Current collector NANO safety coating and preparation method therefor

Abstract

A current collector nano safety coating and a preparation method therefor, and a current collector comprising the current collector nano safety coating. The preparation method comprises: after uniformly mixing a temperature-sensitive high polymer material and a binder A, adding a conductive agent for dispersing and coating, and sequentially carrying out first drying and refining to obtain a coated material; uniformly mixing a binder B, a solvent, and the obtained coated material; and coating the surface of the current collector with an obtained nano safety coating slurry, and carrying out secondary drying to obtain a current collector nano safety coating. According to the preparation method, a temperature-sensitive high polymer material is coated with a conductive agent to obtain a coated material. Therefore, on the one hand, the resistance of the temperature-sensitive high polymer material can be increased along with the rise of the temperature, thereby achieving the objective of inhibiting reaction, and on the other hand, the conductive agent located outside achieves good contact, thereby ensuring good conductivity; and in addition, the preparation method is simple and easy to implement, has no special requirements on devices, has low costs and high efficiency, and is easy to implement on a large scale.

Description

A current collector nano safety coating and preparation method thereof Technical Field

[0001] The embodiments of the present application relate to the field of lithium-ion battery technology, for example, a current collector nano-safety coating and a preparation method thereof. Background Art

[0002] Lithium-ion batteries have been widely used in consumer electronics, electric vehicles, and other fields. The market has also placed higher demands on their energy density, cycle life, and safety. As the energy density of lithium-ion batteries continues to increase, the safety issues they face are becoming increasingly severe. A major safety issue is thermal runaway. Abnormal reactions within the battery generate excessive heat, leading to fire or even explosion.

[0003] To improve this problem, the current collector safety primer technology can effectively block the occurrence of various abnormal reactions and improve the safety characteristics of the battery. At the same time, it can reduce the contact resistance between the electrode material and the current collector, increase the adhesion between the electrode material and the current collector, reduce the internal resistance of the battery, and extend the battery life. For example, the prior art discloses a positive electrode plate and a lithium-ion battery containing a high-safety thermosensitive coating. The thermosensitive coating includes a first conductive agent, a first binder, thermosensitive polymer microspheres, and an additive. The thermosensitive coating has conductive properties at room temperature and has the advantages of increasing the contact area between the active material and the current collector, improving the conductivity, and effectively reducing the polarization of the battery. When the operating temperature of the positive electrode plate reaches 120°C or above, the thermosensitive polymer microspheres will melt to form multiple continuous electron blocking layers. The coating forms a current blockage, forming an internal blockage inside the battery to prevent further thermal runaway of the lithium-ion battery.

[0004] However, the current current collector safety primer technology still has shortcomings, and it is necessary to develop a new type of current collector nano-safety coating and its preparation method.

[0005] Summary of the Invention

[0006] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0007] The embodiments of the present application provide a current collector nano-safety coating, a preparation method thereof, and a current collector.

[0008] In the first aspect, the present application provides a current collector nano-safety coating, which includes a temperature-sensitive polymer material, a conductive agent (including nano-scale conductive particles) coated on the surface of the temperature-sensitive polymer material, and an adhesive A for adhering the conductive agent, the conductive particles forming a conductive network, and the temperature-sensitive polymer material having a microcrystalline structure.

[0009] The current collector nano-safety coating described in the present application comprises a temperature-sensitive polymer material and a conductive agent coated on the surface of the temperature-sensitive polymer material. On the one hand, the resistance of the temperature-sensitive polymer material can increase with increasing temperature, thereby achieving the purpose of inhibiting the reaction; on the other hand, the conductive agents on the outside have good contact with each other, which can ensure good conductive performance.

[0010] The thermosensitive polymer material of the present application has a microcrystalline structure, which is to ensure that the material has initial mechanical properties and a basis for thermosensitive response. When the temperature rises, the material will undergo thermal crystallization, further regulating its performance changes. The interaction between this initial microcrystalline structure and the subsequent crystallization structure enables the thermosensitive polymer material to exhibit excellent performance and reliability in practical applications. Specifically, it has the following beneficial effects: (1) Initial performance optimization: The microcrystalline structure provides initial rigidity and strength, so that it has the required mechanical properties before use. If there is no initial microcrystalline structure, it may appear too soft or lack strength at room temperature or low temperature, and cannot meet application requirements. (2) The initial microcrystalline structure provides the basis for thermosensitive response. The presence of microcrystals allows the material to undergo significant structural changes when the temperature changes to the crystallization temperature. Specifically, when the temperature rises to the crystallization temperature, the crystallization of the thermosensitive polymer further increases, which in turn leads to increased brittleness of the thermosensitive polymer material and makes it more prone to cracks. These cracks will destroy the conductive network formed by the conductive agent, thereby causing the conductive network to be interrupted and the resistance to increase. Compared with related technologies, the thermosensitive polymer material with a microcrystalline structure used in this application can advance the temperature response time from heating to softening or melting temperature to heating to crystallization temperature. This design can effectively increase the resistance when the crystallization temperature is reached, thereby improving the safety of the battery more timely and effectively, and avoiding safety hazards caused by overheating. (3) The initial microcrystalline structure and the crystal structure formed when the temperature rises affect each other and jointly determine the overall performance of the material. The initial microcrystalline structure provides basic mechanical properties and temperature-sensitive response capabilities, while the new crystal structure formed when the temperature rises further regulates the performance changes of the material.

[0011] Preferably, the microcrystalline structure content is 10%-60%, and the calculation formula is (ΔHm / ΔHf)×100%, ΔHm is the melting enthalpy of the sample (i.e., the area of ​​the melting peak), and ΔHf is the theoretical melting enthalpy of a completely crystalline material.

[0012] In order to make the thermosensitive polymer material show the best performance within a specific temperature range, it is necessary to control the proportion of the microcrystalline structure. The control of the microcrystalline structure can be achieved by adjusting the composition of the material, processing conditions and heat treatment. By controlling the proportion of microcrystalline, it is possible to maintain the mechanical properties of the material while ensuring its excellent temperature-sensitive response characteristics when the temperature changes. When the proportion of microcrystalline structure is too high, the excessive number of microcrystalline will not only make the material very brittle and prone to cracking, leading to material failure, but also make the material take longer to fully respond when the temperature changes, reducing the sensitivity of the material and prolonging the response time. When the proportion of microcrystalline structure is too low, not only will the mechanical properties of the material decrease, and it will not be able to maintain the required strength and stability at low temperatures, but it will also cause the material to be less sensitive to temperature changes and fail to achieve the expected performance changes.

[0013] Preferably, the current collector nano-safety coating is provided on the surface of the current collector, and the current collector comprises a composite current collector or a metal foil. The current collector nano-safety coating can form a current blockade inside the battery when the internal temperature of the battery rises, thereby preventing further thermal runaway of the lithium-ion battery.

[0014] Since the materials used in high-capacity batteries are often more active, these materials are more prone to short circuits and thermal runaway when physically damaged. Even if a composite current collector is used to replace a traditional current collector, there is still room for improvement in its needle penetration rate. The inventors have found that coating the current collector nano safety coating described in this application on the composite current collector can more effectively improve the needle penetration rate of high-capacity batteries. The reasons may be as follows: (1) Since the current collector nano safety coating and the composite current collector form a multi-layer structure, the multi-layer structure can form a multi-layer physical barrier inside the battery. When the needle pierces the battery, these physical barriers can effectively prevent the flow of current, thereby reducing the risk of short circuit. (2) When the needle pierces the battery and causes local high temperature, the multi-layer structure can effectively isolate the spread of heat and prevent the heat from diffusing to other parts of the battery, thereby reducing the possibility of thermal runaway. (3) When the temperature rises further to the point where the binder or temperature-sensitive polymer material in the current collector nano safety coating dissolves, the dissolved binder or temperature-sensitive polymer material will contact the intermediate polymer base film material of the composite current collector, further effectively forming a current blockage. (4) The nano-safety coating of the current collector and the intermediate polymer base film material of the composite current collector surround the metal layer in the composite current collector, so that no metal burrs will appear during needle puncture, which more effectively avoids the occurrence of positive and negative short circuits.

[0015] In a second aspect, the present application provides a method for preparing a current collector nano-safety coating, the preparation method comprising the following steps:

[0016] (1) adding a thermosensitive polymer material and a binder A to a first solvent and mixing them uniformly, adding a conductive agent for dispersion and coating, and sequentially performing a first drying process and a refinement process to obtain a coated material;

[0017] (2) uniformly mixing the binder B, the second solvent and the coating material obtained in step (1) to obtain a nano safety coating slurry;

[0018] (3) Applying the nano safety coating slurry described in step (2) on the surface of the current collector, and obtaining the current collector nano safety coating through a second drying process.

[0019] The preparation method described in the present application coats a conductive agent on the outside of a temperature-sensitive polymer material to obtain a coated material. On the one hand, the resistance of the temperature-sensitive polymer material can increase with increasing temperature, thereby achieving the purpose of suppressing the reaction. On the other hand, the conductive agents on the outside are in good contact with each other, which can ensure good conductivity. Moreover, the preparation method described in the present application first mixes the temperature-sensitive polymer material and the binder in a first solvent so that they are evenly dispersed in the solution, thereby forming temperature-sensitive polymer particles with the surface covered with the binder. These particles form a core that is easily coated by the conductive agent. Subsequently, a conductive agent is added, and the conductive agent is coated on the surface of the temperature-sensitive polymer particles using binder A to form a shell structure. This preparation method can cover the conductive agent more evenly, thereby obtaining a more uniform and fine coated material. Compared with existing methods such as mechanochemical methods, it is difficult to achieve the same uniformity and refinement effect due to limitations in physical contact and friction.

[0020] The preparation method described in the present application first uses a binder A to combine the conductive agent with the temperature-sensitive polymer material to form a coating material, and then uses a binder B to adhere the coating material to the surface of the current collector to obtain a current collector nano-safety coating; moreover, the binder A and the binder B described in the present application have opposite solubility in the solvent, for example, the binder A is insoluble in water, and the binder B is soluble in water or dispersed in water, thereby avoiding the coating material from dissolving during the process of uniformly mixing to obtain the nano-safety coating slurry in step (2) and avoiding the conductive agent from falling off.

[0021] As a preferred technical solution of the present application, the temperature-sensitive polymer material in step (1) includes any one of polyethylene, polyvinyl alcohol or poly-ε-caprolactone, or a combination of at least two of them. Typical but non-limiting examples of the combination include: a combination of polyethylene and polyvinyl alcohol, a combination of polyvinyl alcohol and poly-ε-caprolactone, or a combination of polyethylene and poly-ε-caprolactone, etc.

[0022] The thermosensitive polymer material described in this application is a high-molecular-weight thermosensitive polymer material with a microcrystalline structure. Preferably, the microcrystalline content of the thermosensitive polymer material is 10%-60%. This high-molecular-weight thermosensitive polymer material with a microcrystalline structure enables the current collector nano-safety coating to maintain a low resistance at the normal operating temperature of the battery. As the temperature rises, the resistance of the nano-safety coating also increases, achieving the purpose of suppressing the reaction. The increase in resistance is due to the microcrystalline structure of the thermosensitive polymer material and the crystallization generated by the temperature increase, which synergistically hinder the movement of electrons, resulting in a higher resistance.

[0023] Preferably, the molecular weight of the temperature-sensitive polymer material in step (1) is 50,000-200,000, for example, 50,000, 60,000, 70,000, 80,000, 90,000, 100,000, 110,000, 120,000, 130,000, 140,000, 150,000, 160,000, 170,000, 180,000, 190,000 or 200,000, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0024] Preferably, the particle size of the thermosensitive polymer material in step (1) is 1-3 μm, for example, 1 μm, 1.5 μm, 2 μm, 2.5 μm or 3 μm, etc., but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0025] As a preferred technical solution of the present application, the binder A in step (1) includes any one or a combination of at least two of polyurethane resin and its derivatives.

[0026] Preferably, the uniform mixing in step (1) further comprises adding a first solvent for mixing.

[0027] Preferably, the first solvent comprises toluene.

[0028] The first solvent in this application only serves to accelerate mixing, does not chemically react with other materials, and is volatile and can be removed in the subsequent first drying process. Those skilled in the art can reasonably select the amount of the first solvent based on actual conditions.

[0029] Preferably, the solubility of the binder A in the second solvent is less than 0.1 g / 100 g.

[0030] As a preferred technical solution of the present application, the conductive agent in step (1) includes any one or a combination of at least two of conductive carbon black, conductive graphite or carbon nanotubes. Typical but non-limiting examples of the combination are: a combination of conductive carbon black and conductive graphite, a combination of conductive graphite and carbon nanotubes, or a combination of conductive carbon black and carbon nanotubes, etc.

[0031] Preferably, the particle size of the conductive agent in step (1) is 0.2-0.8 μm, such as 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm or 0.8 μm, etc., but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0032] As a preferred technical solution of the present application, the mass ratio of the temperature-sensitive polymer material and the binder A in step (1) is (10-50):1, for example, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1 or 50:1, etc., but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0033] Preferably, the mass ratio of the temperature-sensitive polymer material and the conductive agent in step (1) is (0.5-2):1, for example, 0.5:1, 0.6:1, 0.8:1, 1:1, 1.1:1, 1.3:1, 1.5:1, 1.7:1 or 2:1, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0034] As a preferred technical solution of the present application, the first drying treatment in step (1) includes baking.

[0035] Preferably, the refinement treatment in step (1) includes grinding.

[0036] As a preferred technical solution of the present application, in step (2), the mass ratio of the coating material obtained in step (1) to the binder B is (0.5-2):1, for example, 0.5:1, 0.6:1, 0.8:1, 1:1, 1.1:1, 1.3:1, 1.5:1, 1.7:1 or 2:1, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0037] Preferably, in step (2), the binder B comprises any one or a combination of at least two of polyacrylic acid resin and its derivatives. The polyacrylic acid resin derivatives include but are not limited to polymers of monomers such as acrylate, methacrylic acid, acrylamide, and acrylic anhydride.

[0038] Preferably, the solvent in step (2) comprises water.

[0039] Preferably, the mass ratio of the solvent to the coating material in step (2) is (10-40):1, for example, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1 or 40:1, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0040] Preferably, the uniform mixing in step (2) includes sand grinding dispersion.

[0041] As a preferred technical solution of the present application, the coating in step (3) is carried out using a coating machine.

[0042] Preferably, the current collector in step (3) comprises a composite current collector or a metal foil. Preferably, the composite current collector comprises a polymer base film and a metal layer disposed on the surface of the base film, and the base film is selected from one or more of polyethylene terephthalate, polypropylene, polyethylene, polyimide, or polyetheretherketone. The metal layer is selected from one or more of aluminum, copper, nickel, titanium, silver, nickel-copper alloy, aluminum-zirconium alloy, or copper-zinc alloy. Preferably, the metal foil is selected from one or more of aluminum, copper, nickel, titanium, silver, nickel-copper alloy, aluminum-zirconium alloy, or copper-zinc alloy.

[0043] Preferably, the second drying treatment in step (3) includes oven drying.

[0044] Preferably, the temperature of the second drying treatment in step (3) is 80-120°C, for example, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C or 120°C, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0045] Preferably, the thickness of the current collector nano-safety coating in step (3) is 1-10 μm, for example, 1 μm, 3 μm, 5 μm, 6 μm, 8 μm or 10 μm, etc., but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0046] As a preferred technical solution of this application, the preparation method comprises the following steps:

[0047] (1) adding a thermosensitive polymer material and a binder A to a first solvent and mixing them uniformly, adding a conductive agent for dispersion and coating, and sequentially performing a first drying process, such as baking, and a refinement process, such as grinding, to obtain a coated material;

[0048] Wherein, the first drying process includes drying; the temperature of the first drying process is 60-100°C;

[0049] The thermosensitive polymer material comprises any one or a combination of at least two of polyethylene, polyvinyl alcohol or poly-ε-caprolactone; the molecular weight of the thermosensitive polymer material is 50,000-200,000; the particle size of the thermosensitive polymer material is 1-3 μm; the binder A comprises any one or a combination of at least two of polyurethane resin and its derivatives; the conductive agent comprises any one or a combination of at least two of conductive carbon black, conductive graphite or carbon nanotubes; the particle size of the conductive agent is 0.2-0.8 μm; the mass ratio of the thermosensitive polymer material to the binder A is (10-50):1; the mass ratio of the thermosensitive polymer material to the conductive agent is (0.5-2):1;

[0050] (2) uniformly mixing the binder B, the second solvent and the coating material obtained in step (1) to obtain a nano safety coating slurry;

[0051] The mass ratio of the obtained coating material to the binder B is (0.5-2):1; the binder B comprises any one or a combination of at least two of polyacrylic acid resin and its derivatives; the solvent comprises water; the mass ratio of the second solvent to the coating material is (10-40):1; and the uniform mixing comprises sand grinding and dispersion;

[0052] (3) applying the nano safety coating slurry of step (2) on the surface of the current collector using a coating machine, and performing a second drying process to obtain the nano safety coating of the current collector;

[0053] Wherein, the second drying treatment includes baking; the temperature of the second drying treatment is 80-120° C.; and the thickness of the current collector nano-safety coating is 1-10 μm.

[0054] In a third aspect, the present application provides a current collector comprising the current collector nano-safety coating described in the first aspect or the current collector nano-safety coating obtained according to the preparation method described in the second aspect.

[0055] Compared with the related technical solutions, the embodiments of the present application have at least the following beneficial effects:

[0056] (1) The preparation method described in the embodiment of the present application coats the conductive agent on the outside of the temperature-sensitive polymer material to obtain a coated material. On the one hand, the resistance of the temperature-sensitive polymer material can increase with the increase of temperature, thereby achieving the purpose of inhibiting the reaction. On the other hand, the conductive agents on the outside are in good contact with each other, which can ensure good conductive performance.

[0057] (2) The preparation method described in the examples of the present application is simple and easy to implement, has no special requirements for equipment, is low in cost, high in efficiency, and can be easily implemented on a large scale;

[0058] (3) The thermosensitive polymer material described in the embodiment of the present application is a large molecular weight thermosensitive polymer material with a microcrystalline structure, which can enable the current collector nano-safety coating to maintain a low resistance under normal temperature conditions. As the temperature rises, the resistance of the nano-safety coating also increases, achieving the purpose of inhibiting the reaction; the reason for the increase in resistance is that the microcrystalline structure of the thermosensitive polymer material can hinder the movement of electrons, thereby generating a higher resistance.

[0059] Still other aspects will become apparent upon reading and understanding the detailed description. DETAILED DESCRIPTION

[0060] To facilitate understanding of the present application, the present application lists the following examples. Those skilled in the art should understand that the examples are only provided to help understand the present application and should not be considered as specific limitations of the present application.

[0061] Example 1

[0062] This embodiment provides a method for preparing a current collector nano-safety coating, the preparation method comprising the following steps:

[0063] (1) 10 kg of polyethylene powder (microcrystalline content ratio of 10%) with a particle size of 2 μm and 0.5 kg of polyurethane resin were uniformly mixed in a first solvent of toluene, wherein the molecular weight of the polyethylene was 100,000, and then 10 kg of conductive carbon black with a particle size of 0.5 μm was added for dispersion and coating, i.e., the mass ratio of the temperature-sensitive polymer material to the binder A was 20:1, and the mass ratio of the temperature-sensitive polymer material to the conductive agent was 1:1. The mixture was dried and ground to obtain a coated material;

[0064] (2) 10 kg of the coating material obtained in step (1), 40 kg of a polyacrylic acid resin aqueous solution (solid content of 25 wt%), and an appropriate amount of water are mixed uniformly to obtain a nano safety coating slurry with a solid content of 10 wt%; wherein the mass ratio of the obtained coating material to the binder B is 1:1; the uniform mixing includes sand grinding and dispersion for 4 hours;

[0065] (3) The nano safety coating slurry described in step (2) is coated on both sides of an aluminum current collector with a thickness of 13 μm using a coating machine, and dried at 100° C. to obtain a current collector nano safety coating with a thickness of 1 μm.

[0066] Example 2

[0067] This embodiment provides a method for preparing a current collector nano-safety coating. Compared with the preparation method described in Example 1, the only difference is that the temperature-sensitive polymer material in step (1) is replaced by polyvinyl alcohol of equal mass, and the microcrystalline structure content ratio is 10%.

[0068] Example 3

[0069] This embodiment provides a method for preparing a current collector nano-safety coating. Compared with the preparation method described in Example 1, the only difference is that the temperature-sensitive polymer material in step (1) is replaced by poly-ε-caprolactone of equal mass, and the microcrystalline structure content ratio is 10%.

[0070] Example 4

[0071] This embodiment provides a method for preparing a current collector nano-safety coating. Compared with the preparation method described in Example 1, the only difference is that the temperature-sensitive polymer material in step (1) is replaced by polymethyl methacrylate (PMMA) of equal mass, and the microcrystalline structure content ratio is 10%.

[0072] Example 5

[0073] This embodiment provides a method for preparing a current collector nano-safety coating, the preparation method comprising the following steps:

[0074] (1) 5 kg of polyethylene powder with a particle size of 1 μm and 0.5 kg of polyurethane resin are uniformly mixed in a first solvent of toluene, wherein the molecular weight of the polyethylene is 50,000, and then 10 kg of conductive carbon black with a particle size of 0.2 μm is added for dispersion and coating, that is, the mass ratio of the temperature-sensitive polymer material to the binder A is 10:1, and the mass ratio of the temperature-sensitive polymer material to the conductive agent is 0.5:1. The mixture is dried and ground to obtain a coated material;

[0075] (2) 5 kg of the coating material obtained in step (1), 40 kg of a polyacrylic acid resin aqueous solution (solid content of 25 wt%), and an appropriate amount of water were mixed uniformly to obtain a nano safety coating slurry with a solid content of 10 wt%; wherein the mass ratio of the obtained coating material to the binder B was 0.5:1; the uniform mixing included sand grinding and dispersion for 4 h;

[0076] (3) The nano safety coating slurry described in step (2) is coated on both sides of an aluminum current collector with a thickness of 13 μm using a coating machine, and dried at 80° C. to obtain a current collector nano safety coating with a thickness of 1 μm.

[0077] Example 6

[0078] This embodiment provides a method for preparing a current collector nano-safety coating, the preparation method comprising the following steps:

[0079] (1) 25 kg of polyethylene powder (microcrystalline content ratio of 10%) with a particle size of 3 μm and 0.5 kg of polyurethane resin were uniformly mixed in a first solvent of toluene, wherein the molecular weight of the polyethylene was 200,000, and then 12.5 kg of conductive carbon black with a particle size of 0.8 μm was added for dispersion and coating, i.e., the mass ratio of the temperature-sensitive polymer material to the binder A was 50:1, and the mass ratio of the temperature-sensitive polymer material to the conductive agent was 2:1. The mixture was dried and ground to obtain a coated material;

[0080] (2) 20 kg of the coating material obtained in step (1), 40 kg of a polyacrylic acid resin aqueous solution (solid content of 25 wt%), and an appropriate amount of water are mixed uniformly to obtain a nano safety coating slurry with a solid content of 10 wt%; wherein the mass ratio of the obtained coating material to the binder B is 2:1; the uniform mixing includes sand grinding and dispersion for 4 hours;

[0081] (3) The nano safety coating slurry described in step (2) is coated on both sides of an aluminum current collector with a thickness of 13 μm using a coating machine, and dried at 120° C. to obtain a current collector nano safety coating with a thickness of 1 μm.

[0082] Example 7

[0083] This embodiment is basically the same as embodiment 4, except that a composite aluminum current collector with a thickness of 8 μm is used instead of an aluminum current collector with a thickness of 13 μm. The composite aluminum current collector is prepared by plating a 1 μm metal layer on both sides of a 6 μm PET base film.

[0084] Example 8

[0085] This embodiment is basically the same as embodiment 6, except that the content of the microcrystalline structure accounts for 30%.

[0086] Example 9

[0087] This embodiment is basically the same as embodiment 6, except that the microcrystalline structure content is 60%.

[0088] Comparative Example 1

[0089] This comparative example provides a method for preparing a current collector nano-safety coating, the preparation method comprising the following steps:

[0090] (1) 0.5 kg of polyurethane resin and 10 kg of conductive carbon black with a particle size of 0.5 μm were mixed uniformly in a first solvent of toluene, and then dried and ground to obtain a coated material;

[0091] (2) 10 kg of the coating material obtained in step (1), 40 kg of a polyacrylic acid resin aqueous solution (solid content of 25 wt%), and an appropriate amount of water are mixed uniformly to obtain a nano safety coating slurry with a solid content of 10 wt%; wherein the mass ratio of the obtained coating material to the binder B is 1:1; the uniform mixing includes sand grinding and dispersion for 4 hours;

[0092] (3) The nano safety coating slurry of step (2) is coated on both sides of a 13 μm aluminum current collector with a thickness of 1 μm using a coating machine, and dried at 100° C. to obtain a current collector nano safety coating.

[0093] That is to say, compared with the preparation method described in Example 1, the only difference is that the temperature-sensitive polymer material (polyethylene powder) described in step (1) is completely omitted.

[0094] Preparation example:

[0095] This preparation example uses the current collectors prepared in Examples 1 to 7 and Comparative Example 1 to prepare different batteries. The battery preparation method is as follows:

[0096] (1) Preparation of positive electrode sheet

[0097] The lithium nickel cobalt manganese ternary active material LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) were mixed thoroughly in N-methylpyrrolidone solvent at a weight ratio of 97:1:2 to obtain a positive electrode slurry. The positive electrode slurry was applied to the positive electrode current collector and then dried, cold pressed, slit, and cut to obtain a positive electrode sheet. The compacted density of the positive electrode active material layer was 3.0 g / cm 3 .

[0098] (2) Preparation of negative electrode sheet

[0099] The negative electrode active material artificial graphite, binder SBR, thickener sodium carboxymethyl cellulose (CMC-Na) and conductive carbon black (Super P) were weighed in a weight ratio of 96:2:1:1 and added to a stirring tank in a certain order with deionized water for mixing to prepare a negative electrode slurry. The negative electrode slurry was coated on the negative electrode current collector (8μm Cu foil) and the negative electrode sheet was obtained through drying, cold pressing, slitting, cutting and other processes. Among them, the compaction density of the negative electrode active material layer is 1.4g / cm 3 .

[0100] (3) Diaphragm

[0101] PE film is selected as the diaphragm.

[0102] (4) Preparation of electrolyte

[0103] Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 3:7, and then fully dried lithium salt LiPF6 is dissolved in a mixed organic solvent at a ratio of 1 mol / L to prepare an electrolyte.

[0104] (5) Preparation of batteries

[0105] The positive electrode sheet, separator and negative electrode sheet are stacked in order and wound to obtain an electrode assembly, which is placed in an outer package and the above-mentioned electrolyte is added. After packaging, standing, formation, aging and other processes, a lithium-ion secondary battery with a capacity of 30Ah is finally obtained.

[0106] The current collectors containing the current collector nano-safety coating prepared in the above examples and comparative examples were tested for penetration resistance according to the following method. The relevant test results are shown in Table 1.

[0107] Penetration resistance: Tested using a pole piece resistance meter. Cut the current collector with the nano-safety coating to be tested into a square of approximately 5cm×5cm, place it under the test head, maintain the pressure at 0.3t for 5s, and test the penetration resistance at 25℃ and 160℃ respectively.

[0108] Needle penetration test: The battery (test object) prepared in the preparation example and containing the current collector of the embodiment and the comparative example is placed in a needle penetration test apparatus. The diameter of the steel needle in the needle penetration test apparatus is 3 mm, and the needle penetration speed is set to 10 mm / s. The test object is subjected to a needle penetration test with a battery charge capacity (SOC) of 80%. Each test object is set to 100 repetitions, and each repetition is a lithium-ion battery. During the needle penetration test, if the test object does not explode, catch fire, or smoke, it is marked as "passed", otherwise it is marked as "failed". The number of lithium-ion batteries marked as "passed" and marked as "failed" in the 100 repetitions set for each test object is recorded and counted, and the battery needle penetration pass rate of each test object is calculated. The battery needle penetration pass rate of each test object = the number of lithium-ion batteries marked as "passed" / the total number of lithium-ion batteries in the repeated experiments set for the test object × 100%.

[0109] Table 1

[0110] Table 2

[0111] It can be seen from Tables 1 and 2 that, compared with Comparative Example 1, the penetration resistance / mΩ at 160°C of Examples 1-9 is significantly higher than the penetration resistance / mΩ at 25°C, and the needle penetration rate of Preparation Examples 1-9 is higher than that of Comparative Preparation Example 1, indicating that when encountering high temperatures, the nano safety coating can effectively increase the resistance, thereby improving the safety performance.

[0112] In addition, by comparing Examples 4 and 7, and Preparation Examples 4 and 7, it can be seen that compared with the aluminum current collector containing the nano-safety coating, the composite aluminum current collector containing the nano-safety coating has an infinitely large penetration resistance. Through the combined effect of the nano-safety coating and the composite current collector base film, the battery puncture pass rate is higher and the safety performance is more excellent.

[0113] To sum up, the preparation method described in the present application coats the conductive agent on the outside of the temperature-sensitive polymer material to obtain a coated material. On the one hand, the resistance of the temperature-sensitive polymer material can increase with the increase of temperature, thereby achieving the purpose of inhibiting the reaction. On the other hand, the conductive agents on the outside are in good contact with each other, which can ensure good conductive performance; the preparation method described in the present application is simple and easy, has no special requirements for equipment, is low in cost, high in efficiency, and easy to implement on a large scale; the temperature-sensitive polymer material described in the present application is a large molecular weight temperature-sensitive polymer material with a microcrystalline structure, which can enable the current collector nano-safety coating to maintain a low resistance under normal temperature conditions. As the temperature rises, the resistance of the nano-safety coating also increases, thereby achieving the purpose of inhibiting the reaction; the reason for the increase in resistance is that the microcrystalline structure of the temperature-sensitive polymer material can hinder the movement of electrons, thereby generating a higher resistance.

[0114] This application uses the above-mentioned embodiments to illustrate the detailed process equipment and process flow of this application. However, this application is not limited to the above-mentioned detailed process equipment and process flow, that is, it does not mean that this application must rely on the above-mentioned detailed process equipment and process flow to be implemented. Those skilled in the art should understand that any improvements to this application, equivalent replacement of various raw materials of the product of this application, addition of auxiliary ingredients, selection of specific methods, etc., all fall within the scope of protection and disclosure of this application.

Claims

1. A current collector nano-safety coating, comprising a temperature-sensitive polymer material, a conductive agent coated on the surface of the temperature-sensitive polymer material, and a binder A for adhering the conductive agent, wherein the conductive particles form a conductive network, and the temperature-sensitive polymer material has a microcrystalline structure.

2. The current collector nano-safety coating according to claim 1, wherein: The microcrystalline structure content is 10%-60%.

3. The current collector nano-safety coating according to claim 1 or 2, wherein: The composite nanometer safety coating is arranged on the surface of the current collector, and the current collector comprises a composite current collector or a metal foil.

4. A method for preparing a current collector nano-safety coating, comprising the following steps: (1) adding a temperature-sensitive polymer material and a binder A to a first solvent and mixing them uniformly, adding a conductive agent for dispersion and coating, and sequentially performing a first drying treatment and a refinement treatment to obtain a coated material; (2) mixing the binder B, the second solvent and the coated material obtained in step (1) to obtain a nano safety coating slurry; (3) Applying the nano safety coating slurry described in step (2) on the surface of the current collector, and obtaining the current collector nano safety coating through a second drying process.

5. The preparation method according to claim 4, wherein Meet one or more of the following conditions: (a) the temperature-sensitive polymer material in step (1) comprises any one of polyethylene, polyvinyl alcohol or poly-ε-caprolactone or a combination of at least two thereof; (b) the first solvent comprises toluene; (c) The solubility of the binder A in the second solvent is less than 0.1 g / 100 g.

6. The preparation method according to claim 4 or 5, wherein: The molecular weight of the temperature-sensitive polymer material in step (1) is 50,000-200,000.

7. The preparation method according to any one of claims 4 to 6, wherein: The temperature-sensitive polymer material in step (1) has a microcrystalline structure, and the content of the microcrystalline structure is 10%-60%.

8. The preparation method according to any one of claims 4 to 7, wherein: The particle size of the temperature-sensitive polymer material in step (1) is 1-3 μm.

9. The preparation method according to any one of claims 4 to 8, wherein: The binder A in step (1) comprises any one of polyurethane resin and its derivatives or a combination of at least two thereof.

10. The preparation method according to any one of claims 4 to 9, wherein: The conductive agent in step (1) includes any one of conductive carbon black, conductive graphite or carbon nanotubes, or a combination of at least two thereof; Preferably, the particle size of the conductive agent in step (1) is 0.2-0.8 μm.

11. The preparation method according to any one of claims 4 to 10, wherein: The mass ratio of the temperature-sensitive polymer material to the binder A in step (1) is (10-50):1; Preferably, in step (1), the mass ratio of the temperature-sensitive polymer material to the conductive agent is (0.5-2):

1.

12. The preparation method according to any one of claims 4 to 11, wherein: In step (1), the first drying treatment includes drying; Preferably, the refinement treatment in step (1) includes grinding.

13. The preparation method according to any one of claims 4 to 12, wherein: In step (2), the mass ratio of the coating material obtained in step (1) to the binder B is (0.5-2):1; Preferably, in step (2), the binder B comprises any one or a combination of at least two of polyacrylic acid resin and its derivatives; Preferably, the solvent in step (2) comprises water; Preferably, in step (2), the mass ratio of the solvent to the coating material is (10-40):1; Preferably, the uniform mixing in step (2) includes sand grinding dispersion.

14. The preparation method according to any one of claims 4 to 13, wherein: The coating in step (3) is carried out using a coating machine; Preferably, the current collector in step (3) is selected from a composite current collector or a metal foil; Preferably, the second drying treatment in step (3) includes drying; Preferably, the temperature of the second drying treatment in step (3) is 80-120°C; Preferably, the thickness of the current collector nano-safety coating in step (3) is 1-10 μm.

15. The preparation method according to any one of claims 4 to 14, wherein: The steps include: (1) adding a temperature-sensitive polymer material and a binder A to a first solvent and mixing them uniformly, adding a conductive agent for dispersion and coating, and sequentially drying and grinding to obtain a coated material; Wherein, the temperature-sensitive polymer material comprises any one of polyethylene, polyvinyl alcohol or poly-ε-caprolactone or a combination of at least two thereof; the molecular weight of the temperature-sensitive polymer material is 50000-200000; the particle size of the temperature-sensitive polymer material is 1-3 μm; the temperature-sensitive polymer material has a microcrystalline structure, and the content of the microcrystalline structure is 10%-60%; the binder A comprises any one of polyurethane resin and its derivatives or a combination of at least two thereof; the conductive agent comprises any one of conductive carbon black, conductive graphite or carbon nanotubes or a combination of at least two thereof; the particle size of the conductive agent is 0.2-0.8 μm; the mass ratio of the temperature-sensitive polymer material to the binder A is (10-50):1; the mass ratio of the temperature-sensitive polymer material to the conductive agent is (0.5-2):1; (2) mixing the binder B, the second solvent and the coated material obtained in step (1) to obtain a nano safety coating slurry; The mass ratio of the obtained coating material to the binder B is (0.5-2):1; the binder B includes any one or a combination of at least two of polyacrylic acid resin and its derivatives; the second solvent includes water; the mass ratio of the solvent to the coating material is (10-40):1; the mixing includes sand grinding dispersion; the solubility of the binder A in the second solvent is less than 0.1g / 100g; (3) applying the nanometer safety coating slurry in step (2) onto the surface of the current collector by a coating machine, and obtaining the current collector nanometer safety coating by a second drying process; Wherein, the second drying includes baking; the temperature of the second drying treatment is 80-120°C; the thickness of the current collector nano-safety coating is 1-10 μm; and the current collector in step (3) includes a composite current collector or a metal foil.

16. A composite current collector, comprising the current collector nano-safety coating according to any one of claims 1 to 3 or the current collector nano-safety coating prepared according to the method for preparing the current collector nano-safety coating according to any one of claims 4 to 15.

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