Positive pole piece and preparation method thereof, battery monomer, battery and electric device

Abstract

The embodiment of the invention provides a positive pole piece, a preparation method of the positive pole piece, a battery monomer, a battery and a power utilization device. The positive pole piece comprises a positive current collector and a positive film layer arranged on at least one side of the positive current collector, wherein the positive film layer comprises a positive active material and a hydrophobic additive. According to the technical scheme, the water content in the positive pole piece can be reduced, so that the cycle performance of the battery is improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and more specifically, to a positive electrode plate and a preparation method thereof, a battery cell, a battery and an electrical device. Background Art

[0002] In recent years, lithium-ion batteries have been used in more and more fields, such as wind power, hydropower, thermal power generation and solar power stations, as well as electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. While lithium-ion batteries have made great progress, higher requirements have been put forward for performance in all aspects.

[0003] Therefore, how to improve the performance of lithium-ion batteries is an urgent problem to be solved. Summary of the invention

[0004] The present application is made in view of the above-mentioned problems, and its purpose is to provide a positive electrode plate and its preparation method, a battery cell, a battery and an electrical device, which can improve the cycle performance of the battery.

[0005] In a first aspect, a positive electrode plate is provided, comprising: a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode film layer comprises a positive electrode active material and a hydrophobic additive.

[0006] In the embodiment of the present application, the positive electrode plate includes a positive electrode current collector and a positive electrode film layer, the positive electrode film layer is arranged on at least one side of the positive electrode plate, and the positive electrode film layer includes a positive electrode active material and a hydrophobic additive. By adding a hydrophobic additive to the positive electrode film layer, the water content in the positive electrode active material can be reduced, thereby improving the cycle performance of the battery.

[0007] In a possible implementation, the contact angle between the hydrophobic additive and water is 90°-120°. Optionally, the contact angle between the hydrophobic additive and water is 100°-120°.

[0008] In the embodiment of the present application, the water content of the positive electrode plate can be further reduced by making the contact angle between the hydrophobic additive added in the positive electrode film layer and water be 90°-120°, especially 100°-120°.

[0009] In one possible implementation, the hydrophobic additive includes a functional group containing a CF bond.

[0010] In the embodiment of the present application, the material containing the CF bond functional group has a lower surface energy. By using a hydrophobic additive containing the CF bond functional group, the water content in the positive electrode film layer can be further reduced, thereby further improving the cycle performance of the battery.

[0011] In one possible embodiment, the hydrophobic additive contains at least one of the following functional groups: -CF2, -CF2H, -CF3.

[0012] In the embodiment of the present application, by making the hydrophobic additive include at least one of -CF2, -CF2H, and -CF3, the hydrophobic additive has good hydrophobic properties, which can reduce the water absorption of the positive electrode active material, thereby improving the cycle performance of the battery.

[0013] In a possible implementation, based on 100 parts by weight of the positive electrode film layer, the weight of the hydrophobic additive is 0.3-5 parts by weight. Optionally, the weight of the hydrophobic additive is 0.5-2 parts by weight.

[0014] In the embodiments of the present application, by making the mass content of the hydrophobic additive in the entire positive electrode film layer 0.3%-5%, especially 0.5%-2%, the hydrophobic additive can play its role without affecting the energy density of the battery.

[0015] In a possible implementation, the contact angle between the positive electrode film layer and water is 95°-105°.

[0016] In the embodiment of the present application, by making the contact angle of the positive electrode film layer including the positive electrode active material and the hydrophobic additive be 95°-105°, the positive electrode film layer as a whole can be kept in a hydrophobic state, thereby reducing its water content.

[0017] In a possible implementation, the positive electrode film layer further includes a conductive agent, the conductive agent includes a first carbon material, and the first carbon material includes at least one of Ketjen black and conductive carbon black.

[0018] In the embodiment of the present application, the conductivity of the positive electrode active material can be improved by adding the first carbon material into the positive electrode film layer.

[0019] In a possible implementation, the conductive agent further includes a second carbon material, and the second carbon material includes at least one of multi-walled carbon nanotubes, single-walled carbon nanotubes, and carbon fibers.

[0020] In the embodiment of the present application, by adding a second carbon material including any of the above materials into the positive electrode film layer, the problem of reduced conductivity of the positive electrode sheet due to the addition of hydrophobic material can be overcome, thereby further improving the conductivity of the battery.

[0021] In a possible embodiment, the positive electrode film layer includes a first film layer and a second film layer, and the first film layer is arranged between the positive electrode current collector and the second film layer; wherein the first film layer includes the positive electrode active material and the first carbon material, and the second film layer includes the hydrophobic additive.

[0022] In the embodiment of the present application, by providing a second film layer containing a hydrophobic additive on the first film layer, the water content of the positive electrode plate can be further reduced.

[0023] In a possible embodiment, the positive electrode film layer includes a first film layer and a third film layer, and the first film layer is arranged between the positive electrode current collector and the third film layer; wherein the first film layer includes the positive electrode active material and the first carbon material, and the third film layer includes the positive electrode active material, the first carbon material, the second carbon material and the hydrophobic additive.

[0024] In an embodiment of the present application, the positive electrode film layer includes two coating layers, wherein the first film layer including only the first carbon material and the positive electrode active material is arranged between the positive electrode collector and the third film layer, and the third film layer including the positive electrode active material, the first carbon material, the second carbon material, and the hydrophobic material is arranged at the outermost side of the positive electrode film layer. Such a coating method can reduce the water content of the positive electrode plate.

[0025] In a possible implementation, the hydrophobic additive includes at least one of polytetrafluoroethylene, hexene tetrafluoroethylene copolymer, perfluoroethylene propylene copolymer, trifluoroethyl methacrylate, polyvinylidene fluoride, polyethylene, and ethylene chlorotrifluoroethylene copolymer. Optionally, the hydrophobic additive includes polytetrafluoroethylene.

[0026] In the embodiments of the present application, by using at least one material selected from polytetrafluoroethylene, hexene tetrafluoroethylene copolymer, perfluoroethylene propylene copolymer, trifluoroethyl methacrylate, polyvinylidene fluoride, polyethylene, and ethylene chlorotrifluoroethylene copolymer as a hydrophobic additive, especially using polytetrafluoroethylene as a hydrophobic additive, the cycle performance of the battery can be further improved.

[0027] In a possible implementation manner, the positive electrode active material includes layered oxides, transition metal oxides, and polyanion compounds; optionally, the positive electrode active material includes lithium iron phosphate.

[0028] In a possible implementation, the volume average particle size Dv50 of the positive electrode active material is 100 nm-1000 nm. Optionally, the volume average particle size Dv50 of the positive electrode material is 200 nm-700 nm.

[0029] In the embodiments of the present application, the energy density of the battery can be improved by making the volume average particle size Dv50 of the positive electrode active material 100 nm-1000 nm, especially 200 nm-700 nm.

[0030] In one possible embodiment, the specific surface area of ​​the positive electrode active material is 10 m 2 / g-20m2 / g, optionally, the specific surface area of ​​the positive electrode active material is 12m 2 / g-17m 2 / g.

[0031] In the present embodiment, by making the specific surface area of ​​the positive electrode active material 10m 2 / g-20m 2 / g, especially 12m 2 / g-17m 2 / g, which can improve the energy density of the battery.

[0032] In a second aspect, the present application provides a method for preparing a positive electrode plate, comprising: disposing a positive electrode film layer on at least one side of a positive electrode current collector, wherein the positive electrode film layer comprises a positive electrode active material and a hydrophobic additive.

[0033] In a possible embodiment, the positive electrode film layer also includes a conductive agent, and the conductive agent includes a first carbon material and a second carbon material. The positive electrode film layer is provided on at least one side of the positive electrode current collector, comprising: placing the positive electrode active material, the first carbon material, the hydrophobic additive and the second carbon material into a solvent in sequence and mixing them to obtain a first positive electrode slurry; and coating the first positive electrode slurry on the positive electrode current collector to obtain the positive electrode film layer provided on the positive electrode current collector.

[0034] In the embodiment of the present application, by adding the second carbon material last, the possibility of the hydrophobic additive completely covering the conductive material and thus affecting the conductive performance of the battery can be reduced.

[0035] In a possible embodiment, the positive electrode film layer also includes a conductive agent, and the conductive agent includes a first carbon material; the positive electrode film layer is provided on at least one side of the positive electrode current collector, comprising: placing the positive electrode active material and the first carbon material into a solvent and mixing them to obtain a second positive electrode slurry, placing the hydrophobic additive into a solvent to obtain a third positive electrode slurry; coating the second positive electrode slurry on the positive electrode current collector to obtain a first film layer provided on the positive electrode current collector, and then coating the third positive electrode slurry on the first film layer to obtain the positive electrode film layer provided on the positive electrode current collector.

[0036] In a possible embodiment, the positive electrode film layer also includes a conductive agent, which includes a first carbon material and a second carbon material; the positive electrode film layer is set on at least one side of the positive electrode current collector, including: putting the positive electrode active material and the first carbon material into a solvent and mixing them to obtain a second positive electrode slurry, and putting the positive electrode active material, the first carbon material, the hydrophobic additive and the second carbon material into a solvent in turn and mixing them to obtain a fourth positive electrode slurry; coating the second positive electrode slurry on the positive electrode current collector to obtain a first film layer set on the positive electrode current collector, and then coating the fourth positive electrode slurry on the first film layer to obtain the positive electrode film layer set on the positive electrode current collector.

[0037] In a third aspect, the present application provides a battery cell, comprising the positive electrode sheet described in any one of the first aspect of the present application, or the positive electrode sheet prepared by any one of the embodiments described in the second aspect of the present application.

[0038] In a fourth aspect, the present application provides a battery, comprising the battery cell described in the third aspect of the present application.

[0039] In a fifth aspect, the present application provides an electrical device, comprising the battery described in the fourth aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without paying creative work.

[0041] Figure 1 This is a schematic structural diagram of a positive electrode sheet according to an embodiment of the present application;

[0042] Figure 2 This is a schematic structural diagram of a positive electrode sheet according to another embodiment of the present application;

[0043] Figure 3 This is a schematic structural diagram of a positive electrode sheet according to another embodiment of the present application;

[0044] Figure 4 A flow chart of a method for preparing a positive electrode sheet according to an embodiment of the present application;

[0045] Figure 5 A schematic diagram of a battery cell according to an embodiment of the present application;

[0046] Figure 6 A schematic diagram of the structure of a battery cell according to an embodiment of the present application;

[0047] Figure 7 A schematic diagram of a battery according to an embodiment of the present application;

[0048] Figure 8 A schematic diagram of the structure of a battery according to one embodiment of the present application;

[0049] Fig. 9 It is a schematic diagram of an electrical device according to an embodiment of the present application. DETAILED DESCRIPTION

[0050] The following describes in detail the embodiments of the positive electrode sheet and its preparation method, battery cell, battery and electric device of the present application with appropriate reference to the drawings, but there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0051] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a specific range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can form a scope with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0052] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0053] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0054] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, and can be performed sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), which means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0055] The terms "above", "below", "greater than" or "less than" as used in this application include the number, for example, "at least one" means one or more, and "at least one of A and B" means "A", "B" or "A and B".

[0056] In the 21st century, mankind is facing two serious problems: energy crisis and environmental pollution. Therefore, the development and research of clean, renewable new energy sources are of far-reaching significance. Among them, various types of automobiles account for about 40% of oil consumption, and 42% of global air pollution comes from emissions from traffic vehicles. Countries around the world attach great importance to electric vehicles, and the development of electric vehicles is also listed as an important development direction in my country's 863 Plan. The research on power batteries as vehicle power has become the main bottleneck in the development of power vehicles. At present, the main candidates for power batteries are nickel-hydrogen batteries, lithium-ion batteries and fuel cells. Based on cost-effectiveness considerations, lithium-ion batteries have greater advantages. As an energy storage material, lithium-ion batteries have the advantages of high voltage, large specific capacity, long cycle life and good safety performance compared to traditional materials. They are widely used in portable electronic devices, electric vehicles, aerospace and military engineering, and have a wide range of application scenarios and huge economic benefits.

[0057] Driven by the government's new energy policy, people have higher requirements for the performance of power vehicle batteries in all aspects. Among them, lithium iron phosphate materials, which perform well in all aspects, have always been a research hotspot in the lithium battery industry. Although lithium iron phosphate has obvious advantages, it also has a serious disadvantage, that is, the water content of the battery is high before injection. This is because the primary particles of lithium iron phosphate have a small particle size, a large specific surface area, and are easy to absorb water. In lithium-ion batteries with lithium iron phosphate as the positive electrode material, due to the reaction of water with the electrolyte to produce free acid, this will lead to corrosion of the negative electrode solid electrolyte interface (SEI) film and dissolution of positive electrode metal ions, resulting in deterioration of battery cycle performance. This phenomenon is also particularly prominent in another research hotspot material, ternary materials.

[0058] In view of this, the present application provides a positive electrode sheet, which includes a positive electrode current collector and a positive electrode film layer, and the positive electrode film layer includes a positive electrode active material and a hydrophobic additive. By adding the above-mentioned hydrophobic additive to the positive electrode sheet, the water content in the positive electrode sheet can be reduced, thereby improving the cycle performance of the battery.

[0059] The positive electrode sheet and its preparation method, battery cell, battery and electrical device of the present application are described below with reference to the accompanying drawings.

[0060] The following takes lithium-ion batteries as an example. Lithium-ion batteries are a typical secondary battery. Because they rely on the chemical reaction of lithium ions being embedded and released between the positive and negative electrodes for charging and discharging, lithium-ion batteries are also called rocking-chair batteries. During the charging process of lithium-ion batteries, lithium ions are released from the positive electrode active material, moved to the negative electrode through the conduction of the electrolyte and embedded in the negative electrode active material; and during the discharge process, lithium ions are released from the negative electrode active material, moved to the positive electrode through the conduction of the electrolyte and embedded in the positive electrode active material.

[0061] It should be understood that the "lithium insertion", "embedding" and "embedding" processes described in this application refer to the process in which lithium ions are embedded in the positive electrode active material or the negative electrode active material due to an electrochemical reaction, and the "extraction", "delithium" and "extraction" processes described in this application refer to the process in which lithium ions are extracted from the positive electrode active material or the negative electrode active material due to an electrochemical reaction.

[0062] [Positive electrode]

[0063] The first aspect of the present application provides a positive electrode plate, Figure 1 Schematic diagram of the structure of the positive electrode sheet of one embodiment of the present application. Figure 1 As shown, the positive electrode plate 121 includes a positive electrode current collector 1211 and a positive electrode film layer 1212 disposed on at least one side of the positive electrode current collector 1211 , and the positive electrode film layer 1212 includes a positive electrode active material and a hydrophobic additive.

[0064] By adding a hydrophobic additive to the positive electrode film layer 1212 , the water content in the positive electrode plate 121 can be reduced, thereby improving the cycle performance of the battery.

[0065] The positive electrode sheet 121 includes a positive electrode current collector 1211 and a positive electrode film layer 1212 disposed on at least one surface of the positive electrode current collector 1211 , wherein the positive electrode film layer includes a positive electrode active material and a hydrophobic additive.

[0066] As an example, the positive electrode current collector 1211 has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer 1212 is disposed on any one or both of the two opposite surfaces of the positive electrode current collector 1211 .

[0067] The hydrophobic additive, i.e., a material that repels water, is mixed with the positive electrode active material so that the hydrophobic additive partially wraps the positive electrode active material, thereby reducing the water absorption of the positive electrode active material and lowering the water content in the positive electrode plate 121 .

[0068] Generally speaking, a hydrophobic material refers to a material having a surface energy of no greater than 90 dyn and / or a contact angle with water of no less than 90°.

[0069] Surface energy is the non-volume work done on a substance to reversibly increase the surface area of ​​a system under constant temperature, constant pressure, and constant composition. Another definition of surface energy is the extra work done by surface particles relative to internal particles. The lower the surface energy, the less likely it is to be wetted, that is, the less likely it is to attract water.

[0070] The contact angle refers to the angle from the solid-liquid interface through the liquid to the gas-liquid interface at the junction of solid, liquid and gas. It is also called the wetting angle. The degree of wetting of liquids on solids varies. For example, a drop of water will wet and spread on clean glass, while a drop of water on a waxy surface will remain in a water drop state and will not wet. Generally speaking, when there is a strong affinity between the two, the liquid will form a smaller contact angle on the solid surface, that is, the contact angle is less than 90°; conversely, when the affinity between the two is weak, the liquid drop will not be able to fully spread out and will form a larger contact angle. In this case, we say that the substance is hydrophobic.

[0071] In the above solution, the positive electrode sheet 121 includes a positive electrode current collector 1211 and a positive electrode film layer 1212, and the positive electrode film layer 1212 is disposed on at least one side of the positive electrode sheet 121. The positive electrode film layer 1212 includes a positive electrode active material and a hydrophobic additive. By adding a hydrophobic additive to the positive electrode film layer 1212, the water content in the positive electrode active material can be reduced, thereby improving the cycle performance of the battery.

[0072] In some embodiments, the contact angle between the hydrophobic additive and water is 90°-120°. Optionally, the contact angle between the hydrophobic additive and water is 100°-120°.

[0073] In the above solution, the water content of the positive electrode plate 121 can be further reduced by making the contact angle between the hydrophobic additive added to the positive electrode film layer 1212 and water be 90°-120°, especially 100°-120°.

[0074] Specifically, the contact angle between the hydrophobic additive and water can be 90°, 95°, 98°, 100°, 105°, 110°, 120° or any value within the above range.

[0075] In some embodiments, the surface energy of the hydrophobic additive is 50 dyn-70 dyn, and optionally, the surface energy of the hydrophobic additive is 55 dyn-65 dyn.

[0076] In the above solution, the water content of the positive electrode plate 121 can be further reduced by making the surface energy of the hydrophobic additive added to the positive electrode film layer 1212 50 dyn-70 dyn, especially 55 dyn-65 dyn.

[0077] Specifically, the surface energy of the hydrophobic additive may be 50 dyn, 52 dyn, 55 dyn, 58 dyn, 60 dyn, 65 dyn, 70 dyn or any value within the above range.

[0078] In some embodiments, the hydrophobic additive includes a functional group containing a CF bond.

[0079] In the above solution, the material containing the CF bond functional group has a lower surface energy. By using a hydrophobic additive containing the CF bond functional group, the water content in the positive electrode film layer 1212 can be further reduced, thereby further improving the cycle performance of the battery.

[0080] In some embodiments, the hydrophobic additive contains at least one of the following functional groups: -CF2, -CF2H, -CF3.

[0081] In the above scheme, by making the hydrophobic additive include at least one of -CF2, -CF2H, and -CF3, the hydrophobic additive has good hydrophobic properties, which can reduce the water absorption of the positive electrode active material, thereby improving the cycle performance of the battery.

[0082] In some embodiments, based on 100 parts by weight of the positive electrode film layer 1212 , the weight of the hydrophobic additive is 0.3-5 parts by weight. Optionally, the weight of the hydrophobic additive is 0.5-2 parts by weight.

[0083] In the above scheme, by making the mass content of the hydrophobic additive in the entire positive electrode film layer 1212 0.3%-5%, especially 0.5%-2%, the hydrophobic additive can play its role without affecting the energy density of the battery.

[0084] Specifically, based on 100 parts by weight of the positive electrode film layer 1212, the weight of the hydrophobic additive can be 0.3 parts by weight, 0.5 parts by weight, 1.2 parts by weight, 1.6 parts by weight, 2.4 parts by weight, 3.2 parts by weight, 5 parts by weight or any value within the above range.

[0085] In some embodiments, the contact angle between the positive electrode film layer 1212 and water is 95°-105°.

[0086] In the above solution, by making the contact angle of the positive electrode film layer 1212 including the positive electrode active material and the hydrophobic additive be 95°-105°, the positive electrode film layer 1212 can be kept hydrophobic as a whole, thereby reducing its water content.

[0087] Specifically, the contact angle between the positive electrode film layer 1212 and water can be 95°, 98°, 100°, 102°, 15° or any value within the above range.

[0088] In some embodiments, the positive electrode film layer 1212 further includes a conductive agent, the conductive agent includes a first carbon material, and the first carbon material includes at least one of Ketjen black and conductive carbon black.

[0089] In the above solution, by adding the first carbon material into the positive electrode film layer 1212 , the conductivity of the positive electrode active material can be improved.

[0090] In some embodiments, the positive electrode film layer 1212 further includes a second carbon material, and the second carbon material includes at least one of multi-walled carbon nanotubes, single-walled carbon nanotubes, and carbon fibers.

[0091] In the above solution, by adding the second carbon material to the positive electrode film layer 1212, the problem of reduced conductivity due to the addition of the hydrophobic material can be overcome, thereby further improving the conductivity of the battery.

[0092] It should be noted here that, when the positive electrode film layer contains only the first carbon material, based on 100 parts by weight of the positive electrode film layer 1212, the weight of the first carbon material is 0.1-1.5 parts by weight; when the positive electrode film layer includes both the first carbon material and the second carbon material, based on 100 parts by weight of the positive electrode film layer 1212, the weight of the first carbon material is 0.1-0.8 parts by weight, and the weight of the second carbon material is 0.05-0.25 parts by weight.

[0093] Specifically, the conductive agent in the positive electrode film layer may be composed of the following: it may include only 0.1 weight part, 0.5 weight part, 0.8 weight part, 1 weight part, 1.5 weight parts or any weight part within the above range of the first carbon material; or it may include 0.1 weight part, 0.2 weight part, 0.5 weight part, 0.8 weight part or any weight part within the above range of the first carbon material, and 0.05 weight part, 0.08 weight part, 0.1 weight part, 0.2 weight part, 0.25 weight part or any weight part within the above range of the second carbon material.

[0094] In some embodiments, the resistance of the positive electrode film layer 1212 is not greater than 400 mΩ. Optionally, the resistance of the positive electrode film layer 1212 is 250 mΩ-350 mΩ.

[0095] In the above solution, by making the resistance of the positive electrode film layer 1212 not greater than 400 mΩ, especially 250 mΩ-350 mΩ, the positive electrode film layer 1212 can maintain good conductivity, that is, have good dynamics.

[0096] Specifically, the resistance of the positive electrode film layer 1212 can be 400 mΩ, 380 mΩ, 350 mΩ, 300 mΩ, 280 mΩ, 250 mΩ or any value within the above range.

[0097] Figure 2 FIG. 1 is a schematic diagram of the structure of a positive electrode sheet according to another embodiment of the present invention. Figure 2 As shown, in some embodiments, the positive electrode film layer 1212 includes a first film layer 1213 and a second film layer 1214, and the first film layer 1213 is arranged between the positive electrode current collector 1211 and the second film layer 1214; wherein the first film layer 1213 includes a positive electrode active material and a first carbon material, and the second film layer 1214 includes a hydrophobic additive.

[0098] In the above solution, by providing a second film layer 1214 containing a hydrophobic additive on the first film layer 1213 , the water content of the positive electrode plate 121 can be further reduced.

[0099] Figure 3 FIG. 1 is a schematic diagram of the structure of a positive electrode sheet according to another embodiment of the present invention. Figure 3 As shown, in some embodiments, the positive electrode film layer 1212 includes a first film layer 1213 and a third film layer 1215, and the first film layer 1213 is arranged between the positive electrode collector 1211 and the third film layer 1215; wherein the first film layer 1213 includes a positive electrode active material and a first carbon material, and the third film layer 1215 includes a positive electrode active material, a first carbon material, a second carbon material and a hydrophobic material.

[0100] In the above scheme, the positive electrode film layer 1212 includes two coating layers, wherein the first film layer 1213 including only the first carbon material and the positive electrode active material is arranged between the positive electrode collector 1211 and the third film layer 1215, and the third film layer 1215 including the positive electrode active material, the first carbon material, the second carbon material, and the hydrophobic additive is arranged at the outermost side of the positive electrode film layer 1212. Such a coating method can further reduce the water content of the positive electrode plate 121.

[0101] That is to say, the positive electrode film layer in the present application can be just a mixed film layer, or a double-layer film layer composed of a first film layer and a second film layer, or a double-layer film layer composed of a first film layer and a third film layer. The present application does not limit this.

[0102] In some embodiments, the coating thickness ratio of the first film layer 1213 to the third film layer 1215 is 3:7-7:3.

[0103] In the above scheme, by making the coating thickness ratio of the first film layer 1213 including the first carbon material and the positive electrode active material and the third film layer 1215 including the positive electrode active material, the first carbon material, the second carbon material, and the hydrophobic material be 3:7-7:3, the first film layer 1213 and the third film layer 1215 can have a reasonable thickness, thereby making the third film layer 1215 play an effective role.

[0104] Specifically, the thickness ratio of the first film layer 1213 to the second film layer 1214 may be 3:7, 4:7, 5:5, 3:2, 4:2 or any value within the above range.

[0105] In some embodiments, the resistance of the positive electrode film layer 1212 is 200 mΩ-300 mΩ, and the resistance of the third film layer 1215 is 300 mΩ-400 mΩ.

[0106] In the above range, by making the resistance of the entire positive electrode film layer 1212 200mΩ-300mΩ, and the resistance of the third film layer 1215 including the positive electrode active material, the first carbon material, the second carbon material, and the hydrophobic material 300mΩ-400mΩ, the third film layer 1215 and the entire positive electrode film layer 1212 can have better conductive properties.

[0107] In some embodiments, the hydrophobic additive includes at least one of polytetrafluoroethylene, hexene tetrafluoroethylene copolymer, perfluoroethylene propylene copolymer, trifluoroethyl methacrylate, polyvinylidene fluoride, polyethylene, and ethylene chlorotrifluoroethylene copolymer. Optionally, the hydrophobic additive includes polytetrafluoroethylene.

[0108] In the above scheme, by using at least one material selected from polytetrafluoroethylene, hexene tetrafluoroethylene copolymer, perfluoroethylene propylene copolymer, trifluoroethyl methacrylate, polyvinylidene fluoride, polyethylene, and ethylene chlorotrifluoroethylene copolymer as a hydrophobic additive, especially using polytetrafluoroethylene as a hydrophobic additive, the cycle performance of the battery can be further improved.

[0109] In some embodiments, the positive electrode active material includes layered oxides, transition metal oxides, and polyanionic compounds.

[0110] In some embodiments, the positive electrode active material may adopt a positive electrode active material for a battery that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.1 Al 0.05 O2) and its modified compounds, etc. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0111] In some embodiments, the positive electrode active material may also include Li x (Ni a Co b Mn c ) 1-d M d O 2-y A y, wherein M includes at least one of Zr, Al, B, Ta, Mo, W, Nb, Sb, and La, A includes at least one of S, N, P, F, Cl, Br, or I, 0.2<x≤1.2, 0.5≤a<1.0, 0≤b<0.5, 0≤c<1, 0≤d<1, and 0≤y<0.02.

[0112] Specifically, the positive electrode active material includes but is not limited to the following substances: Li 0.5 Ni 0.5 Co 0.1 Mn 0.4 O2、Li 0.5 (Ni 0.5 Co 0.1 Mn 0.4 ) 0.5 Zr 0.5 O 1.9 A 0.1 、LiNi 0.4 Co 0.3 Mn 0.3 O2.

[0113] It should be noted that in the positive electrode sheet, battery or electrical device, lithium ions will be consumed as the battery goes through the formation and circulation processes, so the lithium content in the positive electrode active material measured will be less than 1. At the same time, if the positive electrode sheet is supplemented with lithium, the lithium content in the positive electrode active material measured will be greater than 1 after the battery goes through the formation and circulation processes.

[0114] Similarly, in the list of positive electrode materials in this application, the molar content of O is only a theoretical value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0115] In some embodiments, the volume average particle size Dv50 of the positive electrode active material is 100 nm-1000 nm. Optionally, the volume average particle size Dv50 of the positive electrode material is 200 nm-700 nm.

[0116] In the above scheme, the energy density of the battery can be improved by making the volume average particle size Dv50 of the positive electrode active material 100nm-1000nm, especially 200nm-700nm.

[0117] Specifically, the volume average particle size Dv50 of the positive electrode active material may be 100 nm, 150 nm, 200 nm, 300 nm, 500 nm, 700 nm, 1000 nm or any value within the above range.

[0118] In some embodiments, the specific surface area of ​​the positive electrode active material is 10 m 2 / g-20m2 / g, optionally, the specific surface area of ​​the positive electrode active material is 12m 2 / g-17m 2 / g.

[0119] In the above scheme, by making the specific surface area of ​​the positive electrode active material 10m 2 / g-20m 2 / g, especially 12m 2 / g-17m 2 / g, which can improve the energy density of the battery.

[0120] Specifically, the specific surface area of ​​the positive electrode active material can be 10 m 2 / g, 12m 2 / g, 15m 2 / g, 17m 2 / g, 20m 2 / g or any value within the above range.

[0121] In some embodiments, the positive electrode current collector 1211 may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0122] In some embodiments, the positive electrode film layer 1212 may further include a binder. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0123] In some embodiments, the positive electrode sheet 121 can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the hydrophobic additive, the first carbon material, the second carbon material and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry, and the positive electrode slurry is coated on the positive electrode collector 1211. After drying, cold pressing and other processes, the positive electrode sheet 121 can be obtained.

[0124] [Method for preparing positive electrode sheet]

[0125] The second aspect of the present application provides a method for preparing a positive electrode sheet. Figure 4Flow chart of a method for preparing a positive electrode sheet according to an embodiment of the present application. Figure 4 As shown, the preparation method 200 includes: disposing a positive electrode film layer on at least one side of a positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material and a hydrophobic additive.

[0126] In some embodiments, the positive electrode film layer also includes a conductive agent, the conductive agent includes a first carbon material and a second carbon material, and the positive electrode film layer is arranged on at least one side of the positive electrode current collector, including: placing the positive electrode active material, the first carbon material, the hydrophobic additive, and the second carbon material into a solvent in sequence and mixing them to obtain a first positive electrode slurry; coating the first positive electrode slurry on the positive electrode current collector to obtain a positive electrode film layer arranged on the positive electrode current collector.

[0127] In the above solution, by adding the second carbon material last, the possibility of the hydrophobic additive completely covering the second carbon material and thus affecting the conductivity of the battery can be reduced.

[0128] In some embodiments, the positive electrode film layer also includes a conductive agent, which includes a first carbon material; the positive electrode film layer is arranged on at least one side of the positive electrode current collector, including: placing the positive electrode active material and the first carbon material into a solvent and mixing them to obtain a second positive electrode slurry, placing a hydrophobic additive into the solvent to obtain a third positive electrode slurry; coating the second positive electrode slurry on the positive electrode current collector to obtain a first film layer arranged on the positive electrode current collector, and then coating the third positive electrode slurry on the first film layer to obtain a positive electrode film layer arranged on the positive electrode current collector.

[0129] In one possible embodiment, the positive electrode film layer also includes a conductive agent, which includes a first carbon material and a second carbon material; the positive electrode film layer is arranged on at least one side of the positive electrode current collector, including: placing the positive electrode active material and the first carbon material into a solvent and mixing them to obtain a second positive electrode slurry, placing the positive electrode active material, the first carbon material, the hydrophobic additive and the second carbon material into the solvent in sequence and mixing them to obtain a fourth positive electrode slurry; coating the second positive electrode slurry on the positive electrode current collector to obtain a first film layer arranged on the positive electrode current collector, and then coating the fourth positive electrode slurry on the first film layer to obtain a positive electrode film layer arranged on the positive electrode current collector.

[0130] It should be noted that in the above preparation method, it is only necessary to ensure that the second carbon material is added last, and there is no special requirement for the order of adding other materials. For example, the order of adding the first carbon material and the hydrophobic additive can be swapped.

[0131] [Negative electrode]

[0132] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0133] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0134] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0135] In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0136] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

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

[0138] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0139] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0140] [Electrolytes]

[0141] The electrolyte plays a role in conducting ions between the positive electrode plate 121 and the negative electrode plate. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0142] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0143] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0144] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0145] In some embodiments, the electrolyte may also optionally include negative electrode film-forming additives, positive electrode film-forming additives, and may also include performance additives that can improve certain battery properties, such as improving battery overcharge performance, improving battery high temperature or low temperature performance, etc.

[0146] [Isolation film]

[0147] The present application does not particularly limit the type of isolation membrane, and any known porous structure isolation membrane with good chemical stability and mechanical stability can be selected.

[0148] In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0149] In some embodiments, the positive electrode sheet 121 , the negative electrode sheet, and the separator may be formed into the electrode assembly 12 by a winding process or a lamination process.

[0150] In some embodiments, the battery cell may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0151] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0152] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 5 It is a schematic diagram of a battery cell according to an embodiment of the present application.

[0153] Figure 6 FIG. 1 is a schematic diagram of the structure of a battery cell according to an embodiment of the present application. Figure 6 As shown, the outer packaging may include a shell 11 and a cover plate 13. Among them, the shell 11 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 11 has an opening connected to the receiving cavity, and the cover plate 13 can be covered on the opening to close the receiving cavity. The positive electrode sheet 121, the negative electrode sheet and the isolation film can form an electrode assembly 12 through a winding process or a lamination process. The electrode assembly 12 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 12. The number of electrode assemblies 12 contained in the battery cell 100 can be one or more, and those skilled in the art can select according to specific actual needs.

[0154] In some embodiments, the battery cells 100 may also be assembled into a battery module. The battery module may contain one or more battery cells 100, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

[0155] In some embodiments, the battery cells 100 may also be directly assembled into a battery. The number of battery cells 100 contained in the battery may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery.

[0156] Figure 7 is a schematic diagram of a battery according to one embodiment of the present application, Figure 8 This is a schematic diagram of the structure of a battery according to one embodiment of the present application. Figure 7 and Figure 8The battery 400 may include a battery box and a plurality of battery cells 100 disposed in the battery box. The battery box includes an upper box body 401 and a lower box body 402. The upper box body 401 can cover the lower box body 402 and form a closed space for accommodating the battery cells 100. The plurality of battery cells 100 may be arranged in the battery box in any manner.

[0157] In addition, the present application also provides an electric device, which includes at least one of the positive electrode sheet 121, battery cell 100 or battery 400 provided in the present application. The positive electrode sheet 121, battery cell 100 or battery 400 can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0158] For example, Fig. 9 Schematic diagram of the structure of an electric device according to an embodiment of the present application. Figure 7 As shown, the power-consuming device 1 can be a vehicle 1, and the vehicle 1 can be a fuel vehicle, a gas vehicle or a new energy vehicle, and the new energy vehicle can be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A motor 500, a controller 600 and a battery 400 can be arranged inside the vehicle 1, and the controller 600 is used to control the battery 400 to supply power to the motor 500. For example, a battery 400 can be arranged at the bottom, front or rear of the vehicle 1. The battery 400 can be used to power the vehicle 1, for example, the battery 400 can be used as an operating power source for the vehicle 1, for the circuit system of the vehicle 1, for example, for the working power requirements during the start-up, navigation and operation of the vehicle 1. In another embodiment of the present application, the battery 400 can not only be used as an operating power source for the vehicle 1, but also as a driving power source for the vehicle 1, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1.

[0159] As the electrical device, the positive electrode sheet 121, the battery cell 100 or the battery 400 can be selected according to its usage requirements.

[0160] The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the electric device's requirements for high power and high energy density of the battery, a battery cell 100 or a battery 400 may be used.

[0161] As another example, the device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be light and thin, and the battery cell 100 may be used as a power source.

[0162] [Example]

[0163] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0164] [Example 1]

[0165] 1). Preparation of lithium-ion batteries

[0166] 1.1) Preparation of positive electrode sheet: The positive electrode active material nano lithium iron phosphate, the hydrophobic additive polytetrafluoroethylene, the first carbon material (SP), and the binder polyvinylidene fluoride are dissolved in the solvent N-methylpyrrolidone (NMP) in a mass ratio of 94.5%:2%:1.5%:2%, and the mixture is fully stirred and evenly mixed to prepare a positive electrode film slurry. The positive electrode film slurry is coated on the positive electrode current collector aluminum foil, and then dried at 100°C, cold pressed at 40T, and cut to obtain a positive electrode sheet; wherein, the hydrophobic additive contains a functional group -CF2, which is 2 parts by weight, and the positive electrode film is a mixed single-layer film.

[0167] [Example 2]

[0168] The lithium ion battery of Example 2 is substantially the same as that of Example 1, except that the hydrophobic additive in Example 2 is hexene tetrafluoroethylene copolymer.

[0169] [Example 3]

[0170] The lithium ion battery of Example 3 is substantially the same as that of Example 1, except that the hydrophobic additive in Example 3 is a perfluoroethylene-propylene copolymer containing a functional group -CF3.

[0171] [Example 4]

[0172] The lithium ion battery of Example 4 is substantially the same as that of Example 1, except that the hydrophobic additive in Example 4 is trifluoroethyl methacrylate, which contains a functional group -CF3.

[0173] [Example 5]

[0174] The lithium ion battery of Example 5 is substantially the same as that of Example 1, except that the hydrophobic additive in Example 5 is polyvinylidene fluoride, which contains a functional group -CF2H.

[0175] [Example 6]

[0176] The lithium ion battery of Example 6 is substantially the same as that of Example 1, except that the hydrophobic additive in Example 6 is polyethylene containing a functional group C=C.

[0177] [Example 7]

[0178] The lithium-ion battery of Example 7 is substantially the same as that of Example 1, except that the mass ratio of the positive electrode active material nano-lithium iron phosphate, the hydrophobic additive polytetrafluoroethylene, the first carbon material (SP), and the binder polyvinylidene fluoride in Example 7 is 96.2%:0.3%:1.5%:2%.

[0179] [Example 8]

[0180] The lithium-ion battery of Example 8 is substantially the same as that of Example 1, except that the mass ratio of the positive electrode active material nano-lithium iron phosphate, the hydrophobic additive polytetrafluoroethylene, the first carbon material (SP), and the binder polyvinylidene fluoride in Example 8 is 91.5%:5%:1.5%:2%.

[0181] [Example 9]

[0182] The lithium-ion battery of Example 9 is substantially the same as that of Example 1, except that the mass ratio of the positive electrode active material nano-lithium iron phosphate, the hydrophobic additive polytetrafluoroethylene, the first carbon material (SP), and the binder polyvinylidene fluoride in Example 9 is 96%:0.5%:1.5%:2%.

[0183] [Example 10]

[0184] The lithium-ion battery of Example 10 is basically the same as that of Example 1, except that the positive electrode plate in Example 10 includes a second carbon material, and the mass ratio of the positive electrode active material nano lithium iron phosphate, the hydrophobic additive polytetrafluoroethylene, the first carbon material (SP), the second carbon material multi-walled carbon nanotubes, and the binder polyvinylidene fluoride is 95%:2%:0.8%:0.2%:2%.

[0185] [Example 11]

[0186] The lithium-ion battery of Example 11 is substantially the same as that of Example 1, except that, in Example 11, the positive electrode film layer consists of a first film layer and a second film layer.

[0187] [Example 12]

[0188] The lithium-ion battery of Example 12 is substantially the same as that of Example 10, except that, in Example 12, the positive electrode film layer consists of a first film layer and a third film layer.

[0189] [Comparative Example 1]

[0190] The lithium ion battery of Comparative Example 1 is substantially the same as that of Example 1, except that the positive electrode plate in Comparative Example 1 does not include a hydrophobic additive.

[0191] 2). Physical properties characterization

[0192] 2.1) Material surface energy measurement: It can be calculated by the Young-Dop equation; specifically, the Young-Dop equation is: γ_s=(γ_l1+γ_l2+γ_l3) / 3+(cosθ_l1+cosθ_l2+cosθ_l3)×(√γ_l1γ_l2+√γ_l2γ_l3+√γ_l3γ_l1) / 3, where γ_l1, γ_l2 and γ_l3 are the surface tensions of the material surface and three different liquids, and θ_l1, θ_l2 and θ_l3 are the contact angles of the material and the three different liquids.

[0193] 2.2) Functional group detection: using Fourier transform infrared spectrometer

[0194] 2.3) Measurement of volume average particle size Dv50: It can be tested with a laser particle size analyzer (such as Master Size 3000) according to GB / T 19077-2016 particle size distribution laser diffraction method.

[0195] 2.4) Measurement of specific surface area: Refer to GB / T 19587-2017, use inert gas (such as nitrogen) adsorption specific surface area analysis test method to test, and calculate by BET (Brunauer Emmett Teller) method, where nitrogen adsorption specific surface area analysis test can be carried out by Tri-Star 3020 specific surface area pore size analysis tester of Micromeritics Company of the United States.

[0196] 2.5). Use a four-probe resistance meter to test the resistance in the thickness direction of the electrode.

[0197] Table 1 Specific experimental parameters of Examples 1-12 and Comparative Example 1

[0198]

[0199] 3). Lithium-ion battery performance test

[0200] 3.1) Contact angle measurement between hydrophobic additive or positive electrode film and water: The test is carried out using a contact angle meter, which is mainly divided into the following steps:

[0201] Place the sample to be tested on the test platform of the contact angle measuring instrument; use the equipped syringe to absorb a certain amount of liquid and adjust its volume; vertically drip the above liquid onto the surface of the sample to be tested, and measure its contact angle with the sample to be tested by calibrating the relevant standard line of the instrument. The test results of the contact angle of the hydrophobic additive, the positive electrode film layer and water are shown in Table 2.

[0202] 3.2) Pole piece moisture content test: After the pole piece is placed in a room temperature environment for 7 days, a moisture content tester (such as a Karl Fischer moisture meter) is used to take the middle position of the positive pole piece and cut it into 10 small pieces. The pieces are placed in the Karl Fischer moisture meter for testing until the moisture is exhausted. The proportion of moisture in the pole piece is determined and the average value of the 10 small pieces is taken, which is the pole piece moisture content before drying. For the test results, please refer to Table 2.

[0203] 3.3) Cycle performance test: At 60°C, keep the battery charge and discharge voltage range at 2.5-3.65V, cycle at 0.5C current density, and record the number of cycles when the battery is cycled to 80% of the power. The test results are shown in Table 2.

[0204] Table 2 Performance tests of Examples 1-12 and Comparative Example 1

[0205]

[0206]

[0207] In the embodiment of the present application, the moisture content of the electrode after being left for 7 days is used to characterize the water absorption of the electrode. If the moisture content value is higher, it means that the electrode has absorbed more water, and vice versa. The number of cycles is used to characterize the cycle performance of the battery. The more cycles, the better the cycle performance of the battery, and vice versa.

[0208] It can be seen from Examples 1-12 and Comparative Example 1 that adding a hydrophobic additive to the positive electrode film layer can reduce the water content in the electrode sheet and effectively improve the cycle performance of the battery.

[0209] According to Examples 1-6, by making the contact angle between the hydrophobic additive and water 90°-120°, especially 100°-120°, the water content of the electrode can be reduced and the cycle performance of the battery can be improved.

[0210] According to Examples 1-5, it can be seen that when the hydrophobic additive contains a CF bond functional group, especially at least one of -CF2, -CF2H, and -CF3, the battery has better performance.

[0211] According to Examples 1 and 7-9, by making the weight proportion of the hydrophobic additive in the positive electrode film layer 0.3-5, especially 0.5-2, the battery can have a lower water content and further improve the cycle performance of the battery.

[0212] According to Examples 1-12, when the contact angle between the positive electrode film layer and water is 95°-105°, the electrode has a lower water content and the battery has better cycle performance.

[0213] It can be seen from Examples 1, 10 and 12 that when a second carbon material is added to the positive electrode film layer, the cycle performance of the battery can be further improved.

[0214] According to Examples 1, 11 and 12, the use of mixed single-layer coating, separate coating of the first film layer and the second film layer, and separate coating of the first film layer and the third film layer can all reduce the water content of the electrode and improve the cycle performance of the battery; in particular, the coating method of the first film layer and the third film layer can further improve the performance of the battery.

[0215] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A positive electrode sheet, characterized in that: include: A positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode film layer comprises a positive electrode active material and a hydrophobic additive.

2. The positive electrode sheet according to claim 1, characterized in that: The contact angle between the hydrophobic additive and water is 90°-120°. Optionally, the contact angle between the hydrophobic additive and water is 100°-120°.

3. The positive electrode sheet according to claim 1 or 2, characterized in that: The hydrophobic additive includes a functional group containing a CF bond.

4. The positive electrode sheet according to any one of claims 1 to 3, characterized in that: The hydrophobic additive contains at least one of the following functional groups: -CF2, -CF2H, -CF3.

5. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: Based on 100 parts by weight of the positive electrode film layer, the weight of the hydrophobic additive is 0.3-5 parts by weight. Optionally, the weight of the hydrophobic additive is 0.5-2 parts by weight.

6. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: The contact angle between the positive electrode film layer and water is 95°-105°.

7. The positive electrode sheet according to any one of claims 1 to 6, characterized in that: The positive electrode film layer further includes a conductive agent, wherein the conductive agent includes a first carbon material, and the first carbon material includes at least one of Ketjen black and conductive carbon black.

8. The positive electrode sheet according to claim 7, characterized in that: The conductive agent further includes a second carbon material, and the second carbon material includes at least one of multi-walled carbon nanotubes, single-walled carbon nanotubes, and carbon fibers.

9. The positive electrode sheet according to claim 7, characterized in that: The positive electrode film layer comprises a first film layer and a second film layer, wherein the first film layer is arranged between the positive electrode current collector and the second film layer; Wherein, the first film layer includes the positive electrode active material and the first carbon material, and the second film layer includes the hydrophobic additive.

10. The positive electrode sheet according to claim 8, characterized in that: The positive electrode film layer comprises a first film layer and a third film layer, wherein the first film layer is arranged between the positive electrode current collector and the third film layer; The first film layer includes the positive electrode active material and the first carbon material, and the third film layer includes the positive electrode active material, the first carbon material, the second carbon material and the hydrophobic additive.

11. The positive electrode sheet according to any one of claims 1 to 10, characterized in that: The hydrophobic additive includes at least one of polytetrafluoroethylene, hexene tetrafluoroethylene copolymer, perfluoroethylene propylene copolymer, trifluoroethyl methacrylate, polyvinylidene fluoride, polyethylene, and ethylene chlorotrifluoroethylene copolymer. Optionally, the hydrophobic additive includes polytetrafluoroethylene.

12. The positive electrode sheet according to any one of claims 1 to 11, characterized in that: The positive electrode active material includes layered oxides, transition metal oxides, and polyanion compounds; optionally, the positive electrode active material includes lithium iron phosphate.

13. The positive electrode sheet according to any one of claims 1 to 12, characterized in that: The volume average particle size Dv50 of the positive electrode active material is 100nm-1000nm. Optionally, the volume average particle size Dv50 of the positive electrode material is 200nm-700nm.

14. The positive electrode sheet according to any one of claims 1 to 13, characterized in that: The specific surface area of ​​the positive electrode active material is 10 m 2 / g-20m 2 / g, optionally, the specific surface area of ​​the positive electrode active material is 12m 2 / g-17m 2 / g.

15. A preparation method, characterized in that: A positive electrode sheet for preparing any one of claims 1 to 14, comprising: A positive electrode film layer is disposed on at least one side of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material and a hydrophobic additive.

16. The preparation method according to claim 15, characterized in that: The positive electrode film layer further includes a conductive agent, and the conductive agent includes a first carbon material and a second carbon material; The positive electrode film layer is provided on at least one side of the positive electrode current collector, comprising: The positive electrode active material, the first carbon material, the hydrophobic additive and the second carbon material are sequentially placed in a solvent and mixed to obtain a first positive electrode slurry; The first positive electrode slurry is coated on the positive electrode current collector to obtain the positive electrode film layer disposed on the positive electrode current collector.

17. The preparation method according to claim 15, characterized in that: The positive electrode film layer further includes a conductive agent, and the conductive agent includes a first carbon material; The positive electrode film layer is provided on at least one side of the positive electrode current collector, comprising: The positive electrode active material and the first carbon material are placed in a solvent and mixed to obtain a second positive electrode slurry, and the hydrophobic additive is placed in a solvent to obtain a third positive electrode slurry; The second positive electrode slurry is coated on the positive electrode current collector to obtain a first film layer disposed on the positive electrode current collector, and then the third positive electrode slurry is coated on the first film layer to obtain the positive electrode film layer disposed on the positive electrode current collector.

18. The preparation method according to claim 15, characterized in that: The positive electrode film layer further includes a conductive agent, and the conductive agent includes a first carbon material and a second carbon material; The positive electrode film layer is provided on at least one side of the positive electrode current collector, comprising: The positive electrode active material and the first carbon material are mixed in a solvent to obtain a second positive electrode slurry, and the positive electrode active material, the first carbon material, the hydrophobic additive and the second carbon material are sequentially mixed in a solvent to obtain a fourth positive electrode slurry; The second positive electrode slurry is coated on the positive electrode current collector to obtain a first film layer disposed on the positive electrode current collector, and then the fourth positive electrode slurry is coated on the first film layer to obtain the positive electrode film layer disposed on the positive electrode current collector.

19. A battery cell, characterized in that: A positive electrode sheet comprising the positive electrode sheet according to any one of claims 1 to 14, or a positive electrode sheet prepared by the method for preparing the positive electrode sheet according to any one of claims 15 to 18.

20. A battery, characterized in that: Comprising the battery cell as claimed in claim 19.

21. An electrical device, characterized in that: Comprising the battery of claim 20.

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