A positive electrode sheet, its preparation method and application

Abstract

This invention provides a positive electrode sheet, its preparation method, and its application. The positive electrode sheet includes a current collector and a positive active layer on at least one surface of the current collector. The positive active layer includes a positive active material, a composite binder, and a composite conductive agent. The composite binder includes AS resin and polyvinyl butyral. By using AS resin and polyvinyl butyral as a composite binder, the positive electrode sheet of this invention not only effectively bonds and protects the positive electrode material from electrolyte corrosion, but also improves the mechanical properties of the positive electrode sheet, thereby further enhancing the cycle performance of the battery.

Description

Technical Field

[0001] This invention belongs to the field of battery technology and relates to a positive electrode sheet, its preparation method and application. Background Technology

[0002] Secondary batteries, such as lithium-ion batteries, are widely used in smartphones, wearable devices, consumer drones, and electric vehicles due to their advantages such as high energy density, long cycle life, and no memory effect. With the widespread application of lithium-ion batteries in these fields, the market demands increasingly higher performance from them.

[0003] However, the binder commonly used in the positive electrode of lithium-ion batteries is PVDF (polyvinylidene fluoride). PVDF has poor high voltage resistance, and PVDF achieves bonding by interacting with other parts of the electrode through weak van der Waals forces formed by F atoms. The bonding ability is weak, and the conductivity of the entire electrode is low. Therefore, it is not only unsuitable for high voltage systems, but also affects the cycle performance of the battery.

[0004] Therefore, there is a need to provide a positive electrode that can adapt to high-voltage systems, has high structural stability, excellent conductivity, and can improve the cycle stability of the battery. Summary of the Invention

[0005] The purpose of this invention is to provide a positive electrode sheet, its preparation method and application. The positive electrode sheet uses AS resin and polyvinyl butyral as a composite binder, which can not only effectively bond and protect the positive electrode material from electrolyte corrosion, but also improve the mechanical properties of the positive electrode sheet, thereby further improving the cycle performance of the battery.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a positive electrode sheet, the positive electrode sheet comprising a positive active layer, the positive active layer comprising a positive active material, a composite binder and a composite conductive agent;

[0008] The composite adhesive comprises AS resin and polyvinyl butyral.

[0009] Preferably, the mass ratio of the AS resin to polyvinyl butyral is (2:8) to (7:3), and more preferably (4:6) to (6:4).

[0010] Preferably, the composite conductive agent includes a first conductive agent and a second conductive agent, wherein the first conductive agent includes carbon nanotubes and / or carbon fibers, and the second conductive agent includes a porous carbon-graphene composite material.

[0011] Preferably, in the composite conductive agent, the content of the second conductive agent is 30-70 wt%.

[0012] Preferably, the first conductive agent comprises carbon nanotubes and carbon fibers;

[0013] Preferably, in the composite conductive agent, the mass ratio of carbon nanotubes to carbon fibers is (2:8) to (8:2).

[0014] Preferably, the lithium removal cutoff potential of the positive electrode active material is ≥4.4V.

[0015] Preferably, the positive electrode active material includes any one or a combination of at least two of lithium nickel manganese oxide, lithium-rich manganese-based positive electrode material, lithium cobalt oxide, or ternary positive electrode material.

[0016] Preferably, the mass ratio of the positive electrode active material, the composite binder, and the composite conductive agent is (80-97):(1.5-10):(1.5-10).

[0017] In a second aspect, the present invention provides a method for preparing a positive electrode sheet as described in the first aspect, the method comprising the following steps:

[0018] (1) Mix the positive electrode active material, composite binder, composite conductive agent and solvent to obtain positive electrode slurry;

[0019] (2) The positive electrode slurry described in step (1) is coated on at least one side of the current collector to obtain the positive electrode sheet.

[0020] Thirdly, the present invention provides a battery comprising a positive electrode as described in the first aspect.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] This invention uses AS resin and polyvinyl butyral as a composite binder. On the one hand, AS resin has a large number of nitrile groups, which can form hydrogen bonds with the active material to achieve effective bonding. It can also form a uniform nano-coating on the surface of the positive electrode particles, protecting the positive electrode material from electrolyte corrosion and preventing parasitic reactions. In addition, the phenyl groups in AS resin have strong mechanical strength, which helps to improve the mechanical strength of the electrode and slows down the expansion of the active material, thereby improving the battery cycle performance. It also improves the ion conductivity and thermodynamic properties of the composite binder. On the other hand, polyvinyl butyral can make the electrode sheet have good flexibility, avoiding the brittleness problem caused by AS resin. Detailed Implementation

[0023] Reference will now be made to detailed embodiments of this application, one or more of which are described below. Each example is provided for explanation and not for limitation of this application. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to this application without departing from its scope or spirit. For example, features described or illustrated as part of one embodiment may be used in another embodiment to produce further embodiments.

[0024] Therefore, this application is intended to cover such modifications and variations falling within the scope of the appended claims and their equivalents. Other objects, features, and aspects of this application are disclosed in or will be apparent from the following detailed description. It will be understood by those skilled in the art that this discussion is merely a description of exemplary embodiments and is not intended to limit the broader aspects of this application.

[0025] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0026] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0027] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0028] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0029] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps S12 and S14, indicating that the method may include steps S12 and S14 performed sequentially, or it may include steps S14 and S12 performed sequentially. For example, the mention that the method may also include step S16 indicates that step S16 may be added to the method in any order. For example, the method may include steps S12, S14, and S16, or it may include steps S12, S16, and S14, or it may include steps S16, S12, and S14, etc.

[0030] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0031] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0032] In existing cathodes, fluorine-based binders such as PVDF are mostly used to bond the cathode active material and conductive agent. PVDF is bonded to other parts of the electrode through weak van der Waals forces formed by F atoms. The bonding ability is weak, resulting in poor cycle performance of the battery.

[0033] This invention provides a positive electrode sheet that uses a composite binder with strong adhesion, which can effectively solve the problem of poor cycle performance caused by using a binder with insufficient adhesion in the positive electrode.

[0034] In one embodiment, the present invention provides a positive electrode sheet, the positive electrode sheet comprising a positive electrode active layer, the positive electrode active layer comprising a positive electrode active material, a composite binder, and a composite conductive agent;

[0035] The composite adhesive comprises AS resin and PVB (polyvinyl butyral), wherein the AS resin refers to a copolymer of styrene and acrylonitrile.

[0036] This invention uses AS resin and polyvinyl butyral as a composite binder. On the one hand, AS resin has a large number of nitrile groups, which can form hydrogen bonds with the active material to achieve effective bonding. It can also form a uniform nano-coating on the surface of the positive electrode particles, protecting the positive electrode material from electrolyte corrosion and preventing parasitic reactions. In addition, the phenyl groups in AS resin have strong mechanical strength, which helps to improve the mechanical strength of the electrode and slows down the expansion of the active material, thereby improving the battery cycle performance. It also improves the ion conductivity and thermodynamic properties of the composite binder. On the other hand, polyvinyl butyral can make the electrode sheet have good flexibility, avoiding the brittleness problem caused by AS resin.

[0037] The parasitic reaction described in this invention refers to the decomposition of the electrolyte by trace amounts of water, which produces HF. The HF reacts with the positive electrode to further generate water, leading to continuous decomposition of the electrolyte and continuous production of HF, resulting in a continuous deterioration of battery performance.

[0038] In one embodiment, the mass ratio of AS resin to polyvinyl butyral is (2:8) to (7:3), for example, it can be 2:8, 4:6, 6:4 or 7:3, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably (4:6) to (6:4).

[0039] When the mass ratio of AS resin to polyvinyl butyral is too small, i.e., when there is too little AS resin, the bonding ability of the composite binder decreases, and a uniform nanoscale coating cannot be formed on the surface of the positive electrode particles. When the mass ratio is too large and there is too much AS resin, the disadvantage is that the prepared positive electrode sheet becomes brittle and the cycle performance deteriorates.

[0040] In one embodiment, the composite conductive agent includes a first conductive agent and a second conductive agent, wherein the first conductive agent includes CNT (carbon nanotubes) and / or VGCF (carbon fiber), and the second conductive agent includes PCG (porous carbon-graphene composite material).

[0041] This invention utilizes a variety of conductive agents to form multi-dimensional contacts with active materials at points, lines, and surfaces, thereby constructing a highly efficient and stable conductive network, reducing battery internal resistance, minimizing polarization, and extending battery life.

[0042] The porous carbon-graphene composite material of the present invention refers to a material in which porous carbon particles are generated on graphene through a chemical reaction. The preparation method includes: mixing phenolic resin with potassium chloride, drying, carbonizing, acid washing, and water washing to obtain the porous carbon-graphene composite material.

[0043] The carbon particles on the porous carbon-graphene composite material can effectively act as a barrier, preventing the agglomeration of graphene, carbon nanotubes and / or carbon fibers, ensuring the uniformity and stability of the conductive paste, thereby effectively ensuring the conductivity of the composite conductive agent and facilitating the rapid transport of lithium ions within the positive electrode.

[0044] Furthermore, since the present invention uses a composite binder, the composite binder coating will be formed on the surface of the positive electrode active material particles, which will inevitably affect the electronic conductivity of the positive electrode, leading to poorer cycle life and increased polarization. Therefore, the present invention uses a composite conductive agent to effectively solve this problem.

[0045] In one embodiment, the content of the second conductive agent in the composite conductive agent is 30-70 wt%, for example, it can be 30 wt%, 40 wt%, 50 wt%, 60 wt% or 70 wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0046] In one embodiment, the first conductive agent includes carbon nanotubes and carbon fibers, and the composite conductive agent includes carbon nanotubes, carbon fibers, and porous carbon-graphene composite materials.

[0047] In one embodiment, the mass ratio of carbon nanotubes to carbon fibers in the composite conductive agent is (2:8) to (8:2), for example, it can be 2:8, 4:6, 6:4 or 8:2, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0048] In one embodiment, the lithium removal cutoff potential of the positive electrode active material is ≥4.4V, for example, it can be 4.4V, 4.6V, 4.8V or 4.9V, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0049] In one embodiment, the positive electrode active material includes any one or a combination of at least two of lithium nickel manganese oxide, lithium-rich manganese-based positive electrode material, lithium cobalt oxide, or ternary positive electrode material.

[0050] In one embodiment, the mass ratio of the positive electrode active material, the composite binder, and the composite conductive agent is (80-97):(1.5-10):(1.5-10), for example, it can be 80:10:10, 85:5:10, 90:5:5 or 97:1.5:1.5, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0051] Understandably, using high-voltage active materials to prepare the cathode is one of the main methods in this field to improve the energy density of batteries. However, the use of high-voltage active materials brings two new technical problems. First, batteries prepared with high-voltage active materials must be used at high operating voltages. On the one hand, existing cathode binders are generally fluorinated binders such as PVDF. During long-term high-voltage cycling, fluorinated binders such as PVDF will gel and swell in the liquid electrolyte, further reducing the contact between active material particles, thus causing rapid capacity degradation. On the other hand, fluorinated binders such as PVDF have weak bonding ability, which is not conducive to the performance of the battery. Second, under high-voltage operating conditions, the active material is prone to side reactions with the electrolyte, causing electrolyte decomposition. Most of the transition metal ions contained in the high-voltage active materials will be released and undergo reduction reactions at the negative electrode. All of these will lead to the degradation of the battery's cycle performance.

[0052] In this invention, by using a combination of high-voltage positive electrode active material and composite binder, on the one hand, the composite binder is more resistant to high voltage and its performance does not change during long-term cycling. On the other hand, the composite binder of this application can form a uniform nano-coating on the surface of positive electrode particles, protecting the positive electrode material from electrolyte corrosion. Nitrile groups and the like can also complex with transition metal ions, preventing the dissolution of transition metal ions in the positive electrode sheet, which would cause a reduction reaction on the negative electrode side, destroying the SEI film on the negative electrode side, causing it to continuously regenerate, consuming lithium ions in the battery, and leading to the deterioration of battery cycle performance.

[0053] In this invention, the combined use of high-voltage positive electrode active material and composite conductive agent effectively avoids the degradation of battery cycle performance caused by the decomposition of electrolyte induced by the use of carbon black or other single conductive agents in traditional positive electrodes under high voltage. It can also form multi-dimensional contact with the positive electrode active material at points, lines and surfaces, thereby constructing a highly efficient and stable conductive network. The prepared high-voltage positive electrode has no edge cracking, no hard brittleness or band breakage problems, and has good cycle stability.

[0054] On the other hand, while the composite binder forms a uniform nano-coating on the surface of the cathode particles, effectively improving the side reactions between the cathode active material and the electrolyte, it also affects the lithium-ion transport of the cathode electrode to some extent. The composite conductive agent forms multi-dimensional contact with the cathode active material at points, lines, and surfaces, which can effectively improve this problem. The combined use of the composite conductive agent and the composite binder can effectively construct a highly efficient lithium-ion and electron conduction network within the cathode.

[0055] In one embodiment, the positive electrode sheet further includes a current collector, and the positive active layer is disposed on one or both surfaces of the current collector.

[0056] In a preferred embodiment, the current collector is selected from metal foil or composite current collector; the composite current collector has a sandwich-like sandwich structure, with the middle polymer layer mainly composed of high molecular insulating resin or similar materials, and metal layers deposited on both sides of the middle polymer layer by electroplating, chemical plating, or other methods. Schematably, the high molecular resin includes polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyetheretherketone, polyimide, polyamide, polyethylene glycol, polyamide-imide, polycarbonate, and cyclic resins. The material is selected from one or more of the following: polyolefins, polyphenylene sulfide, polyvinyl acetate, polytetrafluoroethylene, polymethylene naphthalene, polyvinylidene fluoride, polyethylene naphthalate, polypropylene carbonate, poly(vinylidene fluoride-hexafluoropropylene), poly(vinylidene fluoride-co-trifluorochloroethylene), silicone, vinylon, polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyether nitrile, polyurethane, polyphenylene ether, polyester, polysulfone and its derivatives, sodium carboxymethyl cellulose, styrene-butadiene rubber, fluorinated rubber, polyvinyl alcohol, or polyvinylidene fluoride. The metal layer is selected from at least one of the following: aluminum, copper, nickel, cobalt, tungsten, tin, lead, iron, silver, or gold.

[0057] In a preferred embodiment, the current collector is aluminum foil.

[0058] In one embodiment, a method for preparing a positive electrode sheet is provided, the method comprising the following steps:

[0059] (1) Mix the positive electrode active material, composite binder, composite conductive agent and solvent to obtain positive electrode slurry;

[0060] (2) The positive electrode slurry described in step (1) is coated on at least one side of the current collector to obtain the positive electrode sheet.

[0061] In one embodiment, the thickness of the composite positive electrode active electrode material layer can be 30μm-400μm, such as 30μm, 40μm, 50μm, 80μm, 110μm, 200μm, 300μm, 400μm, preferably 50μm-110μm.

[0062] In one embodiment, a battery is provided, the battery including the positive electrode.

[0063] In one embodiment, the battery includes an electrolyte, which includes an electrolyte salt and a solvent.

[0064] In one embodiment, the electrolyte salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium bisfluorosulfonylimide (LiFSI), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonylimide) (LiTFSI), lithium difluorophosphate (LiPO2F2), lithium bis(oxalateborate) (LiBOB), lithium bis(oxalateborate) (LiODFB), lithium di(oxalateborate) (LiODFP), or lithium tetrafluorooxalateborate (LiTFOP).

[0065] In one embodiment, the mass percentage of the electrolyte salt is 0.5-25% based on the total mass of the electrolyte (100%).

[0066] In one embodiment, the solvent includes at least one selected from: ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0067] In one embodiment, the electrolyte contains additives, and the electrolyte further includes additives including at least one selected from 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, propylene-1,3-sulfonyl lactone, vinyl sulfate, 4-methylvinyl sulfate, propylene sulfate, saturated phosphate compounds and unsaturated phosphate compounds, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, tris(triethylsilane) borate, succinic acid nitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptacyanide, octanoic acid nitrile, azelaic acid nitrile, and sebacate.

[0068] In one embodiment, the battery further includes a negative electrode.

[0069] In one embodiment, the negative electrode comprises a negative electrode current collector and a negative electrode active material layer formed on the surface of the negative electrode current collector, wherein the negative electrode active material layer comprises at least a negative electrode active material and a negative electrode binder.

[0070] In one embodiment, the negative electrode active material in this application is not particularly limited, as long as it is a substance that can electrochemically adsorb and release s-region metal ions such as lithium ions, sodium ions, potassium ions, and magnesium ions, such as carbonaceous materials, metal compound materials, or their oxides, carbides, nitrides, silicides, sulfides, phosphides, etc. These substances can be used alone, or two or more can be used in combination at will.

[0071] In one embodiment, carbon materials can be selected as the negative electrode active material. Specifically, one or more of the following can be selected: graphite, needle coke, amorphous carbon, carbon-containing mesophase, carbon fiber, and carbon materials with low graphitization. Graphite can include natural graphite, artificial graphite, etc. Alternatively, materials obtained by coating these materials with carbon materials, such as amorphous carbon or graphitized compounds, can also be used. Amorphous carbon includes, but is not limited to, particles obtained by sintering an integral mesophase, and particles obtained by sintering a carbon precursor after a non-melting treatment. Examples of carbonaceous particles with low graphitization include particles obtained by sintering organic matter at temperatures typically below 2500°C.

[0072] In one embodiment, non-metallic materials that can be used as negative electrode active materials also include elemental silicon and its compounds, such as Si and SiOx (0≤x<2). Since silicon-containing materials are prone to expansion and easy to fall off from the negative electrode current collector, and have poor conductivity, they are often used in combination with carbon materials, such as core-shell structures containing carbon coating layers.

[0073] In one embodiment, elemental metals and metal compounds may also be selected as negative electrode active materials, such as compounds containing metals or metalloids such as Li, Ag, Al, Bi, Cu, Ga, Ge, In, Ni, Pb, Sb, Si, Sn, Sr, and Zn.

[0074] In one embodiment, the negative electrode active material layer contains a negative electrode active material with a mass percentage of 80-99%, for example, 80%, 85%, 90%, 95%, 97%, 99%, etc., preferably 95-97%.

[0075] In one embodiment, when the negative electrode active material is a non-metallic material such as carbon material, the negative electrode binder can be one or more of water-based binders, such as sodium carboxymethyl cellulose, styrene-butadiene latex, polyacrylic acid, acrylic copolymers, cyclodextrin, etc.

[0076] In one embodiment, the negative electrode active material layer can be obtained by coating a negative electrode slurry onto a negative electrode current collector and then performing operations such as drying. The negative electrode slurry includes at least a negative electrode active material and a negative electrode binder. When an aqueous solvent is used as the liquid medium for forming the negative electrode slurry, a thickener is preferably used for slurry formation. The thickener is typically used to adjust the viscosity of the slurry.

[0077] In one embodiment, the thickener in this application embodiment may be one or more of the following: carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein and their salts, etc.

[0078] In one embodiment, the mass percentage of the thickener in the negative electrode slurry can be 0.1-5%, for example, 0.1%, 0.2%, 0.5%, 0.6%, 1%, 2%, 3%, 4%, 5%, etc., preferably 0.5-3%, and more preferably 0.6-2%.

[0079] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0080] Example 1

[0081] This embodiment provides a positive electrode sheet, which includes a current collector and positive active layers on both sides of the current collector. The positive active layers include a positive active material, a composite binder, and a composite conductive agent in a mass ratio of 96.5:2:1.5.

[0082] The positive electrode active material is LiNiMnO4, and its delithiation cutoff potential is 4.9V;

[0083] The composite adhesive comprises AS resin and polyvinyl butyral in a mass ratio of 4:6, wherein the AS resin comprises styrene-acrylonitrile copolymer;

[0084] The composite conductive agent comprises a porous carbon-graphene composite material, carbon nanotubes, and carbon fibers in a mass ratio of 5:3:2.

[0085] The current collector is aluminum foil;

[0086] The method for preparing the positive electrode sheet includes the following steps:

[0087] (1) Weigh the positive electrode active material, composite binder and composite conductive agent according to the mass ratio, add the composite binder to the solvent NMP, mix evenly, add the positive electrode active material and composite conductive agent and continue mixing until uniform to form a positive electrode active slurry.

[0088] (2) The positive electrode active slurry formed in step (1) is uniformly coated on the current collector to form the positive electrode sheet.

[0089] Example 2

[0090] This embodiment provides a positive electrode sheet, which is the same as that in Example 1 except that the mass ratio of AS resin to polyvinyl butyral is 2:8.

[0091] Example 3

[0092] This embodiment provides a positive electrode sheet, which is the same as that in Example 1 except that the mass ratio of AS resin to polyvinyl butyral is 7:3.

[0093] Example 4

[0094] This embodiment provides a positive electrode sheet, which is the same as that in Example 1 except that the mass ratio of AS resin to polyvinyl butyral is 4:6.

[0095] Example 5

[0096] This embodiment provides a positive electrode sheet, which is the same as that in Example 1 except that the mass ratio of AS resin to polyvinyl butyral is 6:4.

[0097] Example 6

[0098] This embodiment provides a positive electrode sheet, which is the same as that in Embodiment 1 except that the mass ratio of the porous carbon-graphene composite material, carbon nanotubes and carbon fibers is 3:5:2.

[0099] Example 7

[0100] This embodiment provides a positive electrode sheet, which is the same as that in Embodiment 1 except that the mass ratio of the porous carbon-graphene composite material, carbon nanotubes and carbon fibers is 7:2:1.

[0101] Example 8

[0102] This embodiment provides a positive electrode sheet, which is the same as that in Example 1 except that the composite conductive agent is a porous carbon-graphene composite material and carbon nanotubes with a mass ratio of 6:4.

[0103] Example 9

[0104] This embodiment provides a positive electrode sheet, which is the same as that in Embodiment 1 except that the composite conductive agent is a porous carbon-graphene composite material and carbon fiber with a mass ratio of 6:4.

[0105] Example 10

[0106] This embodiment provides a positive electrode sheet, which is the same as that in Example 1 except that the mass ratio of AS resin to polyvinyl butyral is 1:9.

[0107] Example 11

[0108] This embodiment provides a positive electrode sheet, which is the same as that in Example 1 except that the mass ratio of AS resin to polyvinyl butyral is 9:1.

[0109] Example 12

[0110] This embodiment provides a positive electrode sheet, which is the same as that in Embodiment 1 except that the mass ratio of the porous carbon-graphene composite material, carbon nanotubes and carbon fibers is 8:1:1.

[0111] Example 13

[0112] This embodiment provides a positive electrode sheet, which is the same as that in Embodiment 1 except that the mass ratio of the porous carbon-graphene composite material, carbon nanotubes and carbon fibers is 2:4:4.

[0113] Comparative Example 1

[0114] This comparative example provides a positive electrode sheet, which is the same as that in Example 1 except that it does not include polyvinyl butyral.

[0115] Comparative Example 2

[0116] This comparative example provides a positive electrode sheet, which is the same as in Example 1 except that the composite conductive agent is replaced by SP conductive carbon black in equal mass.

[0117] Comparative Example 3

[0118] This comparative example provides a positive electrode sheet, which is the same as in Example 1 except that the composite binder is replaced with PVDF and the composite conductive agent is replaced with SP conductive carbon black.

[0119] The composition of the composite binder and the composite conductive agent in the positive electrode sheets described in the above embodiments and comparative examples are shown in Table 1.

[0120] Table 1

[0121]

[0122]

[0123] The positive electrode sheet obtained in the above examples and comparative examples, together with the negative electrode and electrolyte, are used to prepare a battery. The negative electrode active material is artificial graphite, and the electrolyte is a solution containing 1 mol / L LiPF6 electrolyte and 0.5 vol.% fluoroethylene carbonate in the form of ethylene carbonate + diethyl carbonate + methyl ethyl carbonate.

[0124] The obtained battery was subjected to room temperature cycle performance testing: the charging and discharging potential range was 3.5V to 4.9V, the charging process was constant current 1C to 4.9V, constant voltage charging at 4.9V to cutoff current ≤0.05C, resting for 5 minutes, then discharging at 1C to 3.5V, and resting for 5 minutes; this charging and discharging cycle was repeated to test the cycle performance at room temperature (25℃), and the cycle capacity retention rate after 500 cycles was recorded.

[0125] The test results are shown in Table 2:

[0126] Table 2

[0127] <![CDATA[Positive specific capacity (mAh·g -1 )]]> Retention rate after 500 cycles (%) Example 1 116.5 80 Example 2 112.4 66.5 Example 3 110.5 65.4 Example 4 113.7 77.2 Example 5 113.9 77.6 Example 6 114.6 72.3 Example 7 115.4 74.6 Example 8 114.7 70.1 Example 9 115.1 71.3 Example 10 109.8 64.9 Example 11 113.2 65.1 Example 12 114.1 71.8 Example 13 113.5 69.1 Comparative Example 1 115.2 62.3 Comparative Example 2 113.1 58.9 Comparative Example 3 113.4 55.7

[0128] As can be seen from Tables 1 and 2:

[0129] As shown in Examples 1-5 and 10-11, the preferred mass ratio of AS resin to polyvinyl butyral in this invention is (2:8) to (7:3), and more preferably (4:6) to (6:4), which can further improve the specific capacity and cycle performance of the battery. As shown in Examples 1, 6-9, and 12-13, this invention preferably uses a combination of carbon nanotubes, carbon fibers, and porous carbon-graphene composite materials in a specific mass ratio, which can further promote the formation of point, line, and surface multidimensional contacts between the composite conductive agent and the positive electrode active material, forming a complete conductive network, thereby further improving the battery performance. As shown in Examples 1 and Comparative Examples 1-3, when the composite binder and composite conductive agent described in this invention are used together, the specific capacity and cycle performance of the battery can be guaranteed.

[0130] In summary, this invention provides a positive electrode sheet, its preparation method, and its application. The positive electrode sheet uses AS resin and polyvinyl butyral as a composite binder, which not only effectively bonds and protects the positive electrode material from electrolyte corrosion, but also improves the mechanical properties of the positive electrode sheet, thereby further improving the cycle performance of the battery.

[0131] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A positive electrode plate, characterized in that, The positive electrode sheet includes a positive active layer, which includes a positive active material, a composite binder, and a composite conductive agent. The composite adhesive comprises AS resin and polyvinyl butyral; The mass ratio of the AS resin to the polyvinyl butyral is (4:6) to (6:4); The composite conductive agent includes a first conductive agent and a second conductive agent. The first conductive agent includes carbon nanotubes and / or carbon fibers, and the second conductive agent includes a porous carbon-graphene composite material.

2. The positive electrode sheet according to claim 1, characterized in that, In the composite conductive agent, the content of the second conductive agent is 30-70 wt%.

3. The positive electrode sheet according to claim 1, characterized in that, The first conductive agent includes carbon nanotubes and carbon fibers; In the composite conductive agent, the mass ratio of carbon nanotubes to carbon fibers is (2:8) to (8:2).

4. The positive electrode sheet according to claim 1 or 2, characterized in that, The delithiation cutoff potential of the positive electrode active material is ≥4.4V.

5. The positive electrode sheet according to claim 1, characterized in that, The positive electrode active material includes any one or a combination of at least two of lithium nickel manganese oxide materials, lithium-rich manganese-based positive electrode materials, lithium cobalt oxide, or ternary positive electrode materials.

6. The positive electrode sheet according to claim 1 or 2, characterized in that, The mass ratio of the positive electrode active material, composite binder and composite conductive agent is (80~97):(1.5~10):(1.5~10).

7. A method for preparing a positive electrode sheet as described in any one of claims 1-6, characterized in that, The preparation method includes the following steps: (1) The positive electrode active material, composite binder, composite conductive agent and solvent are mixed to obtain positive electrode slurry; (2) The positive electrode slurry described in step (1) is coated on at least one side of the current collector to obtain the positive electrode sheet.

8. A battery, characterized in that, The battery includes a positive electrode as described in any one of claims 1-6.

Images