Binder, preparation method thereof, composite material using binder and lithium battery

Abstract

The invention provides a binder and a preparation method thereof, and a composite material and a lithium battery using the binder. The binder comprises a block copolymer, the block copolymer comprises a first block, a second block and a third block which respectively contain monomer units with structures shown as formulas I, II and III, the first block provides a rigid framework, and the second block and the third block jointly provide a flexible network. The rigid framework of the first block and the flexible network of the second block / the third block form a synergistic structure, so that the binder has high binding power, the binder can adapt to the volume change of the electrode material in the circulation process, the electrode material is prevented from falling off, and the service life of the electrode material is prolonged. And a three-dimensional conductive network formed by the second block serving as a conductive-like unit in the block copolymer and the third block enables an active material to be in more sufficient contact with a conductive agent, an electron transfer channel is shortened, and the overall conductivity of the binder is enhanced, so that the rate capability and the cycling stability of the lithium battery applying the binder are improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a binder and its preparation method, a composite material using the binder, and a lithium battery. Background Technology

[0002] Lithium-ion batteries are widely used in electric vehicles, energy storage systems, and consumer electronics due to their high energy density, long cycle life, and good safety. In the structure of a lithium-ion battery, the electrode sheet is the direct site of electrochemical reactions, and its structural stability and conductivity directly determine the overall performance of the battery, especially its rate performance and cycle life. In lithium-ion batteries, the performance of the electrode sheet depends not only on the type and content of the active materials but also closely on the performance of its binder and conductive agent. The binder, as a key auxiliary material that adheres the active materials, conductive agents, and other components to the current collector in the electrode sheet, is of paramount importance in terms of its performance.

[0003] Traditional electrode sheets typically consist of three parts: active material, conductive agent, and binder, each performing a different function. However, this separate structural design presents numerous problems in practical applications. For example, the manufacturing process is complex. The binder is primarily responsible for firmly adhering the active material to the current collector, while the conductive agent is used to improve the conductivity of the electrode sheet. The separation of functions between the binder and the conductive agent leads to a complex electrode sheet structure, cumbersome manufacturing process, and susceptibility to interface problems affecting overall performance. Furthermore, the lack of synergy between the binder and the conductive agent, and poor interfacial contact, can result in insufficient contact between the active material and the conductive agent, thus affecting the rate performance and cycle stability of lithium batteries.

[0004] Currently, commonly used binders in lithium-ion battery electrode sheets include polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). However, these binders present several problems in practical applications, such as insufficient bonding strength, high electrolyte swelling ratio, and weak interaction with the active material. This leads to easy detachment of the electrode material during charge and discharge, affecting the cycle performance and safety of the lithium-ion battery. Therefore, developing a novel material system that can simultaneously achieve bonding and conductivity, while ensuring bonding strength and promoting electron and ion transport, is a current research focus. Summary of the Invention

[0005] To address the issues of insufficient synergy between existing binders and conductive agents, as well as inadequate bonding strength, which negatively impact the rate performance and cycle stability of lithium batteries, this invention provides a binder, its preparation method, a composite material using the binder, and a lithium battery.

[0006] According to a first aspect of the invention, an adhesive is provided comprising a block copolymer, the block copolymer comprising a first block, a second block, and a third block; The first block includes a single unit with a structure as shown in Formula I; Formula I; In Formula I, R1 and R2 are independently selected from one of -H, -OH, alkyl, or any substituted alkyl; The second block includes a single unit with a structure as shown in Formula II; Formula II; In Formula II, R3 and R4 are independently selected from one of -H, -OH, alkyl, or any substituted alkyl, and R5 is selected from phenyl or any substituted phenyl. The third block includes a single unit with a structure as shown in Formula III; Formula III; In Formula III, R6 and R7 are independently selected from -H, -OH, alkyl, and any substituted alkyl.

[0007] The binder provided by this invention comprises a block copolymer, which includes a first block, a second block, and a third block. The first block, containing monomer units with the structure shown in Formula I, provides a rigid framework in the block copolymer. The second block, containing monomer units with the structure shown in Formula II, and the third block, containing monomer units with the structure shown in Formula III, together provide a flexible network in the block copolymer. The rigid framework of the first block and the flexible network of the second / third block form a synergistic structure, which not only ensures that the binder has strong adhesion, but also enables the binder to adapt to the volume changes of the electrode material during cycling, preventing the electrode material from falling off. Furthermore, the second block, as a quasi-conductive unit in the block copolymer, forms a three-dimensional conductive network with the third block, which allows for more sufficient contact between the active material and the conductive agent, shortens the electron transfer channel, and enhances the overall conductivity of the binder, thereby improving the rate performance and cycle stability of lithium batteries using this binder.

[0008] Preferably, the mass ratio of the first segment, the second segment, the third segment is (15~35):(5~15):(3~12).

[0009] Preferably, the first block comprises a single-unit structure as shown in Formula IV; Formula IV.

[0010] Preferably, the second block comprises a monomer unit with a structure as shown in Formula V; Formula V.

[0011] Preferably, the third block comprises a single-unit structure as shown in Formula VI; Formula VI.

[0012] According to a second aspect of the present invention, a method for preparing an adhesive is provided, comprising the following steps: S1. Mix the first monomer, the second monomer, the chain transfer agent, and the first initiator, and prepolymerize the first monomer and the second monomer to obtain a prepolymer; S2. Add a third monomer and an anionic initiator to the prepolymer and polymerize the prepolymer with the third monomer to obtain an adhesive, wherein the adhesive includes a block copolymer; The block copolymer includes a first block, a second block, and a third block, wherein the first block is formed by a first monomer, the second block is formed by a second monomer, and the third block is formed by a third monomer; The structure of the first monomer is shown in Formula I, the structure of the second monomer is shown in Formula II, and the structure of the third monomer is shown in Formula III. Formula I; In Formula I, R1 and R2 are independently selected from one of -H, -OH, alkyl, or any substituted alkyl; Formula II; In Formula II, R3 and R4 are independently selected from one of -H, -OH, alkyl, or any substituted alkyl, and R5 is selected from phenyl or any substituted phenyl. Formula III; In Formula III, R6 and R7 are independently selected from -H, -OH, alkyl, and any substituted alkyl.

[0013] The binder provided in this solution is prepared by first prepolymerizing a first monomer (structure shown in Formula I) and a second monomer (structure shown in Formula II) under the action of a chain transfer agent and a first initiator. Then, the resulting prepolymer is polymerized with a third monomer (structure shown in Formula III) under the action of an anionic initiator. The above preparation method, through a stepwise polymerization process, ensures the formation of an ordered structure of the block copolymer, avoids hydrogen bond competition and phase separation problems caused by simple physical mixing, and enables the first, second, and third monomers to form an interpenetrating network structure. This results in a binder that has both good bonding performance and can well adapt to the volume changes of the electrode material during cycling, while also having good conductivity. Therefore, the binder prepared by the method provided in this solution can achieve the integration of bonding and conductivity.

[0014] Preferably, in S1, the reaction temperature used in the prepolymerization process is 50~80℃ and the reaction time is 3~6 hours. Preferably, in S2, the reaction temperature used in the polymerization process is 40~80℃ and the reaction time is 10~20 hours.

[0015] Preferably, the structure of the first monomer is as shown in Formula IV; Formula IV.

[0016] Preferably, the structure of the second monomer is as shown in Formula V. Formula V.

[0017] Preferably, the structure of the third monomer is as shown in Formula VI; Formula VI.

[0018] Preferably, the mass ratio of the first monomer, the second monomer, and the third monomer is (10~12):(1~2):(2~2.5).

[0019] Preferably, in S1, the chain transfer agent includes a RAFT reagent, and the first initiator includes at least one of azobisisobutyronitrile and azobisisoheptanenitrile.

[0020] Preferably, in S2, the anionic initiator includes a potassium alkoxide, and the methanol salt includes at least one of potassium tert-butoxide and potassium isopropoxide.

[0021] According to a third aspect of the present invention, a composite material is provided, which is prepared by the following steps: S1. Mix the above-mentioned binder or the binder prepared by the above preparation method with graphene (GO) suspension and aniline solution to obtain a mixture; S2. Add a second initiator to the mixture and allow aniline to polymerize to obtain a composite material.

[0022] The binder provided by this invention is mixed with graphene suspension and aniline solution. A second initiator is then added to the resulting mixture to induce polymerization of aniline. During this process, the benzimidazole group in the second block of the binder (block copolymer) contains an electron-rich aromatic heterocycle, i.e., a π-conjugated ring. The graphene bulk is a giant sp... 2In a hybrid carbon plane, the benzimidazole ring in the second block of the block copolymer is adsorbed onto the graphene plane through π-π stacking interactions. The resulting composite material, under the action of a second initiator, chemically bonds with functional groups (such as carboxyl groups and epoxy groups) on the graphene surface through nucleophilic substitution. Through in-situ polymerization, aniline forms a conductive polymer, thus producing a composite material. This composite material utilizes the synergistic structure of the binder and the conductive properties of graphene to further construct a continuous conductive network. The binder and conductive agent (graphene and polyaniline) form an integrated material, which is the composite material of this scheme. This composite material can simultaneously achieve bonding and conductivity functions, and can promote the transport of electrons and ions while ensuring bonding strength.

[0023] Preferably, in S1, the mass ratio of graphene suspension to binder is 1:1~3.

[0024] Preferably, in S2, the polymerization conditions are as follows: reaction temperature 30~40℃, reaction time 4~8 hours.

[0025] Preferably, in S2, the second initiator includes at least one of ammonium persulfate, potassium persulfate, and sodium persulfate.

[0026] According to a fourth aspect of the present invention, a lithium battery is provided, the lithium battery comprising a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer comprising the aforementioned composite material.

[0027] The lithium battery provided by this solution uses the aforementioned composite material as the positive electrode active material layer component. By utilizing the integrated bonding and conductive function of the composite material, the rate performance and cycle life of the electrode can be significantly improved, while simplifying the slurry preparation process and reducing the interfacial impedance.

[0028] Preferably, the mass percentage of the composite material in the positive electrode active material layer is 3-6%.

[0029] Preferably, the positive electrode active material layer further includes a positive electrode active material, which includes at least one of lithium iron phosphate and lithium manganese iron phosphate. Detailed Implementation

[0030] The technical features of the technical solution provided by the present invention will be further clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] To address the issues of insufficient synergy between existing binders and conductive agents, as well as inadequate bonding strength, which negatively impact the rate performance and cycle stability of lithium batteries, this invention provides a binder, its preparation method, a composite material using the binder, and a lithium battery.

[0032] According to a first aspect of the invention, an adhesive is provided comprising a block copolymer, the block copolymer comprising a first block, a second block, and a third block; The first block includes a single unit with a structure as shown in Formula I; Formula I; In Formula I, R1 and R2 are independently selected from one of -H, -OH, alkyl, or any substituted alkyl; The second block includes a single unit with a structure as shown in Formula II; Formula II; In Formula II, R3 and R4 are independently selected from one of -H, -OH, alkyl, or any substituted alkyl, and R5 is selected from phenyl or any substituted phenyl. The third block includes a single unit with a structure as shown in Formula III; Formula III; In Formula III, R6 and R7 are independently selected from -H, -OH, alkyl, and any substituted alkyl.

[0033] The binder provided by this invention comprises a block copolymer, which includes a first block, a second block, and a third block. The first block, containing monomer units with the structure shown in Formula I, provides a rigid framework in the block copolymer. The second block, containing monomer units with the structure shown in Formula II, and the third block, containing monomer units with the structure shown in Formula III, together provide a flexible network in the block copolymer. The rigid framework of the first block and the flexible network of the second / third block form a synergistic structure, which not only ensures that the binder has strong adhesion, but also enables the binder to adapt to the volume changes of the electrode material during cycling, preventing the electrode material from falling off. Furthermore, the second block, as a quasi-conductive unit in the block copolymer, forms a three-dimensional conductive network with the third block, which allows for more sufficient contact between the active material and the conductive agent, shortens the electron transfer channel, and enhances the overall conductivity of the binder, thereby improving the rate performance and cycle stability of lithium batteries using this binder.

[0034] Preferably, the mass ratio of the first segment, the second segment, the third segment is (15~35):(5~15):(3~12).

[0035] By optimizing the mass ratio of the first block, the second block, the third block, and the fourth block to ensure that the mass ratio of each block meets the above range, the rigidity, flexibility, and conductivity of the binder can be effectively balanced, enabling the binder to better adapt to the volume changes of the electrode material during cycling and further improving the conductivity of the binder.

[0036] Preferably, the first block comprises a single-unit structure as shown in Formula IV; Formula IV.

[0037] Preferably, the second block comprises a monomer unit with a structure as shown in Formula V; Formula V.

[0038] Preferably, the third block comprises a single-unit structure as shown in Formula VI; Formula VI.

[0039] In the binder provided in this solution, the block copolymer employs a first block containing monomer units as shown in Formula IV, a second block containing monomer units as shown in Formula V, and a third block containing monomer units as shown in Formula VI. Firstly, the first block forms a stable hydrogen bond network with the nitrogen atom on the benzimidazole ring of the second block and the ether bond (-O-) of the third block through its carboxyl group (-COOH). This reduces the risk of bonding failure due to volume expansion and contraction of the electrode material during lithium battery cycling. Secondly, the carboxyl group (-COOH) in the first block can form hydrogen bonds with the electrode material and the conductive agent, and the three-dimensional network structure formed by the second and third blocks ensures... The contact between the conductive material and the conductive agent is more complete, which improves the bonding force between the binder and the electrode material and the conductive agent, and reduces the risk of the electrode material and the conductive agent falling off during the lithium battery cycle. Thirdly, the benzimidazole group of the second block has the ability to chelate or coordinate metal ions, which can coordinate lithium ions (derived from lithium salt) in the electrolyte of the lithium battery. In addition, due to the strong negative charge, the electron cloud enriched on the benzimidazole ring of the second block can also attract and bind positively charged lithium ions through ion-dipole interaction. The first block forms an ion coordination network through the carboxyl group (-COOH) in it and the metal ions coordinated by the second block, and then interacts with the hydrogen bonds in the third block to form a stable hydrogen bond network. Therefore, this scheme uses specific monomer units (Formulas IV, V, and VI) to form block copolymers as binders, which can further enhance the hydrogen bond network and ion coordination, strengthen the interfacial bonding between the block copolymers and active materials and conductive agents, improve the compatibility of the binder and the stability of the hydrogen bond network structure, and avoid the problems of unstable hydrogen bond network structure caused by competition between hydrogen bonds in monomer units with structures as shown in Formula IV and those with structures as shown in Formula VI during the physical mixing process, and the poor compatibility between monomer units with structures as shown in Formula V and those with structures as shown in Formula IV / VI, leading to phase separation rather than interpenetrating networks, thus reducing the performance of the resulting binder.

[0040] According to a second aspect of the present invention, a method for preparing an adhesive is provided, comprising the following steps: S1. Mix the first monomer, the second monomer, the chain transfer agent, and the first initiator, and prepolymerize the first monomer and the second monomer to obtain a prepolymer; S2. Add a third monomer and an anionic initiator to the prepolymer and polymerize the prepolymer with the third monomer to obtain an adhesive, wherein the adhesive includes a block copolymer; The block copolymer includes a first block, a second block, and a third block, wherein the first block is formed by a first monomer, the second block is formed by a second monomer, and the third block is formed by a third monomer; The structure of the first monomer is shown in Formula I, the structure of the second monomer is shown in Formula II, and the structure of the third monomer is shown in Formula III. Formula I; In Formula I, R1 and R2 are independently selected from one of -H, -OH, alkyl, or any substituted alkyl; Formula II; In Formula II, R3 and R4 are independently selected from one of -H, -OH, alkyl, or any substituted alkyl, and R5 is selected from phenyl or any substituted phenyl. Formula III; In Formula III, R6 and R7 are independently selected from -H, -OH, alkyl, and any substituted alkyl.

[0041] The binder provided in this solution is prepared by first prepolymerizing a first monomer (structure shown in Formula I) and a second monomer (structure shown in Formula II) under the action of a chain transfer agent and a first initiator. Then, the resulting prepolymer is polymerized with a third monomer (structure shown in Formula III) under the action of an anionic initiator. The above preparation method, through a stepwise polymerization process, ensures the formation of an ordered structure of the block copolymer, avoids hydrogen bond competition and phase separation problems caused by simple physical mixing, and enables the first, second, and third monomers to form an interpenetrating network structure. This results in a binder that has both good bonding performance and can well adapt to the volume changes of the electrode material during cycling, while also having good conductivity. Therefore, the binder prepared by the method provided in this solution can achieve the integration of bonding and conductivity.

[0042] Preferably, in S1, the reaction temperature used in the prepolymerization process is 50~80℃ and the reaction time is 3~6 hours. Preferably, in S2, the reaction temperature used in the polymerization process is 40~80℃ and the reaction time is 10~20 hours.

[0043] By controlling the prepolymerization reaction temperature and time of the first and second monomers, as well as the polymerization reaction temperature of the prepolymer formed by the prepolymerization of the first and second monomers with the third monomer, within the above range, the molecular chain structure and molecular weight of the final block copolymer can be optimized, ensuring effective linkage between the blocks in the block copolymer and forming a stable three-dimensional network structure, thereby improving the uniformity and performance consistency of the binder.

[0044] Preferably, the structure of the first monomer is as shown in Formula IV; Formula IV.

[0045] Preferably, the structure of the second monomer is as shown in Formula V. Formula V.

[0046] Preferably, the structure of the third monomer is as shown in Formula VI; Formula VI.

[0047] This scheme uses a first monomer with the structure shown in Formula IV, a second monomer with the structure shown in Formula V, and a third monomer with the structure shown in Formula VI as monomer raw materials to prepare a block copolymer, which is then used as a binder. Firstly, the carboxyl group (-COOH) in the first monomer can form a stable hydrogen bond network with the nitrogen atom on the benzimidazole ring of the second monomer and the ether bond (-O-) of the third monomer, reducing the risk of bonding failure due to volume expansion and contraction of the electrode material during lithium battery cycling. Secondly, the hydroxyl group in the first monomer can form extremely strong hydrogen bonds with conductive agents and hydroxyl groups on the surface of the electrode material, and its synergistic effect with the three-dimensional network structure of the second monomer... This approach allows for more thorough contact between the active material and the conductive agent, improving the bonding force between the binder and the conductive agent / electrode material. It also reduces the risk of detachment of the electrode material and conductive agent during lithium battery cycling. Thirdly, the benzimidazole ring of the second monomer has the ability to chelate or coordinate metal ions, enabling it to coordinate lithium ions in the electrolyte of the lithium battery. Furthermore, due to its strong negative charge, the electron cloud enriched on the benzimidazole ring of the second monomer can attract and bind positively charged lithium ions through ion-dipole interactions. The first monomer forms an ion coordination network through its carboxyl groups and the metal ions coordinated to the second block, which then interacts with the hydrogen bonds in the third block to form a stable hydrogen bond network. Therefore, this scheme uses block copolymers prepared with specific monomers (Formulas IV, V, and VI) as binders, which can further enhance the hydrogen bond network and ion coordination, improving the bonding force between the binder and the active material / conductive agent. Simultaneously, it improves the compatibility and hydrogen bond network structure stability of the binder, giving it superior bonding and conductivity properties.

[0048] Preferably, the mass ratio of the first monomer, the second monomer, and the third monomer is (10~12):(1~2):(2~2.5).

[0049] Preferably, in S1, the chain transfer agent includes a RAFT reagent, and the first initiator includes at least one of azobisisobutyronitrile and azobisisoheptanenitrile.

[0050] Preferably, in S2, the anionic initiator includes a potassium alkoxide, and the methanol salt includes at least one of potassium tert-butoxide and potassium isopropoxide.

[0051] In the preparation of block copolymers, the mass ratio of the first monomer, the second monomer, and the third monomer is controlled within the above-mentioned range. At the same time, the use of specific chain transfer agents and initiators can promote the controllable synthesis of block copolymers, so that each monomer can better form block copolymers with interpenetrating network structures through prepolymerization and polymerization reactions. This enhances the formation of three-dimensional network structures, improves the conductivity and mechanical strength of the binder, and the block copolymer can be used as a binder to simultaneously take into account its structural strength, conductivity, and toughness.

[0052] According to a third aspect of the present invention, a composite material is provided, which is prepared by the following steps: S1. Mix the above-mentioned binder or the binder prepared by the above preparation method with graphene (GO) suspension and aniline solution to obtain a mixture; S2. Add a second initiator to the mixture and allow aniline to polymerize to obtain a composite material.

[0053] The binder provided by this invention is mixed with graphene suspension and aniline solution. A second initiator is then added to the resulting mixture to induce polymerization of aniline. During this process, the benzimidazole group in the second block of the binder (block copolymer) contains an electron-rich aromatic heterocycle, i.e., a π-conjugated ring. The graphene bulk is a giant sp... 2 In a hybrid carbon plane, the benzimidazole ring in the second block of the block copolymer is adsorbed onto the graphene plane through π-π stacking interactions. The resulting composite material, under the action of a second initiator, chemically bonds with functional groups (such as carboxyl groups and epoxy groups) on the graphene surface through nucleophilic substitution. Through in-situ polymerization, aniline forms a conductive polymer, thus producing a composite material. This composite material utilizes the synergistic structure of the binder and the conductive properties of graphene to further construct a continuous conductive network. The binder and conductive agent (graphene and polyaniline) form an integrated material, which is the composite material of this scheme. This composite material can simultaneously achieve bonding and conductivity functions, and can promote the transport of electrons and ions while ensuring bonding strength.

[0054] Preferably, in S1, the mass ratio of graphene suspension to binder is 1:1~3.

[0055] By controlling the mass ratio of graphene suspension to binder within the range of 1:1 to 1:3, the microstructure and overall performance of the composite material can be effectively optimized. This mass ratio helps ensure that the binder polymer is fully dispersed and coats the graphene sheets, thereby inhibiting the re-stabilization or agglomeration of the sheets and forming a uniform and stable composite system. Simultaneously, an appropriate amount of binder can establish a strong and continuous bonding interface between the graphene and active material particles, enhancing the overall density and mechanical stability of the electrode. This allows it to better withstand volume changes during repeated charge-discharge cycles, reducing the risk of detachment between the active material and the current collector, and providing structural assurance for long-term capacity retention. Furthermore, this ratio facilitates the construction of a continuous and stable three-dimensional conductive network, allowing the high specific surface area and excellent conductivity of graphene to be fully utilized, forming an efficient electron transport path. This promotes rapid electron and ion migration, reduces electrode polarization, and improves electrode performance under high-rate conditions. On the other hand, this ratio avoids excessive binder use, preventing the formation of an excessively thick insulating layer on the surface of the conductive components, reducing constraints on the utilization of the active material, and contributing to improving the overall specific capacity and energy efficiency of the battery.

[0056] Preferably, in S2, the polymerization conditions are as follows: reaction temperature 30~40℃, reaction time 4~8 hours.

[0057] In the in-situ polymerization of aniline, controlling the reaction temperature between 30 and 40°C and the reaction time between 4 and 8 hours achieves a good balance between reaction efficiency and product quality, thus facilitating the acquisition of composite materials with superior overall performance. These mild yet sufficient reaction conditions help maintain suitable polymerization kinetics, promoting the effective conversion of aniline monomers and the formation of polyaniline with longer molecular chains and a complete conjugated structure. The resulting polyaniline can more uniformly and stably coat the graphene surface or form ideal bridging structures between its layers, laying the foundation for constructing a continuous and robust conductive network. Simultaneously, these conditions avoid problems such as slow reaction and insufficient molecular chain growth due to excessively low temperatures, or excessively rapid reaction, localized overheating, and excessive oxidation side reactions due to excessively high temperatures. This helps reduce structural defects and control the morphology of polyaniline, making it more likely to form conductive nanofiber structures rather than amorphous aggregates. Ultimately, the composite material prepared under these preferred conditions can form a complete and efficient conductive network, thereby improving its conductivity, structural stability and electrochemical performance, and in particular helping the electrode maintain high capacity and cycle stability under high rate conditions.

[0058] Preferably, in S2, the second initiator includes at least one of ammonium persulfate, potassium persulfate, and sodium persulfate.

[0059] According to a fourth aspect of the present invention, a lithium battery is provided, the lithium battery comprising a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer comprising the aforementioned composite material.

[0060] The lithium battery provided by this solution uses the aforementioned composite material as the positive electrode active material layer component. By utilizing the integrated bonding and conductive function of the composite material, the rate performance and cycle life of the electrode can be significantly improved, while simplifying the slurry preparation process and reducing the interfacial impedance.

[0061] Preferably, the mass percentage of the composite material in the positive electrode active material layer is 3-6%.

[0062] Preferably, the positive electrode active material layer further includes a positive electrode active material, which includes at least one of lithium iron phosphate and lithium manganese iron phosphate.

[0063] By optimizing the content of composite materials in the positive electrode active material layer and selecting specific positive electrode active materials, the energy density and structural integrity of the electrode can be further improved, ensuring the stability and safety of lithium batteries under high-rate charge and discharge.

[0064] Example 1 A lithium battery is prepared by the following steps: (1) Preparation of negative electrode The prepared negative electrode active material graphite, conductive agent conductive carbon black and binder sodium carboxymethyl cellulose (CMC) were mixed in a mass ratio of 77:2:21 to obtain a mixed material. The mixed material was thoroughly stirred at high speed in deionized water to obtain a negative electrode slurry. The negative electrode slurry was coated on conventional copper foil to form a negative electrode active material layer. After drying and pressing, a negative electrode sheet was obtained. (2) Preparation of composite materials Step 1: Adhesive Preparation S1. The first monomer and the second monomer are mixed and added to the solvent dimethylformamide (DMF). RAFT reagent (trithiocarbonate chain transfer agent) and the first initiator azobisisobutyronitrile (APS) are added. The mixture is stirred at 70°C for 4 hours and then cooled to room temperature to obtain the prepolymer. S2. Add a third monomer to the prepolymer, stir for 30 minutes, add anionic initiator potassium alkoxide (KOtBu), stir and react at 50°C for 12 hours to obtain a block copolymer, centrifuge the obtained block copolymer at 8000 rpm, and dry at 60°C for 24 hours to obtain the binder. The structure of the first monomer is shown in Formula IV, the structure of the second monomer is shown in Formula V, and the structure of the third monomer is shown in Formula VI. Formula IV; Formula V; Formula VI; The mass ratio of the first monomer, the second monomer, and the third monomer is 11.25:1.5:2.25; Step 2: Preparation of composite materials S1. Weigh 10 g of natural graphite and mix it with 10 L of concentrated sulfuric acid, 20 g of potassium nitrate and 30 g of potassium permanganate in an ice bath (5°C). Then heat it at 40°C for 1.5 h and finally heat it at 90°C for 20 min to oxidize the graphite into graphene (GO). Sonicate the mixture for 60 min to disperse the GO in a solvent (NMP) to form a stable GO suspension. Dissolve 10 g of aniline monomer (AN) in 150 mL of hydrochloric acid (HCl) solution to obtain an aniline solution. Mix the above binder, GO suspension and aniline solution and sonicate for 60 min to disperse them evenly to obtain a mixed solution. The mass ratio of GO suspension to binder is 1:2; S2. Add the second initiator, ammonium persulfate, to the mixture and react at 35°C for 6 hours. Wash the resulting reaction product with deionized water and dry it in a vacuum drying oven at 60°C to obtain the composite material. (3) Preparation of positive electrode sheet Lithium iron phosphate (LFP), the composite material prepared in step (2), and N-methylpyrrolidone (NMP) were mixed in a mass ratio of 96:4:50 and dispersed at a high speed of 15000 rpm to obtain a positive electrode slurry. The positive electrode slurry was coated on a conventional aluminum foil to form a positive electrode active material layer. After drying and pressing, a positive electrode sheet was obtained. (4) Preparation of the separating membrane Porous polypropylene (PP) film is used as the separator.

[0065] (5) Preparation of electrolyte Ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 was dissolved in the organic solvent to prepare an electrolyte with a lithium salt concentration of 1 mol / L. (6) Assembly of lithium batteries The 2032 button cell was assembled in a glove box filled with Ar. The assembly sequence of the battery from top to bottom was as follows: first, the negative electrode shell, gasket, pad, negative electrode sheet, and separator were placed in sequence. Then, an appropriate amount of electrolyte was added to the separator to fully wet it. Next, the positive electrode sheet, pad, and gasket were placed in sequence. Finally, the positive electrode shell was covered and the battery was pressed and sealed using a battery sealing machine to obtain a lithium battery.

[0066] Example 2 This embodiment provides a lithium battery. Compared with embodiment 1, the difference in composition is that in the lithium battery preparation step (2), the mass ratio of the first monomer, the second monomer, and the third monomer in the preparation process of the binder is 10:2:2.5.

[0067] Apart from the differences mentioned above, the materials, formulation ratios, and preparation operations used in this embodiment are strictly consistent with those in Example 1.

[0068] Example 3 This embodiment provides a lithium battery. Compared with embodiment 1, the difference in composition is that in the lithium battery preparation step (2), the mass ratio of the first monomer, the second monomer, and the third monomer in the binder preparation process is 12:1:2.

[0069] Apart from the differences mentioned above, the materials, formulation ratios, and preparation operations used in this embodiment are strictly consistent with those in Example 1.

[0070] Example 4 This embodiment provides a lithium battery. Compared with embodiment 1, the difference in composition is that in the lithium battery preparation step (2), the mass ratio of GO suspension to binder in the preparation process of composite material is 1:1.

[0071] Apart from the differences mentioned above, the materials, formulation ratios, and preparation operations used in this embodiment are strictly consistent with those in Example 1.

[0072] Example 5 This embodiment provides a lithium battery. Compared with embodiment 1, the difference in composition is that in the lithium battery preparation step (2), the mass ratio of GO suspension to binder in the preparation process of composite material is 1:3.

[0073] Apart from the differences mentioned above, the materials, formulation ratios, and preparation operations used in this embodiment are strictly consistent with those in Example 1.

[0074] Example 6 This embodiment provides a lithium battery. Compared with embodiment 1, the difference in composition is that in the lithium battery preparation step (3), the mass ratio of positive electrode active material LFP, composite material obtained in step (2), and organic solvent NMP is 94:6:50.

[0075] Apart from the differences mentioned above, the materials, formulation ratios, and preparation operations used in this embodiment are strictly consistent with those in Example 1.

[0076] Example 7 This embodiment provides a lithium battery. Compared with embodiment 1, the difference in composition is that in the lithium battery preparation step (3), the mass ratio of positive electrode active material LFP, composite material obtained in step (2), and organic solvent NMP is 97:3:50.

[0077] Apart from the differences mentioned above, the materials, formulation ratios, and preparation operations used in this embodiment are strictly consistent with those in Example 1.

[0078] Example 8 This embodiment provides a lithium battery. Compared with embodiment 1, the difference in structure is that in the lithium battery preparation step (2), the structure of the first monomer used in the preparation process of the binder is as shown in formula VII. Formula VII.

[0079] Apart from the differences mentioned above, the materials, formulation ratios, and preparation operations used in this embodiment are strictly consistent with those in Example 1.

[0080] Example 9 This embodiment provides a lithium battery. Compared with embodiment 1, the difference in structure is that in the lithium battery preparation step (2), the structure of the first monomer used in the preparation process of the binder is as shown in formula VIII. Formula VIII.

[0081] Apart from the differences mentioned above, the materials, formulation ratios, and preparation operations used in this embodiment are strictly consistent with those in Example 1.

[0082] Example 10 This embodiment provides a lithium battery. Compared with embodiment 1, the difference in structure is that in the lithium battery preparation step (2), the structure of the third monomer used in the preparation of the binder is as shown in formula IX. Formula IX.

[0083] Apart from the differences mentioned above, the materials, formulation ratios, and preparation operations used in this embodiment are strictly consistent with those in Example 1.

[0084] Example 11 This embodiment provides a lithium battery. Compared with embodiment 1, the difference in structure is that in the lithium battery preparation step (2), the structure of the third monomer used in the preparation process of the binder is as shown in formula X. Formula X.

[0085] Apart from the differences mentioned above, the materials, formulation ratios, and preparation operations used in this embodiment are strictly consistent with those in Example 1.

[0086] Example 12 This embodiment provides a lithium battery. Compared with embodiment 1, the difference in composition is that in the lithium battery preparation step (2), the mass ratio of the first monomer, the second monomer, and the third monomer in the binder preparation process is 8:1:3.

[0087] Apart from the differences mentioned above, the materials, formulation ratios, and preparation operations used in this embodiment are strictly consistent with those in Example 1.

[0088] Example 13 This embodiment provides a lithium battery. Compared with embodiment 1, the difference in composition is that in the lithium battery preparation step (2), the mass ratio of the first monomer, the second monomer, and the third monomer in the binder preparation process is 13:3:1.

[0089] Apart from the differences mentioned above, the materials, formulation ratios, and preparation operations used in this embodiment are strictly consistent with those in Example 1.

[0090] Comparative Example 1 This comparative example provides a lithium battery. Compared with Example 1, the difference in composition is that the preparation method of the positive electrode sheet in step (3) of the lithium battery preparation is different, as follows: The positive electrode active material lithium iron phosphate (LFP), conductive agent conductive carbon black, binder polyvinylidene fluoride (PVDF), and organic solvent N-methylpyrrolidone (NMP) are mixed in a mass ratio of 93:5:2:10 and dispersed at high speed at 15000 rpm to obtain a positive electrode slurry. The positive electrode slurry is coated on conventional aluminum foil to form a positive electrode active material layer. After drying and pressing, a positive electrode sheet is obtained.

[0091] Apart from the differences mentioned above, the materials, formulation ratios, and preparation procedures used in this comparative example are strictly consistent with those in Example 1.

[0092] Test case 1. Participants This test example uses the positive electrode sheets and lithium batteries prepared in Examples 1-13 and Comparative Example 1 as test objects to conduct relevant performance tests.

[0093] 2. Test Content (1) Internal resistance The internal resistance of a lithium battery is tested using a resistance tester.

[0094] (2) Peel strength The positive electrode sheet is cut into dimensions of 20 mm wide and 100 mm long using a custom die. The coated side (i.e., the side with the positive electrode active material layer) of the cut positive electrode sheet is then pasted onto double-sided tape (3M-VHB tape), and air is removed using a rolling roller to ensure a firm bond. The free end of the positive electrode sheet is bent 90° and fixed onto the tensile testing machine fixture, while the other end is clamped to a stainless steel plate. The positive electrode active material layer is then peeled at a constant speed of 50 mm / min, and the peel strength is recorded.

[0095] (3) Capacity retention rate At 25℃, the lithium battery is charged at a constant current rate of 0.33C to 3.65 V, and then charged at a constant voltage of 3.65 V until the current I ≤ 0.05C. The resulting lithium battery charging capacity is recorded as C0. After resting for 5 min, it is discharged at a constant current rate of 0.33C to 2.0 V. After resting for 30 min, the above process is repeated 500 times to obtain the lithium battery discharge capacity, which is recorded as C1. The capacity retention rate of the 500th cycle is calculated as C1 / C0 × 100%.

[0096] 3. Experimental Results Table 1. Performance test results of positive electrode and lithium battery

[0097] The relevant performance test results of the positive electrode sheets and lithium batteries prepared in Examples 1-13 and Comparative Example 1 are shown in Table 1.

[0098] As shown in Table 1: In Comparative Example 1, the lithium battery uses traditional conductive agents and binders in the preparation of the positive electrode slurry. Compared to Comparative Example 1, the lithium batteries provided in Examples 1-13 use an integrated material (i.e., a composite material) formed by the polymerization reaction of a first monomer (structured as shown in Formula I), a second monomer (structured as shown in Formula II), and a third monomer (structured as shown in Formula III) with a binder and conductive agent in the preparation of the positive electrode slurry. Test results show that the peel strength between the current collector (aluminum foil) and the positive electrode active material layer in the positive electrode sheets prepared in Examples 1-13 is higher than that in Comparative Example 1. Furthermore, the internal resistance of the lithium batteries prepared in Examples 1-13 is lower than that in Comparative Example 1, and the capacity retention rate after 500 charge-discharge cycles is higher than that in Comparative Example 1. This is mainly due to the improved positive electrode slurry preparation process in the lithium batteries of Examples 1-13. The preparation process of the electrode uses a composite material formed by polymerizing a first monomer (as shown in Formula I), a second monomer (as shown in Formula II), and a third monomer (as shown in Formula III) with a binder and a conductive agent. The binder can increase the bonding force, effectively connect the active material and the current collector, so that the positive electrode active material layer and the current collector have high peel strength. At the same time, it can reduce the interfacial contact resistance, thereby reducing the internal resistance of the lithium battery. The flexible network structure of the binder can alleviate the volume expansion during the charging and discharging process, reduce the shedding of the active material, and thus maintain a higher capacity. Furthermore, the synergistic effect of the conductive agent (such as graphite) and the binder in the composite material can improve the electronic conductivity, reduce electrode delamination, and increase the cycle performance of the lithium battery, so that the capacity retention rate of the lithium battery is still above 94% after 500 charge-discharge cycles.

[0099] By comparing the data from Examples 1, 2, 3 and Examples 12, 13, it can be seen that the mass ratio of the first monomer, the second monomer, and the third monomer used in the binder of the composite material in the positive electrode sheet of the lithium battery affects the performance of the binder during the preparation process. It is necessary to balance the amount of the three monomers in order to make the binder have high conductivity, strong mechanical strength, and high flexibility, thereby improving the peel strength between the positive electrode active material layer and the current collector in the positive electrode sheet, reducing the resistance of the lithium battery, improving the safety performance of the lithium battery, and improving the long-term cycle stability of the lithium battery.

[0100] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention, but such modifications or substitutions are all within the scope of protection of the present invention.

Claims

1. An adhesive, characterized in that: The adhesive comprises a block copolymer, the block copolymer comprising a first block, a second block, and a third block; The first segment includes a single-unit structure as shown in Formula I; Formula I; In Formula I, R1 and R2 are independently selected from one of -H, -OH, alkyl, and any substituted alkyl; The second segment includes a single unit with a structure as shown in Formula II; Formula II; In Formula II, R3 and R4 are independently selected from one of -H, -OH, alkyl, and any substituted alkyl, and R5 is selected from phenyl or any substituted phenyl. The third segment includes a single unit with a structure as shown in Formula III; Formula III; In Formula III, R6 and R7 are independently selected from one of -H, -OH, alkyl, and any substituted alkyl.

2. The adhesive as described in claim 1, characterized in that: The mass ratio of the first segment, the second segment, the third segment is (15~35):(5~15):(3~12).

3. The adhesive as described in claim 1, characterized in that: The first segment includes a single-unit structure as shown in Formula IV; Formula IV; And / or, The second segment includes a single-unit structure as shown in Formula V; Formula V; And / or, The third segment includes a single unit with a structure as shown in Formula VI; Formula VI.

4. A method for preparing an adhesive, characterized in that, Includes the following steps: S1. Mix the first monomer, the second monomer, the chain transfer agent, and the first initiator, and prepolymerize the first monomer and the second monomer to obtain a prepolymer; S2. Add a third monomer and an anionic initiator to the prepolymer and polymerize the prepolymer with the third monomer to obtain the binder, wherein the binder comprises a block copolymer; The block copolymer includes a first block, a second block, and a third block, wherein the first block is formed by the first monomer, the second block is formed by the second monomer, and the third block is formed by the third monomer; The structure of the first monomer is shown in Formula I, the structure of the second monomer is shown in Formula II, and the structure of the third monomer is shown in Formula III. Formula I; In Formula I, R1 and R2 are independently selected from one of -H, -OH, alkyl, and any substituted alkyl; Formula II; In Formula II, R3 and R4 are independently selected from one of -H, -OH, alkyl, and any substituted alkyl, and R5 is selected from phenyl or any substituted phenyl. Formula III; In Formula III, R6 and R7 are independently selected from one of -H, -OH, alkyl, and any substituted alkyl.

5. The method for preparing the adhesive as described in claim 4, characterized in that: In step S1, the reaction temperature used in the prepolymerization process is 50-80°C, and the reaction time is 3-6 hours. And / or, In S2, the reaction temperature used in the polymerization process is 40~80℃ and the reaction time is 10~20 hours.

6. The method for preparing the adhesive as described in claim 4, characterized in that: The mass ratio of the first monomer, the second monomer, and the third monomer is (10~12):(1~2):(2~2.5).

7. A composite material, characterized in that, The composite material is prepared by the following steps: S1. The adhesive as described in any one of claims 1 to 3 or the adhesive prepared by the preparation method as described in any one of claims 4 to 6 is mixed evenly with graphene suspension and aniline solution to obtain a mixture; S2. Add a second initiator to the mixture and allow aniline to polymerize to obtain the composite material.

8. The composite material as described in claim 7, characterized in that: In S2, the polymerization reaction conditions are as follows: reaction temperature 30~40℃, reaction time 4~8 hours.

9. A lithium battery, characterized in that: The lithium battery includes a positive electrode sheet, 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, the positive active material layer including the composite material as described in claim 7.

10. The lithium battery as described in claim 9, characterized in that: The composite material accounts for 3-6% of the mass of the positive electrode active material layer. And / or, The positive electrode active material layer further includes a positive electrode active material, which includes at least one of lithium iron phosphate and lithium manganese iron phosphate.

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