Negative electrode binder, electrode plate and battery

Abstract

The invention provides a negative electrode binder, an electrode plate and a battery, the negative electrode binder comprises an inner core and a shell layer directly or indirectly grafted on the surface of the inner core, the inner core comprises a polymer containing an aromatic vinyl structure unit and a conjugated diene structure unit, the shell layer comprises a polymer chain segment containing a polar group, and the polymer chain segment is a polymer chain segment containing an aromatic vinyl structure unit and a conjugated diene structure unit. The polymeric chain segment containing the polar group is directly or indirectly grafted on the inner core. The binding property, swelling resistance and flexibility of the negative electrode binder can be improved, so that the cycle performance of the battery is improved, and the service life of the battery is prolonged.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a negative electrode binder, electrode sheet, and battery. Background Technology

[0002] Binders are important polymeric auxiliary materials in batteries, primarily functioning to adhere active materials and conductive agents together. They significantly influence battery characteristics such as rate performance, high and low temperature adaptability, and cycle life. Developing high-performance binders that meet the demands of rapid battery development has become a current research hotspot.

[0003] In related technologies, the mainstream adhesives mainly include styrene-butadiene rubber (SBR) and polyacrylic acid (PAA) adhesives. However, PAA adhesives are relatively hard and brittle with poor flexibility. When applied to electrode sheets, they can easily cause stress integration during the electrode sheet preparation process, leading to defects such as electrode sheet cracking. SBR adhesives have good affinity with electrolytes and are prone to swelling, resulting in poor anti-swelling ability. At the same time, due to the relatively small number of polar functional groups contained in SBR adhesives, the interaction force between SBR adhesives and materials such as electrode current collectors and electrode active materials in the electrode sheet is poor, resulting in poor adhesion. Summary of the Invention

[0004] This invention provides a negative electrode binder, electrode sheet, and battery to at least solve the problems of low adhesion, poor flexibility, high swelling degree, and poor cycle performance and service life of the battery caused by the binder in the prior art.

[0005] The present invention provides a negative electrode binder comprising a core and a shell layer directly or indirectly grafted onto the surface of the core. The core comprises a polymer containing aromatic vinyl structural units and conjugated diene structural units, and the shell layer comprises polymeric segments containing polar groups, which are directly or indirectly grafted onto the core.

[0006] The negative electrode binder as described above, wherein the polar group includes one or more of organic acid groups, amide groups, and cyano groups.

[0007] The negative electrode binder as described above, wherein the core further includes a dielectric layer coated on the surface of the polymer, the dielectric layer comprising styrene-based structural units, cross-linked structural units, and photoinitiating structural units; the polymeric segments containing polar groups are grafted onto the dielectric layer.

[0008] In the negative electrode binder described above, the mass ratio of the styrene-based structural unit, the photoinitiating structural unit, and the crosslinking structural unit in the dielectric layer is (5~80):(1.5~40):1.

[0009] The negative electrode binder as described above, wherein the mass ratio of the dielectric layer to the polymer is (0.05~0.1):1; and / or, the mass ratio of the polymer to the total mass of the dielectric layer and the shell layer is (0.5~1):1.

[0010] The negative electrode binder as described above, wherein the swelling degree of the negative electrode binder is 15% to 35%.

[0011] The negative electrode binder as described above, wherein the core has a D50 of 70nm~200nm.

[0012] The negative electrode binder as described above, wherein the D50 of the negative electrode binder is 120nm~335nm.

[0013] The present invention also provides an electrode sheet comprising the above-described negative electrode binder.

[0014] The present invention also provides a battery comprising the electrode sheets described above.

[0015] This invention provides a negative electrode binder, an electrode sheet, and a battery. The negative electrode binder includes a core and a shell layer directly or indirectly grafted onto the surface of the core. The core comprises a polymer containing aromatic vinyl structural units and conjugated diene structural units. The shell layer comprises polymeric segments containing polar groups, which are directly or indirectly grafted onto the core. In this binder composition system, the polymer containing aromatic vinyl structural units and conjugated diene structural units serves as the core, improving the flexibility of the negative electrode binder. Simultaneously, the introduction of polymeric segments containing polar groups into the shell layer effectively enhances the swelling resistance (anti-swelling capacity) and adhesion of the negative electrode binder. This achieves a balance between improving the adhesion, swelling resistance, and flexibility of the negative electrode binder, thereby enhancing the cycle performance and lifespan of the battery. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of the negative electrode binder in some embodiments of the present invention;

[0017] Figure 2 This is a schematic diagram of the structure of the negative electrode binder in some embodiments of the present invention.

[0018] Explanation of reference numerals in the attached figures:

[0019] 1-Kernel; 2-Shell; 3-Media layer. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0021] In related technologies, the mainstream binders include styrene-butadiene rubber (SBR) and polyacrylic acid (PAA) binders. However, PAA binders are relatively hard and brittle with poor flexibility. When applied to electrode sheets, they can easily cause stress integration during the electrode sheet preparation process, leading to defects such as electrode sheet cracking. SBR binders have good affinity with the electrolyte and are prone to swelling, resulting in poor anti-swelling ability. At the same time, due to the relatively small number of polar functional groups in SBR binders, the interaction force between SBR binders and materials such as electrode current collectors and electrode active materials in the electrode sheet is poor, resulting in poor adhesion and thus poor battery cycle performance and lifespan.

[0022] Specifically, according to the inventors' research, PAA is a high molecular weight linear polymer copolymerized from polar monomers such as acrylic acid and acrylonitrile. The copolymers exhibit strong intermolecular forces and a high glass transition temperature. PAA contains polar functional groups such as carboxyl, cyano, and acrylamide groups. These polar functional groups can form strong hydrogen bonds and other interactions between the current collector and the active material, resulting in a relatively strong bond. Simultaneously, under the influence of an electric field, the polar functional groups in PAA can form strong complexing and decomplexing interactions with active ions, promoting the conduction of active ions and reducing the internal resistance of the battery. PAA typically exhibits high peel strength, low rebound, and good cycle life. However, PAA materials are generally quite hard and brittle, with poor flexibility. When applied to electrode sheets, stress concentration can easily occur during the electrode sheet preparation process (e.g., the baking process after coating the electrode slurry onto the electrode current collector), leading to defects such as cracking in the electrode sheet. SBR is mainly prepared by emulsion polymerization of butadiene and styrene. SBR has a good affinity with electrolyte and is prone to swelling in electrolyte. Its anti-swelling ability is poor. At the same time, the number of polar functional groups such as carboxyl, cyano and acrylamide in SBR is limited, which restricts the establishment of strong interaction between SBR and electrode active material and electrode current collector, resulting in poor adhesion.

[0023] According to the inventor's further research, based on the advantages and disadvantages of SBR and PAA adhesives, in order to make up for the shortcomings of a single type of adhesive, even if SBR and PAA adhesives are compounded, that is, the two types of adhesives are physically mixed and then used, it is still difficult to improve the flexibility, adhesion (peel strength) and anti-swelling ability of the adhesive by relying solely on factors such as intermolecular forces.

[0024] In view of this, embodiments of the present invention provide a negative electrode binder, such as... Figure 1 As shown, it includes a core 1 and a shell 2 directly or indirectly grafted onto the surface of the core 1. The core 1 includes a polymer containing aromatic vinyl structural units and conjugated diene structural units, and the shell 2 includes polymeric segments containing polar groups, which are directly or indirectly grafted onto the core 1.

[0025] In the aforementioned composition system of the negative electrode binder, the binder exhibits high peel strength, excellent flexibility, and anti-swelling ability, thereby improving the cycle performance and lifespan of the battery. The reason for this is that the core, comprising polymers containing aromatic vinyl structural units and conjugated diene structural units, improves the flexibility of the negative electrode binder. Simultaneously, the introduction of polymeric segments containing polar groups into the shell effectively enhances the anti-swelling ability and adhesion of the negative electrode binder, thus simultaneously improving these properties. Furthermore, the direct or indirect grafting of polar groups onto the core improves the structural stability of the negative electrode binder, further contributing to improved cycle performance and lifespan. Therefore, the polymeric segments containing polar groups in the core and shell work synergistically to improve the flexibility, adhesion, and anti-swelling ability of the negative electrode binder, thereby enhancing the cycle performance and lifespan of the battery.

[0026] In some embodiments, polymers containing aromatic vinyl structural units and conjugated diene structural units include styrene-butadiene rubber, which is beneficial for further improving the flexibility of the negative electrode binder.

[0027] In embodiments of the present invention, such as Figure 1 and Figure 2 As shown, the negative electrode binder has a spherical brush structure. In the shell layer 2, polymeric segments containing polar groups are directly or indirectly grafted onto the core layer 1 to form a brush layer structure. Specifically, the brush layer structure contains multiple branch structures, with each polymeric segment forming a branch structure, thus constituting a spherical brush structure.

[0028] In some embodiments, the polar groups include one or more of organic acid groups, amide groups, and cyano groups, which is beneficial for improving the flexibility of the binder while further enhancing the adhesion and anti-swelling properties of the negative electrode binder.

[0029] In some embodiments, the organic acid groups include carboxyl and / or sulfonic acid groups, which are beneficial for improving the flexibility of the binder while further enhancing the adhesion and anti-swelling properties of the negative electrode binder.

[0030] In this embodiment of the invention, the polymeric segment containing a polar group is polymerized from a first monomer containing a polar group. The first monomer may include a monomer containing one or more polar groups selected from organic acid groups, amide groups, and cyano groups, such as a monomer containing an organic acid group (organic acid monomer), a monomer containing an amide group, or a monomer containing a cyano group.

[0031] Specifically, the first monomer contains unsaturated bonds, which may include double bonds. The first monomer polymerizes through these unsaturated bonds to form the aforementioned polymeric chain segment.

[0032] In some embodiments, the first monomer may specifically include an organic acid monomer containing an unsaturated bond, an amide monomer containing an unsaturated bond, or a cyano monomer containing an unsaturated bond, wherein the unsaturated bond may include a double bond, that is, the first monomer includes an organic acid monomer containing a double bond, an amide monomer containing a double bond, or a cyano monomer containing a double bond.

[0033] In this embodiment of the invention, the organic acid monomer containing unsaturated bonds may include one or more of acrylic acid, methacrylic acid, styrene sulfonic acid, and 2-acrylamido-2-methylpropanesulfonic acid, which is beneficial to improve the flexibility of the binder while further enhancing the adhesion and anti-swelling ability of the negative electrode binder.

[0034] In this embodiment of the invention, the amide monomer containing unsaturated bonds may include one or more of acrylamide, methacrylamide, N-hydroxymethylacrylamide, and N-isopropylacrylamide, which is beneficial for improving the flexibility of the binder while further enhancing the adhesion and anti-swelling properties of the negative electrode binder.

[0035] In this embodiment of the invention, the cyano monomer containing unsaturated bonds may include acrylonitrile and / or methacrylonitrile, which is beneficial to improve the flexibility of the binder while further enhancing the adhesion and anti-swelling properties of the negative electrode binder.

[0036] In this embodiment of the invention, the polymeric segment containing polar groups has a structural unit formed by polymerizing a first monomer (including an organic acid monomer containing unsaturated bonds), which serves as a repeating unit of the polymeric segment. Specifically, when the first monomer includes acrylic acid, the polymeric segment contains a polyacrylic acid structural unit; when the first monomer includes methacrylic acid, the polymeric segment contains a polymethacrylic acid structural unit; when the first monomer includes styrene sulfonic acid, the polymeric segment contains a polystyrene sulfonic acid structural unit; and when the first monomer includes 2-acrylamido-2-methylpropanesulfonic acid, the polymeric segment contains a poly(2-acrylamido-2-methylpropanesulfonic acid) structural unit.

[0037] When the first monomer includes acrylic acid and methacrylic acid, the polymerization segment includes an acrylic acid-methacrylic acid copolymer segment; when the first monomer includes acrylic acid and styrene sulfonic acid, the polymerization segment includes an acrylic acid-styrene sulfonic acid copolymer segment; when the first monomer includes acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid, the polymerization segment includes an acrylic acid-2-acrylamido-2-methylpropanesulfonic acid copolymer segment; when the first monomer includes methacrylic acid and styrene sulfonic acid, the polymerization segment includes a methacrylic acid-2-acrylamido-2-methylpropanesulfonic acid copolymer segment; when the first monomer includes styrene sulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid, the polymerization segment includes a styrene sulfonic acid-2-acrylamido-2-methylpropanesulfonic acid copolymer segment.

[0038] In embodiments of the present invention, such as Figure 2 As shown, the core 1 also includes a dielectric layer 3 coating the polymer surface. The dielectric layer 3 comprises styrene-based structural units, cross-linked structural units, and photoinitiating structural units. Polymer segments containing polar groups are grafted onto the dielectric layer 3. Specifically, when the styrene-based monomer includes styrene, the cross-linked monomer includes divinylbenzene, and the photoinitiating functional monomer includes 4-acryloyloxybenzophenone, the dielectric layer 3 comprises a polymer formed by polymerizing styrene in the presence of divinylbenzene and 4-acryloyloxybenzophenone. Polymer segments containing polar groups are grafted onto the core 1 through the dielectric layer 3, thereby forming a shell layer 2 on the surface of the core 1.

[0039] In this embodiment of the invention, the styrene-based structural unit includes a styrene structural unit.

[0040] In this embodiment of the invention, the crosslinking structural unit includes one or more of the following: divinylbenzene structural unit, allyl methacrylate structural unit, diallyl phthalate structural unit, pentaerythritol triallyl ether structural unit, ethylene glycol dimethacrylate structural unit, and N,N-methylenebisacrylamide structural unit. In this embodiment of the invention, the photoinitiating structural unit includes 4-acryloyloxybenzophenone structural unit and / or 4-methacryloyloxybenzophenone structural unit.

[0041] In some embodiments, the mass ratio of styrene structural units to cross-linked structural units is (5~80):1, for example, it can be 5:1, 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1 or 80:1, which is beneficial to further improve the swelling resistance of the negative electrode binder.

[0042] In some embodiments, the mass ratio of photoinitiating structural units to crosslinking structural units is (1.5~40):1, for example, it can be 1.5:1, 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1 or 40:1, which is beneficial to control the length of polymer chain segments containing polar groups and can improve both the molecular strength and ion conduction performance of the negative electrode binder.

[0043] In some embodiments, the medium layer is obtained by a first polymerization reaction from a first raw material comprising styrene monomers, crosslinking monomers and photoinitiating functional monomers.

[0044] In some embodiments, styrene monomers include styrene.

[0045] In some embodiments, the crosslinking monomers include one or more of divinylbenzene, allyl methacrylate, diallyl phthalate, pentaerythritol triallyl ether, ethylene glycol dimethacrylate, and N,N-methylenebisacrylamide; the crosslinking monomers facilitate the formation of a denser crosslinking network structure on the surface of the core, which helps to better restrict the penetration of solvent molecules, thereby further improving the anti-swelling ability of the negative electrode binder.

[0046] In some embodiments, the photoinitiating functional monomers include 4-acryloyloxybenzophenone and / or 4-methacryloyloxybenzophenone. These photoinitiating functional monomers can rapidly generate free radicals under ultraviolet light or other wavelengths of light, which can significantly increase the rate of the second polymerization reaction and shorten the curing time.

[0047] In this embodiment of the invention, by adjusting the mass ratio of the dielectric layer to the polymer, and the ratio of the polymer mass to the total mass of the dielectric layer and the shell layer, the flexibility, adhesion, and anti-swelling ability of the negative electrode binder can be further improved. In some embodiments, the mass ratio of the dielectric layer to the polymer is (0.05~0.1):1, and the ratio of the polymer mass to the total mass of the dielectric layer and the shell layer is (0.5~1):1.

[0048] For example, the mass ratio of the dielectric layer to the polymer can be 0.05:1, 0.07:1, 0.09:1, or 0.1:1, etc.

[0049] For example, the ratio of the mass of the polymer to the total mass of the medium layer and the shell layer can be 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1 or 1:1, etc.

[0050] In some embodiments, the mass ratio of the dielectric layer to the polymer, and the ratio of the polymer mass to the total mass of the dielectric layer and the shell layer are further optimized to further improve the flexibility, adhesion, and anti-swelling ability of the negative electrode binder. The mass ratio of the dielectric layer to the polymer is (0.08~0.1):1, and the ratio of the polymer mass to the total mass of the dielectric layer and the shell layer is (0.7~0.9):1.

[0051] In some implementations, the swelling degree of the negative electrode binder is 15% to 35%, which helps to further improve the structural stability of the electrode and enhance the cycle life of the battery.

[0052] For example, the swelling degree of the negative electrode binder can be 15%, 20%, 25%, 30%, or 35%, etc.

[0053] In this embodiment of the invention, the D50 of the core is 70~120nm, for example, it can be 70nm, 80nm, 90nm, 100nm, 110nm or 120nm, which is conducive to forming a strong interfacial bond with the dielectric layer, thereby improving the structural stability of the negative electrode binder and further improving the bonding performance of the negative electrode binder.

[0054] In some embodiments, the particle size D50 of the negative electrode binder is 120~335nm, for example, it can be 120nm, 150nm, 180nm, 210nm, 240nm, 270nm, 305nm or 335nm, which is beneficial to further improve the adhesion and mechanical stability of the negative electrode binder.

[0055] The present invention also provides a method for preparing the above-mentioned negative electrode binder, comprising the following steps: forming a shell layer on the surface of the core to obtain the negative electrode binder.

[0056] In some embodiments, the process of forming a shell on the surface of the core includes: mixing a first raw material comprising styrene monomers, crosslinking monomers and photoinitiating functional monomers with a second raw material (i.e., the core) comprising a polymer containing aromatic vinyl structural units and conjugated diene structural units, and subjecting the second monomer raw material to a first polymerization reaction to form a dielectric layer on the surface of the core; mixing the core with a first monomer containing polar groups, and subjecting the first monomer to a second polymerization reaction to form a shell on the surface of the core, thereby obtaining a negative electrode binder.

[0057] In this embodiment of the invention, the second raw material may include styrene-butadiene rubber latex.

[0058] In some embodiments, the preparation method further includes: after the second polymerization reaction, adjusting the pH of the reaction system to 7-9, filtering, and obtaining the negative electrode binder.

[0059] In some implementations, an alkaline solution is used to adjust the pH of the reaction system to 7-9.

[0060] In some embodiments, the alkaline solution includes one or more of lithium hydroxide solution (such as aqueous lithium hydroxide solution), sodium hydroxide solution, and potassium hydroxide solution.

[0061] In this embodiment of the invention, both the first polymerization reaction and the second polymerization reaction are carried out under an inert atmosphere to avoid interference from oxygen in the air on the polymerization reaction, while ensuring the safety and controllability of the polymerization reaction process.

[0062] In some implementations, the inert atmosphere includes one or more of nitrogen, argon, and helium.

[0063] In the preparation process of the above-mentioned negative electrode binder, in order to make the first polymerization reaction and the second polymerization reaction more complete, the reaction system can be mixed, such as by using a stirrer.

[0064] By controlling the temperature and time of the first polymerization reaction, and the temperature and time of the second polymerization reaction, it is beneficial for each component monomer to fully undergo the first and second polymerization reactions. Simultaneously, it helps ensure the controllability and uniformity of the first and second polymerization processes. In this embodiment of the invention, the temperature of the first polymerization reaction is 70~90℃, for example, 70℃, 75℃, 80℃, 85℃, or 90℃, and the time of the first polymerization reaction is 4~6 hours, for example, 4 hours, 4.5 hours, 5 hours, 5.5 hours, or 6 hours.

[0065] In some embodiments, the temperature of the second polymerization reaction is 25~50°C, for example, 25°C, 30°C, 35°C, 40°C, 45°C or 50°C, etc., and the time of the second polymerization reaction is 4~6h, for example, 4h, 4.5h, 5h, 5.5h or 6h, etc., which helps to improve the controllability of the second polymerization reaction process and make the second polymerization reaction more complete.

[0066] In some embodiments, the second polymerization reaction is carried out under ultraviolet light irradiation.

[0067] In some implementations, the second polymerization reaction can be carried out in a photoreactor.

[0068] In some embodiments, the mass ratio of the first raw material to the second raw material is 5% to 15%, for example, it can be 5%:1, 8%:1, 10%:1, 12%:1, 14%:1, or 15%:1, etc., preferably (8% to 12%):1. By controlling the mass ratio of the first raw material to the second raw material, it is beneficial to improve the stability of the first and second raw materials, thereby improving the stability of the brush structure and the second raw material.

[0069] In some embodiments, the mass ratio of the first monomer to the core mass is (50%~100%):1, for example, it can be 50%:1, 60%:1, 70%:1, 80%:1, 90%:1 or 100%:1, etc., preferably (70%~90%):1, which is beneficial to adjust the content of polymer segments containing polar groups in the shell, thereby further improving the adhesion and anti-swelling ability of the negative electrode binder.

[0070] In some embodiments, the second raw material also includes a thermal initiator that can initiate a first polymerization reaction of styrene monomers, crosslinking monomers, and photoinitiating functional monomers to form a dielectric layer on the surface of the core, thereby obtaining the core.

[0071] In some embodiments, the thermal initiator includes one or more of peroxides, persulfates, and azo compounds, such as ammonium persulfate among persulfates.

[0072] In some embodiments, the thermal initiator is added to the second raw material in the form of a solution to initiate the first polymerization reaction. Specifically, the thermal initiator can be dissolved in a solvent to form a mixed solution, and then the mixed solution can be added dropwise to the second raw material. The solvent used may include water.

[0073] In some embodiments, the mass percentage of thermal initiator in the mixed solution is 1% to 3%.

[0074] Generally, as the first polymerization reaction proceeds, the initially added thermal initiator is gradually decomposed and consumed, leading to a decrease in the free radical concentration. To improve the efficiency of the first polymerization reaction, in some embodiments, a thermal initiator is added to the reaction system during the first polymerization reaction, which helps to maintain the concentration of free radicals in the reaction system, thereby maintaining the rate of the first polymerization reaction.

[0075] In some embodiments, the first raw material is added to the second raw material dropwise, which helps to control the reaction rate of the first polymerization reaction, so that the first polymerization reaction proceeds smoothly and reduces the occurrence of side reactions.

[0076] In some embodiments, the first raw material is added to the second raw material by dripping for 1 to 2 hours, such as 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, or 2 hours (the time of the first polymerization reaction includes the dripping time), which helps to better control the rate of the first polymerization reaction, avoid the reaction from being too violent, and reduce the occurrence of side reactions.

[0077] In the above preparation process, after the first polymerization reaction is completed, the reaction system is cooled to obtain the core, which is then mixed with the first monomer to carry out the second polymerization reaction, thus obtaining the negative electrode binder. When it is necessary to preserve the core, it is generally necessary to store it in the dark.

[0078] The present invention also provides an electrode sheet comprising the above-described negative electrode binder or a negative electrode binder prepared according to the above-described preparation method. This electrode sheet has advantages corresponding to the above-described negative electrode binder, which will not be elaborated further.

[0079] In some implementations, the electrode sheet includes a negative electrode sheet.

[0080] In some embodiments, the electrode sheet includes an electrode coating, which includes a negative electrode binder.

[0081] In some embodiments, the negative electrode sheet further includes a negative electrode current collector and a negative electrode coating (i.e., an electrode coating) located on at least one side of the negative electrode current collector. Specifically, the negative electrode coating may be located only on one side of the negative electrode current collector, or the negative electrode coating may be provided on both sides of the negative electrode current collector.

[0082] In some embodiments, the electrode coating also includes a negative electrode active material, a conductive agent, and a thickener.

[0083] Specifically, thickeners may include carboxymethyl cellulose thickeners, such as carboxymethyl cellulose salts, like sodium carboxymethyl cellulose.

[0084] In some embodiments, the negative electrode active material includes one or more of graphite, hard carbon, and soft carbon; the conductive agent may include one or more of conductive carbon black, conductive graphite, carbon nanotubes (CNTs), carbon fibers, graphene, acetylene black, and Ketjen black.

[0085] In some embodiments, the mass percentage of the negative electrode active material in the negative electrode active material layer can be 90% to 98.5%, for example, 90%, 93%, 95%, 97%, 98.5%, or any combination thereof; the mass fraction of the conductive agent can be 0.5% to 5%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any combination thereof; and the mass fraction of the negative electrode binder can be 1% to 5%, for example, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any combination thereof.

[0086] The embodiments of the present invention may employ conventional negative electrode current collectors in the art, such as copper foil or carbon-coated copper foil.

[0087] In this embodiment of the invention, the negative electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the components used to form the negative electrode active layer, such as the negative electrode active material, conductive agent, binder, and thickener, can be dispersed in a solvent, such as water, to prepare a negative electrode slurry. This slurry is then coated onto the surface of the negative electrode current collector, and after drying, rolling, and other processes, the negative electrode sheet is obtained. The coating, drying, and rolling processes involved are conventional operations in preparing negative electrode sheets using the coating method, and are not particularly limited thereto.

[0088] The present invention also provides a battery comprising the electrode plates described above. This battery has advantages corresponding to the electrode plates described above, which will not be elaborated further.

[0089] Generally, a battery includes an electrolyte, a battery cell, and a casing for encapsulating the battery cell. The electrolyte is injected into the battery cell within the casing. The battery cell includes electrode plates (including positive and negative electrode plates) and a separator located between the positive and negative electrode plates. The battery cell can be a stacked cell, meaning it is composed of positive electrode plates, a separator, and negative electrode plates stacked alternately; or it can be a wound cell, meaning it is composed of positive electrode plates, a separator, and negative electrode plates stacked and then wound together. In practice, a stacked cell can be formed by alternating layers of positive electrode plates, a separator, and negative electrode plates, and then the cell is encapsulated using an aluminum-plastic film.

[0090] In detail, a positive electrode coating is provided on one side of the surface of the positive electrode current collector in the thickness direction, or a positive electrode coating is provided on both sides of the opposite surface in the thickness direction of the positive electrode current collector.

[0091] The positive electrode coating may include a positive electrode active material, a conductive agent, and a binder. In the positive electrode coating, the mass percentage of the positive electrode active material may be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99%, or any combination thereof. The mass fraction of the binder may be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any combination thereof.

[0092] The binder for the positive electrode coating can be either the negative electrode binder provided in the embodiments of the present invention, or a combination of one or more of the following: polyvinylidene fluoride (PVDF), polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, etc., as the binder for the positive electrode coating.

[0093] In some embodiments, the positive electrode active material may include LiCoO2, LiNiO2, or LiCo. x Ni 1-x O2 (0≤x≤1), LiCo x Ni 1-x-y Al y O2 (0≤x≤1, 0≤y≤1), LiMn2O4, LiFe x Mn y M z O4 (M is one or more of Al, Mg, Ga, Cr, Co, Ni, Cu, Zn or Mo, 0≤x≤1, 0≤y≤1, 0≤z≤1, x+y+z=1), Li 1＋x L 1－y－z M y N z O2 (L, M, N are one or more of Li, Co, Mn, Ni, Fe, Al, Mg, Ga, Ti, Cr, Cu, Zn, Mo, F, I, S, B, -0.1≤x≤0.2, 0≤y≤1, 0≤z≤1, 0≤y+z≤1), LiFePO4, Li3V2(PO4)3, Li3V3(PO4)3, LiVPO4F, Li2CuO2, Li5FeO4, and metal sulfides and oxides (such as TiS2, V2S3, FeS, FeS2, LiMS) x (M is at least one of the transition metal elements such as Ti, Fe, Ni, Cu, Mo, etc., 1≤x≤2.5), TiO2, Cr3O8, V2O5, MnO2, etc.

[0094] The embodiments of the present invention may employ conventional positive current collectors in the art, for example, positive current collectors may include aluminum foil or carbon-coated aluminum foil.

[0095] In this embodiment of the invention, the positive electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the positive electrode active material, conductive agent, binder, and other components used to form the positive electrode active layer can be dispersed in a solvent, such as N-methylpyrrolidone (NMP), to prepare a positive electrode slurry. This slurry is then coated onto the surface of the positive electrode current collector, and after drying, rolling, and other processes, the positive electrode sheet is obtained. The coating, drying, and rolling processes involved are conventional operations for preparing positive electrode sheets using the coating method, and are not particularly limited thereto.

[0096] The electrolyte in this embodiment of the invention can be a conventional electrolyte in the art. For example, the electrolyte is a non-aqueous electrolyte, which may specifically include organic solvents, additives and electrolyte salts. Organic solvents include one or more of ethylene carbonate (EC), diethyl carbonate (DEC) and propylene carbonate (PC). Additives include, for example, fluoroethylene carbonate (FEC) and vinylene carbonate (VC). Electrolyte salts may include lithium salts, such as lithium hexafluorophosphate (LiPF6), but are not limited thereto.

[0097] In this embodiment of the invention, the separator is used to separate the positive electrode and the negative electrode to prevent the positive electrode and the negative electrode from short-circuiting due to contact. Conventional separators in the art can be used in this embodiment of the invention, and there are no special limitations on this.

[0098] In this embodiment of the invention, the battery cell can be packaged using conventional housing materials in the art, such as flexible packaging materials like aluminum-plastic film, but is not limited thereto.

[0099] The embodiments of the present invention can assemble components such as positive electrode, separator and negative electrode into a battery using conventional methods in the art. For example, positive electrode, separator and negative electrode can be stacked in an alternating manner to obtain a stacked cell (or wound into a wound cell); then the cell is placed in a casing (outer packaging) and after conventional processes such as electrolyte injection, encapsulation, formation and capacity testing, a battery is obtained.

[0100] The present invention will be further described below through specific embodiments.

[0101] Example 1

[0102] The negative electrode binder provided in this embodiment is prepared through the following steps:

[0103] (1) Weigh 500g of styrene-butadiene rubber latex (solid content is 40%, that is, the mass of styrene-butadiene rubber is 200g) and add it to a three-necked flask. Turn on the stirrer, purge with nitrogen, and heat to 80℃ (that is, the first polymerization reaction temperature); Weigh 0.1g of ammonium persulfate and dissolve it in 5g of water. Stir and dissolve it and add it to the three-necked flask. The styrene-butadiene rubber latex in this example is Haodian AWG101.

[0104] (2) Weigh 6g of styrene, 1g of divinylbenzene, and 3g of 4-acryloyloxybenzophenone, mix them evenly, and drop them into the three-necked flask of step 1) to start the first polymerization reaction. Control the addition to be completed within 1 hour. After the addition is completed, continue the first polymerization reaction for 2 hours. Add ammonium persulfate aqueous solution (0.1g of ammonium persulfate dissolved in 5g of deionized water to obtain ammonium persulfate aqueous solution), then keep warm for 2 hours, stop the reaction, cool down, and form a medium layer on the surface of the core styrene-butadiene rubber to obtain the core. Store it in the dark.

[0105] (3) Weigh 500g of core (solid content is 10%) and add it to the photoreactor. Turn on the stirring and pass nitrogen gas. Weigh 25g of acrylic acid and add it to the reactor. Stir and mix evenly. Turn on the ultraviolet lamp with a power of 200W and carry out the second polymerization reaction for 5h under a nitrogen atmosphere. After the reaction is completed, stop the ultraviolet lamp irradiation. Then add lithium hydroxide aqueous solution, adjust the pH of the system to 7.0, filter and discharge to obtain the negative electrode binder. In this process, through the second polymerization reaction, polymer segments containing polar groups are grafted onto the surface of the core to form a shell.

[0106] Example 2

[0107] The difference between this embodiment and Example 1 is that in step 2), 10g of styrene, 2g of allyl methacrylate, and 8g of 4-methacryloyloxybenzophenone are weighed, mixed evenly, and then dropped into a three-necked flask to start the first polymerization reaction. The remaining conditions and steps are the same as in Example 1.

[0108] Example 3

[0109] The difference between this embodiment and Embodiment 1 is that in step 3), 25g of acrylic acid is replaced with 50g of methacrylic acid. The remaining conditions and steps are the same as in Embodiment 1.

[0110] Examples 4 to 18 differ from Example 1 in the following aspects: the type of organic acid monomer containing unsaturated bonds, the type of the second raw material (i.e., the core), the type of styrene monomer, the type of crosslinking monomer, the D50 (R1) of the core, the D50 (R2) of the negative electrode binder, the temperature (T) of the first polymerization reaction, the time (t1) of the first polymerization reaction, the time (t2) of the second polymerization reaction, the mass ratio (X1) of the dielectric layer and the polymer (i.e., the core), the ratio (X2) of the mass of the polymer to the total mass of the dielectric layer and the shell, the mass ratio (X3) of the styrene monomer and the crosslinking monomer, and the mass ratio (X4) of the photoinitiating functional monomer and the crosslinking monomer. For details, please refer to Table 1. Except for the differences shown in Table 1, the remaining steps and conditions are the same as in Example 1.

[0111] Comparative Example 1

[0112] This comparative example directly uses styrene-butadiene rubber latex (solid content of 40%, the same as the styrene-butadiene rubber latex in Example 1) as binder-1.

[0113] Comparative Example 2

[0114] This comparative example directly uses polyacrylic acid adhesive (6% solid content) as adhesive-2.

[0115] Comparative Example 3

[0116] The negative electrode binder provided in this comparative example is prepared through the following steps:

[0117] Weigh 500g of styrene-butadiene rubber latex (same as the styrene-butadiene rubber latex of Example 1, with a solid content of 40%, i.e., the mass of styrene-butadiene rubber is 200g) and 1667g of polyacrylic acid binder with a solid content of 6% (same as the polyacrylic acid binder of Comparative Example 2), mix them, and dry them to form a mixed liquid of polyacrylic acid binder and styrene-butadiene rubber latex.

[0118] Comparative Example 4

[0119] The negative electrode binder provided in this comparative example is prepared through the following steps:

[0120] (1) Weigh 500g of styrene-butadiene rubber latex (solid content is 40%, that is, the mass of styrene-butadiene rubber is 200g) and add it to a three-necked flask. Turn on the stirrer, purge with nitrogen, and heat to 80℃ (that is, the first polymerization reaction temperature); weigh 0.1g of ammonium persulfate and dissolve it in 5g of water. Stir and dissolve the solution and add it to the three-necked flask. The styrene-butadiene rubber latex in this comparative example is Haodian AWG101.

[0121] (2) Weigh 6g of styrene, 1g of divinylbenzene and 3g of 4-acryloyloxybenzophenone, mix them evenly and drop them into the three-necked flask of step 1) to start the first polymerization reaction. Control the drop addition to be completed within 1 hour. After the drop addition is completed, continue the first polymerization reaction for 2 hours. Add ammonium persulfate aqueous solution (0.1g of ammonium persulfate dissolved in 5g of deionized water to obtain ammonium persulfate aqueous solution), then keep warm for 2 hours, stop the reaction, cool down, and form a dielectric layer on the surface of the core styrene-butadiene rubber to obtain the negative electrode binder.

[0122] Test case

[0123] The above-mentioned negative electrode binder, graphite, conductive carbon black, sodium carboxymethyl cellulose, and water were mixed evenly in a planetary mixer at a mass ratio of 2:96:1:1:100 to obtain a negative electrode slurry. The negative electrode slurry was then coated onto the surface of copper foil using a coating machine. After drying and rolling, a negative electrode sheet was obtained. Lithium iron phosphate, conductive carbon black, PVDF, and NMP were mixed evenly in a planetary mixer at a mass ratio of 97:1:2:100 to obtain a positive electrode slurry. The positive electrode slurry was then coated onto the surface of aluminum foil using a coating machine. The positive electrode sheet, separator, and electrolyte (EC, EMC, DMC mass ratio = 1:1:1, 1 mol / L) obtained after cutting and pressing were then combined. ), gaskets and springs are converted into button cells.

[0124] Table 1 summarizes the following parameters for each embodiment: type of organic acid monomer containing unsaturated bonds, type of core, type of styrene monomer, type of crosslinking monomer, particle size D50 (R1) of the core, particle size D50 (R2) of the negative electrode binder, temperature (T) of the first polymerization reaction, time (t1) of the first polymerization reaction, time (t2) of the second polymerization reaction, mass ratio of dielectric layer to polymer (i.e., core) (X1), ratio of polymer mass to the total mass of dielectric layer and shell (X2), mass ratio of styrene monomer to crosslinking monomer (X3), and mass ratio of photoinitiating functional monomer to crosslinking monomer (X4). Except for the differences shown in Table 1, the other conditions are basically the same.

[0125] Table 1

[0126]

[0127]

[0128] The negative electrode binder, negative electrode sheet, and battery in the above embodiments and comparative examples were tested as follows:

[0129] (1) D50 of the core and D50 of the negative electrode binder: The D50 of the core and D50 of the negative electrode binder were measured by a laser particle size analyzer, and the results are shown in Table 1.

[0130] (2) Adhesion of negative electrode binder: The adhesion of negative electrode binder was determined according to national standard GB / T 2790-1995, and the results are shown in Table 2;

[0131] (3) Swelling degree test of negative electrode binder: The negative electrode binder was dried in an oven at 50℃ to form a film. A film with a mass of M1 was taken and immersed in the electrolyte (mass ratio of EC, EMC, and DMC = 1:1:1, 1 mol / L LiPF6) and kept in an oven at 60℃ for 48 hours. The electrolyte on the surface of the film was wiped dry with filter paper and weighed as M2. The swelling degree of the negative electrode binder = (M2-M1) / M1×100%, and the results are shown in Table 2.

[0132] (4) Flexibility test of negative electrode sheet: The flexibility of negative electrode sheet was determined according to the national standard GB / T 1731-1993. The results are shown in Table 2.

[0133] (5) Capacity retention rate after 500 cycles at 45℃: Charge and discharge the cell under test 2-3 times at a rate of 0.2C at room temperature to calibrate its initial discharge capacity (discharge capacity of the first cycle). Place the cell in a constant temperature chamber at 45℃ and let it stand for 2-4 hours to allow the cell temperature to stabilize at 45℃. Under constant temperature conditions at 45℃, cycle 500 times according to the following steps: a. Charging: Charge at a constant current of 1C to the cutoff voltage of 4.2V, then switch to constant voltage charging until the current is ≤0.05C; b. Discharging: Discharge at a constant current of 1C to the cutoff voltage of 2.5V; c. Standing: Let it stand for 10 minutes between charging and discharging. Calculation of capacity retention rate: Capacity retention rate after 500 cycles at 45℃ = (500th discharge capacity / initial discharge capacity) × 100%, the results are shown in Table 2.

[0134] Table 2

[0135]

[0136] Analysis of Table 2 shows that, compared to Comparative Examples 1-4, the negative electrode binders in Examples 1-18 exhibit superior adhesion, anti-swelling ability, and flexibility, thereby improving the cycle performance of the battery. This indicates that polymers containing aromatic vinyl structural units and conjugated diene structural units as the core can improve the flexibility of the negative electrode binder. Simultaneously, the introduction of polymeric segments containing polar groups into the shell layer can effectively enhance the anti-swelling ability and adhesion of the negative electrode binder, thus simultaneously improving the adhesion, anti-swelling ability, and flexibility of the negative electrode binder, thereby enhancing the cycle performance of the battery.

[0137] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A negative electrode binder, characterized in that, The negative electrode binder includes a core and a shell layer directly or indirectly grafted onto the surface of the core. The core includes a polymer containing aromatic vinyl structural units and conjugated diene structural units, and the shell layer includes polymeric segments containing polar groups, which are directly or indirectly grafted onto the core.

2. The negative electrode binder according to claim 1, characterized in that, The polar groups include one or more of organic acid groups, amide groups, and cyano groups.

3. The negative electrode binder according to claim 1, characterized in that, The core also includes a dielectric layer coated on the surface of the polymer, the dielectric layer comprising styrene-based structural units, cross-linked structural units, and photoinitiating structural units; the polymeric segments containing polar groups are grafted onto the dielectric layer.

4. The negative electrode binder according to claim 3, characterized in that, In the dielectric layer, the mass ratio of the styrene-based structural unit, the photoinitiating structural unit, and the crosslinking structural unit is (5~80):(1.5~40):

1.

5. The negative electrode binder according to claim 3, characterized in that, The mass ratio of the dielectric layer to the polymer is (0.05~0.1):1; And / or, the ratio of the mass of the polymer to the total mass of the medium layer and the shell layer is (0.5~1):

1.

6. The negative electrode binder according to claim 5, characterized in that, The swelling degree of the negative electrode binder is 15%~35%.

7. The negative electrode binder according to claim 6, characterized in that, The core's D50 is 70nm~200nm.

8. The negative electrode binder according to claim 7, characterized in that, The particle size D50 of the negative electrode binder is 120nm~335nm.

9. An electrode sheet, characterized in that, Includes the negative electrode binder as described in any one of claims 1-8.

10. A battery, characterized in that, Includes the electrode sheet as described in claim 9.

Images