A binder and a preparation method thereof, a positive electrode sheet, and a battery

Abstract

The application belongs to the technical field of batteries, and discloses a kind of binder and its preparation method, positive plate and battery.The binder includes copolymer, and the copolymer includes 10%~15% acrylic monomer polymerization unit, 40%~60% hard monomer polymerization unit, 15%~25% flexible monomer polymerization unit, 5%~20% polar modified monomer polymerization unit by mass percentage.The neutralization degree of acrylic monomer in acrylic monomer polymerization unit is greater than or equal to 10%.The application improves the adhesion of the binder by designing the composition and preparation method of the binder, and the use of the binder in the battery is beneficial to improve the cycle performance of the battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and particularly relates to a binder, a preparation method thereof, a positive electrode sheet and a battery. BACKGROUND

[0002] In recent years, lithium ion batteries (LIB) are closely related to our life, and have broad application prospects and market values in small portable electronic devices and large energy storage systems such as electric vehicles. Nowadays, lithium ion batteries are developed towards the direction of improving cycle performance, high energy density, high transmission rate, low cost and safety. The binder is one of important component materials of the lithium ion battery electrode sheet, although the amount of the binder used in the electrode sheet is small, the performance of the binder directly affects the capacity, service life and cycle performance of the battery. SUMMARY

[0003] The application aims to solve at least one of the technical problems in the related art. To this end, one object of the application is to provide a binder, a preparation method thereof, a positive electrode sheet and a battery. The binder is beneficial to improve the cycle performance of the battery.

[0004] The first aspect of the application provides a binder, which comprises a copolymer, and the copolymer comprises, in terms of mass percentage: 10% to 15% of acrylic monomer polymerization units, 40% to 60% of hard monomer polymerization units, 15% to 25% of flexible monomer polymerization units, and 5% to 20% of polar modification monomer polymerization units; in the acrylic monomer polymerization units, the neutralization degree of the acrylic monomer is greater than or equal to 10%.

[0005] In the binder provided by the application, the content of the hard monomer polymerization units is reduced and the content of the flexible monomer polymerization units is increased, so as to be beneficial to improve the material processing flexibility and the adhesive film strength. The higher content of the flexible monomer polymerization units can reduce the glass transition temperature of the copolymer, so that the mechanical properties of the copolymer are soft and the processing performance of the electrode sheet is improved. In the processing process, the powder dropping is reduced, and the adhesion is indirectly improved, so as to improve the loading capacity of the negative active material and improve the surface density. The improvement of the flexibility and the peel strength can increase the processing window of the positive electrode sheet, can realize the low binder amount (as an example, the adding amount can be reduced by more than 15% compared with the traditional PVDF) and show better adhesion performance. In the electrochemical performance, the cycle performance of the battery can be effectively improved, and the internal resistance of the battery can be reduced.

[0006] In the present application, by controlling the content of each component to meet the above conditions, it is beneficial to improve the cycle performance of the battery. In particular, controlling the content of the flexible monomer polymerization unit and the hard monomer polymerization unit can better improve the cycle performance of the battery, because if the content of the flexible monomer polymerization unit is too high and the content of the hard monomer polymerization unit is too low, it will cause the film to swell and become larger, which will cause the battery cycle performance to drop in the later stage; if the content of the flexible monomer polymerization unit is too low and the content of the hard monomer polymerization unit is too high, it will cause the pole piece to be too hard to meet the high pressure and density processing.

[0007] In addition, in the present application, by using the acrylic monomer polymerization unit, the hard monomer polymerization unit, the flexible monomer polymerization unit and the polar modified monomer polymerization unit in cooperation with each other, it is beneficial to improve the mechanical strength and processing performance of the material, and it is also helpful for long cycle of the battery.

[0008] In some embodiments, the copolymer includes, in terms of mass percentage content: 10% to 15% of the acrylic monomer polymerization unit, 45% to 55% of the hard monomer polymerization unit, 15% to 25% of the flexible monomer polymerization unit, and 5% to 20% of the polar modified monomer polymerization unit.

[0009] In some embodiments, in the hard monomer polymerization unit, the hard monomer includes one or more of acrylonitrile, styrene, and acrylic ester; and / or, in the flexible monomer polymerization unit, the flexible monomer includes at least one of ethyl (meth)acrylate, lauryl (meth)acrylate, octadecyl (meth)acrylate, C13-C16 (meth)acrylate, butyl (meth)acrylate, isooctyl (meth)acrylate, isobornyl methacrylate, vinyl acetate, alkoxyphenol acrylate, glycidyl (meth)acrylate, butene, diisobutylene, octene, isobutyl acrylate, methyl acrylate, butadiene, and ethylene.

[0010] In some embodiments, the hard monomer includes at least one of acrylonitrile, methacrylonitrile, alpha-chloroacrylonitrile, alpha-ethyl acrylonitrile, styrene, and methyl (meth)acrylate; and / or, the flexible monomer includes at least one of isobutyl acrylate, methyl acrylate, butadiene, ethylene, C13-C16 (meth)acrylate, butyl (meth)acrylate, isooctyl (meth)acrylate, isobornyl methacrylate, alkoxyphenol acrylate, and glycidyl (meth)acrylate.

[0011] In some embodiments, the binder satisfies at least one of the following:

[0012] (a) the acrylic monomer includes at least one of acrylic acid and methacrylic acid;

[0013] (b) the neutralization degree of the acrylic monomer is 10% to 100%;

[0014] (c) in the polar-modified monomer polymerized units, the polar-modified monomer comprises at least one of acrylamide, methacrylamide, N-hydroxymethyl acrylamide, N-hydroxyethyl acrylamide, N-methyl acrylamide, N,N-dimethyl acrylamide, itaconic acid, hydroxyethyl (meth)acrylate, and hydroxypropyl methacrylate.

[0015] The second aspect of the present application provides a method for preparing the binder of the first aspect, comprising:

[0016] The acrylic monomer, the hard monomer, the flexible monomer, the polar-modified monomer, and the solvent are subjected to a precipitation polymerization reaction to prepare a copolymer; the solvent comprises an organic solvent.

[0017] The binder is prepared by solution precipitation polymerization. In the precipitation polymerization reaction, the acrylic monomer, the hard monomer, the flexible monomer, and the polar-modified monomer can be well dissolved in the solvent comprising an organic solvent (the solvent used in the embodiments of the present application can be a combination of an organic solvent and an inorganic solvent (such as water), or can be all organic solvents). The solubility of the copolymer obtained by the reaction in the organic solvent is low and precipitates, so that more flexible monomers can be added in the oily reaction system to improve the processing performance of the product, increase the adhesive force and the areal density, and improve the battery cycle performance. In addition, the conventional aqueous precipitation polymerization for preparing the binder also needs to be subjected to complex post-treatment processes such as filtration, drying, and crushing to obtain the target product, and a large amount of wastewater is generated. The precipitation polymerization used in the embodiments of the present application is beneficial to simplify the post-treatment process, and the powder binder sample can be obtained by drying and crushing, and the process simplification can save the preparation time and reduce the production cost.

[0018] In some embodiments, the organic solvent comprises a cyclic hydrocarbon solvent and an ester solvent.

[0019] In some embodiments, the organic solvent satisfies at least one of the following:

[0020] (A) the cyclic hydrocarbon solvent comprises one or more of cyclohexane, cyclopentane, methylcyclohexane, toluene, and xylene;

[0021] (B) the ester solvent comprises one or more of ethyl acetate, butyl acetate, isopropyl acetate, and ethyl propionate;

[0022] (C) the mass ratio of the cyclic hydrocarbon solvent to the ester solvent is 4:1 to 1:1.

[0023] In some embodiments, the mass of the solvent is 0.5 to 6 times the total mass of all the monomers.

[0024] In some embodiments, the solvent satisfies at least one of the following:

[0025] (I) the ratio of the total mass of all monomers to the mass of the solvent is 1.5:8.5~3:7;

[0026] (II) the solvent further comprises water, the mass content of water is 0~10%, the mass content of organic solvent is 90%~100%, based on the total mass of the solvent.

[0027] In some embodiments, the acrylic monomer, the hard monomer, the flexible monomer and the polar modified monomer and the solvent are subjected to a precipitation polymerization reaction, at least one of the following is met:

[0028] (i) the initiator used comprises at least one of azobisisobutyronitrile, azobisisoheptyl nitrile, benzoyl peroxide and lauroyl peroxide;

[0029] (ii) the amount of the initiator used is 0.1%~2% of the total mass of all monomers;

[0030] (iii) the reaction temperature is 30 ℃~100 ℃;

[0031] (iv) the reaction time is 2 h~24 h;

[0032] (v) the precipitation polymerization reaction is carried out under stirring, the stirring speed is 200 rpm~1000 rpm.

[0033] The third aspect of the present application provides a positive electrode sheet comprising the binder as described in the first aspect of the present application, or, comprising the binder prepared by the method as described in the second aspect of the present application.

[0034] The fourth aspect of the present application provides a battery comprising the positive electrode sheet as described in the third aspect of the present application.

[0035] Additional aspects and advantages of the application will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following description or can be learned by practice of the application. DETAILED DESCRIPTION

[0036] The embodiments of the present application are described in detail below, which are intended to explain the present application and cannot be understood as a limitation of the present application.

[0037] Taking a lithium ion battery as an example, in the lithium ion battery, the binder is an important non-active material, which accounts for a small proportion, but plays an important role. It plays a binding role between the active material, the conductive agent and the current collector, stabilizes the SEI film, and makes them have overall connectivity, thereby reducing the ion transmission resistance of the electrode. Among them, polyvinylidene fluoride (PVDF) is the most commonly used positive electrode binder, and its dosage usually accounts for about 3% of the positive active material. The lithium ion battery prepared based on PVDF can exhibit good cycle performance. However, as the demand for lithium ion batteries continues to grow, the demand for binders also continues to grow, especially for commonly used positive electrode binders such as polyvinylidene fluoride, which is in short supply in the overall market. Therefore, developing a new binder to improve the cycle performance of lithium ion batteries is of great significance and value to the development of lithium ion batteries.

[0038] To this end, the first aspect of the embodiments of the present application proposes a binder, which comprises a copolymer, and the copolymer comprises, in terms of mass percentage: 10% to 15% of acrylic monomer polymerization units, 40% to 60% of hard monomer polymerization units, 15% to 25% of flexible monomer polymerization units, and 5% to 20% of polar modification monomer polymerization units; in the acrylic monomer polymerization units, the neutralization degree of the acrylic monomer is greater than or equal to 10%.

[0039] The binder provided by the embodiments of the present application has a high content of flexible monomer polymerization units and a low content of hard monomer polymerization units, which is beneficial to improving the material processing flexibility and film strength. A high content of flexible monomer polymerization units can reduce the glass transition temperature of the copolymer, enhance the softness of the mechanical properties of the copolymer, and thus improve the processing performance of the pole piece, reduce powder loss during processing, and indirectly improve the adhesion, thereby increasing the loading capacity of the negative active material and improving the surface density. The improvement of flexibility and peel strength can increase the processing window of the positive pole piece, reduce the amount of binder used (as an example, the amount of traditional PVDF can be reduced by more than 15%), and exhibit better bonding performance. In terms of electrochemical performance, the battery cycle performance can be effectively improved, and the battery internal resistance can be reduced.

[0040] In the embodiments of the present application, by controlling the content of each component to meet the above conditions, the cycle performance of the battery can be improved. In particular, controlling the content of the flexible monomer polymerization units and the hard monomer polymerization units can better improve the cycle performance of the battery, because: if the content of the flexible monomer polymerization units is too high and the content of the hard monomer polymerization units is too low, the film will swell and become large, which will cause the battery cycle performance to drop in the later stage; if the content of the flexible monomer polymerization units is too low and the content of the hard monomer polymerization units is too high, the pole piece will be too hard to meet the high pressure processing.

[0041] In addition, in the embodiments of the present application, the acrylic monomer polymerization unit, the hard monomer polymerization unit, the flexible monomer polymerization unit and the polar modified monomer polymerization unit are used in cooperation with each other, which is beneficial to improve the mechanical strength and processing performance of the material, and is also good for long cycle of the battery.

[0042] For example, the content of the acrylic monomer polymerization unit can be 10%, 11%, 12%, 13%, 14%, 15%, etc.; the content of the hard monomer polymerization unit can be 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, etc.

[0043] For example, the content of the hard monomer polymerization unit can be 40%-59%, 40%-58%, 40%-57%, 40%-56%, 40%-55%, 40%-54%, 40%-53%, 40%-52%, 40%-51%, 40%-50%, 40%-49%, 40%-48%, 40%-47%, 40%-46%, 40%-45%, etc., and specifically, it can be 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, etc.

[0044] For example, the content of the flexible monomer polymerization unit can be 15%-25%, 16%-25%, 17%-25%, 18%-25%, 19%-25%, 20%-25%, 21%-25%, 22%-25%, etc., and specifically, it can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, etc.

[0045] For example, the neutralization degree of the acrylic monomer can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, etc.

[0046] In some embodiments of the present application, the copolymer includes, in terms of mass percentage:

[0047] 10%-15% of the acrylic monomer polymerization unit, 45%-55% of the hard monomer polymerization unit, 15%-25% of the flexible monomer polymerization unit, and 5%-20% of the polar modified monomer polymerization unit.

[0048] In the embodiments of the present application, the content of the flexible monomer polymerization unit is high and the content of the hard monomer polymerization unit is low, which is beneficial to improve the processability, adhesion and loading capacity of the negative active material of the pole piece, and in turn better improve the cycle performance of the battery; and due to the improvement of the loading capacity of the negative active material, the battery internal resistance can be reduced.

[0049] In addition, the acrylic monomer polymerization unit can provide ion conductivity to improve the conductivity of the product; the hard monomer polymerization unit is beneficial to improve the cohesion and strength of the pole piece; the flexible monomer polymerization unit plays a toughening role to improve the flexibility of the product; the polar modified monomer polymerization unit is obtained from a monomer with strong polarity, which is beneficial to improve the adhesion and form a hydrogen bond to build a more robust crosslinked network. The synergistic effect between the components improves the mechanical flexibility and processability of the material, and is good for long cycle of the battery.

[0050] In some embodiments of the present application, in the hard monomer polymerization unit, the hard monomer includes one or more of acrylonitrile, styrene, and acrylic ester;

[0051] And / or, in the flexible monomer polymerization unit, the flexible monomer includes at least one of ethyl (meth)acrylate, lauryl (meth)acrylate, octadecyl (meth)acrylate, C13-C16 (meth)acrylate, butyl (meth)acrylate, isooctyl (meth)acrylate, isobornyl methacrylate, vinyl acetate, alkoxyphenol acrylate, glycidyl (meth)acrylate, butene, diisobutylene, octene, isobutyl acrylate, methyl acrylate, butadiene, and ethylene.

[0052] In the embodiments of the present application, the hard monomer polymerization unit is beneficial to improve the cohesion and strength of the pole piece, and the flexible monomer polymerization unit plays a toughening role to improve the flexibility of the product, and the two are used in cooperation, which is beneficial to realize the pole piece to obtain better processability.

[0053] In some embodiments of the present application, the hard monomer includes at least one of acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethyl acrylonitrile, styrene, and methyl (meth)acrylate; and / or, the flexible monomer includes at least one of isobutyl acrylate, methyl acrylate, butadiene, ethylene, C13-C16 (meth)acrylate, butyl (meth)acrylate, isooctyl (meth)acrylate, isobornyl methacrylate, alkoxyphenol acrylate, and glycidyl (meth)acrylate.

[0054] In the embodiments of the present application, by using the flexible monomer polymerization unit and the hard monomer polymerization unit in cooperation and controlling the content of each, it is beneficial to realize the pole piece to obtain better processability, improve the cycle performance of the battery, and reduce the battery internal resistance.

[0055] Further, the hard monomer includes at least one of acrylonitrile, methacrylonitrile, a-chloroacrylonitrile, and methyl (meth)acrylate.

[0056] In some embodiments of the present application, the binder satisfies at least one of the following:

[0057] (a) the acrylic monomer includes at least one of acrylic acid and methacrylic acid;

[0058] (b) the acrylic monomer has a neutralization degree of 10% to 100%;

[0059] (c) in the polar modified monomer polymerization unit, the polar modified monomer includes at least one of acrylamide, methacrylamide, N-methylol acrylamide, N-hydroxyethyl acrylamide, N-methyl acrylamide and N,N-dimethyl acrylamide, itaconic acid, hydroxyethyl (meth)acrylate, and hydroxypropyl methacrylate.

[0060] In the embodiments of the present application, the acrylic monomer including at least one of the above-mentioned acrylic acid and methacrylic acid is beneficial to better improve the conductivity of the binder.

[0061] In the embodiments of the present application, the neutralization degree of the acrylic monomer is 10% to 100%. Through experiments, it is found that by controlling the neutralization degree of the acrylic monomer to satisfy the above condition, it is beneficial to improve the adhesion of the binder, increase the loading capacity of the negative active material, and reduce the battery internal resistance with a lower amount of binder.

[0062] Further, the neutralization degree of the acrylic monomer is 70% to 100%.

[0063] In the embodiments of the present application, the above-mentioned polar modified monomer is beneficial to improve the adhesion of the material and form a hydrogen bond to construct a more robust crosslinking network, thereby improving the adhesion of the binder.

[0064] The second aspect of the embodiments of the present application proposes a method for preparing the above-mentioned binder, which includes:

[0065] The acrylic monomer, the hard monomer, the flexible monomer, the polar modified monomer, and the solvent are subjected to a precipitation polymerization reaction to prepare a copolymer; the solvent includes an organic solvent.

[0066] In the embodiments of the present application, the binder is prepared by solution precipitation polymerization. In the precipitation polymerization reaction, the raw materials such as acrylic monomers, hard monomers, flexible monomers and polar modified monomers can be well dissolved in the solvent containing organic solvents, and the copolymer obtained by the reaction has low solubility in the organic solvent and is precipitated, so that more flexible monomers can be added in the reaction system to improve the processing performance of the product, improve the adhesion and area density, and improve the cycle performance of the battery. In addition, the conventional aqueous phase precipitation polymerization for preparing the binder also needs to go through complex post-treatment processes such as filtration, drying and crushing to obtain the target product, and a large amount of wastewater is generated. The precipitation polymerization reaction used in the embodiments of the present application is beneficial to simplify the post-treatment process, and the powder binder sample can be obtained by drying and crushing, and the process simplification can save the preparation time and reduce the production cost.

[0067] In some embodiments, the organic solvent includes a cyclic hydrocarbon solvent and an ester solvent.

[0068] Through the cooperation of the cyclic hydrocarbon solvent and the ester solvent, the reaction efficiency of the precipitation polymerization reaction is promoted.

[0069] In some embodiments, the organic solvent satisfies at least one of the following:

[0070] (A) The cyclic hydrocarbon solvent includes one or more of cyclohexane, cyclopentane, methylcyclohexane, toluene and xylene;

[0071] (B) The ester solvent includes one or more of ethyl acetate, butyl acetate, isopropyl acetate and ethyl propionate;

[0072] (C) The mass ratio of the cyclic hydrocarbon solvent to the ester solvent is 4:1 to 1:1.

[0073] In the embodiments of the present application, the organic solvent is beneficial to dissolve the raw materials such as acrylic monomers, hard monomers, flexible monomers and polar modified monomers, and the organic solvent can precipitate the copolymer, i.e., the copolymer has low solubility or is insoluble in the organic solvent. In addition, the organic solvent provided in the embodiments of the present application has a low boiling point, which is convenient for drying removal.

[0074] As an example, the mass ratio of the cyclic hydrocarbon solvent to the ester solvent is 4:1, 3:1, 2:1, 1:1, etc.

[0075] In some embodiments, the mass of the solvent is 0.5 to 6 times the total mass of all monomers.

[0076] In the embodiments of the present application, the amount of solvent meets the above conditions, which is beneficial to the normal precipitation polymerization. For example, the amount of solvent is 0.5 times, 0.6 times, 0.7 times, 0.8 times, 0.9 times, 1 times, 1.5 times, 2 times, 2.5 times, 3 times, 3.5 times, 4 times, 4.5 times, 5 times, 5.5 times, 6 times, etc. of the total mass of all monomers.

[0077] In some embodiments, the solvent meets at least one of the following conditions:

[0078] (I) the ratio of the total mass of all monomers to the mass of the solvent is 1.5:8.5~3:7;

[0079] (II) the solvent further comprises water, and the mass content of water is 0~10% and the mass content of organic solvent is 90%~100% based on the total mass of the solvent.

[0080] The ratio of the total mass of all monomers to the mass of the solvent is 1.5:8.5~3:7, wherein the sum of the former and the latter of the ratio of the total mass of all monomers to the mass of the solvent is 10. For example, the ratio of the total mass of all monomers to the mass of the solvent is 1.5:8.5, 1.6:8.4, 1.7:8.3, 1.8:8.2, 1.9:8.1, 2.0:8.0, 2.1:7.9, 2.2:7.8, 2.3:7.7, 2.4:7.6, 2.5:7.5, 2.6:7.4, 2.7:7.3, 2.8:7.2, 2.9:7.1, 3:7, etc.

[0081] For example, the mass content of water is 0~10% and the mass content of organic solvent is 90%~100% based on the total mass of the solvent.

[0082] In the embodiments of the present application, all organic solvents can be used as the solvent. Alternatively, a mixed solvent of organic solvent and water can be used as the solvent. For example, the mass content of water is 1%, 2%, 4%, 6%, 8%, 9%, etc. and the mass content of organic solvent is 99%, 98%, 96%, 94%, 92%, 91%, etc. based on the total mass of the solvent.

[0083] In some embodiments of the present application, at least one of the following conditions is met during the precipitation polymerization of the acrylic monomer, the hard monomer, the flexible monomer, the polar modified monomer and the organic solvent:

[0084] (i) the initiator used comprises at least one of azobisisobutyronitrile, azobisisoheptyl nitrile, benzoyl peroxide and dodecanoyl peroxide;

[0085] (ii) the amount of initiator used is 0.1% to 2% of the total mass of all monomers;

[0086] (iii) the reaction temperature is 30°C to 100°C;

[0087] (iv) the reaction time is 2 h to 24 h;

[0088] (v) the precipitation polymerization is carried out under stirring, and the stirring speed is 200 rpm to 1000 rpm.

[0089] In the embodiments of the present application, the initiator is used to initiate the precipitation polymerization to prepare the binder.

[0090] For example, the amount of initiator is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2% or the like of the total mass of all monomers.

[0091] For example, the reaction temperature is 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C or the like.

[0092] For example, the reaction time is 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, 21 h, 22 h, 23 h, 24 h or the like.

[0093] For example, the precipitation polymerization is carried out under stirring, and the stirring speed is 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm or the like.

[0094] The third aspect of the embodiments of the present application provides a positive electrode sheet, which comprises the binder described above, or comprises the binder prepared by the method described above.

[0095] The positive electrode sheet provided by the embodiments of the present application has the binder described above, and has the beneficial effects of the first aspect and the second aspect of the embodiments of the present application, which will not be described here.

[0096] In some embodiments of the present application, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one side surface of the positive electrode current collector, and the positive electrode active material layer comprises a positive electrode active material.

[0097] In some embodiments of the present application, the positive current collector can include a metal foil or a composite positive current collector. For example, the metal foil can employ an aluminum foil. The composite positive current collector can include a polymer material base layer and a metal layer formed on at least one side surface of the polymer material base layer, for example, the composite positive current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer material base material (such as a polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc. base material).

[0098] As an example, the positive current collector has two surfaces opposite in the thickness direction thereof, and the positive active material layer is disposed on either one or both of the two opposite surfaces of the positive current collector.

[0099] In some embodiments of the present application, the positive active material can employ a positive active material for a battery known in the art.

[0100] As an example, when the battery is a lithium ion battery, the positive active material includes, but is not limited to, a lithium iron phosphate material, a lithium cobaltate material (such as LiCoO2), LiNi x Co y Mn z O2(x+y+z = 1) material, a lithium-rich manganese-based material (xLi2MnO3·(1-x)LiMO2), a lithium nickel manganese cobalt oxide (LiNi 0.5 Mn 1.5 O4) material, etc. Thus, matching the high-voltage positive material with the electrolyte of the battery can significantly improve the energy density of the battery.

[0101] As an example, when the battery is a sodium ion battery, the positive active material includes, but is not limited to, a three-dimensional tunnel type Na 0.44 MnO2, a P2 layered type NaMO2 (M is one, two or three of Ni, Mn, Fe), NaFePO4, Na4Fe3(PO4)2P2O7, Na3V2(PO4)3, Na3V2(PO4)2F3, Na2Fe(CN)6, Na2MnFe(CN)6.

[0102] In some embodiments of the present application, the positive active material layer can also optionally include a conductive agent. As an example, the conductive agent can include at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0103] In some embodiments of the present application, the positive electrode material substance layer can be manufactured by the following manufacturing method. The positive electrode active material, the conductive agent, and the positive electrode binder are dry-mixed to prepare a positive electrode material mixture. Subsequently, the positive electrode material mixture is dispersed in a suitable organic solvent to prepare a positive electrode material mixture slurry, and the prepared positive electrode material mixture slurry is coated on a current collector, which is dried and pressed to prepare a positive electrode active material layer.

[0104] A battery according to a fourth aspect of the present application includes the positive electrode sheet described above.

[0105] In some embodiments of the present application, the battery further includes a negative electrode sheet including a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector, the negative electrode active material layer including a negative electrode active material.

[0106] In some embodiments of the present application, the negative electrode active material can employ a negative electrode active material for a battery known in the art. As an example, the negative electrode active material can include at least one of graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, and lithium titanate, etc. The silicon-based material can include at least one of elemental silicon, a silicon oxide compound, a silicon-carbon composite, a silicon-nitrogen composite, and a silicon alloy. The tin-based material can include at least one of elemental tin, a tin oxide compound, and a tin alloy.

[0107] In some embodiments of the present application, the negative electrode current collector can employ a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material base layer such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.

[0108] In some embodiments of the present application, the negative electrode active material layer can further optionally include a binder. The binder can include at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), sodium carboxymethyl cellulose (CMC), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0109] In some embodiments of the present application, the negative electrode active material layer can further optionally include a conductive agent. The conductive agent can include at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0110] In some embodiments of the present application, the battery further includes a separator film. As the separator film, it is desirable to use a porous film, a nonwoven fabric, or the like that exhibits improved high-rate discharge performance, and they can be used alone or in combination. The resin constituting the separator film can be, for example, a polyolefin-based resin such as polyethylene or polypropylene, a polyester resin such as polyethylene terephthalate or polybutylene terephthalate, polyvinylidene fluoride, a vinylidene fluoride-hexafluoropropylene copolymer, a vinylidene fluoride-perfluoro vinyl ether copolymer, a vinylidene fluoride-tetrafluoroethylene copolymer, a vinylidene fluoride-trifluoroethylene copolymer, a vinylidene fluoride-fluoroethylene copolymer, a vinylidene fluoride-hexafluoroacetone copolymer, a vinylidene fluoride-ethylene copolymer, a vinylidene fluoride-propylene copolymer, a vinylidene fluoride-trifluoropropylene copolymer, a vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, a vinylidene fluoride-ethylene-tetrafluoroethylene copolymer, or the like.

[0111] In some embodiments of the present application, the battery further includes an electrolyte. Further, the electrolyte includes a non-aqueous electrolyte. The non-aqueous electrolyte is not particularly limited as long as it is a non-aqueous electrolyte that can be conventionally used in a lithium-ion rechargeable battery. The non-aqueous electrolyte can include an electrolyte salt in a non-aqueous solvent.

[0112] The present application is described below with reference to specific examples, it should be noted that these examples are merely descriptive and do not limit the present application in any way. The reagents used in the examples are all from Aladdin Bioscience Co., Ltd.

[0113] Example 1

[0114] Dissolve acrylic acid in an organic solvent, add lithium hydroxide dropwise under a refrigerated water circulation for neutralization to obtain an acrylic acid monomer with a neutralization degree of 80%; then add acrylonitrile (AN), flexible monomer isobutyl acrylate, and polar modification monomer methacrylamide. The mass percentage of the composition of each monomer is 15% of the acrylic acid monomer, 40% of the acrylonitrile, 25% of the flexible monomer, and 20% of the polar modification monomer, based on the total mass of the raw materials. Then add a mixed solvent of cyclohexane, ethyl acetate, and water (wherein the mass ratio of cyclohexane to ethyl acetate is 2:1) and rapidly stir (stirring speed: 500 rpm) to fully dissolve each monomer, and introduce nitrogen to remove oxygen for about 1 h; after a certain period of time of nitrogen introduction, start to heat to 50 ℃, add initiator azobisisobutyronitrile (the amount of initiator added is 1% of the total mass of all monomers) to initiate the precipitation polymerization reaction, and the polymerization time is 10 h; after the reaction is completed, dry to obtain a powder binder. The mass ratio of the total mass of all monomers to the mass of the solvent is 2:8; based on the total mass of all solvents, the mass content of water is 5%, and the mass content of organic solvent is 95%.

[0115] Examples 2-25

[0116] Examples 2-25 were prepared using the method of Example 1 with the specific differences shown in Table 1-1 and Table 1-2.

[0117] Comparative Example 1

[0118] Comparative Example 1 was prepared using the method of Example 1 with the specific differences shown in Table 1-2.

[0119] Comparative Example 2

[0120] Comparative Example 2 was prepared using the method of Example 1 with the specific differences shown in Table 1-2.

[0121] Comparative Example 3

[0122] Comparative Example 3 was prepared using the method of Example 1 with the specific differences shown in Table 1-2.

[0123] Comparative Example 4

[0124] Comparative Example 4 was prepared using the method of Example 1 with the specific differences shown in Table 1-2.

[0125] Comparative Example 5

[0126] Comparative Example 5 was prepared using the method of Example 1 with the specific differences shown in Table 1-2.

[0127] Preparation parameters for Examples 1-25 and Comparative Examples 1-5 can be found in Table 1-2.

[0128]

[0129]

[0130] Performance Test

[0131] I. Test Method

[0132] 1. Test of processing performance: the binder was mixed with conductive main material, NMP (N-methyl pyrrolidone) and the like according to a certain proportion, homogenized to a certain viscosity and fineness, then filtered and coated, and the flexibility of the electrode sheet and the processing state of the electrode sheet were observed.

[0133] According to the observation results, the results can be evaluated as "brittle", "relatively brittle" and "OK". Among them, "brittle" means that the processing area density is 40 g / cm 2 or less under the condition of powder falling off and demolding; "relatively brittle" means that the processing area density can reach 42 g / cm 2 ~44 g / cm 2 ,and "OK" means that the processing area density can reach more than 44 g / cm2 , no powder dropping phenomenon, higher flexibility.

[0134] 2. Pole piece peeling force test: after the pole piece is prepared by rolling, the 180° peeling force test is carried out.

[0135] 3. Test of area density:

[0136] Cut a certain area of sample (such as 10 cm 2 ) from the pole piece; use a precision balance to weigh the total mass of the sample (m1); use a solvent (such as NMP) to dissolve and remove the active material and the binder, leaving only the current collector; wash the current collector and dry it to remove residual solvent. Use a precision balance to weigh the mass of the current collector (m2). Calculate the area density:

[0137] Calculate the area density according to the formula: σ = (m1-m2) / A, where:

[0138] m1 is the total mass of the sample (mg), m2 is the mass of the current collector (mg), and A is the area of the sample (cm 2 ).

[0139] 4. Test of cycle performance:

[0140] (1) Battery assembly:

[0141] Positive electrode: NCM811 / contai S85E, binder using the binder obtained in the above examples and comparative examples; negative electrode: graphite / bettery S360-L1, separator: xingyuan separator, electrolyte: ternary electrolyte. The batteries obtained based on examples 1-25 are named B1-B25 in turn; the batteries obtained based on comparative examples 1-5 are named D1-D5 in turn.

[0142] (2) Cycle performance test:

[0143] The method for testing the cycle performance of the battery at room temperature is as follows: using an electrochemical workstation, the battery prepared by using the binder obtained in the above examples and comparative examples is subjected to high-temperature cycle test, the temperature is 25 ℃, 1 C constant current and constant voltage charging, the cutoff current is 0.05C, the charging is stopped for 30 min, 1 C constant current discharging, and the discharging is stopped for 30 min; according to the above steps, the cycle test is carried out until the capacity attenuation is 80% of the initial capacity.

[0144] The method for testing the cycle performance of the battery at high temperature is as follows: using an electrochemical workstation, the battery prepared by using the binder obtained in the above examples and comparative examples is subjected to high-temperature cycle test, the temperature is 45 ℃, 1 C constant current and constant voltage charging, the cutoff current is 0.05C, the charging is stopped for 30 min, 1 C constant current discharging, and the discharging is stopped for 30 min; according to the above steps, the cycle test is carried out until the capacity attenuation is 80% of the initial capacity, and the cycle number is recorded.

[0145] The method of battery DCR test is as follows: the battery prepared from the binder obtained in the above examples and comparative examples is tested, and the surface temperature of the battery is ensured to reach 25±2 ℃; 1 C constant current discharge to 2.5 V, 1 C constant current discharge to 2.5 V; then 1 C constant current constant voltage charging to 3.65 V, the current is cut off to 0.05 C, the battery is left for 30 min and the surface temperature of the battery reaches 25±2 ℃; 1 C constant current discharge to 2.5 V, the discharge capacity is recorded as C0, 1 C constant current discharge to 2.5 V; 1 C constant current constant voltage charging to 3.65 V, and the battery is left for 30 min; 1 C constant current discharge for 30 min, the battery is left for 30 min, and the terminal voltage is recorded as U1; 1 C constant current discharge for 10 s, and the terminal voltage is recorded as U2. The above results can be obtained by the DCR calculation formula.

[0146] The calculation formula of DCR is: DCR=(U1-U2) / A; wherein, A represents the discharge current, i.e. 1 C current.

[0147] II. Test results

[0148] The performance test results of examples 1-25 and comparative examples 1-5 are shown in table 2.

[0149] Table 2

[0150]

[0151] As can be seen from table 2, compared with comparative examples 1-5, the binder prepared by deposition polymerization reaction in examples 1-25, by optimizing the composition and amount of hard monomer and flexible monomer, and combining with polar modified monomer (which is beneficial to improve the high temperature aging resistance of the battery), can effectively improve the cycle performance of the battery and reduce the impedance of the battery.

[0152] In addition, by optimizing the preparation parameters of the deposition polymerization reaction, as shown in examples 20-25, by optimizing the composition and amount of the solvent, it is beneficial to better improve the cycle performance of the battery and reduce the impedance of the battery. In the organic solvent, the ratio of cyclohexane to ethyl acetate is increased, which is more beneficial to improve the solubility of the monomer, improve the efficiency of the deposition polymerization reaction, obtain a better binder, and thus improve the comprehensive performance of the battery.

[0153] In the description of the specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are contained in at least one embodiment or example of the present application. In the specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any suitable manner in any one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples without contradiction.

[0154] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and the person skilled in the art can make changes, modifications, replacements and variations to the above-described embodiments within the scope of the present application.

Claims

1. An adhesive, characterized in that, The adhesive comprises a copolymer, which, by weight percentage, includes: The polymer comprises 10%–15% acrylic monomer polymerization units, 40%–60% hard monomer polymerization units, 15%–25% flexible monomer polymerization units, and 5%–20% polar modified monomer polymerization units; wherein the degree of neutralization of the acrylic monomers in the acrylic monomer polymerization units is greater than or equal to 10%. The adhesive is prepared by precipitation polymerization, wherein the solvent used in the precipitation polymerization reaction includes an organic solvent and water. Based on the total mass of the solvent, the mass content of water is 0-10% and the mass content of the organic solvent is 90%-100%. In the polar modified monomer polymerization unit, the polar modified monomer includes at least one of acrylamide, methacrylamide, N-hydroxymethylacrylamide, N-hydroxyethylacrylamide, N-methylacrylamide and N,N-dimethylacrylamide, itaconic acid, hydroxyethyl methacrylate, and hydroxypropyl methacrylate. In the flexible monomer polymerization unit, the flexible monomer includes at least one of isobutyl acrylate, C16 acrylate (meth)acrylate, C18 acrylate (meth)acrylate, butadiene, butyl acrylate, and dodecyl acrylate.

2. The adhesive according to claim 1, characterized in that, The copolymer comprises, by weight percentage: 10%~15% acrylic monomer polymerization units, 45%~55% hard monomer polymerization units, 15%~25% flexible monomer polymerization units, and 5%~20% polar modified monomer polymerization units.

3. The adhesive according to claim 1 or 2, characterized in that, In the hard monomer polymerization unit, the hard monomer includes one or more of acrylonitrile, styrene, and acrylate.

4. The adhesive according to claim 3, characterized in that, The hard monomer includes at least one of acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, styrene, and methyl methacrylate.

5. The adhesive according to claim 1 or 2, characterized in that, The adhesive satisfies at least one of the following: (a) Acrylic monomers include at least one of acrylic acid and methacrylic acid; (b) The degree of neutralization of acrylic monomers is 10% to 100%.

6. A method for preparing the adhesive according to any one of claims 1-5, characterized in that, include: A copolymer is prepared by precipitation polymerization of acrylic monomers, hard monomers, flexible monomers and polar modified monomers with a solvent; the solvent includes an organic solvent.

7. The method according to claim 6, characterized in that, The organic solvents include cyclic hydrocarbon solvents and ester solvents.

8. The method according to claim 7, characterized in that, The organic solvent satisfies at least one of the following: (A) The cyclic hydrocarbon solvents include one or more of cyclohexane, cyclopentane, methylcyclohexane, toluene, and xylene; (B) The ester solvents include one or more of ethyl acetate, butyl acetate, isopropyl acetate, and ethyl propionate; (C) The mass ratio of the cyclic hydrocarbon solvent to the ester solvent is 4:1 to 1:

1.

9. The method according to any one of claims 6-8, characterized in that, The mass of the solvent is 0.5 to 6 times the total mass of all monomers.

10. The method according to claim 9, characterized in that, The ratio of the total mass of all monomers to the mass of the solvent is 1.5:8.5 to 3:

7.

11. The method according to claim 6, characterized in that, In the precipitation polymerization reaction of acrylic monomers, hard monomers, flexible monomers, and polar modified monomers with solvents, at least one of the following conditions must be met: (i) The initiator used includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide and dodecyl peroxide; (ii) The amount of initiator used is 0.1% to 2% of the total mass of all monomers; (iii) The reaction temperature is 30 ℃~100 ℃; (iv) The reaction time is 2 h to 24 h; (v) The precipitation polymerization reaction was carried out under stirring conditions, with a stirring speed of 200 rpm to 1000 rpm.

12. A positive electrode plate, characterized in that, Includes the adhesive according to any one of claims 1-5, or includes the adhesive prepared by the method according to any one of claims 6-11.

13. A battery, characterized in that, Includes the positive electrode sheet as described in claim 12.

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