Secondary battery, negative electrode current collector, preparation method therefor, and electric device

Abstract

The present application provides a secondary battery, a negative electrode current collector, a preparation method therefor, and an electric device. The secondary battery of the present application comprises a positive electrode sheet, a negative electrode sheet, and a separator arranged between the negative electrode sheet and the positive electrode sheet, wherein the negative electrode sheet comprises a negative electrode current collector, the negative electrode current collector comprises a porous membrane layer and a coating layer at least arranged on a surface of the porous film layer on a side close to the separator, and the coating layer comprises an inorganic material, a conductive agent, and a binder, wherein the inorganic material comprises at least one of a metal oxide or a silicon oxide. In the negative electrode current collector of the secondary battery of the present application, the coating layer exhibits excellent adhesion to the porous membrane layer, providing conductivity for the negative electrode current collector. The porous membrane layer of the present application provides a porous structure for the negative electrode current collector, which helps to improve the rate performance of the secondary battery.

Description

Secondary battery, negative current collector, preparation method thereof and electric device

[0001] Cross-reference to related applications

[0002] This application refers to the Chinese Patent Application No. 202411124747.8, filed on August 15, 2024, entitled "Secondary battery, negative current collector, preparation method thereof and electric device", which is incorporated by reference in its entirety. TECHNICAL FIELD

[0003] The present application relates to the technical field of secondary batteries, and in particular to a secondary battery, a negative current collector, a preparation method thereof and an electric device. BACKGROUND

[0004] In recent years, secondary batteries are widely used in energy storage power systems such as hydroelectric, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc.

[0005] With the wide application of batteries in various fields, people's requirements for their performance are also getting higher and higher. How to further improve the rate performance of the battery has become the focus of attention of all circles. SUMMARY

[0006] The present application is made in view of the above-mentioned problems, and aims to solve at least one of the technical problems existing in the prior art. To this end, the present application provides a secondary battery, a negative current collector, a preparation method thereof and an electric device. The secondary battery of the present application has good rate performance.

[0007] The first aspect of the present application provides a secondary battery, which comprises a positive electrode sheet, a negative electrode sheet and a separator arranged between the negative electrode sheet and the positive electrode sheet, wherein the negative electrode sheet comprises a negative current collector, the negative current collector comprises a porous membrane layer and a coating layer arranged at least on the surface of the porous membrane layer close to the separator, the coating layer comprises inorganic matter, conductive agent and binder, and the inorganic matter comprises at least one of metal oxide or silicon oxide.

[0008] As a component of the negative current collector, the porous membrane layer in the secondary battery of the present application has a porous structure and good electrolyte permeability. The porous structure and good electrolyte permeability are beneficial to shorten the migration path of metal ions such as sodium ions and lithium ions, improve the transmission speed of metal ions, and improve the rate performance of the secondary battery.

[0009] Under high rate conditions, when the migration of metal ions is hindered on the negative side, it is more likely to cause metal precipitation, generating dendrites, and when the dendrites pierce the separator, it will cause the positive and negative electrode tabs to short circuit, thereby affecting the safety performance of the secondary battery. Further, in the negative current collector of the secondary battery of the present application, on the one hand, the porous structure and the electrolyte permeability are conducive to the migration of metal ions, which can reduce the generation of metal dendrites; on the other hand, the porous structure helps to provide more deposition sites for metal ions, so that the negative metal is deposited in the porous structure to a greater extent, i.e. uniformly deposited on the porous structure, reducing the generation of lithium dendrites or sodium dendrites, which is conducive to improving the cycle performance and safety performance of the secondary battery.

[0010] The porous membrane layer generally does not have the conductivity required by the negative current collector. The negative current collector of the present application provides the formed current collector with conductivity by coating the coating layer on the porous membrane layer.

[0011] The combination of traditional conductive agent and binder has low affinity with the porous membrane layer, and is prone to powdering and falling off, which greatly affects the cycle performance of the battery. The present application adds inorganic matter to the coating layer, which has a mortise and tenon effect and can rivet the conductive agent, the binder and the porous membrane layer, greatly increasing the affinity of the coating layer and the porous membrane layer, while also increasing the thermal stability and mechanical stability of the current collector and reducing the film-forming property of the binder. The coating layer in the secondary battery of the present application has good coating performance, and the current collector obtained by coating on the porous membrane layer has conductivity, porous structure, electrolyte permeability, good mechanical strength and thermal stability, and the obtained secondary battery has good rate performance.

[0012] In any embodiment, the metal oxide includes at least one of aluminum oxide, boehmite, magnesium oxide, iron oxide, zirconium oxide, titanium oxide, or zinc oxide.

[0013] When the inorganic matter is the above type of substance, it has better affinity with the porous membrane layer, as well as better mechanical stability and thermal stability, which is conducive to further improving the cycle performance and rate performance of the secondary battery.

[0014] In any embodiment, the binder includes at least one of an acrylic monomer unit homopolymer and / or copolymer, an acrylic ester monomer unit homopolymer and / or copolymer, a polyol monomer unit-polyisocyanate monomer unit copolymer, a dibasic amine monomer unit-dibasic anhydride monomer unit copolymer, a butadiene monomer unit-styrene monomer unit copolymer, a styrene monomer unit-acrylic ester monomer unit copolymer, or a derivative thereof, a modified species thereof.

[0015] The binder provides the coating layer with cohesiveness.

[0016] In any embodiment, the binder comprises at least one of butadiene monomer unit-styrene monomer unit copolymer, styrene monomer unit-acrylate monomer unit copolymer, methyl acrylate monomer unit homopolymer, ethyl acrylate monomer unit homopolymer, butyl acrylate monomer unit homopolymer, isooctyl acrylate monomer unit homopolymer, acrylate monomer unit copolymer, or derivatives thereof, modified species thereof.

[0017] The binder of the above type has a lower surface tension, which is conducive to further improving the adhesion of the coating to the porous membrane layer and further improving the cycle performance of the secondary battery.

[0018] In any embodiment, the conductive agent comprises at least one of conductive carbon black, carbon nanotube, graphene, superconducting carbon, acetylene black, ketjen black, carbon dot, or carbon nanofiber.

[0019] The conductive agent can build a conductive network to provide the current collector with conductivity, which is conducive to electron transport.

[0020] In any embodiment, the mass percentage of the inorganic substance is 40%-55% based on the mass of the coating.

[0021] In any embodiment, the mass percentage of the inorganic substance is 45%-50% based on the mass of the coating.

[0022] When the content of the inorganic substance in the coating is appropriate, the coating and the porous membrane layer have better adhesion, which is conducive to further improving the cycle performance of the secondary battery, further reducing the influence on the conductivity of the current collector, and further improving the rate performance of the secondary battery.

[0023] In any embodiment, the mass percentage of the binder is 20%-35% based on the mass of the coating.

[0024] In any embodiment, the mass percentage of the binder is 25%-30% based on the mass of the coating.

[0025] When the content of the binder in the coating is appropriate, it is conducive to further reducing the powder dropping of the coating, thereby further improving the adhesion of the coating to the porous membrane layer and further improving the cycle performance of the secondary battery.

[0026] In any embodiment, the mass percentage of the conductive agent is 5%-15% based on the mass of the coating.

[0027] In any embodiment, the mass percentage of the conductive agent is 8%-12% based on the mass of the coating.

[0028] When the content of the conductive agent in the coating is appropriate, the conductive performance of the negative current collector is improved, thereby further improving the rate performance of the secondary battery. Further, the conductive agent has poor affinity with the porous membrane layer and has active groups on the surface, and too much conductive agent can consume the deposited metal of the negative electrode. Therefore, appropriate content of the conductive agent also helps to further improve the affinity of the coating and the porous membrane layer, reduce the consumption of the deposited metal of the negative electrode, and further improve the cycle performance and the initial coulombic efficiency of the secondary battery.

[0029] In any embodiment, the coating further comprises a dispersant.

[0030] In any embodiment, the dispersant comprises at least one of carboxymethyl cellulose, methyl cellulose, sodium starch phosphate, sodium carboxymethyl cellulose, sodium polyacrylate, polyoxyethylene, or polyvinylpyrrolidone.

[0031] The addition of the dispersant in the coating helps to better disperse the inorganic substance and the conductive agent, reduces their sedimentation and agglomeration, and helps the inorganic substance and the conductive agent to further exert their respective functions.

[0032] In any embodiment, the mass percentage content of the dispersant is 0%-10% based on the mass of the coating.

[0033] In any embodiment, the mass percentage content of the dispersant is greater than 0% based on the mass of the coating.

[0034] In the coating, the dispersant has an appropriate content, which helps to further improve its dispersing ability.

[0035] In any embodiment, the coating has a coating weight per unit area of 1-5 mg / cm 2 .

[0036] In any embodiment, the coating has a coating weight per unit area of 2-3 mg / cm 2 .

[0037] The coating has an appropriate coating weight per unit area, which helps to make the coating on the porous membrane more uniform, thereby further reducing the missing coating situation, providing better conductivity for the current collector, and further improving the rate performance of the secondary battery; further, the appropriate coating weight per unit area also helps to improve the cycle performance of the secondary battery.

[0038] In any embodiment, the porosity of the porous membrane layer is 30%-60%.

[0039] In any embodiment, the porosity of the porous membrane layer is 40%-50%.

[0040] Suitable number of porous structures help to further improve the transport speed of metal ions, thus further improve the rate performance of the secondary battery; also help to provide more suitable number of deposition sites, make the metal deposition more uniform, further reduce the generation of lithium dendrites or sodium dendrites, thus further improve the cycle performance and safety performance of the secondary battery. Further, suitable number of porous structures help to effectively carry the coating.

[0041] In any embodiment, the porous membrane layer comprises at least one of a porous polyolefin membrane, a porous glass fiber, a porous non-woven fabric, a porous polyimide membrane, a porous polyvinylidene fluoride membrane, or a porous polyterephthalate.

[0042] The porous membrane of the above type has porous structure and good electrolyte permeability, which helps to further improve the rate performance of the secondary battery of the application, reduce the generation of dendrites, and improve the safety performance of the secondary battery.

[0043] In any embodiment, the thickness of the porous membrane layer is 6-15 μm.

[0044] The porous membrane layer with suitable thickness helps to provide suitable transport distance, which helps to further improve the rate performance of the secondary battery.

[0045] In any embodiment, the coating is arranged at least on the surface of the porous membrane layer close to the separator.

[0046] In any embodiment, the coating is arranged on the surfaces of both sides of the porous membrane layer.

[0047] When the coating is arranged at least on the surface of the porous membrane layer close to the separator, the secondary battery of the embodiment of the application has high rate performance. When the coating is arranged on the surfaces of both sides of the porous membrane layer, it is more helpful to improve the rate performance of the secondary battery of the embodiment of the application.

[0048] In any embodiment, the secondary battery comprises a metal anode-free battery.

[0049] In any embodiment, the secondary battery comprises a sodium metal anode-free battery or a lithium metal anode-free battery.

[0050] Generally, since the anode electrode sheet of the metal anode-free battery is a metal foil such as copper foil or aluminum foil, the metal foil lacks porous structure and has poor electrolyte wettability. Therefore, the anode current collector of the metal anode-free battery can hinder the migration of metal ions such as sodium ions or lithium ions and increase the migration path, thus reducing the rate performance of the battery. Further, in this case, metal dendrites such as sodium dendrites or lithium dendrites are more likely to be generated. The application of the anode current collector of the embodiment of the application to the metal anode-free battery is more helpful to improve the rate performance of the secondary battery; further, it is helpful to better reduce the generation of dendrites.

[0051] In any embodiment, the negative electrode tab includes a negative film layer disposed on at least one side of the negative current collector, the negative film layer including a negative active material, the negative active material including at least one of artificial graphite, natural graphite, soft carbon, hard carbon, or silicon-based material.

[0052] The negative current collector in the secondary battery of the embodiments of the present application is beneficial to improve the rate capability of the ion battery.

[0053] The second aspect of the present application provides a negative current collector, the negative current collector including a porous film layer and a coating layer disposed on at least one surface of the porous film layer close to the separator, the coating layer including an inorganic substance, a conductive agent, and a binder, wherein the inorganic substance includes a metal oxide or silicon oxide.

[0054] As a component of the negative current collector, the porous film layer of the embodiments of the present application has a porous structure and has electrolyte permeability. The porous structure and the good electrolyte permeability are beneficial to shorten the migration path of metal ions such as sodium ions and lithium ions, improve the transmission speed of the metal ions, and improve the rate capability of the secondary battery.

[0055] Under high rate conditions, when the migration of metal ions at the negative electrode side is hindered, it is more likely to cause metal deposition and generate dendrites, which can cause short circuit of the positive and negative electrode tabs when the dendrites pierce the separator, thereby affecting the safety performance of the secondary battery. Further, in the negative current collector of the embodiments of the present application, on the one hand, the porous structure and the electrolyte permeability are beneficial to the migration of metal ions, which can reduce the generation of metal dendrites; on the other hand, the porous structure helps to provide more deposition sites for metal ions, so that the negative metal is deposited in the porous structure to a greater extent, i.e. uniformly deposited on the porous structure, which reduces the generation of lithium dendrites or sodium dendrites, and is beneficial to improve the cycle performance and safety performance of the secondary battery.

[0056] The porous film layer generally does not have the conductivity required by the negative current collector. The present application provides the conductivity of the formed current collector by coating the coating layer on the porous film layer. The combination of the conventional conductive agent and the binder has low affinity with the porous film layer, which may cause powdering and peeling, and greatly affects the cycle performance of the battery. The present application adds inorganic substance to the coating layer, which has a mortise and tenon effect and can rivet the conductive agent, the binder, and the porous film layer, greatly increasing the affinity of the coating layer and the porous film layer, and also increasing the thermal stability and mechanical stability of the current collector, and reducing the film-forming property of the binder. The coating layer of the embodiments of the present application has good coating performance, and the current collector obtained by coating on the porous film layer has conductivity, porous structure, electrolyte permeability, good mechanical strength, and thermal stability, and the obtained secondary battery has good rate capability.

[0057] In any embodiment, the metal oxide includes at least one of aluminum oxide, boehmite, magnesium oxide, iron oxide, zirconium oxide, titanium oxide, or zinc oxide.

[0058] When the inorganic substance is of the above type, it has better affinity with the porous membrane layer, and has better mechanical stability and thermal stability, which is conducive to further improving the cycle performance and rate performance of the secondary battery.

[0059] In any embodiment, the binder includes at least one of an acrylic monomer unit homopolymer and / or copolymer, an acrylic ester monomer unit homopolymer and / or copolymer, a polyol monomer unit-polyisocyanate monomer unit copolymer, a dibasic amine monomer unit-dibasic anhydride monomer unit copolymer, a butadiene monomer unit-styrene monomer unit copolymer, a styrene monomer unit-acrylic ester monomer unit copolymer, or a derivative thereof, a modified species thereof.

[0060] The binder provides cohesiveness to each composition of the coating.

[0061] In any embodiment, the conductive agent includes at least one of conductive carbon black, carbon nanotube, graphene, superconducting carbon, acetylene black, ketjen black, carbon dot, or carbon nanofiber.

[0062] The conductive agent can build a conductive network, providing the current collector with conductivity, which is conducive to electron transmission.

[0063] In any embodiment, the mass percentage content of the inorganic substance is 40%-55%, based on the mass of the coating.

[0064] When the content of the inorganic substance in the coating is appropriate, the coating and the porous membrane layer have better affinity, which is conducive to further improving the cycle performance of the secondary battery, further reducing the influence on the conductivity of the current collector, and further improving the rate performance of the secondary battery.

[0065] In any embodiment, the mass percentage content of the binder is 20%-35%, based on the mass of the coating.

[0066] When the content of the binder in the coating is appropriate, it is conducive to further reducing the powder dropping of the coating, thereby further improving the affinity of the coating with the porous membrane layer and further improving the cycle performance of the secondary battery.

[0067] In any embodiment, the mass percentage content of the conductive agent is 5%-15%, based on the mass of the coating.

[0068] When the content of the conductive agent in the coating is appropriate, it is beneficial to improve the conductivity of the negative current collector, thereby further improving the rate performance of the secondary battery. Further, the conductive agent has poor affinity with the porous membrane layer, and the conductive agent has active groups. Too much conductive agent can consume the deposited metal of the negative electrode. Therefore, the appropriate content of the conductive agent also helps to further improve the affinity of the coating and the porous membrane layer, reduce the consumption of the deposited metal of the negative electrode, and further improve the cycle performance and the first coulombic efficiency of the secondary battery.

[0069] In any embodiment, the coating further comprises a dispersant.

[0070] In any embodiment, the dispersant comprises at least one of carboxymethyl cellulose, methyl cellulose, sodium starch phosphate, sodium carboxymethyl cellulose, sodium polyacrylate, polyoxyethylene, or polyvinylpyrrolidone.

[0071] The addition of the dispersant in the coating is beneficial to the better dispersion of the inorganic substance and the conductive agent, reduces their sedimentation and agglomeration, and helps the inorganic substance and the conductive agent to further exert their respective functions.

[0072] In any embodiment, the coating has a coating weight per unit area of 1-5 mg / cm 2 .

[0073] The coating has an appropriate coating weight per unit area, which helps to coat more uniformly on the porous membrane, thereby further reducing the leakage coating, providing better conductivity for the current collector, and further improving the rate performance of the secondary battery. Further, the appropriate coating weight per unit area also helps to improve the cycle performance of the secondary battery.

[0074] In any embodiment, the porous membrane layer has a porosity of 30%-60%.

[0075] The appropriate number of porous structures helps to further improve the transmission speed of metal ions, thereby further improving the rate performance of the secondary battery; it is also beneficial to provide a more appropriate number of deposition sites, so that the metal deposition of the negative electrode is more uniform, thereby further reducing the generation of lithium dendrites or sodium dendrites, thereby further improving the cycle performance and safety performance of the secondary battery. Further, the appropriate number of porous structures is more helpful for effectively supporting the coating.

[0076] In any embodiment, the porous membrane layer comprises at least one of a porous polyolefin membrane, a porous glass fiber, a porous non-woven fabric, a porous polyimide membrane, a porous polyvinylidene fluoride membrane, or a porous polyterephthalate.

[0077] The above type of porous membrane has a porous structure and has good electrolyte permeability, which is beneficial to further improve the rate performance of the secondary battery of the present application, reduce the generation of dendrites, and improve the safety performance of the secondary battery.

[0078] In any embodiment, the coating is provided on at least one surface of the porous membrane layer close to the separator.

[0079] In any embodiment, the coating is provided on both surfaces of the porous membrane layer.

[0080] When the coating is provided on at least one surface of the porous membrane layer close to the separator, the secondary battery of the present application has high rate capability. The coating provided on both surfaces of the porous membrane layer is more conducive to improving the rate capability of the secondary battery of the present application.

[0081] The third aspect of the present application provides a method for preparing a negative electrode current collector, the method comprising at least the following steps:

[0082] dissolving the raw material in a solvent to form a coating slurry after stirring;

[0083] applying the coating slurry on at least one surface of the porous membrane layer close to the separator to obtain a negative electrode current collector;

[0084] The raw material comprises inorganic matter, a binder and a conductive agent, and the inorganic matter comprises at least one of metal oxide or silicon oxide.

[0085] The above preparation method can be used to prepare the negative electrode current collector of the present application.

[0086] In any embodiment, the metal oxide comprises at least one of aluminum oxide, boehmite, magnesium oxide, iron oxide, zirconium oxide, titanium oxide or zinc oxide.

[0087] When the inorganic matter is of the above type, it has better affinity with the porous membrane layer, and has better mechanical stability and thermal stability, which is conducive to further improving the cycle performance and rate capability of the secondary battery.

[0088] In any embodiment, the binder comprises at least one of acrylic monomer unit homopolymer and / or copolymer, acrylic ester monomer unit homopolymer and / or copolymer, polyol monomer unit-polyisocyanate monomer unit copolymer, dibasic amine monomer unit-dibasic anhydride monomer unit copolymer, butadiene monomer unit-styrene monomer unit copolymer, styrene monomer unit-acrylic ester monomer unit copolymer, or derivatives thereof, modified species thereof.

[0089] The binder provides adhesion for each composition of the coating.

[0090] In any embodiment, the mass percentage of the inorganic matter is 40%-55% based on the mass of the raw material.

[0091] When the content of the inorganic substance is appropriate, the coating slurry and the porous membrane layer have better adhesion, which is conducive to further improving the cycle performance of the secondary battery, further reducing the influence on the conductive performance of the current collector, and further improving the rate performance of the secondary battery.

[0092] In any embodiment, the content of the binder is 20%-35% by mass percentage based on the mass of the raw materials.

[0093] When the content of the binder is appropriate, it is conducive to further reducing the powder falling of the coating, thereby further improving the adhesion between the coating and the porous membrane layer and further improving the cycle performance of the secondary battery.

[0094] In any embodiment, the content of the conductive agent is 5%-15% by mass percentage based on the mass of the raw materials.

[0095] When the content of the conductive agent is appropriate, it is conducive to improving the conductive performance of the negative current collector, thereby further improving the rate performance of the secondary battery. Further, the adhesion between the conductive agent and the porous membrane layer is poor, and the conductive agent has active groups. Therefore, appropriate content of the conductive agent is also conducive to further improving the adhesion between the coating and the porous membrane layer, reducing the consumption of the deposited metal of the negative electrode, and thereby further improving the cycle performance and the initial coulomb efficiency of the secondary battery.

[0096] In any embodiment, the raw materials further include a dispersant.

[0097] The addition of the dispersant in the coating slurry is conducive to better dispersion of the inorganic substance and the conductive agent, reduces their sedimentation and agglomeration, and helps the inorganic substance and the conductive agent to further exert their respective functions.

[0098] The fourth aspect of the present application provides a power utilization device, which includes the secondary battery of the present application or the negative current collector of the present application.

[0099] The above description is only a summary of the technical solutions of the present application. In order to more clearly understand the technical means of the present application, the specific embodiments of the present application can be implemented in accordance with the content of the description, and in order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS

[0100] FIG. 1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0101] FIG. 2 is an exploded view of the secondary battery according to an embodiment of the present application shown in FIG. 1;

[0102] FIG. 3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0103] FIG. 4 is a schematic view of a battery pack according to an embodiment of the present application;

[0104] FIG. 5 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG. 4;

[0105] FIG. 6 is a schematic view of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0106] BRIEF DESCRIPTION OF DRAWINGS 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 case; 52 electrode assembly; 53 top cap assembly. DETAILED DESCRIPTION

[0107] Hereinafter, embodiments of the positive electrode active material and the method for manufacturing the same, the positive electrode sheet, the secondary battery, the battery module, the battery pack, and the electric device according to the present application are specifically disclosed with appropriate reference to the accompanying drawings. However, there can be cases where unnecessary detailed descriptions are omitted. For example, there can be cases where detailed descriptions of matters well known to those skilled in the art, repetitive descriptions of substantially identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0108] The ranges disclosed herein are defined by their lower and upper limits, and are inclusive of the recited ranges. Ranges are defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. Ranges defined by this approach can be inclusive or exclusive of the end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if a range of 60-120 and a range of 80-110 are listed for a particular parameter, it is understood that a range of 60-110 and a range of 80-120 are also contemplated. In addition, if a minimum range value of 1 and 2 is listed, and if a maximum range value of 3, 4, and 5 is listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise stated, a numerical range "a-b" indicates a shorthand manner of describing any and all possible combinations of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed herein, and "0-5" is merely a shorthand manner of describing these numerical combinations. In addition, when it is stated that a parameter is an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0109] All embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, unless otherwise specified.

[0110] If not particularly specified, all the technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0111] If not particularly specified, all the steps of the present application can be performed in sequence or randomly, and preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) performed in sequence, or steps (b) and (a) performed in sequence. For example, the method mentioned can further comprise step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0112] If not particularly specified, the "comprise" and "include" mentioned in the present application are open-ended, and can also be closed. For example, the "comprise" and "include" can mean that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0113] If not particularly specified, in the present 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 satisfy 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 A and B are both true (or exist).

[0114] With the popularization of the application range of secondary batteries, the requirements for the electrical properties of secondary batteries, such as the rate performance, are gradually improved. The negative current collector in the battery is generally a metal foil, such as a copper foil, which may hinder the migration of metal ions and increase the migration path of metal ions, which is not conducive to improving the rate performance of the secondary battery.

[0115] [Secondary battery]

[0116] Based on this, the present application provides a secondary battery, which comprises a positive electrode sheet, a negative electrode sheet, and a separator arranged between the negative electrode sheet and the positive electrode sheet, wherein the negative electrode sheet comprises a negative current collector, the negative current collector comprises a porous membrane layer and a coating layer arranged at least on the surface of the porous membrane layer close to the separator, and the coating layer comprises inorganic matter, a conductive agent and a binder, wherein the inorganic matter comprises at least one of a metal oxide or silicon oxide.

[0117] As used herein, the term "metal oxide" refers to a binary compound composed of oxygen and metal elements.

[0118] The structure of the negative current collector and the composition of the inorganic substance can be measured by methods and devices known in the art. As an example, the battery is disassembled to obtain the negative electrode sheet, and if there is a negative film layer on the negative electrode sheet, the negative film layer of the negative electrode sheet is peeled off to obtain the negative current collector, and if there is no negative film layer on the negative electrode sheet, the negative current collector can be directly cut into a section using an electron beam or other similar means (for example, a cutter), and the section can be directly observed using a scanning electron microscope. The porous film layer and the coating layer of the negative current collector can be observed, and at least two layers of the structure (two layers of the structure are specifically the porous film layer and the coating layer on the side of the porous film layer close to the separator, and three layers of the structure are specifically the porous film layer and the coating layers on both sides of the porous film layer) can be observed. Further, the obtained negative current collector is subjected to a powder scraping operation to obtain a coating powder. The coating powder is calcined in air or oxygen at a certain temperature (for example, 500°C) until the weight of the powder no longer changes. At this time, the remaining powder is the inorganic substance. The remaining substance is tested by X-ray diffractometry, and compared with a standard spectrum to confirm the composition of the inorganic substance. At the same time, the remaining substance can also be subjected to X-ray fluorescence spectroscopy (XRF) or inductively coupled plasma (ICP) analysis to analyze the elemental composition of the substance, and the test structure of the X-ray diffractometer is verified to further determine the specific composition of the inorganic substance.

[0119] In some embodiments, the porous film layer allows the electrolyte to pass through the thickness of the porous film layer from one side to the other side.

[0120] As a component of the negative current collector, the porous film layer in the secondary battery of the embodiments of the present application has a porous structure and has electrolyte permeability. The porous structure and the good electrolyte permeability are beneficial to shorten the migration path of metal ions such as sodium ions and lithium ions, improve the transmission speed of metal ions, and improve the rate performance of the secondary battery.

[0121] Under high-rate conditions, when the migration of metal ions at the negative electrode side is hindered, it is more likely to cause metal deposition and generate dendrites, and when the dendrites pierce the separator, it will cause short circuit between the positive and negative electrode sheets, thereby affecting the safety performance of the secondary battery. Further, in the negative current collector of the secondary battery of the embodiments of the present application, on the one hand, the porous structure and the electrolyte permeability of the negative current collector are beneficial to the migration of metal ions, which can reduce the generation of metal dendrites; on the other hand, the porous structure helps to provide more deposition sites for metal ions, so that the negative metal is deposited in the porous structure to a greater extent, i.e., uniformly deposited on the porous structure, which reduces the generation of lithium dendrites or sodium dendrites, and is beneficial to improve the cycle performance and safety performance of the secondary battery.

[0122] The porous membrane layer generally does not have the conductivity required by the negative current collector. The secondary battery of the present application provides the formed current collector with conductivity by coating the porous membrane layer with a coating layer. The conventional combination of the conductive agent and the binder has low affinity with the porous membrane layer, and may fall off or peel off, greatly affecting the cycle performance of the battery. The present application adds inorganic matter to the coating layer. The inorganic matter has a mortise and tenon effect, and can rivet the conductive agent, the binder and the porous membrane layer, greatly increasing the affinity of the coating layer with the porous membrane layer, and also increasing the thermal stability and mechanical stability of the current collector, and reducing the film-forming property of the binder. The coating layer of the secondary battery of the present application has good affinity with the porous membrane layer, and the current collector obtained by coating the porous membrane layer has conductivity, a porous structure, electrolyte permeability, good mechanical strength and thermal stability, and the obtained secondary battery has good rate performance.

[0123] In some embodiments, the metal oxide includes at least one of aluminum oxide, boehmite, magnesium oxide, iron oxide, zirconium oxide, titanium oxide, or zinc oxide.

[0124] In some embodiments, the metal oxide includes at least one of aluminum oxide, boehmite, or titanium oxide.

[0125] When the inorganic matter is a substance of the above type, it has better affinity with the porous membrane layer, and has better mechanical stability and thermal stability, which is conducive to further improving the cycle performance and rate performance of the secondary battery.

[0126] In some embodiments, the binder includes at least one of an acrylic monomer unit homopolymer and / or copolymer, an acrylic ester monomer unit homopolymer and / or copolymer, a polyol monomer unit-polyisocyanate monomer unit copolymer, a dibasic amine monomer unit-dibasic anhydride monomer unit copolymer, a butadiene monomer unit-styrene monomer unit copolymer, a styrene monomer unit-acrylic ester monomer unit copolymer, or a derivative thereof, a modified species thereof.

[0127] As used herein, the term "homopolymer" refers to a polymer formed by polymerization of one monomer.

[0128] As used herein, the term "copolymer" refers to a polymer formed by polymerization of two or more monomers, which includes two or more monomer units. According to the arrangement of the monomers in the molecular chain of the copolymer, the copolymer can be divided into random copolymer, alternating copolymer, block copolymer and graft copolymer.

[0129] As used herein, the term "derivative" refers to a substance derived by substituting a group, such as a hydrogen atom, on the original molecule with another group.

[0130] As used herein, the term "modification" refers to a substance formed by further modification of the original molecule by different means, such as physical or chemical means, changing some of its physical or chemical properties.

[0131] In some embodiments, the binder includes at least one of an acrylic monomer unit homopolymer and / or copolymer, an acrylate monomer unit homopolymer and / or copolymer, a butadiene monomer unit-styrene monomer unit copolymer, a styrene monomer unit-acrylate monomer unit copolymer, or a derivative thereof, a modification thereof.

[0132] The binder provides cohesiveness to each composition of the coating.

[0133] In some embodiments, the binder includes at least one of a butadiene monomer unit-styrene monomer unit copolymer, a styrene monomer unit-acrylate monomer unit copolymer, a methyl acrylate monomer unit homopolymer, an ethyl acrylate monomer unit homopolymer, a butyl acrylate monomer unit homopolymer, an isooctyl acrylate monomer unit homopolymer, an acrylate monomer unit copolymer, or a derivative thereof, a modification thereof.

[0134] As used herein, the term "butadiene monomer unit-styrene monomer unit copolymer" refers to a copolymer formed by monomer butadiene and monomer styrene.

[0135] As used herein, the term "styrene monomer unit-acrylate monomer unit copolymer" refers to a copolymer formed by monomer styrene and monomer acrylate, wherein the acrylate can include at least one of methyl acrylate, ethyl acrylate, butyl acrylate, or isooctyl acrylate.

[0136] As used herein, the term "methyl acrylate monomer unit homopolymer" refers to a homopolymer obtained by free radical polymerization of monomer methyl acrylate, and ethyl acrylate monomer unit homopolymer, butyl acrylate monomer unit homopolymer, isooctyl acrylate monomer unit homopolymer have similar definitions.

[0137] In some embodiments, the binder includes at least one of a butadiene monomer unit-styrene monomer unit copolymer, a styrene monomer unit-acrylate monomer unit copolymer, an ethyl acrylate monomer unit homopolymer, or a derivative thereof, a modification thereof.

[0138] In some embodiments, the styrene monomer unit-acrylate monomer unit copolymer includes at least one of a styrene monomer unit-methyl acrylate monomer unit copolymer, a styrene monomer unit-ethyl acrylate monomer unit copolymer, a styrene monomer unit-butyl acrylate monomer unit copolymer, a styrene monomer unit-isooctyl acrylate monomer unit copolymer.

[0139] In some embodiments, the copolymer of butadiene monomer units-styrene monomer units has a copolymerization molar ratio of butadiene monomer units to styrene monomer units of (7-3) : (3-7).

[0140] In some embodiments, the copolymer of butadiene monomer units-styrene monomer units has a copolymerization molar ratio of butadiene monomer units to styrene monomer units of 7:3, 6:4, 5:5, 4:6, 3:7, or a range or a value in the range between any two of the above-mentioned copolymerization molar ratios.

[0141] In some embodiments, the copolymer of styrene monomer units-acrylate monomer units has a copolymerization molar ratio of styrene monomer units to acrylate monomer units of (3-5) : (7-5).

[0142] In some embodiments, the copolymer of styrene monomer units-acrylate monomer units has a copolymerization molar ratio of styrene monomer units to acrylate monomer units of 3:7, 4:6, 5:5, or a range or a value in the range between any two of the above-mentioned copolymerization molar ratios.

[0143] The binder of the above-mentioned type has a lower surface tension, which is conducive to further improving the adhesion of the coating to the porous membrane layer.

[0144] In some embodiments, the conductive agent comprises at least one of conductive carbon black, carbon nanotube, graphene, superconducting carbon, acetylene black, ketjen black, carbon dot, or carbon nanofiber.

[0145] The conductive agent can build a conductive network, which provides the current collector with conductivity and is conducive to electron transmission.

[0146] In some embodiments, the inorganic matter has a mass percentage of 40% to 55% based on the mass of the coating.

[0147] The mass of the inorganic matter in the coating can be measured by methods and devices known in the art. Specifically, the battery is disassembled to obtain a negative electrode sheet. If the negative electrode sheet has a negative electrode membrane layer, the negative electrode membrane layer is peeled off to obtain a negative electrode current collector. If the negative electrode sheet does not have a negative electrode membrane layer, the negative electrode current collector is subjected to a powder scraping operation to obtain a coating powder, and the mass of the coating powder is measured as M1. The coating powder is calcined in air or oxygen at a certain temperature (for example, 500°C) until the weight of the powder no longer changes. At this time, the remaining powder is the inorganic matter, and the mass of the inorganic matter is measured as M0. The mass percentage of the inorganic matter is (M0 / M1) x 100%.

[0148] In some embodiments, the inorganic matter has a mass percentage of 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, or a range or a value in the range formed by any two of the above mass percentages, based on the mass of the coating.

[0149] In some embodiments, the inorganic matter has a mass percentage of 45%-50%, based on the mass of the coating.

[0150] When the content of the inorganic matter in the coating is appropriate, the coating and the porous membrane layer have better adhesion, which is conducive to further improving the cycle performance of the secondary battery and further reducing the influence on the conductive performance of the current collector, thereby further improving the rate performance of the secondary battery.

[0151] In some embodiments, the binder has a mass percentage of 20%-35%, based on the mass of the coating.

[0152] In some embodiments, the binder has a mass percentage of 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, or a range or a value in the range formed by any two of the above mass percentages, based on the mass of the coating.

[0153] In some embodiments, the binder has a mass percentage of 25%-30%, based on the mass of the coating.

[0154] When the content of the binder in the coating is appropriate, it is conducive to further reducing the powder falling of the coating, thereby further improving the adhesion between the coating and the porous membrane layer and improving the cycle performance of the secondary battery.

[0155] In some embodiments, the conductive agent has a mass percentage of 5%-15%, based on the mass of the coating.

[0156] In some embodiments, the conductive agent has a mass percentage of 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or a range or a value in the range formed by any two of the above mass percentages, based on the mass of the coating.

[0157] In some embodiments, the conductive agent has a mass percentage of 8%-12%, based on the mass of the coating.

[0158] When the content of the conductive agent in the coating is appropriate, it is beneficial to further improve the conductive performance of the negative current collector, thereby further improving the rate performance of the secondary battery. The conductive agent has poor affinity with the porous membrane layer, and the conductive agent has active groups. Too much conductive agent can consume the deposited metal of the negative electrode. Therefore, the appropriate content of the conductive agent also helps to further improve the affinity of the coating and the porous membrane layer, reduce the consumption of the deposited metal of the negative electrode, and further improve the cycle performance and the first coulombic efficiency of the secondary battery.

[0159] In some embodiments, the coating further comprises a dispersant.

[0160] In some embodiments, the dispersant comprises at least one of carboxymethyl cellulose, methyl cellulose, sodium starch phosphate, sodium carboxymethyl cellulose, sodium polyacrylate, polyoxyethylene, or polyvinylpyrrolidone.

[0161] In some embodiments, the dispersant comprises at least one of carboxymethyl cellulose or sodium carboxymethyl cellulose.

[0162] The addition of the dispersant in the coating is beneficial to the better dispersion of the inorganic substance and the conductive agent, reduces the settlement and agglomeration thereof, and helps the inorganic substance and the conductive agent to further exert their respective functions.

[0163] In some embodiments, the mass percentage content of the dispersant is 0%-10% based on the mass of the coating.

[0164] In some embodiments, the mass percentage content of the dispersant can be 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range or a value in the range composed of any two of the above mass percentage contents, based on the mass of the coating.

[0165] In some embodiments, the mass percentage content of the dispersant is greater than 0% based on the mass of the coating.

[0166] In the coating, the dispersant has an appropriate content, which is beneficial to further improve the dispersion capacity of the coating.

[0167] In some embodiments, the coating has a coating weight per unit area of 1-5 mg / cm 2 .

[0168] In some embodiments, the coating can have a coating weight per unit area of 1 mg / cm 2 , 1.5 mg / cm 2 , 2 mg / cm 2 , 2.5 mg / cm 2 , 3 mg / cm 2 , 3.5 mg / cm 2, 4 mg / cm 2 , 4.5 mg / cm 2 , 5 mg / cm 2 , or a range or a value in the range of any two of the above mass percentages.

[0169] In some embodiments, the coating has a coating weight per unit area of 2-3 mg / cm 2 .

[0170] The coating has a suitable coating weight per unit area, which helps to make the coating on the porous membrane more uniform, thereby further reducing the leakage of the coating, providing better conductivity for the current collector, further improving the rate performance of the secondary battery; further, the suitable coating weight per unit area also helps to improve the cycle performance of the secondary battery.

[0171] In some embodiments, the porosity of the porous membrane layer is 30%-60%.

[0172] As used herein, the term "porosity" refers to the percentage of the volume of pores in a material to the total volume of the material in a natural state.

[0173] In some embodiments, the porosity of the porous membrane layer can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, or a range or a value in the range of any two of the above porosities.

[0174] In some embodiments, the porosity of the porous membrane layer is 40%-50%.

[0175] The porosity of the porous membrane layer can be measured by methods and devices known in the art. A specific example is to place the porous membrane sample to be measured in a mercury porosimeter, ensuring that the sample is well sealed with the instrument; inject mercury into the instrument and gradually increase the mercury pressure; observe the volume change of the porous membrane sample and record the volume values at different pressures; according to the relationship between the volume change and the mercury pressure, draw a pressure-volume curve; and calculate the porosity of the porous membrane according to the pressure-volume curve.

[0176] The suitable number of porous structures helps to further improve the transmission speed of metal ions, thereby further improving the rate performance of the secondary battery; also helps to provide a more suitable number of deposition sites, making the deposition of the negative metal more uniform, thereby further reducing the generation of lithium dendrites or sodium dendrites, thereby further improving the cycle performance and safety performance of the secondary battery. Further, the suitable number of porous structures is more conducive to effectively supporting the coating.

[0177] In some embodiments, the porous membrane layer comprises at least one of a porous polyolefin membrane, a porous glass fiber, a porous non-woven fabric, a porous polyimide membrane, a porous polyvinylidene fluoride membrane, or a porous polyterephthalate.

[0178] In some embodiments, the porous membrane layer can be a single layer film or a multi-layer composite film. When the porous membrane layer is a multi-layer composite film, the materials of the layers can be the same or different.

[0179] The porous membrane of the above type has a porous structure and good electrolyte permeability, which is beneficial to further improve the rate performance of the secondary battery, reduce dendrite generation, improve the cycle performance of the secondary battery, and even the safety performance.

[0180] In some embodiments, the thickness of the porous membrane layer is 6-15 μm.

[0181] In some embodiments, the thickness of the porous membrane layer is 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or a range or a value in the range formed by any two of the above thicknesses.

[0182] The thickness of the porous membrane layer can be measured by methods and devices known in the art. A specific example is that the battery is disassembled to obtain the negative electrode sheet. If there is a negative electrode membrane layer on the negative electrode sheet, the negative electrode membrane layer of the negative electrode sheet is peeled off to obtain the negative electrode current collector. If there is no negative electrode membrane layer on the negative electrode sheet, the negative electrode current collector can be directly cleaned with a suitable solvent (such as water) to remove the coating to obtain the porous membrane layer, and the thickness of the porous membrane layer can be measured by using a micrometer.

[0183] The porous membrane layer with a suitable thickness is beneficial to provide a suitable transmission distance, which is beneficial to further improve the rate performance of the secondary battery.

[0184] In some embodiments, the coating is provided on at least one surface of the porous membrane layer close to the separator.

[0185] In some embodiments, the coating is provided on the surface close to the separator.

[0186] In some embodiments, the coating is provided on the surfaces of the porous membrane layer on both sides.

[0187] When the coating is provided on at least one surface of the porous membrane layer close to the separator, the secondary battery of the embodiments of the present application has high rate performance. When the coating is provided on the surfaces of the porous membrane layer on both sides, it is more beneficial to improve the rate performance of the secondary battery of the embodiments of the present application.

[0188] In some embodiments, the secondary battery comprises a negative electrode-free metal battery.

[0189] In some embodiments, the secondary battery comprises a negative electrode-free sodium metal battery or a negative electrode-free lithium metal battery.

[0190] As used herein, the term "negative electrode metal-free battery" refers to a battery configured without a negative electrode active material layer being actively provided at the negative electrode side during the manufacturing process of the battery, for example, without a sodium metal or lithium metal or carbonaceous active material layer being provided at the negative electrode by a coating or deposition or the like process during the manufacturing process of the battery. Upon the first charge, metal ions such as sodium ions or lithium ions obtain electrons at the anode side to form a metal phase such as a sodium metal phase or a lithium metal phase by deposition of the metal such as sodium or lithium on the surface of the current collector, and upon discharge, the metal such as sodium or lithium can be converted into metal ions such as sodium ions or lithium ions to return to the positive electrode, achieving cyclic charging and discharging.

[0191] Generally, since the negative electrode current collector of the negative electrode metal-free battery is a metal foil such as a copper foil, the metal foil lacks a porous structure and has poor electrolyte wettability, and thus the negative electrode current collector of the negative electrode metal-free battery can hinder the migration of metal ions such as sodium ions or lithium ions and increase the migration path thereof, reducing the rate performance of the battery. Furthermore, in this case, metal dendrites such as sodium dendrites or lithium dendrites are more likely to be generated. The application of the negative electrode current collector of the embodiments of the present application to the negative electrode metal-free battery is more conducive to improving the rate performance of the secondary battery; furthermore, it is conducive to better reducing the generation of dendrites.

[0192] In some embodiments, the secondary battery includes an ion battery.

[0193] In some embodiments, the secondary battery includes a lithium ion battery or a sodium ion battery.

[0194] In some embodiments, the negative electrode tab includes a negative electrode film layer disposed on at least one side of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, or a silicon-based material.

[0195] In some embodiments, in the ion battery, for example, the negative electrode current collector has two opposite surfaces in the thickness direction thereof, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0196] The negative electrode current collector in the secondary battery of the embodiments of the present application is conducive to improving the rate performance of the ion battery.

[0197] In some embodiments, the negative electrode film layer includes a binder. 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).

[0198] In some embodiments, the negative electrode film layer comprises a conductive agent. The conductive agent can be selected from at least one of super-P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0199] In some embodiments, the negative electrode film layer can also optionally comprise other auxiliary agents, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0200] In some embodiments, the negative electrode sheet of the ion battery can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on the negative electrode current collector of the present application, and after drying, cold pressing, and the like, the negative electrode sheet can be obtained.

[0201] [Negative electrode current collector]

[0202] The present application provides a negative electrode current collector, which comprises a porous film layer and a coating layer provided at least on the surface of the porous film layer close to the side of the separator, wherein the coating layer comprises inorganic matter, a conductive agent, and a binder, and the inorganic matter comprises at least one of metal oxide or silicon oxide.

[0203] In some embodiments, the negative electrode current collector comprises a porous film layer and a coating layer provided at least on the surface of the porous film layer close to the side of the separator.

[0204] As a component of the negative electrode current collector, the porous film layer of the embodiments of the present application has a porous structure and has electrolyte permeability. The porous structure and the good electrolyte permeability are conducive to shortening the migration path of metal ions such as sodium ions and lithium ions, improving the transmission speed of the metal ions, and improving the rate performance of the secondary battery.

[0205] Under high-rate conditions, when the migration of metal ions at the negative electrode side is hindered, it is more likely to cause metal precipitation and generate dendrites, and when the dendrites pierce the separator, it will cause short circuit of the positive and negative electrode sheets, thereby affecting the safety performance of the secondary battery. Further, in the negative electrode current collector of the embodiments of the present application, on the one hand, the porous structure and the electrolyte permeability of the negative electrode current collector are conducive to the migration of metal ions, which can reduce the generation of metal dendrites; on the other hand, the porous structure helps to provide more deposition sites for metal ions, so that the negative electrode metal is deposited in the porous structure to a greater extent, i.e., uniformly deposited on the porous structure, which reduces the generation of lithium dendrites or sodium dendrites, and is conducive to improving the cycle performance and safety performance of the secondary battery.

[0206] The porous film layer generally does not have the conductivity required by the negative electrode current collector. The present application provides the conductivity for the formed current collector by coating the coating layer on the porous film layer.

[0207] The conventional conductive agent and binder composition has low affinity with the porous film layer, and powder dropping and peeling may occur, which greatly affects the cycle performance of the battery. By adding inorganic matter to the coating layer, the inorganic matter has a mortise and tenon effect, which can rivet the conductive agent, the binder and the porous film layer, greatly increasing the affinity of the coating layer with the porous film layer, and also increasing the thermal stability and mechanical stability of the current collector and reducing the film-forming property of the binder. The coating layer of the embodiment has good coating performance, and the current collector obtained by coating on the porous film layer has conductivity, porous structure, electrolyte permeability, good mechanical strength and thermal stability, and the obtained secondary battery has good rate performance.

[0208] In some embodiments, the metal oxide includes at least one of aluminum oxide, boehmite, magnesium oxide, iron oxide, zirconium oxide, titanium oxide, or zinc oxide.

[0209] In some embodiments, the metal oxide includes at least one of aluminum oxide, boehmite, or titanium oxide.

[0210] When the inorganic matter is the above type of matter, it has better affinity with the porous film layer, and has better mechanical stability and thermal stability, which is conducive to further improving the cycle performance and rate performance of the secondary battery.

[0211] In some embodiments, the binder includes at least one of an acrylic monomer unit homopolymer and / or copolymer, an acrylate monomer unit homopolymer and / or copolymer, a polyol monomer unit-polyisocyanate monomer unit copolymer, a dibasic amine monomer unit-dibasic anhydride monomer unit copolymer, a butadiene monomer unit-styrene monomer unit copolymer, a styrene monomer unit-acrylate monomer unit copolymer, or a derivative thereof, a modified species thereof.

[0212] In some embodiments, the binder includes at least one of an acrylic monomer unit homopolymer and / or copolymer, an acrylate monomer unit homopolymer and / or copolymer, a butadiene monomer unit-styrene monomer unit copolymer, a styrene monomer unit-acrylate monomer unit copolymer, or a derivative thereof, a modified species thereof.

[0213] The binder provides cohesiveness to the compositions of the coating layer.

[0214] In some embodiments, the binder includes at least one of a butadiene monomer unit-styrene monomer unit copolymer, a styrene monomer unit-acrylate monomer unit copolymer, a methyl acrylate monomer unit homopolymer, an ethyl acrylate monomer unit homopolymer, a butyl acrylate monomer unit homopolymer, an isooctyl acrylate monomer unit homopolymer, an acrylate monomer unit copolymer, or a derivative thereof, a modified species thereof.

[0215] In some embodiments, the binder comprises at least one of a butadiene monomer unit-styrene monomer unit copolymer, a styrene monomer unit-acrylate monomer unit copolymer, an ethyl acrylate monomer unit homopolymer, or a derivative thereof, a modified species thereof.

[0216] In some embodiments, the styrene monomer unit-acrylate monomer unit copolymer comprises at least one of a styrene monomer unit-methyl acrylate monomer unit copolymer, a styrene monomer unit-ethyl acrylate monomer unit copolymer, a styrene monomer unit-butyl acrylate monomer unit copolymer, a styrene monomer unit-iso-octyl acrylate monomer unit copolymer.

[0217] In some embodiments, the butadiene monomer unit-styrene monomer unit copolymer has a copolymerization molar ratio of butadiene monomer unit to styrene monomer unit of (7-3):(3-7).

[0218] In some embodiments, the butadiene monomer unit-styrene monomer unit copolymer has a copolymerization molar ratio of butadiene monomer unit to styrene monomer unit of 7:3, 6:4, 5:5, 4:6, 3:7, or a range or a value in the range between any two of the above-mentioned copolymerization molar ratios.

[0219] In some embodiments, the styrene monomer unit-acrylate monomer unit copolymer has a copolymerization molar ratio of styrene monomer to acrylate monomer of (3-5):(7-5).

[0220] In some embodiments, the styrene monomer unit-acrylate monomer unit copolymer has a copolymerization molar ratio of styrene monomer to acrylate monomer of 3:7, 4:6, 5:5, or a range or a value in the range between any two of the above-mentioned copolymerization molar ratios.

[0221] The binder of the above-mentioned type has a lower surface tension, which is beneficial to further improve the adhesion of the coating layer to the porous membrane layer.

[0222] In some embodiments, the conductive agent comprises at least one of conductive carbon black, carbon nanotube, graphene, superconducting carbon, acetylene black, ketjen black, carbon dot, or carbon nanofiber.

[0223] The conductive agent is capable of constructing a conductive network, which provides the current collector with conductivity and is beneficial to electron transport.

[0224] In some embodiments, the inorganic matter has a mass percentage of 40%-55% based on the mass of the coating layer.

[0225] In some embodiments, the inorganic matter has a mass percentage of 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, or a range between any two of the above values, or a value within the range.

[0226] In some embodiments, the inorganic matter has a mass percentage of 45%-50%, based on the mass of the coating.

[0227] When the content of the inorganic matter in the coating is appropriate, the coating and the porous membrane layer have better adhesion, which is conducive to further improving the cycle performance of the secondary battery and further reducing the influence on the conductivity of the current collector, thereby further improving the rate performance of the secondary battery.

[0228] In some embodiments, the binder has a mass percentage of 20%-35%, based on the mass of the coating.

[0229] In some embodiments, the binder has a mass percentage of 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, or a range between any two of the above values, or a value within the range.

[0230] In some embodiments, the binder has a mass percentage of 25%-30%, based on the mass of the coating.

[0231] When the content of the binder in the coating is appropriate, it is conducive to further reducing the powder falling of the coating, thereby further improving the adhesion between the coating and the porous membrane layer and improving the cycle performance of the secondary battery.

[0232] In some embodiments, the conductive agent has a mass percentage of 5%-15%, based on the mass of the coating.

[0233] In some embodiments, the conductive agent has a mass percentage of 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or a range between any two of the above values, or a value within the range.

[0234] In some embodiments, the conductive agent has a mass percentage of 8%-12%, based on the mass of the coating.

[0235] When the content of the conductive agent in the coating is appropriate, it is beneficial to further improve the conductive performance of the negative current collector, thereby further improving the rate performance of the secondary battery. The conductive agent has poor affinity with the porous membrane layer, and the conductive agent has active groups. Too much conductive agent can consume the deposited metal of the negative electrode. Therefore, the appropriate content of the conductive agent also helps to further improve the affinity of the coating and the porous membrane layer, reduce the consumption of the deposited metal of the negative electrode, and further improve the cycle performance and the first coulombic efficiency of the secondary battery.

[0236] In some embodiments, the coating further comprises a dispersant.

[0237] In some embodiments, the dispersant comprises at least one of carboxymethyl cellulose, methyl cellulose, sodium starch phosphate, sodium carboxymethyl cellulose, sodium polyacrylate, polyoxyethylene, or polyvinylpyrrolidone.

[0238] In some embodiments, the dispersant comprises at least one of carboxymethyl cellulose or sodium carboxymethyl cellulose.

[0239] The addition of the dispersant in the coating is beneficial to the better dispersion of the inorganic substance and the conductive agent, reduces the settlement and agglomeration thereof, and helps the inorganic substance and the conductive agent to further exert their respective functions.

[0240] In some embodiments, the mass percentage content of the dispersant is 0%-10% based on the mass of the coating.

[0241] In some embodiments, the mass percentage content of the dispersant can be 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range or a value in the range composed of any two of the above mass percentage contents, based on the mass of the coating.

[0242] In some embodiments, the mass percentage content of the dispersant is greater than 0% based on the mass of the coating.

[0243] In the coating, the dispersant has an appropriate content, which is beneficial to further improve the dispersion capacity of the coating.

[0244] In some embodiments, the coating has a coating weight per unit area of 1-5 mg / cm 2 .

[0245] In some embodiments, the coating can have a coating weight per unit area of 1 mg / cm 2 , 1.5 mg / cm 2 , 2 mg / cm 2 , 2.5 mg / cm 2 , 3 mg / cm 2 , 3.5 mg / cm 2, 4 mg / cm 2 , 4.5 mg / cm 2 , 5 mg / cm 2 , or a range or a value in the range of the composition of any two of the above mass percentages.

[0246] In some embodiments, the coating has a coating weight per unit area of 2-3 mg / cm 2 .

[0247] The coating has a suitable coating weight per unit area, which helps to make the coating on the porous membrane more uniform, thereby further reducing the leakage of the coating, providing better conductivity for the current collector, and further improving the rate performance of the secondary battery. Further, the suitable coating weight per unit area also helps to improve the cycle performance of the secondary battery.

[0248] In some embodiments, the porosity of the porous membrane layer is 30%-60%.

[0249] In some embodiments, the porosity of the porous membrane layer can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, or a range or a value in the range of the composition of any two of the above mass percentages.

[0250] In some embodiments, the porosity of the porous membrane layer is 40%-50%.

[0251] The suitable number of porous structures helps to further improve the transmission speed of metal ions, thereby further improving the rate performance of the secondary battery; it is also beneficial to provide a more suitable number of deposition sites, making the deposition of the negative metal more uniform, thereby further reducing the generation of lithium dendrites or sodium dendrites, thereby further improving the cycle performance and safety performance of the secondary battery. Further, the suitable number of porous structures is more conducive to effectively supporting the coating.

[0252] In some embodiments, the porous membrane layer includes at least one of a porous polyolefin membrane, a porous glass fiber, a porous non-woven fabric, a porous polyimide membrane, a porous polyvinylidene fluoride membrane, or a porous polyterephthalate.

[0253] In some embodiments, the porous membrane layer can be a single-layer film or a multi-layer composite film. When the porous membrane layer is a multi-layer composite film, the materials of the layers can be the same or different.

[0254] The porous membrane of the above type has a porous structure and good electrolyte permeability, which is beneficial to further improve the rate performance of the secondary battery of the present application, reduce the generation of dendrites, improve the cycle performance of the secondary battery, and even the safety performance.

[0255] In some embodiments, the thickness of the porous membrane layer is 6-15 μm.

[0256] In some embodiments, the thickness of the porous membrane layer is 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or a range between any two of the aforementioned thicknesses or a value within the range.

[0257] The porous membrane layer with a suitable thickness is conducive to providing a suitable transmission distance and further improving the rate performance of the secondary battery.

[0258] In some embodiments, the coating layer is provided on at least the surface of the porous membrane layer close to the separator.

[0259] In some embodiments, the coating layer is provided on both surfaces of the porous membrane layer.

[0260] When the coating layer is provided on at least the surface of the porous membrane layer close to the separator, the secondary battery of the embodiments of the present application has high rate performance. The coating layer provided on both surfaces of the porous membrane layer is more conducive to improving the rate performance of the secondary battery of the embodiments of the present application.

[0261] [Method for preparing negative electrode current collector]

[0262] The present application provides a method for preparing a negative electrode current collector, which comprises at least the following steps:

[0263] dissolving the raw materials in a solvent to form a coating slurry after stirring;

[0264] coating the coating slurry on at least the surface of the porous membrane layer close to the separator to obtain a negative electrode current collector;

[0265] The raw materials comprise inorganic matter, a binder and a conductive agent, and the inorganic matter comprises at least one of metal oxide or silicon oxide.

[0266] In some embodiments, the preparation method of the present application can be used to prepare the negative electrode current collector of the present application.

[0267] In some embodiments, the coating weight per unit area of the coating slurry is 1-5 mg / cm 2 .

[0268] In some embodiments, the coating slurry is coated on at least the surface of the porous membrane layer close to the separator.

[0269] In some embodiments, the coating slurry is coated on both surfaces of the porous membrane layer.

[0270] In some embodiments, the solvent comprises a water-soluble solvent.

[0271] In some embodiments, the solvent comprises water.

[0272] In some embodiments, the porous membrane comprises at least one of a porous polyolefin membrane, a porous glass fiber, a porous non-woven fabric, a porous polyimide membrane, a porous polyvinylidene fluoride membrane, or a porous polyterephthalate.

[0273] The preparation method described above can be used to prepare the negative electrode current collector of the present application.

[0274] In some embodiments, the metal oxide comprises at least one of aluminum oxide, boehmite, magnesium oxide, iron oxide, zirconium oxide, titanium oxide, or zinc oxide.

[0275] When the inorganic substance is of the type described above, it has better affinity with the porous membrane layer, and has better mechanical stability and thermal stability, which is conducive to further improving the cycle performance and rate performance of the secondary battery.

[0276] In some embodiments, the binder comprises at least one of an acrylic monomer unit homopolymer and / or copolymer, an acrylate monomer unit homopolymer and / or copolymer, a polyol monomer unit-polyisocyanate monomer unit copolymer, a dibasic amine monomer unit-dibasic anhydride monomer unit copolymer, a butadiene monomer unit-styrene monomer unit copolymer, a styrene monomer unit-acrylate monomer unit copolymer, or a derivative thereof, a modified species thereof.

[0277] In some embodiments, the binder comprises at least one of a butadiene monomer unit-styrene monomer unit copolymer, a styrene monomer unit-acrylate monomer unit copolymer, a methyl acrylate monomer unit homopolymer, an ethyl acrylate monomer unit homopolymer, a butyl acrylate monomer unit homopolymer, an isooctyl acrylate monomer unit homopolymer, an acrylate monomer unit copolymer, or a derivative thereof, a modified species thereof.

[0278] The binder provides adhesion to the respective compositions of the coating.

[0279] In some embodiments, the mass percentage content of the inorganic substance is 40%-55%, based on the mass of the raw materials.

[0280] When the content of the inorganic substance is appropriate, the coating slurry and the porous membrane layer have better affinity, which is conducive to further improving the cycle performance of the secondary battery, further reducing the impact on the conductive performance of the current collector, and further improving the rate performance of the secondary battery.

[0281] In some embodiments, the mass percentage content of the binder is 20%-35%, based on the mass of the raw materials.

[0282] When the content of the binder is appropriate, it is beneficial to further reduce the powder dropping of the coating layer, thereby further improving the adhesion of the coating slurry to the porous membrane layer and further improving the cycle performance of the secondary battery.

[0283] In some embodiments, the mass percentage content of the conductive agent is 5%-15%, based on the mass of the raw materials.

[0284] When the content of the conductive agent is appropriate, it is beneficial to improve the conductive performance of the negative current collector, thereby further improving the rate performance of the secondary battery. Further, the adhesion of the conductive agent to the porous membrane layer is poor, and the conductive agent has active groups. Too much conductive agent may consume the deposited metal of the negative electrode. Therefore, appropriate content of the conductive agent is also helpful to further improve the adhesion of the coating layer and the porous membrane layer, reduce the consumption of the deposited metal of the negative electrode, and thereby further improve the cycle performance and the initial coulombic efficiency of the secondary battery.

[0285] In some embodiments, the raw materials further include a dispersant.

[0286] In some embodiments, the mass percentage content of the dispersant is 0%-10%, based on the mass of the raw materials.

[0287] In some embodiments, the mass percentage content of the dispersant is greater than 0%, based on the mass of the raw materials.

[0288] The addition of the dispersant in the coating slurry is beneficial to the better dispersion of the inorganic substance and the conductive agent, reduces the settlement and agglomeration thereof, and is helpful to the further exertion of the respective functions of the inorganic substance and the conductive agent.

[0289] [Positive electrode sheet]

[0290] In some embodiments, the positive electrode sheet includes a positive current collector and a positive membrane layer arranged on at least one surface of the positive current collector, and the positive membrane layer includes a positive active material.

[0291] In some embodiments, the positive active material can employ a positive active material for a battery known in the art. As an example, the positive active material of the sodium secondary battery can include at least one of a Prussian blue compound, a sodium-containing layered oxide, a sodium-containing polyanion compound, and a modified compound of each thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive active material for a battery can also be used. These positive active materials can be used alone only or in combination of two or more. Among them, examples of the Prussian blue compound include, but are not limited to, an iron-based Prussian blue or a manganese-based Prussian blue; examples of the sodium-containing layered oxide include, but are not limited to, one or more of an iron-based layered oxide, a manganese-based layered oxide, an iron-manganese-based layered oxide, and a transition metal element (such as Ti, Cu, Ni) doped iron-based layered oxide. For example, the iron-based layered oxide includes, but is not limited to, NaFe02, the manganese-based layered oxide includes, but is not limited to, NaMn02, the iron-manganese-based layered oxide includes, but is not limited to, Na x Fe y Mn 1- y O2(x = 0.2 ~ 1, y = 0.1 ~ 0.9, such as Na 0.67 Fe 0.5 Mn 0.5 O2, Na 0.67 Fe 0.45 Mn 0.65 O2); the sodium-containing polyanion compound includes, but is not limited to, one or more of a sodium-containing phosphate, a sodium-containing pyrophosphate, a sodium-containing fluorophosphate, and a sodium-containing mixed phosphate, wherein the sodium-containing phosphate includes, but is not limited to, one or more of Na3V2(PO4)3, Na4Mn V (PO4)3, the sodium-containing pyrophosphate includes, but is not limited to, one or more of NaFeP2O7, NaMnP2O7, NaCoP2O7, the sodium-containing fluorophosphate includes, but is not limited to, NaVPO4F, and the sodium-containing mixed phosphate includes, but is not limited to, one or more of Na4Fe3(PO4)2P2O7, Na4Mn3(PO4)2P2O7.

[0292] As an example, the positive electrode active material of the lithium secondary battery can include at least one of a lithium-containing phosphate of an olivine structure, a lithium transition metal oxide, and a modified compound of each thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery positive electrode active material can also be used. These positive electrode active materials can be used alone only one or two or more in combination. Among them, examples of the lithium transition metal oxide can include, but are not limited to, lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., 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 ), LiNi 0.8 Co 0.1 Mn 0.1 O2(also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.15 Al 0.05 O2), and a modified compound thereof, etc. Examples of the lithium-containing phosphate of an olivine structure can include, but are not limited to, at least one of lithium iron phosphate (e.g., LiFePO4(also referred to as LFP)), a composite of lithium iron phosphate and carbon, lithium manganese phosphate (e.g., LiMnPO4), a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite of lithium manganese iron phosphate and carbon.

[0293] As an example, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode film layer is disposed on either one or both of the two opposite surfaces of the positive electrode current collector.

[0294] In some embodiments, the positive current collector can employ an electrically conductive carbon sheet, a metal foil, a carbon-coated metal foil, a porous metal plate, or a composite current collector. The electrically conductive carbon material of the electrically conductive carbon sheet can be selected from one or more of Super P, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite, graphene, and carbon nanofibers. The metal material of the metal foil, the carbon-coated metal foil, and the porous metal plate can each independently be selected from at least one of copper, aluminum, nickel, and stainless steel. The composite current collector can be a composite current collector formed by combining a metal foil and a polymer-based film.

[0295] In some embodiments, the positive electrode film layer further includes a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), polyvinyl alcohol (PVA), ethylene-vinyl acetate copolymer (EVA), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), sodium alginate (SA), polymethacrylic acid (PMA), and carboxymethyl chitosan (CMCS).

[0296] In some embodiments, the positive electrode film layer further includes a conductive agent. As an example, the conductive agent can include at least one of super conductive carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0297] In some embodiments, the positive electrode tab can be prepared by dispersing the components described above for preparing the positive electrode tab, such as the positive electrode active material, the additive, the conductive agent, the binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector; and drying, cold-pressing, and the like to obtain the positive electrode tab.

[0298] [Electrolyte]

[0299] In some embodiments, the secondary battery further includes an electrolyte between the negative electrode tab and the positive electrode tab.

[0300] The electrolyte functions to conduct ions between the positive electrode tab and the negative electrode tab.

[0301] In some embodiments, the electrolyte is liquid, gel, or all-solid.

[0302] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0303] In some embodiments, the electrolyte salt is a sodium salt. As an example, the sodium salt includes one or more of sodium hexafluorophosphate (NaPF6), sodium chlorate (NaClO4), sodium chloride (NaCl), sodium tetrafluoroborate (NaBF4), sodium nitrate (NaNO3), sodium cyanide (NaCN), or sodium bisulfate (NaHSO4).

[0304] In some embodiments, the electrolyte salt is a lithium salt. Exemplary lithium salts include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium bisoxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate phosphate (LiDFOP), or lithium tetrafluorooxalate phosphate (LiTFOP).

[0305] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl 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, cyclobutane sulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0306] In some embodiments, the electrolyte can further optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can further include an additive capable of improving certain properties of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, etc.

[0307] [Separator]

[0308] In some embodiments, the secondary battery further includes a separator. The type of the separator is not particularly limited in the present application, and any known porous structure separator having good chemical stability and mechanical stability can be used.

[0309] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separator is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0310] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be made into an electrode assembly through a winding process or a stacking process.

[0311] In some embodiments, the secondary battery can include an outer package. The outer package can be used to package the above-described electrode assembly and electrolyte.

[0312] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, or the like. The outer package of the secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, or the like can be listed.

[0313] The shape of the secondary battery is not particularly limited in the present application, and the secondary battery can be cylindrical, square, or any other shape. For example, FIG. 1 is a secondary battery 5 of a square structure as an example.

[0314] In some embodiments, referring to FIG. 2, the outer package can include a shell 51 and a cover plate 53. The shell 51 can 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 communicating with the receiving cavity, and the cover plate 53 can be provided on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator can form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, which can be selected by a person skilled in the art according to specific actual needs.

[0315] In some embodiments, the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, which can be selected by a person skilled in the art according to the application and capacity of the battery module.

[0316] FIG. 3 is a battery module 4 as an example. Referring to FIG. 3, in the battery module 4, a plurality of secondary batteries 5 can be arranged in sequence along the length direction of the battery module 4. Of course, other arrangements can also be used. Further, the plurality of secondary batteries 5 can be fixed by fasteners.

[0317] Optionally, the battery module 4 can also include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0318] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, which can be selected by a person skilled in the art according to the application and capacity of the battery pack.

[0319] FIGS. 4 and 5 are a battery pack 1 as an example. Referring to FIGS. 4 and 5, the battery pack 1 can include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be provided on the lower box body 3 to form a closed space for receiving the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0320] [Power consuming device]

[0321] The present application provides a power consuming device, which includes the secondary battery of the present application or the negative current collector of the present application.

[0322] In some embodiments, the power consuming device of the present application can further include at least one of a battery module or a battery pack. The secondary battery, the battery module, or the battery pack can be used as a power source of the power consuming device, or can be used as an energy storage unit of the power consuming device. The power consuming device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0323] As the power consuming device, the secondary battery, the battery module, or the battery pack can be selected according to the use requirement thereof.

[0324] FIG. 6 is a power consuming device as an example. The power consuming device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirement of high power and high energy density of the secondary battery for the power consuming device, a battery pack or a battery module can be used.

[0325] The device as another example can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thin and light, and a secondary battery can be used as a power source.

[0326] The above description is only a summary of the technical solutions of the present application. In order to make the technical means of the present application more clear, the following specific embodiments of the present application can be implemented according to the content of the description, and in order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand.

[0327] Embodiments

[0328] Hereinafter, the embodiments of the present application are described. The embodiments described below are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application. If the specific technology or condition is not specified in the embodiments, the technology or condition described in the literature in the art or according to the product instruction is used. If the reagent or instrument is not specified by the manufacturer, it is a conventional product that can be obtained by market purchase.

[0329] I. Preparation method

[0330] Embodiment 1

[0331] 1) Preparation of positive electrode sheet

[0332] The positive active material NFPP (Na4Fe3(PO4)2P2O7), the conductive agent conductive carbon black, and the binder polyvinylidene fluoride are mixed in N-methylpyrrolidone in a mass percentage of 96:1:3, and the positive electrode slurry is formed by fully stirring. The positive electrode slurry is coated on the aluminum foil at a single-sided weight of 20 mg / cm 2 After the coating is completed, cold pressing and slitting are performed to obtain the positive electrode sheet.

[0333] 2) Preparation of the negative electrode sheet

[0334] The inorganic substance alumina, the binder styrene-butadiene emulsion (butadiene monomer unit-styrene monomer unit copolymer, Japan A&L Corporation, model SBR-1002), the conductive agent conductive carbon black (Super-P), and the dispersant carboxymethyl cellulose (CMC) are mixed in water in a mass percentage of 50:30:10:10, and the coating slurry is formed by fully stirring. The coating slurry is coated on both sides of the polypropylene film at a single-sided coating weight of 3 mg / cm 2 After the coating is completed, slitting is performed to obtain the negative current collector, which is the negative electrode sheet. The porosity of the polypropylene film is 45%, and the thickness is 12 μm.

[0335] 4) Preparation of the separator film

[0336] The polypropylene film is used as the separator film.

[0337] 5) Preparation of the electrolyte

[0338] In an argon atmosphere glove box (H2O <0.1 ppm, O2 <0.1 ppm), the sodium salt sodium hexafluorophosphate NaPF6 is dissolved in the organic solvent propylene carbonate (PC) with 5% FEC (fluoroethylene carbonate) by mass ratio, and stirring is performed until the electrolyte with a sodium salt concentration of 1 mol / L is obtained.

[0339] 6) Preparation of the battery

[0340] The above positive electrode sheet, the separator film, and the negative electrode sheet are stacked in order, the separator film is arranged between the positive electrode sheet and the negative electrode sheet to play a role of isolation, and then the bare cell is obtained by winding. The bare cell is welded with tabs, is placed in an aluminum shell, and is baked in a 100°C vacuum oven for 8 h. Then, the electrolyte is injected and sealed to obtain the uncharged battery. The uncharged battery is sequentially subjected to processes such as standing, cold and hot pressing, formation, shaping, and capacity testing to obtain the negative electrode-free sodium metal battery of Example 1.

[0341] Examples 2-3 and the battery preparation method of Example 1 are the same, except that the types of inorganic substances in the coating of the negative current collector are different. Specifically, the inorganic substance of Example 2 is boehmite, and the inorganic substance of Example 3 is titanium dioxide. Other parameters are shown in Table 1.

[0342] Example 4-5 were prepared in the same way as Example 1, except that the type of binder in the coating of the negative current collector was different, specifically, the type of binder in the coating of Example 4 was styrene-acrylate emulsion (styrene monomer unit-acrylate monomer unit copolymer, Japan Lanson Co., Ltd., Model LB-150J), and the type of binder in the coating of Example 5 was polyethyl acrylate emulsion (BASF (China) Co., Ltd., Model Acronal ECO 6370), and other parameters were as shown in Table 1.

[0343] Examples 6-10 were prepared in the same way as Example 1, except that the mass percentage of each component in the coating of the negative current collector was different, specifically as shown in Table 1.

[0344] Examples 11-12 were prepared in the same way as Example 1, except that the coating weight per unit area of the coating of the negative current collector was different, specifically as shown in Table 1.

[0345] Example 13 was prepared in the same way as Example 1, except that the positive active material was different, and the positive active material of Example 13 was LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0346] Example 14 was prepared in the same way as Example 1, except that Example 14 was a common sodium ion battery, wherein the preparation method of the negative electrode sheet of Example 14 was as follows:

[0347] The negative active material hard carbon, the conductive agent carbon black, the thickening agent carboxymethyl cellulose, and the binder styrene-butadiene rubber were added to deionized water in a mass ratio of 97:0.5:0.5:2, and stirred uniformly to obtain a negative electrode slurry;

[0348] Then the negative electrode slurry was uniformly coated on the negative current collector at a single-sided weight of 10 mg / cm 2 After the double-sided coating was completed, it was dried, cold-pressed, and cut to obtain the negative electrode sheet, wherein the preparation method of the negative current collector was the same as that of Example 1.

[0349] Comparative Example 1 was prepared in the same way as Example 1, except that the negative current collector of Comparative Example 1 was a copper foil.

[0350] Comparative Example 2 was prepared in the same way as Example 1, except that the coating of the negative current collector of Comparative Example 2 did not include inorganic matter, and the mass ratio of the binder, the conductive agent, and the dispersant was 35:55:10.

[0351] The battery preparation method of Comparative Example 3 is the same as that of Example 1, except that the negative electrode tab preparation method of Comparative Example 3 is as follows:

[0352] The negative electrode active material hard carbon, the conductive agent carbon black, the thickening agent carboxymethyl cellulose, and the binder styrene-butadiene rubber were added into deionized water in a mass ratio of 97:0.5:0.5:2, and stirred uniformly to obtain a negative electrode slurry.

[0353] Then the negative electrode slurry was uniformly coated on the copper foil with a single side weight of 10 mg / cm 2 After the double-side coating was completed, drying, cold pressing, and slitting were performed to obtain the negative electrode tab, wherein the preparation method of the negative electrode current collector was the same as that of Example 1.

[0354] II. Performance test

[0355] 1. Test of the negative electrode current collector and the negative electrode tab

[0356] 1) Test of the inorganic component and content in the coating

[0357] Inorganic mass percentage content test: The battery was disassembled to obtain the negative electrode tab. If there was a negative electrode film layer on the negative electrode tab, the negative electrode film layer of the negative electrode tab was peeled off to obtain the negative electrode current collector. If there was no negative electrode film layer on the negative electrode tab, the following operation was directly performed. The negative electrode current collector was scraped to obtain a coating powder, and the mass of the coating powder was measured as M1. The coating powder was calcined in air or oxygen at 500°C until the weight of the powder no longer changed. At this time, the remaining powder was the inorganic substance, and the mass of the inorganic substance was measured as M0. The mass percentage content of the inorganic substance was (M0 / M1) x 100%.

[0358] Inorganic component test: The battery was disassembled to obtain the negative electrode tab. If there was a negative electrode film layer on the negative electrode tab, the negative electrode film layer of the negative electrode tab was peeled off to obtain the negative electrode current collector. If there was no negative electrode film layer on the negative electrode tab, the following operation was directly performed. The negative electrode current collector was scraped to obtain a coating powder. The coating powder was calcined in air or oxygen at a certain temperature (for example, 500°C) until the weight of the powder no longer changed. At this time, the remaining powder was the inorganic substance. The remaining substance was tested by an X-ray diffractometer, and compared with a standard spectrum to determine the inorganic component. At the same time, the remaining substance can be analyzed by X-ray fluorescence spectroscopy (XRF) or inductively coupled plasma analysis (ICP) to analyze the elemental composition of the substance, and the test structure of the X-ray diffractometer is verified to further determine the specific component of the inorganic substance.

[0359] 2) Porosity test of the porous film

[0360] Place the sample to be tested in the mercury intrusion porosimeter, ensuring that the sample is sealed well with the instrument; inject mercury into the instrument and gradually increase the mercury pressure; observe the volume change of the porous membrane sample and record the volume values at different pressures; plot the pressure-volume curve according to the relationship between the volume change and the mercury pressure; and calculate the porosity of the porous membrane according to the pressure-volume curve.

[0361] 2. Performance test of the battery

[0362] 1) Test of cycle performance

[0363] At 25°C, the prepared battery is charged to 3.65V at a constant current of 1C, then charged to 3.65V at a constant voltage until the current drops to 0.05C, and then discharged to 1.5V at a constant current of 1C after 10 minutes of standing. This is one charge / discharge cycle of the battery. Taking the first discharge capacity as 100%, the charge / discharge cycle is repeated, and when the discharge capacity decays to 80%, the test is stopped, and the cycle number is recorded. The cycle number at which the capacity retention rate reaches 80% is used as an index for evaluating the cycle performance of the battery.

[0364] 2) Test of high-rate performance

[0365] 4C rate charge capacity retention rate: After the battery is assembled and stands for 10 hours at 25°C, the charge / discharge test is performed. The secondary battery is first charged to 3.65V at a constant current at different rates (specifically 0.33C and 4C), and the charge capacity value C is recorded. The 4C rate charge capacity retention rate = C4 / C 0.33 (C 0.33 which is the basic charge capacity, and the charge capacity retention rate is 100%;

[0366] 4C rate discharge capacity retention rate: After the battery is assembled and stands for 10 hours at 25°C, the battery is charged to 100% SOC, and then discharged to the lower limit cutoff voltage 1.5V at a constant current at different rates (specifically 0.33C and 4C), and the discharge capacity value D is recorded. The 4C rate discharge capacity retention rate = D4 / D 0.33 (D 0.33 which is the basic discharge capacity, and the capacity retention rate is 100%.

[0367] 3) Test of first coulombic efficiency

[0368] At 25°C, after the battery is assembled and stands for 10 hours, the first charge / discharge test is performed. The secondary battery is first charged to 3.65V at a constant current of 0.33C, and then further charged to 3.65V at a constant voltage until the current is 0.05C, and the charge capacity value C0 is recorded. Then, the battery is discharged to the lower limit cutoff voltage 1.5V at a constant current of 0.33C, and the discharge capacity value D0 is recorded. The first coulombic efficiency FCE = D0 / C0.

[0369] III. Analysis of test results of each embodiment and comparative example

[0370] The batteries of each embodiment and comparative example were prepared according to the above method, and each performance parameter was measured. The secondary battery related parameters are shown in Table 1, and the battery performance test results are shown in Table 2.

[0371] Table 1: Secondary battery related parameters

[0372] Table 1: Secondary battery related parameters (continued)

[0373] Table 2: Secondary battery performance test results

[0374] As can be seen from Examples 1-14, the negative current collector of the battery of the present application comprises a porous film layer and a coating layer provided on the surface of the porous film layer close to the separator, and the coating layer comprises inorganic matter, conductive agent and binder. The inorganic matter comprises metal oxide or silicon oxide. The secondary battery of the present application has high rate performance.

[0375] As can be seen from the comparison between Examples 1-13 and Comparative Example 1, and the comparison between Examples 14 and Comparative Example 3, the negative current collector of the battery of the present application has a porous film layer, and the porous structure on the porous film layer is beneficial to improve the rate performance of the secondary battery.

[0376] As can be seen from the comparison between Examples 1-14 and Comparative Example 2, the addition of inorganic matter in the coating layer is beneficial to improve the cycle performance of the secondary battery.

[0377] As can be seen from Examples 1-3, the coating layer of the present application can use various inorganic matter. When the inorganic matter is aluminum oxide, it is beneficial to further improve the cycle performance of the secondary battery. As can be seen from Examples 1, 4-5, the coating layer of the present application can use various binders. The use of butadiene monomer structural unit-styrene monomer structural unit is beneficial to further improve the rate performance and cycle performance of the secondary battery.

[0378] As can be seen from Examples 1, 6-10, the appropriate mass percentage of inorganic matter, binder and conductive agent is beneficial to further improve the cycle performance, rate performance and / or initial coulomb efficiency of the secondary battery.

[0379] As can be seen from Examples 1, 11-12, the appropriate coating weight per unit area is beneficial to further improve the cycle performance, rate performance and initial coulomb efficiency of the secondary battery.

[0380] From Examples 13 and 14, it can be seen that the negative current collector of the present application is also applicable to the scenarios of negative electrode-free lithium metal batteries and ion batteries.

[0381] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration as the technical idea and exerting the same effects within the scope of the technical solution of the present application are all included in the technical scope of the present application. Furthermore, within the scope of the gist of the present application, other modes obtained by applying various modifications that can be thought of by those skilled in the art to the embodiments or by combining part of the constituent elements of the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery characterized by comprising: The secondary battery includes a positive electrode sheet, a negative electrode sheet, and a separator disposed between the negative electrode sheet and the positive electrode sheet, wherein the negative electrode sheet includes a negative electrode current collector, the negative electrode current collector includes a porous membrane layer and a coating layer disposed at least on a surface of the porous membrane layer close to the separator, and the coating layer includes an inorganic substance, a conductive agent, and a binder, wherein the inorganic substance includes at least one of a metal oxide or silicon oxide.

2. The secondary battery according to claim 1, characterized by The metal oxide includes at least one of aluminum oxide, boehmite, magnesium oxide, iron oxide, zirconium oxide, titanium oxide, or zinc oxide.

3. The secondary battery according to claim 1 or 2, characterized by The binder includes at least one of an acrylic monomer unit homopolymer and / or copolymer, an acrylate monomer unit homopolymer and / or copolymer, a polyol monomer unit-polyisocyanate monomer unit copolymer, a dibasic amine monomer unit-dibasic anhydride monomer unit copolymer, a butadiene monomer unit-styrene monomer unit copolymer, a styrene monomer unit-acrylate monomer unit copolymer, or a derivative thereof, a modified species thereof.

4. The secondary battery according to any one of claims 1 to 3, characterized by, The binder includes at least one of a butadiene monomer unit-styrene monomer unit copolymer, a styrene monomer unit-acrylate monomer unit copolymer, a methyl acrylate monomer unit homopolymer, an ethyl acrylate monomer unit homopolymer, a butyl acrylate monomer unit homopolymer, an isooctyl acrylate monomer unit homopolymer, an acrylate monomer unit copolymer, or a derivative thereof, a modified species thereof.

5. The secondary battery according to any one of claims 1 to 4, characterized by, The conductive agent includes at least one of conductive carbon black, a carbon nanotube, graphene, superconducting carbon, acetylene black, ketjen black, a carbon dot, or a carbon nanofiber.

6. The secondary battery according to any one of claims 1 to 5, characterized by, The mass percentage content of the inorganic substance is 40% to 55%, or 45% to 50%, based on the mass of the coating layer; and / or, The mass percentage content of the binder is 20% to 35%, or 25% to 30%; and / or, The mass percentage content of the conductive agent is 5% to 15%, or 8% to 12%.

7. The secondary battery according to any one of claims 1-6, characterized by The coating layer further includes a dispersant, and the dispersant includes at least one of carboxymethyl cellulose, methyl cellulose, sodium starch phosphate, sodium carboxymethyl cellulose, sodium polyacrylate, polyoxyethylene, or polyvinylpyrrolidone.

8. The secondary battery according to claim 7, characterized by The mass percentage content of the dispersant is 0% to 10%, or greater than 0%, based on the mass of the coating layer.

9. The secondary battery according to any one of claims 1-8, characterized by, The single-sided unit area coating weight of the coating is 1-5 mg / cm 2 , optionally 2-3 mg / cm 2 .

10. The secondary battery according to any one of claims 1-9, characterized in that, The porosity of the porous membrane layer is 30% to 60%, or 40% to 50%.

11. The secondary battery according to any one of claims 1-10, characterized in that, The porous membrane layer includes at least one of a porous polyolefin membrane, a porous glass fiber, a porous non-woven fabric, a porous polyimide membrane, a porous polyvinylidene fluoride membrane, or a porous polyterephthalate.

12. The secondary battery according to any one of claims 1-11, characterized by, The thickness of the porous membrane layer is 6 to 15 µm.

13. The secondary battery according to any one of claims 1-12, characterized by, The coating layer is disposed on the surfaces of both sides of the porous membrane layer.

14. The secondary battery according to any one of claims 1-13, characterized by, The secondary battery includes a negative electrode-free metal battery, and the secondary battery includes a negative electrode-free sodium metal battery or a negative electrode-free lithium metal battery.

15. The secondary battery according to any one of claims 1-14, characterized by, The negative electrode sheet includes a negative electrode membrane layer disposed on at least one side of the negative electrode current collector, and the negative electrode membrane layer includes a negative electrode active material including at least one of artificial graphite, natural graphite, soft carbon, hard carbon, or a silicon-based material.

16. A negative current collector, characterized by, The negative electrode current collector includes a porous membrane layer and a coating layer provided at least on a surface of the porous membrane layer on a side close to the separator, the coating layer including an inorganic substance, a conductive agent, and a binder, wherein the inorganic substance includes at least one of a metal oxide or silicon oxide.

17. The negative current collector according to claim 16, wherein The metal oxide includes at least one of aluminum oxide, boehmite, magnesium oxide, iron oxide, zirconium oxide, titanium oxide, or zinc oxide.

18. A method of preparing a negative current collector, characterized by, The method includes at least the following steps: dissolving raw materials in a solvent to form a coating slurry after stirring; applying the coating slurry at least on a surface of the porous membrane layer on a side close to the separator to obtain the negative electrode current collector; wherein the raw materials include an inorganic substance, a binder, and a conductive agent, and the inorganic substance includes at least one of a metal oxide or silicon oxide.

19. The method of claim 18, wherein, The metal oxide includes at least one of aluminum oxide, boehmite, magnesium oxide, iron oxide, zirconium oxide, titanium oxide, or zinc oxide.

20. An electrical device, comprising: The electrical device includes the secondary battery according to any one of claims 1 to 15 or the negative electrode current collector according to any one of claims 16 to 17.

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