode active material (negative electrode active material) and the carbon nanotube is 100 mass%.
For the same reason, in the composition (2) for forming an electrode active material layer for a lithium ion secondary battery according to the second aspect of the present invention, the volume ratio of the electrode active material (negative electrode active material) is 93.38 to 99.98% by volume, preferably 95.00 to 99.70% by volume, and more preferably 96.00 to 99.50% by volume. When a plurality of electrode active materials (negative electrode active materials) are used, the total volume is preferably adjusted so as to fall within the above-described range. In the composition (2) for forming a negative electrode active material layer for a lithium ion secondary battery according to the second aspect of the present invention, 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) excluding the electrode active material (negative electrode active material) and the carbon nanotube is 100% by volume.
[1-2-2] Carbon nanotubes
The composition for forming an electrode active material layer for a lithium ion secondary battery according to the second aspect of the present invention (composition for forming a negative electrode active material layer for a lithium ion secondary battery) can collect current between active material particles, maintain the shape of an electrode, and the like by using a very small amount of carbon nanotubes, and as a result: although the number of interfaces between the electrode active material (anode active material) particles increases due to the reduction of the particle size of the electrode active material (anode active material), the starting point of structural collapse increases, even if the amount of the electrode constituent material (anode constituent material) other than the electrode active material (anode active material) is reduced, the strength to such an extent that the shape of the electrode (anode) can be maintained is provided; further, since the electrode active material (negative electrode active material) has a larger reaction area due to the smaller particle diameter, the lithium ion flux per unit area is smaller, and particularly, the risk of lithium precipitation during long-term use under high-load conditions is smaller; further, the amount of electrode constituent materials (anode constituent materials) other than the electrode active material (anode active material) is significantly reduced, and thus the life characteristics are significantly improved. Carbon nanotubes are also substances that inhibit movement of lithium ions, but if small amounts, do not inhibit movement of lithium ions, i.e., can have strength to such an extent that the shape of an electrode (negative electrode) can be maintained while maintaining uniformity of reaction in the battery.
As the usable carbon nanotubes, the same carbon nanotubes as those described in the above [1-1-2] can be used.
The composition for forming an electrode active material layer for a lithium ion secondary battery according to the second aspect of the present invention can collect electricity between electrode active material (negative electrode active material) particles, maintain the shape of an electrode, and the like by a very small amount of carbon nanotubes, and as a result, although the number of interfaces between electrode active material (negative electrode active material) particles increases due to the reduction of the particle size of the electrode active material (negative electrode active material), the starting point of structural collapse increases, but 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 strength to the extent that the shape of the electrode (negative electrode) can be maintained is increased, and the reaction area of the electrode active material (negative electrode active material) increases due to the reduction of the particle size, so that the lithium ion flux per unit area decreases, particularly, the risk of precipitation of lithium in high-load conditions during long-term use decreases, and the amount of electrode constituent materials (negative electrode constituent materials) other than the electrode active material (negative electrode active material) increases significantly, and thus the life characteristics increases significantly. Therefore, in the composition for forming an electrode active material layer for a lithium ion secondary battery according to the second aspect of the present invention (composition for forming a negative electrode active material layer for a lithium ion secondary battery), the content of carbon nanotubes is small. Accordingly, in the composition (1) for forming an electrode active material layer for a lithium ion secondary battery according to the second aspect of the present invention, the content of the 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. When a plurality of types of carbon nanotubes are used, the total amount is preferably adjusted so as to fall within the above range. Carbon nanotubes are also substances that inhibit movement of lithium ions, but if they are about 1.4 mass% or less, they are complementary to the case where the particle size of the electrode active material (negative electrode active material) is small, and do not inhibit movement of lithium ions easily, and can have strength to such an extent that the shape of the electrode (negative electrode) can be maintained while maintaining uniform reaction in the battery, even though the particle size of the electrode active material (negative electrode active material) is small. In the composition (1) for forming an electrode active material layer for a lithium ion secondary battery according to the second aspect of the present invention, the total amount (total composition) of the electrode active material (negative electrode active material), the carbon nanotube, and the electrode constituent material (negative electrode constituent material) excluding the electrode active material (negative electrode active material) and the carbon nanotube is 100 mass%.
For the same reason, in the composition (2) for forming an electrode active material layer for a lithium ion secondary battery according to the second aspect of the present invention, the volume ratio of the 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. When a plurality of types of carbon nanotubes are used, the total volume is preferably adjusted so as to fall within the above range. In the composition (2) for forming an electrode active material layer for a lithium ion secondary battery according to the second aspect of the present invention, 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) excluding the electrode active material (negative electrode active material) and the carbon nanotube is 100% by volume.
[1-2-3] Electrode constituent Material other than electrode active Material and carbon nanotube
The composition for forming an electrode active material layer for a lithium ion secondary battery according to the second aspect of the present invention (composition for forming a negative electrode active material layer for a lithium ion secondary battery) can collect current between active material particles, maintain the shape of an electrode, and the like by using a very small amount of carbon nanotubes, and as a result: although the electrode active material (anode active material) has a smaller particle diameter and the interface between the particles of the electrode active material (anode active material) increases, the starting point of structural collapse increases, but even if the amount of the electrode constituent material (anode constituent material) other than the electrode active material (anode active material) is reduced, the strength to the extent that the shape of the electrode (anode) can be maintained is provided, and the reaction area increases due to the smaller particle diameter of the electrode active material (anode active material), so that the lithium ion flux per unit area decreases, and particularly, the risk of lithium precipitation during long-term use under high-load conditions decreases, and the amount of the electrode constituent material (anode constituent material) other than the electrode active material (anode active material) is significantly reduced, so that the lifetime 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 as the material described in [1-1-3 ].
The composition for forming an electrode active material layer for a lithium ion secondary battery according to the second aspect of the present invention (composition for forming a negative electrode active material layer for a lithium ion secondary battery) can collect current between active material particles, maintain the shape of an electrode, and the like by using a very small amount of carbon nanotubes, and as a result: although the number of interfaces between particles of the electrode active material (anode active material) increases due to the reduction of the particle size of the electrode active material (anode active material), the starting point of structural collapse increases, but even if the amount of the electrode constituent material (anode constituent material) other than the electrode active material (anode active material) is reduced, the strength to the extent that the shape of the electrode (anode) can be maintained, and the reaction area increases due to the reduction of the particle size of the electrode active material (anode active material), so that the lithium ion flux per unit area decreases, and particularly, the risk of lithium deposition during long-term use under high-load conditions decreases, and the amount of the electrode constituent material (anode constituent material) other than the electrode active material (anode active material) is significantly reduced, so that the lifetime characteristics are significantly improved. Therefore, the electrode constituent material (anode constituent material) other than the electrode active material (anode active material) and the carbon nanotube is not contained, or even if contained, the content thereof is small. Therefore, in the composition (1) for forming an electrode active material layer for a lithium ion secondary battery according to the second aspect 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. In the case where a plurality of electrode constituent materials (anode constituent materials) other than the electrode active material (anode active material) and the carbon nanotube are used, the total amount thereof is preferably adjusted so as to fall within the above-described range. The electrode constituent material (negative electrode constituent material) other than the electrode active material (negative electrode active material) and the carbon nanotube is a material that inhibits movement of lithium ions, but if it is about 2.0 mass% or less, it is complementary to the case where the particle size of the electrode active material (negative electrode active material) is small, movement of lithium ions is not easily inhibited, and in addition, the electrode active material (negative electrode active material) has strength to such an extent that the shape of the electrode (negative electrode) can be maintained while maintaining uniform reaction in the battery, even though the particle size of the electrode active material (negative electrode active material) is small. In the composition (1) for forming an electrode active material layer for a lithium ion secondary battery according to the second aspect of the present invention, the total amount (total composition) of the electrode active material (negative electrode active material), the carbon nanotube, and the electrode constituent material (negative electrode constituent material) excluding the electrode active material (negative electrode active material) and the carbon nanotube is 100 mass%.
For the same reason, in the composition (2) for forming an electrode active material layer for a lithium ion secondary battery according to the second aspect of the present invention, 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. When a plurality of electrode active materials (negative electrode active materials) are used, the total volume is preferably adjusted so as to fall within the above-described range. In the composition (2) for forming an electrode active material layer for a lithium ion secondary battery according to the second aspect of the present invention, 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) excluding the electrode active material (negative electrode active material) and the carbon nanotube is 100% by volume.
[1-2-4] Composition for forming 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 according to the second aspect of the present invention (composition for forming an electrode active material layer for a lithium ion secondary battery), when an electrode active material (anode active material), carbon nanotubes, and an electrode constituent material (anode constituent material) other than the electrode active material (anode active material) and the carbon nanotubes are mixed to prepare a paste composition for forming an electrode active material layer for a lithium ion secondary battery (paste composition for forming an electrode active material layer for a lithium ion secondary battery), the paste composition may be prepared by containing 1 or 2 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), the carbon nanotube, and the electrode constituent material (negative electrode constituent material) other than the electrode active material (negative electrode active material) and the carbon nanotube, that is, the total amount of the solid components is 100 mass% or 100 volume%.
The method for producing 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) according to the second aspect of the present invention is not particularly limited. For example, the electrode active material layer forming composition for a lithium ion secondary battery according to the second aspect of the present invention (negative electrode active material layer forming composition for a lithium ion secondary battery) can be produced by mixing the above components by a conventional method. The mixing may be performed by mixing all the components simultaneously or sequentially.
(1-3) Composition for Forming electrode active Material layer for lithium ion Secondary Battery (third mode)
The composition (1) for forming an electrode active material layer for a lithium ion secondary battery according to the third aspect of the present invention is a composition for forming an electrode active material layer for a lithium ion secondary battery, which contains an electrode active material and carbon nanotubes, wherein the content of the electrode active material is 88.6 to 99.9 mass%, the content of the carbon nanotubes is 0.01 to 1.4 mass%, the content of a conductive auxiliary agent other than the carbon nanotubes is 0 to 10.0 mass%, and the composition does not contain an electrode constituent material other than the electrode active material, the carbon nanotubes, and the conductive auxiliary agent other than the carbon nanotubes, and the composition is a composition for forming an anode active material layer for a lithium ion secondary battery. In the composition (1) for forming an electrode active material layer for a lithium ion secondary battery according to the third aspect of the present invention, the total amount of the electrode active material (positive electrode active material), the carbon nanotube, and the conductive auxiliary agent other than the electrode active material (positive electrode active material) and the carbon nanotube (total amount of the composition) is 100 mass%. In the same manner, the composition (2) for forming an electrode active material layer for a lithium ion secondary battery according to the third aspect of the present invention is a composition for forming an electrode active material layer for a lithium ion secondary battery comprising 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 a conductive auxiliary agent other than the carbon nanotubes is 0 to 21.56% by volume. In the composition (2) for forming an electrode active material layer for a lithium ion secondary battery according to the third aspect of the present invention, the total amount of the electrode active material (positive electrode active material), the carbon nanotubes, and the conductive auxiliary agent other than the carbon nanotubes (total volume of the composition) is 100% by volume.
By adopting such a configuration, the mass of the lithium ion inhibitor is reduced while maintaining the strength at a level at which the shape of the electrode (positive electrode) can be maintained, and thus the inhibition of lithium ion movement can be suppressed, and as a result, the reaction of the battery can be uniformized, and the battery can have a long life. That is, the composition for forming an electrode active material layer for a lithium ion secondary battery according to the third aspect of the present invention (composition for forming a positive electrode active material layer for a lithium ion secondary battery) can be used to reduce reaction non-uniformity in a lithium ion secondary battery.
[1-3-1] Electrode active material
As the electrode active material (positive electrode active material), there is no particular limitation, and a material that can be used as the electrode active material (positive electrode active material) in a lithium ion secondary battery, that is, a material that can absorb and release lithium ions, may be used, for example: lithium transition metal composite oxide having alpha-NaFeO 2 type crystal structure, lithium transition metal oxide having spinel type crystal structure, polyanion compound, chalcogenide, sulfur, and the like. Examples of the lithium transition metal composite oxide having an α -NaFeO 2 crystal structure include ：Li[Lix1Niγ1Mnβ1Co(1-x1-γ1-β1)]O2(0≤x1<0.5、0≤γ1≤1、0≤β1≤1、0≤γ1+β1≤1)、Li[Lix2Niγ2Coβ2Al(1-x2-γ2-β2)]O2(0≤x2<0.5、0≤γ2≤1、0≤β2≤1、0≤γ2+β2≤1). Examples of the lithium transition metal oxide having a spinel crystal structure include Lix3Mn2O4(0.9≤x3<1.5)、Lix4Niγ4Mn(2-γ4)O4(0.9≤x4<1.5、0≤γ4≤2). As the polyanion compound, LiFePO4、LiMnPO4、LiNiPO4、LiCoPO4、Li3V2(PO4)3、Li2MnSiO4、Li2CoPO4F and the like are mentioned. Examples of the chalcogenides include titanium disulfide, molybdenum disulfide, and molybdenum dioxide. Some of the atoms or polyanions in these materials may be replaced by atomic or anionic species containing other elements. These electrode active materials (positive electrode active materials) may be used alone or in combination of 2 or more. Among these, the lithium transition metal composite oxide is preferable from the viewpoint of increasing the energy density, and the polyanion compound is preferable from the viewpoint of increasing the safety.
The form 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, scaly, block, fibrous, whisker-like, broken and the like can be used. In addition, positive electrode active materials of various shapes may be used in combination. The spherical shape may be a regular spherical shape, or may be an elliptical shape.
The particle size of the electrode active material (positive electrode active material) is not particularly limited, but the average particle size is preferably 0.1 to 25 μm, more preferably 1 to 20 μm, from the viewpoint that the current collection between the particles of the electrode active material (positive electrode active material) is easily performed by a small amount of carbon nanotubes and the battery is easily further prolonged. In addition, in view of homogenization of the reaction at low temperature, the average particle diameter of the electrode active material (positive electrode active material) may be 0.1 to 13.0 μm, preferably 0.5 to 10.0 μm, and more preferably 1.0 to 8.0 μm. The average particle diameter of the electrode active material (positive electrode active material) was measured by a laser diffraction/scattering method.
The electrode active material layer forming composition for a lithium ion secondary battery according to the third aspect of the present invention is capable of collecting current between active material particles, maintaining the shape of an electrode (positive electrode), and the like by a very small amount of carbon nanotubes, and therefore, is configured to be free of an electrode constituent material (positive electrode constituent material) other than a conductive additive, and is also capable of reducing the amount of an electrode constituent material (positive electrode constituent material) other than an electrode active material (positive electrode active material), and as a result, has strength at such a level that the shape of an electrode (positive electrode) can be maintained, and is less likely to inhibit movement of lithium ions, and therefore, can uniformize the reaction in a battery and lengthen the life of a battery, and therefore, the content of an electrode active material (positive electrode active material) is larger than that of a conventional electrode active material layer forming composition (positive electrode active material layer forming composition). Therefore, in the composition (1) for forming an electrode active material layer for a lithium ion secondary battery according to the third aspect of the present invention, the content of the electrode active material (positive electrode active material) is 88.6 to 99.9 mass%, preferably 90.8 to 98.4 mass%, and more preferably 93.0 to 97.8 mass%. When a plurality of electrode active materials (positive electrode active materials) are used, the total amount thereof is preferably adjusted so as to fall within the above-described range. In the composition (1) for forming a positive electrode active material layer for a lithium ion secondary battery according to the third aspect of the present invention, the total amount of the electrode active material (positive electrode active material), the carbon nanotubes, and the conductive auxiliary agent other than the carbon nanotubes (total amount of the composition) is 100% by mass.
For the same reason, in the composition (2) for forming a positive electrode active material layer for a lithium ion secondary battery according to the third aspect of the present invention, the volume ratio of the electrode active material (positive electrode active material) is 75.06 to 99.97% by volume, preferably 79.20 to 94.99% by volume, and more preferably 83.63 to 93.93% by volume. When a plurality of electrode active materials (positive electrode active materials) are used, the total volume is preferably adjusted so as to fall within the above-described range. In the composition (2) for forming an electrode active material layer for a lithium ion secondary battery according to the second aspect of the present invention, the total amount of the electrode active material (positive electrode active material), the carbon nanotubes, and the conductive auxiliary agent other than the carbon nanotubes (total volume of the composition) 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 an electrode (positive electrode), and the like by a very small amount of carbon nanotubes, and therefore, is made to contain no electrode constituent material (positive electrode constituent material) other than a conductive auxiliary agent, and also can reduce the amount of the electrode constituent material (positive electrode constituent material) other than the electrode active material (positive electrode active material), and as a result, has strength to such an extent that the shape of an electrode (positive electrode) can be maintained, and movement of lithium ions is not easily hindered, and thus, the reaction in the battery can be uniformized, and the battery can be prolonged. Carbon nanotubes are also substances that inhibit movement of lithium ions, but if small amounts, do not inhibit movement of lithium ions, i.e., can have strength to such an extent that the shape of an electrode (positive electrode) can be maintained while maintaining uniformity of reaction in the battery.
As the usable carbon nanotubes, the same carbon nanotubes as those described in the above [1-1-2] can be used.
The composition for forming an electrode active material layer for a lithium ion secondary battery according to the third aspect of the present invention can collect electricity between electrode active material (positive electrode active material) particles, maintain the shape of an electrode (positive electrode), and the like by a very small amount of carbon nanotubes, and therefore, it is possible to reduce the amount of electrode constituent materials (positive electrode constituent materials) other than an electroconductive aid by providing the electrode constituent materials (positive electrode constituent materials) other than the electrode active material (positive electrode active material), and as a result, it is possible to maintain the strength of the electrode (positive electrode) shape degree, and it is not easy to hinder the movement of lithium ions, and therefore, it is possible to uniformize the reaction in the battery and lengthen the life of the battery, and therefore, the content of carbon nanotubes is small. Accordingly, in the composition (1) for forming an electrode active material layer for a lithium ion secondary battery according to the third aspect of the present invention, the content of the 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. When a plurality of types of carbon nanotubes are used, the total amount is preferably adjusted so as to fall within the above range. Carbon nanotubes are also substances that inhibit movement of lithium ions, but if they are about 1.4 mass% or less, movement of lithium ions is not easily inhibited, and strength to such an extent that the shape of an electrode (positive electrode) can be maintained while keeping the reaction in the battery uniform can be obtained. In the composition (1) for forming an electrode active material layer for a lithium ion secondary battery according to the third aspect of the present invention, the total amount of the electrode active material (positive electrode active material), the carbon nanotubes, and the conductive auxiliary agent other than the carbon nanotubes (total composition) is 100% by mass.
For the same reason, in the composition (2) for forming an electrode active material layer for a lithium ion secondary battery according to the third aspect of the present invention, the volume ratio of the 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. When a plurality of types of carbon nanotubes are used, the total volume is preferably adjusted so as to fall within the above range. In the composition (2) for forming an electrode active material layer for a lithium ion secondary battery according to the third aspect of the present invention, the total amount of the electrode active material (positive electrode active material), the carbon nanotubes, and the conductive auxiliary agent other than the carbon nanotubes (total volume of the composition) is 100% by volume.
[1-3-3] Conductive auxiliary agent other than carbon nanotube
The composition for forming an electrode active material layer for a lithium ion secondary battery according to the third aspect of the present invention can collect electricity between electrode active materials (positive electrode active materials) and maintain the shape of an electrode (positive electrode) by a very small amount of carbon nanotubes, and therefore, the composition can be made to contain no electrode constituent material (positive electrode constituent material) other than a conductive additive, and the amount of electrode constituent material (positive electrode constituent material) other than the electrode active materials (positive electrode active materials) can be reduced, and as a result, the composition has strength to such an extent that the shape of an electrode (positive electrode) can be maintained, and movement of lithium ions is not easily blocked, and thus, the reaction in the battery can be uniformized, and the battery life can be prolonged.
However, in the composition for forming an electrode active material layer for a lithium ion secondary battery according to the third aspect of the present invention (composition for forming a positive electrode active material layer for a lithium ion secondary battery), a certain amount of a conductive auxiliary agent may be contained in addition to a very small amount of carbon nanotubes from the viewpoint of facilitating maintenance of current collection between particles of an electrode active material (positive electrode active material) or the like, depending on the particle morphology, particle diameter, particle shape, and electron conductivity of the electrode active material (positive electrode active material). For example, in the case of 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 preferable that a certain amount of a conductive auxiliary agent is contained in addition to the carbon nanotubes.
Examples of the conductive auxiliary agent other than carbon nanotubes 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) according to the third aspect of the present invention include: carbon black such as acetylene black, furnace black, ketjen black, etc.; flake graphite; a graphene; amorphous carbon obtained by heat-treating an organic substance, and the like. These conductive assistants other than carbon nanotubes may be used alone or in combination of 2 or more. Among them, carbon black is preferable from the viewpoints of being less likely to inhibit movement of lithium ions, being easy to uniformize reaction in a battery, and being easy to lengthen the life of the battery.
In the composition (1) for forming an electrode active material layer for a lithium ion secondary battery according to the third aspect of the present invention, the content of the conductive auxiliary agent 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, from the viewpoints of not being liable to inhibit movement of lithium ions, being liable to uniformize reaction in the battery, and being liable to lengthen the life of the battery. In the case of using a plurality of conductive auxiliaries other than carbon nanotubes, the total amount thereof is preferably adjusted so as to fall within the above-described range. In the composition (1) for forming an electrode active material layer for a lithium ion secondary battery according to the third aspect of the present invention, the total amount of the electrode active material (positive electrode active material), the carbon nanotubes, and the conductive auxiliary agent other than the carbon nanotubes (total composition) is 100% by mass.
For the same reason, in the composition (2) for forming an electrode active material layer for a lithium ion secondary battery according to the third aspect of the present invention, the volume ratio of the conductive auxiliary agent 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. In the case of using a plurality of conductive auxiliaries other than carbon nanotubes, the total amount thereof is preferably adjusted so as to fall within the above-described range. In the composition (2) for forming an electrode active material layer for a lithium ion secondary battery according to the third aspect of the present invention, the total amount of the electrode active material (positive electrode active material), the carbon nanotubes, and the conductive auxiliary agent other than the carbon nanotubes (total volume of the composition) is 100% by volume.
[1-3-4] Electrode constituent Material other than electrode active Material, carbon nanotube and conductive auxiliary agent other than carbon nanotube
The composition for forming an electrode active material layer for a lithium ion secondary battery according to the third aspect of the present invention can collect electricity between electrode active material (positive electrode active material) particles, maintain the shape of an electrode (positive electrode), and the like by a very small amount of carbon nanotubes, and therefore, it is possible to reduce the amount of electrode constituent materials (positive electrode constituent materials) other than the electrode active material (positive electrode active material) and the conductive auxiliary agent, and as a result, it is possible to maintain the strength of the electrode (positive electrode) shape, and it is not easy to hinder movement of lithium ions, and therefore, it is possible to uniformize the reaction in the battery, and it is possible to lengthen the life of the battery.
In a conventional 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), in addition to an electrode active material (positive electrode active material) and a conductive auxiliary agent, a substance (lithium ion movement blocking substance) that blocks movement of lithium ions such as a substance (binder) having adhesiveness to an electrode active material (positive electrode active material) and an electrode current collector (positive electrode current collector), a dispersant, or the like is generally included more or less.
In contrast, the composition for forming an electrode active material layer for a lithium ion secondary battery according to the third aspect of the present invention (composition for forming a positive electrode active material layer for a lithium ion secondary battery) can collect electricity between particles of an electrode active material (positive electrode active material), maintain the shape of an electrode (positive electrode), and the like by a very small amount of carbon nanotubes, and therefore can be configured to have a structure that does not contain an electrode constituent material other than a conductive additive (positive electrode constituent material), as described above.
The electrode active material layer forming composition for a lithium ion secondary battery according to the third aspect of the present invention (positive electrode active material layer forming composition for a lithium ion secondary battery) may be any other electrode constituent material (positive electrode constituent material) that is not contained, and examples thereof include a binder, a thickener, and 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 sodium salt, carboxymethyl cellulose ammonium, polyurethane, hydroxypropyl cellulose, hydroxyethyl cellulose, methyl cellulose, etc.
[1-3-5] Composition for forming 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 according to the third aspect of the present invention (composition for forming a positive electrode active material layer for a lithium ion secondary battery), when an electrode active material (positive electrode active material), carbon nanotubes, and a conductive additive other than carbon nanotubes are mixed to prepare a paste composition for forming an electrode active material layer for a lithium ion secondary battery (paste composition for forming a positive electrode active material layer for a lithium ion secondary battery), the paste composition may be prepared by containing 1 or 2 or more of water or alcohol (methanol, ethanol, N-propanol, isopropanol, etc.), acetone, N-methylpyrrolidone, dimethylsulfoxide, dimethylformamide, etc. as an organic solvent. In this case, the content of each component is a value obtained by setting the total amount of the electrode active material (positive electrode active material), the carbon nanotubes, and the conductive auxiliary agent other than the carbon nanotubes, that is, the total amount of the solid components to 100 mass% or 100 volume%.
The method for producing 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) according to the third aspect of the present invention is not particularly limited. For example, the electrode active material layer forming composition for a lithium ion secondary battery (positive electrode active material layer forming composition for a lithium ion secondary battery) according to the third aspect of the present invention can be produced by mixing the above-described components by a conventional method. The mixing may be performed by mixing all the components simultaneously or sequentially.
(1-4) Composition for Forming electrode active Material layer for lithium ion Secondary Battery (fourth aspect)
The composition for forming an electrode active material layer for a lithium ion secondary battery according to the fourth aspect of the present invention is a composition for forming an electrode active material layer for a lithium ion secondary battery comprising an electrode active material and carbon nanotubes, wherein the electrode active material contains an amorphous carbon material, and the content of carbon nanotubes is 0.01 to 0.8 mass% when the total amount of the composition is 100 mass%, and the composition is a composition for forming a negative electrode active material layer for a lithium ion secondary battery.
Since the amorphous carbon material has low electron conductivity if it is a graphite material, it is necessary to form a uniform electron conduction path in order to keep the reaction in the battery uniform. On the other hand, when a conductive additive having a small aspect ratio such as carbon black is used, the amount of the conductive additive required for forming the electron conductive path becomes large, and lithium ions may be hindered from moving. On the other hand, carbon nanotubes having a high aspect ratio can form uniform electron conduction paths in a small amount. By using the amorphous carbon material and the carbon nanotubes in combination in this manner, it is possible to form a uniform electron conduction path while suppressing the inhibition of lithium ion movement, and thus it is possible to maintain uniformity of reaction in the battery. In addition, although the carbon nanotubes are substances capable of blocking lithium ion movement, in the present invention, the content of the carbon nanotubes is very small, so that the reaction in the battery can be kept uniform, and the battery can be prolonged by the synergistic effect of amorphous carbon materials. That is, the composition for forming an electrode active material layer for a lithium ion secondary battery according to the fourth aspect of the present invention (composition for forming a negative electrode active material layer for a lithium ion secondary battery) can be used to reduce reaction non-uniformity in a lithium ion secondary battery.
[1-4-1] Electrode active material
As the amorphous carbon material used as the electrode active material (negative electrode active material), an amorphous layered carbon material is preferable from the viewpoint of easily uniformizing the reaction in the battery and easily prolonging the life of the battery.
The interlayer distance of the (002) plane of the amorphous layered carbon material is preferably 0.35nm or more, more preferably 0.36nm or more, from the viewpoint of facilitating the homogenization of the reaction in the battery and the prolongation of the battery life. The upper limit of the interlayer distance of the (002) plane of the amorphous layered carbon material is not particularly limited, and is usually 0.40nm. The interlayer distance of the amorphous layered carbon material was measured by an X-ray diffraction method.
The average particle diameter of the amorphous layered carbon material is preferably 1 to 10 μm, more preferably 3 to 8 μm, from the viewpoint of easily uniformizing the reaction in the battery and easily prolonging the life of the battery. The average particle diameter of the amorphous layered carbon material was measured by a laser diffraction/scattering method.
Examples of the amorphous carbon material satisfying the above conditions include hard carbon (hard graphitizable carbon material), soft carbon (graphitizable carbon material), and mesophase pitch carbide. These amorphous carbon materials may be used alone or in combination of 2 or more. Among them, hard carbon is preferable from the viewpoint of facilitating the homogenization of the reaction in the battery and the long life of the battery. In the present invention, hard carbon means an amorphous carbon material having an interlayer distance of the (002) plane of not less than 0.34nm when fired at 3000 ℃. The soft carbon is an amorphous carbon material having an interlayer distance of the (002) plane of less than 0.34nm when fired at 3000 ℃.
The shape of the electrode active material (anode active material) is not particularly limited, and various shapes such as spherical, scaly, block, fibrous, whisker-like, and crushed can be used. In addition, electrode active materials (negative electrode active materials) of various shapes may be used in combination. The spherical shape may be a regular spherical shape, or may be an elliptical shape.
The composition for forming an electrode active material layer for a lithium ion secondary battery according to the fourth aspect of the present invention (composition for forming a negative electrode active material layer for a lithium ion secondary battery) can suppress the inhibition of movement of lithium ions and form a uniform electron conduction path by using an amorphous carbon material as an electrode active material (negative electrode active material) and using an extremely small amount of carbon nanotubes, thereby making the reaction in the battery uniform and prolonging the life of the battery. In the present invention, the content of the electrode active material (anode active material) is preferably 79.2 to 99.8 mass%, more preferably 83.5 to 96.4 mass%, and even more preferably 77.8 to 94.9 mass%. When a plurality of electrode active materials (negative electrode active materials) are used, the total amount thereof is preferably adjusted so as to fall within the above-described range. In the composition for forming an electrode active material layer for a lithium ion secondary battery according to the fourth aspect of the present invention (composition for forming an anode active material layer for a lithium ion secondary battery), the total amount (total composition) of the electrode active material (anode active material), the carbon nanotube, the conductive auxiliary agent other than the carbon nanotube, and the electrode constituent material (anode constituent material) other than the electrode active material (anode active material), the carbon nanotube, and the conductive auxiliary agent other than the carbon nanotube is 100 mass%.
[1-4-2] Carbon nanotubes
The composition for forming an electrode active material layer for a lithium ion secondary battery according to the fourth aspect of the present invention (composition for forming a negative electrode active material layer for a lithium ion secondary battery) can suppress the inhibition of movement of lithium ions and form a uniform electron conduction path by using an amorphous carbon material as an electrode active material (negative electrode active material) and using an extremely small amount of carbon nanotubes, thereby making the reaction in the battery uniform and prolonging the life of the battery. Carbon nanotubes are also substances that inhibit movement of lithium ions, but if the amount is small, movement of lithium ions is not inhibited, that is, the reaction in the battery can be made uniform, and the battery can be made longer.
As the usable carbon nanotubes, the same carbon nanotubes as those described in the above [1-1-2] can be used.
The composition for forming an electrode active material layer for a lithium ion secondary battery according to the fourth aspect of the present invention uses an amorphous carbon material as an electrode active material (negative electrode active material) and uses an extremely small amount of carbon nanotubes, thereby suppressing the inhibition of lithium ion movement and forming a uniform electron conduction path, thereby making it possible to uniformize the reaction in the battery and to lengthen the life of the battery, and therefore the content of carbon nanotubes is small. Accordingly, in the present invention, the content of the carbon nanotubes is 0.01 to 0.8 mass%, preferably 0.02 to 0.5 mass%, more preferably 0.05 to 0.2 mass%. When a plurality of types of carbon nanotubes are used, the total amount is preferably adjusted so as to fall within the above range. Carbon nanotubes are also substances that inhibit movement of lithium ions, but if they are about 0.8 mass% or less, movement of lithium ions is not easily inhibited, and the reaction uniformity in the battery can be maintained. In the composition for forming an electrode active material layer for a lithium ion secondary battery according to the fourth aspect of the present invention (composition for forming an anode active material layer for a lithium ion secondary battery), the total amount (total composition) of the electrode active material (anode active material), the carbon nanotube, the conductive auxiliary agent other than the carbon nanotube, and the electrode constituent material (anode constituent material) other than the electrode active material (anode active material), the carbon nanotube, and the conductive auxiliary agent other than the carbon nanotube is 100 mass%.
[1-4-3] Conductive auxiliary agent other than carbon nanotube
The composition for forming an electrode active material layer for a lithium ion secondary battery according to the fourth aspect of the present invention (composition for forming a negative electrode active material layer for a lithium ion secondary battery) can suppress the inhibition of movement of lithium ions and form a uniform electron conduction path by using an amorphous carbon material as an electrode active material (negative electrode active material) and using an extremely small amount of carbon nanotubes, thereby making the reaction in the battery uniform and prolonging the life of the battery.
However, in the composition for forming an electrode active material layer for a lithium ion secondary battery according to the fourth aspect of the present invention (composition for forming a negative electrode active material layer for a lithium ion secondary battery), a certain amount of a conductive auxiliary agent may be contained in addition to a very small amount of carbon nanotubes from the viewpoint of facilitating maintenance of current collection between particles of an electrode active material (negative electrode active material) or the like, depending on the particle morphology, particle diameter, particle shape, and electron conductivity of an amorphous carbon material. For example, in the case of using an amorphous carbon material having a spherical particle shape as an electrode active material (negative electrode active material), it is preferable that a certain amount of a conductive auxiliary agent is contained in addition to the carbon nanotubes.
As the conductive auxiliary agent other than carbon nanotubes that can be used, the same conductive auxiliary agents other than carbon nanotubes as those described in the above [1-3-3] can be used.
In the present invention, when the conductive additive other than carbon nanotubes is contained, the content of the conductive additive other than carbon nanotubes is preferably 0.1 to 10.0% by mass, more preferably 1.0 to 8.0% by mass, and even more preferably 2.0 to 6.0% by mass, from the viewpoint of facilitating the homogenization of the reaction in the battery and the prolongation of the battery life. In the case of using a plurality of conductive auxiliaries other than carbon nanotubes, the total amount thereof is preferably adjusted so as to fall within the above-described range. In the composition for forming an electrode active material layer for a lithium ion secondary battery according to the fourth aspect of the present invention (composition for forming an anode active material layer for a lithium ion secondary battery), the total amount (total composition) of the electrode active material (anode active material), the carbon nanotube, the conductive auxiliary agent other than the carbon nanotube, and the electrode constituent material (anode constituent material) other than the electrode active material (anode active material), the carbon nanotube, and the conductive auxiliary agent other than the carbon nanotube is 100 mass%.
For the same reason, the content of the carbon nanotubes is preferably 0.1 to 100.0 mass%, more preferably 0.5 to 50 mass%, and even more preferably 1.0 to 20.0 mass% based on 100 mass% of the total amount of the carbon nanotubes and the conductive auxiliary agent other than the carbon nanotubes. In the case of using a plurality of conductive auxiliaries other than carbon nanotubes, the total amount thereof is preferably adjusted so as to fall within the above-described range.
[1-4-4] Electrode constituent Material (other electrode constituent Material) other than electrode active Material, carbon nanotube and conductive auxiliary agent other than carbon nanotube
The composition for forming an electrode active material layer for a lithium ion secondary battery according to the fourth aspect of the present invention (composition for forming a negative electrode active material layer for a lithium ion secondary battery) can suppress the inhibition of movement of lithium ions and form a uniform electron conduction path by using an amorphous carbon material as an electrode active material (negative electrode active material) and using an extremely small amount of carbon nanotubes, thereby making the reaction in the battery uniform and prolonging the life of the battery.
In the present invention, 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), the carbon nanotube, and the conductive auxiliary agent other than the carbon nanotube is generally referred to as a substance (binder), a dispersant, or the like having adhesiveness to the electrode active material (negative electrode active material) and the electrode current collector (negative electrode current collector), and the concept of a substance (lithium ion movement inhibitor) other than the carbon nanotube and the conductive auxiliary agent other than the carbon nanotube that inhibits movement of lithium ions.
As for the electrode constituent materials (anode constituent materials) (other electrode constituent materials (anode constituent materials)) other than the electrode active material (anode active material), the carbon nanotubes, and the conductive auxiliary agent 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 (anode constituent materials) (other electrode constituent materials (anode constituent materials)) other than the electrode active material (anode active material), the carbon nanotubes, and the conductive auxiliary agent other than the carbon nanotubes may be used alone, or 2 or more may be used in combination.
The composition for forming an electrode active material layer for a lithium ion secondary battery according to the fourth aspect of the present invention (composition for forming a negative electrode active material layer for a lithium ion secondary battery) can suppress the inhibition of movement of lithium ions and form a uniform electron conduction path by using an amorphous carbon material as an electrode active material (negative electrode active material) and using an extremely small amount of carbon nanotubes, thereby making the reaction in the battery uniform and prolonging the life of the battery. From this viewpoint, 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), the carbon nanotube, and the conductive auxiliary agent other than the carbon nanotube is preferably small, and from the viewpoint of easily having strength to such an extent that the electrode shape can be maintained, the content is preferably a constant or more. Therefore, in the composition for forming an electrode active material layer for a lithium ion secondary battery according to the fourth aspect of the present invention (composition for forming an anode active material layer for a lithium ion secondary battery), the content of the electrode constituent material (anode constituent material) (other electrode constituent material (anode constituent material)) excluding the electrode active material (anode active material), the carbon nanotube and the conductive auxiliary agent other than the carbon nanotube is preferably 0.1 to 10.0% by mass, more preferably 1.0 to 8.0% by mass, and even more preferably 2.0 to 6.0% by mass. In the case where a plurality of electrode constituent materials (anode constituent materials) (other electrode constituent materials (anode constituent materials)) other than the electrode active material (anode active material), the carbon nanotube, and the conductive auxiliary agent other than the carbon nanotube are used, the total amount thereof is preferably adjusted so as to fall within the above-described range. In the composition for forming an electrode active material layer for a lithium ion secondary battery according to the fourth aspect of the present invention (composition for forming an anode active material layer for a lithium ion secondary battery), the total amount (total composition) of the electrode active material (anode active material), the carbon nanotube, the conductive auxiliary agent other than the carbon nanotube, and the electrode constituent material (anode constituent material) other than the electrode active material (anode active material), the carbon nanotube, and the conductive auxiliary agent other than the carbon nanotube is 100 mass%.
[1-4-5] Composition for forming 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 according to the fourth aspect of the present invention (composition for forming an electrode active material layer for a lithium ion secondary battery), the composition may be prepared by mixing an electrode active material (anode active material), carbon nanotubes, a conductive auxiliary agent other than carbon nanotubes as needed, and an electrode constituent material (anode constituent material) other than an electrode active material (anode active material), carbon nanotubes, and a conductive auxiliary agent other than carbon nanotubes (other electrode constituent material) (anode constituent material)) as needed to prepare a paste composition for forming an electrode active material layer for a lithium ion secondary battery (paste composition for forming an anode active material layer for a lithium ion secondary battery), and may be prepared by mixing the composition with one or more of organic solvents including water or alcohols (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 by setting the total amount of the electrode active material (negative electrode active material), the carbon nanotube, the conductive auxiliary agent other than the carbon nanotube as needed, and the electrode constituent material (negative electrode constituent material) other than the electrode active material (negative electrode active material), the carbon nanotube, and the conductive auxiliary agent other than the carbon nanotube as needed (other electrode constituent material (negative electrode constituent material)), that is, the total amount of the solid components, to 100 mass%.
The method for producing 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) according to the fourth aspect of the present invention is not particularly limited. For example, the electrode active material layer forming composition for a lithium ion secondary battery (negative electrode active material layer forming composition for a lithium ion secondary battery) according to the fourth aspect of the present invention can be produced by mixing the above-described components by a conventional method. The mixing may be performed by mixing all the components simultaneously or sequentially.
2. Electrode active material layer for lithium ion secondary battery
The electrode active material layer for a lithium ion secondary battery (negative electrode active material layer for a lithium ion secondary battery or positive electrode active material layer for a lithium ion secondary battery) of the present invention contains 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 or composition for forming a positive electrode active material layer for a lithium ion secondary battery) of the present invention.
The thickness of the electrode active material layer for a lithium ion secondary battery (negative electrode active material layer for a lithium ion secondary battery or positive electrode active material layer for a lithium ion secondary battery) of the present invention is not particularly limited, and the thinner the electrode active material layer is, the better the reaction uniformity is in terms of ensuring permeation and conductivity of lithium ions, and on the other hand, the present invention is intended to improve the life by uniformizing the battery reaction for the main reason of reducing the inhibition of movement of lithium ions, and therefore can also be thickened for the energy density of each electrode. Therefore, the thickness of the electrode active material layer for a lithium ion secondary battery (negative electrode active material layer for a lithium ion secondary battery or positive electrode active material layer for a lithium ion secondary battery) of the present invention is preferably 1 to 300 μm, more preferably 10 to 150 μm, and even more preferably 50 to 100 μm.
Such an electrode active material layer for a lithium ion secondary battery (negative electrode active material layer for a lithium ion secondary battery or positive electrode active material layer for a lithium ion secondary battery) of the present invention can be produced by shaping the aforementioned 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 or composition for forming 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 (composition for forming a negative electrode active material layer for a lithium ion secondary battery or composition for forming a positive electrode active material layer for a lithium ion secondary battery) of the present invention is prepared as 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 or paste composition for forming a positive electrode active material layer for a lithium ion secondary battery), the paste composition can be dried by a conventional method to form a layer.
3. Electrode for lithium ion secondary battery
The electrode for a lithium ion secondary battery (negative electrode for a lithium ion secondary battery or positive electrode for a lithium ion secondary battery) of the present invention includes the electrode active material layer for a lithium ion secondary battery (negative electrode active material layer for a lithium ion secondary battery or positive electrode active material layer for a lithium ion secondary battery) of the present invention described above, and specifically, preferably includes an electrode current collector (negative electrode current collector or positive electrode current collector) and the electrode active material layer for a lithium ion secondary battery (negative electrode active material layer for a lithium ion secondary battery or positive electrode active material layer for a lithium ion secondary battery) of the present invention disposed on the electrode current collector (negative electrode current collector or positive electrode current collector).
The negative electrode current collector preferably contains a material that is electrochemically stable at the potential used and has high electron conductivity, such as copper, stainless steel, nickel, a carbon material, or the like. The negative electrode current collector may be formed, for example, as a foil-like or mesh-like member.
The positive electrode current collector preferably contains a material that is electrochemically stable at the potential used and has high electron conductivity, such as aluminum, stainless steel, a carbon material, or the like. The positive electrode current collector may be formed, for example, as a member such as a foil or a mesh.
In the case of manufacturing such an electrode for a lithium ion secondary battery (negative electrode for a lithium ion secondary battery or positive electrode for a lithium ion secondary battery) according to the present invention, 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 or composition for forming a positive electrode active material layer for a lithium ion secondary battery) according to the present invention can be manufactured by forming the above-described 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 or composition for forming a positive electrode active material layer for a lithium ion secondary battery) in a layer on an electrode current collector (negative electrode current collector or positive electrode current collector). For example, when 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 or composition for forming a positive electrode active material layer for a lithium ion secondary battery) of the present invention is prepared as 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 or paste composition for forming a positive electrode active material layer for a lithium ion secondary battery), the electrode for a lithium ion secondary battery (negative electrode for a lithium ion secondary battery or positive electrode for a lithium ion secondary battery) of the present invention can be produced by drying the paste composition for forming a layer by a conventional method for an electrode active material (negative electrode active material or positive electrode for a lithium ion secondary battery).
4. Lithium ion secondary battery
The lithium ion secondary battery of the present invention includes the electrode for a lithium ion secondary battery of the present invention (negative electrode for a lithium ion secondary battery or positive electrode for a lithium ion secondary battery) described above. In the case where the electrode for a lithium ion secondary battery of the present invention is used as a negative electrode, the electrode for a lithium ion secondary battery of the present invention can be used as a positive electrode, and a known positive electrode suitable for a lithium ion secondary battery can also be used. In addition, when the electrode for a lithium ion secondary battery of the present invention is used as a positive electrode, the electrode for a lithium ion secondary battery of the present invention can be used as a negative electrode, and a known negative electrode suitable for a lithium ion secondary battery can also be used. The lithium ion secondary battery of the present invention may further include a known electrolyte solution suitable for a lithium ion secondary battery and a container for housing these electrode constituent members.
In the case of using a known negative electrode suitable for a lithium ion secondary battery 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.
As the negative electrode current collector constituting the negative electrode, a material having high electron conductivity and electrochemical stability at the potential used, such as copper, stainless steel, nickel, and carbon material, is preferably contained. The negative electrode current collector may be formed, for example, as a foil-like or mesh-like member.
In addition, as a negative electrode active material constituting a negative electrode, a material capable of absorbing and releasing lithium ions is generally used. Examples include: carbon materials such as natural graphite, artificial graphite, amorphous carbon, and the like; a metal material capable of alloying with lithium, such as Si, al, sn, pb, zn, bi, in, mg, ga, si alloy, sn alloy, and Al alloy; siO x(0＜x＜2)、SnOx(0＜x＜2)、Si、Li2TiO3, vanadium oxide, and other metal oxides capable of absorbing and releasing lithium ions; and composite materials including a metal material and a carbon material such as si—c composite and sn—c composite. These negative electrode active materials may be used alone or in combination of 2 or more. From the viewpoint of particularly suppressing the volume change of the electrode active material (negative electrode active material) at the time of charge and discharge and particularly easily improving the charge and discharge cycle characteristics, a silicon-free material, namely: a carbon material; silicon-free metal materials such as Al, sn, pb, zn, bi, in, mg, ga, sn alloy and Al alloy which can be alloyed with lithium; metal oxides such as SnO x(0＜x＜2)、Si、Li2TiO3 and vanadium oxides which do not contain silicon and can absorb and release lithium ions; and a composite material containing a metal material and a carbon material without containing silicon, such as a sn—c composite. In the case where a conductive material such as a carbon material is used as the negative electrode active material, the negative electrode active material also functions as the conductive material, and the content of a substance that inhibits movement of lithium ions is particularly easy to reduce.
As the electrode active material (negative electrode active material) described above, the volume change of the electrode active material (negative electrode active material) at the time of charge and discharge is preferably 150% or less, more preferably 120% or less, from the viewpoints of particularly suppressing the volume change of the electrode active material (negative electrode active material) at the time of charge and discharge, easily suppressing the decrease in capacity due to the volume change, and particularly easily improving the charge and discharge cycle characteristics. The smaller the volume change, the better, the lower limit value is not set, but the lower limit value is set to 0%. The value of the volume change was set to 0% when there was no volume change at all, and it was shown how much the electrode active material (negative electrode active material) swelled at the time of full charge compared with the electrode active material (negative electrode active material) at the time of full discharge by the following formula:
(volume at full charge) - (volume at full discharge)/(volume at full discharge) ×100
And (5) calculating.
As the negative electrode constituent material other than the negative electrode active material constituting the negative electrode, the same materials as the conductive auxiliary agent other than carbon nanotubes and the other positive electrode constituent materials in the electrode for a lithium ion secondary battery of the present invention described above can be used, and the content thereof can be set to the extent of usual use.
In the case of using a known positive electrode suitable for a lithium ion secondary battery as the positive electrode, the positive electrode may be any positive electrode 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 the potential used and have high electron conductivity, such as aluminum, stainless steel, and carbon materials.
As a positive electrode active material constituting a positive electrode, a material capable of absorbing and releasing lithium ions is generally used. Examples thereof include lithium transition metal composite oxides having an α -NaFeO 2 type crystal structure, lithium transition metal oxides having a spinel type crystal structure, polyanion compounds, chalcogenides, sulfur, and the like. Examples of the lithium transition metal composite oxide having an α -NaFeO 2 crystal structure include Li[Lix1Niγ1Mnβ1Co(1-x1-γ1-β1)]O2(0≤x1<0.5、0≤γ1≤1、0≤β1≤1、0≤γ1+β1≤1)、Li[Lix2Niγ2Coβ2Al(1-x2-γ2-β2)]O2(0≤x2<0.5、0≤γ2≤1、0≤β2≤1、0≤γ2+β2≤1). Examples of the lithium transition metal oxide having a spinel crystal structure include Lix3Mn2O4(0.9≤x3<1.5)、Lix4Niγ4Mn(2-γ4)O4(0.9≤x4<1.5、0≤γ4≤2). As the polyanion compound, LiFePO4、LiMnPO4、LiNiPO4、LiCoPO4、Li3V2(PO4)3、Li2MnSiO4、Li2CoPO4F and the like are mentioned. Examples of the chalcogenides include titanium disulfide, molybdenum disulfide, and molybdenum dioxide. Some of the atoms or polyanions in these materials may be replaced by atomic or anionic species containing other elements. These positive electrode active materials may be used alone or in combination of 2 or more. Among these, the lithium transition metal composite oxide is preferable from the viewpoint of increasing the energy density.
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 electrode for a lithium ion secondary battery of the present invention described above can be used, and the content thereof can be the same as the electrode constituent material other than the electrode active material and the carbon nanotubes in the electrode for a lithium ion secondary battery of the present invention.
The electrolyte is an electrolyte in which a salt is dissolved in an aprotic organic solvent, and is disposed between the positive electrode and the negative electrode, and is preferably impregnated and held in a separator made of, for example, a nonwoven fabric for preventing short-circuiting between the positive electrode and the negative electrode.
The aprotic organic solvent constituting the electrolyte may be, for example: esters such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methylethyl carbonate, gamma-butyrolactone, methyl formate, and methyl acetate; 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, and the like. These aprotic organic solvents may be used alone or in combination of 2 or more.
On the other hand, examples of the salt dissolved in such an aprotic organic solvent include lithium salts such as lithium perchlorate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium halide, lithium aluminate chloride, and lithium bis (fluorosulfonyl) imide. These salts may be used alone or in combination of 2 or more.
Such a lithium ion secondary battery of the present invention uses the composition for forming an electrode active material layer for a lithium ion secondary battery (composition for forming an anode active material layer for a lithium ion secondary battery or composition for forming a cathode active material layer for a lithium ion secondary battery) of the present invention in a negative electrode and/or a positive electrode, and therefore has strength such that the shape of the electrode can be maintained, and movement of lithium ions is not easily inhibited, and therefore, the reaction in the battery can be uniformized, and the lifetime of the battery can be prolonged. Therefore, the lithium ion secondary battery is expected to be popularized in the market in the future, and can be effectively used for electric vehicle applications commonly shared by automobiles, particularly AIEV (ARTIFICIAL INTELLIGENCE ELECTRIC VEHICLE, artificial intelligent electric vehicle) applications, which are required to have a longer life in the future.
5. Method for evaluating internal resistance and reaction non-uniformity of lithium ion secondary battery
In general, the reaction resistance of a battery is usually measured by ac impedance measurement. However, according to the ac impedance measurement, the resistance of the battery reaction is almost the same value regardless of the amount of the binder or the amount of the carbon nanotube. That is, the reaction resistance measured by ac impedance measurement is an index that does not include an influence due to the reaction unevenness, and the magnitude of the reaction unevenness cannot be evaluated. As described above, even if the binder amount is increased, the reaction resistance of the battery is almost the same value, and the non-uniformity of the reaction cannot be evaluated, so there is no incentive to further reduce the binder amount by adding a considerable amount of binder to the electrode active material (negative electrode active material, positive electrode active material, etc.) for the purpose of electrode strength.
On the other hand, under high load conditions, reaction unevenness easily occurs. Therefore, by measuring the internal resistance under high load conditions, the reaction inhibition by the binder and the inhibition of lithium ion movement can be evaluated.
However, under high load conditions during charging, lithium may be electrodeposited on the negative electrode, and it is difficult to accurately measure the resistance, so that it is necessary to measure the internal resistance under high load conditions during discharging.
Therefore, in the present invention, the charging rate SOC is defined as the following equation (1):
SOC (%) =residual capacity (Ah)/full charge capacity (Ah) ×100 (1)
After discharging from a state of 100% SOC to a state of 90% SOC at 25 ℃ and 2.5C or higher, the test was stopped for 10 minutes, and the voltage rise during the stop was measured. On the basis of this, 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).
As described above, since the reaction unevenness is easily evaluated by setting the conditions under which the reaction unevenness easily occurs, the discharge rate is set to 2.5C or more (preferably 2.7 to 10.0C) which is a high load condition, and is set to 0.3C or more (preferably 0.4 to 4.0C) which is a high load condition at 0 ℃.
The SOC at the start of discharge was set to 100% in order to sufficiently absorb lithium ions in the negative electrode and to make the state before measurement a state where reaction unevenness did not occur.
After discharge under this condition, the reaction is stopped, and the voltage rises. Since the voltage rise is saturated after 10 minutes and a constant voltage is maintained, the voltage rise during the rest period can be measured after 10 minutes, and the internal resistance can be 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 rest time varies depending on the temperature condition and the discharge rate condition, and the time until saturation varies, and may be set to 1 minute when the discharge rate is 0.5C or 10 minutes when the discharge rate is 3.0C, for example.
As a result, when the internal resistance is large, it can be evaluated that the reaction is large in non-uniformity and short in lifetime, and when the internal resistance is small, it can be evaluated that the reaction is small in non-uniformity and long in lifetime.
Specifically, when the electrode active material layer forming composition for a lithium ion secondary battery (the negative electrode active material layer forming composition for a lithium ion secondary battery or the positive electrode active material layer forming composition for a lithium ion secondary battery) of the present invention is used, the internal resistance calculated as described above under the condition of 3.0C at 25 ℃ is preferably 1.0 to 35.0 Ω·cm 2, more preferably 1.0 to 33.6 Ω·cm 2, and even more preferably 1.0 to 33.2 Ω·cm 2. In the case of using an amorphous carbon material as an electrode active material (in the case of the fourth embodiment), the internal resistance measured in the same manner is preferably 1.0 to 25.0 Ω·cm 2, more preferably 1.0 to 24.0 Ω·cm 2, and even more preferably 1.0 to 23.0 Ω·cm 2. In the case of using an electrode active material having an average particle diameter of 0.1 to 13.0 μm as the electrode active material (in 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 still more preferably 1.0 to 17.0 Ω·cm 2. The lower limit of the internal resistance is preferably 1.0Ω·cm 2 as described above, but 2.0Ω·cm 2、3.0Ω·cm2 or the like may be used as the lower limit.
In the case of using an electrode active material having an average particle diameter of 0.1 to 13.0 μm as the electrode active material (in the case of the second embodiment described above), the internal resistance calculated as described above under the condition of 0.5C at 0 ℃ is preferably 1.0 to 45.0 Ω·cm 2, more preferably 1.0 to 40.0 Ω·cm 2, and even more preferably 1.0 to 38.0 Ω·cm 2. That is, according to the present invention, the internal resistance can be sufficiently reduced and the reaction can be made uniform even under low temperature conditions in which the internal resistance tends to increase. The lower limit of the internal resistance is preferably 1.0Ω·cm 2 as described above, but 2.0Ω·cm 2、3.0Ω·cm2 or the like may be used as the lower limit.
In the charging process for setting the SOC to 100%, as described above, when charging is performed at 3.0C, which is a high load condition, there is a concern that electrodeposition of lithium in the negative electrode occurs, and therefore, it is preferable not to perform charging under the high load condition. The temperature condition is preferably 20 ℃ or higher, in which the internal resistance is reduced. Further, since the object is to make the state before measurement a state where reaction unevenness does not occur by sufficiently absorbing lithium ions in the negative electrode, it is preferable to charge the battery by constant current low voltage charge (CCCV charge) up to an upper limit voltage corresponding to 100% of SOC in the charge process for achieving 100% of SOC described above. The charging rate is preferably 0.01 to 1.0C, more preferably 0.01 to 0.75C. As described above, the lower limit of the charging rate is preferably 0.01C, but 0.02C, 0.03C, or the like may be used as the lower limit.
Examples
Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.
In the following examples, graphite particles and hard carbon used as the negative electrode active material were produced by the following formula:
(volume at full charge) - (volume at full discharge)/(volume at full discharge)) ×100
The calculated volume changes were all 0%.
First mode
Comparative examples 1 to 7
Graphite particles (spherical coated natural graphite; average particle diameter 17 μm) as a negative electrode active material, carboxymethylcellulose (CMC) and Styrene Butadiene Rubber (SBR) as other negative electrode constituent materials, and an appropriate amount of water were added to the compositions shown in tables 1 to 2, and kneaded to prepare a slurry. The slurry was coated on a copper foil (thickness 10 μm) with a doctor blade so that the weight per unit area of the dried anode active material layer became 10.3 to 10.9mg/cm 2, dried at 60 ℃, and then rolled so that the density of the anode active material layer became 1.3g/cm 3, and dried under reduced pressure at 120 ℃.
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 graphite particles, single-layer carbon nanotubes (bundled single-layer CNT aggregate; average outer diameter of 2nm per 1 single-layer CNT, average length > 5 μm, G/D: 80-150), CMC and SBR as other negative electrode constituent materials, and a proper amount of water were mixed and kneaded to prepare a slurry, with the compositions shown in tables 1-2. The slurry was applied to the copper foil with a doctor blade so that the weight per unit area of the dried negative electrode active material layer became 10.3 to 10.9mg/cm 2, dried at 60 ℃, and then rolled so that the density of the negative electrode active material layer became 1.3g/cm 3, and dried under reduced pressure at 120 ℃.
However, in comparative example 9, the amount of single-layer CNT relative to CMC as a dispersant was large, and dispersion failure of single-layer CNT occurred, and thus a negative electrode could not be produced.
Example 7
The graphite particles, the single-layer CNTs, and an appropriate amount of N-methylpyrrolidone (NMP) were added to the compositions shown in tables 1 and 2, and kneaded to prepare a slurry. The slurry was applied to the copper foil with a doctor blade so that the weight per unit area of the dried negative electrode active material layer became 10.3 to 10.9mg/cm 2, dried at 100 ℃, and then rolled so that the density of the negative electrode active material layer became 1.3g/cm 3, and dried under reduced pressure at 170 ℃.
The compositions of the respective examples and comparative examples are shown in tables 1 and 2. The mass ratio is shown in table 1, and the volume ratio is shown in table 2.
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.
To the total weight of the positive electrode composition, liNi 1/3Mn1/3Co1/3O2 (NMC 111; average particle diameter 10 μm) as a positive electrode active material, 93.0 wt%, polyvinylidene fluoride (PVdF) as another positive electrode constituent material, 4.0 wt% of acetylene black, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) were added, kneaded to prepare a slurry, and the slurry was applied onto an aluminum foil (thickness 15 μm) with a doctor blade so that the weight per unit area of the dried positive electrode active material layer became 20.6 to 21.8mg/cm 2, dried at 100 ℃, and then rolled so that the density of the positive electrode active material layer became 2.55g/cm 3, and dried under reduced pressure at 170 ℃.
As the electrolyte, an electrolyte composed of a solvent in which Ethylene Carbonate (EC) and ethylmethyl carbonate (MEC) were mixed at a volume ratio of 3:7 and 1mol/L lithium hexafluorophosphate (LiPF 6) as a salt was used. The electrolyte was impregnated into a polyethylene porous membrane as a separator.
A lithium ion secondary battery comprising the above-described negative electrode, positive electrode, electrolyte and separator was fabricated. The area of the lithium ion secondary battery to be fabricated facing the positive electrode and the negative electrode was set to 2.8cm 2.
Test example 1: initial charge-discharge characteristics
In the lithium ion secondary batteries of each of the examples and comparative examples, a charge/discharge test was performed for the purpose of confirming the initial charge/discharge capacity.
For charge and discharge, constant current low voltage charge (CCCV charge) was performed at a charge rate of 0.2C up to an upper limit voltage of 4.2V until a current value of 0.05C, and after 10 minutes of rest, discharge was performed at a discharge rate of 0.2C up to a lower limit voltage of 2.7V, and then 10 minutes of rest. The results of the initial charge/discharge characteristics are shown in table 3.
Even when the total amount of the active material and the single-layer carbon nanotubes is 1.2% by mass or less (1.63% by volume or less), the initial charge/discharge characteristics are substantially less affected than those of the conventional lithium ion secondary battery having a large total amount of the active material and the single-layer carbon nanotubes, and the initial charge/discharge characteristics are comparable to those of the case where the single-layer carbon nanotubes are not included.
Test example 2: measurement of reaction resistance
In the lithium ion secondary batteries of each example and comparative example, charge and discharge reactions with respect to the graphite anode active material were measured:
[ chemical 1]
For the purpose of measuring the resistance of (2), ac impedance measurement is performed as a general measurement method of the reaction resistance.
Regarding the reaction resistance, the minimum intercept of the Z' axis in the Nyquist Plot (Nyquist Plot) is taken as the body resistance, and a value obtained by subtracting the body resistance from the arc-shaped termination resistance value is analyzed as the reaction resistance. As measurement conditions, the amplitude was set to 10mV at 25 ℃ and the frequency was set from 500kHz to 0.1Hz with the SOC (State of Charge) of 100% based on the battery voltage. Fig. 2 schematically shows an analysis method in ac impedance measurement.
The results of the ac impedance measurement are shown in table 3 and fig. 3. As a result, the difference in reaction resistance due to the difference in the amounts of the negative electrode constituent materials other than the negative electrode active material was hardly confirmed. Therefore, the reaction resistance generally evaluated is an index that does not include an influence caused by the reaction unevenness, and it is understood that it is impossible to evaluate the reaction unevenness by measurement of the general electrode resistance.
Test example 3: internal resistance under high load conditions
In the lithium ion secondary batteries of examples and comparative examples, measurement of internal resistance was performed by a high-load rest method for the purpose of confirming the degree of reaction unevenness.
Specifically, for the lithium ion secondary batteries of each example and comparative example, a constant current low voltage charge (CCCV charge) was performed to an upper limit voltage of 4.2V corresponding to 100% of SOC, with an off current of 0.05C at 25 ℃. Next, after 10 minutes of rest, discharge (2 minutes) to SOC90% was performed under a discharge rate of 3.0C, followed by 10 minutes of rest. The electric power rate SOC is defined as the following formula (1):
SOC (%) =residual capacity (Ah)/full charge capacity (Ah) ×100 (1).
On this basis, the following formula is used:
Internal resistance= (rise of voltage during rest "Δv (10 min)"/current value at discharge "3C current value") ×opposing area of positive and negative electrodes "2.8cm 2".
The internal resistance was calculated. Fig. 4 schematically shows an analysis method in the high load rest method.
The results of the high load rest method are shown in table 3 and fig. 5.
As a result, it was confirmed that: the internal resistance under high load conditions is drastically reduced, that is, the reaction unevenness of the electrode is suppressed by making the total amount other than the active material and the single-layer carbon nanotube small, although the reaction resistance is the same level, regardless of the total amount other than the active material and the single-layer carbon nanotube.
TABLE 3
Test example 4: life characteristics
For the lithium ion secondary batteries of each example and comparative example, a charge-discharge cycle test was performed at 45 ℃. The conditions of charge and discharge are as follows: constant current low voltage charging (CCCV charging) was performed at a charging rate of 0.5C up to an upper limit voltage of 4.2V until a current value of 0.05C, and after 10 minutes of rest, discharge was performed at a discharging rate of 0.5C up to a lower limit voltage of 2.7V, and then 10 minutes of rest. The charge and discharge cycle test was performed using these charge and discharge steps as 1 cycle. Further, the charge and discharge for confirming the capacities of the lithium ion secondary batteries of each example and comparative example were performed every 25 cycles until 100 cycles, and every 100 cycles after 100 cycles. To confirm the charge and discharge of the capacity, constant current low voltage charge (CCCV charge) was performed at a charge rate of 0.2C up to an upper limit voltage of 4.2V until the current value was 0.05C, and after 10 minutes of rest, discharge was performed at a discharge rate of 0.2C up to a lower limit voltage of 2.7V, and then rest for 10 minutes.
The results of the charge-discharge cycle characteristics are shown in fig. 6.
As a result, in the case where the single-layer carbon nanotubes were not contained, when the total amount of the 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), secondary deterioration in which the rate of decrease in the capacity retention rate with respect to the number of cycles was increased was confirmed after 200 cycles, and the capacity retention rate after 300 cycles was 73%. It is presumed that since the proportion of the negative electrode constituent materials other than the negative electrode active material and the carbon nanotubes is large, reaction unevenness in the electrode occurs, and secondary degradation occurs. When the amount of the negative electrode constituent material other than the negative electrode active material and the carbon nanotube is reduced to 1.0 mass% in order to suppress the reaction unevenness in the electrode, the strength of the electrode is reduced, and the life characteristics are further deteriorated from the initial cycle confirmation to the rapid decrease in the capacity considered to be caused by the isolation of the active material due to the volume change of the active material layer of the electrode accompanying the charge and discharge. From this, it was found that by reducing the total amount of the negative electrode constituent materials other than the negative electrode active material and the carbon nanotubes, even if the negative electrode in which the internal resistance at high load shown in test example 3 was reduced, that is, the reaction was suppressed from being uneven, was used in a lithium ion secondary battery, good life characteristics could not be obtained unless the electrode strength was provided to such an extent that it could follow the volume change accompanying charge and discharge.
On the other hand, it was confirmed that: when a small amount (1.4 mass% or less) of single-layer carbon nanotubes is contained, even when the total amount of the negative electrode constituent materials other than the negative electrode active material and the carbon nanotubes is small (1.2 mass% or less) or none (0 mass%), the aforementioned rapid decrease in capacity considered to be caused by the isolation of the active material does not occur, and the electrode strength of such an extent that it can follow the volume change accompanying charge and discharge is provided. In addition, it is understood that secondary degradation is suppressed even after 200 cycles, and life characteristics are improved. Regarding the battery of example 7, the following formula was used
Capacity reduction = a× (number of cycles) β
The above a and β are determined by the least square method from the measured data, and the lifetime is estimated, and the result is shown in fig. 7. As described above, in comparative example 1, the capacity retention rate after 300 cycles was 73%, and thus the number of cycles at which the battery of example 7 reached 73% of the capacity retention rate was calculated. As a result, it was estimated that the cycle number at which the battery of example 7 reached 73% of the capacity maintenance rate was 1300 cycles, and the life of the battery was improved by about 4.3 times as compared with the 300 cycles of comparative example 1.
Fig. 8 shows the results of the internal resistance of test example 3 and the lifetime characteristics of test example 4.
Second mode
Comparative examples 10 and 12
Graphite particles as a negative electrode active material, carboxymethyl cellulose (CMC) and Styrene Butadiene (SBR) as other negative electrode constituent materials, and an appropriate amount of water were added to the compositions shown in tables 4 and 5, and kneaded to prepare a slurry. The slurry was coated on a copper foil (10 μm) with a doctor blade so that the weight per unit area of the dried anode active material layer became 10.3 to 10.9mg/cm 2, dried at 60 ℃, and then rolled so that the density of the anode active material layer became 1.3g/cm 3, and dried under reduced pressure at 120 ℃. As the graphite particles, coated natural graphite (average particle diameter 17.0 μm) or coated natural graphite (average particle diameter 5.0 μm) was used.
Examples 8 to 9 and comparative example 11
Graphite particles, single-layer carbon nanotubes (bundled single-layer CNT aggregate; average outer diameter of 2nm per 1 single-layer CNT, average length > 5 μm, G/D: 80-150) as a negative electrode active material, and an appropriate amount of N-methylpyrrolidone (NMP) were added and kneaded to prepare a slurry in the compositions shown in tables 4 and 5. The slurry was applied to the copper foil with a doctor blade so that the weight per unit area of the dried negative electrode active material layer became 10.3 to 10.9mg/cm 2, dried at 100 ℃, and then rolled so that the density of the negative electrode active material layer became 1.3g/cm 3, and dried under reduced pressure at 170 ℃. As the graphite particles, coated natural graphite (average particle diameter 17.0 μm), coated natural graphite (average particle diameter 12.0 μm), or coated natural graphite (average particle diameter 5.0 μm) was used.
Examples 10 to 12
Graphite particles as a negative electrode active material, the above-described single-layer CNT, carboxymethylcellulose (CMC) as another negative electrode constituent material, and an appropriate amount of water were added to the compositions shown in tables 4 and 5, and kneaded to prepare a slurry. The slurry was applied to the copper foil with a doctor blade so that the weight per unit area of the dried negative electrode active material layer became 10.3 to 10.9mg/cm 2, dried at 60 ℃, and then rolled so that the density of the negative electrode active material layer became 1.3g/cm 3, and dried under reduced pressure at 120 ℃. As graphite particles, coated natural graphite (average particle diameter 5.0 μm) was used.
The compositions of the respective examples and comparative examples are shown in tables 4 and 5. The mass ratio is shown in table 4, and the volume ratio is shown in table 5.
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.
To the total mass of the positive electrode composition, 92.0 mass% of LiNi 0.8Co0.15Al0.05O2 (NCA; average particle diameter 6 μm) as a positive electrode active material, 4.0 mass% of polyvinylidene fluoride (PVdF) as another positive electrode constituent material, 4.0 mass% of acetylene black, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) were added, kneaded to prepare a slurry, and the slurry was applied onto an aluminum foil (thickness 17 μm) with a doctor blade so that the mass per unit area of the dried positive electrode active material layer became 20.05 to 21.29mg/cm 2, dried at 100 ℃, and then rolled so that the density of the positive electrode active material layer became 3.0g/cm 3, and dried under reduced pressure at 170 ℃.
As the electrolyte, an electrolyte composed of a solvent in which Ethylene Carbonate (EC) and ethylmethyl carbonate (MEC) were mixed at a volume ratio of 3:7 and 1mol/L lithium hexafluorophosphate (LiPF 6) as a salt was used. The electrolyte was impregnated into a polyethylene porous membrane as a separator.
A lithium ion secondary battery comprising the above-described negative electrode, positive electrode, electrolyte and separator was fabricated. The area of the positive electrode and the negative electrode of the lithium ion secondary battery fabricated was 2.8cm 2.
Test example 5: initial charge-discharge characteristics
In the lithium ion secondary batteries of each of the examples and comparative examples, a charge/discharge test was performed for the purpose of confirming the initial charge/discharge capacity.
For charge and discharge, constant current and constant voltage charge (CCCV charge) was performed at a charge rate of 0.1C up to an upper limit voltage of 4.0V until a current value of 0.05C, and after 10 minutes of rest, discharge was performed at a discharge rate of 0.1C up to a lower limit voltage of 2.7V, and then 10 minutes of rest. The results of the initial charge/discharge characteristics are shown in table 6.
Even when the particle size of the negative electrode active material is reduced or the total amount of the negative electrode active material and the single-layer carbon nanotubes is as small as 2.0% by mass or less (4.52% by volume or less), the initial charge/discharge characteristics are hardly affected as compared with the case where the negative electrode active material is large or the total amount of the negative electrode active material and the single-layer carbon nanotubes is large, and the initial charge/discharge characteristics are equivalent.
Test example 6: measurement of reaction resistance
In the lithium ion secondary batteries of each example and comparative example, charge and discharge reactions with respect to the graphite anode active material were measured:
[ chemical 2]
For the purpose of measuring the resistance of (2), ac impedance measurement is performed as a general measurement method of the reaction resistance.
Regarding the reaction resistance, the minimum intercept of the Z' axis in the Nyquist Plot (Nyquist Plot) is taken as the body resistance, and a value obtained by subtracting the body resistance from the arc-shaped termination resistance value is analyzed as the reaction resistance. As measurement conditions, the amplitude was set to 10mV at 25 ℃ with the battery voltage as a reference and the SOC (State of Charge) at 100%, and the frequency was set from 500kHz to 0.1 Hz. Fig. 2 schematically shows an analysis method in ac impedance measurement.
The results of the ac impedance measurement are shown in table 6 and fig. 9. As a result, some differences in the reaction resistance due to the difference in the particle diameter of the negative electrode active material and the amount of the negative electrode constituent material other than the negative electrode active material were observed, and a tendency was observed that the reaction resistance was lowered when the particle diameter of the negative electrode active material was reduced and the amount of the negative electrode constituent material other than the negative electrode active material was lowered. However, the reaction resistance generally evaluated is an index that does not include an influence caused by the reaction unevenness, and it is conceivable that it is difficult to evaluate the reaction unevenness by measuring the general electrode resistance.
Test example 7: internal resistance under high load conditions
In the lithium ion secondary batteries of examples and comparative examples, measurement of internal resistance by a high load rest method at room temperature (25 ℃) and measurement of internal resistance by a high load rest method at low temperature (0 ℃) were carried out for the purpose of confirming the degree of reaction unevenness.
Specifically, for the lithium ion secondary batteries of examples and comparative examples, the off-current was set to 0.05C at room temperature (25 ℃) under the condition of a charge rate of 0.5C, and the constant current constant voltage charge (CCCV charge) was set to 4.0V, which corresponds to an upper limit voltage of 100% of SOC, with respect to measurement of internal resistance by the high load rest method at room temperature (25 ℃). Then, after 10 minutes of rest, the discharge was performed to SOC90% (2 minutes) at a discharge rate of 3.0C, and then 10 minutes of rest was performed. The charge rate SOC is defined as the following equation (1):
SOC (%) =residual capacity (Ah)/full charge capacity (Ah) ×100 (1).
On this basis, the following formula is used:
Internal resistance= (rise of voltage during rest "Δv (10 min)"/current value at discharge "3.0C current value") ×opposing area of positive and negative electrodes "2.8cm 2".
The internal resistance was calculated. Fig. 4 schematically shows an analysis method in the high load rest method.
In addition, regarding measurement of internal resistance by a high load rest method at a low temperature (0 ℃), specifically, for the lithium ion secondary batteries of each example and comparative example, the off-current was set to 0.05C under the condition of a charge rate of 0.5C at room temperature (25 ℃), and the constant current constant voltage charge (CCCV charge) was set to 4.0V, which corresponds to an upper limit voltage of 100% of SOC. Then, the temperature was changed to 0 ℃, and after 180 minutes of rest, the discharge was performed at a discharge rate of 0.5C (12 minutes) to SOC90%, and then 1 minute of rest was performed. The charge rate SOC is defined as the following equation (1):
SOC (%) =residual capacity (Ah)/full charge capacity (Ah) ×100 (1).
On this basis, the following formula is used:
Internal resistance= (rise of voltage during rest "Δv (1 min)"/current value at discharge "0.5C current value") ×opposing area of positive and negative electrodes "2.8cm 2".
The internal resistance was calculated.
The results of these high load rest methods are shown in table 6 and fig. 10 to 11.
As a result, it was confirmed that, although only some differences in the reaction resistance due to the difference in the particle diameter of the anode active material and the amount of the anode constituent material other than the anode active material were observed, by making the anode active material small in particle diameter and reducing the amount of the anode constituent material other than the anode active material, the internal resistance under high load conditions was reduced, that is, the reaction unevenness of the electrode was suppressed. It is understood that this tendency is particularly remarkable at low temperatures where the internal resistance tends to become large, and the effect of the present invention is remarkably observed under severe conditions where the internal resistance tends to become large.
TABLE 6
Test example 8: limit load characteristics
As shown in table 5, the lithium ion secondary batteries of example 9 and comparative examples 10 to 12 were subjected to charge/discharge cycle tests with increasing overvoltage load from condition 1 to condition 12. The conditions were charged and discharged in 10 cycles and 120 cycles in total. In each charging cycle, constant current charging (CC charging) was performed up to an upper limit voltage of 4.0V, and after 10 minutes of rest, discharging was performed up to a lower limit voltage of 2.7V, and then 10 minutes of rest.
Then, the following formula is used:
current value (mA) x charge-discharge rate (C) x direct current resistance (Ω) in case of overvoltage load (mV) =1c
And (5) performing calculation. In addition, an overvoltage load with a capacity retention rate of less than 99.0% for the first time was evaluated as a limit overvoltage load in 10 cycles of charge and discharge under each condition.
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 charge and discharge cycles 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 at the time of charge and discharge cycles are shown in fig. 12, and the results of the capacity maintenance rate at 10 cycles for the overvoltage load are shown in fig. 13.
TABLE 7
TABLE 8
TABLE 9
From the above results, it is understood that, even in the case of making the anode active material small in particle size, or in the case of adding a small amount of carbon nanotubes to reduce the amount of the anode constituent material other than the anode active material, the overvoltage load alone cannot be sufficiently reduced at any temperature, and the charge-discharge cycle characteristics and the rate characteristics are also insufficient. In contrast, in the present invention, in which the particle size of the negative electrode active material is reduced, and the amount of the negative electrode constituent material other than the negative electrode active material is reduced by adding a small amount of carbon nanotubes, it is understood that the overvoltage load can be sufficiently reduced at any temperature, and the charge-discharge cycle characteristics and the rate characteristics can be improved. It is to be understood that in example 9, even if the overvoltage load is increased to the condition 12, the capacity retention rate of 10 cycles is not lower than 99%, and thus the value of the limit overvoltage load in table 10 is 195mV or more than the overvoltage load of the condition 12.
Test example 9: life characteristics
The lithium ion secondary batteries of example 9, comparative example 10 and comparative example 12 were subjected to a charge-discharge cycle test at 25 ℃. The conditions of charge and discharge are as follows: constant current constant voltage charging (CCCV charging) was performed at a charging rate of 0.5C up to an upper limit voltage of 4.0V until a current value of 0.05C, and after 10 minutes of rest, discharge was performed at a discharging rate of 0.5C up to a lower limit voltage of 2.7V, and then 10 minutes of rest. The charge and discharge cycle test was performed using 1 cycle of these charge and discharge steps.
The results of the charge-discharge cycle characteristics are shown in table 10 and fig. 13.
TABLE 10
As a result, it is understood that in the present invention, in which the particle size of the anode active material is reduced and the amount of the anode constituent material other than the anode active material is reduced by adding a small amount of carbon nanotubes, the overvoltage load can be sufficiently reduced, and the charge-discharge cycle characteristics and the rate characteristics can be improved.
Third mode
Comparative example 13
93.0 Mass% of LiNi 1/3Mn1/3Co1/3O2 (NMC 111; average particle diameter 10 μm), 4.0 mass% of Acetylene Black (AB) as a conductive auxiliary agent 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 as a positive electrode active material, and kneaded to prepare a slurry. The slurry was coated on an aluminum foil (thickness: 15 μm) with a doctor blade so that the weight per unit area of the dried positive electrode active material layer became 21.2mg/cm 2, dried at 100℃and then rolled so that the density of the positive electrode active material layer became 2.55g/cm 3, and dried under reduced pressure at 170℃to obtain a positive electrode.
Example 13
LiNi 1/3Mn1/3Co1/3O2 (NMC 111; average particle diameter 10 μm) as a positive electrode active material, 96.0 mass% of single-layer carbon nanotubes (bundled single-layer CNT aggregate; average outer diameter 2nm per 1 single-layer CNT, average length >5 μm, G/D:80 to 150), 0.5 mass% of Acetylene Black (AB) as a conductive additive other than carbon nanotubes, 3.5 mass% of N-methyl-2-pyrrolidone (NMP) in an appropriate amount, and kneading them to prepare a slurry. The slurry was coated on an aluminum foil (thickness: 15 μm) with a doctor blade so that the weight per unit area of the dried positive electrode active material layer became 20.6mg/cm 2, dried at 100 ℃, and then rolled so that the density of the positive electrode active material layer became 2.55g/cm 3, and dried under reduced pressure at 170 ℃.
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.
97.5 Mass% of graphite particles (spherical coated natural graphite; average particle diameter 17 μm) as a negative electrode active material, 1.0 mass% of carboxymethyl cellulose (CMC) as another negative electrode constituent material, 1.5 mass% of Styrene Butadiene Rubber (SBR), and an appropriate amount of water were added to the total weight of the negative electrode composition, and kneaded to prepare a slurry, which was coated on a copper foil (thickness 10 μm) with a doctor blade so that the weight per unit area of the dried negative electrode active material layer became 10.6mg/cm 2, dried at 60 ℃, and then rolled so that the density of the negative electrode active material layer became 1.3g/cm 3, and dried under reduced pressure at 120 ℃.
As the electrolyte, an electrolyte composed of a solvent in which Ethylene Carbonate (EC) and ethylmethyl carbonate (MEC) were mixed at a volume ratio of 3:7 and 1mol/L lithium hexafluorophosphate (LiPF 6) as a salt was used. The electrolyte was impregnated into a polyethylene porous membrane as a separator.
A lithium ion secondary battery comprising the above positive electrode, negative electrode, electrolyte and separator was fabricated. The area of the positive electrode and the negative electrode of the lithium ion secondary battery fabricated was 2.8cm 2.
Test example 10: initial charge-discharge characteristics
In the lithium ion secondary batteries of each of example 13 and comparative example 13 produced, a charge-discharge test was performed for the purpose of confirming the initial charge-discharge capacity.
For charge and discharge, constant current and constant voltage charge (CCCV charge) was performed at a charge rate of 0.2C up to an upper limit voltage of 4.2V until a current value of 0.05C, and after 10 minutes of rest, discharge was performed at a discharge rate of 0.2C up to a lower limit voltage of 2.7V, and then 10 minutes of rest. As a result, in example 13, the charge capacity was 9.32mAh, the discharge capacity was 7.93mAh, the coulomb efficiency was 85.09%, and in comparative example 13, the charge capacity was 9.53mAh, the discharge capacity was 8.24mAh, and the coulomb efficiency was 86.46%.
Even when the positive electrode constituent material other than the positive electrode active material, the carbon nanotube, and the conductive auxiliary agent other than the carbon nanotube is not contained, the initial characteristics are hardly affected, and the initial charge-discharge characteristics are substantially the same as those of the case where the positive electrode constituent material is contained.
Test example 11: internal resistance under high load conditions
In the lithium ion secondary batteries of example 13 and comparative example 13, the internal resistance was measured by the high-load rest method in order to confirm the degree of reaction unevenness.
Specifically, for the lithium ion secondary batteries of example 13 and comparative example 13, the off-current was set to 0.05C at 25 ℃ under the condition of a charge rate of 0.5C, and the constant current constant voltage charge (CCCV charge) was set to 4.2V, which corresponds to an upper limit voltage of 100% of SOC. Next, after 10 minutes of rest, discharge (2 minutes) to SOC90% was performed under a discharge rate of 3.0C, followed by 10 minutes of rest. The charge rate SOC is defined as the following equation (1):
SOC (%) =residual capacity (Ah)/full charge capacity (Ah) ×100 (1).
On this basis, the following formula is used:
Internal resistance= (rise of voltage during rest "Δv (10 min)"/current value at discharge "3C current value") ×opposing area of positive and negative electrodes "2.8cm 2".
The internal resistance was calculated. Fig. 4 schematically shows an analysis method in the high load rest method.
As a result of the high load resting method, the internal resistance of example 13 was 25.90. Omega. Cm 2, and the internal resistance of comparative example 13 was 36.46. Omega. Cm 2.
As a result, it was confirmed that: by providing a constitution in which a small amount of carbon nanotubes is added and no positive electrode constituent material other than the positive electrode active material, carbon nanotubes, and conductive auxiliary agent other than carbon nanotubes are contained, internal resistance under high load conditions is significantly reduced, that is, reaction unevenness of the electrode is suppressed.
Test example 12: life characteristics
The lithium ion secondary batteries of example 13 and comparative example 13 were subjected to a charge-discharge cycle test at 45 ℃. The conditions of charge and discharge are as follows: constant current constant voltage charging (CCCV charging) was performed at a charging rate of 0.5C up to an upper limit voltage of 4.2V until a current value of 0.05C, and after 10 minutes of rest, discharge was performed at a discharging rate of 0.5C up to a lower limit voltage of 2.7V, and then 10 minutes of rest. The charge and discharge cycle test of 400 cycles was performed using 1 cycle of these charge and discharge steps. In 50 cycles, 100 cycles, 200 cycles and 300 cycles, charge and discharge were performed to confirm the capacities of the lithium ion secondary batteries of example 13 and comparative example 13. For confirmation of charge and discharge of capacity, constant current low voltage charge (CCCV charge) was performed at a charge rate of 0.2C up to a current value of 0.05C up to an upper limit voltage of 4.2V, and after 10 minutes of rest, discharge was performed at a discharge rate of 0.2C up to a lower limit voltage of 2.7V, and then rest for 10 minutes.
The results of the charge-discharge cycle characteristics are shown in fig. 15, and 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 comparative example 13, after 200 cycles, it was confirmed that the capacity retention rate was degraded secondarily to increase the rate of decrease with respect to the number of cycles. It is assumed that the secondary degradation is caused by the non-uniformity of the reaction accompanying the charge-discharge cycle. On the other hand, it was confirmed that in example 13, which was configured to add a small amount of carbon nanotubes and to not contain a positive electrode constituent material other than the positive electrode active material, the carbon nanotubes, and the conductive auxiliary agent other than the carbon nanotubes, secondary degradation was suppressed, and charge-discharge cycle characteristics were improved. It is to be noted that, in comparative example 13, the capacity rapidly increased upon charge and discharge for confirmation of the capacity at 50 cycles, 100 cycles, 200 cycles and 300 cycles, and it is also understood that in comparative example 13, the reaction unevenness was remarkable upon charge and discharge cycles, and the reaction unevenness was alleviated and the capacity was recovered by charge and discharge for confirmation of the capacity. On the other hand, in example 13, it is also understood that the capacity does not rapidly increase when the charge/discharge of the capacity is confirmed, and thus the reaction unevenness is suppressed.
Fourth mode
Comparative example 14
90.0 Mass% of hard carbon (hard graphitized carbon material; particle shape: spherical; average particle diameter 5 μm), 5.0 mass% of Acetylene Black (AB) as a conductive auxiliary agent other than carbon nanotubes, 5.0 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 onto a copper foil (thickness: 10 μm) with a doctor blade so that the weight per unit area of the dried anode active material layer became 10.6mg/cm 2, dried at 100℃and then rolled so that the density of the anode active material layer became 1.0g/cm 3, and dried under reduced pressure at 170℃to obtain an anode.
Example 14
A slurry was prepared by kneading 90.0% by mass of hard carbon (hardly graphitizable carbon material; particle shape: spherical shape: average particle diameter 5 μm), 0.1% by mass of single-walled carbon nanotubes (bundled single-walled CNT aggregate; average outer diameter 2nm per 1 single-walled CNT, average length > 5 μm, G/D:80 to 150), 4.9% by mass of Acetylene Black (AB) as a conductive additive 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) as a negative electrode active material. The slurry was applied to the copper foil with a doctor blade so that the weight per unit area of the dried anode active material layer became 10.6mg/cm 2, dried at 100 ℃, and then rolled so that the density of the anode active material layer became 1.0g/cm 3, and dried under reduced pressure at 170 ℃.
The compositions of the examples and comparative examples are shown in Table 12.
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.
With respect to the total weight of the positive electrode composition,
The positive electrode was obtained by adding LiNi 0.8Co0.15Al0.05O2 (NCA; average particle diameter 6 μm) as a positive electrode active material 92.0 mass%, polyvinylidene fluoride (PVdF) as another positive electrode constituent material 4.0 mass%, acetylene Black (AB) 4.0 mass%, and an appropriate amount of N-methyl-2-pyrrolidone (NMP), kneading to prepare a slurry, coating the slurry on an aluminum foil (thickness 17 μm) with a doctor blade so that the mass per unit area of the dried positive electrode active material layer became 16.2mg/cm 2, drying at 100 ℃, and rolling so that the density of the positive electrode active material layer became 3.0g/cm 3, and drying under reduced pressure at 170 ℃.
As the electrolyte, a solvent in which Ethylene Carbonate (EC) and ethylmethyl carbonate (MEC) were mixed at a volume ratio of 3:7 and an electrolyte composed of 1mol/L lithium hexafluorophosphate (LiPF 6) as a salt were used. The electrolyte was impregnated into a polyethylene porous membrane as a separator.
A lithium ion secondary battery comprising the above-described negative electrode, positive electrode, electrolyte and separator was fabricated. The area of the positive electrode and the negative electrode of the lithium ion secondary battery fabricated was 2.8cm 2.
Test example 13: initial charge-discharge characteristics
In the lithium ion secondary batteries of example 14 and comparative example 14, charge and discharge tests were performed in order to confirm the initial charge and discharge capacities.
For charge and discharge, constant current and constant voltage charge (CCCV charge) was performed at a charge rate of 0.1C up to an upper limit voltage of 4.05V until a current value of 0.05C, and after 10 minutes of rest, discharge was performed at a discharge rate of 0.1C up to a lower limit voltage of 2.0V, and then 10 minutes of rest. As a result, in example 14, the charge capacity was 7.68mAh, the discharge capacity was 5.14mAh, and the coulombic efficiency was 66.9%, and in comparative example 14, the charge capacity was 7.76mAh, the discharge capacity was 4.90mAh, and the coulombic efficiency was 63.1%.
It was confirmed that the initial coulomb efficiency was improved and the discharge capacity was increased by including a small amount of carbon nanotubes to form a uniform electron conduction path.
Test example 14: internal resistance under high load conditions
In the lithium ion secondary batteries of example 14 and comparative example 14, the internal resistance was measured by the high-load rest method in order to confirm the degree of reaction unevenness.
Specifically, for the lithium ion secondary batteries of example 14 and comparative example 14, the off-current was set to 0.05C at 25 ℃ under the condition of a charge rate of 0.5C, and the constant current constant voltage charge (CCCV charge) was set to 4.05V, which corresponds to an upper limit voltage of 100% of SOC. Next, after 10 minutes of rest, discharge (2 minutes) to SOC90% was performed under a discharge rate of 3.0C, followed by 10 minutes of rest. The charge rate SOC is defined as the following equation (1):
SOC (%) =residual capacity (Ah)/full charge capacity (Ah) ×100 (1).
On this basis, the following formula is used:
Internal resistance= (rise of voltage during rest "Δv (10 min)"/current value at discharge "3C current value") ×opposing area of positive and negative electrodes "2.8cm 2".
The internal resistance was calculated. Fig. 4 schematically shows an analysis method in the high load rest method.
As a result of the high load rest method, the internal resistance of example 14 was 21.67. Omega. Cm 2, and the internal resistance of comparative example 14 was 28.25. Omega. Cm 2.
As a result, it was confirmed that by adding a small amount of carbon nanotubes while using hard carbon, the internal resistance under high load conditions was significantly reduced, that is, the reaction unevenness of the electrode was suppressed.
Test example 15: life characteristics
For the lithium ion secondary batteries of example 14 and comparative example 14, a charge-discharge cycle test was performed at 25 ℃. The conditions of charge and discharge are as follows: constant current constant voltage charging (CCCV charging) was performed at a charging rate of 0.5C up to an upper limit voltage of 4.05V until a current value of 0.05C, and after 10 minutes of rest, discharge was performed at a discharging rate of 0.5C up to a lower limit voltage of 2.0V, and then 10 minutes of rest. The charge and discharge cycle test was performed using 1 cycle of these charge and discharge steps.
The results of the charge-discharge cycle characteristics are shown in fig. 16, and 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 adding a small amount of carbon nanotubes together with the use of hard carbon.
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 mass%,
The content of the carbon nanotubes is 0.01 to 1.4 mass%,
The content of the electrode constituent material other than the electrode active material and the carbon nanotubes is 0 to 10.0 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 to 99.9 mass%,
The content of the electrode constituent material other than the electrode active material and the carbon nanotube 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.
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 to 99.9 mass%,
The content of the electrode constituent material other than the electrode active material and the carbon nanotubes is 0 to 1.2 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 claim 1 to 4, wherein,
The content of the carbon nanotubes is 0.01 to 0.8 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% by volume,
The volume ratio of the electrode active material is 75.06 to 99.97% by volume,
The volume ratio of the carbon nano tube is 0.02-4.55%,
The volume ratio of the electrode constituent materials other than the electrode active material and the carbon nanotubes is 0 to 21.56% by volume.
7. The electrode active material layer-forming composition for a lithium ion secondary battery according to claim 6, wherein,
When the total volume of the composition is set to 100% by volume,
The volume ratio of the electrode active material is 93.38 to 99.98% by volume,
The volume ratio of the carbon nano tube is 0.02-2.18 volume percent,
The volume ratio of the electrode constituent materials other than the anode active material and the carbon nanotubes is 0 to 4.52% by volume, and
The composition is a composition for forming a negative electrode active material layer for a lithium ion secondary battery.
8. The electrode active material layer-forming composition for a lithium ion secondary battery according to claim 6, wherein,
The volume ratio of the electrode active material is 96.19 to 99.98% by volume,
The volume ratio of the carbon nano tube is 0.02-2.18 volume percent,
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.
9. The electrode active material layer-forming composition 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 claim 1 to 9, wherein,
The average particle diameter of the electrode active material is 0.1-13.0 mu m.
11. The composition for forming an electrode active material layer for a lithium ion secondary battery according to claim 10, wherein,
The electrode active material has an average particle diameter of 0.1 to 13.0 [ mu ] m and a content of 96.6 to 99.9 mass%,
The content of the carbon nanotubes is 0.01 to 1.4 mass%,
The content of the electrode constituent material other than the electrode active material and the carbon nanotube 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 electrode active material has an average particle diameter of 0.1 to 13.0 [ mu ] m and a volume ratio of 93.38 to 99.98% by volume,
The volume ratio of the carbon nano tube is 0.02-2.18 volume percent,
The volume ratio of the electrode constituent materials other than the electrode active material and the carbon nanotubes is 0 to 4.52% by 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 to 99.9 mass%,
The content of the conductive auxiliary agent other than the carbon nanotubes is 0 to 10.0 mass%,
The composition is free of electrode constituent materials other than the electrode active material, the carbon nanotubes and a conductive assistant 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 nano tube is 0.03-4.55% by volume,
The content of the conductive auxiliary agent other than the carbon nanotubes is 0 to 21.56% by volume,
The composition is free of electrode constituent materials other than the electrode active material, the carbon nanotubes and a conductive assistant 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 claim 1 to 14, wherein,
The electrode active material is a material capable of absorbing and releasing lithium ions.
16. The composition for forming an electrode active material layer for a lithium ion secondary battery according to any one of claim 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 claim 1 to 16, wherein,
The composition is used for reducing reaction non-uniformity 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 claim 1 to 17, wherein,
The lithium ion secondary battery using the composition is used in an electric vehicle for vehicle 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 any one of claims 1 to 18.
20. The electrode active material layer for a lithium ion secondary battery according to claim 19, wherein,
The lithium ion secondary battery using the electrode active material layer for a lithium ion secondary battery is used in an electric vehicle for vehicle 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 a lithium ion secondary battery according to claim 21, wherein,
The lithium ion secondary battery using the electrode for a lithium ion secondary battery is used in an electric vehicle for vehicle sharing.
23. A lithium ion secondary battery comprising the electrode for a lithium ion secondary battery 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 equation (1):
Soc=residual capacity/full charge capacity×100 (1)
In the formula (1), the unit of SOC is Ah, the unit of the residual capacity and the unit of the full charge capacity are,
After discharging from the state of 100% SOC to the state of 90% SOC at 25℃and 3.0C, the test was stopped for 10 minutes, the voltage rise during the stop was measured,
The internal resistance calculated by the following formula (2) is 1.0 to 35.0 Ω·cm 2:
internal resistance= (current value at voltage rise/discharge during rest) ×opposing area of positive and negative electrodes (2)
In the formula (2), the unit of the rise of the voltage during the rest is V, the unit of the current value during the 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 equation (1):
Soc=residual capacity/full charge capacity×100 (1)
In the formula (1), the unit of SOC is Ah, the unit of the residual capacity and the unit of the full charge capacity are,
After discharging from the state of 100% SOC to the state of 90% SOC at 0℃and 0.5C, the test was stopped for 1 minute, and the voltage rise during the stop was measured,
The internal resistance calculated by the following formula (2) is 1.0 to 45.0 Ω·cm 2:
internal resistance= (current value at voltage rise/discharge during rest) ×opposing area of positive and negative electrodes (2)
In the formula (2), the unit of the rise of the voltage during the rest is V, the unit of the current value during the 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 any one of claims 23 to 25, which is used in an electric vehicle for vehicle sharing.
27. A method for evaluating reaction non-uniformity in a lithium ion secondary battery is characterized by comprising the following steps:
The charge rate SOC is defined as the following equation (1):
Soc=residual capacity/full charge capacity×100 (1)
In the formula (1), the unit of SOC is Ah, the unit of the residual capacity and the unit of the full charge capacity are,
After discharging from a state of 100% of SOC to a state of 90% of SOC at 25 ℃ and 2.5C or higher, the test was stopped for 10 minutes, and the rise of the voltage during the stop was measured,
The internal resistance was calculated by the following equation (2):
internal resistance= (current value at voltage rise/discharge during rest) ×opposing area of positive and negative electrodes (2)
In the formula (2), the unit of the rise of the voltage during the rest is V, the unit of the current value during the discharge is a, and the unit of the facing area of the positive and negative electrodes is cm 2.
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| JP2022-044154 | 2022-03-18 | ||
| JP2022044156A JP2023137785A (en) | 2022-03-18 | 2022-03-18 | Composition for forming negative electrode active material layer for lithium ion secondary battery |
| JP2022-044152 | 2022-03-18 | ||
| PCT/JP2022/043005 WO2023090443A1 (en) | 2021-11-22 | 2022-11-21 | Composition for forming electrode active material layer for lithium ion secondary batteries |
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