A negative electrode binder, its preparation method and application

Abstract

This invention relates to the field of battery technology, specifically to a negative electrode binder, its preparation method, and its application. The negative electrode binder comprises: a core, wherein the polymer monomers of the core include styrene, butadiene, and heterocyclic compounds; and an ion-conducting network, wherein the ion-conducting network includes branches and a dynamically cross-linked network, wherein the dynamically cross-linked network is a cross-linked structure obtained by coordination reaction between the branches and metal ions, wherein the branches include carboxylic acid-terminated polyethylene glycol and borate ester-terminated polyethylene glycol, and the metal ions include Ca... 2+ Zn 2+ Mg 2+ One or more of the following; the ion-conducting network is grafted onto the core. Compared with the prior art, the present invention improves the mechanical strength and adhesion of the binder through butadiene-styrene doped heterocyclic compound copolymerization, achieves self-healing of the material through the ion-conducting network, maintains the stability of the internal structure of the battery, and extends the service life of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a negative electrode binder, its preparation method, and its application. Background Technology

[0002] Currently, graphite remains the mainstream choice for lithium-ion battery anode materials. Shipments of synthetic and natural graphite have reached 360,000 tons in recent years, accounting for over 97% of the market share. Although graphite boasts good cycle performance and low cost, its theoretical specific capacity is only 372 mAh / g, nearing its performance limit. Silicon-based anodes, with their high specific capacity and technological innovation, are expected to become an important choice for lithium-ion battery anode materials in the future. However, silicon-based anodes still face challenges in practical applications, such as severe volume expansion and poor electrode structure stability. Summary of the Invention

[0003] In view of this, the present invention aims to at least partially solve one of the technical problems in the related art. To this end, the present invention provides a negative electrode binder, its preparation method, and its application. The mechanical strength of the binder is improved through butadiene-styrene copolymerization, ensuring it remains almost undeformed during rolling. Heterocyclic compound doping simultaneously accommodates the severe volume expansion of the silicon-based negative electrode and provides electronic connection pathways, thereby enhancing lithium-ion transport rate and electrochemical performance. Dynamic crosslinking through covalent and coordination bonds strengthens the adhesion, enabling the material to self-heal, maintaining the stability of the battery's internal structure, and extending the battery's lifespan.

[0004] To solve the above-mentioned technical problems, the present invention is implemented as follows: According to one aspect of the present invention, a negative electrode binder is provided, comprising: The core, wherein the polymer monomers of the core include styrene, butadiene, and heterocyclic compounds; An ion-conducting network, comprising branches and a dynamically cross-linked network, wherein the dynamically cross-linked network is a cross-linked structure obtained by coordination reaction between the branches and metal ions, the branches comprising carboxylic acid-terminated polyethylene glycol and borate ester-terminated polyethylene glycol, and the metal ions comprising Ca... 2+ Zn 2+ Mg 2+ One or more of the following; The ion-conducting network is grafted onto the core.

[0005] In some of these implementations, one end of the branch is connected to the kernel, and the other end is a free end.

[0006] In some embodiments, the molecular weight of the branched chain is 450 Da to 550 Da.

[0007] In some embodiments, the sum of the degree of polymerization of ethylene glycol in the carboxylic acid-terminated polyethylene glycol and the degree of polymerization of ethylene glycol in the borate ester-terminated polyethylene glycol is 30 to 40.

[0008] In some embodiments, the molar ratio of the borate-terminated polyethylene glycol to the carbon atoms in the core is (1~2):100.

[0009] In some embodiments, the heterocyclic compound includes one or more of ethylene oxide, thiophene, and aniline.

[0010] In some embodiments, the molar ratio of the styrene, the butadiene, and the heterocyclic compound is 1:(2.5~3.5):(0.4~0.5).

[0011] In some of these embodiments, the degree of polymerization of the styrene is 80 to 120.

[0012] In some of these embodiments, the polymeric monomer of the core also includes a fluorinated monomer.

[0013] According to another aspect of the present invention, the present invention also provides a method for preparing a negative electrode binder, comprising the following steps: a) Styrene copolymer, butadiene, heterocyclic compound, first initiator and first solvent are mixed and heated to carry out polymerization reaction to obtain block copolymer; b) The block copolymer obtained in step a) is mixed with m-chloroperoxybenzoic acid and subjected to an epoxidation reaction. Then, a carboxyl-terminated heterocyclic compound and a first catalyst are added and a grafting reaction is carried out to obtain a carboxylic acid-terminated polyethylene glycol graft copolymer. c) Trimethyl borate, the second catalyst, the second solvent, and the carboxylic acid-terminated polyethylene glycol graft copolymer obtained in step b) are mixed and subjected to a crosslinking reaction. A metal salt solution is then added to initiate a coordination reaction to obtain the crosslinked polymer. After purification, the negative electrode binder is obtained.

[0014] In some embodiments, the method for preparing the styrene copolymer in step a) includes the following steps: A third solvent, styrene, RAFT reagent, a second initiator, and p-fluorostyrene are added to a reaction vessel, and the mixture is heated to the reaction temperature to obtain a styrene copolymer.

[0015] In some embodiments, the mass ratio of the styrene, the RAFT reagent, the second initiator, and the p-fluorostyrene is (8~12):(0.1~0.2):(0.01~0.02):(0.3~0.8).

[0016] In some embodiments, the reaction is carried out in an inert atmosphere, which includes one or more of nitrogen and helium.

[0017] In some of these embodiments, the reaction temperature is 70°C to 80°C.

[0018] In some of these embodiments, the reaction time is 6 to 8 hours.

[0019] In some embodiments, the third solvent includes one or more of toluene, xylene, and dichloromethane.

[0020] In some of these embodiments, the RAFT reagent comprises one or more of 2-cyano-2-propylbenzodisulfide, 2-(dodecyltrithiocarbonyl)-2-methylpropionic acid, and 4-cyano-4-(phenylthiocarboxylthio)valerate.

[0021] In some of these embodiments, the second initiator includes one or more of AIBN, BPO, and CHP.

[0022] In some embodiments, the components, by weight, include: 24-36 parts butadiene, 4-5 parts heterocyclic compound, 0.005-0.01 parts first initiator, 50-70 parts first solvent, 4-6 parts m-chloroperoxybenzoic acid, 8-12 parts carboxyl-terminated heterocyclic compound, 0.1-0.3 parts first catalyst, 1-2 parts trimethyl borate, 0.05-0.1 parts second catalyst, and 0.1-0.2 parts metal salt solution.

[0023] In some of these embodiments, the first initiator includes one or more of AIBN, BPO, and CHP.

[0024] In some embodiments, the first solvent includes one or more of tetrahydrofuran, N-methylpyrrolidone, and diethyl ether.

[0025] In some embodiments, the second solvent includes one or more of N,N-dimethylformamide and water.

[0026] In some embodiments, the first catalyst comprises one or more of boron trifluoride diethyl ether, boron trichloride, and boron tribromide.

[0027] In some embodiments, the second catalyst comprises one or more of p-toluenesulfonic acid, methanesulfonic acid, and benzenesulfonic acid.

[0028] In some embodiments, the polymerization reaction is carried out at a temperature of 60°C to 65°C for 12 to 15 hours.

[0029] In some of these embodiments, the epoxidation reaction is carried out at a temperature of 22°C to 28°C for 4 to 5 hours.

[0030] In some embodiments, the grafting reaction is carried out at a temperature of 60°C to 65°C for 8 hours to 10 hours.

[0031] In some embodiments, the grafting reaction is followed by dialysis with carbon monoxide of molecular weight 10 kDa to remove unreacted carboxyl-terminated heterocyclic compounds.

[0032] In some embodiments, the crosslinking reaction is carried out at a temperature of 80°C to 85°C for 4 hours to 6 hours.

[0033] In some of these embodiments, the coordination reaction is specifically performed by stirring for 2 to 3 hours followed by ultrafiltration to remove free metal ions.

[0034] In some of these embodiments, the purification process involves dropping the cross-linked polymer into ice-cold methanol, precipitating a white fibrous solid, and then drying it in a vacuum oven at 40°C to 50°C for 24 to 30 hours.

[0035] According to another aspect of the present invention, the present invention also provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector along the thickness direction, the negative electrode active material layer comprising a silicon negative electrode material and a binder, the binder comprising the negative electrode binder described in the above technical solution or the negative electrode binder prepared by the preparation method described in the above technical solution.

[0036] According to another aspect of the present invention, the present invention also provides a battery comprising the negative electrode sheet described in the above technical solution.

[0037] Implementing the technical solution of the present invention has at least the following beneficial effects: 1. This invention uses styrene, butadiene, and heterocyclic compounds to form a core. Polystyrene can serve as a supporting skeleton to improve the mechanical strength of the binder, making it almost undeformed during rolling. This can improve the shortcomings of traditional SBR homopolymer chains, such as insufficient mechanical strength and easy breakage due to volume expansion during charging and discharging, and suppress electrode expansion. At the same time, the doping of heterocyclic compounds in the butadiene chain can provide electronic connection channels, thereby improving the lithium-ion transport rate.

[0038] 2. In this invention, polyethylene glycol is grafted onto the end of butadiene to obtain branched chains, which enable the polyethylene glycol segments to form lithium-ion transport channels and reduce internal resistance. The modification of the carboxyl groups further enhances the hydrogen bonding force between the binder and the negative electrode active material, while the borate ester bonds can dynamically "break" and "reorganize" during charging and discharging, thereby buffering the stress of volume change and preventing the negative electrode sheet from cracking and shedding powder during this process. This reduces the volume expansion of the negative electrode sheet and the battery cell, helps maintain the stability of the internal structure of the battery, and extends the battery life.

[0039] 3. This invention utilizes the coordination structure formed by metal ions and oxygen atoms of polyethylene glycol units in the branch chain to enhance the adhesion of the negative electrode binder, so that the negative electrode slurry adheres more firmly to the negative electrode current collector.

[0040] 4. This invention introduces SEI film-forming additives to optimize the interface, enabling the binder and electrolyte to work synergistically to promote the formation of a stable LiF-rich SEI film, thereby extending battery life and improving battery safety.

[0041] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0042] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0043] Figure 1 This is a schematic diagram of the structure of the negative electrode binder obtained in Example 1 of the present invention.

[0044] Figure reference numerals: 1. Core; 2. Ion-conducting network; 3. Branch; 4. Dynamic conductive network.

[0045] The accompanying drawings have illustrated specific embodiments of the invention, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0046] The present application will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0047] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0048] In the description of this application, "same chemical composition" should be interpreted broadly, that is, the main components of the two have the same chemical composition, or the two have substantially the same chemical composition, but may have errors or impurities within the acceptable range that can be understood by those skilled in the art.

[0049] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0050] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0051] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0052] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0053] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0054] Currently, graphite remains the mainstream choice for lithium-ion battery anode materials. Although graphite has good cycle performance and low cost, its theoretical specific capacity is only 372 mAh / g, which is close to its performance limit. Silicon-based anode materials, due to their extremely high theoretical specific capacity (up to 4200 mAh / g), are considered key materials for next-generation high-energy-density lithium-ion batteries. In addition to having a much higher specific capacity than traditional graphite anodes, silicon anodes can significantly improve battery energy density and battery life, and offer other advantages such as fast charging speed (silicon anodes can accelerate lithium-ion insertion and extraction, reducing charging time); abundant and low-cost resources (silicon is abundant in the Earth's crust, inexpensive, and environmentally friendly); and good safety (silicon-based anodes do not have the risk of lithium plating, making them safer than graphite anodes and less likely to cause lithium-ion battery combustion or explosion).

[0055] However, silicon-based anodes still face problems such as severe volume expansion and poor electrode structure stability in practical applications. Severe volume expansion is due to the huge volume change (300%~400%) that occurs during charging and discharging of silicon, leading to pulverization and peeling of the electrode material and reducing the cycle life of the battery. Poor electrode structure stability is due to the easy formation of an unstable solid electrolyte interphase (SEI) film on the surface of the silicon anode, which increases the internal resistance of the battery and affects the charging and discharging efficiency.

[0056] In conclusion, although graphite anodes currently dominate the market, silicon-based anodes demonstrate broad application prospects due to their high specific capacity and technological innovation. With the increasing demand from electric vehicles and other high-energy applications, silicon-based anode materials, due to their high energy density, continuous technological maturation, and cost reduction, are expected to become an important choice for lithium-ion battery anode materials in the future.

[0057] Based on this, this invention addresses the shortcomings of severe volume expansion and poor electrode structure stability in silicon anodes by designing a novel anode binder to improve performance and provide better high-capacity fast-charging batteries. For fast-charging batteries, styrene-butadiene rubber (SBR) anode binders have advantages over polyacrylic acid (PAA) binders. First, SBR binders have better wettability with the electrolyte, facilitating the passage of electrolyte ions and thus improving fast-charging performance. Second, the bonding between SBR binders and graphite anodes is point bonding, resulting in a relatively small total contact area, which helps reduce obstacles to electron and ion conduction, further enhancing fast-charging capability. However, traditional SBRs suffer from insufficient mechanical strength of homopolymer chains, leading to easy breakage during charge and discharge due to volume expansion.

[0058] This invention modifies the structure of traditional SBR by introducing polystyrene microblocks to provide a supporting framework and suppress electrode expansion. At the same time, polyhexane compounds are doped into butadiene segments to improve lithium-ion transport efficiency. The resulting core improves the mechanical strength of the negative electrode binder. By constructing carboxylic acid-terminated and borate-terminated branches and a dynamic cross-linked network obtained by the coordination of branches with metal ions, an ion-conducting network is formed, which enhances adhesion, reduces internal resistance, improves volume expansion and interface stability, and provides a better high-capacity fast-charging battery.

[0059] Specifically, the present invention adopts the following technical solution: According to one aspect of the present invention, a negative electrode binder is provided, comprising: The core, wherein the polymer monomers of the core include styrene, butadiene, and heterocyclic compounds; An ion-conducting network, comprising branches and a dynamically cross-linked network, wherein the dynamically cross-linked network is a cross-linked structure obtained by coordination reaction between the branches and metal ions, the branches comprising carboxylic acid-terminated polyethylene glycol and borate ester-terminated polyethylene glycol, and the metal ions comprising Ca... 2+ Zn 2+ Mg 2+ One or more of the following; The ion-conducting network is grafted onto the core.

[0060] In a specific embodiment of the present invention, the polymerizable monomers of the core preferably include styrene, butadiene, and heterocyclic compounds. The polystyrene obtained after styrene polymerization provides a supporting framework and suppresses electrode expansion. The doping of heterocyclic compounds into the butadiene segments accommodates the severe volume expansion of the silicon-based negative electrode and provides electronic connection channels, thereby improving lithium-ion transport efficiency and electrochemical performance. In this invention, the heterocyclic compounds preferably include one or more of ethylene oxide, thiophene, and aniline, more preferably ethylene oxide. The present invention uses the above-mentioned styrene, butadiene, and heterocyclic compounds copolymerized to form the core to improve the mechanical strength of the negative electrode binder, making it less prone to deformation during rolling.

[0061] In a specific embodiment of the present invention, the molar ratio of styrene, butadiene, and the heterocyclic compound is preferably 1:(2.5~3.5):(0.4~0.5), specifically 1:2.5:0.4, 1:2.5:0.5, 1:3:0.4, 1:3:0.5, 1:3.5:0.4, 1:3.5:0.5, and any value between the two mentioned above. The present invention selects the above-mentioned suitable molar ratio to ensure that the subsequently obtained core has good performance, thereby obtaining a negative electrode binder that meets the expected performance of the present invention.

[0062] In a specific embodiment of the present invention, the degree of polymerization of the styrene is preferably 80-120, specifically 80, 85, 90, 95, 100, 105, 110, 115, 120, and any value between the two mentioned above. The present invention selects the above-mentioned suitable degree of polymerization of styrene to ensure that the subsequently obtained core has good performance, thereby obtaining a negative electrode binder that meets the expected performance of the present invention.

[0063] In a specific embodiment of the present invention, the polymer monomer of the core further includes a fluorinated monomer, preferably fluorinated styrene, and preferably p-fluorostyrene. The present invention uses the above-mentioned fluorinated monomer to promote the formation of a stable LiF-rich SEI film, optimize the interface, thereby extending battery life and improving battery safety.

[0064] In a specific embodiment of the present invention, the ion-conducting network includes branches and a dynamically cross-linked network. The branches include carboxylic acid-terminated polyethylene glycol and borate ester-terminated polyethylene glycol. One end of each branch is connected to the core, and the other end is a free end. The branches are grafted onto the butadiene end of the core with polyethylene glycol to form lithium-ion transport channels, exhibiting a "solid electrolyte" effect, thereby reducing internal resistance.

[0065] In a specific embodiment of the present invention, the sum of the degree of polymerization of ethylene glycol in the carboxylic acid-terminated polyethylene glycol and the degree of polymerization of ethylene glycol in the borate ester-terminated polyethylene glycol is 30-40. By controlling the degree of polymerization of ethylene glycol in the branches within the above range, the present invention avoids excessively long branches that would lead to a decrease in mechanical properties, thereby obtaining a negative electrode binder that meets the expected performance of the present invention.

[0066] In a specific embodiment of the present invention, the molecular weight of the branched chain is preferably 450 Da to 550 Da, specifically 450 Da, 460 Da, 470 Da, 480 Da, 490 Da, 500 Da, 510 Da, 520 Da, 530 Da, 540 Da, 550 Da, and any value between the above two. By controlling the molecular weight of the branched chain within the above range, the present invention avoids excessively long branches that could lead to a decrease in mechanical properties, thereby obtaining a negative electrode binder that meets the expected performance of the present invention.

[0067] In a specific embodiment of the present invention, the branched chain includes carboxylic acid-terminated polyethylene glycol (PEG) and borate ester-terminated PEG. The carboxylic acid-terminated PEG is formed by replacing the terminal groups of PEG with carboxyl groups, which enhances the hydrogen bonding force with active materials (such as silicon particles), i.e., strengthens adhesion. The borate ester-terminated PEG is formed by the esterification reaction of trimethyl borate replacing the hydroxyl groups on the carboxylic acid-terminated PEG, generating borate ester bonds (-BO-). Borate ester bonds are dynamic covalent bonds that can undergo reversible "breakage" and "recombination" under external conditions, such as temperature and pH, giving materials based on borate ester bonds self-healing and reprocessing capabilities. In this invention, the borate ester-terminated PEG can dynamically break / recombine during charging and discharging, buffering volume change stress, thereby preventing the negative electrode sheet from cracking and shedding powder during this process, reducing the volume expansion of the negative electrode sheet and the battery cell, and maintaining the stability of the negative electrode sheet in the electrolyte.

[0068] In a specific embodiment of the present invention, the molar ratio of the borate-terminated polyethylene glycol to the carbon atoms in the core is preferably (1~2):100, specifically 1:100, 1.5:100, 2:100, and any value between the two. The present invention avoids excessive crosslinking that increases the brittleness of the negative electrode binder by controlling the borate-terminated polyethylene glycol within the above-mentioned suitable range.

[0069] In a specific embodiment of the present invention, the dynamic cross-linking network is a cross-linking structure obtained by coordination reaction between the branches and metal ions, wherein the metal ions preferably include Ca. 2+ Zn 2+ Mg 2+ One or more of the following. Specifically, a metal ion can form a coordination structure with the four oxygen atoms of the four polyethylene glycols in the branch chain. However, this coordination structure is not strong and will break when the battery is charged and discharged, causing volume changes. It only temporarily crosslinks during slurry coating, providing better adhesion, enhancing the slurry coating strength, and allowing the slurry to adhere better to the negative electrode current collector.

[0070] In this invention, the core is used to improve the mechanical strength of the negative electrode binder, making it less prone to deformation during rolling. The side chains can enhance the bonding force, improve the lithium-ion transport rate, and buffer the volume change stress during charging and discharging, reducing the volume expansion of the electrode sheet and the battery cell. The dynamic cross-linking network enhances the coating strength of the negative electrode slurry, ensuring a better negative electrode sheet.

[0071] According to another aspect of the present invention, the present invention also provides a method for preparing a negative electrode binder, comprising the following steps: a) Styrene copolymer, butadiene, heterocyclic compound, first initiator and first solvent are mixed and heated to carry out polymerization reaction to obtain block copolymer; b) The block copolymer obtained in step a) is mixed with m-chloroperoxybenzoic acid and subjected to an epoxidation reaction. Then, a carboxyl-terminated heterocyclic compound and a first catalyst are added and a grafting reaction is carried out to obtain a carboxylic acid-terminated polyethylene glycol graft copolymer. c) Trimethyl borate, the second catalyst, the second solvent, and the carboxylic acid-terminated polyethylene glycol graft copolymer obtained in step b) are mixed and subjected to a crosslinking reaction. A metal salt solution is then added to initiate a coordination reaction to obtain the crosslinked polymer. After purification, the negative electrode binder is obtained.

[0072] In this invention, all raw materials used in the above preparation method may be from commercially available sources or self-made sources known to those skilled in the art, and this invention does not have any special restrictions on this.

[0073] This invention first involves mixing styrene copolymer, butadiene, a heterocyclic compound, a first initiator, and a first solvent, then heating the mixture to induce a polymerization reaction, yielding a block copolymer. The ring-opening polymerization of the heterocyclic compound is initiated by the end groups of the styrene copolymer.

[0074] In a specific embodiment of the present invention, the preparation method of the styrene copolymer in step a) includes the following steps: A third solvent, styrene, a RAFT reagent, a second initiator, and p-fluorostyrene are added to a reaction vessel and heated to the reaction temperature to obtain a styrene copolymer. Specifically, the obtained styrene copolymer contains -[CH2-CH(C6H4F)]- units with RAFT groups at the ends. The preferred mass ratio of styrene, the RAFT reagent, the second initiator, and the p-fluorostyrene is (8~12):(0.1~0.2):(0.01~0.02):(0.3~0.8); the reaction atmosphere is an inert atmosphere, preferably including one or more of nitrogen and helium; the preferred reaction temperature is 70℃~80℃, specifically 70℃, 72℃, 74℃, 76℃, 78℃, 80℃, and any value between the above two; the preferred reaction time is 6h~8h, specifically 6h, 7h, 8h, and... The values ​​between any two of the above; the third solvent preferably includes one or more of toluene, xylene, and dichloromethane; the RAFT reagent preferably includes one or more of 2-cyano-2-propylbenzodisulfide, 2-(dodecyltrithiocarbonyl)-2-methylpropionic acid, and 4-cyano-4-(phenylthiocarboxylthio)valerate; the second initiator preferably includes one or more of AIBN, BPO, and CHP; the present invention selects the above-mentioned suitable reaction conditions to ensure that the styrene copolymer obtained subsequently has good performance, thereby obtaining a block copolymer that meets the expectations of the present invention.

[0075] In a specific embodiment of the present invention, the components, by weight, include: 24-36 parts butadiene, 4-5 parts heterocyclic compound, 0.005-0.01 parts first initiator, 50-70 parts first solvent, 4-6 parts m-chloroperoxybenzoic acid, 8-12 parts carboxyl-terminated heterocyclic compound, 0.1-0.3 parts first catalyst, 1-2 parts trimethyl borate, 0.05-0.1 parts second catalyst, and 0.1-0.2 parts metal salt solution. By controlling the above amounts, the present invention avoids excessively long branched chains that reduce mechanical strength, and simultaneously avoids excessive cross-linking of trimethyl borate that increases the brittleness of the negative electrode binder.

[0076] In a specific embodiment of the present invention, the first initiator preferably includes one or more of AIBN, BPO, and CHP; the present invention uses the above-mentioned first initiator to initiate the polymerization reaction of styrene copolymer, butadiene, and heterocyclic compound to generate block copolymer.

[0077] In a specific embodiment of the present invention, the first solvent preferably includes one or more of tetrahydrofuran, N-methylpyrrolidone, and diethyl ether; the present invention uses the above-mentioned first solvent to dissolve styrene copolymer, butadiene, and heterocyclic compounds, which is beneficial to the smooth progress of subsequent polymerization reactions.

[0078] In a specific embodiment of the present invention, the polymerization reaction temperature is preferably 60℃~65℃, specifically 60℃, 61℃, 62℃, 63℃, 64℃, 65℃, and any value between these two; the polymerization reaction time is 12h~15h, specifically 12h, 13h, 14h, 15h, and any value between these two. The present invention selects the above polymerization reaction conditions to ensure that the subsequently obtained segment copolymer has good performance, thereby obtaining a negative electrode binder that meets the expectations of the present invention.

[0079] After obtaining the block copolymer, the present invention mixes the obtained block copolymer with m-chloroperoxybenzoic acid, performs an epoxidation reaction, and then adds a carboxyl-terminated heterocyclic compound and a first catalyst to perform a grafting reaction to obtain a carboxylic acid-terminated polyethylene glycol graft copolymer.

[0080] In a specific embodiment of the present invention, the preferred temperature for the epoxidation reaction is 22℃~28℃, specifically 22℃, 23℃, 24℃, 25℃, 26℃, 27℃, 28℃, and any value between two of the above; the preferred time for the epoxidation reaction is 4~5 hours, specifically 4 hours, 4.1 hours, 4.2 hours, 4.3 hours, 4.4 hours, 4.5 hours, 4.6 hours, 4.7 hours, 4.8 hours, 4.9 hours, 5 hours, and any value between two of the above. The present invention selects the above epoxidation reaction conditions to convert the butadiene double bond portion into an epoxy group, facilitating the subsequent grafting reaction of carboxyl-terminated heterocyclic compounds.

[0081] In a specific embodiment of the present invention, the first catalyst preferably comprises one or more of boron trifluoride diethyl ether, boron trichloride, and boron tribromide; the carboxyl-terminated heterocyclic compound is preferably carboxyl-terminated polyethylene glycol. The present invention uses the above-mentioned first catalyst and carboxyl-terminated heterocyclic compound. The first catalyst catalyzes the grafting reaction between the epoxidation product and the carboxyl-terminated heterocyclic compound, causing polyethylene glycol to graft onto the butadiene end of the core, forming a lithium-ion transport channel and reducing internal resistance.

[0082] In a specific embodiment of the present invention, the grafting reaction temperature is preferably 60℃~65℃, specifically 60℃, 61℃, 62℃, 63℃, 64℃, 65℃, and any value between two of the above; the grafting reaction time is preferably 8h~10h, specifically 8h, 8.2h, 8.4h, 8.6h, 8.8h, 9h, 9.2h, 9.4h, 9.6h, 9.8h, 10h, and any value between two of the above. The present invention selects the above grafting reaction conditions to ensure that polyethylene glycol is grafted onto butadiene to obtain a negative electrode binder that meets the expectations of the present invention.

[0083] In a specific embodiment of the present invention, the grafting reaction is further followed by the following operation: dialysis with carbon monoxide with a molecular weight of 10 kDa to remove unreacted carboxyl-terminated heterocyclic compounds.

[0084] After obtaining the carboxylic acid-terminated polyethylene glycol graft copolymer, the present invention mixes trimethyl borate, a second catalyst, a second solvent and the obtained carboxylic acid-terminated polyethylene glycol graft copolymer to carry out a crosslinking reaction, and then adds a metal salt solution to carry out a coordination reaction to obtain a crosslinked polymer; after purification, a negative electrode binder is obtained.

[0085] In a specific embodiment of the present invention, the second solvent preferably includes one or more of N,N-dimethylformamide and water. The second solvent is used to dissolve trimethyl borate and carboxylic acid-terminated polyethylene glycol graft copolymer, facilitating subsequent crosslinking reactions to ensure the acquisition of a negative electrode binder that meets the expectations of the present invention.

[0086] In a specific embodiment of the present invention, the second catalyst preferably comprises one or more of p-toluenesulfonic acid, methanesulfonic acid, and benzenesulfonic acid. The second catalyst catalyzes the crosslinking reaction of trimethyl borate and carboxylic acid-terminated polyethylene glycol graft copolymer to ensure that a negative electrode binder meeting the expectations of the present invention is obtained.

[0087] In a specific embodiment of the present invention, the temperature of the crosslinking reaction is preferably 80℃~85℃, specifically 80℃, 81℃, 82℃, 83℃, 84℃, 85℃, and any value between these two; the time of the crosslinking reaction is 4h~6h, specifically 4h, 4.2h, 4.4h, 4.6h, 4.8h, 5h, 5.2h, 5.4h, 5.6h, 5.8h, 6h, and any value between these two. The crosslinking reaction refers to the esterification reaction in which trimethyl borate replaces the hydroxyl groups on the carboxylic acid-terminated polyethylene glycol graft copolymer, generating borate ester bonds to obtain borate ester-terminated polyethylene glycol. In the present invention, during the charging and discharging process of a lithium battery, the borate ester bonds on the surface of the negative electrode are affected by the electrolyte environment. When lithium ions are inserted or extracted, the volume of the negative electrode changes, causing the borate ester bonds to break. However, under appropriate conditions, these broken borate ester bonds can reform, thereby achieving self-repair of the negative electrode binder.

[0088] In a specific embodiment of the present invention, the coordination reaction is specifically performed as follows: stirring for 2-3 hours followed by ultrafiltration to remove free metal ions. The coordination reaction refers to the formation of a coordination structure between a metal ion and the oxygen atoms of four repeating units in polyethylene glycol. However, this coordination structure only provides temporary crosslinking during the electrode preparation stage and gradually dissociates during the battery charging and discharging stages.

[0089] In a specific embodiment of the present invention, the purification process involves: dropping the crosslinked polymer into ice-cold methanol, precipitating a white fibrous solid, and then drying it in a vacuum oven at 40°C to 50°C for 24 to 30 hours. The present invention employs the above purification process to ensure that the negative electrode binder meets the expectations of the present invention.

[0090] This invention utilizes a polymerization reaction to form a copolymer of styrene, butadiene, and heterocyclic compounds, resulting in a core that provides a supporting framework and electronic connection pathways. A grafting reaction is then used to obtain carboxylic acid-terminated polyethylene glycol (PEG) that connects to the core, enhancing adhesion. A crosslinking reaction converts some of the carboxylic acid-terminated PEG into borate-terminated PEG, buffering volume change stress, suppressing cell expansion, and maintaining the stability of the battery's internal structure. Finally, a coordination reaction yields a dynamic crosslinked network, enhancing the slurry coating strength during battery fabrication, resulting in a negative electrode binder that meets the expected performance of this invention.

[0091] According to another aspect of the present invention, the present invention also provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector along the thickness direction, the negative electrode active material layer comprising a silicon negative electrode material and a binder, the binder comprising the negative electrode binder described in the above technical solution or the negative electrode binder prepared by the preparation method described in the above technical solution.

[0092] In a specific embodiment of the present invention, the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector along its thickness direction; wherein, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0093] In a specific embodiment of the present invention, the negative electrode active material layer comprises a silicon negative electrode material, a binder, and a conductive agent; wherein, the silicon negative electrode active material comprises silicon particles; the binder comprises the negative electrode binder described in the above-described technical solution or the negative electrode binder prepared by the preparation method described in the above-described technical solution, as well as PAA-type binders; the conductive agent comprises one or more of conductive carbon, acetylene black, conductive carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The present invention does not impose any special restrictions on the source of the above-described silicon negative electrode material, PAA-type binder, and conductive agent; commercially available products well known to those skilled in the art can be used.

[0094] In a specific embodiment of the present invention, the method for preparing the negative electrode sheet includes: thoroughly mixing silicon negative electrode material, binder, and conductive agent to prepare a slurry; coating the slurry onto a negative electrode current collector; drying, cold pressing, and slitting to obtain the negative electrode sheet. The negative electrode current collector can be a metal foil such as copper foil.

[0095] According to another aspect of the present invention, the present invention also provides a battery comprising the negative electrode sheet described in the above-described technical solution. Thus, the battery possesses all the features and advantages of the negative electrode sheet described in the above-described technical solution, which will not be repeated here.

[0096] In this invention, the battery further includes a positive electrode, a separator, and an electrolyte. Preferably, the battery is formed by stacking the positive electrode, separator, and negative electrode and then winding them together. In a preferred embodiment of this invention, the battery fabrication process includes: sequentially stacking the positive electrode, separator, and negative electrode and then winding them to form an electrode assembly; packaging with a polymer; filling with electrolyte; and then performing formation and other processes to form the battery. The specific conditions and parameters for each step in the above fabrication process can be achieved using battery fabrication techniques well-known to those skilled in the art; this invention does not impose any special limitations on these aspects.

[0097] In a specific embodiment of the present invention, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector along the thickness direction; wherein, the positive current collector has two surfaces opposite to each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0098] In a specific embodiment of the present invention, the positive electrode active material layer includes a positive electrode active material, a binder, and a conductive agent; wherein, the positive electrode active material includes lithium iron phosphate; the binder includes one or more of polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS); the conductive agent includes one or more of conductive carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The present invention does not impose any special restrictions on the source of the above-mentioned positive electrode active material, binder, and conductive agent; commercially available products well known to those skilled in the art can be used.

[0099] In a specific embodiment of the present invention, the method for preparing the positive electrode includes: thoroughly mixing the positive electrode active material, binder, and conductive agent to prepare a slurry; coating the slurry onto a positive electrode current collector; and drying, cold pressing, and slitting to obtain the positive electrode. The positive electrode current collector can be a metal foil such as aluminum foil.

[0100] In specific embodiments of the present invention, the separator and electrolyte can both be conventional separators and electrolytes for batteries that are well known to those skilled in the art, and the present invention does not have any special limitations on this.

[0101] The present application will be described in detail below with reference to the accompanying drawings and embodiments. However, the implementation and protection of the present invention are not limited thereto. The following embodiments are only some embodiments of the present application and are not intended to limit the present application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0102] Example 1 S1. Preparation of block copolymers: 50 parts by weight of anhydrous toluene solvent, 10 parts by weight of styrene monomer, 0.1 parts by weight of RAFT reagent (2-cyano-2-propylbenzodithioester), 0.01 parts by weight of AIBN initiator, and 0.5 parts by weight of p-fluorostyrene were added to a reactor and polymerized at 70°C under nitrogen protection for 6 hours. 1 ¹H NMR monitoring showed a conversion rate of ≥95%, yielding a styrene copolymer. The styrene copolymer contained -[CH₂-CH(C₆H₄F)]- units.

[0103] The styrene copolymer was mixed with 60 parts by weight of tetrahydrofuran solvent, 30 parts by weight of butadiene (BR), and 5 parts by weight of ethylene oxide. Then, 0.005 parts by weight of AIBN initiator was added, and the grafting reaction was carried out at 60°C for 12 hours to obtain the block copolymer.

[0104] S2. Preparation of carboxylic acid-terminated polyethylene glycol graft copolymer: The block copolymer obtained in step S1 was mixed with 5 parts by weight of m-chloroperoxybenzoic acid and stirred at 25°C for 4 hours to convert the butadiene double bond to epoxy groups, with a conversion rate of 40%. After precipitation, the product was washed with a methanol-water (volume ratio 8:2) mixed solution. Then, 10 parts by weight of carboxyl-terminated polyethylene glycol 500 (HOOC-PEG500) and 0.1 parts by weight of boron trifluoride diethyl ether were added as catalysts, and the grafting reaction was carried out at 60°C under nitrogen protection for 8 hours. Finally, the mixture was dialyzed with carbon monoxide with a molecular weight of 10 kDa to remove unreacted carboxyl-terminated polyethylene glycol, yielding a carboxylic acid-terminated polyethylene glycol graft copolymer with a grafting rate of 35%.

[0105] S3. Preparation of negative electrode binder: The carboxylic acid-terminated polyethylene glycol graft copolymer obtained in step S2, along with 1 part by weight of trimethyl borate and 0.05 parts by weight of p-toluenesulfonic acid, was dissolved in a mixed solution of N,N-dimethylformamide and water (volume ratio 95:5). A crosslinking reaction was carried out at 80°C for 4 hours. Then, 0.1 parts by weight of calcium chloride solution was added, and the mixture was stirred for 2 hours to carry out a coordination reaction. Finally, free calcium ions were removed by ultrafiltration to obtain the crosslinked polymer. The crosslinked polymer was dropped into ice-cold methanol, and a white fibrous solid precipitated. This solid was then vacuum-dried at 40°C for 24 hours to obtain the negative electrode binder.

[0106] The obtained negative electrode binder was tested: GPC confirmed the molecular weight (Mn≈55kDa) and PDI (<1.3); FTIR testing showed that at 1720cm⁻¹... -1 and 1100cm -1 Characteristic peaks appeared at the locations, corresponding to ester groups and ether bonds, respectively; the glass transition temperatures detected by DSC were: Tg (polystyrene) ≈ 100℃, Tg (butadiene) ≈ -80℃.

[0107] S4. Preparation of lithium-ion secondary batteries: 95.5 parts by weight of silicon particles, 1.5 parts by weight of conductive carbon black, 2 parts by weight of PAA-type negative electrode binder (main chain is acrylate multi-polymer, side chain contains CN groups), and 1 part by weight of negative electrode binder are mixed to obtain a slurry. The slurry has a solid content of 50%, a viscosity of 2000 mPa·s, and a fineness of less than 30 μm. The slurry is coated onto copper foil, dried, and rolled to obtain electrode sheets. Then, it is slited and sliced ​​to form positive and negative electrode sheets of a set size. The swelling rate of the PAA-type negative electrode binder is 20%, and the swelling rate of the negative electrode binder is 50%.

[0108] A 9µm thick polyethylene base film is first coated with a 3µm ceramic layer on one side, and then coated with a 3µm polyvinylidene fluoride layer on both sides to obtain a separator.

[0109] The positive electrode, separator, and negative electrode are wound to obtain a bare cell. Positive and negative electrode tabs are then welded together, the bare cell is fitted into an aluminum-plastic film battery casing, electrolyte is injected, it is sealed, left to stand, formed, and capacity tested to obtain a lithium-ion secondary battery. The low-temperature DC internal resistance of the lithium-ion secondary battery is shown in Table 2.

[0110] Example 2 The difference between Example 2 and Example 1 is that in step S1, the amount of fluorostyrene used in preparing the block copolymer is 0.3 parts by weight.

[0111] Example 3 The difference between Example 3 and Example 1 is that in step S2, when preparing the carboxylic acid-terminated polyethylene glycol graft copolymer, carboxylic acid-terminated polyethylene glycol 800 (HOOC-PEG800) replaces carboxylic acid-terminated polyethylene glycol 500 (HOOC-PEG500).

[0112] Example 4 The difference between Example 4 and Example 1 is that in step S3, 2 parts by weight of trimethyl borate and 0.1 parts by weight of p-toluenesulfonic acid are added to prepare the negative electrode binder.

[0113] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that in step S4, when preparing the lithium-ion secondary battery, an SBR-type negative electrode binder was used instead of the negative electrode binder prepared in Example 1. The SBR-type negative electrode binder uses butadiene-styrene as a small core seed and grafts polycarboxylic acid groups and amides. The swelling rate of the PAA-type negative electrode binder is 20%, and the swelling rate of the SBR-type negative electrode binder is 52%.

[0114] Comparative Example 2 The difference between Comparative Example 2 and Comparative Example 1 is that in step S4, the structure of the PAA-type negative electrode binder is changed in the preparation of the lithium-ion secondary battery. Specifically, it is a ternary copolymer of acrylic acid, acrylate, and acrylonitrile. The swelling rate of the PAA-type negative electrode binder is 20%, while the swelling rate of the SBR-type negative electrode binder is 52%.

[0115] Comparative Example 3 The difference between Comparative Example 3 and Comparative Example 1 is that in step S4, when preparing the lithium-ion secondary battery, the SBR-type negative electrode binder is acrylonitrile- and acrylate-modified styrene-butadiene SBR.

[0116] Comparative Example 4 The difference between Comparative Example 4 and Comparative Example 1 is that in step S4, when preparing the lithium-ion secondary battery, the amount of PAA-type negative electrode binder is 1.5 parts by weight and the amount of SBR-type negative electrode binder is 1.5 parts by weight.

[0117] Performance testing: The negative electrode binder, negative electrode sheet, and lithium-ion secondary battery prepared in the above embodiments and comparative examples were subjected to performance tests, and the specific operations are as follows: Negative electrode wettability test: 10 μL of electrolyte is dropped onto the negative electrode using a micropipette, and the time it takes for the electrolyte to completely disappear from the electrode is tested, i.e., the absorption time. The longer the absorption time, the worse the wettability between the negative electrode and the electrolyte.

[0118] Electrode peeling force test: Cut the negative electrode into 25mm wide samples and stick them onto a steel plate. Gently peel off one end of the electrode and clamp it vertically on a tensile testing instrument (tensile testing machine) to test the electrode peeling force at 180°.

[0119] Separator and electrode adhesion test: Cut the separator and negative electrode into 25mm wide samples, gently peel off one end of the separator, clamp it vertically on the tensile tester, and test the adhesion between the separator and electrode at 180°.

[0120] Electrode flexibility test: Take a negative electrode sheet and cut it into a strip 25mm wide. Take a winding needle of different diameters and wind the electrode strip around the needle. The smaller the diameter of the needle, the less likely the electrode sheet will crack when wound, and the better the flexibility of the corresponding electrode sheet.

[0121] Full charge expansion rate test: Measure the average thickness of the positive and negative electrode plates, and record it as d1. Fully charge the lithium-ion secondary battery, then disassemble it, measure the average thickness of the positive and negative electrode plates after full charge, and record it as d2. Full charge expansion rate = (d2-d1) / d1×100%.

[0122] DC internal resistance test: Under normal temperature conditions, the lithium-ion secondary battery is charged to 3.65V at 1C and cut off at 0.05C. Then it is discharged to 50% SOC at 1C. The ambient temperature is adjusted to -20℃ and the discharge DC internal resistance is recorded after 0.36C discharge for 30s.

[0123] Cyclic testing: After the lithium-ion secondary battery was left to stand at 45℃ for 2 days, it was first discharged at 1C to 2.0V, and the initial capacity was recorded. Then, at 25℃, the battery was clamped using a double-sided clamp with a clamping force of 3000N. The charging process was as follows: 2C constant current charging to 3.65V, 3.65V constant voltage charging to current <0.5C, and resting for 5 minutes; 2C constant current charging to 3.65V, 3.65V constant voltage charging to current <0.1C, and resting for 5 minutes; then 2C constant current charging to 3.65V, 3.65V constant voltage charging to current <0.05C. The discharging process was as follows: resting for 5 minutes, 1C constant current discharging to 2.0V, and so on until the discharge capacity reached 80% of the initial capacity.

[0124] The test results are shown in Tables 1, 2 and 3 below.

[0125] Table 1 Test data for the examples and comparative examples As shown in Table 1, the full-charge expansion rate of Example 2 is greater than that of Example 1. This is because silicon materials undergo significant volume changes during charging and discharging, which may lead to SEI film rupture and regeneration, thereby consuming more lithium ions and reducing the coulombic efficiency of the battery. If the content of SEI film-forming additives is reduced, this volume expansion problem may become more severe. The full-charge expansion rate of Example 3 is significantly greater because the excessively long functionalized branches lead to a decrease in mechanical properties, which will not effectively suppress the volume expansion of the silicon anode. The longer liquid absorption time, worse electrode peeling force, and greater full-charge expansion rate of Example 4 are due to the excessive cross-linking of trimethyl borate, which makes the binder network too rigid, resulting in poor electrode flexibility. This makes it unable to effectively disperse stress and reduces the effect of suppressing volume expansion. Furthermore, the dense cross-linked network hinders the passage of electrolyte ions, thus increasing the liquid absorption time. In addition, excessive cross-linking causes the binder to lose the necessary flexibility, which in turn exacerbates the stress concentration of the silicon anode during charging and discharging, and may ultimately lead to a decrease in electrode peeling force.

[0126] Compared to Comparative Example 1, the structural change of the PAA-type negative electrode binder in Comparative Example 2 resulted in a significant increase in the fully charged expansion rate and a decrease in the electrode peel force. This is because the PAA-type negative electrode binder in Comparative Example 1 has a higher content of strongly polar side groups, resulting in higher cohesive strength. The prepared negative electrode exhibits excellent cohesion, low rebound, and a higher molecular weight, thus possessing higher adhesive strength. Comparative Example 3 altered the structure of the SBR-type negative electrode binder, but various test data showed no significant difference compared to Comparative Example 1. In Comparative Example 4, the ratio of PAA-type negative electrode binder to SBR-type negative electrode binder was changed from 2:1 to 1:1. This resulted in a decrease in the electrode peel force and an increase in the fully charged expansion rate. This is because the reduced content of PAA-type negative electrode binder led to poorer adhesion, and the decreased cohesive strength resulted in a reduced ability to suppress fully charged expansion.

[0127] Comparing Comparative Example 1 and Example 1, the negative electrode binder in Example 1 contains more electrolyte-loving components and has a higher swelling rate (50%), while the SBR-based binder in the Comparative Example has a swelling rate of 52%, which is comparable. However, the gaps formed by the polyethylene glycol (PEG) segments in the functional branches of the negative electrode binder in Example 1 are beneficial for electrolyte wetting, resulting in better electrolyte wetting of the negative electrode sheet in Example 1. Furthermore, the negative electrode binder in Example 1 has more grafted polar functional groups, leading to higher adhesion between the binder and the silicon particles. The reversible crosslinking points of the borate ester bonds (-BO-) in the negative electrode binder in Example 1 can dynamically break / reassemble during charging and discharging, buffering volume change stress and significantly reducing the fully charged expansion rate of the electrode sheet. The negative electrode binder in Example 1 also has better flexibility, allowing for better position adjustment during electrode winding deformation and reducing the likelihood of localized cracking.

[0128] Table 2 DC internal resistance test data As shown in Table 2, compared to Example 1, the internal resistance of Example 2 is almost the same as that of Example 1. The internal resistance of Example 3 is greater because the excessively long functionalized branches lead to a decrease in mechanical properties. This decrease in the mechanical properties of the binder weakens its ability to maintain electrical contact between the active material and the current collector, resulting in an interruption of the conductive network. This not only affects electron transport efficiency but also increases the battery's internal resistance. The internal resistance of Example 4 is significantly greater because the over-crosslinked binder may form an excessively dense network structure, which restricts electrolyte penetration and ion transport, thereby increasing interfacial impedance. Furthermore, excessive crosslinking also affects the contact between the binder and the active material, leading to a decrease in electronic conductivity and thus increasing the cell's internal resistance.

[0129] Compared to Comparative Example 1, the internal resistance of Comparative Examples 2 and 3 increased slightly. The internal resistance of Comparative Example 4 increased significantly because the SBR in Comparative Example 1 was grafted with polycarboxylic acid groups, amides and other polar functional groups, which comprehensively improved adhesion and reduced internal resistance. In contrast, Comparative Examples 2 and 3 had different SBR structures, while the SBR content in Comparative Example 4 was reduced.

[0130] Comparative Example 1 and Example 1 are compared. In Example 1, the flexible butadiene (BR) chain segment of the core of the negative electrode binder is doped with polyethylene oxide (PEO) side chains (to improve the lithium-ion transport rate); the functionalized side chains are grafted with polyethylene glycol (PEG), and the PEG chain segments form lithium-ion transport channels (similar to the "solid electrolyte" effect), which reduces the obstruction to lithium-ion permeability.

[0131] Table 3. Cyclic Test Data As shown in Table 3, the cycle life of Example 2 is significantly shorter than that of Example 1 because reducing the content of SEI film-forming additives leads to a decrease in the stability of the SEI film. A stable SEI film is crucial for improving the electrochemical performance of silicon-based anodes, including cycle stability and capacity retention, so the extent to which battery life is extended is reduced. The cycle life of Example 3 is significantly shorter because excessively long functional branches lead to a decrease in the mechanical properties of the binder, which cannot effectively suppress the volume expansion of the silicon anode, ultimately resulting in a significant reduction in the battery's cycle life. The cycle life of Example 4 is significantly worse because moderate crosslinking helps maintain the structural integrity of the silicon anode and improves the cycle stability of the battery; however, excessive crosslinking may limit the interaction between the binder and silicon particles, leading to more cracks and detachment of the electrode during cycling, thereby reducing the battery's capacity retention and life. The cycle lives of the comparative examples are almost equivalent.

[0132] Compared with Comparative Example 1, Example 1 introduced SEI film-forming additive fluorinated styrene into the negative electrode binder to optimize the interface, which made the binder-electrolyte synergistic, improved the wettability of the negative electrode sheet and the electrolyte, and helped to reduce the internal resistance of the cell. At the same time, the adhesion between the negative electrode sheet and the separator in the entire core package increased, which is more conducive to improving the problem of electrode misalignment during cycling and improving cycle performance.

[0133] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0134] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the aforementioned specific details.

[0135] In the foregoing description of this specification, references to terms such as "one embodiment," "another embodiment," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples. Additionally, it should be noted that in this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features.

[0136] 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 of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A negative electrode binder characterized by, include: The core, wherein the polymer monomers of the core include styrene, butadiene, and heterocyclic compounds; An ion-conducting network, comprising branches and a dynamically cross-linked network, wherein the dynamically cross-linked network is a cross-linked structure obtained by coordination reaction between the branches and metal ions, the branches comprising carboxylic acid-terminated polyethylene glycol and borate ester-terminated polyethylene glycol, and the metal ions comprising Ca... 2+ Zn 2+ Mg 2+ One or more of the following; The ion-conducting network is grafted onto the core.

2. The negative electrode binder according to claim 1, characterized by, One end of the branch is connected to the kernel, and the other end is a free end; And / or, the molecular weight of the branched chain is 450 Da to 550 Da; And / or, the sum of the degree of polymerization of ethylene glycol in the carboxylic acid-terminated polyethylene glycol and the degree of polymerization of ethylene glycol in the borate ester-terminated polyethylene glycol is 30 to 40; And / or, the molar ratio of the borate-terminated polyethylene glycol to the carbon atoms in the core is (1~2):

100.

3. The negative electrode binder according to claim 1, wherein The heterocyclic compound includes one or more of ethylene oxide, thiophene, and aniline; And / or, the molar ratio of the styrene, the butadiene, and the heterocyclic compound is 1:(2.5~3.5):(0.4~0.5); And / or, the degree of polymerization of the styrene is 80 to 120.

4. The negative electrode binder according to claim 1, characterized in that, The polymer monomers in the core also include fluorinated monomers.

5. A method for preparing the negative electrode binder according to any one of claims 1 to 4, characterized in that, Includes the following steps: a) Styrene copolymer, butadiene, heterocyclic compound, first initiator and first solvent are mixed and heated to carry out polymerization reaction to obtain block copolymer; b) The block copolymer obtained in step a) is mixed with m-chloroperoxybenzoic acid and subjected to an epoxidation reaction. Then, a carboxyl-terminated heterocyclic compound and a first catalyst are added and a grafting reaction is carried out to obtain a carboxylic acid-terminated polyethylene glycol graft copolymer. c) Trimethyl borate, the second catalyst, the second solvent, and the carboxylic acid-terminated polyethylene glycol graft copolymer obtained in step b) are mixed and subjected to a crosslinking reaction. Then, a metal salt solution is added to carry out a coordination reaction to obtain a crosslinked polymer. After purification, a negative electrode binder is obtained.

6. The preparation method according to claim 5, characterized in that, The method for preparing the styrene copolymer described in step a) Includes the following steps: A third solvent, styrene, RAFT reagent, second initiator, and p-fluorostyrene are added to a reaction vessel and heated to the reaction temperature to obtain a styrene copolymer. Wherein: the mass ratio of the styrene, the RAFT reagent, the second initiator, and the p-fluorostyrene is (8~12):(0.1~0.2):(0.01~0.02):(0.3~0.8); and / or, the reaction atmosphere is an inert atmosphere, the inert atmosphere including one or more of nitrogen and helium; and / or, the reaction temperature is 70℃~80℃; and / or, the reaction time is 6h~8h; and / or, the third solvent includes one or more of toluene, xylene, and dichloromethane; and / or, the RAFT reagent includes one or more of 2-cyano-2-propylbenzodisulfide, 2-(dodecyltrithiocarbonyl)-2-methylpropionic acid, and 4-cyano-4-(phenylthiocarboxylthio)valerate; and / or, the second initiator includes one or more of AIBN, BPO, and CHP.

7. The preparation method according to claim 5, characterized in that, It satisfies at least one of the following features (1) to (6): (1) By weight, each component includes: 24-36 parts butadiene, 4-5 parts heterocyclic compound, 0.005-0.01 parts first initiator, 50-70 parts first solvent, 4-6 parts m-chloroperoxybenzoic acid, 8-12 parts carboxyl-terminated heterocyclic compound, 0.1-0.3 parts first catalyst, 1-2 parts trimethyl borate, 0.05-0.1 parts second catalyst, and 0.1-0.2 parts metal salt solution; (2) The first initiator includes one or more of AIBN, BPO, and CHP; (3) The first solvent includes one or more of tetrahydrofuran, N-methylpyrrolidone, and diethyl ether; (4) The second solvent includes one or more of N,N-dimethylformamide and water; (5) The first catalyst comprises one or more of boron trifluoride diethyl ether, boron trichloride, and boron tribromide; (6) The second catalyst includes one or more of p-toluenesulfonic acid, methanesulfonic acid, and benzenesulfonic acid.

8. The preparation method according to claim 5, characterized in that, It satisfies at least one of the following features (1) to (7): (1) The polymerization reaction temperature is 60℃~65℃, and the polymerization reaction time is 12h~15h; (2) The temperature of the epoxidation reaction is 22℃~28℃, and the time of the epoxidation reaction is 4h~5h; (3) The temperature of the grafting reaction is 60℃~65℃, and the time of the grafting reaction is 8h~10h; (4) The grafting reaction is followed by the following operation: dialysis with carbon monoxide with a molecular weight of 10 kDa to remove unreacted carboxyl-terminated heterocyclic compounds; (5) The temperature of the cross-linking reaction is 80℃~85℃, and the time of the cross-linking reaction is 4h~6h; (6) The specific operation of the coordination reaction is as follows: stir for 2-3 hours and then remove free metal ions by ultrafiltration; (7) The specific purification operation is as follows: the cross-linked polymer is dropped into ice-cold methanol, and after a white fibrous solid is precipitated, it is dried in a vacuum oven at 40℃~50℃ for 24h~30h.

9. A negative electrode sheet, characterized in that, The present invention includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector along the thickness direction. The negative electrode active material layer includes a silicon negative electrode material and a binder. The binder includes the negative electrode binder according to any one of claims 1 to 4 or the negative electrode binder prepared by the preparation method according to any one of claims 5 to 8.

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

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