WO2023134486A1

WO2023134486A1 - Negative electrode plate and manufacturing method therefor, secondary battery, battery module, battery pack, and electric device

Info

Publication number: WO2023134486A1
Application number: PCT/CN2022/144329
Authority: WO
Inventors: 陆雷; 王正; 李世松
Original assignee: 宁德时代新能源科技股份有限公司
Priority date: 2022-01-13
Filing date: 2022-12-30
Publication date: 2023-07-20
Also published as: CN116487585A

Abstract

The present application provides a negative electrode plate and a manufacturing method therefor, a secondary battery, a battery module, a battery pack, and an electric device. The negative electrode plate comprises a negative electrode current collector, and a negative electrode film layer provided on at least one surface of the negative electrode current collector; the negative electrode film layer comprises a negative electrode active material, an adipic acid polybutadiene ester softening agent and an optional additive; the single-sided coating weight of the negative electrode plate is greater than or equal to 180 mg/1540.25 mm ².

Description

Negative pole piece and preparation method thereof, secondary battery, battery module, battery pack and electrical device

Cross References to Related Applications

This application claims the priority of the Chinese patent application 202210036632.8 entitled "Negative electrode sheet and its preparation method, secondary battery, battery module, battery pack and electrical device" filed on January 13, 2022. The entire contents are incorporated herein by reference.

technical field

The present application relates to the technical field of secondary batteries, in particular to a negative pole piece and a preparation method thereof, a secondary battery, a battery module, a battery pack and an electrical device.

Background technique

In recent years, as the application range of secondary ion batteries has become more and more extensive, secondary sub-batteries are widely used in energy storage power systems such as hydraulic, thermal, wind and solar power plants, as well as electric tools, electric bicycles, electric motorcycles, electric Automotive, military equipment, aerospace and other fields. Due to the great development of secondary ion batteries, higher requirements have been put forward for their energy density, cycle performance and safety performance.

Among them, energy density is considered to be the biggest bottleneck restricting the development of current secondary batteries. Based on this, a lot of research has been carried out on how to improve the energy density of secondary batteries. Among them, under the premise of not affecting the performance of the secondary battery, increasing the thickness of the pole piece is currently an important direction for improving the energy density of the secondary battery.

However, as the thickness of the pole piece increases, its processing difficulty also increases, and the ultra-thick coated pole piece is prone to film cracking during the drying process. In addition, the thickness of the film layer is too large, which will also lead to the problems of difficult electrolyte wetting and poor kinetics. Therefore, the existing pole pieces still need to be improved.

Contents of the invention

The present application is made in view of the above problems, and its purpose is to provide a negative electrode sheet with ultra-thick coating and good electrolyte wetting performance, so that the secondary battery can have high energy density and good electrochemical performance.

In order to achieve the above purpose, the present application provides a negative pole piece and a preparation method thereof, a secondary battery, a battery module, a battery pack and an electrical device.

The first aspect of the present application provides a negative electrode sheet, including a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, the negative electrode film layer includes a negative electrode active material, adipate polybutadiene ester softener and optional additives, the coating weight of one side of the negative pole sheet is ≥180mg/1540.25mm ² .

Thus, the present application includes adipate polybutadiene ester softener in the negative electrode film layer, in the case of high coating weight, it is not easy to crack the film layer, and can have a higher electrolysis rate. Liquid wetting velocity and interface properties. The negative electrode sheet of the present application is applied to a secondary battery, which can make the secondary battery have high energy density and good electrochemical performance.

In any embodiment, the adipate polybutadiene ester softener is selected from the compounds shown in formula 1,

In Formula 1, n is an integer ranging from 10 to 150, M and M' are each independently selected from H or Li, and optionally, both M and M' are Li.

The adipate polybutadiene ester softener is selected from the compounds shown in formula 1, which can make the negative electrode sheet have better electrolyte affinity, thereby further improving the electrolyte wetting performance and Liquid retention performance, thereby improving the rate performance of the secondary battery. In addition, the polybutadiene adipate softener shown in Formula 1 can improve the lithium ion transport capacity of the negative electrode sheet, thereby further improving the cycle performance of the secondary battery. Furthermore, compared with the case where H exists in the M element and the M' element, when both the M element and the M' element are Li, the migration kinetics of lithium ions in the negative electrode sheet can be further improved, thereby reducing the secondary battery's Internal resistance, improving the rate performance of the secondary battery.

In any embodiment, the weight average molecular weight of the adipate polybutadiene ester softener is 1600-18000, optionally 4800-18000. Controlling the weight-average molecular weight of the polybutadiene adipate softener in the negative electrode film layer within the above-mentioned appropriate range can effectively avoid cracking of the negative electrode film layer and ensure excellent cycle performance of the secondary battery.

In any embodiment, based on the total mass of the negative film layer, the mass proportion of the adipate polybutadiene ester softener is 0.05wt% to 0.6wt%, optionally 0.1wt% to 0.5wt%, More preferably, it is 0.2wt%-0.5wt%. When the mass ratio of the adipate polybutadiene ester softener in the negative electrode film layer is within the above-mentioned appropriate range, it can effectively prevent the negative electrode film layer from cracking and at the same time make the negative electrode sheet have a higher energy density , Good electrolyte wettability and liquid retention, so that the secondary battery has good cycle performance and rate performance.

In any embodiment, optional additives include conductive agents, dispersants and binders, based on the total mass of the negative electrode film layer, the mass proportion of the conductive agent is 0.3wt% to 3wt%, and the mass proportion of the negative electrode active material is 90wt% to 98wt%, the mass proportion of adipate polybutadiene ester softener is 0.05wt% to 0.6wt%, the mass proportion of the dispersant is 0.5wt% to 3wt%, and the mass proportion of the binder is The mass proportion is 0.5wt%-5wt%. The negative electrode film layer contains the above components, and the proportion of each component is within the above-mentioned suitable range, not only can the negative electrode sheet have good electrical conductivity, but also can make the negative electrode film layer have a uniform thickness distribution, and make the negative electrode The film layer is firmly adhered to the surface of the negative electrode current collector. The negative electrode film layer has the above-mentioned components and component ratios, which can ensure that the secondary battery has excellent electrochemical performance and long cycle life.

In any embodiment, the thickness of the single-sided negative electrode film layer is 65 μm˜125 μm. The thickness of the single-sided negative electrode film layer is within the above range, which can make the secondary battery have high volumetric energy density, good cycle performance, and long cycle life.

In any embodiment, the negative electrode film layer has a compacted density of 1.3 g/cm ³ to 1.7 g/cm ³ . If the compacted density of the negative electrode film layer is within the above-mentioned appropriate range, the negative electrode sheet can have good electrolyte wetting performance, and the secondary battery can have a small internal resistance, thereby improving the electrochemical performance of the secondary battery.

In any embodiment, the thickness of the negative electrode current collector is ≤8 μm, and may be 4 μm˜8 μm. The thickness of the negative electrode current collector is controlled within the above-mentioned appropriate range, which can make the negative electrode sheet have high energy density, good conductivity and processability, so that the secondary battery has high energy density, good cycle performance and low battery life. Processing costs.

The second aspect of the present application also provides a method for preparing the negative electrode sheet according to the first aspect of the present application, the method comprising:

Provide slurry, which includes negative electrode active material, polybutadiene adipate softener and optional additives;

The preparation of the negative electrode sheet includes coating the slurry on at least one surface of the negative electrode collector, drying and cold pressing to obtain the negative electrode sheet, and the coating weight of one side of the negative electrode sheet is ≥180mg/1540.25mm ² .

According to the method of the present application, polybutadiene adipate softener is added to the negative electrode slurry, which can effectively prevent the negative electrode film layer from cracking during the processing of the negative electrode sheet, thereby realizing the ultra-thinning of the negative electrode sheet. Apply thickly. In addition, the adipate polybutadiene ester softener is non-toxic and harmless, and does not need to be recycled, which can make the method of the present application have a lower cost. The negative electrode sheet prepared according to the method of the present application has high energy density, high electrolyte infiltration speed and interface performance, and can effectively improve the energy density and electrochemical performance of the secondary battery.

In any embodiment, the coating speed is ≥45 m/min, optionally 45-60 m/min. Controlling the coating speed within the above-mentioned higher range can shorten the preparation time of the negative electrode sheet and improve the production efficiency of the negative electrode sheet.

The third aspect of the present application provides a secondary battery, comprising the negative electrode sheet of the first aspect of the present application or the negative electrode sheet prepared according to the method of the second aspect of the present application.

The secondary battery of the present application includes the negative electrode sheet of the first aspect of the application or the negative electrode sheet prepared according to the method of the second aspect of the application, which can have high energy density, good electrochemical performance and long cycle life.

In any embodiment, the coating weight on one side of the positive electrode sheet of the secondary battery is 250 mg/1540.25 mm ² to 450 mg/1540.25 mm ² . The coating weight of one side of the positive electrode sheet is controlled within an appropriate range, which can enable the positive electrode sheet to have high energy density and good electrolyte wetting performance, thereby improving the energy density and electrochemical performance of the secondary battery.

In any embodiment, the compacted density of the positive electrode sheet of the secondary battery is 2.4 g/cm ³ to 3.7 g/cm ³ . If the compacted density of the positive pole piece is within the above-mentioned appropriate range, the positive pole piece can have good electrolyte wettability, and can also make the secondary battery have a small internal resistance, thereby improving the electrochemical performance of the secondary battery.

In any embodiment, the thickness of the positive electrode film layer on one side of the secondary battery is 50 μm to 100 μm. The thickness of the positive electrode film layer is controlled within the above-mentioned appropriate range, which can make the positive electrode sheet have higher volumetric energy density, good electrolyte wetting performance and electron conductivity, thereby improving the volumetric energy density and electrochemical performance of the secondary battery .

In any embodiment, the ratio N/P of the negative electrode capacity per unit area to the positive electrode capacity per unit area of the secondary battery satisfies: N/P=1.05˜1.15. The ratio of the negative electrode capacity per unit area to the positive electrode capacity per unit area is within the above appropriate range, which can ensure that both the positive and negative electrode capacities can be fully utilized, thereby increasing the energy density of the secondary battery.

A fourth aspect of the present application provides a battery module including the secondary battery according to any embodiment of the third aspect of the present application.

A fifth aspect of the present application provides a battery pack, including the battery module of the fourth aspect of the present application.

The sixth aspect of the present application provides an electric device, including the secondary battery selected from any embodiment of the third aspect of the present application, the battery module of the fourth aspect of the present application, or the battery pack of the fifth aspect of the present application at least one of the

The battery module, battery pack and electric device of the present application include the secondary battery provided by the present application, and thus have at least the same advantages as the secondary battery.

Description of drawings

FIG. 1 is a schematic diagram of polybutadiene adipate-based softener molecules and carboxymethylcellulose-based dispersant (CMC) molecules in an embodiment of the negative electrode sheet of the present application.

FIG. 2 is a schematic diagram of an embodiment of the secondary battery of the present application.

FIG. 3 is an exploded view of the embodiment of the secondary battery of the present application shown in FIG. 2 .

Fig. 4 is a schematic diagram of an embodiment of the battery module of the present application.

FIG. 5 is a schematic diagram of an embodiment of the battery pack of the present application.

Fig. 6 is an exploded view of the embodiment of the battery pack of the present application shown in Fig. 5 .

FIG. 7 is a schematic diagram of an electric device used as a power source by an embodiment of the secondary battery of the present application.

FIG. 8 is a test chart of the 25° C. cycle capacity retention rate of the secondary battery of Example 5 of the present application.

FIG. 9 is a test chart of the 25° C. cycle capacity retention rate of the secondary battery of Comparative Example 3 of the present application.

Explanation of reference signs:

01 polybutadiene adipate ester softener molecule; 02 CMC molecule; 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 top cover assembly.

Detailed ways

Hereinafter, embodiments of the negative electrode sheet of the present application, its preparation method, secondary battery, battery module, battery pack, and electrical device will be specifically disclosed in detail with reference to the accompanying drawings. However, unnecessary detailed description may be omitted. For example, detailed descriptions of well-known items and repeated descriptions of substantially the same configurations may be omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the application, and are not intended to limit the subject matter described in the claims.

A "range" disclosed herein is defined in terms of lower and upper limits, and a given range is defined by selecting a lower limit and an upper limit that define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive and may be combined arbitrarily, ie any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are contemplated. Additionally, if the

minimum range values

1 and 2 are listed, and if the

maximum range values

3, 4, and 5 are listed, the following ranges are all expected: 1-3, 1-4, 1-5, 2- 3, 2-4 and 2-5. In this application, unless otherwise stated, the numerical range "a-b" represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article, and "0-5" is only an abbreviated representation of the combination of these values. In addition, when expressing that a certain parameter is an integer ≥ 2, it is equivalent to disclosing that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

If there is no special description, all the implementation modes and optional implementation modes of the present application can be combined with each other to form new technical solutions.

If there is no special description, all the technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

Unless otherwise specified, all steps in the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed in sequence, and may also include steps (b) and (a) performed in sequence. For example, mentioning that the method may also include step (c) means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c) , may also include steps (a), (c) and (b), may also include steps (c), (a) and (b) and so on.

If there is no special description, the "comprising" and "comprising" mentioned in this application mean open or closed. For example, the "comprising" and "comprising" may mean that other components not listed may be included or included, or only listed components may be included or included.

In this application, the term "or" is inclusive unless otherwise stated. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied by either of the following: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists) ; or both A and B are true (or exist).

As mentioned in the background art, on the premise of not affecting the performance of the secondary battery, increasing the thickness of the pole piece is currently an important direction for improving the energy density of the secondary battery. However, as the thickness of the pole piece increases, its processing difficulty also increases, and the ultra-thick coated pole piece is prone to film cracking during the drying process. In addition, the thickness of the film layer is too large, which will also lead to the problems of difficult electrolyte wetting and poor kinetics.

The inventors conducted research on ultra-thick coated negative electrode sheets, and found that adding a softener to the negative electrode slurry can improve the problem of film cracking during the drying process of the negative electrode sheet.

At present, it is mostly to add high-boiling point alcohols, ethylene carbonate or other low surface tension solvents to the negative electrode slurry to improve the cracking of the film layer. However, the above three substances have their own shortcomings.

Alcohols with high boiling points are easy to absorb water and difficult to completely volatilize, and remain in the pole piece, resulting in excessive time and economic costs in the subsequent baking process and reduced production capacity. In addition, due to the poor compatibility between high-boiling point alcohols and the electrolyte, it will make it difficult for the electrolyte to infiltrate, and even hinder the electrochemical reaction, resulting in lithium deposition on the negative electrode, which will lead to safety hazards.

Ethylene carbonate is a solid substance at room temperature and needs to be pre-dissolved before it can be mixed with the negative electrode slurry, and the process is relatively complicated. In addition, ethylene carbonate has a high boiling point and cannot be completely volatilized, and part of it remains in the pole piece. The residual ethylene carbonate cannot be completely dissolved in the electrolyte, thus increasing the interfacial charge transfer resistance, deteriorating the interfacial dynamics, and even leading to lithium precipitation, which seriously affects the safety performance of the secondary battery. What's more serious is that when the amount of ethylene carbonate added is too large, the residual amount of the pole piece will increase. Since the material is a crystalline substance, there is a risk of difficulty in cold pressing during the pole piece processing.

Low surface tension solvents, such as isopropanol, ethyl acetate, etc., generally require a larger amount to improve the cracking of the film layer. Excessive addition of low surface tension solvent will not only increase the manufacturing cost, but also affect the rheological properties of the slurry and increase the risk of thick edges of the pole piece. In addition, adding a low surface tension solvent to the negative electrode slurry will, on the one hand, aggravate the floating of the binder during the drying process of the pole piece, which will lead to the risk of powder falling off the pole piece in the later stage; on the other hand, the low surface tension solvent The boiling point of the pole piece is usually lower than that of water, which can easily lead to overdrying during the drying process of the pole piece, which in turn will cause the edge of the pole piece to crack.

In view of this, the inventor has selected a suitable softener after in-depth research, and provided a negative electrode sheet and a preparation method thereof, a secondary battery, a battery module, a battery pack, and an electrical device.

Negative pole piece

The first aspect of the present application proposes a negative electrode sheet, including a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector. agent and optional additives, and the coating weight of one side of the negative electrode sheet is ≥180mg/1540.25mm ² .

As an example, the negative electrode current collector has two opposing surfaces in its own thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposing surfaces of the negative electrode current collector.

Although the mechanism is not yet clear, the inventors unexpectedly found that the present application can not only effectively reduce the cracking of the negative electrode film under ultra-thick coating by adding adipate polybutadiene ester softener to the negative electrode film layer , It can also reduce the difficulty of wetting the negative electrode sheet, so that the secondary battery has high energy density and good electrochemical performance.

Specifically, the inventors found that the adipate polybutadiene ester softener has good solubility in the aqueous solvent system, can be uniformly dispersed in the negative electrode slurry system, and thus can be uniformly present in the negative electrode film layer. In addition, the negative electrode slurry added with adipate polybutadiene ester softener, even in the case of single-sided coating weight ≥ 180mg/1540.25mm ² , rarely occurs during the drying process of the pole piece. The phenomenon of cracking of the negative electrode film layer.

In general, during the drying process of the negative electrode sheet, the surface tension and capillary force of the curved liquid surface of water exist in the negative electrode film layer. In the case where carboxymethylcellulose dispersant (CMC) is added to the negative electrode film layer, there will also be a force of CMC drying shrinkage in the negative electrode film layer. The forces of surface tension, capillary force and drying shrinkage will make the material particles in the negative electrode film layer close together and squeeze each other. Since the material particles at the bottom of the negative electrode film layer are bonded to the current collector, the negative electrode film layer is fixed in the horizontal direction. The surface of the film layer continues to shrink to generate stress that causes the pole piece to warp, and the bend in the middle area of the film layer produces cracks due to insufficient toughness. In addition, the pole piece at the curled edge is flattened when passing through the roll. At this time, cracks are also generated due to the lack of toughness of the negative pole piece. The greater the degree of curling and warping, the more obvious the crack phenomenon.

Not intending to be limited by any theory or explanation, the inventors found that adding polybutadiene adipate softener to the negative electrode slurry, the polybutadiene adipate softener can be combined with the negative electrode film The moisture in the negative electrode layer acts on it, thereby reducing the moisture volatilization rate of the negative electrode sheet during the drying process, thereby reducing the drying stress of the negative electrode film layer, and reducing the cracking degree of the negative electrode film layer. In addition, when CMC is added to the negative electrode film layer, the polybutadiene adipate softener can be uniformly dispersed among the CMC molecules. As shown in Figure 1, the adipate polybutadiene ester softener molecule 01 can be evenly dispersed among the CMC molecules 02, thereby increasing the distance between the CMC molecules and improving the rotation and twisting ability of the CMC molecular chain Improve, and then increase the flexibility of the negative electrode film layer, and avoid the cracking of the negative electrode film layer. Further, the polar groups in polybutadiene adipate can also interact with groups in CMC molecules, reducing the connection points between CMC molecules and replacing the interaction between CMC molecules, thereby weakening the The strong force between CMC molecules reduces the degree of warpage during the drying process of the pole piece, thereby reducing the risk of cracking of the negative electrode film layer during the drying of the pole piece and the cold pressing process.

In addition, the inventors also found that the polybutadiene adipate softener has good electrolyte affinity and can increase the electrolyte infiltration rate of the negative electrode sheet. The negative electrode sheet has a high electrolyte infiltration speed. On the one hand, it can shorten the infiltration time of the negative electrode sheet, reduce the manufacturing cost, and increase the production capacity; cycle performance of the battery. The adipate polybutadiene ester softener exists in the negative electrode film layer, which will not reduce the electrochemical performance of the secondary battery and is non-toxic and harmless, and does not need to be recycled. In this way, the production of the negative electrode of the application can be reduced. The manufacturing cost required for the film.

According to the negative electrode sheet of the present application, the adipate polybutadiene ester flexibilizer is included in the negative electrode film layer. In the case of high coating weight, it is not easy to produce film layer cracking, and can have a higher The electrolyte wetting speed and interfacial properties. The negative electrode sheet of the present application is applied to a secondary battery, which can make the secondary battery have high energy density and good electrochemical performance.

In this application, polybutadiene adipate refers to the esterification product of hydroxyl-terminated polybutadiene and adipic acid, which includes the molecular skeleton of polybutadiene and the esterification of adipic acid and terminal hydroxyl terminal base.

In some embodiments, the polybutadiene adipate softener can be selected from compounds represented by Formula 1.

In Formula 1, n is an integer of 10 to 150, and the M element and the M' element are each independently selected from H or Li. Optionally, both the M element and the M' element are Li.

It is easy to understand that when the M element or the M' element is H, the H atom and the O atom may be connected in the form of a covalent bond. When the M element or M' element is Li, Li ⁺ and -COO ^- can be connected in the form of an ionic bond.

The adipate polybutadiene ester softener shown in Formula 1 can be obtained in various ways, which is not particularly limited in this application. In some embodiments, the polybutadiene adipate softener can be obtained by self-made. Some possible preparation methods of the polybutadiene adipate softener of the present application are described below in the form of examples. It should be noted that the following examples are only for explaining the present application rather than limiting the present application.

As an example, in the case where the M element and the M' element are both H, the adipate polybutadiene ester softener can be formed by the presence of adipic acid and hydroxyl-terminated polybutadiene in the presence of a catalyst for the esterification reaction Under the reaction conditions, the reaction is obtained. In one embodiment, the catalyst may be an acid catalyst, such as sulfuric acid or hydrochloric acid, and the reaction conditions may be inert atmosphere conditions, such as N ₂ atmosphere, and a temperature of 60-80°C.

As an example, in the case that at least one of the M element and the M' element is Li, the adipate polybutadiene ester softener can be prepared through the following steps S110 and S120.

S110, mixing adipic acid, hydroxyl-terminated polybutadiene, and a catalyst for esterification reaction under reaction conditions, so that adipic acid and hydroxyl-terminated polybutadiene undergo esterification reaction, thereby obtaining an esterification reaction product.

S120, mixing the above-mentioned esterification reaction product with LiOH, so that the esterification reaction product and LiOH undergo a neutralization reaction, so as to obtain polybutadiene adipate in which at least one of the M element and the M' element is Li softener.

Wherein, the catalyst may be an acid catalyst, such as sulfuric acid or hydrochloric acid, and the reaction conditions may be inert atmosphere conditions, such as _N2 atmosphere, and a temperature condition of 60-80°C.

The adipate polybutadiene ester softener is selected from the compounds shown in formula 1, which can have better electrolyte affinity, thereby further improving the electrolyte wetting performance and liquid retention performance of the negative electrode sheet, thereby improving Rate performance of secondary batteries. In addition, the adipate polybutadiene ester softener shown in Formula 1 has a strong electronegativity in the ester group in the molecule, which is conducive to improving the lithium ion transmission capacity, thereby further improving the cycle life of the secondary battery. performance.

Furthermore, compared with the case where H exists in the M element and the M' element, when both the M element and the M' element are Li, on the one hand, it can avoid the reaction of the carboxyl group at a low potential, transform into -COOLi and generate hydrogen, thereby avoiding The loss of active ions and the increase of gas production can avoid affecting the first coulombic efficiency and safety performance of the secondary battery; on the other hand, Li ⁺ is connected to -COO ^- through ionic bonds, which can improve the lithium ion conductivity of the negative electrode film layer, Therefore, the migration kinetics of lithium ions in the negative electrode sheet is improved, thereby reducing the internal resistance of the secondary battery and improving the rate performance of the secondary battery.

The present application does not specifically limit the weight average molecular weight of the adipate polybutadiene ester softener.

In some embodiments, the weight average molecular weight of the adipate polybutadiene ester softener may be 1600-18000, 4800-18000, 4800-13800, 4800-9200.

Not intending to be bound by any theory or explanation, the inventors have found that the weight average molecular weight of the polybutadiene adipate ester softener within the above range can ensure that the polybutadiene adipate ester softener The molecules are evenly dispersed between the CMC molecules, so that there is an appropriate distance between the CMC molecules, thereby weakening the strong force between the CMC molecules, improving the ability of the CMC molecular chains to rotate and twist, and then fully exerting the effect of improving the cracking of the negative electrode film. In addition, the weight-average molecular weight of polybutadiene adipate ester softener within the above range can also make the negative electrode sheet have better lithium ion migration kinetics, and prevent the intercalation and degradation of active lithium ions in the cycle process. Deintercalation is hindered, thereby avoiding an increase in the impedance of the secondary battery.

In the embodiment of the present application, by including the adipate polybutadiene ester softener with a weight-average molecular weight in the above-mentioned suitable range in the negative electrode film layer, it is possible to effectively avoid cracking of the negative electrode film layer while ensuring Secondary batteries have excellent cycle performance.

In some embodiments, based on the total mass of the negative electrode film layer, the mass proportion of polybutadiene adipate ester softener can be 0.05wt% to 0.6wt%, 0.1wt% to 0.6wt%, 0.1wt% %～0.5wt%, 0.2wt%～0.5wt%, 0.25wt%～0.5wt%. Optionally, the mass proportion of adipate polybutadiene ester softener can be 0.1wt%～0.5wt%, more optionally, the mass proportion of adipate polybutadiene ester softener The ratio may be 0.2 wt% to 0.5 wt%.

Not intending to be limited by any theory or explanation, the inventors have found that the mass proportion of polybutadiene adipate ester softener in the negative electrode film layer is within the above-mentioned appropriate range, which is enough to effectively prevent the negative electrode film layer from At the same time of cracking, the negative electrode sheet has high energy density, good electrolyte wettability and liquid retention, so that the secondary battery has good cycle performance and rate performance.

In some embodiments, the optional additives include a conductive agent, a dispersant and a binder. Based on the total mass of the negative electrode film layer, the mass proportion of the conductive agent can be 0.3wt% to 3wt%, and the amount of the negative electrode active material The mass proportion can be 90wt% ~ 98wt%, the mass proportion of adipate polybutadiene ester softener can be 0.05wt% ~ 0.6wt%, the mass proportion of dispersant can be 0.5wt% ~ 3wt% %, the mass proportion of the binder can be 0.5wt%-5wt%.

In some embodiments, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the dispersant can be selected from CMC-based dispersants, such as CMC-Li, CMC-Na, and the like.

In some embodiments, the binder may be selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate ( SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

The negative electrode film layer contains the above components, and the proportion of each component is within the above-mentioned suitable range, not only can the negative electrode sheet have good electrical conductivity, but also can make the negative electrode film layer have a uniform thickness distribution, and make the negative electrode The film layer is firmly adhered to the surface of the negative electrode current collector. The negative electrode film layer has the above-mentioned components and component ratios, which can ensure that the secondary battery has excellent electrochemical performance and long cycle life.

In some embodiments, the thickness of the single-sided negative electrode film layer can be 65 μm-125 μm, 70 μm-120 μm, 75 μm-115 μm, 80 μm-110 μm, 85 μm-105 μm.

The thickness of the single-sided negative electrode film layer is controlled within an appropriate range, which can make the negative electrode sheet have a higher volume energy density, a higher electrolyte infiltration rate, and a lower internal resistance, and can effectively reduce the cycle time of the negative electrode film layer. Risk of late shedding. When the thickness of the single-sided negative electrode film layer is within the above range, the secondary battery can have high volumetric energy density, good cycle performance and long cycle life.

In some embodiments, the compacted density of the negative electrode film layer can be 1.3g/cm ³ ~ 1.7g/cm ³ , 1.3g/cm ³ ~ 1.6g/cm ³ , 1.35g/cm ³ ~ 1.55g/cm ³ , 1.4g/cm ³ to 1.5g/cm ³ .

If the compaction density is too large, the contact between the material particles of the negative electrode film layer is too close, the electrolyte is difficult to infiltrate the material particles, and the active ions cannot be smoothly embedded in the negative electrode material during pre-charging. If the compaction density is too small, the material particles in the negative electrode film layer will not be in close contact, which will not only increase the porosity of the negative electrode sheet, but also cause the interface contact resistance to be too large, thereby increasing the internal resistance of the secondary battery. Affect the electrochemical performance of the secondary battery. If the compacted density of the negative electrode film layer is within the above-mentioned appropriate range, the negative electrode sheet can have good electrolyte wetting performance, and the secondary battery can have a small internal resistance, thereby improving the electrochemical performance of the secondary battery.

In some embodiments, the thickness of the negative electrode current collector may be ≦8 μm. Specifically, the thickness of the negative electrode current collector may be 4 μm˜8 μm. More specifically, the thickness of the negative electrode collector may be 4.5 μm, 6 μm, or 8 μm.

The smaller the thickness of the negative electrode collector, the higher the energy density of the negative electrode sheet, but correspondingly, the electrical conductivity and mechanical properties of the negative electrode sheet will decrease accordingly. According to the negative electrode sheet of the present application, the adipate polybutadiene ester softener is included in the negative electrode film layer, even if the thickness of the negative electrode current collector is small, the negative electrode sheet can maintain good mechanical properties, thereby being able to Prevent the warping of the negative electrode sheet during processing, thereby preventing the negative electrode film layer from cracking. According to the thickness of the negative electrode current collector of the negative electrode sheet of the present application is controlled in the above-mentioned suitable range, the negative electrode sheet can be made to have high energy density, good conductivity and workability, so that the secondary battery has high energy density, Good cycle performance and low processing cost.

It should be noted that the present application does not specifically limit the material of the negative electrode collector. In some embodiments, the negative electrode current collector can use a metal foil or a composite current collector. For example, copper foil can be used as the metal foil. The composite current collector may include a base layer of polymer material and a metal layer formed on at least one surface of the base material of polymer material. Composite current collectors can be formed by metal materials (copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) on polymer material substrates (such as polypropylene (PP), polyethylene terephthalic acid It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

It should be noted that the present application does not specifically limit the negative electrode active material. In some embodiments, the negative electrode active material can be a negative electrode active material known in the art for batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, lithium titanate, and the like. The silicon-based material may be selected from at least one of elemental silicon, silicon-oxygen compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of simple tin, tin oxide compounds and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials of batteries can also be used. These negative electrode active materials may be used alone or in combination of two or more.

In some embodiments, the negative electrode film layer may optionally include other additives, such as wetting aids, dispersion aids, viscosity-increasing aids, electrolyte wetting aids, and the like.

It should be noted that the negative electrode sheet of the present application does not exclude other additional functional layers other than the negative electrode film layer. For example, in some embodiments, the negative electrode sheet described in the present application may further include a conductive primer layer (for example, composed of a conductive agent and a binder) disposed between the negative electrode current collector and the negative electrode film layer. In some other embodiments, the negative electrode sheet described in the present application also includes a protective layer covering the surface of the negative electrode film layer.

In the present application, the thickness of the negative electrode film layer is a well-known meaning in the art, and can be tested by methods known in the art, for example, a micrometer (such as Mitutoyo 293-100 type, with an accuracy of 0.1 μm) for testing.

In the present application, the compacted density of the negative electrode film layer is a well-known meaning in the art, and can be tested by methods known in the art. The compacted density of the negative electrode film layer=areal density of the negative electrode film layer/thickness of the negative electrode film layer. Wherein, the areal density of the negative electrode film layer is a well-known meaning in the art, and can be tested by methods known in the art. For example, take the negative electrode sheet coated on one side and after cold pressing, punch it into a small disc with an area of _S1 , weigh it, and record it as _M1 ; the uncoated negative electrode current collector is also punched out with an area of For the small disc of S ₁ , weigh the weight of the negative electrode collector and record it as M ₀ ; the surface density of the negative electrode film = (the weight of the negative electrode sheet M ₁ - the weight of the negative electrode collector M ₀ )/S ₁ (if the double For the surface-coated negative electrode sheet, the surface density of the negative electrode film layer=(the weight M ₁ of the negative electrode sheet−the weight M ₀ of the negative electrode current collector)/2S ₁ ).

It should be noted that the above-mentioned various parameter tests for the negative electrode film layer or the negative electrode active material can be sampled and tested during the battery preparation process, or can be sampled and tested from the prepared secondary battery.

When the above-mentioned test sample is taken from a prepared secondary battery, as an example, the following steps (1) to (3) may be used for sampling.

(1) Discharge the secondary battery (for safety reasons, the battery is generally in a fully charged state); after disassembling the battery, take out the negative electrode piece, and use dimethyl carbonate (DMC) to soak the negative electrode piece for a certain period of time (for example 2-10 hours); then take out the negative pole piece and dry it at a certain temperature and time (for example, 60° C., 4 hours), and take out the negative pole piece after drying. At this point, samples can be taken from the dried negative electrode sheet to test various parameters related to the above-mentioned negative electrode film layer of the present application.

(2) Bake the negative electrode sheet dried in step (1) at a certain temperature and time (for example, 400°C, 2 hours), and select a region in the baked negative electrode sheet to sample the negative electrode active material (A blade scraping powder can be selected for sampling).

(3) The negative electrode active material collected in step (2) is sieved (for example, sieved with a 200-mesh sieve), and finally a sample that can be used to test the parameters of each negative electrode active material mentioned above in this application is obtained.

Method for preparing negative electrode sheet

The second aspect of the present application provides a method for preparing the negative electrode sheet of the present application, including step S210, providing a slurry, which includes the negative electrode active material, polybutadiene adipate according to the first aspect of the present application Ester softener and optional additives.

As the negative electrode active material, known negative electrode active materials for batteries can be used. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, lithium titanate, and the like. The silicon-based material may be selected from at least one of elemental silicon, silicon-oxygen compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of simple tin, tin oxide compounds and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials of batteries can also be used. These negative electrode active materials may be used alone or in combination of two or more.

In some embodiments, optional additives also optionally include a binder. The binder can be selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), poly At least one of methacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

In some embodiments, optional additives also optionally include conductive agents. The conductive agent can be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

In some embodiments, the optional additives may also optionally include other auxiliary agents, such as dispersants (such as sodium carboxymethylcellulose (CMC-Na)) and the like.

The aforementioned providing the slurry may specifically include dispersing the aforementioned components for preparing the negative electrode slurry in a solvent (such as deionized water) to form the negative electrode slurry.

The method of the present application also includes step S220, preparing the negative electrode sheet, including coating the slurry on at least one surface of the negative electrode current collector, drying and cold pressing to obtain the negative electrode sheet, and the single-side coating weight of the negative electrode sheet ≥180mg/1540.25mm ² .

In some embodiments, the coating speed can be ≥45 m/min, specifically, the coating speed can be 45-65 m/min, 45-60 m/min, 45-55 m/min, 45-55 m/min.

According to the method of the present application, adipate polybutadiene ester softener is added to the negative electrode slurry, even at a higher coating speed, it is not easy to cause the negative electrode film layer to crack due to the tortuosity of the pole piece . Controlling the coating speed within the above-mentioned higher range can shorten the preparation time of the negative electrode sheet and improve the production efficiency of the negative electrode sheet.

In addition, the secondary battery, the battery module, the battery pack, and the power consumption device of the present application will be described below with appropriate reference to the accompanying drawings.

In one embodiment of the present application, a secondary battery is provided.

Typically, a secondary battery includes a positive pole piece, a negative pole piece, an electrolyte, and a separator. During the charging and discharging process of the battery, active ions are intercalated and extracted back and forth between the positive electrode and the negative electrode. The electrolyte plays the role of conducting active ions between the positive pole piece and the negative pole piece. The separator is arranged between the positive pole piece and the negative pole piece, which mainly plays a role in preventing the short circuit of the positive and negative poles, and at the same time allows active ions to pass through.

[Positive pole piece]

The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode collector, and the positive electrode film layer includes the positive electrode active material according to the first aspect of the present application.

As an example, the positive electrode current collector has two opposing surfaces in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposing surfaces of the positive electrode current collector.

In some embodiments, the coating weight of one side of the positive electrode sheet can be 250mg/1540.25mm ² to 450mg/1540.25mm ² , 280mg/1540.25mm ² to 420mg/1540.25mm ² , 300mg/1540.25mm ² to 400mg/1540.25mm 2 mm ² , 350 mg/1540.25 mm ² to 400 mg/1540.25 mm ² .

The coating weight of one side of the positive electrode sheet is controlled within an appropriate range, which can enable the positive electrode sheet to have high energy density and good electrolyte wetting performance, thereby improving the energy density and electrochemical performance of the secondary battery.

In some embodiments, the compacted density of the positive electrode sheet can be 2.4g/cm ³ ~ 3.7g/cm ³ , 2.5g/cm ³ ~ 3.5g/cm ³ , 2.8g/cm ³ ~ 3.2g/cm ³ .

If the compacted density of the positive pole piece is within the above-mentioned appropriate range, the positive pole piece can have good electrolyte wettability, and can also make the secondary battery have a small internal resistance, thereby improving the electrochemical performance of the secondary battery.

In some embodiments, the thickness of the positive film layer on one side may be 50 μm˜100 μm, 60 μm˜90 μm, 70 μm˜90 μm, 70 μm˜80 μm.

The thickness of the positive electrode film layer is controlled within the above-mentioned appropriate range, which can make the positive electrode sheet have higher volumetric energy density, good electrolyte wetting performance and electron conductivity, thereby improving the volumetric energy density and electrochemical performance of the secondary battery .

In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector can be formed by forming metal materials (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalic acid It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

The present application does not specifically limit the type of the positive electrode active material, and the positive electrode active material used in batteries known in the art may be used. As an example, the positive active material may include at least one of the following materials: olivine-structured lithium-containing phosphate, lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials of batteries can also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO ₂ ), lithium nickel oxides (such as LiNiO ₂ ), lithium manganese oxides (such as LiMnO ₂ , LiMn ₂ O ₄ ), lithium Nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (also referred to as NCM ₃₃₃ ), LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (also abbreviated as NCM ₅₂₃ ), LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (also abbreviated as NCM ₂₁₁ ), LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (also abbreviated as NCM ₆₂₂ ), LiNi At least one of _0.8 Co _0.1 Mn _0.1 O ₂ (also referred to as NCM ₈₁₁ ), lithium nickel cobalt aluminum oxide (such as LiNi _0.85 Co _0.15 Al _0.05 O ₂ ) and its modified compounds. The olivine structure contains Examples of lithium phosphates may include, but are not limited to, lithium iron phosphate (such as LiFePO ₄ (also may be abbreviated as LFP)), composite materials of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO ₄ ), lithium manganese phosphate and carbon At least one of a composite material, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

In some embodiments, the positive electrode active material may include LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (also abbreviated as NCM ₅₂₃ ), LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (also abbreviated as NCM ₈₁₁ ), LiNi _0.8 Co _0.15 Al _0.05 O ₂ (also abbreviated as NCA), lithium cobalt oxide (such as LiCoO ₂ , abbreviated as LCO), LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (also abbreviated as NCM ₃₃₃ ), LiNi _0.6 At least one of Co _0.2 Mn _0.2 O ₂ (also abbreviated as NCM ₆₂₂ ), lithium iron phosphate (LiFePO ₄ ).

The positive electrode active materials selected from the above categories have relatively high energy density, and when used in the secondary battery of the present application, the theoretical capacity of the negative electrode sheet can be fully utilized, and the secondary battery has high energy density.

In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene At least one of ethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.

In some embodiments, the positive electrode film layer may also optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the positive electrode sheet can be prepared in the following manner: the above-mentioned components used to prepare the positive electrode sheet, such as positive electrode active material, conductive agent, binder and any other components, are dispersed in a solvent (such as N -methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[Negative pole piece]

The negative electrode sheet is selected from the negative electrode sheet according to any embodiment of the first aspect of the present application.

[Electrolyte]

The electrolyte plays the role of conducting ions between the positive pole piece and the negative pole piece. The present application has no specific limitation on the type of electrolyte, which can be selected according to requirements. For example, electrolytes can be liquid, gel or all solid.

In some embodiments, the electrolyte is an electrolytic solution. The electrolyte solution includes an electrolyte salt and a solvent.

In some embodiments, the electrolyte salt may be selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, trifluoromethane At least one of lithium sulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium difluorooxalate borate, lithium difluorodifluorooxalatephosphate and lithium tetrafluorooxalatephosphate.

In some embodiments, the solvent may be selected from ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, Butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate At least one of ester, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

In some embodiments, the electrolyte may optionally include additives. For example, additives can include negative film-forming additives, positive film-forming additives, and additives that can improve certain performances of batteries, such as additives that improve battery overcharge performance, additives that improve high-temperature or low-temperature performance of batteries, and the like.

[Isolation film]

In some embodiments, a separator is further included in the secondary battery. The present application has no particular limitation on the type of the isolation membrane, and any known porous structure isolation membrane with good chemical stability and mechanical stability can be selected.

In some embodiments, the material of the isolation film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without any particular limitation. When the separator is a multilayer composite film, the materials of each layer may be the same or different, and there is no particular limitation.

In some embodiments, the ratio N/P of the negative electrode capacity per unit area to the positive electrode capacity per unit area of the secondary battery can satisfy: N/P=1.05˜1.15. Specifically, N/P can be 1.05, 1.1, 1.12, 1.15.

The ratio of the negative electrode capacity per unit area to the positive electrode capacity per unit area is within the above appropriate range, which can ensure that both the positive and negative electrode capacities can be fully utilized, thereby increasing the energy density of the secondary battery.

In some embodiments, the positive pole piece, the negative pole piece and the separator can be made into an electrode assembly through a winding process or a lamination process.

In some embodiments, the secondary battery may include an outer package. The outer package can be used to package the above-mentioned electrode assembly and electrolyte.

In some embodiments, the outer packaging of the secondary battery may be a hard case, such as a hard plastic case, aluminum case, steel case, and the like. The outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag. The material of the soft case may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.

The present application has no special limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. For example, FIG. 2 shows a square-shaped secondary battery 5 as an example.

In some embodiments, referring to FIG. 3 , the outer package may include a housing 51 and a cover 53 . Wherein, the housing 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plates enclose to form an accommodating cavity. The housing 51 has an opening communicating with the accommodating cavity, and the cover plate 53 can cover the opening to close the accommodating cavity. The positive pole piece, the negative pole piece and the separator can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is packaged in the accommodating cavity. Electrolyte is infiltrated in the electrode assembly 52 . The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

In some embodiments, the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

FIG. 4 is a battery module 4 as an example. Referring to FIG. 4 , in the battery module 4 , a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 . Of course, it can also be arranged in any other manner. Further, the plurality of secondary batteries 5 can be fixed by fasteners.

Optionally, the battery module 4 may also include a case having a housing space in which a plurality of secondary batteries 5 are accommodated.

In some embodiments, the above-mentioned battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

FIG. 5 and FIG. 6 serve as an example of the battery pack 1 . Referring to FIGS. 5 and 6 , the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3 , the upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery module 4 . Multiple battery modules 4 can be arranged in the battery box in any manner.

In addition, the present application also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source of the electric device, and can also be used as an energy storage unit of the electric device. The electric devices may include mobile devices (such as mobile phones, notebook computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, etc.) , electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but not limited thereto.

As the electric device, a secondary battery, a battery module or a battery pack can be selected according to its use requirements.

FIG. 7 is an example of an electrical device. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the electric device for the secondary battery, a battery pack or a battery module may be used.

As another example, a device may be a cell phone, tablet, laptop, or the like. The device is generally required to be light and thin, and a secondary battery can be used as a power source.

Example

Hereinafter, examples of the present application will be described. The embodiments described below are exemplary and are only used for explaining the present application, and should not be construed as limiting the present application. If no specific technique or condition is indicated in the examples, it shall be carried out according to the technique or condition described in the literature in this field or according to the product specification. The reagents or instruments used were not indicated by the manufacturer, and they were all commercially available conventional products.

Examples 1-14

[Preparation of negative electrode sheet]

The negative electrode active material graphite, conductive carbon, dispersant CMC-Na, binder SBR, adipate polybutadiene ester softener are fully stirred and mixed in a deionized water solvent system according to a certain ratio, and the negative electrode is obtained. Slurry, wherein, with the solid content of the negative electrode slurry being 100wt%, the mass proportion of the negative electrode active material graphite is A, the mass proportion of the conductive carbon is 0.7wt%, and the mass proportion of the thickener CMC-Na is 1 wt%, the mass proportion of the binder SBR is 1.5 wt%, and the mass proportion of the adipate polybutadiene ester softener is B. The negative electrode slurry was uniformly coated on the Cu foil at a coating speed of 60 m/min, and the coating weight on one side was controlled so that the coating weight CW on one side was within a certain range. After drying in an oven, cold pressing, and cutting, the negative electrode sheet is obtained, and the compacted density of the electrode sheet is controlled to 1.65g/cm ³ .

In each embodiment, the mass ratio A of the negative electrode active material in the negative electrode film layer, the element types of M and M' in the molecule of the polybutadiene adipate softener, the polybutadiene adipate The weight average molecular weight M _w of the softener, the mass proportion B in the negative electrode film layer, and the coating weight CW are not completely the same, and the specific preparation parameters are shown in Table 1.

【Preparation of Positive Electrode】

Fully stir the positive electrode active material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , conductive carbon SP, conductive graphite, binder PVDF, and dispersant in the N-methylpyrrolidone solvent system at a weight ratio of 96.94:1.7:0.3:1:0.06 After mixing evenly, it is evenly coated on Al foil, dried in an oven, cold-pressed, and cut to obtain a positive pole piece. The compacted density of the pole piece is controlled at 3.45g/cm ³ , and the N/P value is controlled at 1.1.

【Preparation of Electrolyte】

In a dry argon atmosphere glove box (H ₂ O<0.1ppm, O ₂ <0.1ppm), the organic solvents propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC) according to 1: Mix evenly at a weight ratio of 1:1, add fully dried lithium salt LiPF ₆ and dissolve in the above organic solvent, stir and mix evenly, and finally obtain an electrolyte solution with a lithium salt concentration of 1.15mol/L.

【Isolation film】

A polypropylene film is used as the separator.

【Preparation of secondary battery】

Stack the positive electrode, separator, and negative electrode in order, so that the separator is between the positive and negative electrodes for isolation, then wind the electrode assembly, weld the tabs to the electrode assembly, and place the electrode assembly Put it into an aluminum shell, bake it at 80°C to remove water, then inject electrolyte and seal it, and then go through the processes of standing, hot and cold pressing, chemical formation, and shaping in order to complete the preparation of lithium-ion batteries.

Comparative example 1～3

The preparation of the negative pole piece, the preparation of the positive pole piece, the preparation of the electrolyte, the separator used, and the preparation of the secondary battery are the same as in Examples 1-14, the difference is that no softener is added, and the specific preparation parameters are shown in the table. 1.

test part

【Viscosity test of negative electrode slurry】

Viscosity tests were carried out on the negative electrode slurries in the above-mentioned Examples 1-14 and Comparative Examples 1-3, and the specific test methods were as follows:

Use a rotary viscometer, select the rotor according to the viscosity of the sample, use the viscometer lifting stand to slowly lower the viscometer, and immerse the rotor in the slurry until the mark on the rotor is equal to the liquid level. Test temperature: 25°C, speed: 12rpm, Press the measurement key to start measurement, and after 5 minutes the data remains stable, just read the viscosity value.

See Table 1 for the viscosities of the negative electrode slurries in Examples 1-14 and Comparative Examples 1-3.

[Negative plate warpage height test]

Bake the wet film negative electrode sheet coated on one side at 100°C for 1 min to remove most of the water; then cut it into 10 negative electrode sheets with a size of 4cm*4cm; then cut the negative electrode Place the pole piece on the heating plate whose temperature is stable at 120°C, and keep it for 1min. Use a scale to measure the height of the four corners of each negative pole piece, which are recorded as h ₁ , h ₂ , h ₃ , and h ₄ . Calculate the average value of h ₁ , h ₂ , h ₃ , and h ₄ corresponding to each negative pole piece, and denote it as H. The average value H corresponding to the 10 negative pole pieces is taken as the warpage height of the negative pole pieces.

Table 2 shows the test results of the warpage height of negative pole pieces of Examples 1-14 and Comparative Examples 1-3.

【Cracking test of negative electrode film】

After the negative electrode sheet is dried, directly observe whether the edge and middle of the negative electrode film are cracked.

See Table 2 for the test results of the cracking of the negative electrode film in Examples 1-14 and Comparative Examples 1-3.

【Negative Electrode Excellent Rate Test】

The dried and cold-pressed negative pole pieces were cut, and the number of negative pole pieces obtained was recorded as n, and the number of negative pole pieces that could not be used to prepare secondary batteries due to cracking was recorded as m. Then the yield of the negative pole piece is defined as: (1-m/n)*100%.

Table 2 shows the test results of the goodness of the negative electrodes of Examples 1-14 and Comparative Examples 1-3.

【Electrolyte Wetting Rate Test】

The capillary method was used to quantitatively test the wetting rate of the pole piece. Draw a certain amount of electrolyte and contact with the surface of the negative pole piece. Under the capillary force, the electrolyte in the capillary is sucked out, and the time when the electrolyte is completely absorbed is recorded. According to the amount of electrolyte absorbed and soaking time, the absorption rate can be calculated.

See Table 2 for the test results of the electrolyte infiltration rate of the negative electrode sheets of Examples 1-14 and Comparative Examples 1-3.

[The first Coulombic efficiency test]

At 25°C, discharge the formed secondary battery with a constant current (DC) at a rate of 1/3C to 2.8V, and let it stand for 10 minutes; then charge with a constant current (CC) at a rate of 1/3C to 4.2V , then charged at a constant voltage (CV) of 4.2V to a current of 0.05C, stood still for 10min, and recorded the charging capacity; then discharged at a constant current (DC) at a rate of 1/3C to 2.8V, and recorded the discharging capacity.

The first coulombic efficiency = discharge capacity / charge capacity * 100%

Table 3 shows the first Coulombic efficiency test results of the secondary batteries of Examples 1-14 and Comparative Examples 1-3.

[50% SOC discharge DC resistance DCR test]

At 25°C, charge the secondary battery with a constant current (CC) at a rate of 1/3C to 4.2V, then charge with a constant voltage (CV) at 4.2V to a current of 0.05C, and leave it for 5 minutes. Then discharge at a rate (DC) of 1/3C for 90 minutes, adjust the electrode assembly to 50% SOC, let it stand for 60 minutes, and then discharge (DC) at a rate of 3C for 30 seconds, and obtain 50% SOC discharge DCR according to the test data.

The 50% SOC discharge DCR test results of the secondary batteries of Examples 1-14 and Comparative Examples 1-3 are shown in Table 3.

【Capacity retention test】

At 25°C, charge the secondary battery with a constant current (CC) at a rate of 0.5C to 4.2V, then charge with a constant voltage (CV) at 4.2V to a current of 0.05C, leave it for 5 minutes, and then discharge it at a rate of 0.5C (DC) to 2.8V, this is a cyclic charge and discharge process, record the discharge capacity at this time, which is the initial capacity C ₀ . Repeat the above cycle charging and discharging process for the same battery above, and record the discharge capacity C _n of the battery after the nth cycle at the same time, then the battery capacity retention rate P _n = C _n /C ₀ *100% after each cycle.

8 is a test graph of the 25°C cycle capacity retention rate of the secondary battery of Example 5, and FIG. 9 is a test graph of the 25°C cycle capacity retention rate of the secondary battery of Comparative Example 3.

【5C Capacity Retention Rate Test】

At 25°C, charge the secondary battery with a constant current (CC) at a rate of 1/3C to 4.2V, then charge with a constant voltage (CV) at 4.2V to a current of 0.05C, leave it for 10 minutes, and then charge it at a rate of 1/3C Constant current discharge (DC) to 2.8V, record the discharge capacity at this time as D ₀ , let it stand for 10 minutes; constant current charge (CC) to 4.2V at a rate of 1/3C, and then charge to 4.2V constant voltage (CV) to The current is 0.05C, put it on hold for 10 minutes, and then discharge at a constant current (DC) at a rate of 5C to 2.8V, record the discharge capacity at this time as D ₁ , then the 5C capacity retention rate is η=D ₁ /D ₀ *100%.

See Table 3 for the test results of the capacity retention rates of the secondary batteries of Examples 1-14 and Comparative Examples 1-3.

【Lithium analysis test at full charge interface】

The secondary battery is formed with a certain formation process (stand still for 20min, 0.02C constant current charge to 3.0V, stand still for 5min, 0.05C constant current charge to 3.4V, stand for 5min, 0.2C constant current charge to 3.75V) Finally, after standing for 30 minutes, fully charge the above secondary battery (charging at a constant current rate of 0.33C to 4.2V, constant voltage charging to 0.05C current cut-off). Disassemble the secondary battery in a dry room (humidity<0.2%). The surface of the negative electrode is golden yellow, indicating that there is no lithium precipitation, and the surface of the negative electrode is partially silvery white, indicating that there is lithium precipitation.

Table 3 shows the test results of the lithium desorption at the fully charged interface of the secondary batteries of Examples 1-14 and Comparative Examples 1-3.

Table 1: Preparation parameters of Examples 1-14 and Comparative Examples 1-3

Table 2: Negative electrode sheet parameters of Examples 1-14 and Comparative Examples 1-3

序号serial number	负极极片翘曲高度Negative pole piece warpage height	负极膜层开裂情况Cracking of negative electrode film	负极极片优率Negative electrode excellent rate	电解液浸润速率Electrolyte Wetting Rate
实施例1Example 1	7.4mm7.4mm	不开裂no cracking	100％100%	7.8μg/s7.8μg/s
实施例2Example 2	8.3mm8.3mm	不开裂no cracking	100％100%	7.63μg/s7.63μg/s
实施例3Example 3	8.6mm8.6mm	不开裂no cracking	100％100%	7.55μg/s7.55μg/s
实施例4Example 4	8.5mm8.5mm	不开裂no cracking	100％100%	7.72μg/s7.72μg/s
实施例5Example 5	8.4mm8.4mm	不开裂no cracking	100％100%	7.65μg/s7.65μg/s
实施例6Example 6	8.9mm8.9mm	轻微开裂slightly cracked	90％90%	7.06μg/s7.06μg/s
实施例7Example 7	8.2mm8.2mm	不开裂no cracking	100％100%	7.81μg/s7.81μg/s
实施例8Example 8	7.7mm7.7mm	不开裂no cracking	100％100%	7.66μg/s7.66μg/s
实施例9Example 9	7.3mm7.3mm	不开裂no cracking	100％100%	6.35μg/s6.35μg/s
实施例10Example 10	9.5mm9.5mm	轻微开裂slightly cracked	87％87%	7.1μg/s7.1μg/s
实施例11Example 11	9.1mm9.1mm	不开裂no cracking	100％100%	7.41μg/s7.41μg/s
实施例12Example 12	7.6mm7.6mm	不开裂no cracking	100％100%	8.15μg/s8.15μg/s
实施例13Example 13	7.2mm7.2mm	不开裂no cracking	100％100%	8.3μg/s8.3μg/s
实施例14Example 14	6.7mm6.7mm	不开裂no cracking	100％100%	7.05μg/s7.05μg/s
对比例1Comparative example 1	10.2mm10.2mm	严重开裂severely cracked	69％69%	5.91μg/s5.91μg/s
对比例2Comparative example 2	12.0mm12.0mm	严重开裂severely cracked	48％48%	5.77μg/s5.77μg/s
对比例3Comparative example 3	14.0mm14.0mm	严重开裂severely cracked	54％54%	5.65μg/s5.65μg/s

Table 3: Secondary battery performance test results of Examples 1-14 and Comparative Examples 1-3

It can be seen from the pole piece parameters in Table 2 that, compared with Comparative Examples 1-3, Examples 1-14 include the adipate polybutadiene ester softener according to the present application in the negative electrode film layer, which can not only be used in ultra-thick In the case of coating, the cracking degree of the negative electrode film layer can be significantly reduced, and the electrolyte infiltration rate of the negative electrode sheet can also be increased.

It can also be seen from the test results in Table 3 and Fig. 8 and Fig. 9 that including the adipate polybutadiene ester softener according to the present application in the negative electrode film layer can not only improve the first Coulombic efficiency of the secondary battery , rate performance and capacity retention rate, and can also improve the interface performance of the secondary battery, so that the secondary battery has a lower internal resistance. However, in Comparative Examples 1-3, the above-mentioned softener was not added, and the electrochemical performance of the secondary battery was lower than that of Examples 1-14.

It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present application, embodiments that have substantially the same configuration as the technical idea and exert the same function and effect are included in the technical scope of the present application. In addition, without departing from the scope of the present application, various modifications conceivable by those skilled in the art are added to the embodiments, and other forms constructed by combining some components in the embodiments are also included in the scope of the present application. .

Claims

A negative electrode sheet, comprising a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, the negative electrode film layer includes a negative electrode active material, adipate polybutadiene ester softener and any The selected additives, the coating weight of one side of the negative electrode sheet is ≥180mg/1540.25mm 2 .
The negative electrode sheet according to claim 1, wherein the polybutadiene adipate softener is selected from compounds shown in formula 1,

In Formula 1, n is an integer ranging from 10 to 150, and the M element and the M' element are each independently selected from H or Li. Optionally, both the M element and the M' element are Li.
The negative electrode sheet according to any one of claims 1-2, wherein the weight average molecular weight of the polybutadiene adipate softener is 1600-18000, optionally 4800-18000.
The negative electrode sheet according to any one of claims 1-3, wherein, based on the total mass of the negative electrode film layer, the mass proportion of the adipate polybutadiene ester softener is 0.05wt% ~0.6wt%, optionally 0.1wt%~0.5wt%, more preferably 0.2wt%~0.5wt%.
The negative electrode sheet according to any one of claims 1-4, wherein the optional additives include conductive agents, dispersants and binders, based on the total mass of the negative electrode film layer, the amount of the conductive agent The mass proportion is 0.3wt%～3wt%, the mass proportion of the negative electrode active material is 90wt%～98wt%, the mass proportion of the adipate polybutadiene ester softener is 0.05wt%～ 0.6wt%, the mass proportion of the dispersant is 0.5wt%-3wt%, and the mass proportion of the binder is 0.5wt%-5wt%.
The negative electrode sheet according to any one of claims 1-5, wherein the thickness of the negative electrode film layer on one side is 65 μm˜125 μm.
The negative electrode sheet according to any one of claims 1-6, wherein the compacted density of the negative electrode film layer is 1.3g/cm 3 -1.7g/cm 3 .
The negative electrode sheet according to any one of claims 1-7, wherein the thickness of the negative electrode current collector is ≤8 μm, optionally 4 μm˜8 μm.
A method for preparing the negative electrode sheet according to any one of claims 1-8, comprising:

Provide slurry, which includes the negative electrode active material, the polybutadiene adipate softener and optional additives;

The preparation of the negative electrode sheet includes coating the slurry on at least one surface of the negative electrode current collector, drying and cold pressing to obtain the negative electrode sheet, and the single-sided coating of the negative electrode sheet Weight ≥ 180mg/1540.25mm 2 .
The method according to claim 9, wherein the coating speed is ≥45 m/min, optionally 45-60 m/min.
A secondary battery, comprising the negative electrode sheet according to any one of claims 1 to 8 or the negative electrode sheet produced by the method for preparing the negative electrode sheet according to claim 9 or 10.
The secondary battery according to claim 11, wherein the coating weight of one side of the positive electrode sheet of the secondary battery is 250 mg/1540.25 mm 2 to 450 mg/1540.25 mm 2 .
The secondary battery according to claim 11 or 12, wherein the positive electrode sheet of the secondary battery has a compacted density of 2.4g/cm 3 -3.7g/cm 3 .
The secondary battery according to any one of claims 11-13, wherein the thickness of the positive electrode film layer on one side of the secondary battery is 50 μm˜100 μm.
The secondary battery according to any one of claims 11-14, wherein the ratio N/P of the negative electrode capacity per unit area to the positive electrode capacity per unit area of the secondary battery satisfies: N/P=1.05˜1.15.
A battery module comprising the secondary battery according to any one of claims 11-15.
A battery pack, comprising the battery module according to claim 16.
An electric device, comprising at least one selected from the secondary battery according to any one of claims 11-15, the battery module according to claim 16, or the battery pack according to claim 17.