Styrene acrylic emulsion and preparation method therefor, negative electrode sheet, secondary battery, and electrical device

Abstract

The present application relates to a styrene-acrylic emulsion and a method for manufacturing the same, a cathode plate, a secondary battery, and an electric device. Herein, the Dv50 particle size of the latex particles of the styrene-acrylic emulsion is 350 to 900 nm, optionally 350 to 800 nm. The cathode plate comprises a cathode current collector and a cathode active material layer, wherein the cathode active material layer is located on at least one surface of the cathode current collector, and the components of the cathode active material layer include a hard carbon material and an adhesive, wherein the adhesive is derived from the styrene-acrylic emulsion described above.

Description

Technology Field

[0001] The present application belongs to the field of secondary battery technology, and more specifically, relates to a styrene-acrylic emulsion and a method for manufacturing the same, a negative plate, a secondary battery and an electric device. Background Technology

[0002] Secondary batteries are widely used in various consumer electronics and electric vehicles due to their excellent characteristics, such as being lightweight, pollution-free, and free from the memory effect.

[0003] Hard carbon materials can be used as negative electrode active materials in currently used secondary batteries, such as lithium-ion batteries and sodium-ion batteries. Hard carbon materials have the advantages of low energy storage voltage, high capacity, and excellent cycle stability, as well as abundant supply and simple manufacturing processes. As such, they are one of the most promising negative electrode materials and have a large application market in both lithium-ion and sodium-ion batteries. The problem to be solved

[0004] Considering the technical challenges existing in the background technology, the present application aims to provide a negative electrode plate containing a hard carbon material capable of combining excellent adhesion, cohesion, and flexibility, thereby enabling a secondary battery containing the same to have excellent cycle stability. means of solving the problem

[0005] To achieve the above objective, a first aspect of the present application provides a styrene-acrylic emulsion, wherein the Dv50 particle size of the latex particles of the styrene-acrylic emulsion is 350 to 900 nm, and optionally 350 to 800 nm.

[0006] In any embodiment of the present application, the latex particles are a styrene acrylate copolymer, and the glass transition temperature of the styrene acrylate copolymer is 10 to 70°C, optionally 10 to 60°C.

[0007] A second aspect of the present application provides a method for preparing a styrene-acrylic emulsion according to a first aspect of the present application, comprising the following steps:

[0008] A pre-emulsion is prepared by mixing some emulsifiers, some acrylate-based monomers, and some styrene-based monomers with water;

[0010] Some other emulsifier, some other acrylate-based monomers, and some other styrene-based monomers are mixed with water, and then an initiator is added to initiate polymerization to prepare a seed emulsion;

[0011] The above pre-emulsion is added to the above seed emulsion by a dropwise method, and a polymerization reaction is performed by adding an initiator to prepare a styrene-acrylic emulsion having a Dv50 particle size of latex particles of 350 to 900 nm;

[0012] Herein, the total mass of the emulsifier is 0.7% to 5% of the total mass of the manufacturing monomer, optionally 1% to 4.5%; and the manufacturing monomer comprises the step of including an acrylate-based monomer and a styrene-based monomer.

[0013] In any embodiment of the present application, based on the total mass of the monomers produced, the styrene-acrylic emulsion comprises 30% to 80% of a styrene-based monomer, 20% to 70% of an acrylate-based monomer, and 0% to 10% of a functional monomer according to mass percentage content.

[0014] Optionally, the functional monomer is added during the preparation step of the pre-emulsion and / or the seed emulsion.

[0015] Optionally, the functional monomer is at least one of an acrylic acid-based monomer, a phosphate-based monomer, and a fluorine-containing acrylate-based monomer.

[0016] A third aspect of the present application provides a cathode plate, wherein,

[0017] cathode current collector; and

[0018] A negative active material layer is included that is located on at least one surface of the negative current collector. The components of the negative active material layer include a hard carbon material and an adhesive, and the adhesive is derived from a styrene-acrylic emulsion according to the first aspect of the present application.

[0019] In any embodiment of the present application, the components of the negative electrode active material layer further include a conductive agent and a dispersant. Based on the mass percentage content in the negative electrode active material layer, the hard carbon material is 85% to 97%, the styrene acrylate copolymer is 1% to 8%, the conductive agent is 0.3% to 5%, and the dispersant is 0.5% to 4%.

[0020] In any embodiment of the present application, the coating weight of the negative electrode active material layer is 2 to 13 mg / cm² 2 and optionally 5 to 12 mg / cm² 2 am.

[0021] In any embodiment of the present application, the hard carbon material is at least one of irregularly shaped particles, spherical particles, and spherical-like particles, and optionally, the hard carbon material is irregularly shaped particles.

[0022] In any embodiment of the present application, the Dv particle size of the hard carbon material is 1 to 10 μm, and optionally 4 to 9 μm.

[0023] In any embodiment of the present application, the hard carbon material is a particle of irregular shape, and the adhesion force between the negative electrode active material layer and the negative electrode current collector is 10 to 40 N / m; and the cohesion force of the negative electrode active material layer is 150 to 800 N / m.

[0024] In any embodiment of the present application, the hard carbon material is at least one of spherical particles and spherical-like particles, and the adhesion force between the negative electrode active material layer and the negative electrode current collector is 10 to 30 N / m; and the cohesion force of the negative electrode active material layer is 150 to 600 N / m.

[0025] A fourth aspect of the present application provides a secondary battery, which includes a negative plate according to a third aspect of the present application.

[0026] A fifth aspect of the present application provides an electric device, which includes a secondary battery according to a fourth aspect of the present application. Effects of the invention

[0027] In relation to the prior art, the present application includes at least the beneficial effects described below.

[0028] The present application provides a styrene-acrylic emulsion having a Dv50 particle size of 350 to 900 nm and creatively improves the adhesion, cohesion, and flexibility issues of a cathode plate made of a hard carbon material as a cathode active material by using this as an adhesive. The cathode active material layer of the cathode plate according to the present application adopts a hard carbon material as the cathode active material and uses a styrene acrylate copolymer having a Dv50 particle size of latex particles within a specific range as an adhesive for the cathode active material layer. Since the latex particles in the styrene-acrylic emulsion adhesive have a large particle size and excellent dispersion so they do not aggregate, they effectively improve the effective adhesion between the hard carbon material and the cathode current collector and within the hard carbon material, thereby improving the adhesion between the hard carbon material and the cathode current collector and the cohesion between the hard carbon material and the hard carbon material. As such, the aforementioned cathode plate not only improves the adhesion between the cathode active material layer and the cathode current collector and the cohesion of the cathode active material layer, but also exhibits excellent flexibility, thereby maintaining high adhesion and flexibility of the cathode plate even when the coating weight of the cathode active material layer is high. The cathode plate according to the present application is applied to a secondary battery, and since it ensures stable performance of the cathode plate without affecting the energy performance of the battery, the cycle stability of the secondary battery is relatively excellent. Brief explanation of the drawing

[0029] To more clearly explain the technical solution of the present application, the attached drawings used in the present application are briefly described below. Of course, the attached drawings described below are merely partial embodiments of the present application, and a person skilled in the art can obtain other attached drawings without creative effort based on the attached drawings. Figure 1 is a scanning electron microscope image of a cathode plate manufactured in the embodiment of the present application. FIG. 2 is a schematic diagram according to one embodiment of a secondary battery. Figure 3 is an exploded view of Figure 2. FIG. 4 is a schematic diagram according to one embodiment of a battery module. FIG. 5 is a schematic diagram according to one embodiment of a battery pack. Figure 6 is an exploded view of Figure 5. FIG. 7 is a schematic diagram of one embodiment of an electric device in which a secondary battery is used as a power source. Specific details for implementing the invention

[0030] The present application is described in more detail below with reference to specific embodiments. It should be noted that such specific embodiments are used solely for the purpose of explaining the present application and do not limit the scope of the application.

[0031] For the sake of brevity, only specific numerical ranges have been disclosed herein. However, any lower limit may be combined with any upper limit to form an ambiguously described range, and any lower limit may be combined with other lower limits to form an ambiguously described range. Likewise, any upper limit may be combined with any other upper limit to form an ambiguously described range. Furthermore, each individually disclosed point or individual numerical value may be used as an upper or lower limit itself and combined with any other point or individual numerical value, or combined with other lower or upper limits to form an ambiguously described range.

[0032] Note that unless otherwise specified herein, “more than” and “less than” include the corresponding numbers, and that “more than” in “one or more” means two and two or more.

[0033] Unless otherwise specified in this description, the term “or” is used in a comprehensive sense. That is, the phrase “A or B” means “A, B, or both A and B.” More specifically, if A is true (or exists) and B is false (or does not exist), if A is false (or does not exist) and B is true (or exists), or if both A and B are true (or exist), these all satisfy the “A or B” condition. Unless otherwise specified, the terms used in this application have the known meanings generally understood by those skilled in the art. Unless otherwise specified, the value of each parameter mentioned in this application may be measured by various measurement methods commonly used in the art (e.g., may be tested according to the methods presented in the embodiments of this application).

[0034] Hard carbon materials serve as negative electrode active materials for secondary batteries and are characterized by dispersed hard carbon crystals, wide lattice spacing, chemical bonding centers between layers, mechanical rivet connection centers between hard carbon particles, and a large specific surface area. However, these characteristics of the hard carbon particles result in very low adhesion of the hard carbon negative electrode plate. This is particularly pronounced when the coating weight of the negative electrode active material layer is relatively large. Consequently, the negative electrode plate is prone to decarburization during the coating process, leading to problems that prevent the continuation of normal production.

[0035] Currently, some technologies are attempting to improve the adhesion of cathode plates containing hard carbon materials. For example, water-soluble adhesives such as polyacrylamide copolymers with strong adhesive properties are used; however, due to the high hardness and brittleness of the cathode plate, this method causes problems such as cold-press tape breakage and winding cracking, and the degree of adhesion improvement by this method is limited. There is also a technology that significantly increases the capacity of the adhesive to improve the adhesion of the cathode plate, but increasing the capacity of the adhesive may reduce the energy density of the battery. In addition, some conventional adhesives such as styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB) cannot solve the above problems. Therefore, ensuring that cathode plates containing hard carbon materials have better adhesion, cohesion, and flexibility is an urgent problem that needs to be solved.

[0036] [Styrene-Acrylic Emulsion]

[0037] The present application provides a styrene-acrylic emulsion, said styrene-acrylic emulsion being used as an adhesive for a negative electrode active material layer, which can solve the problem of enabling a negative electrode material using a hard carbon material as a negative electrode active material to possess superior adhesion, cohesion, and flexibility.

[0038] The present application provides a styrene-acrylic emulsion, wherein the latex particles of the styrene-acrylic emulsion have a Dv50 particle size of 350 to 900 nm. Herein, the latex particles are a styrene acrylate copolymer.

[0039] Generally, currently, to ensure high stability of styrene-acrylic emulsions and for the purpose of long-term storage, most latex particles in styrene-acrylic emulsions have a Dv50 particle size of 300 nm or less. In addition, the conventional idea for improving the adhesion of cathode plates is to reduce the particle size of emulsion adhesives as much as possible and increase the specific surface area to improve the adhesion of the plates.

[0040] The styrene acrylate copolymer in the styrene-acrylic emulsion provided in this application is spherical, and larger particles, for example, the Dv50 particle size of this application is 350 to 900 nm, exist stably. A styrene acrylate copolymer in which the latex particle size is within a specific Dv50 particle size range is used as an adhesive for the negative electrode active material layer. Since the latex particles in the styrene-acrylic emulsion acting as the adhesive have a large particle size and are well dispersed without aggregation, they effectively improve the effective adhesion between the hard carbon material and the negative electrode current collector, and within the hard carbon material, thereby improving the adhesion between the hard carbon material and the negative electrode current collector and the cohesion between the hard carbon material and the hard carbon material. In this way, the negative electrode plate described above not only improves the adhesion between the negative electrode active material layer and the negative electrode current collector and the cohesion of the negative electrode active material layer, but also has excellent flexibility, so the high adhesion and flexibility of the negative electrode plate can be maintained even when the coating weight of the negative electrode active material layer is high. The negative electrode plate according to the present application is applied to a secondary battery, and since it does not affect the energy performance of the battery while ensuring stable performance of the negative electrode plate, the cycle stability of the secondary battery is relatively excellent.

[0041] The present application further provides a method for manufacturing a styrene-acrylic emulsion, comprising the following steps S11 to S13.

[0042] Step S11 Pre-emulsion process: Some emulsifiers, some acrylate-based monomers, and some styrene-based monomers are mixed with water, and optionally functional monomers are added to prepare a uniformly stable and non-divided pre-emulsion.

[0043] In some embodiments, in step S11, the mixing temperature is 30 to 80°C and the mixing time is 0.5 to 2 hours.

[0044] Step S12 Preparation of seed emulsion: Some other emulsifiers, some other acrylate-based monomers, and some other styrene-based monomers are mixed with water, optionally a functional monomer is added, and then some initiator is added to initiate polymerization to obtain a seed emulsion.

[0045] In some embodiments, in step S12, the mixing temperature is 50 to 90°C and the mixing time is 0.1 to 1 hour, and polymerization is initiated by adding 1 / 4 of an initiator to obtain a seed emulsion.

[0046] Step S13 continuous drop step: The pre-emulsion prepared in Step S11 is added to the seed emulsion prepared in Step S12 by drop, some other initiator is added, and a polymerization reaction is performed to prepare a styrene-acrylic emulsion with a Dv50 particle size of 350 to 900 nm.

[0047] The monomers for manufacturing the above styrene-acrylic emulsion include acrylate-based monomers and styrene-based monomers, and optionally further include functional monomers. As described above, the functional monomer is added during the manufacturing step of the pre-emulsion and / or seed emulsion. That is, the functional monomer may be added during the step of manufacturing the pre-emulsion or seed emulsion, or in both steps, respectively.

[0048] Here, the total mass of the emulsifier is 0.7% to 5% of the total mass of the monomers produced. The Dv50 particle size of the latex particles in the styrene-acrylic emulsion can be controlled primarily by adjusting and controlling the amount of the emulsifier. Furthermore, the mass of the emulsifier is 1% to 4.5% of the total mass of the monomers produced.

[0049] In some embodiments, the pre-emulsion drop is controlled to be completed within 1 to 5 hours.

[0050] In some embodiments, after adding an initiator in step S13, the temperature of the reaction system is controlled to be 50 to 90°C and the holding time is 1 to 4 hours so that the untreated free monomer is further polymerized.

[0051] Furthermore, in step S11, the volume of each raw material excluding the initiator is 3 / 4 to 2 / 3 of the total mass of the corresponding raw material. Correspondingly, in step S12, the volume of each raw material excluding the initiator is 1 / 4 to 1 / 3 of the total mass of the corresponding raw material.

[0052] In step S12, the amount of the initiator is 1 / 4 to 1 / 3 of the total mass of the initiator. In step S13, the amount of the initiator is 3 / 4 to 2 / 3 of the total mass of the initiator.

[0053] Furthermore, the method further includes the step of performing a polymerization reaction by adding another initiator in step S13, cooling, adjusting the pH value of the system to 6 to 9 with a pH adjuster, and filtering to obtain a styrene-acrylic emulsion.

[0054] In some embodiments, the monomers for preparing the styrene-acrylic emulsion comprise, based on mass percentage content, 30% to 80% of a styrene-based monomer, 20% to 70% of an acrylate-based monomer, and 0% to 10% of a functional monomer. The functional monomer is at least one of an acrylic acid-based monomer, a phosphate-based monomer, and a fluorine-containing acrylate-based monomer. The function of the functional monomer is to increase the stability of the styrene-acrylic emulsion and to improve the mechanical properties of an adhesive film formed using the styrene-acrylic emulsion as an adhesive.

[0055] Furthermore, the monomers for manufacturing the styrene-acrylic emulsion comprise 30% to 80% of styrene-based monomers, 19% to 70% of acrylate-based monomers, and 1% to 10% of functional monomers based on mass percentage content.

[0056] Styrene-based monomers include styrene and its derivatives. Furthermore, derivatives of styrene include alkyl-substituted styrenes. In some embodiments, the styrene-based monomer may be selected from styrene and methylstyrene, optionally styrene.

[0057] Acrylate monomers are a general term for esters of acrylic acid and esters of homologues of acrylic acid. In some embodiments, the acrylate monomer may be selected from at least one of C1-C16 alkyl acrylate and C1-C16 alkyl methacrylate. Acrylate-based monomers include, but are not limited to, at least one of methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, hexyl acrylate, hexyl methacrylate, isooctyl acrylate, isooctyl methacrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, hydroxypropyl acrylate, hydroxyethyl acrylate, N,N-dimethylaminoethyl acrylate, N,N-dimethylaminopropyl methacrylate, N,N-dimethylaminopropyl acrylate, N,N-dimethylaminoethyl acrylamide, N,N-dimethylaminopropyl acrylamide, and acrylonitrile.

[0058] Furthermore, the acrylate monomer may optionally be at least one of methyl acrylate, methyl methacrylate, and n-butyl acrylate.

[0059] In some embodiments herein, the functional monomer comprises at least one of an acrylic acid-based monomer, a phosphate-based monomer, and a fluorine-containing acrylate-based monomer.

[0060] Acrylic acid-based monomers include one or more of acrylic acid and its homologues, and include, but are not limited to, one or more of methacrylic acid and acrylic acid.

[0061] Phosphate monomers are ester derivatives of phosphoric acid. Phosphate-based monomers include polyfunctional acidic acrylate phosphate, alkyl acrylate phosphate, ethylene glycol methacrylate phosphate, 2-hydroxyethyl methacrylate phosphate, siloxane phosphate, 2-hydroxyethyl methacrylate phosphate, vinyl alkoxyphosphate (PAM100), methacrylate alkoxyphosphate (PAM200), monofunctional acrylate phosphate (PAM300), hydroxyethyl methacrylate phosphate (PAM4000), alkyl phosphate-based specialty monomer (PAM5000), COPS-3, alkyl (aryl) phosphate, fatty alcohol (alkylphenol) polyoxyethylene ether phosphate, alkyl alcohol amide phosphate, imidazoline-based phosphate, hydroxyethyl phosphate, polymer polyphosphate, and siloxane. It includes at least one of the phosphates, but is not limited thereto.

[0062] Fluorine-containing acrylate monomers are acrylate monomers containing fluorine. Fluorine-containing acrylates include, but are not limited to, perfluoroalkyl (meth)acrylates. Perfluoroalkyl (meth)acrylates include, but are not limited to, one or more of perfluorooctyl ethyl acrylate, perfluorohexyl ethyl acrylate, and perfluoropolyether methacrylate.

[0063] In some embodiments, the functional monomer is methacrylic acid, acrylic acid, perfluorooctyl ethyl acrylate, perfluorohexyl ethyl acrylate, perfluoropolyether methacrylate, polyfunctional acidic acrylate phosphate, alkyl acrylate phosphate, ethylene glycol methacrylate phosphate, 2-hydroxyethyl methacrylate phosphate, alkyl phosphate-based special monomer, siloxane phosphate, phosphate, 2-hydroxyethyl methacrylate phosphate, vinyl alkoxy phosphate (PAM100), methacrylate alkoxy phosphate (PAM200), monofunctional acrylate phosphate (PAM300), hydroxyethyl methacrylate phosphate (PAM4000), alkyl phosphate-based special monomer (PAM5000), COPS-3, It is selected from at least one of alkyl (aryl) phosphate, fatty alcohol (alkylphenol) polyoxyethylene ether phosphate, alkyl alcohol amide phosphate, imidazoline-based phosphate, hydroxyethyl phosphate, polymer polyphosphate, and siloxane phosphate.

[0064] Furthermore, the functional monomer may be selected from at least one of acrylic acid, acrylate phosphate, and perfluorooctyl ethyl acrylate.

[0065] In some embodiments, the emulsifier is selected from one of a reactive emulsifier, an anionic emulsifier, and a nonionic emulsifier.

[0066] Furthermore, the reactive emulsifier comprises one or more of ammonium allyloxynonylphenol polyoxyethylene ether sulfate (KL-100), sodium allyloxyhydroxypropyl sulfonate (COPS-1), 2-acrylamide-2-methylpropanesulfonic acid (AMPS), SR-10, 3-allyloxy-1-hydroxy-propanesulfonate, sodium 2-acrylamide-2-methylpropanesulfonic acid, 3-allyloxy-1-hydroxy-propanephosphate, sodium ethylenesulfonate, fatty alcohol ether sodium ethylenesulfonate, decaperfluorononanoic acid amine, sodium dodecyl diphenyl ether disulfonate (2A1), SR-10, 1-allyloxy-3-(4-nonylphenol)-2-propanol polyoxyethylene (10) ether ammonium sulfate, ER-10, and sodium ethylenesulfonate. The mixture includes, but is not limited to. Additionally, the reactive emulsifier may be selected from at least one of ammonium allyloxynonylphenol polyoxyethylene ether sulfate (KL-100) and sodium allyloxyhydroxypropyl sulfonate (COPS-1).

[0067] Furthermore, the anionic emulsifier comprises, but is not limited to, a mixture of one or more of nonylphenol polyether sulfosuccinate monoester sodium salt (A-103), nonylphenol polyoxyethylene ether ammonium sulfate salt (CO-436), dialkyl sodium sulfate (SLS), sodium dodecyl sulfonate (SDS), sodium dodecyl benzene sulfonate (SDBS), allyl polyoxyethylene ether ammonium sulfate, and sodium stearate. Additionally, the anionic emulsifier may be selected from nonylphenol polyether sulfosuccinate monoester sodium salt (A-103).

[0068] Furthermore, the nonionic emulsifier comprises, but is not limited to, a mixture of one or more of polyoxyethylene sorbitan monolaurate (TW-20), polyoxyethylene sorbitan monooleate (TW-80), polyoxyethylene ether, Span, Tween, allyl polyoxyethylene ether, and vinyl polyoxyethylene ether. Optionally, the nonionic emulsifier may be selected from at least one of polyoxyethylene sorbitan monolaurate (TW-20) and polyoxyethylene sorbitan monooleate (TW-80).

[0069] In some embodiments, the initiator is selected from at least one of potassium persulfate, sodium persulfate, and ammonium persulfate.

[0070] In some embodiments, the pH adjuster is selected from at least one of sodium hydroxide, potassium hydroxide, ammonium hydroxide, N,N-dimethylethanolamine, sodium bicarbonate, and sodium carbonate, and optionally may be sodium hydroxide.

[0071] In some embodiments, the solid content of the manufactured styrene-acrylic emulsion is 35% to 50%, the viscosity at 25°C is 10 to 60 mPa·s, and the pH value is 6 to 9.

[0072] [Rechargeable Battery]

[0073] A secondary battery refers to a battery that can be used continuously by activating the active material through a charging method after discharge.

[0074] Generally, a secondary battery includes a positive plate, a negative plate, a separator, and an electrolyte. During the battery charging and discharging process, active ions move back and forth between the positive and negative plates. The separator is installed between the positive and negative plates and serves to separate them. The electrolyte serves to conduct ions between the positive and negative plates.

[0075] [Cathode]

[0076] In a secondary battery, the negative electrode plate typically comprises a negative current collector and a negative active material layer installed on at least one surface of the negative current collector. The negative active material layer comprises a hard carbon material and an adhesive, wherein the adhesive is derived from a styrene-acrylic emulsion according to the present application. That is, latex particles (styrene acrylate copolymer) in the styrene-acrylic emulsion are used as an adhesive, and the Dv50 particle size of the latex particles is 350 to 900 nm.

[0077] Not limited to any theory, the negative active material layer of the negative electrode plate according to the present application adopts a hard carbon material as the negative active material and uses a styrene acrylate copolymer having a latex particle size Dv50 within a specific range as the adhesive of the negative active material layer. Since the styrene acrylate copolymer acting as the adhesive has a large particle size and excellent dispersion so as not to aggregate, it effectively improves the effective adhesion between the hard carbon material and the negative current collector and within the hard carbon material, thereby improving the adhesion between the hard carbon material and the negative current collector and the cohesion between the hard carbon material and the hard carbon material. In this way, the negative electrode plate described above not only improves the adhesion between the negative active material layer and the negative current collector and the cohesion of the negative active material layer, but also has excellent flexibility, so the high adhesion and flexibility of the negative electrode plate can be maintained even when the coating weight of the negative active material layer is high. The negative electrode plate according to the present application is applied to a secondary battery, and since it does not affect the energy performance of the battery while ensuring stable performance of the negative electrode plate, the cycle stability of the secondary battery is relatively excellent.

[0078] The above-mentioned negative current collector may be a general metal foil or a composite current collector (for example, a composite current collector may be formed by installing a metal material on a polymer substrate). For example, the negative current collector may be a copper foil.

[0079] A cathode active material layer is coated onto a cathode current collector using a cathode slurry and obtained through processes such as drying, cold pressing, and cutting. The cathode slurry comprises a hard carbon material and the styrene-acrylic emulsion of the present application. Here, the hard carbon material is used as the cathode active material, and the styrene-acrylic emulsion is used as an adhesive.

[0080] The above cathode slurry may optionally further include a conductive agent and other optional auxiliary agents. The above cathode slurry is used to form a cathode active material layer on a cathode current collector. It can be understood that the above cathode slurry further includes a solvent.

[0081] In addition, the manufacturing process of the above-mentioned cathode plate is simple and inexpensive.

[0082] Optionally, the Dv50 particle size of the styrene acrylate copolymer in the cathode plate may be 350 nm, 400 nm, 450 nm, 500 nm, 600 nm, 700 nm, 800 nm, and 900 nm. Furthermore, the Dv50 particle size of the styrene acrylate copolymer in the cathode plate is 350 to 800 nm. Within the above additional selection range, the manufactured cathode plate has better flexibility, adhesion, and cohesion, so the manufactured secondary battery has a smaller DCR and better cycle performance. Since a smaller DCR indicates better high-current discharge capability, this means that the secondary battery can possess both excellent cycle stability and high-current discharge capability.

[0083] In some embodiments, the components of the cathode active material layer further include a conductive agent and a dispersant.

[0084] Furthermore, based on the mass percentage content in the cathode active material layer, the hard carbon material is 85% to 97%, the styrene acrylate copolymer is 1% to 8%, the conductive agent is 0.3% to 5%, and the dispersant is 0.5% to 4%. By using this combination of hard carbon material and styrene acrylate copolymer, the adhesion between the cathode active material layer and the cathode current collector and the cohesion of the cathode active material layer can be improved without increasing the capacity of the adhesive styrene acrylate copolymer.

[0085] Furthermore, based on the mass percentage content in the cathode active material layer, the styrene acrylate copolymer is 2% to 5%.

[0086] In some embodiments, the coating weight of the negative electrode active material layer is 2 to 13 mg / cm² 2 , for example, 2 mg / cm² 2 , 5mg / cm 2 , 7mg / cm 2 , 8mg / cm 2 , 10mg / cm 2 , 11mg / cm 2 , 12mg / cm 2 and 13 mg / cm² 2 This combination of hard carbon material and styrene acrylate copolymer can meet the requirements for adhesion and cohesion even when the coating weight of the cathode active material layer is relatively high. Optionally, the coating weight of the cathode active material layer is 5 to 12 mg / cm² 2 am.

[0087] For example, the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0088] For example, the dispersant may be sodium carboxymethyl cellulose CMC-Na. Furthermore, the cathode active material layer may include other optional auxiliary materials, such as PTC thermistor materials.

[0089] In some embodiments, the glass transition temperature Tg of the latex particles (styrene acrylate copolymer) in the styrene-acrylic emulsion used is 10 to 70°C. The glass transition temperature of the styrene acrylate copolymer is related to the monomer ratio of styrene acrylate. Therefore, by controlling the monomer ratio during the preparation of the styrene-acrylic emulsion, the glass transition temperature of the styrene acrylate copolymer can be achieved to be 10 to 70°C.

[0090] The art of the present application has discovered that the glass transition temperature of a styrene acrylate copolymer is correlated with the flexibility of the manufactured negative electrode plate. If the Tg of the styrene acrylate copolymer is too low, the styrene acrylate copolymer dissolves when the electrolyte swelling is relatively large, posing a risk of reduced stability of the negative electrode active material layer in the secondary battery. Furthermore, if the Tg of the styrene acrylate copolymer is relatively high, the negative electrode plate becomes hard and brittle, which can also affect the processing performance of the battery, such as problems like cold pressing tape breakage, winding breakage, and die-cutting powder drop. Therefore, it is preferable to use a styrene acrylate copolymer with a glass transition temperature Tg of 10 to 70°C as an adhesive, and the manufactured negative electrode plate not only has excellent stability but also excellent flexibility, which can fully satisfy processing and manufacturing demands.

[0091] Optionally, the glass transition temperature Tg of the styrene acrylate copolymer used may be 10°C, 12°C, 15°C, 16°C, 17°C, 18°C, 19°C, 20°C, 25°C, 28°C, 30°C, 40°C, 50°C, 60°C, and 70°C. Furthermore, the glass transition temperature Tg of the latex particles (styrene acrylate copolymer) in the styrene-acrylic emulsion used is in the range of 10 to 60°C. Within the above additional selection range, the manufactured negative electrode plate has better flexibility, so the manufactured secondary battery has a smaller DCR and better cycle performance. Since a smaller DCR indicates better high-current discharge capability, this means that the secondary battery can possess both excellent cycle stability and high-current discharge capability.

[0092] In some embodiments, the hard carbon material is at least one of irregularly shaped particles, spherical particles, and spherical-like particles. It should be noted that when the hard carbon material is irregularly shaped particles, such as particles with edges and corners, the hardness and brittleness problems present in conventional adhesives become more pronounced. The styrene-acrylic emulsion provided in this application is particularly applicable to the problem of improving adhesion and cohesion of such types of hard carbon material cathode plates, and the improvement in adhesion and cohesion becomes more evident when the styrene-acrylic emulsion is used as an adhesive.

[0093] Furthermore, through numerous studies by the person skilled in the art of the present application, it has been revealed that in the cathode plate according to the present application, when a styrene-acrylic emulsion having a Dv50 particle size of 350 to 900 nm is adopted as an adhesive, when the hard carbon material is a particle of irregular shape, the adhesion force between the cathode active material layer and the cathode current collector in the manufactured cathode plate is 10 to 40 N / m and the cohesive force of the cathode active material layer is 150 to 800 N / m.

[0094] Furthermore, through numerous studies by the person skilled in the art of the present application, it has been revealed that in the cathode plate according to the present application, when a styrene-acrylic emulsion having a Dv50 particle size of 350 to 900 nm is adopted as an adhesive, and when the hard carbon material is at least one of spherical particles and spherical-like particles, the adhesion force between the cathode active material layer and the cathode current collector in the manufactured cathode plate is 10 to 30 N / m and the cohesive force of the cathode active material layer is 150 to 600 N / m.

[0095] In addition, the Dv50 particle size of the hard carbon material is 1 to 10 μm, and optionally 4 to 9 μm.

[0096] As shown in FIG. 1, a scanning electron microscope (SEM) image of the cathode active material layer on the cathode plate of the specific example (specifically, the cathode plate prepared in Example 2 below) is shown in the specific example illustrated in FIG. 1. As can be seen here, the hard carbon material is a particle with an irregular shape and edges and corners, and its Dv50 particle size is 5 μm. The adhesive, a styrene acrylate copolymer, is introduced into the surface of the hard carbon particles after cold pressing, and the Dv50 particle size of the styrene acrylate copolymer is 450 nm. As can be seen in the figure, the dispersibility of the styrene acrylate copolymer is excellent.

[0097] Unless otherwise specified, all of the above raw materials can be obtained by purchasing them from the market.

[0098] positive plate

[0099] In a secondary battery, the positive plate typically comprises a positive current collector and a positive film layer installed on the positive current collector, and the positive film layer comprises a positive active material.

[0100] The above positive current collector may be a general metal foil or a composite current collector (a composite current collector may be formed by installing a metal material on a polymer substrate). For example, the positive current collector may be an aluminum foil.

[0102] The specific type of the above-mentioned positive electrode active material is not limited, and any active material known in the art that can be used for a secondary battery positive electrode may be used. Those skilled in the art may select according to actual needs.

[0103] For example, the above-mentioned cathode active material may include a lithium ion active material, and the lithium ion active material includes, but is not limited to, one or more of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and modified compounds thereof. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and modified compounds thereof. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, one or more of lithium iron phosphate, composite materials of lithium iron phosphate and carbon, lithium manganese phosphate, composite materials of lithium manganese phosphate and carbon, lithium iron manganese phosphate, composite materials of lithium iron manganese phosphate and carbon, and modified compounds thereof. All of these materials can be obtained through commercial channels.

[0104] The positive electrode active material may include a sodium ion active material, and the sodium ion active material may be a positive electrode active material for a sodium ion battery known to those skilled in the art. For example, the sodium ion active material may be a Prussian blue (PBA) type compound composed of sodium, a transition metal, and a cyanide, such as Na4Fe2(CN)6, Na4Fe(CN)6, Na1.72MnFe2(CN)6, NaMnMn(CN)6, NaNiFe(CN)6, etc. (NaxMA[MB(CN)6]·zH2O(MA and MB are transition metal ions)); NaCrO2, NaMnO2, NaMnO2, NaO. 61 Ti0. 48 Mn0. 52O2, Na[Fe0.5Co0.5]O2, NaMnO2, Na[Ni0. 25 Fe0.5Mn0. 25 It is composed of transition metal oxides, such as ]O2, and the related variable valence transition metals mainly include vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), and copper (Cu), among which manganese and iron, which are relatively abundant resources, are the most commonly used oxide types (NaxMO2(0)). <x≤1, M은 전이 금속 원소)); 및 NaMnFe2(PO4)6, Na2MnP2O7, Na3V2(PO4)3, Na2Fe2(SO4)3, NaFePO4, Na3V2(PO4)2F3, Na4Co3(PO4)2(P2O7)와 같이, 나트륨, 전이 금속 및 음이온으로 구성되고, 그중 전이 금속은 주로 철, 바나듐, 코발트 등이며, 음이온에는 주로 인산염, 피로인산염, 플루오로인산염 및 황산염이 포함되는, 다가 음이온 화합물형(Na x M y [(XO m ) n- ] z It may include at least one of the following materials: (M is a metal ion in a variable valence state, X is an element such as P, S, and V).

[0105] In some embodiments, the modified compound of each of the above materials may have undergone doping modification and / or surface coating modification with respect to the material.

[0106] The above anode film layer may typically further include an adhesive, a conductive agent, and other optional auxiliary agents.

[0107] For example, the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, Super P(SP), graphene, and carbon nanofibers.

[0108] For example, the adhesive may be one or more of styrene butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0109] Separator

[0110] In some embodiments, the secondary battery further includes a separator. The present application does not particularly limit the type of separator, and any known separator of a porous structure with excellent chemical and mechanical stability may be selected.

[0111] In some embodiments, the material of the separator may be selected from at least one of glass fiber, nonwoven fabric, polyethylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multilayer composite film, and there are no particular limitations. If the separator is a multilayer composite film, the material of each layer may be the same or different, and there are no particular limitations.

[0112] electrolyte

[0113] A secondary battery may include an electrolyte, and the electrolyte serves to conduct ions between the positive and negative electrodes. The electrolyte may include an electrolyte salt and a solvent.

[0114] For example, the electrolyte salt may be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), bis lithium trifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0115] For example, the solvent may be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), ethylmethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0116] In some embodiments, the electrolyte further comprises additives. For example, the additives may include a negative electrode forming additive or a positive electrode forming additive, and may also include additives capable of improving specific characteristics of the battery, such as an additive for improving the overcharge performance of the battery, an additive for improving the high-temperature performance of the battery, an additive for improving the low-temperature performance of the battery, etc.

[0117] In some embodiments, the secondary battery of the present application is a lithium-ion secondary battery.

[0118] A secondary battery can be manufactured according to general methods in the industry, for example, by sequentially winding (or stacking) a positive plate, a separator, and a negative plate, and having the separator act as a separator between the positive plate and the negative plate, a battery cell is obtained. A secondary battery is obtained by placing the battery cell into an external package, injecting an electrolyte, and sealing it.

[0119] The embodiments of the present application do not particularly limit the shape of the secondary battery, and it may be cylindrical, prismatic, or any other shape. FIG. 2 illustrates a secondary battery (5) with a prismatic structure as an example.

[0120] In some embodiments, the secondary battery may include an external package. The external package is used to package a positive electrode, a negative electrode, and an electrolyte.

[0121] In some embodiments, referring to FIG. 3, the external package may include a housing (51) and a cover plate (53). Here, the housing (51) may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate surround and form a receiving cavity. The housing (51) has an opening communicating with the receiving cavity, and the cover plate (53) may cover the opening to block the receiving cavity.

[0122] The positive electrode plate, the negative electrode plate, and the separator can form an electrode assembly (52) through a winding process or a lamination process. The electrode assembly (52) is packaged in the receiving cavity. The electrolyte is infiltrated into the electrode assembly (52). The number of electrode assemblies (52) included in the secondary battery (5) may be one or more, and this can be adjusted according to demand.

[0123] In some embodiments, the external package of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The external package of the secondary battery may also be a soft pack, such as a pouch-type soft pack. The material of the soft pack may be a plastic comprising one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0124] In some embodiments, the secondary battery may be assembled into a battery module, and the number of secondary batteries included in the battery module may be multiple, and the specific number may be adjusted according to the application and capacity of the battery module.

[0125] FIG. 4 illustrates a battery module (4) according to one example. In the battery module (4), a plurality of secondary batteries (5) may be arranged sequentially along the length direction of the battery module (4). Of course, they may also be arranged in any other arbitrary way. Additionally, the plurality of secondary batteries (5) may be further secured through a clamping member.

[0126] Optionally, the battery module (4) may further include a housing having a receiving space for accommodating a plurality of secondary batteries (5).

[0127] In some embodiments, the battery module may be assembled into a battery pack, and the number of battery modules included in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0128] FIGS. 5 and 6 illustrate an exemplary battery pack (1). The battery pack (1) may include a battery box and a plurality of battery modules (4) installed in the battery box. The battery box includes an upper box (2) and a lower box (3), and the upper box (2) is installed to cover the lower box (3) to form a sealed space for accommodating the battery modules (4). The plurality of battery modules (4) may be arranged within the battery box in any manner.

[0129] electrical device

[0130] The present application further provides an electric device. The electric device comprises at least one of the secondary battery, battery module, or battery pack. The secondary battery, battery module, or battery pack may be used as a power source for the device or as an energy storage unit for the device. Such devices include, but are not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc.

[0131] The above device can select a secondary battery, a battery module, or a battery pack depending on usage demand.

[0132] FIG. 7 illustrates an exemplary device. The electric device (6) is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the device for a secondary battery, a battery pack or a battery module may be used.

[0133] Other exemplary devices may include mobile phones, tablet PCs, laptops, etc. The above devices should generally be light and thin and be able to use a secondary battery as a power source.

[0134] The beneficial effects of the present application will be explained below with reference to the examples.

[0135] Examples

[0136] To more clearly explain the technical problems, technical solutions, and beneficial effects resolved by the present application, the following description is provided in more detail with reference to the embodiments and the accompanying drawings. Of course, it should be noted that the described embodiments are merely some of the embodiments of the present application and not all of them. The following description of at least one exemplary embodiment is merely illustrative and does not limit the present application and its application in any way. All other embodiments obtained by a person skilled in the art without creative labor based on the embodiments of the present application fall within the scope of protection of the present application.

[0137] All materials used in the embodiments of the present application can be obtained by purchasing them from the market.

[0138] Preparation and Performance Testing of Styrene-Acrylic Emulsion

[0139] Preparation of Styrene-Acrylic Emulsion 1-9

[0140] The monomers for the preparation of styrene-acrylic emulsion 1-9 comprise 30% to 80% of styrene-based monomers, 20% to 70% of acrylate-based monomers, and 0% to 10% of functional monomers based on mass percentage content. In addition to the above-mentioned preparation monomers, the raw materials for the preparation of the styrene-acrylic emulsion further comprise an emulsifier, an initiator, a pH adjuster, and water.

[0141] The initiator is ammonium persulfate, with a mass of 0.5% of the total mass of the monomers produced.

[0142] The emulsifier is ammonium allyloxynonylphenol polyoxyethylene ether sulfate, and its mass is 0.7% to 5% of the total mass of the monomers produced, and the specific content is as shown in Table 1.

[0143] The pH adjuster is sodium hydroxide, and its mass is 0.2% of the total weight of the monomers produced.

[0144] The mass of water is 150% of the total weight of the monomers produced.

[0145] The manufacturing steps are as follows.

[0146] Pre-emulsion process: A uniform, stable, and non-divided pre-emulsion was prepared by stirring 3 / 4 mass of water, an emulsifier, an acrylate-based monomer, a styrene-based monomer, and a functional monomer at 50°C for 1 hour.

[0147] Preparation of seed emulsion: 1 / 4 mass of water, an emulsifier, an acrylate-based monomer, a styrene-based monomer, and a functional monomer were stirred at 50°C for 1 hour, 1 / 4 mass of an initiator was added and polymerization was initiated to obtain a seed emulsion.

[0148] Continuous dropping step: The pre-emulsion was dropped onto the seed emulsion for 2 hours, and the remaining 3 / 4 mass of the initiator was added. After dropping was completed, the reaction was carried out for 30 minutes, the mixture was held at 85°C for 3 hours, and the free monomer that had not been reacted was removed.

[0149] Final processing step: The system was cooled to 40°C, adjusted to 8 to 9 with a pH regulator, and then filtered to discharge the material.

[0150] The difference between styrene-acrylic emulsions 1-9 is the amount of emulsifier. This is as shown in Table 1.

[0151] 2. Performance Test of Styrene-Acrylic Emulsion

[0152] The styrene-acrylic emulsion prepared above was tested for particle size using a Mastersizer 3000 laser particle size analyzer. The specific steps are as follows: During the test, the parameters for transporting the styrene-acrylic emulsion sample are a refractive index of 1.42 and an absorbance of 0.1, and the dispersant is water with a refractive index of 1.33. The sample to be tested did not require further processing; it was uniformly stirred and added directly to the sample pool until the light shielding level reached 5% to 20% to start the measurement, and the results were recorded upon completion of the test. The particle size Dv50 of the latex particles (styrene acrylate copolymer) within the styrene-acrylic emulsion was measured.

[0153] The above-prepared styrene-acrylic emulsion was dried at 80°C for 12 hours to produce an adhesive film, and the glass transition temperature of the styrene acrylate copolymer was tested using differential scanning calorimetry. The instrument used was a NETZSCH DSC200F3.

[0154] The monomers, manufacturing parameters, and performance test results of styrene-acrylic emulsion 1-9 are shown in Table 1.

[0155]

[0156] B. Manufacture of cathode plate and performance testing thereof

[0157] Manufacturing of cathode plates

[0158] Cathode plate 1-9

[0159] A cathode slurry was prepared by mixing 94% by mass of hard carbon material 1 (cathode active material), 1.0% of conductive carbon black (SP), styrene-acrylic emulsion (adhesive, styrene-acrylic emulsion 1-9 prepared by the above manufacturing process, calculated as styrene acrylate copolymer therein, with a mass of styrene acrylate copolymer being 4%), and 1.0% sodium carboxymethyl cellulose, and dissolving them in deionized water. Then, the cathode slurry was coated onto a copper foil 6 μm thick, dried, and cold-pressed to form a cathode active material layer, and then cut into a cathode plate 1-9.

[0160] Here, hard carbon material 1 is an irregularly shaped particle, and the Dv50 particle size is 5 μm.

[0161] Cathode plate 10-11

[0162] The cathode plate 10 is substantially identical to the cathode plate 2, the only difference being that the hard carbon material 1 among them has been replaced with hard carbon material 2 of the same mass, and that hard carbon material 2 is a spherical particle with a Dv50 particle size of 6 μm.

[0163] The cathode plate 11 is substantially identical to the cathode plate 2, the only difference being that the hard carbon material 1 among them has been replaced with hard carbon material 3 of the same mass, and hard carbon material 3 is a spherical-like particle with a Dv50 particle size of 5 μm.

[0164] Cathode plate 12-15

[0165] Cathode 12 is substantially identical to cathode 2, the only difference being that the styrene-acrylic emulsion 2 of cathode 2 has been replaced with a styrene-butadiene emulsion, and the mass content of emulsion balls in the styrene-butadiene emulsion on the cathode is 4%. Here, the Dv50 particle size of the latex particles in the styrene-butadiene rubber emulsion is 120 nm.

[0166] Cathode 13 is substantially identical to cathode 2, the only difference being that the styrene-acrylic emulsion 2 of cathode 2 is replaced with styrene-acrylic emulsion 10 having a Dv50 particle size of 280 nm, and the mass content of the styrene acrylate copolymer in the cathode is 4%.

[0167] The cathode plate 14 is substantially identical to the cathode plate 10, the only difference being that the styrene-acrylic emulsion 2 of the cathode plate 10 is replaced with the styrene-acrylic emulsion 10 having a Dv50 particle size of 280 nm, and the mass content of the styrene acrylate copolymer in the cathode plate is 4%.

[0168] The cathode plate 15 is substantially identical to the cathode plate 11, the only difference being that the styrene-acrylic emulsion 2 of the cathode plate 11 is replaced with the styrene-acrylic emulsion 11 having a Dv50 particle size of 200 nm, and the mass content of the styrene acrylate copolymer in the cathode plate is 4%.

[0169] Cathode plate 16

[0170] The cathode plate 16 is substantially identical to the cathode plate 2, the only difference being that the hard carbon material 1 among them has been replaced with graphite of the same mass and the Dv50 particle size is 13 μm.

[0171] 2. Performance test of the cathode plate

[0172] For the test method of cathode plate flexibility, please refer to the following.

[0173] The flexibility of the cathode plate manufactured above was measured using a winding pin. A sample of the electrode plate with a width of 40 mm × a length of 100 mm was manufactured and wound onto a specially made winding pin. The condition of the electrode plate cracks was observed visually and under a microscope, and the flexibility grade was determined.

[0174] The diameter of the winding pin is R.

[0175] When R≤1.0mm, no cracks occur in the electrode plate, which is a Grade 1 flexibility and met production demand.

[0176] When R=1.0mm, there were cracks, and when R=2.0mm, there were no cracks, which is flexibility grade 2 and met production demand.

[0177] There were cracks when R=2.0mm and cracks when R=3.0mm, which is a flexibility grade 3 and could not meet production demand.

[0178] When R=3.0mm, there were no cracks, and when R=4.0mm, there were cracks, which is a flexibility grade 4 and did not meet production demand.

[0179] Here, the method for manufacturing the winding pin is as follows.

[0180] Generally, 304 stainless steel bars with diameters of 1.0mm, 2.0mm, 3.0mm, and 4.0mm are cut to a length of 60mm, welded to a 150mm × 300mm steel plate, and fixed to manufacture the above-mentioned winding pin.

[0181] The smaller the diameter of the winding pin used and the less the electrode plate cracks, the better the flexibility of the electrode plate; conversely, the larger the diameter of the winding pin and the more the electrode plate cracks, the lower the flexibility of the electrode plate.

[0182] (2) Method for testing the adhesion of the cathode plate:

[0183] The cathode plate to be tested prepared above is measured along a direction perpendicular to the machine direction (TD), and a sample with dimensions of 20 mm (width) × (100-160) mm (length) is cut. A dedicated double-sided adhesive is attached to the steel plate, and the adhesive tape has dimensions of 20 mm (width) × (90-150) mm (length). After attaching the cut electrode plate sample to the double-sided adhesive, it is rolled three times along the same direction using a 2 kg hand roller. The adhesion strength of the electrode plate is tested using a tensioner. Among the hard carbon electrode plates, the greater the adhesion strength between the film layer and the current collector, the stronger the interaction force between the active material and the current collector in the hard carbon electrode plate, and conversely, the weaker the interaction force between the active material and the current collector in the electrode plate.

[0184] (3) Cohesion test method:

[0185] The cathode plate to be tested prepared above is measured along a direction perpendicular to the machine direction (TD), and a sample measuring 20 mm (width) × 100 mm (length) is cut. A dedicated double-sided adhesive is attached to the steel plate, and the size of the double-sided adhesive tape is 20 mm (width) × 100 mm (length). After attaching the cut electrode sample onto the double-sided adhesive, a green adhesive tape is attached onto the electrode plate sample. The size of the green adhesive tape is 20 mm (width) × 120 mm (length). The green adhesive for the non-contact electrode plate portion is attached to a piece of paper measuring 20 mm (width) × 60 mm (length), and the paper and the green adhesive form a straight line. The bonding head portion between the green adhesive and the paper is bonded with crepe adhesive, and for the green tape for the contact electrode plate portion, the electrode plate and the double-sided tape must be uniformly compressed before testing. The cohesion of the electrode plate was tested using a tensioner. The greater the force between active particles in the film layer of the hard carbon electrode, the stronger the interaction between active materials in the hard carbon electrode, and conversely, the weaker the interaction between active materials in the electrode.

[0186] The adhesive tapes used in the adhesion and cohesion tests were all standard adhesive tapes sold on the market.

[0187] C. Battery manufacturing

[0188] Anode plate: Active material LiNi0.8Co0.1Mn0.1O2, conductive carbon black (SP), and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 96.8:2.2:1 and dissolved in N-methylpyrrolidone (NMP). After mixing the slurry, an anode slurry was prepared, coated onto an aluminum foil with a width of 400 mm, dried, cold-pressed, and cut to obtain an anode plate.

[0189] Separator: A polyethylene (PE) porous polymer membrane was used as the separator.

[0190] Cathode plate: The cathode plate 1-16 prepared above was used.

[0191] Electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 3:6:1, and then a sufficiently dried lithium salt (LiPF6) was dissolved in a mixed organic solvent at a ratio of 1 mol / L. The required electrolyte was obtained.

[0192] Overall battery assembly: The positive plate, separator, and negative plate are stacked in sequence, with the separator positioned between the positive and negative electrodes to perform a separating function, and then wound to obtain a bare battery cell. The bare battery cell is placed in an external package aluminum case, the electrolyte prepared above is injected into the high-temperature dried battery, and a lithium-ion secondary battery 1-16 is obtained through processes such as vacuum packaging, settling, formation, and molding. This is as shown in Table 2.

[0193] D. Battery Performance Evaluation

[0194] The performance evaluation of each battery 1-16 was performed according to the following method.

[0195] Measurement of Battery Direct Current Resistance (DCR)

[0196] A battery capacity test was performed at 25℃. Specifically, after performing a formation capacity test on the battery, the battery was left standing at 25℃ for 10 minutes, then charged at 0.33C to 100% SOC (State of Charge), depolarized at low current, left standing for 10 minutes, and discharged at 0.33C to 0% SOC; the obtained capacity was set as the battery's 0.33C capacity. Then, it was charged at a constant voltage of 0.05C, left standing for 60 minutes, discharged at 0.33C to 50% SOC, left standing for 60 minutes, discharged at 0.33C to 20% SOC, left standing for 60 minutes, and discharged at 0.33C to 0% SOC to test the open circuit voltage at 0% SOC, and the DCR data for 30s was compiled.

[0197] 2. Cycle Performance Test:

[0198] A first charge and discharge cycle was performed in a constant temperature environment of 25°C, and constant current and constant voltage charging was performed under a charging current of 1.0C (i.e., a current value that completely discharges the theoretical capacity within 1 hour) until the upper limit voltage reached 4.25V (charging up to a current of 0.05C), and after standing for 5 minutes, constant current discharge was performed under a discharge current of 1.0C until the final voltage reached 2.8V, and the discharge capacity of the first cycle was recorded, and then the charge and discharge cycles were continued.

[0199] Capacity retention rate of the nth cycle = (discharge capacity of the nth cycle / discharge capacity of the first cycle) × 100%, and when the cycle capacity retention rate reaches 80%, the test is stopped and the number of cycles at that time is obtained.

[0200] Some of the raw materials and performance test results of cathode plates 1-16 are shown in Table 2.

[0201]

[0202] In the case of the negative plate 12 of Comparative Example 1, due to the hard and brittle nature of the hard carbon particles themselves, the adhesive strength and cohesive strength of the negative active material layer of the negative plate made using styrene-butadiene rubber (SBR) as an adhesive were both low, the flexibility was reduced, and it was abnormally hard and brittle, resulting in a large DCR of the manufactured battery and poor cycle performance.

[0203] In the cathode plate 13 of Comparative Example 2, the hard carbon material was an irregular particle, and a styrene-acrylic emulsion 10 with a Dv50 particle size of 280 nm was used as an adhesive. Here, the particle size of the styrene acrylate copolymer was small, and the adhesive strength and cohesive strength were 3 N / m and 35 N / m, respectively; compared to the example, the adhesive strength and cohesive strength were still very low, so the cycle performance was poor.

[0204] In the cathode plates 14-15 of Comparative Examples 3 and 4, the hard carbon material was spherical and spherical-like particles, respectively, and styrene-acrylic emulsion 10 with a Dv50 particle size of 280 nm and styrene-acrylic emulsion 11 with a Dv50 particle size of 200 nm, respectively, were used as adhesives. Although the adhesion and cohesion of the manufactured cathode plates were improved compared to Comparative Examples 1-2, they were still at a low level compared to the examples, so the cycle performance was poor.

[0205] The negative active material of the negative plate 16 of Comparative Example 5 was graphite, and at the same time, the adhesive was styrene-acrylic emulsion 2. The adhesion of the manufactured negative plate and the cohesion of the negative active material layer were still lower than those of Example 2, which indicates that the styrene-acrylic emulsion adhesive has a superior improvement effect on the adhesion of the negative plate and the cohesion of the negative active material layer, where the negative active material is hard carbon.

[0206] The Dv50 particle size of the styrene acrylate copolymer in the styrene-acrylic emulsion used in the cathode plates of Examples 1-5 was 350 nm to 900 nm, and all exhibited excellent flexibility, adhesion, and cohesion. Furthermore, compared to Example 5, the cathode plate prepared in Examples 1-4 exhibited excellent flexibility, adhesion, and cohesion, and the manufactured secondary battery had a low DCR and excellent cycle performance. A low DCR indicates excellent high-current discharge performance. Therefore, the Dv50 particle size of the styrene acrylate copolymer is preferably 350 nm to 800 nm.

[0207] The Dv50 particle size of the styrene acrylate copolymer in the styrene-acrylic emulsion used in the cathode plates of Examples 6-9 is 450 nm for all of them, and the main difference is that the copolymer monomer components of the styrene acrylate copolymer differ, resulting in different glass transition temperatures. As can be seen in Examples 6-9, the glass transition temperatures of the styrene acrylate copolymers range from 15 to 70°C, and all exhibit relatively excellent flexibility, adhesion, cohesion, and cycle performance. Furthermore, compared to Example 9, the cathode plate prepared in Example 6-7 has excellent flexibility and cycle performance and a small DCR; therefore, the glass transition temperature of the styrene acrylate copolymer is preferably 15 to 60°C.

[0208] Examples 10-11 are applied to hard carbon materials in which the Dv50 particle size of the styrene acrylate copolymer in the styrene-acrylic emulsion used in the cathode plate is within 350 nm to 900 nm, and likewise spherical particles or spherical-like particles are applied. The adhesion to the cathode plate and the cohesion of the cathode active material layer also show excellent improvement effects.

[0209] The foregoing merely describes specific embodiments of the present application, and the scope of protection of the application is not limited thereto. Anyone skilled in the art can readily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and all such modifications or substitutions fall within the scope of protection of the present application. Accordingly, the scope of protection of the present application is based on the scope of protection of the claims. Explanation of the symbols

[0210] 1: Battery pack 2: Upper box 3: Bottom box 4: Battery Module 5: Secondary battery 51: Housing 52: Electrode assembly 53: Cover plate 6: Electrical device

Claims

Claim 1 A cathode plate comprises: a cathode current collector; and a cathode active material layer located on at least one surface of the cathode current collector; wherein the components of the cathode active material layer include a hard carbon material and an adhesive, the adhesive is derived from a styrene-acrylic emulsion, and the coating weight of the cathode active material layer is 2 to 13 mg / cm² 2 A cathode plate characterized by being. Claim 2 A cathode plate according to claim 1, characterized in that the Dv50 particle size of the latex particles of the styrene-acrylic emulsion is 350 to 900 nm. Claim 3 A cathode plate according to claim 2, wherein the latex particles are styrene acrylate copolymers, and the glass transition temperature of the styrene acrylate copolymer is 10 to 70°C. Claim 4 A cathode plate according to claim 1, wherein the components of the cathode active material layer further include a conductive agent and a dispersant; wherein, based on the mass percentage content in the cathode active material layer, the hard carbon material is 85% to 97%, the styrene acrylate copolymer is 1% to 8%, the conductive agent is 0.3% to 5%, and the dispersant is 0.5% to 4%. Claim 5 In claim 1, the coating weight of the negative electrode active material layer is 5 to 12 mg / cm² 2 A cathode plate characterized by being. Claim 6 A cathode plate according to claim 1, wherein the hard carbon material is at least one of irregularly shaped particles, spherical particles, and spherical-like particles. Claim 7 A cathode plate according to claim 1, characterized in that the Dv50 particle size of the hard carbon material is 1 to 10 μm. Claim 8 A cathode plate according to claim 1, wherein the hard carbon material is a particle of irregular shape, the adhesion force between the cathode active material layer and the cathode current collector is 10 to 40 N / m; and the cohesion force of the cathode active material layer is 150 to 800 N / m. Claim 9 A cathode plate according to claim 1, wherein the hard carbon material is at least one of spherical particles and spherical-like particles, the adhesion force between the cathode active material layer and the cathode current collector is 10 to 30 N / m; and the cohesive force of the cathode active material layer is 150 to 600 N / m. Claim 10 A secondary battery characterized by including a negative plate according to any one of claims 1 to 9. Claim 11 An electric device characterized by including a secondary battery according to claim 10.

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