Binder, positive electrode sheet, and battery

Abstract

The present application provides a kind of binder, positive plate and battery, including polymer, the polymer includes multifunctional structure unit, and at least three branched chains connected with multifunctional structure unit, branched chain includes soft segment, and hard segment connected with soft segment;The glass transition temperature of soft segment is lower than 25 DEG C;The glass transition temperature of hard segment is higher than 50 DEG C.The binder of the present application has excellent flexibility, cohesive strength and electrolyte swelling resistance, and can be adapted to lithium cobaltate, lithium iron phosphate and ternary positive active material, significantly improve the cycle and processing stability of battery.

Description

Technical Field

[0001] This application relates to the field of batteries, and more particularly to an adhesive, a positive electrode sheet, and a battery. Background Technology

[0002] Lithium-ion batteries, as rechargeable batteries with excellent performance, have gained widespread popularity across various industries due to their outstanding advantages such as high energy density, long cycle life, small size, maintenance-free operation, and environmental friendliness. They have successfully expanded from small portable electronic devices such as mobile phones and laptops to large-scale applications such as electric bicycles, electric vehicles, and energy storage systems, becoming one of the most promising mobile power sources. The core components of a lithium-ion battery include the positive electrode, negative electrode, separator, electrolyte, and battery casing. The positive electrode, as the key component for energy storage and release, is typically made with a metal current collector, and the active material is firmly attached to the metal surface using a binder. The performance of the binder directly affects the structural stability, electrochemical performance, and overall reliability of the positive electrode, making it one of the core auxiliary materials in the lithium-ion battery manufacturing process.

[0003] Currently, the binder used in commercial lithium-ion battery cathodes is mainly polyvinylidene fluoride (PVDF). Although it has good electrochemical and thermal stability, it still has obvious limitations: On the one hand, PVDF is a fluorine-containing material, which has high production costs, causes significant pollution, and has scarce raw material resources, making it difficult to use on a large scale in the long term; on the other hand, in high-nickel ternary and lithium cobalt oxide material systems, alkaline lithium salts remain on the material surface, which can easily cause PVDF to degrade by HF, resulting in slurry gelation, which seriously affects the processing technology such as batching and coating.

[0004] Currently, common fluorine-free cathode binders mainly include polyacrylonitrile, hydrogenated nitrile rubber, and polyimide, etc. However, these fluorine-free binders generally suffer from defects such as brittle and easily shed electrodes, large electrolyte swelling, high battery internal resistance, and poor kinetic performance. Furthermore, these binders are mostly linear or weakly cross-linked structures, which generally exhibit poor dispersibility, large viscosity fluctuations, and low solid content in lithium cobalt oxide, lithium iron phosphate, and ternary cathode slurries, making it difficult to balance the processing compatibility and electrochemical performance of different cathode systems.

[0005] Therefore, developing an environmentally friendly, cost-effective, and suitable cathode active materials such as lithium cobalt oxide, lithium iron phosphate, and ternary cathodes, while also possessing excellent flexibility, low electrolyte swelling, and good slurry dispersibility, has become an urgent technical problem to be solved in this field. Summary of the Invention

[0006] This invention provides a binder, a positive electrode sheet, and a battery. The binder provided by this invention effectively solves the defects of traditional fluorine-free binders, such as being hard and brittle, prone to powdering, having large electrolyte swelling, and poor slurry dispersibility. This binder has excellent flexibility, cohesive strength, and resistance to electrolyte swelling, and is compatible with positive electrode active materials such as lithium cobalt oxide, lithium iron phosphate, and ternary cathodes, significantly improving battery cycle and processing stability.

[0007] The present invention provides an adhesive comprising a polymer, the polymer comprising a multifunctional structural unit as a central backbone and at least three branches connected to the multifunctional structural unit, the branches comprising soft segments and hard segments connected to the soft segments; the glass transition temperature of the soft segments is below 25°C; and the glass transition temperature of the hard segments is above 50°C.

[0008] According to one embodiment of the present invention, the number of branches is 3 to 6.

[0009] According to one embodiment of the present invention, the end of the branch chain contains an active end group; the active end group includes a trithiocarbonate group and / or a dithioester group.

[0010] According to one embodiment of the present invention, the multifunctional structural unit includes a polyol structural unit.

[0011] According to one embodiment of the present invention, the weight-average molecular weight of the adhesive is 200,000 Da to 1,200,000 Da.

[0012] According to one embodiment of the present invention, the non-aqueous electrolyte mass swelling rate of the adhesive is 0% to 100%.

[0013] According to one embodiment of the present invention, the non-aqueous electrolyte dissolution rate of the adhesive is not higher than 5%.

[0014] According to one embodiment of the present invention, in the adhesive, the mass ratio of the soft segment to the hard segment is (20~80):(80~20).

[0015] According to one embodiment of the present invention, the hard segment includes one or more of cyano, phenyl, and carboxyl groups.

[0016] According to one embodiment of the present invention, the hard segment comprises a first (meth)acrylate structural unit and / or a vinyl structural unit; wherein the vinyl structural unit comprises an acrylonitrile structural unit and / or an aromatic vinyl structural unit.

[0017] According to one embodiment of the present invention, the soft segment includes one or more of ester, alkyl, ethoxy, methylethoxy, ethylethoxy, and butyloxy groups.

[0018] According to one embodiment of the present invention, the soft segment comprises a second (meth)acrylate structural unit.

[0019] In another aspect, the present invention provides a positive electrode sheet comprising a positive current collector and a positive active material layer located on at least one side of the positive current collector, the positive active material layer comprising a positive active material and a binder, the binder comprising the binder described above.

[0020] In another aspect, the present invention provides a battery comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the positive electrode comprises the aforementioned positive electrode.

[0021] The implementation of this invention has at least the following beneficial effects: The binder provided by this invention constructs a stable star-shaped topology through a central framework multifunctional structural unit, at least three branches connected to it, and the synergistic design of soft and hard segments, effectively solving the defects of traditional fluorine-free binders such as hardness, brittleness, easy powdering, large electrolyte swelling, and poor slurry dispersibility. This binder has excellent flexibility, cohesive strength, and resistance to electrolyte swelling, and can be adapted to positive electrode active materials such as lithium cobalt oxide, lithium iron phosphate, and ternary materials, significantly improving battery cycle and processing stability. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. The specific embodiments listed below are merely descriptions of the principles and features of this invention, and the examples given are only for explaining this invention and are not intended to limit the scope of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0023] This invention provides an adhesive comprising a polymer, the polymer comprising a multifunctional structural unit as a central backbone and at least three branches connected to the multifunctional structural unit, the branches comprising soft segments and hard segments connected to the soft segments; the glass transition temperature of the soft segments is below 25°C; and the glass transition temperature of the hard segments is above 50°C.

[0024] The adhesive provided by this invention solves the technical problems of poor stability and poor bonding effect of traditional adhesives through the synergistic design of multifunctional structural units, at least three branches, and soft and hard segments. Specifically, the multifunctional structural unit acts as the central skeleton of the polymer, enabling the branches to be firmly connected to the central skeleton, thereby constructing a radial star-shaped topology. This makes the polymer molecular chains more regularly arranged, reduces molecular entanglement, and improves the overall structural stability. At least three branches are connected to the multifunctional structural unit, and each branch functions independently. Compared with linear adhesives, this significantly increases the number of interaction sites between the adhesive and the positive electrode active material and current collector, improving the bonding uniformity. At the same time, the spatial arrangement of the star-shaped structure allows the adhesive to more uniformly coat the surface of the active material, enhancing the interfacial bonding force. The soft and hard segments contained in the branches are connected by C-C covalent bonds to form a block structure, which is synergistic and complementary.

[0025] Preferably, each of the above branches includes a soft segment and a hard segment connected to the soft segment.

[0026] In some embodiments, the connection order of the soft segment and hard segment in the above-mentioned branch can be flexibly adjusted according to actual needs: Optionally, one end of the hard segment is stably connected to the multifunctional structural unit through a CS covalent bond, and the other end of the hard segment is connected to the soft segment through a CC covalent bond, with the end of the branch retaining a trithiocarbonate group and / or a dithioester group as an active end group; or, one end of the soft segment is stably connected to the multifunctional structural unit through a CS covalent bond, and the other end of the soft segment is connected to the hard segment through a CC covalent bond, with the end of the branch retaining a trithiocarbonate group and / or a dithioester group as an active end group.

[0027] In some embodiments, each of the above-mentioned branches may include one or more soft segments and one or more hard segments, and the soft segments and hard segments may be connected in an alternating sequence to form a two-segment, three-segment, or more-segment structure.

[0028] In some embodiments, the multifunctional structural unit includes a polyol structural unit; by using a polyol structural unit as the central framework, different numbers of branches can be precisely introduced to construct a regular radial star topology, reduce molecular entanglement, improve the structural uniformity and slurry dispersibility of the binder, and adapt to large-scale industrial production.

[0029] Specifically, the aforementioned polyol structural units include one or more of the following: glycerol structural units, diglycerol structural units, triglycerol structural units, pentaerythritol structural units, trimethylolethane structural units, triethanolamine structural units, and erythritol structural units.

[0030] Specifically, in the binder provided by this invention, the soft segment has a glass transition temperature (Tg) below 25°C, remaining in a highly elastic state at room temperature and battery operating temperature. This strong molecular chain mobility enhances the binder's flexibility, ductility, and bending resistance, making it suitable for electrode cold pressing, winding, and other processing steps, reducing the risk of electrode brittleness and material loss. The hard segment has a glass transition temperature (Tg) above 50°C, maintaining a glassy state at normal battery operating temperatures. This restricted molecular chain mobility enhances the binder's cohesive strength and resistance to electrolyte swelling, reducing dissolution and excessive swelling in the electrolyte environment and maintaining long-term stability of the bonded structure. In summary, the synergistic effect of these features enables the binder to balance flexibility, bonding strength, and excellent interfacial compatibility, reducing active material shedding and providing reliable support for the stability of the subsequent positive electrode and battery. Overall, its performance surpasses that of traditional linear binders.

[0031] Specifically, the glass transition temperature (Tg) of the aforementioned soft segment is below 25°C. A Tg below 25°C helps the soft segment maintain a highly elastic state within the range of room temperature and battery operating temperature, further enhancing the flexibility and deformation resistance of the binder. This alleviates the stress caused by the volume expansion and contraction of the positive electrode active material during battery charging and discharging, reduces cracking and detachment of the active material layer, and further improves the defects of polyacrylonitrile-based fluorine-free binders, such as hardness, brittleness, and easy breakage during processing. Simultaneously, the flexibility of the soft segment reduces fatigue fracture of the binder during long-term cycling, improving the long-term service stability of the binder.

[0032] In some embodiments, the glass transition temperature of the soft segment can be -60°C to 25°C, for example, a range of -60°C, -50°C, -40°C, -30°C, -20°C, -10°C, 10°C, 20°C, 25°C, or any combination thereof. A glass transition temperature of not less than -60°C helps avoid insufficient cohesive strength and decreased adhesion caused by overly flexible molecular chains, while also preventing excessive swelling of the soft segment in the electrolyte and maintaining the stability of the bonded structure. A glass transition temperature of not more than 25°C ensures that the soft segment remains in a highly elastic state within the range of room temperature and the battery's normal operating temperature (-20°C to 60°C), allowing the molecular chains to possess excellent mobility, fully utilizing their stress-buffering function, effectively mitigating the volume expansion and contraction of the positive electrode active material during charging and discharging, improving the defects of hard, brittle, and easily cracked fluorine-free binders, and simultaneously enhancing the binder's fatigue fracture resistance and extending its long-term service life. Controlling the glass transition temperature of the soft segment within the above range helps to balance the flexibility of the adhesive with the cohesive strength of the base, and adapt to the usage requirements under different temperature conditions.

[0033] Specifically, the glass transition temperature (Tg) of the aforementioned hard segment is higher than 50°C. A Tg higher than 50°C helps the hard segment maintain its glassy state within the battery's operating temperature range, providing stable rigid support, further enhancing the bonding strength of the binder, improving the bonding stability between positive electrode active materials and between active materials and current collectors, and reducing active material shedding. Simultaneously, the hard segment effectively resists electrolyte intrusion, reduces binder swelling and dissolution, and prevents the star-shaped structure from collapsing. Furthermore, the rigidity of the hard segment also enhances the mechanical strength of the positive electrode active material layer.

[0034] In some embodiments, the glass transition temperature of the hard segment can be 50°C to 150°C, for example, a range of 50°C, 70°C, 90°C, 100°C, 130°C, 150°C, or any combination thereof. A glass transition temperature of not less than 50°C ensures that the hard segment remains in a glassy state under normal battery operating temperatures (up to approximately 60°C) and high-temperature service environments, providing stable rigid support, significantly improving the cohesive strength and resistance to electrolyte swelling of the binder, preventing the collapse of the bonded structure and electrode bulging deformation caused by hard segment softening, and reducing the dissolution and loss of the binder in the electrolyte. A glass transition temperature of not more than 150°C helps avoid the overall embrittlement of the binder and decreased processing performance caused by excessive rigidity of the hard segment, while also reducing the difficulty of controlling the polymerization reaction and preventing an excessively wide molecular weight distribution from affecting the uniformity of binder performance. Controlling the glass transition temperature of the hard segment within the above range is beneficial for balancing the structural rigidity and processing adaptability of the binder, maintaining the long-term stability of the electrode structure over a wide temperature range.

[0035] In some embodiments, the weight-average molecular weight of the binder can be from 200,000 Da to 1,200,000 Da, for example, a range consisting of 200,000 Da, 400,000 Da, 600,000 Da, 800,000 Da, 1,000,000 Da, 1,200,000 Da, or any combination thereof. A weight-average molecular weight of not less than 200,000 Da helps ensure sufficient length of the binder molecular chains, enhancing intermolecular entanglement and cohesive forces, thereby improving the binder's bonding strength and reducing the shedding of the active material layer. A weight-average molecular weight of not more than 1,200,000 Da helps avoid decreased solubility due to excessively long molecular chains, facilitating uniform dispersion of the binder in the electrode slurry and improving electrode uniformity. Controlling the weight-average molecular weight within the above range helps to balance the binder's bonding strength, dispersibility, and flexibility.

[0036] In some embodiments, the non-aqueous electrolyte swelling rate of the above-mentioned binder can be 0% to 100%, for example, a range of 0%, 20%, 40%, 60%, 80%, 100%, or any combination thereof. A swelling rate not exceeding 100% helps to effectively inhibit the excessive intrusion of electrolyte into the binder, preventing the binder molecular chains from becoming loose and entangled due to excessive swelling, thereby preventing the collapse of the star-shaped structure; at the same time, it can avoid a significant decrease in the cohesive strength of the binder, reducing problems such as active material shedding, electrode cracking, and decreased peel strength during charge-discharge cycles and high-temperature service, and maintaining the long-term stability of the electrode structure.

[0037] In some embodiments, the non-aqueous electrolyte dissolution rate of the binder is not higher than 5%. A dissolution rate of not higher than 5% helps reduce the dissolution and loss of the binder in the non-aqueous electrolyte, allowing the binder to continue to exert its bonding effect, firmly bonding the positive electrode active material and conductive agent to the current collector surface. This avoids the loosening of the electrode structure and the detachment of the active material due to binder loss, thereby reducing problems such as increased internal resistance of the electrode and decreased cycle performance, and maintaining the long-term structural integrity of the electrode.

[0038] In some embodiments, the mass ratio of the soft segment to the hard segment in the binder is (20~80):(80~20), for example, 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, 80:20, or any combination thereof. In the binder, a mass percentage of soft segment to hard segment not less than 20:80 helps to ensure sufficient flexibility of the binder, alleviating the volume expansion stress of the positive electrode active material during battery charging and discharging, and reducing cracking and detachment of the active material layer. In the binder, a mass percentage of soft segment to hard segment not greater than 80:20 helps to avoid insufficient bonding strength due to excessive binder flexibility, maintaining the cohesive strength and anti-electrolyte swelling ability of the binder, and improving the overall integrity of the positive electrode active material layer. Controlling the mass ratio within the above range is beneficial for balancing the flexibility and bonding strength of the binder, improving the cycle stability and rate performance of the battery.

[0039] In some embodiments, the hard segment comprises one or more of cyano, phenyl, and carboxyl groups. These groups help enhance the polar interaction between the binder and the positive electrode active material and current collector, improving adhesion strength and reducing the shedding of the positive electrode active material. Simultaneously, they help reduce the solubility of the binder in non-aqueous electrolytes, reducing dissolution and contributing to improved battery cycle stability and safety.

[0040] In some embodiments, the hard segment comprises one or more of a first (meth)acrylate structural unit and / or a vinyl structural unit. The structural unit contains one or more of cyano, phenyl, and carboxyl groups, which helps improve the adhesive strength and compatibility with the positive electrode active material, while also improving the flexibility of the adhesive and preventing brittleness caused by excessive rigidity of the hard segment. The inclusion of vinyl structural units in the hard segment helps improve its rigidity and polarity, enhancing its interaction with the active material and current collector. Furthermore, these structural units exhibit strong chemical stability and can remain stable in high-nickel, strongly alkaline environments, preventing hard segment degradation from causing a decrease in adhesive strength.

[0041] In some embodiments, the first (meth)acrylate structural unit comprises a first acrylate structural unit and / or a first methacrylate structural unit; the first acrylate structural unit comprises one or more of the following: phenoxyethyl acrylate structural unit, benzyl acrylate structural unit, carboxyethyl acrylate structural unit, methyl acrylate structural unit, ethyl acrylate structural unit, n-propyl acrylate structural unit, isopropyl acrylate structural unit, n-butyl acrylate structural unit, isobutyl acrylate structural unit, tert-butyl acrylate structural unit, n-pentyl acrylate structural unit, isopentyl acrylate structural unit, n-hexyl acrylate structural unit, n-octyl acrylate structural unit, isooctyl acrylate structural unit, isobornyl acrylate structural unit, phenoxyethyl acrylate structural unit, dicyclopentenyl acrylate structural unit, cyclohexyl acrylate structural unit, benzyl acrylate structural unit, hydroxyethyl acrylate structural unit, hydroxypropyl acrylate structural unit, hydroxybutyl acrylate structural unit, and polyethylene glycol monoacrylate structural unit. The benzene ring in the above structural unit can enhance the rigidity of the hard segment, and the carboxyl group can enhance the interfacial bonding force with high-nickel active materials and current collectors, thus alleviating the interfacial peeling problem caused by strong alkalinity.

[0042] In some embodiments, the first methacrylate structural unit includes one or more of the following: methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-pentyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, isooctyl methacrylate, isobornyl methacrylate, phenoxyethyl methacrylate, dicyclopentenyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, polyethylene glycol mono(methacrylate), aminoethyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, tert-butylaminoethyl methacrylate, glycidyl methacrylate, and tetrahydrofuran methacrylate.

[0043] The aforementioned vinyl-based structural units include acrylonitrile-based structural units and / or aromatic vinyl-based structural units. Acrylonitrile-based structural units help enhance the polarity of the hard segment, improve the adhesion strength between the binder and the positive electrode active material and current collector, reduce the shedding of the active material layer, and further optimize the adhesion performance. Aromatic vinyl-based structural units help improve the rigidity and glass transition temperature of the hard segment, enabling the hard segment to remain stable within the battery operating temperature range, reducing electrolyte swelling, and simultaneously enhancing the mechanical strength of the binder, thereby improving the cycle life of the battery, adapting to different types of positive electrode active materials, and improving the compatibility of the binder.

[0044] In some embodiments, the acrylonitrile structural unit includes an acrylonitrile structural unit and / or a methacrylonitrile structural unit. All of these structural units contain a highly polar cyano group (-CN). The cyano group is highly polar and can form a strong polar interaction with the hydroxyl and oxygen atoms on the surface of high-nickel cathode active materials, thereby increasing the cohesive strength and glass transition temperature of the hard segment.

[0045] In some embodiments, the aromatic vinyl structural units include one or more of the following: styrene, α-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, ethylstyrene, isopropylstyrene, butylstyrene, phenylstyrene, cyclohexylstyrene, benzylstyrene, crotonylstyrene, divinylbenzene, divinyltoluene, divinylxylene, trivinylbenzene, vinylnaphthalene, and p-tert-butylstyrene. The conjugated structure of the benzene ring in these structural units can enhance the interfacial interaction with the positive electrode active material, improve interfacial adhesion, and alleviate the interfacial delamination problem caused by strong alkalinity.

[0046] Specifically, the aforementioned first acrylate structural unit is derived from a first acrylate monomer, which includes one or more of the following: phenoxyethyl acrylate, benzyl acrylate, carboxyethyl acrylate, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-pentyl acrylate, isoamyl acrylate, n-hexyl acrylate, n-octyl acrylate, isooctyl acrylate, isobornyl acrylate, phenoxyethyl acrylate, dicyclopentenyl acrylate, cyclohexyl acrylate, benzyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, carboxyethyl acrylate, and polyethylene glycol monoacrylate.

[0047] The aforementioned first methacrylate structural unit is derived from a first methacrylate monomer, which includes one or more of the following: methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-pentyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, isooctyl methacrylate, isobornyl methacrylate, phenoxyethyl methacrylate, dicyclopentenyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, polyethylene glycol mono(methacrylate), aminoethyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, tert-butylaminoethyl methacrylate, glycidyl methacrylate, and tetrahydrofuran methacrylate.

[0048] The aforementioned acrylonitrile structural units are derived from acrylonitrile monomers, which include acrylonitrile and / or methacrylonitrile.

[0049] The aforementioned aromatic vinyl structural units are derived from aromatic vinyl groups. Aromatic vinyl monomers include one or more of styrene, α-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, ethylstyrene, isopropylstyrene, butylstyrene, phenylstyrene, cyclohexylstyrene, benzylstyrene, crotonylstyrene, divinylbenzene, divinyltoluene, divinylxylbenzene, trivinylbenzene, vinylnaphthalene, and p-tert-butylstyrene.

[0050] In some embodiments, the soft segment comprises one or more of ester groups, alkyl groups, ethoxy groups, methyl ethoxy groups, ethyl ethoxy groups, and butyl ethoxy groups. The inclusion of these groups in the soft segment helps to further improve the flexibility of the molecular chain, enhance the flexibility and deformation resistance of the binder, alleviate the stress caused by the volume expansion of the positive electrode active material, and further improve the problem of the hardness and brittleness of fluorine-free binders; it also helps to reduce the aggregation between soft segment molecules, improve the dispersibility of the binder in the electrode slurry, and solve the problem of poor dispersibility of existing fluorine-free binders; at the same time, it can also improve the compatibility of the binder with non-aqueous electrolytes, reduce the swelling of the binder by the electrolyte, and help improve the cycle stability of the battery.

[0051] In some embodiments, the total number of carbon atoms in the alkyl group is 2 to 22, for example, an integer range consisting of 2, 5, 10, 15, 20, 22, or any two of these. Having at least 2 carbon atoms avoids increased molecular chain rigidity due to excessively short alkyl chains, ensuring that the soft segments effectively improve the flexibility of the binder and alleviate the stress caused by the volume expansion of the positive electrode active material. Having at least 22 carbon atoms avoids excessively long alkyl chains leading to excessively strong intermolecular van der Waals forces and increased chain entanglement, preventing soft segment aggregation and ensuring the uniform dispersion of the binder in the electrode slurry. It also avoids the problems of decreased compatibility between the binder and the electrolyte and increased swelling rate caused by excessively long alkyl chains.

[0052] In some embodiments, the soft segment comprises a second (meth)acrylate structural unit; the second (meth)acrylate structural unit comprises a second acrylate structural unit and / or a second methacrylate structural unit. The second acrylate structural unit helps improve the flexibility of the molecular chain, enhances the binder's resistance to deformation, alleviates the volume expansion stress of the positive electrode active material, and further improves the hardness and brittleness problem of polyacrylonitrile-based fluorine-free binders; the methacrylate structural unit helps to appropriately increase the rigidity of the soft segment, avoiding insufficient bonding strength due to excessive flexibility, thus balancing flexibility and adhesion.

[0053] In some embodiments, the second acrylate structural unit includes one or more of the following: methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-pentyl acrylate, isoamyl acrylate, n-hexyl acrylate, n-octyl acrylate, isooctyl acrylate, isobornyl acrylate, phenoxyethyl acrylate, dicyclopentenyl acrylate, cyclohexyl acrylate, benzyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, and polyethylene glycol monoacrylate. These structural units help to flexibly adjust the flexibility of the soft segment, meet the volume change requirements of different positive electrode active materials, and alleviate expansion stress.

[0054] In some embodiments, the second methacrylate structural unit includes one or more of the following: methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-pentyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, isooctyl methacrylate, isobornyl methacrylate, phenoxyethyl methacrylate, dicyclopentenyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, polyethylene glycol mono(methacrylate), aminoethyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, tert-butylaminoethyl methacrylate, glycidyl methacrylate, and tetrahydrofuran methacrylate. The aforementioned unit structure helps to improve the flexibility of the soft segment while appropriately enhancing its rigidity, balancing flexibility and bonding strength, and preventing the active material from falling off due to excessive flexibility.

[0055] Furthermore, even if identical monomers are used to polymerize and form the same structural unit, the mass ratio of the structural unit in the corresponding block can be adjusted, and combined with copolymerization with other structural units, so that the block containing the structural unit meets the glass transition temperature requirements of the hard segment or the soft segment respectively. This design can realize the reuse of the same monomer in the hard segment and the soft segment, greatly simplify the procurement of raw materials, flexibly adjust the proportion of each structural unit in the block, and accurately control the balance between the flexibility and rigidity of the binder, further improving the versatility and industrial feasibility of the technical solution of this invention.

[0056] Specifically, the aforementioned second acrylates are derived from second acrylate monomers, which include one or more of the following: methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-pentyl acrylate, isoamyl acrylate, n-hexyl acrylate, n-octyl acrylate, isooctyl acrylate, isobornyl acrylate, phenoxyethyl acrylate, dicyclopentenyl acrylate, cyclohexyl acrylate, benzyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, carboxyethyl acrylate, and polyethylene glycol monoacrylate.

[0057] The aforementioned second methacrylates are derived from second methacrylate monomers, which include one or more of the following: methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-pentyl methacrylate, isopentyl methacrylate, n-hexyl methacrylate, isooctyl methacrylate, isobornyl methacrylate, phenoxyethyl methacrylate, dicyclopentenyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, polyethylene glycol mono(methacrylate), aminoethyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, tert-butylaminoethyl methacrylate, glycidyl methacrylate, and tetrahydrofuran methacrylate.

[0058] In some embodiments, the binder has 3 to 6 branches. Having at least 3 branches helps form a stable star-shaped spatial structure, improves the binder's dispersibility and its ability to encapsulate the positive electrode active material, enhances bonding strength, and reduces the risk of electrode powder shedding and detachment. Having at least 6 branches helps avoid problems such as uneven polymer chain growth and decreased dispersibility caused by excessive steric hindrance, while also avoiding the increased preparation cost and performance instability caused by too many branches. Controlling the number of branches within the range of 3 to 6 is beneficial for balancing the structural stability and bonding performance of the binder, further improving the mechanical properties of the positive electrode active material layer and the electrochemical performance of the battery, thus meeting the needs of industrial production.

[0059] In some embodiments, the ends of the aforementioned branches contain active end groups, including trithiocarbonate groups and / or dithioester groups. Further, each of the aforementioned branches contains an active end group, and the aforementioned multifunctional structural unit serves as the central backbone of the polymer, with each branch stably connected to the multifunctional structural unit via ester bonds. The active end groups gradually transfer during the controlled growth of the branches and are eventually stably retained at the branch ends. These active end groups ensure more uniform branch length and composition during growth, improving the structural uniformity of the adhesive and thus enhancing the stability of the adhesive's performance.

[0060] Correspondingly, the binder has 3 to 6 active end groups. Having 3 to 6 active end groups ensures that each branch has an active end group to regulate the uniformity of the branch structure, avoiding problems such as uneven chain length and molecular entanglement caused by some branches lacking active end groups. Furthermore, the synergistic effect of multiple active end groups further enhances the interaction between the binder and the positive electrode active material. Simultaneously, it avoids problems such as steric hindrance superposition and decreased dispersibility caused by an excessive number of active end groups, thus meeting the application requirements of high-nickel ternary cathode systems.

[0061] Preferably, the binder has 3 to 4 branches. Controlling the number of branches to 3 to 4 maximizes the balance between the stability of the star-shaped structure and the dispersibility of the polymer chains. The star-shaped structure formed by 3 to 4 branches has minimal steric hindrance, effectively preventing entanglement between branches, further improving the uniformity of binder dispersion in the electrolyte, enhancing the tightness of the coating on the positive electrode active material, and reducing electrode porosity. Simultaneously, this number of branches reduces the difficulty of controlling chain growth during preparation, minimizing branch length and composition inconsistencies, reducing preparation costs while further improving the stability of binder performance. Furthermore, the molecular size of the binder corresponding to 3 to 4 branches is more suitable for the gaps between positive electrode active material particles, better filling inter-particle voids, improving the density and mechanical strength of the positive electrode active material layer, reducing electrode expansion and powder shedding during battery cycling, significantly improving battery cycle stability and rate performance, and better meeting the consistency requirements of large-scale industrial production.

[0062] Correspondingly, the number of active end groups in the above-mentioned binder is consistent with the preferred number of side chains, that is, the number of active end groups is 3 to 4. The precise matching of 3 to 4 active end groups with 3 to 4 side chains ensures that each side chain has an active end group at its end, precisely controls the growth process of the side chains, ensures that the length and composition of each side chain are uniform, and further improves the structural uniformity and performance stability of the binder; at the same time, it avoids the steric hindrance caused by an excessive number of active end groups, ensuring that the binder molecules can be flexibly dispersed and tightly wrapped around the positive electrode active material, further extending the service life of the binder and improving the long-term electrochemical performance of the battery.

[0063] Specifically, the aforementioned active end groups originate from multifunctional chain transfer agents. Multifunctional chain transfer agents play a role in regulating free radical activity and molecular weight distribution during reversible addition-fragmentation chain transfer polymerization. Furthermore, they ensure that the polymer chain ends retain chain transfer activity after polymerization, allowing the polymer molecular weight to increase again upon the reintroduction of monomers.

[0064] For example, the above-mentioned multifunctional chain transfer agent is prepared by the following steps: adding a chain transfer agent monomer containing a carboxyl group, the above-mentioned polyol and condensing agent to a first solvent and mixing them, adding a catalyst, carrying out a condensation reaction at room temperature, and after reacting for 20 h to 28 h, obtaining a reaction solution, and filtering and washing the reaction solution to obtain the above-mentioned multifunctional chain transfer agent.

[0065] Polyols contain at least three hydroxyl groups (-OH), which can undergo condensation reactions with chain transfer agent monomers containing carboxyl groups. Through dehydration of -OH and -COOH, ester bonds (-COO-) are formed, allowing the carboxyl-containing chain transfer agent monomers to be covalently linked to the central backbone, forming a multifunctional structural unit. This multifunctional structural unit has at least three active sites, providing a stable basis for branch formation. Each active site can independently serve as the initiation site for branch growth, reacting sequentially with hard-segment and soft-segment monomers during polymerization. This allows the branches to be firmly connected to the multifunctional structural unit via CC covalent bonds, thereby constructing a radial star-shaped topology. Simultaneously, the active sites gradually transfer to the ends of the branches as they grow, transforming into stable active end groups. This structure results in a more regular arrangement of polymer molecular chains, reduces molecular entanglement, and improves overall structural stability.

[0066] The condensation reactions mentioned above include esterification reactions.

[0067] The aforementioned chain transfer agent monomers containing carboxyl groups include, but are not limited to, one or more of 4-cyano-4-[(dodecylthioalkylthiocarbonyl)thioalkyl]valeric acid, 4-cyano-4-(phenylcarbonylthio)valeric acid, 2-[[(2-carboxyethyl)thioalkylthiocarbonyl]thioalkyl]propionic acid, and 2-(dodecyltrithiocarbonate)-2-methylpropionic acid.

[0068] Specifically, the aforementioned polyols include, but are not limited to, one or more of glycerol, diglycerol, triglycerol, pentaerythritol, trimethylolethane, trimethylolpropane, triethanolamine, and erythritol. The polyol molecules contain at least three hydroxyl groups and can react with chain transfer agent monomers containing carboxyl groups to obtain a multifunctional chain transfer agent with at least three active groups, thus meeting the binder's requirement for the number of active sites on the central backbone structural unit.

[0069] Specifically, the molar ratio of the carboxyl group in the chain transfer agent monomer containing the carboxyl group to the hydroxyl group in the polyol can be (1~1.5):1, for example, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1 or any combination thereof.

[0070] Specifically, the first solvent mentioned above includes, but is not limited to, dichloromethane.

[0071] The condensing agent mentioned above can be selected from conventional reagents in the art, such as dicyclohexylcarbodiimide, and there is no particular limitation thereto.

[0072] Specifically, the molar ratio of the chain transfer agent monomer containing the carboxyl group to the condensing agent can be 1:(1~2), for example, 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, 1:2 or any combination thereof.

[0073] The catalysts described above can be selected from conventional reagents in the art, such as 4-dimethylaminopyridine, and there are no particular limitations on them.

[0074] Specifically, the molar ratio of the chain transfer agent monomer containing the carboxyl group to the catalyst can be 1:(0.05~0.2), for example, 1:0.05, 1:0.1, 1:0.13, 1:0.17, 1:0.2 or any combination thereof.

[0075] Specifically, the reaction solution is washed with an alkaline solution; the alkaline solution may be selected from one or more conventional reagents in the art, such as ammonia, sodium hydroxide solution, and lithium hydroxide solution, and there is no particular limitation thereto. The mass percentage concentration of the sodium hydroxide solution is 6% to 10%, for example, 6%, 7%, 8%, 9%, 10%, or any combination thereof; the mass percentage concentration of the lithium hydroxide solution is 6% to 10%, for example, 6%, 7%, 8%, 9%, 10%, or any combination thereof.

[0076] The adhesive provided by the present invention can be prepared by polymerization reaction; the above polymerization reaction includes one or more of the following: atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer radical polymerization (RAFT), nitrile radical controlled polymerization (NMP), and anionic polymerization.

[0077] In specific implementation, taking reversible addition-fragmentation chain transfer radical polymerization (RAFT) as an example, the binder provided by the present invention comprises the following steps:

[0078] Hard segment monomers, multifunctional chain transfer agents, initiators, and a second solvent are mixed, and nitrogen gas is introduced to completely remove oxygen before carrying out a first polymerization reaction to obtain a second reaction solution. The second reaction solution is then precipitated under the action of a precipitant, and after the precipitate is dried, the first polymer is obtained.

[0079] The first polymer, soft segment monomer, initiator, and second solvent are mixed, and nitrogen gas is introduced to completely remove oxygen before a second polymerization reaction is carried out to obtain a third reaction solution. The third reaction solution is precipitated under the action of a precipitant, and after the precipitate is dried, the above-mentioned binder is obtained.

[0080] Specifically, the molar ratio of the active end group to the initiator in the above-mentioned multifunctional chain transfer agent can be (2-8):1, for example, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1 or any combination thereof.

[0081] Specifically, the mass ratio of the multifunctional chain transfer agent to the soft segment monomer and the hard segment monomer can be adjusted according to the final molecular weight of the product. A larger amount of multifunctional chain transfer agent results in a lower molecular weight, and a smaller amount results in a higher molecular weight.

[0082] Specifically, the aforementioned initiator is used to decompose and generate free radicals, which helps to promote the initiation of the polymerization reaction, enables the branches to grow controllably at the active sites of the multifunctional structural units, and allows the branches to be covalently linked to the multifunctional structural units, ultimately forming a uniform binder.

[0083] The aforementioned initiators include oil-soluble initiators and / or water-soluble initiators.

[0084] Specifically, the oil-soluble initiators mentioned above include peroxide initiators and / or azo initiators; the peroxide initiators mentioned above can be selected from conventional reagents in the art, such as benzoyl peroxide, dilauryl peroxide, tert-amyl peroxide, tert-butyl peroxide, di(2-ethylhexyl) percarbonate, diisopropyl peroxide, diisobutyryl peroxide, tert-butyl peroxide, tert-butyl peroxyneodecanate, tert-butyl peroxynepentanoate, and tert-butyl peroxyisononanoate, without particular limitation.

[0085] Specifically, the aforementioned azo initiators may be selected from conventional reagents in the art, such as one or more of azobisisobutyronitrile, azobisisoheptanenitrile, azobisisovalerate, dimethyl 2,2'-azobis(2,4-dimethylvalerate), 2,2'-azobis(2-methylbutyronitrile), 4,4'-azobis(4-cyanopentanoic acid), and dimethyl 2,2'-azobisisobutyronitrile, without particular limitation.

[0086] Specifically, the water-soluble initiator mentioned above includes sulfate initiators; the sulfate initiator may be selected from conventional reagents in the art, such as one or more of ammonium persulfate, sodium persulfate, and potassium persulfate, without any particular limitation.

[0087] Specifically, the second solvent mentioned above includes dimethyl sulfoxide.

[0088] Specifically, the reaction temperature of the first polymerization reaction is 50℃ to 85℃, for example, a range of 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃ or any two of these; the reaction time of the first polymerization reaction is 60h to 86h, for example, a range of 60h, 65h, 70h, 75h, 80h, 86h or any two of these.

[0089] Specifically, the precipitant can be selected from conventional materials in the art, including methanol or other solvents that are incompatible with the polymer but compatible with dimethyl sulfoxide. There is no particular limitation on the amount of precipitant added, as long as it can precipitate the polymer as completely as possible.

[0090] Specifically, the reaction temperature of the second polymerization reaction is 50℃ to 85℃, for example, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃ or any two of these ranges; the reaction time of the second polymerization reaction is 60h to 86h, for example, 60h, 65h, 70h, 75h, 80h, 86h or any two of these ranges.

[0091] In summary, the binder provided by this invention constructs a stable star-shaped topology through a multifunctional structural unit central framework, at least three branches connected to the central framework, and a synergistic design of soft and hard segments. This design avoids the problems of structural instability and weak interfacial bonding of traditional binders, balancing flexibility and bonding strength, and solving the defects of existing binders being hard, brittle, and prone to powdering. By limiting the glass transition temperatures of the soft and hard segments, flexibility and structural stability are further optimized, making it suitable for high-nickel ternary cathode systems, which helps improve bonding uniformity and provides support for the structural stability of lithium-ion battery cathodes.

[0092] The present invention also provides a positive electrode sheet, including a positive current collector and a positive active material layer located on at least one side of the positive current collector, wherein the positive active material layer includes a positive active material and a binder, and the binder includes the aforementioned binder.

[0093] The binder provided by this invention generates a strong interfacial interaction with the positive electrode active material and conductive agent through polar groups, and at the same time relies on its own cohesive strength to bond the components into a whole. This is beneficial to improving the structural stability, peel strength and electrolyte resistance of the positive electrode sheet, reducing the shedding of active material in high nickel systems, and providing a foundation for stable battery operation.

[0094] In some embodiments, the above-mentioned positive electrode active material can be selected from conventional materials in the art, including lithium cobalt oxide materials, ternary materials, lithium iron phosphate materials, etc.; wherein, the above-mentioned ternary positive electrode material includes lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide. Specifically, in the above-mentioned ternary positive electrode material, the molar content of nickel can be 50 mol% to 95 mol%, for example, 50 mol%, 60 mol%, 70 mol%, 80 mol%, 90 mol%, 95 mol%, or any combination thereof. High-nickel systems place higher demands on the structural stability, alkali resistance, bonding strength, and anti-electrolyte swelling performance of the binder. Combined with the binder provided by this invention, it can better adapt to the strongly alkaline environment of the high-nickel positive electrode surface, alleviating problems such as gelation, brittleness, powdering, and decreased peel strength that are prone to occur with traditional binders in high-nickel systems. Specifically, the above-mentioned lithium nickel cobalt manganese oxide material includes LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.2 Mn 0.2 O2 (NCM822), LiNi 0.94 Co 0.05 Mn 0.01 One or more of O2 (NCM94).

[0095] This invention also provides a battery, including a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode, wherein the positive electrode includes the aforementioned positive electrode.

[0096] Specifically, a battery includes a cell and a casing that encapsulates the cell. The cell includes a positive electrode, a separator, and a negative electrode. The separator is located between the positive and negative electrodes and is used to separate the positive and negative electrodes, preventing them from short-circuiting. At the same time, the separator also allows active ions such as lithium ions to pass through, so that active ions such as lithium ions can be inserted and extracted between the positive and negative electrodes, realizing the charging and discharging process of the battery.

[0097] In this embodiment of the invention, the battery cell can be packaged using conventional housing materials in the art, such as flexible packaging materials like aluminum-plastic film, but is not limited thereto.

[0098] Specifically, the positive electrode active material layer also includes a conductive agent, which can be selected from conventional materials in the art, such as one or more of conductive carbon black (Super. P), conductive graphite, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, carbon fiber, and conductive polymer.

[0099] In this embodiment of the invention, conventional positive current collectors in the art can be used, for example, the positive current collector includes aluminum foil.

[0100] In this embodiment of the invention, the positive electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the positive electrode active material, conductive agent, binder, and other components used to form the positive electrode active material layer can be dispersed in a positive electrode solvent, such as N-methylpyrrolidone (NMP), to prepare a positive electrode slurry. This slurry is then coated onto the surface of the positive electrode current collector, and after drying, rolling, and other processes, the positive electrode sheet is obtained. The coating, drying, and rolling processes involved are conventional operations for preparing positive electrode sheets using the coating method, and are not particularly limited thereto.

[0101] In addition, the negative electrode sheet may include a metal negative electrode sheet, specifically a lithium metal negative electrode sheet (i.e., the negative electrode sheet is a lithium metal negative electrode), but is not limited thereto. In other embodiments, the negative electrode sheet may also include a negative current collector and a negative electrode coating located on at least one side surface of the negative current collector. Specifically, the negative electrode coating may be provided on one side surface of the negative current collector, or the negative electrode coating may be provided on both sides of the negative current collector in the thickness direction.

[0102] Specifically, the aforementioned negative electrode coating (negative electrode active material layer) may include materials such as negative electrode active material, conductive agent, and binder. These materials can be conventional materials in the field. For example, the negative electrode active material may include one or more of silicon-based materials, siloxy-based materials, silicon-carbon-based materials, graphite, lithium metal, and lithium-indium alloy materials. Graphite may include artificial graphite and / or natural graphite. The conductive agent may include one or more of conductive carbon black, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber. The binder may include one or more of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0103] The embodiments of the present invention may employ conventional negative electrode current collectors in the art, for example, negative electrode current collectors include copper foil.

[0104] In this embodiment of the invention, the negative electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the components used to form the negative electrode coating, such as the negative electrode active material, conductive agent, and binder, can be dispersed in a fourth solvent, such as water (specifically deionized water), to prepare a negative electrode slurry. Then, the slurry is coated on the surface of the negative electrode current collector, and after drying, rolling and other processes, the negative electrode sheet is obtained.

[0105] In this embodiment of the invention, solid-state batteries can be prepared by conventional methods in the art. The preparation process may include: assembling positive electrode, separator and negative electrode layers into a cell, and then encapsulating it with a casing to obtain a solid-state battery. All the processes involved are conventional preparation processes for solid-state batteries and are not particularly limited.

[0106] The present invention will be further described below through specific embodiments.

[0107] Example 1

[0108] 1. Preparation of adhesive

[0109] S1. Add 3.3 mol of 4-cyano-4-[(dodecylthioalkylthiocarbonyl)thioalkyl]valeric acid, 1 mol of trimethylolpropane, and 3.63 mol of dicyclohexylcarbodiimide to dichloromethane and mix. Add 0.3 mol of 4-dimethylaminopyridine as a catalyst and carry out a condensation reaction at 25 °C. After reacting for 24 h, the first reaction solution is obtained. Filter the first reaction solution and wash it with ammonia water to obtain a multifunctional chain transfer agent.

[0110] S2. By mass, 200 parts acrylonitrile, 1.43 parts multifunctional chain transfer agent, 0.15 parts azobisisobutyronitrile and 300 parts dimethyl sulfoxide are mixed. After nitrogen gas is introduced to completely remove oxygen, the first polymerization reaction is carried out at 60°C for 72 h to obtain the second reaction solution. The second reaction solution is precipitated in methanol solvent. After the precipitate is dried, the first polymer is obtained.

[0111] S3. Mix 180 parts of the first polymer, 300 parts of isooctyl acrylate, 0.15 parts of azobisisobutyronitrile and 1600 parts of dimethyl sulfoxide, and after thoroughly removing oxygen by purging with nitrogen, carry out a second polymerization reaction at 60°C for 72 h to obtain a third reaction solution; precipitate the third reaction solution in methanol solvent, and after drying the precipitate, obtain the binder;

[0112] The weight-average molecular weight of the adhesive is 391,000 Da.

[0113] 2. Preparation of the positive electrode sheet

[0114] Lithium nickel cobalt manganese oxide (with a nickel molar content of 80 mol%), carbon black (Super P), and the binder were mixed in a mass ratio of 97.3:1.5:1.2, and N-methylpyrrolidone (NMP) solvent was added. The mixture was stirred until homogeneous to prepare a positive electrode slurry. The positive electrode slurry was then coated onto both sides of an aluminum foil, with a single-sided coating density of 170 g / m². 2 After drying, rolling, slitting, and welding of electrode tabs, a compacted density of 3.4 g / cm³ is obtained. 3 The positive electrode plate.

[0115] 3. Battery manufacturing

[0116] (1) Preparation of negative electrode:

[0117] By weight, 97 parts graphite, 1.5 parts binder, and 1 part carbon black were mixed and stirred at 15 rpm for 15 minutes, while deionized water was added to adjust the solid content (the percentage of the total mass of the components other than the solvent in the mixed solution) to 55 wt%. The mixture was then pre-stirred at 40 rpm for 15 minutes, followed by kneading. Stirring continued at 40 rpm for 40 minutes, followed by a high-speed dispersion process at 15 m / s for 40 minutes. Then, 0.5 parts binder were added to the system, and dispersion was carried out at 5 m / s for 20 minutes. Finally, the mixture was defoamed under vacuum and discharged to obtain the negative electrode slurry. The obtained negative electrode slurry was coated on both sides of the copper foil of the negative electrode current collector, with a single-sided coating surface density of 90 g / m². 2 After processes such as drying, cold pressing, slitting, and welding of electrode tabs, a compacted density of 1.6 g / cm³ is obtained. 3 The negative electrode plate.

[0118] (2) Lithium-ion battery preparation:

[0119] The negative electrode, separator, and positive electrode are wound sequentially, with the separator positioned between the positive and negative electrodes to act as a separator, thus forming an electrode assembly. The electrode assembly is then placed in an outer package, injected with electrolyte, and sealed. After formation and degassing processes, a secondary battery is obtained. The electrolyte includes lithium salt and additives, wherein the lithium salt is lithium hexafluorophosphate (LIPF6) at a concentration of 1 mol / L; the organic solvent is a 1:1 mass mixture of ethylene carbonate and methyl ethyl carbonate.

[0120] The difference between Example 2 and Example 1 is as follows: In step S1, 5.5 mol of 4-cyano-4-[(dodecylthioalkylthiocarbonyl)thioalkyl]valeric acid, 1 mol of triglyceride, and 6.05 mol of dicyclohexylcarbodiimide are added to dichloromethane and mixed. 0.3 mol of 4-dimethylaminopyridine catalyst is added, and a condensation reaction is carried out at 25°C. After 24 h of reaction, the first reaction solution is obtained. The first reaction solution is filtered and washed with ammonia water to obtain a multifunctional chain transfer agent. The types of other raw materials, addition ratios, and reaction conditions are the same as in Example 1, as detailed in Table 1.

[0121] The difference between Example 3 and Example 1 is as follows: In step S1, 4.4 mol of 2-(dodecyltrithiocarbonate)-2-methylpropionic acid, 1 mol of diglycerol and 4.84 mol of dicyclohexylcarbodiimide are added to dichloromethane and mixed. 0.3 mol of 4-dimethylaminopyridine catalyst is added, and a condensation reaction is carried out at 25°C. After 24 h of reaction, the first reaction solution is obtained. The first reaction solution is filtered and washed with ammonia water to obtain a multifunctional chain transfer agent. The other raw material types, addition ratios and reaction conditions are the same as in Example 1, as detailed in Table 1.

[0122] The difference between Examples 4 to 6 and Example 1 is that the hard segment monomer, the Tg of the hard segment, the soft segment monomer, and the Tg of the soft segment used in steps S2 and S3 are different. The other raw material types, addition ratios, and reaction conditions are the same as in Example 1. See Table 1 for details.

[0123] The difference between Examples 7 to 10 and Example 1 is that the mass ratio of soft segments to hard segments is different. The other raw material types, addition ratios and reaction conditions are the same as in Example 1. See Table 1 for details.

[0124] The difference between Examples 11 and 12 and Example 1 is that the weight-average molecular weight of the binder is different. The other raw material types, addition ratios and reaction conditions are the same as in Example 1, as detailed in Table 1.

[0125] Example 13

[0126] 1. Preparation of adhesive

[0127] S1. Add 3.3 mol of 4-cyano-4-[(dodecylthioalkylthiocarbonyl)thioalkyl]valeric acid, 1 mol of trimethylolpropane, and 3.63 mol of dicyclohexylcarbodiimide to dichloromethane and mix. Add 0.3 mol of 4-dimethylaminopyridine as a catalyst and carry out a condensation reaction at 25 °C. After reacting for 24 h, the first reaction solution is obtained. Filter the first reaction solution and wash it with ammonia water to obtain a multifunctional chain transfer agent.

[0128] S2. By weight, 300 parts of isooctyl acrylate, 1.43 parts of multifunctional chain transfer agent, 0.15 parts of azobisisobutyronitrile, and 450 parts of dimethyl sulfoxide are mixed. After nitrogen gas is introduced to completely remove oxygen, the first polymerization reaction is carried out at 60°C for 72 h to obtain the second reaction solution. The second reaction solution is precipitated in the presence of methanol solvent. After the precipitate is dried, the first polymer is obtained.

[0129] S3. Mix 260 parts of the first polymer, 200 parts of acrylonitrile, 0.15 parts of azobisisobutyronitrile and 1500 parts of dimethyl sulfoxide, and after thoroughly removing oxygen by purging with nitrogen, carry out a second polymerization reaction at 60°C for 72 h to obtain a third reaction solution; precipitate the third reaction solution in methanol solvent, and after drying the precipitate, obtain the binder;

[0130] The weight-average molecular weight of the above-mentioned adhesive is 399,000 Da.

[0131] The other raw material types, addition ratios, and reaction conditions are the same as in Example 1.

[0132] Example 14

[0133] 1. Preparation of adhesive

[0134] S1. Add 3.3 mol of 4-cyano-4-[(dodecylthioalkylthiocarbonyl)thioalkyl]valeric acid, 1 mol of trimethylolpropane, and 3.63 mol of dicyclohexylcarbodiimide to dichloromethane and mix. Add 0.3 mol of 4-dimethylaminopyridine as a catalyst and carry out a condensation reaction at 25 °C. After reacting for 24 h, the first reaction solution is obtained. Filter the first reaction solution and wash it with ammonia water to obtain a multifunctional chain transfer agent.

[0135] S2. By weight, 150 parts of isooctyl acrylate, 1.43 parts of multifunctional chain transfer agent, 0.15 parts of azobisisobutyronitrile, and 225 parts of dimethyl sulfoxide are mixed. After nitrogen gas is introduced to completely remove oxygen, the first polymerization reaction is carried out at 60°C for 72 h to obtain the second reaction solution. The second reaction solution is precipitated in the presence of methanol solvent. After the precipitate is dried, the first polymer is obtained.

[0136] S3. Mix 120 parts of the first polymer, 200 parts of acrylonitrile, 0.15 parts of azobisisobutyronitrile and 750 parts of dimethyl sulfoxide, and after thoroughly removing oxygen by purging with nitrogen, carry out the second polymerization reaction at 60°C for 72 h to obtain the third reaction solution; precipitate the third reaction solution in methanol solvent, and after drying the precipitate, obtain the second polymer.

[0137] S4. Mix 300 parts of the second polymer, 150 parts of isooctyl acrylate, 0.15 parts of azobisisobutyronitrile and 1500 parts of dimethyl sulfoxide, and after thoroughly removing oxygen by purging with nitrogen, carry out the first polymerization reaction at 60°C for 72 h to obtain the second reaction solution; precipitate the second reaction solution in the presence of methanol solvent, and after drying the precipitate, obtain the third polymer.

[0138] The weight-average molecular weight of the adhesive is 396,000 Da.

[0139] The other raw material types, addition ratios, and reaction conditions are the same as in Example 1.

[0140] Comparative Examples 1 to 3

[0141] The difference between Comparative Example 1 and Example 1 is that, in S1, 2 mol of 4-cyano-4-[(dodecylthioalkylthiocarbonyl)thioalkyl]valeric acid, 1 mol of trimethylolpropane, and 2 mol of dicyclohexylcarbodiimide were added to dichloromethane and mixed. 0.3 mol of 4-dimethylaminopyridine catalyst was added, and a condensation reaction was carried out at 25°C. After 24 h of reaction, the first reaction solution was obtained. The first reaction solution was filtered and washed with ammonia water to obtain a multifunctional chain transfer agent (with 2 active groups). The other raw material types, addition ratios, and reaction conditions were the same as in Example 1, as detailed in Table 1.

[0142] The difference between Comparative Examples 2 and 3 and Example 1 is that the hard segment monomer, the Tg of the hard segment, the soft segment monomer, and the Tg of the soft segment used in steps S2 and S3 are different. The other raw material types, addition ratios, and reaction conditions are the same as in Example 1, as detailed in Table 1.

[0143] Comparative Example 4

[0144] 1. Preparation of adhesive

[0145] S1. Mix 300 parts of isooctyl acrylate, 0.15 parts of azobisisobutyronitrile and 300 parts of dimethyl sulfoxide, and after purging with nitrogen to remove oxygen, carry out the first polymerization reaction at 60°C. After reacting for 72 h, a soft segment polymer solution is obtained.

[0146] S2. By mass, 200 parts acrylonitrile, 0.15 parts azobisisobutyronitrile and 300 parts dimethyl sulfoxide are mixed, and nitrogen is introduced to completely remove oxygen. The second polymerization reaction is carried out at 60°C for 72 h to obtain a hard segment polymer solution.

[0147] S3. Mix 300 parts of soft segment A polymer and 200 parts of hard segment B polymer (the solid ratio of soft segment A to hard segment B polymer is 60:40) evenly, precipitate in methanol and dry to obtain a fluorine-free binder.

[0148] Table 1

[0149]

[0150]

[0151]

[0152] The properties of the binder, positive electrode sheet, and battery in each embodiment and comparative example were tested through the following process, and the test results are shown in Table 2.

[0153] 1. Weight-average molecular weight test of the adhesive: The test was performed using gel permeation chromatography (GPC). Specifically, the solution containing the adhesive was diluted with deionized water before injection and analysis to obtain the weight-average molecular weight of the adhesive.

[0154] 2. Glass Transition Temperature (Tg) Testing: The glass transition temperature (Tg) of the sample was measured using a simultaneous thermal analyzer (DSC 3500 Sirius). High-purity nitrogen gas was turned on and its flow rate was controlled at 0.6 L / min. The DSC instrument and control system were then started. The temperature program was set as follows: initial temperature -10℃, held for 10 min to eliminate thermal history; then, scanning was performed in the temperature range of -100℃ to 200℃ at a heating rate of 10 K / min. After the program was set, the sample was placed in the heating furnace, the furnace lid was sealed, and an appropriate amount of liquid nitrogen was added to the thermostatic container to ensure the low-temperature environment was maintained. When the sample chamber temperature stabilized at -100℃, the test program was run and data acquisition began.

[0155] 3. Electrolyte mass swelling rate test: An aqueous solution containing the binder was poured into a polytetrafluoroethylene (PTFE) petri dish to remove moisture and volatile components, yielding a thin film. The film was cut into circular sheets (20 mm in diameter and 20 μm in thickness) for later use. A precise weight (m0) of the dried film sample was then immersed in an electrolyte solution at 25°C (this electrolyte solution includes lithium salt and additives, where the lithium salt is lithium hexafluorophosphate (LIPF6) at a concentration of 1 mol / L; the organic solvent is a 1:1 mass mixture of ethylene carbonate and methyl ethyl carbonate). The sample was allowed to stand for 72 h to ensure sufficient swelling and absorption equilibrium. After removal, the residual electrolyte on the surface was quickly wiped off, and the sample was weighed within 30 seconds and recorded as (m1). The formula for calculating the electrolyte mass swelling rate is as follows:

[0156]

[0157] 4. Electrolyte dissolution rate test: An aqueous solution containing the binder was poured into a polytetrafluoroethylene (PTFE) petri dish to remove moisture and volatile components, yielding a thin film. The film was cut into circular sheets (20 mm in diameter and 20 μm in thickness) for later use. The sheets were then dried in an 85°C oven for 24 hours until constant weight, and the weight of the dried sheets was recorded as m0. The weighed sheets were then completely immersed in the aforementioned electrolyte system (the electrolyte includes lithium salt and additives, where the lithium salt is lithium hexafluorophosphate (LIPF6) at a concentration of 1 mol / L; the organic solvent is a 1:1 mass mixture of ethylene carbonate and methyl ethyl carbonate). After sealing, the solution was heated at 60°C for 72 hours. After immersion, the sheets were removed and dried again in an 85°C oven for 24 hours until constant weight, and the weight was recorded as m1. The dissolution rate was calculated using the formula: Weight dissolution rate = (m0 - m1) / m0 × 100%. Calculate the weight dissolution rate of the sheet in the electrolyte.

[0158] 5. Testing the viscosity stability of the cathode slurry: The viscosity of the cathode slurry was tested using a rotational viscometer (Shanghai Fangrui, NDJ-5S) (test conditions: rotational speed set to 60 r / min, temperature 25℃). The viscosity of the cathode slurry at 0 h was recorded as the initial viscosity η. (0h) The positive electrode slurry was placed at room temperature and allowed to stand for 24 hours under sealed conditions. The viscosity of the slurry was then measured again using a rotational viscometer under the same conditions as the initial test, and recorded as the viscosity η after standing. (24h) The viscosity stability of the cathode slurry was characterized by the viscosity ratio M between 24 h and 0 h. The viscosity stability was calculated using the formula M = η. (24h) / η (0h) ×100%.

[0159] 6. Positive Electrode Flexibility Test: The flexibility of the positive electrode is tested using a steel needle winding method. The specific testing procedure is as follows: Cut the positive electrode into test samples of 50mm in length and 20mm in width, ensuring that the sample surface is free of damage, powder, and wrinkles, and that the active material layer is uniform and intact. Prepare a series of cylindrical steel shafts of different diameters (diameter range of 1 mm to 10 mm). With the positive electrode active material layer of the sample facing outward, smoothly wind it onto a steel shaft of a certain diameter. During the winding process, maintain a uniform speed and uniform force to avoid applying additional external force that could damage the electrode. After winding, let it stand for 5 minutes and visually observe whether cracks, powder, or peeling of the active material layer appear on the electrode surface. Repeat the above winding and observation steps with steel shafts of different diameters, and record the diameter of the steel shaft corresponding to the first appearance of cracks, powder, or peeling of the electrode.

[0160] 7. Positive Electrode Peel Strength Test: Cut a 30 mm × 200 mm sample from the positive electrode. Take a flat steel plate and attach 3M double-sided tape to its surface. Securely fix the sample to the tape with the positive electrode active material layer facing down. Use a 2.5 kg standard roller to roll back and forth on the back of the electrode at a uniform speed 6 times to ensure full adhesion between the electrode and the steel plate and to eliminate air bubbles. Subsequently, use a tensile testing machine with a range of 10 N to perform the test: the clamps hold the aluminum foil end of the electrode and stretch it at a constant speed of 10 mm / min at a peel angle of 180° to peel off the positive electrode active material layer from the aluminum foil. Record the average value of the stable segment in the tensile curve as the peel strength of the positive electrode, in Newtons per meter (N / m).

[0161] 8. Testing the cohesive strength of the positive electrode sheet: Cut a 30 mm × 200 mm sample from the positive electrode sheet. Take a flat steel plate and attach 3M double-sided tape to its surface. Securely fix the sample to the tape with the aluminum foil side facing down. Use a 2.5 kg standard roller to roll back and forth on the back of the electrode sheet 6 times at a uniform speed to ensure full adhesion between the electrode sheet and the steel plate and to eliminate air bubbles. Subsequently, use a tensile testing machine with a range of 10 N to test: the clamps hold the tape and the positive electrode coating end, and stretch it at a constant speed of 10 mm / min at a peel angle of 180° until the tape peels the entire positive electrode active material layer from the aluminum foil surface. Record the average value of the stable segment in the tensile curve as the cohesive strength of the positive electrode sheet, in Newtons per meter (N / m).

[0162] 9. Battery internal resistance test: At 25℃, the battery internal resistance is tested using a battery internal resistance tester (TH2523). The test value after stabilization is read and recorded, and the unit is milliohms (mΩ).

[0163] 10. Battery Cycle Performance Test: At 25℃, the battery is charged at a constant current rate of 0.5C to 4.35V, then switched to constant voltage charging until the current decays to 0.05C, and allowed to stand for 5 minutes. It is then discharged at a constant current rate of 1C to 2.75V, and the initial discharge capacity is recorded as Q0. This charge-discharge cycle is repeated 500 times, and the discharge capacity after 500 cycles is recorded as Q1. The battery's 500-cycle capacity retention rate (%) is calculated using the following formula:

[0164]

[0165] 11. Battery Rate Performance Test: The rate discharge performance of the battery is determined according to the test methods in GB / T 31486-2024 "Electrical Performance Requirements and Test Methods for Power Batteries for Electric Vehicles". The discharge rate in this application is 3C, that is, the battery is discharged at a 3C rate to obtain the discharge capacity C1. C0 is the rated capacity of the battery at 0.2C (i.e., the initial capacity before 3C discharge). The 3C discharge capacity retention rate (%) of the battery is calculated by the following formula:

[0166]

[0167] Table 2

[0168]

[0169] As shown in Table 2, the embodiments of the present invention have significant performance advantages compared with the comparative examples. The embodiments employ a central framework multifunctional group structural unit, at least three branches, and a synergistic design of soft and hard segments with a specific Tg to construct a stable star-shaped topology. Its electrolyte mass swelling rate is 28%~60%, dissolution rate is ≤1.5%, flexibility can reach 1.0mm~2.5mm, peel strength and cohesive strength are significantly improved, battery internal resistance is lower, and the capacity retention rate after 500 cycles and the 3C discharge capacity retention rate are both better than those of the comparative examples. Comparative Example 1 contains only two branches, which cannot form a stable star-shaped topology. The molecular chains are prone to entanglement, resulting in significantly poor slurry viscosity stability, increased internal resistance, and insufficient interfacial bonding, leading to a significant deterioration in cycle and rate performance. Comparative Example 2 has a hard segment Tg below 50°C, resulting in insufficient rigid support, a significant decrease in cohesive strength, easy breakage of the binder itself, insufficient electrode structure stability, and poor cycle performance. Comparative Example 3 has a soft segment Tg above 25°C, resulting in insufficient flexibility, poor electrode flexibility, and easy brittleness. At the same time, the electrolyte mass swelling rate is high, leading to decreased structural stability. Comparative Example 4 is a simple physical blend of linear polymers without a star-shaped structure, resulting in poor dispersibility, the worst slurry viscosity stability, the lowest peel strength, weak interfacial bonding, high internal resistance, and poor cycle performance. This fully demonstrates that the star-shaped topology of this invention has significant advantages over traditional linear binders.

[0170] As can be seen from the internal data of the examples, the optimal overall performance is achieved when the number of branches is 3-6, the molecular weight is 200,000-1,200,000 Da, and the mass ratio of soft to hard segments is (20-80):(80-20). Controlling the Tg of the soft segments within -60℃ to 25℃ ensures excellent electrode flexibility, making it suitable for winding processing; the Tg of the hard segments within 50℃ to 150℃ provides sufficient cohesive strength and anti-swelling ability. At the same time, the active end groups and the regular star-shaped structure make the slurry more uniformly dispersed and have better viscosity stability, thereby improving the structural stability of the electrode and reducing the internal resistance of the battery. Adjusting the monomer type, the ratio of soft to hard segments, and the molecular weight can fine-tune the balance between flexibility and bonding strength within a certain range, all of which can maintain good cycle and rate performance.

[0171] In summary, the binder of this invention achieves a balanced improvement in flexibility, cohesive strength, resistance to electrolyte swelling, and slurry stability through the synergistic effect of star-shaped topology and soft and hard segment blocks. It is compatible with cathode materials such as lithium cobalt oxide, lithium iron phosphate, and ternary systems, significantly improving electrode processing performance and battery cycle and rate performance, while also being environmentally friendly and industrially adaptable.

[0172] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An adhesive, characterized in that, The polymer includes a multifunctional structural unit as a central framework and at least three branches connected to the multifunctional structural unit, the branches including soft segments and hard segments connected to the soft segments; the glass transition temperature of the soft segments is below 25°C; and the glass transition temperature of the hard segments is above 50°C.

2. The adhesive according to claim 1, characterized in that, The number of branches is 3 to 6.

3. The adhesive according to claim 1 or 2, characterized in that, The ends of the branched chains contain active end groups; the active end groups include trithiocarbonate groups and / or dithioester groups; And / or, the multifunctional structural unit includes a polyol structural unit.

4. The adhesive according to claim 1, characterized in that, The weight-average molecular weight of the adhesive is 200,000 Da to 1,200,000 Da.

5. The adhesive according to claim 1 or 4, characterized in that, The non-aqueous electrolyte swelling rate of the adhesive is 0%~100%; And / or, the non-aqueous electrolyte dissolution rate of the adhesive is not higher than 5%.

6. The adhesive according to claim 1, characterized in that, In the adhesive, the mass ratio of the soft segment to the hard segment is (20~80):(80~20).

7. The adhesive according to claim 1 or 6, characterized in that, The hard segment includes one or more of cyano, phenyl, and carboxyl groups; And / or, the hard segment comprises a first (meth)acrylate structural unit and / or a vinyl structural unit; the vinyl structural unit comprises an acrylonitrile structural unit and / or an aromatic vinyl structural unit.

8. The adhesive according to claim 1 or 6, characterized in that, The soft segment includes one or more of the following: ester group, alkyl group, ethoxy group, methyl ethoxy group, ethyl ethoxy group, and butyl ethoxy group; And / or, the soft segment includes a second (meth)acrylate structural unit.

9. A positive electrode plate, characterized in that, The device includes a positive current collector and a positive active material layer located on at least one side of the positive current collector, the positive active material layer comprising a positive active material and a binder, the binder comprising any one of claims 1-8.

10. A battery, characterized in that, It includes a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode, wherein the positive electrode includes the positive electrode as described in claim 9.

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