Binder, electrode plate and battery

Abstract

The invention provides a binder, an electrode plate and a battery, the binder comprises a copolymer, the copolymer comprises an aromatic unsaturated hydrocarbon structure unit, an aliphatic conjugated unsaturated hydrocarbon structure unit, an unsaturated carboxylic ester structure unit, a vinyl carboxylic acid structure unit and a crosslinking structure unit; at normal temperature, the gel rate of the copolymer in toluene is greater than or equal to 93%, and the binder has high cohesiveness, is beneficial to reducing the rebound of a pole piece, improving the energy density of a battery, prolonging the cycle life of the battery and the like, and overcomes the defects in the prior art.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of batteries, in particular to a binder, an electrode sheet and a battery. BACKGROUND

[0002] A battery is a common electrochemical energy storage device at present, an electrode sheet is an important component of the battery, the electrode sheet usually comprises an electrode active material layer, and a binder is one of important components of the electrode active material layer. However, due to the poor adhesion and high dosage of the binder (such as SBR), the battery generally has problems such as large electrode sheet rebound, poor cycle life, low energy density and the like. SUMMARY

[0003] The present application provides a binder, an electrode sheet and a battery, the binder has high adhesion, can reduce the electrode sheet rebound, improve the energy density and cycle life of the battery and the like, and solves the defects in the prior art.

[0004] In one aspect of the present application, a binder is provided, comprising a copolymer, the copolymer comprises aromatic unsaturated hydrocarbon structural units, aliphatic conjugated unsaturated hydrocarbon structural units, unsaturated carboxylic ester structural units, vinyl carboxylic acid structural units and cross-linking structural units; the gel rate of the copolymer in toluene at room temperature is greater than or equal to 93%.

[0005] According to an embodiment of the present application, the glass transition temperature of the binder is -73-0℃.

[0006] According to an embodiment of the present application, the average particle size D 50 is 100-500 nm.

[0007] According to an embodiment of the present application, the copolymer further comprises functional structural units, the functional structural units comprise one or more of (meth) acrylonitrile structural units, vinyl pyrrolidone structural units, butenyl nitrile structural units and vinyl ether structural units.

[0008] According to an embodiment of the present application, the mass ratio of the aromatic unsaturated hydrocarbon structural units, the aliphatic conjugated unsaturated hydrocarbon structural units, the unsaturated carboxylic ester structural units, the vinyl carboxylic acid structural units, the cross-linking structural units and the functional structural units is (0.1-50):(0.1-100):(0.1-100):(0.1-20):(0.1-30):(10-20).

[0009] Another aspect of the present application provides an electrode sheet, comprising an electrode active material layer, the electrode active material layer comprises the above binder.

[0010] According to an embodiment of the present application, the binder accounts for 0.3-1.5% of the mass percentage of the electrode active material layer; and / or, the electrode sheet is a negative electrode sheet.

[0011] Another aspect of the present application provides a battery comprising the electrode sheet.

[0012] The present application uses a copolymer comprising aromatic unsaturated hydrocarbon structural units, aliphatic conjugated unsaturated hydrocarbon structural units, unsaturated carboxylic ester structural units, vinyl carboxylic acid structural units, and cross-linking structural units as a binder, and the gel rate of the copolymer in toluene at room temperature is greater than or equal to 93%, which is beneficial to improve the adhesion of the binder, reduce the electrode sheet rebound, and improve the energy density and cycle life of the battery. DETAILED DESCRIPTION

[0013] To make the objectives, technical solutions, and advantages of the present application clearer, the technical solutions in the embodiments of the present application will be described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0014] According to the research of the inventor, improving the adhesion of the binder can reduce the amount of the binder in the battery, increase the amount of the electrode active material in the battery, and thus improve the energy density and kinetic performance of the battery. In addition, the binder with high adhesion is also beneficial to reduce the electrode sheet rebound and improve the cycle life of the battery.

[0015] Therefore, the embodiments of the present application provide a binder comprising a copolymer, wherein the copolymer comprises aromatic unsaturated hydrocarbon structural units, aliphatic conjugated unsaturated hydrocarbon structural units, unsaturated carboxylic ester structural units, vinyl carboxylic acid structural units, and cross-linking structural units; and the gel rate of the copolymer in toluene at room temperature is greater than or equal to 93%.

[0016] In the above system, the copolymer has good adhesion, which is conducive to reducing the amount of binder in the electrode sheet, thereby reducing the hindrance in the transmission process of active ions (for example, the active ions in a lithium ion battery are lithium ions) in the battery, improving the kinetic performance and energy density of the battery, and reducing the rebound of the electrode sheet. In addition, the copolymer has a high gel rate, which is conducive to the stability of long-term cycling of the battery, reduces the generation of side reactions of the battery, thereby improving the cycling performance of the battery. Specifically, the aromatic unsaturated hydrocarbon structural unit plays a hard segment skeleton supporting role, which is conducive to improving the cycle stability of the battery, the aliphatic conjugated unsaturated hydrocarbon structural unit and the unsaturated carboxylic acid ester structural unit play a flexible tackifying role, which is conducive to improving the flexibility and adhesion of the binder, the vinyl carboxylic acid structural unit is conducive to improving the adhesion of the binder to the substrate (such as the current collector), and the above monomers are cross-linked through the cross-linking structural unit, which is conducive to improving the adhesion and gel rate of the binder and other properties.

[0017] Therefore, the above-mentioned binder has good adhesion, which is conducive to improving the peeling strength of the electrode active material layer and the electrode current collector, reducing the rebound of the electrode sheet, and improving the energy density and cycle life of the battery.

[0018] Specifically, the gel rate of the copolymer in toluene at room temperature can be greater than or equal to 93%, greater than or equal to 94%, greater than or equal to 95%, greater than or equal to 96%, greater than or equal to 97%, greater than or equal to 98%, greater than or equal to 99%, or a range composed of any two of them, and the upper limit of the gel rate can be 100% or 99.9%.

[0019] Specifically, the room temperature can be 25±5℃, for example, 20℃, 21℃, 22℃, 23℃, 24℃, 25℃, 26℃, 27℃, 28℃, 29℃, 30℃, or a range composed of any two of them.

[0020] The gel rate of the copolymer in toluene in the embodiments of the present application can be measured by the following method:

[0021] The copolymer is made into a film, a certain amount of the film is taken as a test sample, weighed by an electronic balance to obtain the initial weight W1 of the sample, the test sample is soaked in toluene, then taken out after being stored in a room temperature oven for 72h (3 days), the excess liquid on the surface of the test sample is wiped off using filter paper and / or a dust-free cloth to obtain the treated test sample, weighed by an electronic balance to obtain the weight W2 of the treated sample, and the gel rate (i.e. the gel rate of the copolymer in toluene at room temperature) = W2 / W1x100%, the gel rate is calculated, and the above operation is repeated three times, and the average value is taken as the gel rate of the copolymer in toluene at room temperature.

[0022] In the present application, the aromatic unsaturated hydrocarbon structural unit is derived from an aromatic unsaturated hydrocarbon monomer, the aliphatic conjugated unsaturated hydrocarbon structural unit is derived from an aliphatic conjugated unsaturated hydrocarbon monomer, the unsaturated carboxylic ester structural unit is derived from an unsaturated carboxylic ester monomer, the vinyl carboxylic acid structural unit is derived from a vinyl carboxylic acid monomer, and the crosslinking structural unit is derived from a crosslinking agent. The copolymer is prepared by copolymerization of monomer raw materials (i.e., copolymer raw materials) including the aromatic unsaturated hydrocarbon monomer, the aliphatic conjugated unsaturated hydrocarbon monomer, the unsaturated carboxylic ester monomer, the vinyl carboxylic acid monomer, and the crosslinking agent, specifically, by copolymerization in the presence of a solvent. The prepared adhesive is in the form of an emulsion, which can be dried to form the above-mentioned adhesive film. Then, the gel content of the copolymer in toluene at room temperature is measured according to the above-mentioned process.

[0023] Specifically, the copolymer as a whole has a high gel content (gel content ≥ 93%). In the present application, the gel content of the copolymer in toluene is substantially equivalent to the percentage of the copolymer (hereinafter referred to as the second copolymer) that is insoluble in toluene at room temperature in the total mass of the copolymer.

[0024] In the present application, during the preparation of the above-mentioned copolymer, due to the randomness of the polymerization reaction, there is a small amount of copolymer (hereinafter referred to as the first copolymer) that is soluble in toluene at room temperature and has a low degree of polymerization. It can be understood that, corresponding to the gel content of the copolymer being ≥ 93%, the content of the first copolymer in the copolymer is ≤ 7%, for example, it can be 6%, 5%, 4%, 3%, 2%, 1%, 0.1%, or a range formed by any two of them. That is, in the present application, it can be considered that when the gel content of the copolymer is 93%, the content of the first copolymer in the copolymer is 7%.

[0025] In some embodiments, the copolymer includes a first copolymer and a second copolymer, the first copolymer is soluble in toluene at room temperature, and the second copolymer is insoluble in toluene at room temperature. The reason for this is that the second copolymer is a copolymer that is insoluble in toluene at room temperature, and the first copolymer is a copolymer that is soluble in toluene at room temperature, that is, there are two types of copolymers in the copolymer. Generally, the larger the molecular weight of the copolymer, the more difficult it is to dissolve. Therefore, the weight average molecular weight of the second copolymer is greater than that of the first copolymer. In this way, the second copolymer with a larger molecular weight can exhibit better mechanical strength and stability, thereby improving the mechanical strength and stability of the binder, which is beneficial to improving the gel rate of the copolymer in toluene at room temperature. The copolymer with a high gel rate can exhibit longer cycle stability and other properties during the battery cycle process. At the same time, the first copolymer that can be dissolved in toluene at room temperature also exists in the copolymer. The first copolymer has a small molecular weight, so that the binder has better flexibility and adhesion properties, further improving the processing performance and use performance of the binder when applied to the electrode sheet, further improving the peeling strength between the electrode active material layer and the electrode current collector, reducing the rebound of the electrode sheet, and improving the energy density and cycle life of the battery and other properties.

[0026] In the present application, the first copolymer is identified by the following method: a binder copolymer is made into a film, a certain amount of the film is taken as a test sample, weighed by an electronic balance to obtain the initial weight W1 of the sample, the test sample is soaked in toluene, then placed in a room temperature oven for 72 hours (3 days) and taken out, filtered and washed the residue, the residue is placed in a 100°C oven for drying for 24 hours, the weight of the residue is W2, and the filtrate is collected, the organic polymer copolymer in the filtrate is the first copolymer, and the weight of the first copolymer is W1-W2.

[0027] In some embodiments, the weight average molecular weight of the first copolymer is less than or equal to 500000 g / mol, such as less than or equal to 500000 g / mol, less than or equal to 400000 g / mol, less than or equal to 300000 g / mol, less than or equal to 200000 g / mol, less than or equal to 100000 g / mol, less than or equal to 50000 g / mol, less than or equal to 40000 g / mol, or a range composed of any two of them.

[0028] In some embodiments, the glass transition temperature of the binder is -73~0°C, such as -70°C, -60°C, -50°C, -40°C, -30°C, -20°C, -10°C, 0°C, or a range composed of any two of them, which is beneficial to improving the flexibility and adhesion of the binder, and more beneficial to reducing the rebound of the electrode sheet and improving the cycle life of the battery and other properties.

[0029] In some embodiments, the average particle size D 50For 100-500 nm, for example 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm or a range consisting of any two of them, it is advantageous to further improve the adhesion of the binder, reduce the pole piece rebound, improve the energy density and cycle life of the battery and other performances.

[0030] The average particle size D 50 For Dv 50 , which represents the particle size at which the cumulative volume of the particles reaches 50% from the small particle size side in the particle size distribution on a volume basis, can be measured by a conventional method in the art, for example, by using a laser particle size analyzer. Illustratively, the average particle size D 50 For Dv 50 , which represents the particle size at which the cumulative volume of the particles reaches 50% from the small particle size side in the particle size distribution on a volume basis, can be measured by a conventional method in the art, for example, by using a laser particle size analyzer. Illustratively, the average particle size D

[0031] In some embodiments, the aromatic unsaturated hydrocarbon monomer includes one or more of styrene, a-methylstyrene, vinyltoluene, methylvinyl naphthalene, vinyl anthracene, methylvinyl anthracene.

[0032] In some embodiments, the aliphatic conjugated unsaturated hydrocarbon monomer includes one or more of 1,3-butadiene, 1,3-pentadiene, 2-methyl-1,3-butadiene, 1,3-cyclopentadiene, 1,3-hexadiene.

[0033] In some embodiments, the unsaturated carboxylic ester monomer includes an acrylate monomer and / or an alkyl acrylate monomer, which can specifically include a methacrylate monomer.

[0034] In some specific embodiments, the unsaturated carboxylic ester monomer can specifically include a (meth)acrylate monomer, which can include one or more of methyl (meth)acrylate, ethyl (meth)acrylate, isobutyl acrylate, butyl (meth)acrylate, 2-iso octyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, behenyl (meth)acrylate, hexyl lactone acrylate, benzyl acrylate. Specifically, the above (meth)acrylate monomer includes an acrylate monomer and / or a methacrylate monomer, for example, methyl (meth)acrylate includes methyl acrylate and / or methyl methacrylate.

[0035] In some embodiments, the acrylate monomer includes one or more of methyl acrylate, ethyl acrylate, isobutyl acrylate, butyl acrylate, 2-isooctyl acrylate, lauryl acrylate, stearyl acrylate, behenyl acrylate, hexyl lactone acrylate, benzyl acrylate.

[0036] In some embodiments, the methacrylate includes one or more of methyl methacrylate, ethyl methacrylate, isobutyl acrylate, butyl methacrylate, 2-isooctyl methacrylate, lauryl methacrylate, stearyl methacrylate, behenyl methacrylate.

[0037] In some embodiments, the vinyl carboxylic monomer (or vinyl unsaturated carboxylic monomer) includes a vinyl carboxylic monomer and / or an anhydride compound of the vinyl carboxylic monomer.

[0038] Specifically, the vinyl carboxylic monomer includes one or more of acrylic acid, methacrylic acid, fumaric acid, maleic acid, itaconic acid, citraconic acid, sorbic acid, cinnamic acid.

[0039] In some embodiments, the crosslinking agent includes a multifunctional crosslinking agent, which includes a multifunctional crosslinking monomer and / or a polymer of the multifunctional crosslinking monomer.

[0040] Specifically, the multifunctional crosslinking monomer includes one or more of trimethylolpropane triacrylate, 2 (ethoxy) trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, methacryloyloxypropyl trimethoxysilane, vinyl triethoxysilane, vinyl trimethoxysilane, allyl trimethoxysilane, methyl allyl trimethoxysilane, aminopropyl trimethoxysilane.

[0041] In some embodiments, the copolymer further includes a functional structure unit, which includes one or more of a (meth) acrylonitrile structure unit, a vinyl pyrrolidone structure unit, a butenyl nitrile structure unit, a vinyl ether structure unit, which is beneficial to improve the affinity of the binder to the electrode active material, further improve the adhesion of the binder, reduce the electrode sheet rebound, and improve the energy density and cycle performance of the battery.

[0042] Specifically, the functional structure unit is derived from a functional monomer in the copolymer raw material, which includes one or more of a (meth) acrylonitrile monomer, a vinyl pyrrolidone monomer, a butenyl nitrile monomer, a vinyl ether monomer.

[0043] In some embodiments, the mass ratio of the aromatic unsaturated hydrocarbon structural unit, the aliphatic conjugated unsaturated hydrocarbon structural unit, the unsaturated carboxylic ester structural unit, the vinyl carboxylic acid structural unit, the crosslinking structural unit, and the functional structural unit is (0.1-50):(0.1-100):(0.1-100):(0.1-20):(0.1-30):(10-20), which is more conducive to improving the adhesion of the binder, further improving the peeling strength between the electrode active material layer and the electrode current collector, reducing the electrode springback, and improving the energy density and cycle life of the battery.

[0044] Specifically, the mass ratio of the aromatic unsaturated hydrocarbon monomer, the aliphatic conjugated unsaturated hydrocarbon monomer, the unsaturated carboxylic ester monomer, the vinyl carboxylic acid monomer, the crosslinking agent, and the functional monomer in the copolymer raw material is substantially equal to the mass ratio of the aromatic unsaturated hydrocarbon structural unit, the aliphatic conjugated unsaturated hydrocarbon structural unit, the unsaturated carboxylic ester structural unit, the vinyl carboxylic acid structural unit, the crosslinking structural unit, and the functional structural unit.

[0045] Specifically, the mass ratio of the aromatic unsaturated hydrocarbon monomer and the aliphatic conjugated unsaturated hydrocarbon monomer is (0.1:100)-(50:0.1), for example (0.1:100), (1:90), (5:80), (10:70), (20:60), (20:50), (30:30), (40:20), (45:10), (50:0.1), or a range consisting of any two of them.

[0046] Specifically, the mass ratio of the aromatic unsaturated hydrocarbon monomer and the unsaturated carboxylic ester monomer is (0.1:100)-(50:0.1), for example (0.1:100), (1:90), (5:80), (10:70), (20:60), (20:50), (30:30), (40:20), (45:10), (50:0.1), or a range consisting of any two of them.

[0047] Specifically, the mass ratio of the aromatic unsaturated hydrocarbon monomer and the vinyl carboxylic acid monomer is (0.1:20)-(50:0.1), for example (0.1:20), (1:15), (10:10), (20:5), (40:4), (50:0.1), or a range consisting of any two of them.

[0048] Specifically, the mass ratio of the crosslinking agent and the aromatic unsaturated hydrocarbon monomer is (0.1:50)-(30:0.1), for example (0.1:50), (1:40), (10:30), (15:20), (20:10), (25:5), (30:0.1), or a range consisting of any two of them.

[0049] The embodiment of the present application also provides a preparation method of the binder, comprising the following steps: mixing raw materials of the copolymer, and performing a copolymerization reaction under the action of a catalyst to obtain the binder.

[0050] Specifically, the raw materials of the copolymer can be mixed in a solvent, and the solvent comprises water. Specifically, the catalyst (or an auxiliary agent) comprises a persulfide, and the persulfide comprises sodium persulfate and / or potassium persulfate. The mass ratio of the added amount of the catalyst to the total amount of the raw materials of the copolymer is (0.1-3):(20.5-320), for example, can be (0.1:320), (0.5:250), (1:150), (2:75), (3:20.5) or a range formed by any two of them.

[0051] In specific implementation, after the raw materials of the copolymer are mixed, the raw materials are reacted under the action of the catalyst at 50-80°C (denoted as a first temperature) for 5-10h (denoted as a first time) to obtain an intermediate product, and then the temperature is increased to 80-92°C (denoted as a second temperature) for 5-10h (denoted as a second time) to obtain the binder.

[0052] Specifically, the first temperature can be 50°C, 60°C, 70°C, 80°C or a range formed by any two of them, the first time can be 5h, 6h, 7h, 8h, 9h, 10h or a range formed by any two of them, the second temperature can be 80°C, 83°C, 85°C, 88°C, 90°C, 92°C or a range formed by any two of them, and the second time can be 5h, 6h, 7h, 8h, 9h, 10h or a range formed by any two of them.

[0053] It can be understood that the skilled in the art can adjust the polymerization degree of the copolymer obtained by adjusting the content of each component in the raw materials and the catalyst, the temperature and time of the reaction, so as to adjust the gel rate of the copolymer.

[0054] The embodiment of the present application also provides an electrode sheet, comprising an electrode active material layer, the electrode active material layer comprising the binder or the binder prepared according to the preparation method of the binder, and having properties corresponding to the binder.

[0055] Specifically, the electrode sheet comprises an electrode current collector and an electrode active material layer located on at least one side of the electrode current collector, and the electrode active material layer comprises the binder or the binder prepared according to the preparation method of the binder.

[0056] In some embodiments, the binder accounts for 0.3-1.5% of the mass of the electrode active material layer, for example, 0.3%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, or a range consisting of any two of them. Since the binder of the present application has good binding performance, a small amount of addition can achieve good binding effect in practical application, which is conducive to improving the energy density and other electrochemical properties of the battery.

[0057] In some embodiments, the electrode sheet is a negative electrode sheet, and the sheet rebound of the negative electrode sheet is large during the charging and discharging process of the battery, resulting in degradation of the cycle life and other properties of the battery. Adding the above binder to the negative electrode sheet is conducive to reducing the sheet rebound of the negative electrode sheet and improving the cycle life and other properties of the battery.

[0058] Specifically, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located on at least one side of the negative electrode current collector, and the negative electrode active material layer includes the above binder or the binder prepared according to the preparation method of the above binder.

[0059] In specific implementation, the negative electrode current collector includes a copper foil, and the negative electrode active material layer further includes a negative electrode active material, a negative electrode conductive agent, and a thickening agent.

[0060] In the above system, the binder interacts with the negative electrode active material and the negative electrode current collector (or foil), which is conducive to improving the peeling strength between the negative electrode active material layer and the negative electrode current collector (or the peeling force of the negative electrode sheet) and the cohesion of the negative electrode sheet, reducing the sheet rebound, and improving the cycle performance and other electrochemical properties of the battery.

[0061] In some embodiments, the average particle size D 50 of the negative electrode active material is 2-20 μm, for example, 2 μm, 4 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, or a range consisting of any two of them. According to the research of the inventors, in the process of preparing the negative electrode sheet, the components such as the negative electrode active material and the binder need to be dispersed in the negative electrode solvent to configure the negative electrode slurry. An increase in the amount of the binder will increase the viscosity of the negative electrode slurry, which is not conducive to the dispersion of the negative electrode active material, especially the negative electrode active material with a small particle size. The binder in the embodiments of the present application has high binding property, which can reduce the amount of the binder and in turn reduce the viscosity of the negative electrode slurry, which is conducive to the dispersion of the negative electrode active material, improves the peeling strength between the negative electrode active material layer and the negative electrode current collector, reduces the sheet rebound, and improves the cycle life and other properties of the battery.

[0062] In some embodiments, the negative active material includes graphite, which has poor dispersibility in the negative slurry due to its surface tension and other properties. The high adhesion of the binder in the embodiments of the present application can reduce the amount of binder, thereby reducing the viscosity of the negative slurry, facilitating the dispersion of graphite, improving the peeling strength of the negative active material layer and the negative current collector, reducing the rebound of the electrode sheet, and improving the cycle life and other properties of the battery.

[0063] Specifically, the negative conductive agent can include one or more of conductive carbon black, carbon nanotubes (CNT), acetylene black, graphene, ketjen black, and carbon fiber.

[0064] In some embodiments, the thickening agent can include a water-soluble polymer, which includes one or more of carboxymethyl cellulose salt, polyacrylic acid, and modified versions of the foregoing polymers. The carboxymethyl cellulose salt includes lithium carboxymethyl cellulose and / or sodium carboxymethyl cellulose (CMC).

[0065] In the embodiments of the present application, the negative electrode sheet can be prepared by conventional methods in the art, for example, by a coating method. Specifically, the negative active material, conductive agent, thickening agent, binder, and other components used to form the negative active material layer can be dispersed in a negative solvent, for example, water, to prepare a negative slurry, which is then coated on the surface of the negative current collector, and then subjected to drying, rolling, and other processes to prepare the negative electrode sheet. The coating, drying, rolling, and other processes involved in the preparation of the negative electrode sheet by the coating method are conventional operations and are not particularly limited.

[0066] The embodiments of the present application also provide a battery including the electrode sheet described above, which has properties corresponding to the electrode sheet and will not be described here.

[0067] In some embodiments, the battery described above can be a lithium-ion battery.

[0068] Generally, the battery includes a cell, an electrolyte, and a housing that encapsulates the cell. The electrolyte is injected into the cell in the housing. The cell includes a positive electrode sheet, a negative electrode sheet, and a separator between the positive electrode sheet and the negative electrode sheet. The cell can be a laminated cell, i.e., the cell is formed by interleaving and stacking the positive electrode sheet, the separator, and the negative electrode sheet.

[0069] The embodiments of the present application can prepare the battery by conventional methods in the art. For example, the positive electrode sheet, the separator, and the negative electrode sheet can be interleaved and stacked to prepare a laminated cell. Then, the cell is placed in the housing and subjected to conventional processes such as liquid injection (i.e., injection of the electrolyte), encapsulation, standing, formation, and capacity distribution to prepare the battery.

[0070] The positive electrode sheet in the embodiment of the present application can adopt a conventional positive electrode sheet in the art. Generally, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer on at least one side surface of the positive electrode current collector. Specifically, the positive electrode active material layer can be arranged on one side surface of the positive electrode current collector, or the positive electrode active material layer can be arranged on both side surfaces of the positive electrode current collector in the thickness direction.

[0071] Specifically, the positive electrode active material layer can comprise a positive electrode active material, a conductive agent and a positive electrode binder, which can all be conventional materials in the art. For example, the positive electrode active material can comprise one or more of lithium iron phosphate, lithium cobaltate, lithium manganate, a positive electrode ternary material, the positive electrode ternary material can comprise a nickel-cobalt-manganese ternary material and / or a nickel-cobalt-aluminum ternary material, the conductive agent can comprise one or more of conductive carbon black (Super. P), conductive graphite, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, carbon fibers, and the positive electrode binder can comprise one or more of polyvinylidene fluoride (PVDF), polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, an oxirane-containing polymer, polyvinyl pyrrolidone, polyurethane, etc.

[0072] The embodiment of the present application can adopt a conventional positive electrode current collector in the art. For example, the positive electrode current collector comprises an aluminum foil.

[0073] In the embodiment of the present application, the positive electrode sheet can be prepared by a conventional method in the art, for example, by a coating method. Specifically, the positive electrode active material, the positive electrode conductive agent, the positive electrode binder and other components for forming the positive electrode active material layer can be dispersed in a positive electrode solvent, for example, N-methyl pyrrolidone (NMP), to prepare a positive electrode slurry, which is then coated on the surface of the positive electrode current collector, and then subjected to drying, rolling and other processes to prepare the positive electrode sheet. The coating, drying, rolling and other processes involved are conventional operations for preparing the positive electrode sheet by the coating method, and are not particularly limited.

[0074] In the embodiment of the present application, the separator is used to separate the positive electrode sheet and the negative electrode sheet to avoid short circuiting of the positive electrode sheet and the negative electrode sheet. The separator in the embodiment of the present application can adopt a conventional separator in the art, for example, a polypropylene film (PP film) and polyethylene (PE), but is not limited thereto.

[0075] The electrolyte in the embodiment of the present application can be a non-aqueous electrolyte, which generally comprises a lithium salt, a carbonate solvent and an additive. The carbonate solvent can comprise one or more of a cyclic carbonate solvent and a chain carbonate solvent, and specifically comprises one or more of ethylene carbonate (EC), dimethyl carbonate (DMC) and methyl ethyl carbonate (EMC). The lithium salt can comprise one or more of lithium hexafluorophosphate (LiPF6) and lithium perchlorate. The additive can comprise one or more of fluoroethylene carbonate, difluoroethylene carbonate, fluorinated cyclotriphosphazene and hexafluorocyclotriphosphazene.

[0076] In the embodiment of the present application, the battery cell can be packaged with a conventional shell material in the art, such as a soft packaging material (in this case, the battery is a soft packaging battery) including an aluminum plastic film, but is not limited thereto.

[0077] The present application will be further described below through specific embodiments.

[0078] Embodiment 1

[0079] 1. Preparation of the binder

[0080] 2 parts by mass of α-methylstyrene, 40 parts by mass of 1,3-butadiene, 2 parts by mass of itaconic acid, 5 parts by mass of lauryl methacrylate and 2 parts by mass of pentaerythritol triacrylate were mixed in water, 0.5 parts by mass of sodium persulfate was added, heated to 60°C, stirred, reacted for 6 h, then warmed to 80°C for 10 h of curing to obtain the binder.

[0081] 2. Preparation of the negative electrode sheet

[0082] The graphite (D 50 :12 nm), SP, CMC and the binder prepared in step 1 were mixed in a mass ratio of 96:1:1:1.2, deionized water was added, and stirred uniformly to prepare a negative electrode slurry.

[0083] The negative electrode slurry was coated on the positive and negative surfaces of the copper foil, and after drying and rolling, the negative electrode coating was formed on the positive and negative surfaces of the copper foil to obtain the negative electrode sheet.

[0084] 3. Preparation of the positive electrode sheet

[0085] Lithium iron phosphate, SP and PVDF were mixed in a mass ratio of 97.5:1:1.5, N-methylpyrrolidone was added, and stirred uniformly to prepare a positive electrode slurry. Then, the positive electrode slurry was coated on the positive and negative surfaces of the aluminum foil, and after drying and rolling, the positive electrode sheet was obtained.

[0086] 4. Assembly of the battery

[0087] The positive electrode sheet, the separator (PP film) and the negative electrode sheet are alternately stacked to form a laminated cell;

[0088] The laminated cell is placed in an aluminum plastic film, and a liquid injection port is reserved. An electrolyte (EC: EMC: DEC = 5:2:3) is injected into the laminated cell through the liquid injection port, and then the liquid injection port is closed to obtain a battery precursor. After aging, formation and aging treatment, and after processes such as capacity distribution, a soft package battery is prepared.

[0089] Example 2

[0090] The difference from Example 1 is that the mass fraction of α-methylstyrene is 50, the mass fraction of 1,3-butadiene is 100, the mass fraction of itaconic acid is 0.1, and the mass fraction of lauryl methacrylate is 0.1. The remaining steps and conditions are the same as those of Example 1.

[0091] Example 3

[0092] The difference from Example 1 is that the mass fraction of pentaerythritol triacrylate is 1. The remaining steps and conditions are the same as those of Example 1.

[0093] Example 4

[0094] The difference from Example 1 is that it also contains 15 parts of a functional monomer, and the functional monomer is acrylonitrile.

[0095] Examples 5-12

[0096] The difference from Example 1 is that the types and mass fractions of the binder raw monomers are different, as shown in Table 1. The remaining steps and conditions are the same as those of Example 1.

[0097] Comparative Examples 1-5

[0098] The difference from Example 1 is that the types and mass fractions of the binder raw monomers are different, as shown in Table 1. The remaining steps and conditions are the same as those of Example 1.

[0099] The copolymers, binders, negative electrode sheets, and batteries in the examples and comparative examples are tested by the following processes, respectively, and the results are shown in Tables 2 and 3:

[0100] (1) Gel rate test: The adhesive copolymer is made into a film, and a certain amount of the film is taken as a test sample. It is weighed with an electronic balance to obtain the initial weight of the sample W1. The test sample is soaked in toluene and then stored in a room temperature oven for 72 hours (3 days). After that, the test sample is taken out, filtered and the filter residue is washed, and the filtrate is collected. The filter residue is placed in a 100℃ oven and dried for 24 hours to obtain the treated test sample. It is weighed with an electronic balance to obtain the weight of the treated sample W2 (i.e., the second copolymer). The gel rate (i.e., the gel rate of the copolymer in toluene at room temperature) = W2 / W1×100% is used to calculate the gel rate. The above operation is repeated three times, and the average value is taken as the gel rate of the copolymer in toluene at room temperature.

[0101] (2) Particle size test: Laser particle size analyzer (Zhuhai OMEC Instrument Co., Ltd., model: LS-909E) was used to detect the particle size of polymer particles.

[0102] (3) Weight-average molecular weight test of the first copolymer: Detection instrument: Waters e2695-2414; Chromatographic column: Shodex KD-806M; Instrument method: Use organic NMP solution as mobile phase, the mobile phase adopts single-pass mode, and turn off the UV detector for testing; Column temperature: 55 °C; Injection volume: 50 μL; Mobile phase: 0.03 mol / L NMP solution with added LiBr; Elution method: Isocratic elution at a flow rate of 0.7 mL / min for 50 min to obtain the elution curve of the first copolymer. The weight-average molecular weight of the first copolymer is calculated by the calibration curve and is shown in Table 2; The first copolymer is the organic polymer copolymer in the filtrate in the gel fraction test.

[0103] (4) Negative electrode sheet rebound test: The thickness of the negative electrode sheet after rolling is taken as the initial thickness T0, and the battery is charged to 4.35V at 1C constant current and constant voltage, with a cut-off current of 0.05C; discharged to 2.75V at 1C constant current and constant voltage; then charged to 4.35V at 1C constant current and constant voltage, with a cut-off current of 0.05C, at this time, the thickness T1 of the negative electrode sheet in the fully charged state of the battery cell is measured; the rebound of the negative electrode sheet when fully charged is measured = T1 / T0×100%, the results are shown in Table 3.

[0104] (5) Battery energy density (mass energy density) test: Use an electronic balance to accurately measure the mass of the battery cell and record it as m (unit: kg). Charge the battery cell at a constant current of 0.5C to the specified charging cut-off voltage (4.35V) at a constant temperature (25°C). Stop charging. Then discharge it at 0.5C to the cut-off voltage (2.75V). Record the current I0 (A) and discharge time T0 (h) during the discharge process. The capacity C (unit: ampere-hour) of the battery cell is I0×T0; the battery cell E (watt-hour) is C×V a (V aThe average voltage of the discharging process) is calculated; the mass energy density p of the battery is calculated m = E / m (watt-hour / kg), and the results are shown in Table 3.

[0105] (6) The cycle performance (i.e. cycle life) of the battery is tested: the battery cell is discharged at 0.5C to 2.75V, charged to 4.35V, and then discharged to 2.75V after standing, and the first week discharge capacity is recorded as X1. After 500 cycles, the 500th week discharge capacity is recorded as X2, and the cycle performance of the battery is X2 / X1 x 100%, and the results are shown in Table 3.

[0106] (7) The glass transition temperature of the binder is tested: the instrument used is a France Setaram-setline, the binder is kept at 15°C for 30 min, then the temperature program is set to 15°C-180°C, the heating rate is 10°C / min, the N2 flow rate is 40 mL / min, and the heat flow change of the binder during heating is measured. When the specific heat capacity C p The temperature range of the mutation (baseline shift) is the glass transition temperature of the binder, and the results are shown in Table 3.

[0107] (8) The peel strength of the negative electrode sheet (i.e. the peel force of the negative electrode sheet) is tested: the negative electrode sheet prepared above is compacted, and the peel strength of the negative electrode sheet is measured using a tensile testing machine. The test method is referred to GB / T 2792-2014 Test Method for Adhesive Tape Peel Strength, and the peel strength of the negative electrode sheet is shown in Table 3.

[0108] Table 1 Raw materials for preparing the binder

[0109]

[0110] Table 2 Properties of the copolymer and the binder

[0111]

[0112] Table 3 Properties of the negative electrode sheet and the battery

[0113]

[0114] Compared with Comparative Examples 1-5, it can be found that the copolymer raw materials in Example 1-Example 12 include aromatic unsaturated hydrocarbon monomers, aliphatic conjugated unsaturated hydrocarbon monomers, unsaturated carboxylic ester monomers, vinyl carboxylic acid monomers, and crosslinking agents (i.e., the copolymer in the adhesive includes aromatic unsaturated hydrocarbon structural units, aliphatic conjugated unsaturated hydrocarbon structural units, unsaturated carboxylic ester structural units, vinyl carboxylic acid structural units, and crosslinking structural units), and the gel rate of the copolymer in toluene at room temperature is greater than or equal to 93%, the adhesive has high adhesion, which is beneficial to reduce the pole piece rebound, improve the energy density and cycle life of the battery and other performances, and solves the defects in the prior art.

[0115] Compared with other examples, the copolymer in Example 4 further includes functional structural units, which can be beneficial to improve the affinity of the adhesive and the electrode active material, further improve the adhesion of the adhesive, reduce the pole piece rebound, improve the energy density and cycle performance of the battery and other performances.

[0116] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solution deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A binder, characterized in that: The copolymer comprises an aromatic unsaturated hydrocarbon structural unit, an aliphatic conjugated unsaturated hydrocarbon structural unit, an unsaturated carboxylic acid ester structural unit, a vinyl carboxylic acid structural unit, and a cross-linking structural unit; At room temperature, the gel fraction of the copolymer in toluene is greater than or equal to 93%.

2. The adhesive according to claim 1, characterized in that The glass transition temperature of the binder is -73~0°C.

3. The adhesive according to claim 1, characterized in that The average particle size D of the copolymer 50 100-500nm.

4. The adhesive according to claim 1, characterized in that The copolymer includes a first copolymer that is soluble in toluene at room temperature.

5. The adhesive according to claim 4, characterized in that The weight average molecular weight of the first copolymer is less than or equal to 500,000 g / mol.

6. The adhesive according to any one of claims 1 to 5, characterized in that The copolymer further comprises functional structural units, and the functional structural units include one or more of a (meth)acrylonitrile structural unit, a vinyl pyrrolidone structural unit, a butenyl nitrile structural unit, and a vinyl ether structural unit.

7. The adhesive according to claim 6, characterized in that The mass ratio of the aromatic unsaturated hydrocarbon structural unit, the aliphatic conjugated unsaturated hydrocarbon structural unit, the unsaturated carboxylic acid ester structural unit, the vinyl carboxylic acid structural unit, the cross-linking structural unit, and the functional structural unit is (0.1-50): (0.1-100): (0.1-100): (0.1-20): (0.1-30): (10-20).

8. An electrode sheet, characterized in that: The invention comprises an electrode active material layer, wherein the electrode active material layer comprises the binder according to any one of claims 1 to 7.

9. The electrode sheet according to claim 8, characterized in that The mass percentage of the binder in the electrode active material layer is 0.3-1.5%; And / or, the electrode sheet is a negative electrode sheet.

10. A battery, characterized in that: The electrode sheet according to claim 8 or 9 is included.

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