Negative electrode sheet and preparation method thereof, secondary battery, battery module, battery pack and power-consuming device

Abstract

The present application provides a negative electrode sheet and a preparation method thereof, a secondary battery, a battery module, a battery pack and an electric device. The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer includes a negative electrode active material, a polybutadiene adipate softener and optional additives, and the single-side coating weight of the negative electrode sheet is ≥180mg / 1540.25mm <supgt;2< / supgt;。

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a negative electrode plate and a preparation method thereof, a secondary battery, a battery module, a battery pack and an electrical device. Background Art

[0002] In recent years, as the application scope of secondary ion batteries becomes wider and wider, secondary ion batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. As secondary ion batteries have made great progress, higher requirements have been put forward for their energy density, cycle performance and safety performance.

[0003] Among them, energy density is considered to be the biggest bottleneck restricting the current development of secondary batteries. Based on this, people have conducted a lot of research on how to improve the energy density of secondary batteries. Among them, increasing the thickness of the pole piece without affecting the performance of the secondary battery is an important direction for improving the energy density of secondary batteries.

[0004] However, as the thickness of the pole piece increases, the difficulty of processing also increases. The pole piece with ultra-thick coating is prone to film cracking during the drying process. In addition, the excessive thickness of the film layer will also lead to problems such as difficulty in electrolyte infiltration and poor dynamics. Therefore, the existing pole piece still needs to be improved. Summary of the invention

[0005] The present application is made in view of the above-mentioned 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.

[0006] In order to achieve the above-mentioned objectives, the present application provides a negative electrode plate and a preparation method thereof, a secondary battery, a battery module, a battery pack and an electrical device.

[0007] The first aspect of the present application provides a negative electrode plate, comprising a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer comprises a negative electrode active material, a polybutadiene adipate-based softener and optional additives, and the single-side coating weight of the negative electrode plate is ≥180 mg / 1540.25 mm 2 .

[0008] Therefore, by including a polybutadiene adipate-based softener in the negative electrode film layer, the present application is not prone to film cracking under the condition of high coating weight, and can have a higher electrolyte infiltration speed and interface performance. The negative electrode plate of the present application is applied to a secondary battery, which can make the secondary battery have high energy density and good electrochemical performance.

[0009] In any embodiment, the polybutadiene adipate flexibilizer is selected from the compound shown in Formula 1,

[0010]

[0011] In Formula 1, n is an integer of 10 to 150, M and M' are each independently selected from H or Li, and optionally, M and M' are both Li.

[0012] The polybutadiene adipate type softener is selected from the compound shown in Formula 1, which can make the negative electrode plate have better electrolyte affinity, thereby further improving the electrolyte wetting performance and liquid retention performance of the negative electrode plate, and then improving the rate performance of the secondary battery. In addition, the polybutadiene adipate type softener shown in Formula 1 can improve the lithium ion transmission capacity of the negative electrode plate, 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 the M element and the M' element are both Li, the migration kinetics of lithium ions in the negative electrode plate can be further improved, thereby reducing the internal resistance of the secondary battery and improving the rate performance of the secondary battery.

[0013] In any embodiment, the weight average molecular weight of the polybutadiene adipate softener is 1600 to 18000, and can be 4800 to 18000. Controlling the weight average molecular weight of the polybutadiene adipate softener in the negative electrode film layer within the above appropriate range can effectively avoid cracking of the negative electrode film layer while ensuring that the secondary battery has excellent cycle performance.

[0014] In any embodiment, based on the total mass of the negative electrode film layer, the mass proportion of the polybutadiene adipate flexibilizer is 0.05wt% to 0.6wt%, optionally 0.1wt% to 0.5wt%, and more optionally 0.2wt% to 0.5wt%. When the mass proportion of the polybutadiene adipate flexibilizer in the negative electrode film layer is within the above-mentioned appropriate range, it can effectively prevent the cracking of the negative electrode film layer while making the negative electrode plate have a higher energy density, good electrolyte wettability and liquid retention, so that the secondary battery has good cycle performance and rate performance.

[0015] In any embodiment, 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 is 0.3wt% to 3wt%, the mass proportion of the negative electrode active material is 90wt% to 98wt%, the mass proportion of the polybutadiene adipate 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 0.5wt% to 5wt%. The negative electrode film layer contains the above components, and the ratio of each component is within the above appropriate range, which can not only make the negative electrode sheet have good conductivity, but also make the negative electrode film layer have a uniform thickness distribution, and make the negative electrode film layer firmly adhere to the surface of the negative electrode collector. The negative electrode film layer has the above components and component ratios, which can ensure that the secondary battery has excellent electrochemical properties and long cycle life.

[0016] In any embodiment, the thickness of the single-sided negative electrode film layer is 65 μm to 125 μm. When the thickness of the single-sided negative electrode film layer is within the above range, the secondary battery can have high volume energy density, good cycle performance, and long cycle life.

[0017] In any embodiment, the compaction density of the negative electrode film layer is 1.3 g / cm 3 ~1.7g / cm 3 The compaction density of the negative electrode film layer is within the above-mentioned suitable range, which can make the negative electrode plate have good electrolyte infiltration performance and also make the secondary battery have a smaller internal resistance, thereby improving the electrochemical performance of the secondary battery.

[0018] In any embodiment, the thickness of the negative electrode current collector is ≤8 μm, and can be 4 μm to 8 μm. The thickness of the negative electrode current collector is controlled within the above-mentioned suitable range, so that the negative electrode plate has high energy density, good conductivity and processability, thereby making the secondary battery have high energy density, good cycle performance and low processing cost.

[0019] The second aspect of the present application also provides a method for preparing a negative electrode sheet according to the first aspect of the present application, the method comprising:

[0020] Providing a slurry, the slurry comprising a negative electrode active material, a polybutadiene adipate-based softener, and optional additives;

[0021] Prepare 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 is ≥180mg / 1540.25mm 2 .

[0022] According to the method of the present application, a polybutadiene adipate-type softener is added to the negative electrode slurry, which can effectively prevent the negative electrode film from cracking during the processing of the negative electrode plate, thereby achieving ultra-thick coating of the negative electrode plate. In addition, the polybutadiene adipate-type softener is non-toxic and harmless, and does not require recycling, which can make the method of the present application have a lower cost. The negative electrode plate 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.

[0023] In any embodiment, the coating speed is ≥45 m / min, and can be 45-60 m / min. The coating speed is controlled within the above relatively high range, which can shorten the preparation time of the negative electrode sheet and improve the production efficiency of the negative electrode sheet.

[0024] 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.

[0025] The secondary battery of the present application includes the negative electrode plate of the first aspect of the present application or the negative electrode plate prepared according to the method of the second aspect of the present application, and can have high energy density, good electrochemical performance and long cycle life.

[0026] In any embodiment, the single-sided coating weight of the positive electrode sheet of the secondary battery is 250 mg / 1540.25 mm 2 ~450mg / 1540.25mm 2 The single-side coating weight of the positive electrode sheet is controlled within a suitable range, so that the positive electrode sheet has a high energy density and good electrolyte infiltration performance, thereby improving the energy density and electrochemical performance of the secondary battery.

[0027] In any embodiment, the compaction density of the positive electrode sheet of the secondary battery is 2.4 g / cm 3 ~3.7g / cm 3 The compaction density of the positive electrode sheet is within the above-mentioned suitable range, which can make the positive electrode sheet have good electrolyte infiltration performance and also make the secondary battery have a smaller internal resistance, thereby improving the electrochemical performance of the secondary battery.

[0028] In any embodiment, the thickness of the single-sided positive electrode film layer of the secondary battery is 50 μm to 100 μm. When the thickness of the positive electrode film layer is controlled within the above-mentioned appropriate range, the positive electrode sheet can have a higher volume energy density, good electrolyte wetting performance and electronic conductivity, thereby improving the volume energy density and electrochemical performance of the secondary battery.

[0029] 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 to 1.15. The ratio of the negative electrode capacity per unit area to the positive electrode capacity per unit area is within the above-mentioned appropriate range, which can ensure that both the positive and negative electrode capacities are fully utilized, thereby improving the energy density of the secondary battery.

[0030] A fourth aspect of the present application provides a battery module, comprising a secondary battery according to any embodiment of the third aspect of the present application.

[0031] A fifth aspect of the present application provides a battery pack comprising the battery module of the fourth aspect of the present application.

[0032] The sixth aspect of the present application provides an electrical device comprising at least one of a secondary battery selected from any embodiment of the third aspect of the present application, a battery module of the fourth aspect of the present application, or a battery pack of the fifth aspect of the present application.

[0033] 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of polybutadiene adipate-based softener molecules and carboxymethyl cellulose-based dispersant (CMC) molecules in one embodiment of the negative electrode plate of the present application.

[0035] Figure 2 It is a schematic diagram of an embodiment of the secondary battery of the present application.

[0036] Figure 3 yes Figure 2 An exploded view of an embodiment of a secondary battery of the present application is shown.

[0037] Figure 4 It is a schematic diagram of an embodiment of a battery module of the present application.

[0038] Figure 5 It is a schematic diagram of an embodiment of the battery pack of the present application.

[0039] Figure 6 yes Figure 5 An exploded view of an embodiment of a battery pack of the present application is shown.

[0040] Figure 7 Schematic diagram of an electrical device using the secondary battery of the present application as a power source.

[0041] Figure 8 This is a 25°C cycle capacity retention rate test graph of the secondary battery of Example 5 of the present application.

[0042] Fig. 9 This is a test chart of the 25°C cycle capacity retention rate of the secondary battery of Comparative Example 3 of the present application.

[0043] Description of reference numerals:

[0044] 01 polybutadiene adipate softener molecule; 02 CMC molecule; 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0045] Below, the negative electrode plate and its preparation method, secondary battery, battery module, battery pack and electric device of the present application are described in detail with appropriate reference to the drawings. However, there are cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are 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 present application and are not intended to limit the subject matter described in the claims.

[0046] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0047] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0048] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0049] If there is no special explanation, all steps of 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 sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0050] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0051] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": 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).

[0052] As described in the background technology, increasing the thickness of the pole piece is an important direction for improving the energy density of secondary batteries without affecting the performance of the secondary battery. However, as the thickness of the pole piece increases, its processing difficulty also increases. The pole piece with ultra-thick coating is prone to film cracking during the drying process. In addition, if the thickness of the film layer is too large, it will also lead to problems such as difficulty in electrolyte infiltration and poor dynamics.

[0053] 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 sheets.

[0054] At present, high boiling point alcohols, ethylene carbonate or other low surface tension solvents are often added to the negative electrode slurry to improve the film cracking problem. However, the above three substances each have their own shortcomings.

[0055] High-boiling-point alcohols easily absorb water and are difficult to completely volatilize, and remain in the electrode, causing the subsequent baking process to consume too much time and economic costs, reducing production capacity. In addition, due to the poor compatibility of high-boiling-point alcohols with the electrolyte, it will make it difficult for the electrolyte to infiltrate, and even hinder the electrochemical reaction, causing lithium precipitation in the negative electrode, which in turn leads to safety hazards.

[0056] Ethylene carbonate is a solid substance at room temperature and needs to be pre-dissolved before mixing 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 some of it remains in the pole piece. The residual ethylene carbonate cannot be completely dissolved in the electrolyte, thus increasing the interfacial charge transfer impedance, worsening the interfacial dynamics, and even causing lithium precipitation, seriously affecting the safety performance of the secondary battery. What is more serious is that when the amount of ethylene carbonate added is too large, the amount of pole piece residue will increase. Since the material is a crystalline substance, there is a risk of difficulty in cold pressing during the pole piece processing.

[0057] Low surface tension solvents, such as isopropyl alcohol, ethyl acetate, etc., generally need to be added in larger amounts to improve the cracking of the film layer. Adding too much 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 low surface tension solvents to the negative electrode slurry will, on the one hand, aggravate the floating of the binder during the drying process of the pole piece, thereby causing the risk of powder loss in the later stage of the pole piece; on the other hand, the boiling point of low surface tension solvents is usually lower than that of water, which can easily lead to over-drying during the drying process of the pole piece, and then cause cracking of the edge of the pole piece.

[0058] In view of this, the inventors conducted in-depth research and selected a suitable softener, and provided a negative electrode plate and a preparation method thereof, a secondary battery, a battery module, a battery pack and an electrical device.

[0059] Negative electrode

[0060] The first aspect of the present application provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer comprises a negative electrode active material, a polybutadiene adipate-based softener and optional additives, and the single-side coating weight of the negative electrode sheet is ≥180 mg / 1540.25 mm 2 .

[0061] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0062] Although the mechanism is not yet clear, the inventor unexpectedly discovered that the present application, by adding a polybutadiene adipate-based softener to the negative electrode film layer, can not only effectively reduce the cracking of the negative electrode film layer under ultra-thick coating, but also reduce the difficulty of wetting the negative electrode plate, thereby enabling the secondary battery to have high energy density and good electrochemical performance.

[0063] Specifically, the inventors found that the polybutadiene adipate softener has good solubility in the aqueous solvent system and can be evenly dispersed in the negative electrode slurry system, so that it can be evenly present in the negative electrode film layer. In addition, the negative electrode slurry with the polybutadiene adipate softener has good solubility in the aqueous solvent system and can be evenly dispersed in the negative electrode slurry system, so that it can be evenly present in the negative electrode film layer. In addition, even if the single-sided coating weight is ≥180mg / 1540.25mm 2 In this case, during the drying process of the electrode, the negative electrode film rarely cracks.

[0064] In general, during the drying process of the negative electrode sheet, there is surface tension and capillary force of the curved liquid surface of the water in the negative electrode film layer. When carboxymethyl cellulose dispersants (CMC) are added to the negative electrode film layer, there will also be a force of CMC drying shrinkage in the negative electrode film layer. These surface tensions, capillary forces and drying shrinkage forces will cause the material particles in the negative electrode film layer to move closer to each other 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 and generate stress, causing the electrode sheet to warp. Cracks are generated at the bend in the middle area of ​​the film layer due to insufficient toughness. In addition, the curled edge of the electrode sheet is flattened when it passes over the roller. At this time, cracks are also generated due to insufficient toughness of the negative electrode sheet. The greater the degree of curling and warping, the more obvious the crack phenomenon.

[0065] Without intending to be bound by any theory or explanation, the inventors have found that when polybutadiene adipate-based softeners are added to the negative electrode slurry, the polybutadiene adipate-based softeners can react with the moisture in the negative electrode film layer, 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 degree of cracking of the negative electrode film layer. In addition, when CMC is added to the negative electrode film layer, the polybutadiene adipate-based softener can be evenly dispersed between the CMC molecules. Figure 1 As shown, the polybutadiene adipate-based softener molecules 01 can be evenly dispersed between the CMC molecules 02, thereby increasing the distance between the CMC molecules, improving the rotation and twisting capabilities of the CMC molecular chain, and thereby increasing the flexibility of the negative electrode film layer and avoiding cracking of the negative electrode film layer. Furthermore, the polar groups in polybutadiene adipate can also interact with the groups in the CMC molecules, reducing the connection points between the CMC molecules, replacing the effects between the CMC molecules, thereby weakening the strong forces between the CMC molecules, reducing the degree of warping during the drying process of the pole piece, and thereby reducing the risk of cracking of the negative electrode film layer during the drying and cold pressing of the pole piece.

[0066] In addition, the inventors have also found that polybutadiene adipate-based softeners have good electrolyte affinity and can increase the electrolyte infiltration rate of the negative electrode plate. The negative electrode plate has a high electrolyte infiltration rate, which can shorten the infiltration time of the negative electrode plate, reduce manufacturing costs, and increase production capacity on the one hand; on the other hand, it can improve the interface performance of the electrode assembly in the secondary battery, improve the interface dynamics and the cycle performance of the secondary battery. Polybutadiene adipate-based softeners are present in the negative electrode film layer, will not reduce the electrochemical performance of the secondary battery, are non-toxic and harmless, and do not require recycling. In this way, the manufacturing cost required to produce the negative electrode plate of the present application can be reduced.

[0067] According to the negative electrode plate of the present application, the negative electrode film layer contains a polybutadiene adipate softener, and the film layer is not prone to cracking under the condition of high coating weight, and can have a higher electrolyte infiltration speed and interface performance. The negative electrode plate of the present application is applied to a secondary battery, which can make the secondary battery have high energy density and good electrochemical performance.

[0068] In the present application, the polybutadiene adipate esters refer to the esterification products of terminal hydroxyl polybutadiene and adipic acid, which contain a polybutadiene molecular skeleton and esterified end groups of adipic acid and terminal hydroxyl groups.

[0069] In some embodiments, the polybutadiene adipate flexibilizer may be selected from the compounds shown in Formula 1,

[0070]

[0071] 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, the M element and the M' element are both Li.

[0072] It is easy to understand that when the M element or M' element is H, the H atom and the O atom can be connected in the form of a covalent bond. When the M element or M' element is Li, Li + With —COO - They can be connected in the form of ionic bonds.

[0073] The polybutadiene adipate softener shown in Formula 1 can be obtained in a variety of ways, and this application is not particularly limited to this. In some embodiments, the polybutadiene adipate softener can be obtained by homemade methods. 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 this application, not for limiting this application.

[0074] As an example, when both the M element and the M' element are H, the adipic acid polybutadiene ester softener can be obtained by reacting adipic acid and terminal hydroxyl polybutadiene in the presence of an esterification catalyst under reaction conditions. In one embodiment, the catalyst can be an acid catalyst, such as sulfuric acid or hydrochloric acid, and the reaction conditions can be an inert atmosphere condition, such as N2 atmosphere, and a temperature condition of 60 to 80°C.

[0075] As an example, when at least one of the M element and the M′ element is Li, the polybutadiene adipate-based softener can be prepared by the following steps S110 and S120 .

[0076] S110, mixing adipic acid, hydroxyl-terminated polybutadiene and a catalyst for esterification reaction under reaction conditions to allow adipic acid and hydroxyl-terminated polybutadiene to undergo esterification reaction, thereby obtaining an esterification reaction product;

[0077] S120, mixing the esterification reaction product with LiOH to allow the esterification reaction product and LiOH to undergo a neutralization reaction to obtain a polybutadiene adipate-based softener in which at least one of the M element and the M′ element is Li.

[0078] The catalyst may be an acid catalyst, such as sulfuric acid or hydrochloric acid, and the reaction conditions may be an inert atmosphere, such as N2 atmosphere, and a temperature of 60 to 80°C.

[0079] The polybutadiene adipate flexibilizer is selected from the compound 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 plate, thereby improving the rate performance of the secondary battery. In addition, the polybutadiene adipate flexibilizer shown in Formula 1 has a strong electronegativity in the ester group in its molecule, which is conducive to improving the lithium ion transmission capacity, thereby further improving the cycle performance of the secondary battery.

[0080] Furthermore, compared with the case where H exists in M ​​element and M' element, when M element and M' element are both Li, on the one hand, the carboxyl group can be prevented from reacting at a low potential and converting into -COOLi and producing hydrogen, thereby avoiding the loss of active ions and the increase of gas production, thereby avoiding affecting the initial coulombic efficiency and safety performance of the secondary battery; on the other hand, Li + Through ionic bond with —COO - Connection can improve the lithium ion conductivity of the negative electrode film layer, thereby improving the migration kinetics of lithium ions in the negative electrode plate, thereby reducing the internal resistance of the secondary battery and improving the rate performance of the secondary battery.

[0081] The present application does not impose any particular limitation on the weight average molecular weight of the polybutadiene adipate based softener.

[0082] In some embodiments, the weight average molecular weight of the polybutadiene adipate-based softener may be 1,600 to 18,000, 4,800 to 18,000, 4,800 to 13,800, or 4,800 to 9,200.

[0083] Without intending to be limited by any theory or explanation, the inventors have found that the weight average molecular weight of the polybutadiene adipate flexibilizer is within the above range, which can ensure that the polybutadiene adipate flexibilizer molecules are evenly dispersed between the CMC molecules, so that the CMC molecules have a suitable distance, thereby weakening the strong interaction between the CMC molecules, improving the rotation and twisting ability of the CMC molecular chain, and thus giving full play to the effect of improving the cracking of the negative electrode film layer. In addition, the weight average molecular weight of the polybutadiene adipate flexibilizer is within the above range, which can also make the negative electrode plate have better lithium ion migration kinetics, prevent the active lithium ions from being blocked in the cycle process, and thus avoid the increase of the impedance of the secondary battery.

[0084] In the embodiment of the present application, by including a polybutadiene adipate-based softener having a weight average molecular weight within 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 that the secondary battery has excellent cycle performance.

[0085] In some embodiments, based on the total mass of the negative electrode film layer, the mass proportion of the polybutadiene adipate flexibilizer may be 0.05wt% to 0.6wt%, 0.1wt% to 0.6wt%, 0.1wt% to 0.5wt%, 0.2wt% to 0.5wt%, 0.25wt% to 0.5wt%. Alternatively, the mass proportion of the polybutadiene adipate flexibilizer may be 0.1wt% to 0.5wt%, and more optionally, the mass proportion of the polybutadiene adipate flexibilizer may be 0.2wt% to 0.5wt%.

[0086] Without intending to be limited by any theory or explanation, the inventors have found that when the mass proportion of polybutadiene adipate-based softeners in the negative electrode film layer is within the above-mentioned appropriate range, it is able to effectively prevent the negative electrode film layer from cracking while allowing the negative electrode plate to have a higher energy density, good electrolyte wettability and liquid retention, thereby allowing the secondary battery to have good cycle performance and rate performance.

[0087] 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 may be 0.3wt% to 3wt%, the mass proportion of the negative electrode active material may be 90wt% to 98wt%, the mass proportion of the polybutadiene adipate softener may be 0.05wt% to 0.6wt%, the mass proportion of the dispersant may be 0.5wt% to 3wt%, and the mass proportion of the binder may be 0.5wt% to 5wt%.

[0088] 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.

[0089] In some embodiments, the dispersant may be selected from CMC-based dispersants, such as CMC-Li, CMC-Na, and the like.

[0090] In some embodiments, the binder can be selected from at least one of 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).

[0091] The negative electrode film layer contains the above components, and the ratio of each component is within the above appropriate range, which can not only make the negative electrode sheet have good conductivity, but also make the negative electrode film layer have a uniform thickness distribution, and make the negative electrode film layer firmly adhere to the surface of the negative electrode current collector. The negative electrode film layer has the above components and component ratios, which can ensure that the secondary battery has excellent electrochemical performance and long cycle life.

[0092] In some embodiments, the thickness of the single-sided negative electrode film layer may be 65 μm to 125 μm, 70 μm to 120 μm, 75 μm to 115 μm, 80 μm to 110 μm, or 85 μm to 105 μm.

[0093] When the thickness of the single-sided negative electrode film layer is controlled within an appropriate range, the negative electrode plate can have a higher volume energy density, a higher electrolyte infiltration rate, and a lower internal resistance, and can effectively reduce the risk of the negative electrode film layer falling off in the later stage of the cycle. When the thickness of the single-sided negative electrode film layer is within the above range, the secondary battery can have a high volume energy density, good cycle performance, and a long cycle life.

[0094] In some embodiments, the compaction density of the negative electrode film layer can be 1.3 g / 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 ~1.5g / cm 3 .

[0095] If the compaction density is too large, the material particles in the negative electrode film layer will be in too close contact, making it difficult for the electrolyte to infiltrate the material particles, and the active ions will not be able to 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 and affecting the electrochemical performance of the secondary battery. When the compaction density of the negative electrode film layer is within the above-mentioned appropriate range, the negative electrode sheet can have good electrolyte infiltration performance, and the secondary battery can have a smaller internal resistance, thereby improving the electrochemical performance of the secondary battery.

[0096] 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 to 8 μm. More specifically, the thickness of the negative electrode current collector may be 4.5 μm, 6 μm, or 8 μm.

[0097] The smaller the thickness of the negative electrode current collector, the higher the energy density of the negative electrode plate, but correspondingly, the conductivity and mechanical properties of the negative electrode plate will decrease. According to the negative electrode plate of the present application, a polybutadiene adipate-based softener is included in the negative electrode film layer, so that the negative electrode plate can maintain good mechanical properties even if the thickness of the negative electrode current collector is small, thereby preventing the negative electrode plate from warping during processing, and further preventing the negative electrode film layer from cracking. According to the thickness of the negative electrode current collector of the negative electrode plate of the present application is controlled within the above-mentioned appropriate range, the negative electrode plate can have high energy density, good conductivity and processability, so that the secondary battery has high energy density, good cycle performance and low processing cost.

[0098] It should be noted that the present application does not particularly limit the material of the negative electrode current collector. In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0099] 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 may be a negative electrode active material for a battery known in the art. 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 materials, tin-based materials, lithium titanate, and the like. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0100] In some embodiments, the negative electrode film layer may also optionally include other additives, such as a wetting aid, a dispersing aid, a viscosity increasing aid, an electrolyte infiltration aid, and the like.

[0101] It should be noted that the negative electrode plate of the present application does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode plate described in the present application may also include a conductive primer layer (e.g., composed of a conductive agent and a binder) disposed between the negative electrode current collector and the negative electrode film layer. In other embodiments, the negative electrode plate described in the present application also includes a protective layer covering the surface of the negative electrode film layer.

[0102] In the present application, the thickness of the negative electrode film layer has a well-known meaning in the art and can be tested by methods known in the art, such as using a micrometer (such as Mitutoyo 293-100, with an accuracy of 0.1 μm) for testing.

[0103] In the present application, the compaction density of the negative electrode film layer has a meaning well known in the art and can be tested by methods known in the art. The compaction density of the negative electrode film layer = the surface density of the negative electrode film layer / the thickness of the negative electrode film layer. Among them, the surface density of the negative electrode film layer has a meaning well known in the art and can be tested by methods known in the art. For example, take a single-sided coated and cold-pressed negative electrode pole piece, punch it into small discs with an area of ​​S1, weigh it, and record it as M1; the uncoated negative electrode current collector is also punched into small discs with an area of ​​S1, weigh the weight of the negative electrode current collector, and record it as M0; the surface density of the negative electrode film layer = (the weight of the negative electrode pole piece M1-the weight of the negative electrode current collector M0) / S1 (if it is a double-sided coated negative electrode pole piece, the surface density of the negative electrode film layer = (the weight of the negative electrode pole piece M1-the weight of the negative electrode current collector M0) / 2S1).

[0104] It should be noted that the above-mentioned various parameter tests on the negative electrode film layer or the negative electrode active material can be conducted by sampling during the battery preparation process or by sampling from a prepared secondary battery.

[0105] When the test sample is sampled from a prepared secondary battery, as an example, the sampling can be performed according to the following steps (1) to (3).

[0106] (1) Discharge the secondary battery (for safety reasons, the battery is generally fully discharged); disassemble the battery and remove the negative electrode sheet, and soak the negative electrode sheet in dimethyl carbonate (DMC) for a certain period of time (e.g., 2 to 10 hours); then remove the negative electrode sheet and dry it at a certain temperature and time (e.g., 60°C, 4 hours), and then remove the negative electrode sheet after drying. At this point, the dried negative electrode sheet can be sampled to test the various parameters related to the negative electrode film layer described above in this application.

[0107] (2) The negative electrode sheet dried in step (1) is baked at a certain temperature and time (e.g., 400° C., 2 hours), and a region of the baked negative electrode sheet is selected to sample the negative electrode active material (sampling can be performed by scraping powder with a blade).

[0108] (3) The negative electrode active material collected in step (2) is sieved (for example, sieved with a 200-mesh sieve) to finally obtain a sample that can be used to test the parameters of the negative electrode active material mentioned above in the present application.

[0109] Method for preparing negative electrode sheet

[0110] The second aspect of the present application provides a method for preparing the negative electrode plate of the present application, comprising step S210, providing a slurry, wherein the slurry includes a negative electrode active material, a polybutadiene adipate-based softener according to the first aspect of the present application, and optional additives.

[0111] The negative electrode active material may be a negative electrode active material for a battery known in the art. 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 materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0112] In some embodiments, the optional additives may further include a binder. The binder may be selected from at least one of 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).

[0113] In some embodiments, the optional additives may further include a conductive agent. 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.

[0114] In some embodiments, the optional additives may further include other auxiliary agents, such as a dispersant (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0115] The providing of the slurry may specifically include dispersing the components for preparing the negative electrode slurry in a solvent (eg, deionized water) to form the negative electrode slurry.

[0116] The method of the present application also includes step S220, preparing a negative electrode sheet, including coating the slurry on at least one surface of the negative electrode current collector, drying and cold pressing to obtain a negative electrode sheet, and the single-side coating weight of the negative electrode sheet is ≥180mg / 1540.25mm 2 .

[0117] According to the method of the present application, a polybutadiene adipate-type softener is added to the negative electrode slurry, which can effectively prevent the negative electrode film from cracking during the processing of the negative electrode plate, thereby achieving ultra-thick coating of the negative electrode plate. In addition, the polybutadiene adipate-type softener is non-toxic and harmless, and does not require recycling, which can make the method of the present application have a lower cost. The negative electrode plate 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.

[0118] In some embodiments, the coating speed may be ≥45 m / min, specifically, the coating speed may be 45-65 m / min, 45-60 m / min, 45-55 m / min, 45-55 m / min.

[0119] According to the method of the present application, a polybutadiene adipate ester softener is added to the negative electrode slurry, and even at a higher coating speed, it is not easy to cause the negative electrode film layer to crack due to the bending of the electrode sheet. The coating speed is controlled within the above-mentioned higher range, which can shorten the preparation time of the negative electrode sheet and improve the production efficiency of the negative electrode sheet.

[0120] In addition, the secondary battery, battery module, battery pack, and electric device of the present application will be described below with reference to the drawings as appropriate.

[0121] In one embodiment of the present application, a secondary battery is provided.

[0122] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting active ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing active ions to pass through.

[0123] [Positive electrode]

[0124] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes the positive electrode active material of the first aspect of the present application.

[0125] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0126] In some embodiments, the single-sided coating weight of the positive electrode sheet can be 250 mg / 1540.25 mm 2 ~450mg / 1540.25mm 2 , 280mg / 1540.25mm 2 ~420mg / 1540.25mm 2 , 300mg / 1540.25mm 2 ~400mg / 1540.25mm 2 , 350mg / 1540.25mm 2 ~400mg / 1540.25mm 2 .

[0127] Controlling the single-sided coating weight of the positive electrode sheet within an appropriate range can enable the positive electrode sheet to have a high energy density and good electrolyte infiltration performance, thereby improving the energy density and electrochemical performance of the secondary battery.

[0128] In some embodiments, the compaction density of the positive electrode sheet can be 2.4 g / cm 3 ~3.7g / cm 3 , 2.5g / cm 3 ~3.5g / cm 3 , 2.8g / cm 3 ~3.2g / cm 3 .

[0129] The compaction density of the positive electrode sheet is within the above-mentioned suitable range, which can make the positive electrode sheet have good electrolyte infiltration performance and also make the secondary battery have a smaller internal resistance, thereby improving the electrochemical performance of the secondary battery.

[0130] In some embodiments, the thickness of the single-sided positive electrode film layer may be 50 μm to 100 μm, 60 μm to 90 μm, 70 μm to 90 μm, or 70 μm to 80 μm.

[0131] When the thickness of the positive electrode film layer is controlled within the above-mentioned appropriate range, the positive electrode plate can have a higher volume energy density, good electrolyte wetting performance and electronic conductivity performance, thereby improving the volume energy density and electrochemical performance of the secondary battery.

[0132] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may 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 may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0133] The present application does not particularly limit the type of positive electrode active material, and the positive electrode active material may be a positive electrode active material for a battery that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may 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 oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), 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 O2 (also referred to as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 )、LiNi0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds, etc. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0134] In some embodiments, the positive electrode active material may include LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), LiNi 0.8 Co 0.15 Al 0.05 O2 (also referred to as NCA), lithium cobalt oxide (such as LiCoO2, referred to as LCO), LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), at least one of lithium iron phosphate (LiFePO4).

[0135] The positive electrode active material selected from the above types has a high energy density, and when applied to the secondary battery of the present application, the theoretical capacity of the negative electrode plate can be fully utilized, and the secondary battery can have a high energy density.

[0136] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0137] In some embodiments, the positive electrode film layer may further include a conductive agent, which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0138] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the 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 collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0139] [Negative electrode]

[0140] The negative electrode sheet is selected from the negative electrode sheet according to any embodiment of the first aspect of the present application.

[0141] [Electrolytes]

[0142] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0143] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0144] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0145] In some embodiments, the solvent can be selected from at least one of 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, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0146] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0147] [Isolation film]

[0148] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

[0149] In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0150] 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 may satisfy: N / P = 1.05 to 1.15. Specifically, N / P may be 1.05, 1.1, 1.12, or 1.15.

[0151] The ratio of the negative electrode capacity per unit area to the positive electrode capacity per unit area is within the above-mentioned appropriate range, which can ensure that both the positive and negative electrode capacities are fully utilized, thereby improving the energy density of the secondary battery.

[0152] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0153] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0154] In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0155] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 2 The secondary battery 5 is a square structure as an example.

[0156] In some embodiments, reference Figure 3, the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The 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.

[0157] In some embodiments, secondary batteries may be assembled into a battery module. The number of secondary batteries contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

[0158] Figure 4 4 is an example of a battery module. Figure 4 In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.

[0159] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0160] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

[0161] Figure 5 and Figure 6 As an example, a battery pack 1 is shown. Figure 5 and Figure 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 modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0162] In addition, the present application also provides an electrical 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 for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0163] As the electrical device, a secondary battery, a battery module or a battery pack may be selected according to its usage requirements.

[0164] Figure 7 The power consumption device is taken as an example. The power consumption 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 power consumption device for the secondary battery, a battery pack or a battery module can be used.

[0165] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0166] Example

[0167] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0168] Examples 1 to 14

[0169]

Preparation of negative electrode sheet

[0170] The negative electrode active material graphite, conductive carbon, dispersant CMC-Na, binder SBR, and polybutadiene adipate type softener are fully stirred and mixed in a deionized water solvent system in a certain proportion to obtain a negative electrode slurry, wherein, based on the solid content of the negative electrode slurry as 100wt%, the mass proportion of the negative electrode active material graphite is A, the mass proportion of the conductive carbon is 0.7wt%, the mass proportion of the thickener CMC-Na is 1wt%, the mass proportion of the binder SBR is 1.5wt%, and the mass proportion of the polybutadiene adipate type softener is B. The negative electrode slurry is evenly coated on the Cu foil at a coating speed of 60m / min, and the single-sided coating weight is controlled to be within a certain range of the single-sided coating weight CW. After oven drying, cold pressing, and slitting, the negative electrode plate is obtained, and the compaction density of the plate is controlled to be 1.65g / cm 3 .

[0171] In each embodiment, the mass proportion of the negative electrode active material in the negative electrode film layer A, the element types of M and M' in the polybutadiene adipate flexibilizer molecule, the weight average molecular weight M of the polybutadiene adipate flexibilizer w , the mass proportion B in the negative electrode film layer, and the coating weight CW are not exactly the same. The specific preparation parameters are shown in Table 1.

[0172]

Preparation of positive electrode

[0173] The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2, conductive carbon SP, conductive graphite, binder PVDF, and dispersant were fully stirred and mixed in N-methylpyrrolidone solvent system in a weight ratio of 96.94:1.7:0.3:1:0.06, and then evenly coated on Al foil. After oven drying, cold pressing, and slitting, the positive electrode sheet was obtained. The compaction density of the electrode sheet was controlled to be 3.45g / cm 3 , N / P value is controlled at 1.1.

[0174]

Preparation of electrolyte

[0175] In a dry argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), the organic solvents propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) were mixed in a weight ratio of 1:1:1, and fully dried lithium salt LiPF6 was added to dissolve in the above organic solvents. After fully stirring and mixing, an electrolyte with a lithium salt concentration of 1.15 mol / L was obtained.

[0176]

Isolation film

[0177] Polypropylene film is used as the isolation film.

[0178]

Preparation of secondary batteries

[0179] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is between the positive and negative electrode sheets to play an isolating role, and then they are wound to obtain an electrode assembly, the electrode lugs are welded to the electrode assembly, and the electrode assembly is placed in an aluminum shell, baked at 80°C to remove water, and then the electrolyte is injected and sealed. Then, the lithium-ion battery is prepared through the processes of standing, hot and cold pressing, formation, and shaping.

[0180] Comparative Examples 1 to 3

[0181] The preparation of the negative electrode sheet, the preparation of the positive electrode sheet, the preparation of the electrolyte, the isolation membrane used, and the preparation of the secondary battery are the same as those in Examples 1 to 14, except that no softener is added. The specific preparation parameters are detailed in Table 1.

[0182] Test Section

[0183]

Viscosity test of negative electrode slurry

[0184] The viscosity of the negative electrode slurries in the above Examples 1 to 14 and Comparative Examples 1 to 3 was tested, and the specific test method is as follows:

[0185] Use a rotational viscometer, select the rotor according to the sample viscosity, use the viscometer lifting frame to slowly lower the viscometer, immerse the rotor in the slurry until the mark on the rotor is level with the liquid surface, test temperature: 25°C, speed: 12rpm, press the measurement key to start measuring, and read the viscosity value after the data remains stable for 5 minutes.

[0186] The viscosity of the negative electrode slurries in Examples 1 to 14 and Comparative Examples 1 to 3 is shown in Table 1.

[0187] [Negative electrode warping height test]

[0188] Bake the wet film negative electrode sheet after single-sided coating at 100℃ for 1min to remove most of the water; then cut it into 10 pieces of 4cm*4cm negative electrode sheets; then place the cut negative electrode sheets on a heating plate with a temperature stabilized at 120℃ for 1min, and use a ruler to measure the height of the four corners of each negative electrode sheet, which are recorded as h1, h2, h3, and h4 respectively. Calculate the average value of h1, h2, h3, and h4 corresponding to each negative electrode sheet, and record it as H. Take the average value H corresponding to the 10 negative electrode sheets as the warping height of the negative electrode sheet.

[0189] The test results of the negative electrode warping height of Examples 1 to 14 and Comparative Examples 1 to 3 are shown in Table 2.

[0190] [Negative electrode film cracking test]

[0191] After the negative electrode sheet is dried, directly observe whether cracks occur at the edge and middle of the negative electrode film layer.

[0192] The test results of the cracking of the negative electrode film layers of Examples 1 to 14 and Comparative Examples 1 to 3 are shown in Table 2.

[0193] [Negative electrode quality test]

[0194] The negative electrode sheets after drying and cold pressing are cut, and the number of negative electrode sheets obtained is recorded as n, among which the number of negative electrode sheets that are cracked and cannot be used to prepare secondary batteries is recorded as m. The quality rate of the negative electrode sheet is defined as: (1-m / n)*100%.

[0195] The test results of the negative electrode plate quality rate of Examples 1 to 14 and Comparative Examples 1 to 3 are shown in Table 2.

[0196]

Electrolyte wetting rate test

[0197] The capillary method is used to quantitatively test the electrode wetting rate. A certain amount of electrolyte is absorbed and contacted with the surface of the negative electrode. Under the capillary force, the electrolyte in the capillary is sucked out, and the time when the electrolyte is completely absorbed is recorded. The absorption rate can be calculated based on the amount of electrolyte absorbed and the wetting time.

[0198] The electrolyte infiltration rate test results of the negative electrode plates of Examples 1 to 14 and Comparative Examples 1 to 3 are shown in Table 2.

[0199]

First Coulomb efficiency test

[0200] At 25°C, the formed secondary battery was first discharged at a constant current rate of 1 / 3C (DC) to 2.8V and allowed to stand for 10 min; then charged at a constant current rate of 1 / 3C (CC) to 4.2V, then charged at a constant voltage rate of 4.2V (CV) to a current of 0.05C, allowed to stand for 10 min, and the charging capacity was recorded; then discharged at a constant current rate of 1 / 3C (DC) to 2.8V, and the discharge capacity was recorded.

[0201] First coulombic efficiency = discharge capacity / charge capacity*100%

[0202] The first coulombic efficiency test results of the secondary batteries of Examples 1 to 14 and Comparative Examples 1 to 3 are shown in Table 3.

[0203] 【50% SOC discharge DC resistance DCR test】

[0204] At 25°C, the secondary battery was charged at a constant current rate (CC) of 1 / 3C to 4.2V, and then charged at a constant voltage rate (CV) of 4.2V to a current of 0.05C, and left for 5 minutes. Then, it was discharged at a rate of 1 / 3C (DC) for 90 minutes, the electrode assembly was adjusted to 50% SOC, and left for 60 minutes, and then discharged at a rate of 3C (DC) for 30S, and the 50% SOC discharge DCR was obtained according to the test data.

[0205] The 50% SOC discharge DCR test results of the secondary batteries of Examples 1 to 14 and Comparative Examples 1 to 3 are shown in Table 3.

[0206]

Capacity retention rate test

[0207] At 25°C, the secondary battery is charged at a constant current rate of 0.5C (CC) to 4.2V, then charged at a constant voltage rate of 4.2V (CV) to a current of 0.05C, left for 5 minutes, and then discharged at a rate of 0.5C (DC) to 2.8V. This is a cycle charge and discharge process. The discharge capacity at this time is recorded as the initial capacity C0. Repeat the above cycle charge and discharge process for the same battery, and record the discharge capacity C0 of the battery after the nth cycle. n , then the battery capacity retention rate P after each cycle n =C n / C0*100%.

[0208] Figure 8 This is a test graph of the 25°C cycle capacity retention rate of the secondary battery of Example 5. Fig. 9 This is a test chart of the 25°C cycle capacity retention rate of the secondary battery of Comparative Example 3.

[0209] 【5C capacity retention rate test】

[0210] At 25°C, the secondary battery is charged at a constant current rate of 1 / 3C (CC) to 4.2V, then charged at a constant voltage rate of 4.2V (CV) to a current of 0.05C, left for 10 minutes, and then discharged at a constant current rate of 1 / 3C (DC) to 2.8V, and the discharge capacity at this time is recorded as D0, and left for 10 minutes; charged at a constant current rate of 1 / 3C (CC) to 4.2V, then charged at a constant voltage rate of 4.2V (CV) to a current of 0.05C, left for 10 minutes, and then discharged at a constant current rate of 5C (DC) to 2.8V, and the discharge capacity at this time is recorded as D1, then the 5C capacity retention rate is η = D1 / D0*100%

[0211] The test results of the capacity retention rate of the secondary batteries of Examples 1 to 14 and Comparative Examples 1 to 3 are shown in Table 3.

[0212]

Lithium deposition test on full charge interface

[0213] After the secondary battery is formed with a certain formation process (standing for 20 minutes, 0.02C constant current charging to 3.0V, standing for 5 minutes, 0.05C constant current charging to 3.4V, standing for 5 minutes, 0.2C constant current charging to 3.75V), the secondary battery is fully charged (0.33C constant current charging to 4.2V, constant voltage charging to 0.05C current cutoff) after standing for 30 minutes. The secondary battery is disassembled in a drying room (humidity <0.2%). The negative electrode surface is golden yellow, indicating that there is no lithium precipitation, and the negative electrode surface is partially silvery white, indicating that there is lithium precipitation.

[0214] The test results of lithium plating on the fully charged interface of the secondary batteries of Examples 1 to 14 and Comparative Examples 1 to 3 are shown in Table 3.

[0215] Table 1: Preparation parameters of Examples 1 to 14 and Comparative Examples 1 to 3

[0216]

[0217] Table 2: Negative electrode sheet parameters of Examples 1 to 14 and Comparative Examples 1 to 3

[0218] Serial number Negative electrode warping height Negative electrode film cracking Negative electrode quality rate Electrolyte wetting rate Example 1 7.4mm No cracking 100％ 7.8 μg / s Example 2 8.3mm No cracking 100％ 7.63 μg / s Example 3 8.6mm No cracking 100％ 7.55 μg / s Example 4 8.5mm No cracking 100％ 7.72 μg / s Example 5 8.4mm No cracking 100％ 7.65 μg / s Example 6 8.9mm Slight cracking 90％ 7.06 μg / s Example 7 8.2mm No cracking 100％ 7.81 μg / s Example 8 7.7mm No cracking 100％ 7.66 μg / s Example 9 7.3mm No cracking 100％ 6.35 μg / s Example 10 9.5mm Slight cracking 87％ 7.1 μg / s Embodiment 11 9.1mm No cracking 100％ 7.41 μg / s Example 12 7.6mm No cracking 100％ 8.15 μg / s Embodiment 13 7.2mm No cracking 100％ 8.3 μg / s Embodiment 14 6.7mm No cracking 100％ 7.05 μg / s Comparative Example 1 10.2mm Severe cracking 69％ 5.91 μg / s Comparative Example 2 12.0mm Severe cracking 48％ 5.77 μg / s Comparative Example 3 14.0mm Severe cracking 54％ 5.65 μg / s

[0219] Table 3: Secondary battery performance test results of Examples 1 to 14 and Comparative Examples 1 to 3

[0220]

[0221] It can be seen from the electrode parameters in Table 2 that, relative to Comparative Examples 1 to 3, Examples 1 to 14 include the polybutadiene adipate-based softener according to the present application in the negative electrode film layer, which can not only significantly reduce the degree of cracking of the negative electrode film layer in the case of ultra-thick coating, but also increase the electrolyte infiltration rate of the negative electrode plate.

[0222] From Table 3 and Figure 8 , Fig. 9 The test results also show that the inclusion of the polybutadiene adipate-based softener according to the present application in the negative electrode film layer can not only improve the initial coulombic efficiency, rate performance and capacity retention rate of the secondary battery, but also improve the interface performance of the secondary battery, so that the secondary battery has a lower internal resistance. In Comparative Examples 1 to 3, the above-mentioned softener was not added, and the electrochemical performance of the secondary battery was reduced compared with Examples 1 to 14.

[0223] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A negative electrode plate, characterized in that: It comprises a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, wherein the negative electrode film layer comprises a negative electrode active material, a polybutadiene adipate softener and optional additives, and the single-side coating weight of the negative electrode sheet is ≥180mg / 1540.25mm 2 ; The polybutadiene adipate flexibilizer is selected from the compound shown in 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.

2. The negative electrode sheet according to claim 1, characterized in that: Both the M element and the M' element are Li.

3. The negative electrode sheet according to claim 1, characterized in that: The weight average molecular weight of the polybutadiene adipate flexibilizer is 1,600 to 18,000.

4. The negative electrode sheet according to claim 3, characterized in that: The weight average molecular weight of the polybutadiene adipate flexibilizer is 4800-18000.

5. The negative electrode sheet according to claim 1, characterized in that: Based on the total mass of the negative electrode film layer, the mass proportion of the polybutadiene adipate-based softener is 0.05wt% to 0.6wt%.

6. The negative electrode sheet according to claim 5, characterized in that: Based on the total mass of the negative electrode film layer, the mass proportion of the polybutadiene adipate-based softener is 0.1wt% to 0.5wt%.

7. The negative electrode sheet according to claim 5, characterized in that: Based on the total mass of the negative electrode film layer, the mass proportion of the polybutadiene adipate-based softener is 0.2wt% to 0.5wt%.

8. The negative electrode sheet according to claim 1, characterized in that: 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 is 0.3wt% to 3wt%, the mass proportion of the negative electrode active material is 90wt% to 98wt%, the mass proportion of the polybutadiene adipate 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 0.5wt% to 5wt%.

9. The negative electrode sheet according to claim 1, characterized in that: The thickness of the negative electrode film layer on one side is 65 μm to 125 μm.

10. The negative electrode sheet according to claim 1, characterized in that: The compaction density of the negative electrode film layer is 1.3 g / cm 3 ~1.7g / cm 3 .

11. The negative electrode sheet according to claim 1, characterized in that: The thickness of the negative electrode current collector is ≤8 μm.

12. The negative electrode sheet according to claim 1, characterized in that: The thickness of the negative electrode current collector is 4 μm to 8 μm.

13. A method for preparing a negative electrode sheet according to any one of claims 1 to 12, characterized in that: include: Providing a slurry, wherein the slurry includes the negative electrode active material, the polybutadiene adipate-based softener, and optional additives; The negative electrode sheet is prepared by coating the slurry on at least one surface of the negative electrode current collector, drying and cold pressing to obtain the negative electrode sheet, wherein the single-side coating weight of the negative electrode sheet is ≥180 mg / 1540.25 mm 2 .

14. The method for producing a negative electrode sheet according to claim 13, characterized in that: The coating speed is ≥45 m / min.

15. The method for producing a negative electrode sheet according to claim 14, characterized in that: The coating speed is 45-60 m / min.

16. A secondary battery, characterized in that: A negative electrode sheet comprising the negative electrode sheet according to any one of claims 1 to 12 or a negative electrode sheet made by the method for making a negative electrode sheet according to claim 13 or 14.

17. The secondary battery according to claim 16, characterized in that: The single-sided coating weight of the positive electrode sheet of the secondary battery is 250 mg / 1540.25 mm 2 ~450mg / 1540.25mm 2 .

18. The secondary battery according to claim 16 or 17, characterized in that: The compaction density of the positive electrode sheet of the secondary battery is 2.4 g / cm 3 ~3.7g / cm 3 .

19. The secondary battery according to claim 16, characterized in that: The thickness of the single-sided positive electrode film layer of the secondary battery is 50 μm to 100 μm.

20. The secondary battery according to claim 16, characterized in that 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.

21. A battery module, characterized in that: A secondary battery comprising any one of claims 16 to 20.

22. A battery pack, characterized in that: Comprising the battery module as claimed in claim 21.

23. An electrical device, characterized in that: The battery comprises at least one selected from the secondary battery of any one of claims 16 to 20, the battery module of claim 21, or the battery pack of claim 22.

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