Negative electrode binder, negative electrode sheet, and sulfide all-solid battery

Abstract

The application discloses a negative electrode binder, a negative electrode sheet and a sulfide full-solid-state battery. The negative electrode binder comprises a copolymer, the copolymer comprises aromatic vinyl-diene copolymerization units, weak coordination type ion-conducting structure units and acrylic ester type flexible structure units, the weak coordination type ion-conducting structure units comprise lithium-containing salt type anion structure units, polyether chain segment-containing acrylic ester type structure units and at least one of amide group structure units and nitrile group structure units, and the content of the weak coordination type ion-conducting structure units in the copolymer is less than or equal to 15 wt%. The negative electrode binder has the functions of mechanical bonding, stress buffering, interface fitting retention and ion migration assistance, and can maintain the continuous contact state of the solid-solid interface in the negative electrode composite layer in the compaction and cycle processes, so that the continuous increase of the interface impedance is inhibited, and the sulfide full-solid-state battery is more suitable.

Description

Technical Field

[0001] This application belongs to the field of battery materials technology, specifically relating to a negative electrode binder, a negative electrode sheet and its sulfide all-solid-state battery. Background Technology

[0002] In sulfide all-solid-state batteries, the contact between negative electrode active material particles, conductive agent particles, sulfide solid electrolyte particles and current collectors relies more on the physical bonding of solid-solid interfaces, compaction molding and polymer network constructed by binders to maintain the contact. If the binder design is unreasonable, it is easy to cause problems such as deterioration of interface contact, local ion migration obstruction, increased impedance and decreased cycle stability.

[0003] In existing technologies, binders used for negative electrodes typically include CMC, SBR, PAA, PVDF, and their modified systems. Among them, SBR or SSBR possesses certain flexibility and bonding capabilities, which can buffer stress changes in the electrode sheet during compaction and cycling to a certain extent, thus having a basis for application in negative electrode systems. However, conventional SSBR mainly focuses on mechanical bonding functions and usually lacks effective ion conduction capabilities. In sulfide all-solid-state battery negative electrodes, the binder's adverse effect on lithium-ion transport can easily cause local ion migration bottlenecks, leading to enhanced interfacial polarization and increased impedance.

[0004] In addition, existing technologies also include methods to improve the ion migration capability or interfacial compatibility of polymers by introducing ionic groups, coordination-type polar structures, or flexible segments into the polymer. However, when targeting the anode of sulfide all-solid-state batteries, if the type, form, or content of the introduced functional structures is not properly controlled, it may still be difficult to simultaneously achieve mechanical bonding, flexible buffering, ion conduction assistance, and interfacial stability. For example, an excessively high content of functional structures may enhance the interaction between polymer segments, weakening the flexibility and stress buffering capacity of rubber-like polymers; structures containing free strong acid groups or highly reactive groups may increase the risk of adverse interfacial reactions with sulfide solid electrolytes; when polymer segments are too rigid, they are difficult to adapt to particle rearrangement and microscopic deformation during compaction and cycling, while a low overall polymer modulus or insufficient resistance to deformation may lead to a decrease in mechanical support and insufficient creep resistance. Therefore, existing binders still struggle to achieve an effective balance between mechanical properties, interfacial contact retention, sulfide interfacial stability, and local ion migration capability.

[0005] Therefore, there is an urgent need to develop a functionalized SSBR binder specifically for sulfide all-solid-state battery anodes to solve the technical problem that existing binder systems cannot simultaneously achieve mechanical properties, interfacial stability, and ion-conducting auxiliary properties in solid-state anodes. Summary of the Invention

[0006] To address the aforementioned issues, this application provides a negative electrode binder, a negative electrode sheet, and a sulfide-based all-solid-state battery thereof.

[0007] The purpose of this application is to achieve the following technical solution.

[0008] In a first aspect, this application provides a negative electrode binder comprising a copolymer, wherein the copolymer comprises aromatic vinyl-diene copolymer units, weakly coordinated ion-conducting structural units, and acrylate flexible structural units; the weakly coordinated ion-conducting structural units comprise at least one of lithium salt anionic structural units, acrylate structural units containing polyether segments, and amide and nitrile structural units, wherein the weakly coordinated ion-conducting structural units account for less than 15 wt% of the total mass of the copolymer.

[0009] Further, the gel content of the negative electrode binder is 10wt% to 60wt%; and / or, the weight-average molecular weight of the negative electrode binder is 300,000 Da to 1,200,000 Da; and / or, the molecular weight distribution index (PDI) of the negative electrode binder is 2.0 to 4.0; and / or, the glass transition temperature (Tg) of the negative electrode binder is -70℃ to 20℃; and / or, the ionic conductivity of the negative electrode binder is 1×10⁻⁶. -7 S / cm~1×10 -6 S / cm.

[0010] Furthermore, the copolymer also includes crosslinking structural units; in the copolymer, the mass ratio of the aromatic vinyl-diene copolymer unit, the weakly coordinated ion-conducting structural unit, the acrylate flexible structural unit and the crosslinking structural unit is (70-90):(3-15):(16-25):(0.5-4).

[0011] Furthermore, the crosslinking structural unit includes a siloxane-containing crosslinking structural unit.

[0012] Furthermore, the aromatic ethylene-diene copolymer unit comprises aromatic ethylene structural units and diene structural units, wherein the mass ratio of the aromatic ethylene structural units to the diene structural units is (15-30):(55-75).

[0013] Furthermore, the lithium salt-containing anionic structural unit includes at least one of a lithium carboxylate-based structural unit and a lithium sulfonate-based structural unit; and / or, the polyether-segment-containing acrylate structural unit includes at least one of a polyethylene glycol-segment-containing methacrylate structural unit and a polyethylene glycol-segment-containing acrylate structural unit.

[0014] Further, the lithium salt-containing anionic structural unit includes at least one of lithium methacrylate, lithium acrylate, and lithium 2-acrylamido-2-methylpropanesulfonate; and / or, the polyether-containing acrylate structural unit includes at least one of polyethylene glycol methyl ether methacrylate and polyethylene glycol methyl ether acrylate; and / or, the amide structural unit includes lithium 2-acrylamido-2-methylpropanesulfonate; and / or, the nitrile structural unit includes at least one of acrylonitrile and methacrylonitrile.

[0015] Further, the acrylate flexible structural unit includes at least one of the following: ethyl acrylate structural unit, n-propyl acrylate structural unit, isopropyl acrylate structural unit, n-butyl acrylate structural unit, isobutyl acrylate structural unit, n-pentyl acrylate structural unit, isopentyl acrylate structural unit, n-hexyl acrylate structural unit, isohexyl acrylate structural unit, n-heptyl acrylate structural unit, isoheptyl acrylate structural unit, n-octyl acrylate structural unit, isooctyl acrylate structural unit, 2-ethylhexyl acrylate structural unit, n-nonyl acrylate structural unit, n-decyl acrylate structural unit, and lauryl acrylate structural unit.

[0016] Secondly, this application provides a negative electrode sheet, the negative electrode sheet including a negative electrode current collector and a negative electrode composite layer disposed on at least one side surface of the negative electrode current collector, the negative electrode composite layer including the negative electrode binder described in the first aspect.

[0017] Thirdly, this application provides a sulfide all-solid-state battery, the sulfide all-solid-state battery including the negative electrode sheet described in the second aspect.

[0018] Compared with the prior art, this application has the following advantages: 1) It has both mechanical bonding and stress buffering capabilities. This application uses aromatic ethylene-diene copolymer units as the main body and constructs a continuous polymer bridging structure through an elastic backbone, which can simultaneously achieve interparticle bonding and structural support in the negative electrode composite layer. Compared with conventional binders that only have a single bonding function, this application can more effectively buffer local stress during electrode compaction and cycling, reducing particle detachment, interface cracking, and structural loosening.

[0019] 2) It helps to reduce interfacial polarization and suppress the growth of interfacial impedance. This application introduces weakly coordinated ion-conducting structural units into the aromatic ethylene-diene copolymer units, transforming the binder from a purely mechanically inert phase into one that assists lithium-ion migration in the adjacent regions of the binder and at the binder / sulfide solid electrolyte interface, thereby reducing local ion migration resistance and interfacial polarization. Especially in sulfide all-solid-state anodes, where solid-solid interface contact is highly dependent on local structural continuity and ion pathway connectivity, this application effectively mitigates the rapid increase in interfacial impedance with increasing cycling.

[0020] 3) More friendly to the interface of sulfide solid electrolytes This application regulates the type and content of weakly coordinated ion-conducting structural units in the copolymer, enabling the negative electrode binder to provide local ion-conducting capability while maintaining a relatively mild interaction with the sulfide solid electrolyte interface. This reduces mass changes and impedance fluctuations caused by interfacial side reactions, local contact mismatch, or the formation of unstable interfacial layers, making it more suitable for sulfide all-solid-state battery negative electrode systems.

[0021] 4) Superior interface fit and contact retention This application introduces acrylate-based flexible structural units, giving the negative electrode binder superior flexibility and interfacial compliance. This allows for more thorough adhesion to the negative electrode active material particles, sulfide solid electrolyte particles, and current collector surfaces, improving the peel strength of the negative electrode sheet. During compaction and cycling, this flexible structure helps maintain continuous interfacial contact, reducing contact losses caused by particle displacement, local deformation, and stress concentration, thereby enhancing the long-term stability of the composite negative electrode layer.

[0022] 5) More suitable for specific application scenarios of sulfide-based all-solid-state battery anodes Unlike traditional liquid battery anodes, sulfide all-solid-state battery anodes present multiple synergistic requirements for binders, including mechanical bonding, flexible buffering, interface stability, and ion-conducting assistance. The anode binder constructed in this application can be structurally designed to address this specific technical challenge. Therefore, compared to conventional SBR, SSBR, or general polar polymer binders, it is more advantageous in balancing electrode processability, interface stability, and electrochemical performance.

[0023] 6) It helps improve cycle performance and overall electrochemical performance. Based on the synergistic effect of the aforementioned mechanical network, ion-guided assistance, and flexible bonding, the negative electrode binder of this application can effectively improve the stability of the composite layer and the interface region when used as a negative electrode in a sulfide all-solid-state battery, reduce the performance degradation caused by contact failure and impedance accumulation during cycling, thereby helping to improve the battery's capacity retention, cycle stability, and overall electrochemical performance. Detailed Implementation

[0024] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the following detailed description is provided in conjunction with specific embodiments. It should be understood that the embodiments described herein are only a part of the embodiments of this application, not all of them, and are merely used to explain this application and are not intended to limit it. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the protection scope of this application.

[0025] It should be noted that, in this application, as is known to those skilled in the art of chemical synthesis, each structural unit represents the structural portion of the corresponding monomer present in the resulting polymer after the monomer participates in the polymerization reaction. The mass ratio of each structural unit is the mass ratio of the monomers providing each structural unit.

[0026] In a first aspect, this application provides a negative electrode binder comprising a copolymer, wherein the copolymer comprises aromatic vinyl-diene copolymer units, weakly coordinated ion-conducting structural units, and acrylate flexible structural units; the weakly coordinated ion-conducting structural units comprise at least one of lithium salt anionic structural units, acrylate structural units containing polyether segments, and amide and nitrile structural units, wherein the weakly coordinated ion-conducting structural units account for less than 15 wt% of the total mass of the copolymer.

[0027] In some specific embodiments, the weakly coordinated ion-conducting structural unit in the copolymer has a mass percentage of 3wt% to 15wt%.

[0028] Aromatic vinyl-diene copolymer units provide mechanical bonding and stress buffering capabilities, constructing a continuous polymer bridging structure in the negative electrode composite layer; improving the bonding strength between negative electrode active material particles, conductive agent particles, sulfide solid electrolyte particles, and current collectors; absorbing, dispersing, and buffering local stress during compaction and charge-discharge cycling; and reducing the risk of particle displacement, local debonding, and interface cracking. Limiting the types and mass proportions of weakly coordinated ion-conducting structural units in the copolymer facilitates reversible coordination with lithium ions, improving local lithium ion migration capabilities in adjacent binder interface regions, rather than forming continuous host ion-conducting channels. Acrylic ester flexible structural units can undergo reversible deformation during compaction and cycling, filling microscopic gaps between particles, maintaining solid-solid interface contact continuity, enhancing the adhesion between particles and the particle / sulfide solid electrolyte interface, and improving contact retention during cycling.

[0029] The core of this application is not simply to improve the ionic conductivity of the binder, but to use the elastic chain entanglement and continuous bridging structure formed by aromatic vinyl-diene copolymer units as the mechanical support basis, and to introduce flexible structural units and weakly coordinated ion-conducting structural units. Among them, the unsaturated structure contained in the diene segments can further form branched or micro-crosslinked structures in subsequent reactions or treatments, and can be further constructed with reactive coupling agents or crosslinking agents to build a moderately crosslinked network. This allows the binder to maintain the continuous contact state of the solid-solid interface in the negative electrode composite layer during compaction and cycling, thereby improving interface stability, suppressing the continuous growth of interface impedance, and reducing interface polarization.

[0030] In some specific embodiments, the gel content in the negative electrode binder is 10wt% to 60wt%; specifically, the gel content is 10wt%, 15wt%, 21wt%, 27wt%, 32wt%, 36wt%, 40wt%, 45wt%, 50wt%, 55wt%, or 60wt%, etc.; preferably 15wt% to 45wt%. A higher gel content indicates a higher proportion of cross-linked networks in the negative electrode binder. The gel content is used to characterize the proportion of insoluble network structures or highly branched structures in the negative electrode binder, and can reflect, to a certain extent, the degree of cross-linking, creep resistance, and structural retention during cycling of the negative electrode binder. When the gel content is 10wt% to 60wt%, the negative electrode binder can form a polymer network with certain continuity and stability. While providing mechanical bonding, creep resistance and structural support, it can still maintain the segment mobility required by the flexible chain segments and weakly coordinated ion-conducting structural units. This is beneficial for the binder to adapt to the local deformation of the negative electrode composite layer during compaction and cycling, and to maintain the solid-solid interface contact between the negative electrode active material, sulfide solid electrolyte and current collector.

[0031] When the gel content is below 10 wt%, the network structure in the negative electrode binder is insufficient, and the polymer chains mainly rely on physical entanglement to maintain connection. During negative electrode compaction and charge-discharge cycling, chain segment slippage and network relaxation are prone to occur, leading to weakened interparticle bridging, decreased interfacial contact retention, and potentially increased risks of particle displacement, local debonding, and increased interfacial impedance. When the gel content is above 60 wt%, the cross-linked or highly branched network in the negative electrode binder may be too dense, significantly restricting the movement of polymer chain segments. This results in decreased binder flexibility, interfacial conformability, and stress buffering capacity, which is not conducive to filling the micro-gap between particles and adapting to particle displacement during cycling. At the same time, excessively high gel content may also reduce the mobility of weakly coordinated ion-conducting structural units, restricting the coordination and decoupling processes of lithium ions, and may cause poor slurry dispersibility, increased processing viscosity, or the formation of gel particles.

[0032] In some specific embodiments, the weight-average molecular weight of the negative electrode binder is 300,000 Da to 1,200,000 Da. Specifically, the weight-average molecular weight can be 300,000 Da, 400,000 Da, 500,000 Da, 600,000 Da, 700,000 Da, 800,000 Da, 900,000 Da, 1,000,000 Da, 1,100,000 Da, or 1,200,000 Da, etc.; more preferably, it is 500,000 Da to 900,000 Da. Further, the weight-average molecular weight of the negative electrode binder is the weight-average molecular weight of the soluble portion in tetrahydrofuran (THF) or toluene in the copolymer. The weight-average molecular weight of the soluble portion is mainly used to characterize the chain length and chain entanglement ability of the polymer segments in the negative electrode binder that do not form an insoluble gel network, and it, together with the gel content, reflects the molecular structure state of the negative electrode binder. Controlling the weight-average molecular weight to 300,000 Da to 1,200,000 Da is beneficial for balancing mechanical support, structural retention, interfacial adhesion, and processing performance. When the weight-average molecular weight is between 300,000 Da and 1,200,000 Da, the copolymer can form sufficient chain entanglement and continuous polymer bridging structure. While improving cohesive strength, peel strength, creep resistance and structure retention, it still has suitable solubility, dispersibility, interfacial spreading and processing fluidity.

[0033] When the weight-average molecular weight is below 300,000 Da, the polymer chain length and chain entanglement may be insufficient, resulting in poor stability of the continuous bridging network formed by the binder. This can easily lead to chain segment slippage and network relaxation during the compaction and cycling of the negative electrode, which is detrimental to maintaining stable contact between the negative electrode active material, the sulfide solid electrolyte, and the current collector. When the weight-average molecular weight is above 1,200,000 Da, the viscosity of the copolymer solution or slurry may be too high, leading to a decrease in dissolution, dispersion, degassing, and coating performance, and making it difficult for the binder to uniformly penetrate the micro-gap between particles. At the same time, excessively high molecular weight may also restrict the movement of polymer chain segments, which is not conducive to the binder adapting to local deformation and interface reconstruction during compaction and cycling.

[0034] The molecular weight distribution index (PDI) of the negative electrode binder is 2.0–4.0. Specifically, the PDI can be 2.0, 2.2, 2.5, 2.7, 2.9, 3.3, 3.5, 3.8, or 4.0, etc. The molecular weight distribution index is used to characterize the distribution of different molecular weight segments in the copolymer. When the PDI is 2.0–4.0, the relatively low molecular weight segments and the relatively high molecular weight segments in the system can form a synergistic effect. The relatively low molecular weight segments are beneficial to improving the binder's ability to wet the particle surface, spread, and fill the interparticle gaps, while the relatively high molecular weight segments are beneficial to improving chain entanglement, particle bridging, cohesive strength, and creep resistance. Thus, the negative electrode binder simultaneously possesses good processability, interfacial conformability, and structure retention.

[0035] When the PDI is below 2.0, the molecular weight distribution of the copolymer is relatively narrow. If the proportion of high molecular weight segments is high, it may lead to insufficient system flowability and interfacial spreading ability. If the proportion of low molecular weight segments is high, it may lead to insufficient mechanical strength and creep resistance, which is not conducive to balancing processability and structural stability. When the PDI is above 4.0, the difference between low molecular weight components and ultra-high molecular weight components in the copolymer may be too large. Low molecular weight components are prone to migration, precipitation or interfacial enrichment, while ultra-high molecular weight components may cause dissolution difficulties, local agglomeration, abnormal slurry viscosity or gel particles, thereby reducing coating uniformity, batch stability and performance consistency during cycling.

[0036] The negative electrode binder of this application preferably has a certain molecular weight and network structure to ensure that it can form a continuous polymer bridging network during the preparation, compaction and cycling of the negative electrode sheet, and maintain stable contact between particles and between particles and current collector.

[0037] In some specific embodiments, the glass transition temperature (Tg) of the negative electrode binder obtained in this application is -70℃ to 20℃. If the overall Tg of the negative electrode binder is too high (above 20℃), the polymer chain segment mobility is insufficient, and the binder is difficult to adapt to particle rearrangement during compaction and cycling, which can easily lead to solid-solid interface contact loss and increased interfacial impedance. If the overall Tg is too low (below -70℃), although the binder is soft, its cohesive strength and creep resistance may be insufficient, and it is prone to excessive deformation and loosening of the bonding network during high compaction or long-term cycling, affecting the maintenance of the negative electrode composite layer structure. Therefore, controlling the Tg of the negative electrode binder within -70℃ to 20℃, preferably -60℃ to 10℃, and more preferably -50℃ to 0℃, better reflects the balance between "flexible bonding" and "structural support".

[0038] In some specific embodiments, the mass change rate of the negative electrode binder after contact with the sulfide solid electrolyte is less than 1%. A smaller mass change rate indicates a milder interfacial interaction between the negative electrode binder and the sulfide solid electrolyte, making it less likely to trigger side reactions or the formation of an unstable interfacial layer. The mass change rate is used to characterize the effectiveness of the negative electrode binder in promoting the interface between the negative electrode binder and the sulfide solid electrolyte.

[0039] In some specific embodiments, the ionic conductivity of the negative electrode binder is 1×10⁻⁶. -7 S / cm~1×10 - 6 S / cm. Ionic conductivity is used to characterize the weakly coordinated ion-conducting structural units in the negative electrode binder for Li. + The auxiliary role of local coordination and migration. When the ionic conductivity is below 1×10⁻⁶. -7 When S / cm, it indicates that the adhesive can be used in the adjacent area of ​​Li. +The lack of effective sites for local migration assistance makes it difficult to effectively reduce local ion migration resistance and interfacial polarization; when the ionic conductivity is too high (above 1×10⁻⁶), the problem persists. -6 A conductivity of 1 × 10⁻⁶ S / cm typically indicates a high content of polar or ion-conducting structures in the copolymer, which may enhance intersegmental interactions, weaken the flexibility and mechanical support provided by aromatic vinyl-diene copolymer units, and increase the risk of adverse interfacial interactions with sulfide solid electrolytes. Therefore, controlling the ionic conductivity to 1 × 10⁻⁶ is crucial. -7 S / cm~1×10 -6 Within the S / cm range, it is beneficial to achieve a balance between local ion-guided assistance, mechanical bonding, flexible buffering, and sulfide interface stability.

[0040] In some specific embodiments, the mass ratio of the aromatic vinyl-diene copolymer units, the weakly coordinated ion-conducting structural units, and the acrylate flexible structural units in the copolymer is (70-90):(3-15):(16-25). Specifically, the mass ratio of the three structural units can be 70:3:25, 70:5:25, 70:10:20, 70:12:18, 72:8:20, 72:10:18, 75:5:20, 75:8:17, 80:5:16, 80:7:18, 85:8:25, 85:10:22, 88:5:17, 88:8:20, or 90:15:25, etc. In the copolymer, the mass of each structural unit is based on the mass of monomers used to form the corresponding structural unit.

[0041] The aromatic vinyl-diene copolymer units form the main structure of the copolymer, used to form continuous polymer bridging and chain entanglement structures, and provide mechanical bonding, cohesive strength, elastic buffering, and structural retention during cycling. The weakly coordinated ion-conducting structural units are used to form dynamic, reversible weak coordination with lithium ions in the adjacent regions of the binder and at the interface between the binder and the sulfide solid electrolyte, improving local lithium ion migration conditions and reducing interfacial polarization. The acrylate flexible structural units are used to improve the segmental mobility, flexibility, and interfacial compliance of the copolymer, enabling the binder to spread and adhere more fully to the surfaces of the negative electrode active material particles, sulfide solid electrolyte particles, and current collectors, and to adapt to particle rearrangement and local deformation during compaction and cycling.

[0042] When the content of weakly coordinated ion-conducting structural units is too low, there are insufficient effective sites for forming weak coordination interactions with lithium ions, which limits the improvement effect on local lithium ion migration and interfacial polarization in adjacent regions of the binder. When the content is too high, the polarity of the copolymer and the intersegmental interactions may be too strong, which may not only restrict the coordination and decoordination exchange of lithium ions, but also weaken the flexibility, mechanical support and stress buffering capacity of aromatic ethylene-diene copolymer units, and increase the risk of adverse interfacial interactions with sulfide solid electrolytes.

[0043] When the content of acrylate flexible structural units is too low, the copolymer's chain segment mobility, interfacial spreadability, and conformability are insufficient, making it difficult to fully fill the micro-gap between particles or adapt to particle displacement during compaction and cycling, which can easily lead to stress concentration and solid-solid interface contact loss. When the content is too high, the overall modulus, cohesive strength, and creep resistance of the copolymer may decrease, and the polymer is prone to excessive deformation or network relaxation under continuous pressure or cyclic stress, which is not conducive to the long-term structural maintenance of the negative electrode composite layer.

[0044] When the content of aromatic ethylene-diene copolymer units is too low, the main chain entanglement, particle bridging, and mechanical support of the copolymer are insufficient, which may lead to a decrease in peel strength, creep resistance, and cycle stability. When the content is too high, the relative proportion of weakly coordinated ion-conducting structural units and acrylate flexible structural units is insufficient, which has a limited effect on improving local lithium-ion migration, interface spreading, and solid-solid contact maintenance, making it difficult for the resulting binder to fully reflect the technical effect of functionalized SSBR in the anode of sulfide all-solid-state batteries.

[0045] Therefore, controlling the mass ratio of the aromatic ethylene-diene copolymer unit, the weakly coordinated ion-conducting structural unit, and the acrylate flexible structural unit to (70-90):(3-15):(16-25) is beneficial to achieving a balance between mechanical bonding and structural support, flexible buffering and interface bonding, local lithium-ion migration assistance, and sulfide interface stability. This allows the negative electrode binder to maintain a relatively stable solid-solid interface contact during compaction and cycling, and suppresses the continuous increase of interface impedance.

[0046] In some specific embodiments, the copolymer further includes crosslinking structural units. In the copolymer, the mass ratio of the aromatic vinyl-diene copolymer units, weakly coordinated ion-conducting structural units, acrylate flexible structural units, and crosslinking structural units is (70–90):(3–15):(16–25):(0.5–4). The crosslinking structure can further improve the creep resistance, dimensional stability, and structural retention during cycling of the negative electrode binder, making it more stable in high-compact, low-porosity, and strong solid-solid contact systems of sulfide all-solid-state batteries.

[0047] When the content of cross-linked structural units is too low, there are insufficient effective connection points between polymer chains. The binder mainly relies on physical chain entanglement to maintain the network structure. During the compaction and cycling of the negative electrode sheet, chain segment slippage, network relaxation and irreversible deformation are likely to occur. This is not conducive to maintaining stable contact between the negative electrode active material particles, sulfide solid electrolyte particles and current collector, and may increase the risk of particle displacement, local debonding and interfacial impedance growth.

[0048] When the content of cross-linked structural units is too high, the polymer network may become too dense, which will significantly restrict the movement of chain segments, reduce the flexibility, interfacial conformability and stress buffering capacity of the binder, and make it difficult for the binder to fully adhere to the particle surface and fill the micro gaps between particles. At the same time, an excessively high degree of cross-linking may also restrict the movement of weakly coordinated ion-conducting structural units and the coordination and decoordination process of lithium ions, and cause difficulties in dissolving or dispersing the binder, increased slurry viscosity, increased gel particles and decreased coating uniformity.

[0049] When the content of cross-linked structural units is within the above range, the resulting copolymer can form a moderately branched or cross-linked network. While improving creep resistance, dimensional stability and structural support, it can still maintain the segment mobility and interfacial compliance required by the flexible structural units of acrylates, as well as the coordination and decoordination capabilities required by the weakly coordinated ion-conducting structural units. Thus, it can balance mechanical stability, flexible buffering, interfacial adhesion and local lithium-ion migration assistance properties.

[0050] In some specific embodiments, the crosslinking structural unit includes a siloxane-containing crosslinking structural unit. The siloxane-containing crosslinking structural unit is incorporated into the molecular chain of the copolymer through polymerizable unsaturated groups, and forms silanols through hydrolyzable silane groups, further condensing with the surface of inorganic particles or forming a Si–O–Si crosslinking structure, thereby forming an interfacial connection between the copolymer and the inorganic particles.

[0051] The crosslinking structural unit is derived from the crosslinking monomer, and the siloxane-containing crosslinking structural unit is derived from a silane coupling agent containing polymerizable unsaturated groups and hydrolyzable silane groups. The silane coupling agent preferably includes γ-methacryloyloxypropyltrimethoxysilane (KH-570) and / or 3-glycidoxypropyltrimethoxysilane.

[0052] In some specific embodiments, the aromatic ethylene-diene copolymer unit comprises aromatic ethylene structural units and diene structural units, wherein the mass ratio of the aromatic ethylene structural units to the diene structural units is (15-30):(55-75); specifically, the mass ratio of the aromatic ethylene structural units to the diene structural units can be 15:55, 15:60, 15:68, 20:55, 20:60, 20:72, 25:56, 25:62, 25:71, 30:60, 30:65, 30:75, etc. Such a mass ratio can form a continuous polymer bridging and chain entanglement structure, providing mechanical bonding, cohesive strength, elastic cushioning, and structural retention during cycling.

[0053] More specifically, the aromatic vinyl structural units are derived from aromatic vinyl monomers, which are selected from, but are not limited to, styrene, α-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, and ethylstyrene. The diene structural units are derived from diene monomers, which are selected from, but are not limited to, 1,3-butadiene (referred to as "butadiene") and isoprene. Preferably, the aromatic vinyl-dien copolymer units include styrene-butadiene copolymer units.

[0054] The weakly coordinated ion-conducting structural unit is derived from a weakly coordinated ion-conducting functional monomer. Specifically, the lithium salt-containing anionic structural unit includes at least one of a lithium carboxylate-based structural unit and a lithium sulfonate-based structural unit. Preferably, the lithium carboxylate-based structural unit is derived from at least one of methacrylic acid and acrylic acid, and the lithium sulfonate-based structural unit is derived from 2-acrylamido-2-methylpropanesulfonic acid. The above-mentioned carboxylate-containing monomers or sulfonic acid monomers, after participating in polymerization and subsequent lithiation, form lithium salt-containing anionic groups, respectively generating lithium methacrylate structural units, lithium acrylate structural units, or lithium 2-acrylamido-2-methylpropanesulfonic acid structural units.

[0055] The polyether-segment-containing acrylate structural unit includes at least one of a polyethylene glycol segment-containing methacrylate structural unit and a polyethylene glycol segment-containing acrylate structural unit. Preferably, the polyether-segment-containing acrylate structural unit includes at least one of a polyethylene glycol methyl ether methacrylate structural unit and a polyethylene glycol methyl ether acrylate structural unit, derived from at least one of a polyethylene glycol methyl ether methacrylate and a polyethylene glycol methyl ether acrylate. The polyether segment is used to provide Li + Local coordination and migration assistance.

[0056] The amide structural unit that can form a reversible weak coordination with lithium ions includes the lithium 2-acrylamido-2-methylpropanesulfonic acid structural unit, which is derived from 2-acrylamido-2-methylpropanesulfonic acid.

[0057] The nitrile structural unit that can form a reversible weak coordination interaction with lithium ions includes at least one of an acrylonitrile structural unit and a methacrylonitrile structural unit, derived from acrylonitrile or methacrylonitrile.

[0058] In this structure, structural units derived from methacrylic acid, acrylic acid, and / or 2-acrylamido-2-methylpropanesulfonic acid exist at least partially in the form of lithium salts. Weakly coordinated ion-conducting structural units are introduced in a lithied, partially lithied, weakly reactive, or non-acidic form to maintain the ion-conducting assist function of the binder, improve the local migration ability of lithium ions, and suppress interfacial polarization. Simultaneously, this reduces the risk of side reactions after contact with sulfide solid electrolytes and minimizes adverse effects on the sulfide solid electrolyte interface.

[0059] In some specific embodiments, the acrylate flexible structural unit is derived from acrylate monomers having polymerizable unsaturated groups and whose homopolymer glass transition temperature Tg ≤ 0°C.

[0060] In some specific embodiments, the acrylate flexible structural unit is selected from at least one of the following: ethyl acrylate structural unit, n-propyl acrylate structural unit, isopropyl acrylate structural unit, n-butyl acrylate structural unit, isobutyl acrylate structural unit, n-pentyl acrylate structural unit, isopentyl acrylate structural unit, n-hexyl acrylate structural unit, isohexyl acrylate structural unit, n-heptyl acrylate structural unit, isoheptyl acrylate structural unit, n-octyl acrylate structural unit, isooctyl acrylate structural unit, 2-ethylhexyl acrylate structural unit, n-nonyl acrylate structural unit, n-decyl acrylate structural unit, and lauryl acrylate structural unit.

[0061] Specifically, the acrylate flexible structural unit is preferably introduced from a low-Tg acrylate monomer. Preferably, the low-Tg acrylate monomer is selected from at least one of ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-pentyl acrylate, isopentyl acrylate, n-hexyl acrylate, isohexyl acrylate, n-heptyl acrylate, isoheptyl acrylate, n-octyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, n-nonyl acrylate, n-decyl acrylate, and lauryl acrylate.

[0062] By introducing acrylate-based flexible structural units, the binder can maintain overall mechanical strength while possessing superior flexibility, interfacial compliance, and contact retention during cycling. This makes it easier for the binder to adhere to the surfaces of active material particles, sulfide solid electrolyte particles, and current collectors in the composite negative electrode layer, reducing contact loss caused by particle rearrangement, interfacial deformation, and local stress concentration.

[0063] The negative electrode binder of this application can be prepared using conventional emulsion polymerization methods in the art. The weakly coordinated ion-conducting structural units and acrylate flexible structural units can be formed through one or more of the following methods: copolymerization, end-capping, coupling, and post-functionalization modification. However, by using the preparation conditions and steps of this application, the main chain segments of aromatic vinyl-diene copolymer units are constructed through anionic solution polymerization, and the weakly coordinated ion-conducting structural units and acrylate flexible structural units are further introduced. This results in a binder that combines mechanical bonding, stress buffering, interfacial adhesion maintenance, and ion migration assistance functions, ensuring the structural stability and performance consistency of the negative electrode binder.

[0064] Specifically, the negative electrode binder of this application can be prepared according to a process including the following steps: 1) Using anhydrous cyclohexane and anhydrous n-hexane as polymerization solvents, aromatic vinyl monomers and diene monomers in a mass ratio of (15-30):(55-75) are added. The amount of polymerization solvent is 100%-300% of the total amount of the two monomers. The system temperature is controlled at 45℃-50℃ under stirring. To adjust the microstructure of the diene segments and improve the degree of randomization, tetrahydrofuran is added as a structure regulator. The amount of tetrahydrofuran is 0.2%-0.9% of the total amount of the two monomers. After the system stabilizes, sec-butyllithium is added as an anionic polymerization initiator. The amount of sec-butyllithium is 0.1%-0.3% of the total amount of the two monomers. The polymerization reaction is carried out under anhydrous and oxygen-free conditions for 3-5 hours to obtain an active SSBR polymer solution.

[0065] 2) Add a capping agent to the obtained active SSBR polymer solution. The amount of the capping agent is 0.6% to 1.7% of the total amount of the two monomers mentioned above. The capping agent is selected from one or more of ethylene oxide, tin tetrachloride, silicon tetrachloride, 3-glycidoxypropyltrimethoxysilane, or N,N-dimethylaminopropyltrimethoxysilane to obtain SSBRs with hydroxyl-terminated, tin-coupled, silicon-coupled, epoxysilane-terminated, or aminesilane-terminated groups, respectively. After capping, add anhydrous methanol to finish the process. To stop polymerization, anhydrous methanol is used at 1%~3.5% of the total amount of styrene and butadiene. After desolventizing under reduced pressure and vacuum drying at 50℃~70℃ for 10h~15h, a basic functionalized SSBR resin is obtained. The resulting basic functionalized SSBR resin is an aromatic ethylene-diene copolymer. The aromatic ethylene-diene copolymer units provide rubber elasticity and mechanical bonding ability, while hydroxyl-terminated, tin-coupled, silicon-coupled, epoxysilane-type, or aminesilane-type end groups provide reaction sites for interfacial functionalization.

[0066] In step 2), the end-capping / coupling structure is not mandatory but an auxiliary reinforcing structure. One or more of the following structures—hydroxyl-capped structure, tin coupling structure, silicon coupling structure, epoxy silane-derived structure, or amine silane-derived structure—are used to functionalize and regulate the SSBR molecular chain, thereby improving the interfacial bonding ability of the basic functionalized SSBR resin.

[0067] 3) Dissolve the basic functionalized SSBR resin in a post-copolymerization modification solvent. The amount of the post-copolymerization modification solvent is 100%~400% of the mass of the basic functionalized SSBR resin. Stir at 60℃~90℃ until completely dissolved. Then, add low-Tg acrylate monomers and weakly coordinating ion-conducting functional monomers sequentially. The mass ratio of the basic functionalized SSBR resin to the weakly coordinating ion-conducting functional monomers and low-Tg acrylate monomers is (70~90):(3~15):(16~25). The post-copolymerization modification solvent is selected from one or more of toluene, xylene, methyl ethyl ketone, ethyl acetate, and N-methylpyrrolidone. Subsequently, add an initiator. The initiator is used at a rate of 0.01% to 0.3% of the total amount of polymerizable monomers (the sum of the mass of the basic functionalized SSBR resin, the weakly coordinated ion-conducting functional monomer, and the low-Tg acrylate monomer). The copolymerization reaction is carried out at 78°C to 85°C for 5 to 7 hours under nitrogen protection. Through post-copolymerization modification, the low-Tg acrylate monomer and the weakly coordinated ion-conducting functional monomer are grafted or composite copolymerized on the molecular chain of the basic functionalized SSBR resin to form a modified SSBR copolymer containing aromatic vinyl-diene copolymer unit segments, acrylate flexible structural units, and weakly coordinated ion-conducting structural units, which is the negative electrode binder of this application.

[0068] As an optional implementation, a crosslinking monomer (such as a silane coupling agent) is added to the copolymerization reaction of the three monomers in step 3) to further enhance the connection between the polymer side chain and the main chain, as well as the interface between the binder and the inorganic particles. The mass ratio of the basic functionalized SSBR resin to the weakly coordinated ion-conducting functional monomer, the low Tg acrylate monomer, and the crosslinking monomer is (70-90):(3-15):(16-25):(0.5-4).

[0069] In some specific embodiments, after the copolymerization reaction in step 3) is completed, an ethanol / water mixed solution of LiOH is added, and a neutralization reaction is carried out under stirring conditions, so that LiOH reacts uniformly with the carboxyl and / or sulfonic acid structural units in the weakly coordinated ion-conducting functional monomer to lithiate and generate lithium carboxylate structural units and / or lithium sulfonate structural units; then, ethanol and water are removed under reduced pressure, and the mixture is vacuum dried at 50°C to 60°C to finally obtain the negative electrode binder of this application.

[0070] Specifically, in step 3), the ethanol / water mixed solution of LiOH is prepared by dissolving LiOH in water beforehand and then adding ethanol; wherein, the mass percentage of LiOH in the mixed solution is 2% to 15%, preferably 3% to 10%; the mass ratio of ethanol to water is (1 to 4):1, preferably (2 to 3):1.

[0071] Specifically, in step 3), the degree of neutralization in the neutralization reaction is controlled to be 40%–70%. The degree of neutralization refers to the molar proportion of carboxyl and / or sulfonic acid structural units in the copolymer that are neutralized by lithium hydroxide and converted into lithium salt-type structural units. The degree of neutralization is calculated as the ratio of the actual molar amount of lithium hydroxide used for neutralization to the theoretical molar amount of lithium hydroxide required for complete neutralization of the acidic structural unit, i.e.: Degree of neutralization = Actual molar amount of lithium hydroxide added / Theoretical molar amount of lithium hydroxide required for complete neutralization of the acidic structural unit × 100%.

[0072] Specifically, in step 3), the post-copolymerization modification solvent is selected from one or more of toluene, xylene, methyl ethyl ketone, ethyl acetate, and N-methylpyrrolidone. The initiator is selected from at least one of azobisisobutyronitrile (AIBN), benzoyl peroxide (BPO), and dicumyl peroxide.

[0073] In a second aspect, this application provides a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector (copper foil) and a negative electrode composite layer located on the surface of the negative electrode current collector; the negative electrode composite layer comprises a negative electrode active material, a sulfide solid electrolyte, a conductive agent and a negative electrode binder as described in the first aspect.

[0074] The negative electrode active material can be selected from one or more of graphite, soft carbon, hard carbon, silicon-based materials, silicon-oxygen materials, lithium alloy materials, and combinations thereof. The sulfide solid electrolyte can be selected from Li3PS4 and Li7P3S. 11 , Li6PS5Cl, Li6PS5Br, Li6PS5I, Li 10 GeP2S 12 Li 10 SiP2S 12 Li 10 SnP2S 12 Li3PS 4-x O x And at least one of the following: Li2S–P2S5-based or Li2S–P2S5–P2O5-based glassy or glass-ceramic solid electrolytes. The conductive agent may be selected from at least one of conductive carbon black (SuperP), Ketjen black, acetylene black, carbon nanotubes, carbon fibers, graphene, and conductive polymers. The amount of the negative electrode binder added is 0.5wt% to 10wt% of the total solid mass of the negative electrode composite layer, preferably 1wt% to 5wt%.

[0075] Preferably, in the negative electrode composite layer, the mass ratio of the negative electrode active material, the sulfide solid electrolyte, the conductive agent, and the negative electrode binder is (70~80):(15~20):(1~5):(1~5); specifically, the mass ratio can be 70:20:5:5, 72:22:3:3, 74:21:2:3, 76:18:2:4, 78:17:3:2, 80:15:2:3, or 80:16:1:3, etc.

[0076] Preparation of the negative electrode sheet: First, the negative electrode active material (such as graphite), sulfide solid electrolyte (such as Li6PS5Cl), and conductive agent (SuperP) are dry-mixed in a glove box for 10-30 minutes to obtain a mixed powder. Then, the negative electrode binder of this application is prepared into a 1wt%-5wt% anhydrous toluene / xylene mixed solution, which is slowly added to the above mixed powder. The mixture is then stirred in a planetary mixer for 30-50 minutes to form a uniform, slightly moist composite negative electrode slurry. The solid content of the negative electrode slurry is 56%, and the viscosity is 2000 mPa·s-4000 mPa·s. The negative electrode slurry is spread on copper foil, and the wet film thickness is controlled to be about 120 μm-150 μm with a scraper. Then, it is dried under vacuum conditions of 50℃-70℃ for 8-16 hours until the solvent is basically removed. After drying, it is rolled or pressed under 70 MPa-90 MPa for 3-8 minutes to obtain the negative electrode sheet of the sulfide all-solid-state battery.

[0077] Thirdly, this application provides a sulfide all-solid-state battery, including the negative electrode as described in the second aspect.

[0078] Preparation of sulfide all-solid-state battery: In a dry, inert atmosphere, sulfide solid electrolyte powder is placed in a mold and pre-pressed at 200MPa to 400MPa for 1 to 5 minutes to form a sulfide solid electrolyte layer; then, the negative electrode, the sulfide solid electrolyte layer, and the positive electrode are stacked sequentially, so that the negative electrode composite layer contacts one side of the sulfide solid electrolyte layer and the positive electrode composite layer contacts the other side of the sulfide solid electrolyte layer; then, pressing is performed at 100MPa to 300MPa for 1 to 10 minutes to form a stable solid-solid interface contact between the negative electrode, the sulfide solid electrolyte layer, and the positive electrode, thus obtaining a sulfide all-solid-state battery.

[0079] The positive electrode of a sulfide all-solid-state battery comprises a positive electrode active material, a sulfide solid electrolyte, a conductive agent, and a binder. The positive electrode active material can be selected from LiFePO4, LiCoO2, NCM ternary materials, and LiNi. 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.8 Co 0.15 Al0.05 O2 and one or more combinations thereof; the sulfide solid electrolyte may be selected from Li6PS5Cl, Li7P3S11, Li 10 GeP2S 12 One or more; the conductive agent may be selected from one or more of conductive carbon black (SuperP), acetylene black, VGCF, and carbon nanotubes; the binder may be selected from polyvinylidene fluoride, PTFE, and other binders suitable for sulfide all-solid-state cathode systems. Preferably, in the cathode sheet, the mass ratio of the cathode active material, sulfide solid electrolyte, conductive agent, and binder is (65-90):(5-25):(1-10):(0.5-10), more preferably (70-85):(10-20):(2-5):(1-5).

[0080] The positive electrode sheet is prepared using methods commonly used in the art. For example, it can be prepared according to the following steps: In a dry and inert atmosphere, the positive electrode active material, sulfide solid electrolyte, conductive agent, and binder are weighed by mass. The positive electrode active material, sulfide solid electrolyte, and conductive agent are premixed in a glove box for 10-60 minutes, and then the binder is added and mixing is continued to obtain a uniform positive electrode composite mixture. Subsequently, the positive electrode composite mixture is spread on the surface of an aluminum foil current collector, or directly placed in a mold for pre-pressing. If a solvent-assisted film-forming method is used, the binder can be pre-dispersed in a suitable anhydrous organic medium and then added to the mixing system. A positive electrode composite slurry is prepared under low humidity and inert atmosphere conditions and coated on the surface of an aluminum foil. The solvent is removed by vacuum drying. If a dry mixing-pressing method is used, the obtained positive electrode composite mixture can be directly pressed onto the surface of an aluminum foil under a certain pressure to obtain a positive electrode sheet.

[0081] The specific implementation methods of this application will be further explained and illustrated below through examples and comparative examples.

[0082] Unless otherwise specified, all reagents, materials, and instruments used in the following description are conventional reagents, materials, and instruments, all of which are commercially available. The reagents involved can also be synthesized using conventional synthetic methods. Unless otherwise specified, the methods in the examples are conventional methods in the art. Monomers conforming to this application are commercially available.

[0083] Example 1 1) Preparation of negative electrode binder: In a stainless steel polymerization reactor that has been dried at 120°C and dehydrated under vacuum, high-purity nitrogen is introduced to purge the reactor three times. 120 parts of anhydrous cyclohexane and 30 parts of anhydrous n-hexane are added as polymerization solvents, followed by 22 parts of styrene and 68 parts of butadiene. The system temperature is controlled at 45°C under stirring. 0.5 parts of tetrahydrofuran are added as a structure modifier. After the system stabilizes, 0.18 parts of sec-butyllithium are added as an anionic polymerization initiator. The polymerization reaction is carried out for 4 hours under anhydrous and oxygen-free conditions to obtain an active SSBR polymer solution.

[0084] One part of ethylene oxide was added to the obtained active SSBR polymer solution as a capping agent to convert the active chain end into hydroxyl-terminated SSBR; after capping, two parts of anhydrous methanol were added to terminate the polymerization, and then the solution was desolventized under reduced pressure and dried under vacuum at 60°C for 12 hours to obtain the basic functionalized SSBR resin.

[0085] Fifty parts of the above-mentioned basic functionalized SSBR resin were dissolved in a mixed solvent of 80 parts anhydrous toluene and 20 parts xylene. After stirring at 70°C until completely dissolved, 8 parts of n-butyl acrylate (BA), 6 parts of 2-ethylhexyl acrylate (2-EHA), 5 parts of polyethylene glycol methyl ether methacrylate (PEGMA, Mn≈300), and 2 parts of methacrylic acid (MAA) were added sequentially, along with 1.0 part of silane coupling agent γ-methacryloyloxypropyltrimethoxysilane (KH-570). Subsequently, 0.01 parts of azobisisobutyronitrile (AIBN) and 0.03 parts of benzoyl peroxide (BPO) were added as a composite initiator system, and the copolymerization reaction was carried out at 80°C for 6 hours under nitrogen protection.

[0086] After the copolymerization reaction is completed, the mixture is cooled to 50°C, and a LiOH ethanol / water mixed solution is added. The LiOH ethanol / water mixed solution is prepared by pre-dissolving LiOH in water and then adding ethanol. The mass percentage of LiOH in the mixed solution is 5 wt%, and the mass ratio of ethanol to water is 2.5:1. A neutralization reaction is carried out under stirring conditions to uniformly partially lithiumize the methacrylic acid units with LiOH. The degree of neutralization is controlled to be 50%. The ethanol and water are then removed under reduced pressure and the mixture is vacuum dried at 55°C to finally obtain the negative electrode binder of this application.

[0087] 2) Preparation of the negative electrode: First, 76 parts of graphite, 18 parts of Li6PS5Cl, and 2 parts of conductive agent (SuperP) were dry-mixed in a glove box for 20 minutes to obtain a mixed powder. Then, 4 parts of the negative electrode binder of this application were prepared into a 5wt% anhydrous toluene / xylene mixed solution, which was slowly added to the above mixed powder. The mixture was then stirred in a planetary mixer for 40 minutes to form a uniform, slightly moist composite negative electrode slurry. The solid content of the negative electrode slurry was 56%, and the viscosity was 3000 mPa·s. The negative electrode slurry was spread on copper foil, and the wet film thickness was controlled to be about 150 μm with a doctor blade. It was then dried under vacuum at 60 °C for 12 hours until the solvent was basically removed. After drying, it was rolled and pressed at 80 MPa for 5 minutes to obtain the negative electrode sheet of the sulfide all-solid-state battery.

[0088] 3) Preparation of sulfide all-solid-state batteries: In a dry, inert atmosphere, sulfide solid electrolyte powder is placed in a mold and pre-pressed at 300 MPa for 3 minutes to form a sulfide solid electrolyte layer. Subsequently, the negative electrode, the sulfide solid electrolyte layer, and the positive electrode are stacked sequentially, so that the negative electrode composite layer contacts one side of the sulfide solid electrolyte layer and the positive electrode composite layer contacts the other side of the sulfide solid electrolyte layer. Then, the mixture is pressed at 200 MPa for 5 minutes to form a stable solid-solid interface contact between the negative electrode, the sulfide solid electrolyte layer, and the positive electrode, thus obtaining a sulfide all-solid-state battery.

[0089] Example 2 This embodiment uses most of the operating steps described in Example 1 to prepare the negative electrode binder, negative electrode sheet, and sulfide all-solid-state battery. The difference is that in the preparation of the negative electrode binder, the crosslinking monomer added in the copolymerization reaction of the three monomers is 2 parts of the silane coupling agent 3-glycidoxypropyltrimethoxysilane. The rest is the same as in Example 1.

[0090] Example 3 This embodiment employs most of the operational steps described in Example 1 to prepare the negative electrode binder, negative electrode sheet, and sulfide all-solid-state battery. The difference lies in the preparation of the negative electrode binder: the weakly coordinating ion-conducting functional monomer and its dosage differ, as does the dosage of the crosslinking monomer. Specifically, 8 parts of n-butyl acrylate (BA), 6 parts of 2-ethylhexyl acrylate (2-EHA), 10 parts of polyethylene glycol methyl ether methacrylate (PEGMA), and 2.6 parts of the silane coupling agent γ-methacryloyloxypropyltrimethoxysilane (KH-570) are added to 50 parts of the basic functionalized SSBR resin. Because no carboxyl and / or sulfonic acid group-containing monomers are added to the weakly coordinating ion-conducting functional monomer, subsequent lithiation treatment is unnecessary. The rest is the same as in Example 1.

[0091] Example 4 This embodiment employs most of the operational steps described in Example 1 to prepare the negative electrode binder, negative electrode sheet, and sulfide all-solid-state battery. The differences lie in the following: the weakly coordinated ion-conducting functional monomer and its dosage, and the dosage of the crosslinking monomer. Specifically, 8 parts of n-butyl acrylate (BA), 6 parts of 2-ethylhexyl acrylate (2-EHA), 10 parts of polyethylene glycol methyl ether acrylate, and 0.35 parts of the silane coupling agent γ-methacryloyloxypropyltrimethoxysilane (KH-570) are added to 50 parts of the basic functionalized SSBR resin. Because no carboxyl and / or sulfonic acid group-containing monomers are added to the weakly coordinated ion-conducting functional monomer, subsequent lithiation treatment is unnecessary. The rest is the same as in Example 1.

[0092] Example 5 This embodiment uses most of the steps described in Example 1 to prepare the negative electrode binder, negative electrode sheet, and sulfide all-solid-state battery, except that no crosslinking monomer is added. The rest is the same as in Example 1.

[0093] Example 6 This embodiment employs most of the operational steps described in Example 1 to prepare the negative electrode binder, negative electrode sheet, and sulfide all-solid-state battery. The difference lies in the following: In the preparation of the negative electrode binder, the low-Tg acrylate flexible structural unit is sourced from 7 parts isobutyl acrylate (IBA) and 7 parts isooctyl acrylate (IOA), while the weakly coordinated ion-conducting structural unit is sourced from 4 parts polyethylene glycol methyl ether acrylate and 3 parts acrylic acid. The 2-acrylamide-2-methylpropanesulfonic acid unit is partially lithium-ionized using a LiOH ethanol / water mixed solution, with the neutralization degree controlled at 50%. The rest is the same as in Example 1.

[0094] Example 7 This embodiment employs most of the operational steps described in Example 1 to prepare the negative electrode binder, negative electrode sheet, and sulfide all-solid-state battery. The difference lies in the preparation of the negative electrode binder: the low-Tg acrylate flexible structural unit is sourced from 7 parts isobutyl acrylate (IBA) and 7 parts n-hexyl acrylate (HA), while the weakly coordinated ion-conducting structural unit is sourced from 4 parts polyethylene glycol methyl ether acrylate and 3 parts 2-acrylamido-2-methylpropanesulfonic acid. The 2-acrylamido-2-methylpropanesulfonic acid unit is partially lithium-ionized using a LiOH ethanol / water mixed solution, with a neutralization degree controlled at 50%. The rest is the same as in Example 1.

[0095] Example 8 This embodiment uses most of the operating steps described in Example 1 to prepare the negative electrode binder, negative electrode sheet, and sulfide all-solid-state battery. The difference lies in the following: In the preparation of the negative electrode binder, the acrylate flexible structural unit is sourced from 7 parts isobutyl acrylate (IBA) and 5 parts lauryl acrylate, and the weakly coordinated ion-conducting structural unit is sourced from 6 parts polyethylene glycol methyl ether acrylate and 3 parts acrylic acid. The acrylic acid unit is partially lithium-ionized using a LiOH ethanol / water mixed solution, with the neutralization degree controlled at 50%. The rest is the same as in Example 1.

[0096] Example 9 This embodiment uses most of the operating steps described in Example 1 to prepare the negative electrode binder, negative electrode sheet, and sulfide all-solid-state battery. The difference lies in the preparation of the negative electrode binder: the acrylate flexible structural unit is sourced from 6.3 parts isooctyl acrylate and 7.5 parts n-pentyl acrylate, and the weakly coordinated ion-conducting structural unit is sourced from 2 parts polyethylene glycol methyl ether acrylate and 1 part 2-acrylamido-2-methylpropanesulfonic acid. The 2-acrylamido-2-methylpropanesulfonic acid unit is partially lithium-ionized using a LiOH ethanol / water mixed solution, with the neutralization degree controlled at 50%. The rest is the same as in Example 1.

[0097] Example 10 This embodiment uses most of the operating steps described in Example 1 to prepare the negative electrode binder, negative electrode sheet, and sulfide all-solid-state battery. The difference lies in that: in the preparation of the negative electrode binder, the weakly coordinated ion-conducting structural unit is sourced from 4 parts polyethylene glycol methyl ether methacrylate, 2 parts methacrylic acid, and 1 part acrylonitrile; wherein, the methacrylic acid unit is partially lithiated using a LiOH ethanol / water mixed solution, with the degree of neutralization controlled at 50%. The rest is the same as in Example 1.

[0098] Example 11 This embodiment uses most of the operating steps described in Example 1 to prepare the negative electrode binder, negative electrode sheet, and sulfide all-solid-state battery. The difference is that in the preparation of the negative electrode binder, the amount of styrene used is 15 parts and the amount of butadiene used is 75 parts. The rest is the same as in Example 1.

[0099] Example 12 This embodiment uses most of the operating steps described in Example 1 to prepare the negative electrode binder, negative electrode sheet, and sulfide all-solid-state battery. The difference is that in the preparation of the negative electrode binder, the amount of styrene used is 30 parts and the amount of butadiene is 55 parts. The rest is the same as in Example 1.

[0100] Comparative Example 1 This comparative example uses some of the operational steps in Example 1 to prepare the negative electrode binder, negative electrode sheet and sulfide all-solid-state battery. The difference is that this comparative example only prepares ordinary SSBR binder without post-copolymerization modification, and does not introduce weakly coordinated ion-conducting functional monomers, low Tg acrylate monomers and crosslinking monomers.

[0101] Specifically, in the preparation of the negative electrode binder, 22 parts of styrene and 68 parts of butadiene were added according to the preparation method of the basic functionalized SSBR resin in Example 1. After polymerization, the resin was capped with ethylene oxide, terminated with methanol, desolventized under reduced pressure and dried under vacuum to obtain the ordinary SSBR binder.

[0102] Except for the absence of post-copolymerization modification with low-Tg acrylate monomers, weakly coordinated ion-conducting functional monomers, and crosslinking monomers, the preparation methods of the negative electrode sheet and the preparation methods of the sulfide all-solid-state battery are the same as in Example 1.

[0103] Comparative Example 2 This comparative example uses most of the operating steps in Example 1 to prepare the negative electrode binder, negative electrode sheet, and sulfide all-solid-state battery. The difference is that in the preparation of the negative electrode binder, weakly coordinated ion-conducting functional monomers are not added, that is, polyethylene glycol methyl ether methacrylate (PEGMA) and methacrylic acid (MAA) are not added, and subsequent LiOH lithiation treatment is not performed.

[0104] Specifically, a basic functionalized SSBR resin was prepared according to the method of Example 1, wherein 22 parts of styrene and 68 parts of butadiene were used. 50 parts of the basic functionalized SSBR resin were dissolved in a mixed solvent of 80 parts anhydrous toluene and 20 parts xylene. After stirring at 70°C until completely dissolved, 8 parts of n-butyl acrylate (BA) and 6 parts of 2-ethylhexyl acrylate (2-EHA) were added as sources of low-Tg acrylate flexible structural units, and 1.0 part of γ-methacryloyloxypropyltrimethoxysilane (KH-570) was added. Subsequently, 0.01 parts of azobisisobutyronitrile (AIBN) and 0.03 parts of benzoyl peroxide (BPO) were added, and a copolymerization reaction was carried out at 80°C for 6 hours under nitrogen protection. After the reaction, the solvent was removed under reduced pressure and the mixture was vacuum dried at 55°C to obtain the negative electrode binder of Comparative Example 2.

[0105] In this comparative example, the mass ratio of aromatic ethylene-diene copolymer units, acrylate flexible structural units, and cross-linked structural units was 50:14:1, and no weakly coordinated ion-conducting structural units were introduced. The remaining methods for preparing the negative electrode and the sulfide all-solid-state battery were the same as in Example 1.

[0106] Comparative Example 3 This comparative example uses most of the operating steps in Example 1 to prepare the negative electrode binder, negative electrode sheet and sulfide all-solid-state battery. The difference is that in the preparation of the negative electrode binder, low Tg acrylate monomers are not added, that is, n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2-EHA) are not added, but weakly coordinated ion-conducting functional monomers and crosslinking monomers are retained.

[0107] Specifically, a basic functionalized SSBR resin was prepared according to the method of Example 1, wherein 22 parts of styrene and 68 parts of butadiene were used. 50 parts of the basic functionalized SSBR resin were dissolved in a mixed solvent of 80 parts of anhydrous toluene and 20 parts of xylene. After stirring at 70°C until completely dissolved, 5 parts of polyethylene glycol methyl ether methacrylate (PEGMA, Mn≈300) and 2 parts of methacrylic acid (MAA) were added as sources of weakly coordinated ion-conducting structural units, and 1.0 part of γ-methacryloyloxypropyltrimethoxysilane (KH-570) was added. Subsequently, 0.01 parts of azobisisobutyronitrile (AIBN) and 0.03 parts of benzoyl peroxide (BPO) were added, and a copolymerization reaction was carried out at 80°C for 6 hours under nitrogen protection.

[0108] After the copolymerization reaction was completed, the mixture was cooled to 50°C, and a LiOH ethanol / water mixed solution was added. The methacrylic acid unit was partially lithiated under stirring conditions, and the degree of neutralization was controlled to be 50%. Then, the ethanol and water were removed under reduced pressure and the mixture was dried under vacuum at 55°C to obtain the negative electrode binder of Comparative Example 3.

[0109] In this comparative example, the mass ratio of aromatic ethylene-diene copolymer units, weakly coordinated ion-conducting structural units, and cross-linked structural units was 50:7:1, and no low-Tg acrylate flexible structural units were introduced. The remaining methods for preparing the negative electrode and the sulfide all-solid-state battery were the same as in Example 1.

[0110] Comparative Example 4 This comparative example uses most of the operating steps in Example 1 to prepare the negative electrode binder, negative electrode sheet and sulfide all-solid-state battery. The difference is that in the preparation of the negative electrode binder, instead of acrylate monomers with low Tg values, 14 parts of methyl methacrylate (Tg of 105°C) are added.

[0111] Comparative Example 5 This comparative example uses most of the operating steps in Example 1 to prepare the negative electrode binder, negative electrode sheet, and sulfide all-solid-state battery. The difference is that in the preparation of the negative electrode binder, the methacrylic acid (MAA) in the weakly coordinated ion-conducting functional monomer was not subsequently lithiated to form a lithium carboxylate type weakly coordinated ion-conducting cell; specifically, after the copolymerization reaction, LiOH ethanol / water mixed solution was not added to partially lithiate the MAA unit.

[0112] Comparative Example 6 This comparative example uses most of the operating steps in Example 1 to prepare the negative electrode binder, negative electrode sheet, and sulfide all-solid-state battery. The difference is that in the preparation of the negative electrode binder, the mass percentage of the weakly coordinated ion-conducting structural unit in the copolymer is greater than 15%; specifically, the weakly coordinated ion-conducting functional monomer added is 8 parts of polyethylene glycol methyl ether methacrylate (PEGMA, Mn≈300) and 7 parts of methacrylic acid (MAA).

[0113] Performance testing: To better understand the technical solutions in this application, the negative electrode binder, negative electrode sheet and sulfide all-solid-state battery prepared in the above embodiments and comparative examples were characterized and their performance was tested. The test results are shown in Table 1.

[0114] [Molecular Weight Related Parameters] A Waterse2695-2414 instrument was used, with two Shidex SB-806MHQ columns connected in series. The weight-average molecular weight (Mw) and molecular weight distribution index (PDI) of the soluble fraction in the negative electrode binder were determined using GPC. The specific method was as follows: an appropriate amount of dried negative electrode binder was weighed, added to tetrahydrofuran (THF) or toluene for complete swelling and dissolution, and allowed to stand or shake until the soluble fraction was fully dissolved. The solution was then filtered through a 0.45 μm polytetrafluoroethylene (PTFE) membrane, and the filtrate was injected for testing. The test temperature was controlled at 35–40 °C, and the mobile phase flow rate was 0.8–1.0 mL / min. Calibration was performed using a polystyrene standard. The weight-average molecular weight (Mw) and molecular weight distribution index (PDI) of the soluble fraction in the negative electrode binder were recorded. For the crosslinked or gelled portion of the negative electrode binder, it was not included in the GPC test system; its content was characterized by the gel content.

[0115] [Glass Transition Temperature Tg] The glass transition temperature Tg of the negative electrode binders in the above examples and comparative examples was measured using a differential scanning calorimeter (Shanghai Qunhong Instrument Equipment Co., Ltd., model: DSC-100). The steps included: turning on high-purity nitrogen, setting the nitrogen flow rate to 0.5-0.6 L / min, turning on the DSC power, and running the desktop. The temperature was set to 0℃, held for 10 min, with a temperature range of -100℃ to 180℃ and a heating rate of 10 K / min. After setting, the prepared sample was placed on the heating furnace, the furnace cover was closed, and an appropriate amount of liquid nitrogen was added to the constant temperature container. The test was conducted when the sample temperature reached -60℃.

[0116] [Gel Content] After the negative electrode binder is made into a dry film, the initial mass m0 is weighed and placed in a Soxhlet extractor. Extraction is performed by reflux for 48–72 h using toluene or THF as the extraction solvent. After extraction, the sample is removed, vacuum dried to constant weight, and the mass of residual insoluble matter m1 is weighed. According to (m...1 / Calculate the gel content by multiplying m0 by 100%.

[0117] [Mass Change Rate] The mass change rate of the negative electrode binder after contact with the sulfide solid electrolyte was tested: In an argon glove box, the negative electrode binder and the sulfide solid electrolyte Li6PS5Cl were mixed evenly at a mass ratio of 1:4. The initial mass M0 of the mixed sample was weighed, sealed and stored in a sample bottle, and placed at 25℃ for 24h and at 60℃ for 24-72h respectively. The mass M1 was then weighed and the mass change rate was calculated as [|M1-M0| / M0]×100%.

[0118] [Ionic Conductivity] The negative electrode binder was made into a uniform thin film and assembled with a stainless steel blocking electrode under dry conditions to form an SS / film / SS test structure. Its bulk ionic conductivity was measured using electrochemical impedance spectroscopy (EIS). Specifically, the test frequency range was 1MHz to 0.1Hz, and the AC perturbation voltage was 5 to 10mV. Based on the bulk resistance R corresponding to the high-frequency intercept, the ionic conductivity of the negative electrode binder was calculated using σ = L / (R × A), where σ is the ionic conductivity (S / cm), L is the film thickness (cm), and A is the electrode area (cm²). 2 .

[0119] [Peel Strength] The coated single-sided negative electrode sheet was tested at 1.6 g / cm². 3 After compaction, the negative electrode sheet is cut into 20cm long x 3cm wide pieces. 3M double-sided tape is attached to the steel plate, and the coated side of the negative electrode sheet is fixed to the tape on the steel plate with the coated side facing down. After rolling back and forth 6 times with a 2.5kg roller, a tensile testing machine with a range of 20N is used. The upper plate clamps the copper foil side, and the coating and copper foil are torn apart at a speed of 50mm / min and a 180° stretch. The data of the stable tensile section is recorded as the peel strength (N / m).

[0120] [Interfacial Impedance Growth Rate] A negative electrode sheet containing a negative electrode binder is pressed together with a sulfide solid electrolyte layer in a dry, inert atmosphere to form a contact interface between the negative electrode composite layer and the sulfide solid electrolyte layer. Subsequently, a stainless steel sheet is used as a blocking electrode to assemble a Cu / negative electrode composite layer / sulfide solid electrolyte layer / SS test structure, or an SS / negative electrode composite layer / sulfide solid electrolyte layer / SS test structure. The interfacial impedance is measured at room temperature using electrochemical impedance spectroscopy (EIS). The test frequency range is 1MHz to 0.1Hz, and the AC perturbation voltage is 5 to 10mV. The interfacial impedance value is obtained based on the impedance response related to the negative electrode composite layer / sulfide solid electrolyte layer interface in the EIS spectrum, or through equivalent circuit fitting. The interfacial impedance growth rate is calculated using the following formula: Interfacial impedance growth rate = (R1 - R0) / R0 × 100%; where R0 is the interfacial impedance measured in the initial state of the sample, and R1 is the interfacial impedance measured after the sample has been left to stand or heat-treated. The smaller the growth rate of interfacial impedance, the more effective the negative electrode binder is in suppressing interfacial polarization and maintaining interfacial stability.

[0121] [Initial Charge / Discharge and Cycling Performance] After assembling the negative electrode, sulfide solid electrolyte layer, and positive electrode into a sulfide all-solid-state battery, constant current charge / discharge tests were conducted under isothermal conditions to test the initial charge / discharge and cycle performance of the sulfide all-solid-state battery. The initial charge / discharge was performed at 0.1C, and the initial charge capacity and initial discharge capacity were recorded. The initial coulombic efficiency was calculated as (initial discharge capacity / initial charge capacity) × 100%. Subsequently, 500 cycles were performed at the same rate, and the discharge capacity Qt of the first cycle and Qret of the 500th cycle were recorded. The capacity retention rate after 500 cycles was calculated as Qret / Qt × 100%. A higher capacity retention rate indicates that it is more effective in improving interface stability and reducing impedance accumulation.

[0122] Table 1 The test results in Table 1 show that the weight-average molecular weight of the negative electrode binders obtained in Examples 1-12 of this application is 300,000 Da to 1,200,000 Da, the molecular weight distribution index (PDI) is 2.0 to 4.0, the glass transition temperature (Tg) is -70℃ to 20℃, the gel content is 10wt% to 60wt%, the mass change rate of the negative electrode binder after contact with the sulfide solid electrolyte is less than 1%, and the ionic conductivity is 1×10⁻⁶. -7 S / cm~1×10 -6The peel strength of the negative electrode is greater than 150 N / m, the interfacial impedance growth rate is ≤25%, the initial coulombic efficiency is greater than 87%, and the capacity retention is greater than 82%. The cross-linked structure can further improve the creep resistance, dimensional stability, and structural retention of the negative electrode binder during cycling, making it more stable in high-compact, low-porosity, and strong solid-solid contact systems of sulfide all-solid-state batteries.

[0123] Comparative analysis of Examples 1-12 with Comparative Examples 1-3 reveals that: all three functional structural units in the negative electrode binder of this application are indispensable. Their role in the negative electrode of sulfide all-solid-state batteries is not a contribution of a single structure, but rather the result of the synergistic effect of the three functional structural units: the aromatic ethylene-diene copolymer unit is responsible for providing basic mechanical bonding and stress buffering; the weakly coordinated ion-conducting structural unit is responsible for improving the lithium-ion migration conditions near the binder phase and its interface region, reducing local polarization, and can reduce mass changes and impedance fluctuations caused by interface side reactions, local contact mismatch, or the formation of unstable interface layers; the negative electrode binder of this application has better ion migration ability than ordinary SSBR negative electrode binders, and Comparative Examples 1 and 2 verify the effect of introducing the weakly coordinated ion-conducting structural unit; the acrylate flexible structural unit is responsible for enhancing adhesion and contact retention, reducing solid-solid interface mismatch, and can reduce the interface impedance growth rate and improve the peel strength of the negative electrode sheet. Therefore, the synergistic effect of these three types of functional structural units enables the negative electrode binder in the negative electrode of the sulfide all-solid-state battery to not only maintain the structural integrity of the negative electrode composite layer, but also to slow down the increase of interfacial impedance after contact with the sulfide solid electrolyte, thereby improving the interfacial stability during cycling.

[0124] A comparative analysis of Example 1 and Comparative Example 4 reveals that when methyl methacrylate with a higher Tg value is used to replace low-Tg acrylate monomers, the resulting negative electrode binder exhibits decreased chain flexibility, interfacial spreadability, and stress buffering capacity. This makes it difficult to fully fill the microscopic gaps between particles in the negative electrode composite layer, and also makes it difficult to maintain continuous contact between the negative electrode active material particles, sulfide solid electrolyte particles, and current collector during compaction and cycling. Therefore, Comparative Example 4 is more prone to solid-solid interface mismatch, localized debonding, and enhanced interfacial polarization, manifested as decreased peel strength, increased interfacial impedance growth rate, and reduced initial coulombic efficiency, ultimately leading to a significant decrease in capacity retention after charge / discharge and cycling.

[0125] A comparative analysis of Example 1 and Comparative Example 5 reveals that if the acidic polar structural unit in the weakly coordinated lithium-conducting structural unit is not subsequently lithiated, a significant number of free carboxylic acid groups will remain in the polymer. These free acidic groups, upon contact with the sulfide solid electrolyte, easily generate strong interfacial interactions, potentially leading to interfacial side reactions or the formation of unstable interfacial layers, resulting in a significant increase in the rate of mass change and the rate of increase in interfacial impedance. Simultaneously, due to the absence of a lithium carboxylic acid-type weakly coordinated lithium-conducting structural unit, the binder's effect on Li... + The decreased local coordination and migration assist capabilities of the lithium lead to increased local ion migration resistance and enhanced interfacial polarization, ultimately resulting in a significant decrease in initial coulombic efficiency and post-cycle capacity retention. This indicates that the structural units derived from methacrylic acid, acrylic acid, and / or 2-acrylamido-2-methylpropanesulfonic acid, existing at least partially in lithium salt form, are beneficial in reducing the adverse effects of acidic groups on the sulfide solid electrolyte interface and improving the interfacial stability of the negative electrode composite layer.

[0126] A comparative analysis of Example 1 and Comparative Example 6 shows that: if the mass percentage of the weakly coordinated ion-conducting structural unit in the copolymer is greater than 15 wt%, although it can be combined with Li... + While an increase in polar sites for coordination may improve the ionic conductivity of the binder, excessive polarity can enhance inter-segment interactions in the polymer, restricting segmental mobility and weakening the original flexibility, elastic buffering capacity, and mechanical support of the aromatic vinyl-diene copolymer units. Furthermore, excessive polar groups may increase the risk of adverse interfacial interactions between the binder and the sulfide solid electrolyte, leading to a higher rate of mass change and an increased rate of increase in interfacial impedance. This results in the anode composite layer struggling to maintain stable solid-solid interfacial contact during compaction and cycling, manifesting as decreased peel strength, enhanced interfacial polarization, reduced initial coulombic efficiency, and decreased cycle capacity retention. Therefore, a higher content of weakly coordinated ion-conducting structural units is not necessarily better; rather, the content should be controlled between 3 wt% and 15 wt% to balance local ion-conducting assistance, mechanical bonding, flexible buffering, and sulfide interfacial stability.

[0127] Therefore, the negative electrode binder of this application has the functions of mechanical bonding, stress buffering, interface adhesion maintenance and ion migration assistance. During compaction and cycling, it can maintain the continuous contact state of the solid-solid interface in the negative electrode composite layer, thereby suppressing the continuous increase of interface impedance and making it more suitable for sulfide all-solid batteries.

[0128] The present application has been further described above with reference to specific embodiments. However, it should be understood that the specific descriptions herein should not be construed as limiting the substance and scope of the present application. Various modifications made by those skilled in the art to the above embodiments after reading this specification are all within the scope of protection of the present application.

Claims

1. A negative electrode binder, characterized in that, The negative electrode binder includes a copolymer, which includes aromatic vinyl-diene copolymer units, weakly coordinated ion-conducting structural units, and acrylate flexible structural units. The weakly coordinated ion-conducting structural unit includes at least one of lithium salt anionic structural unit, acrylate structural unit containing polyether segment, amide structural unit, and nitrile structural unit; the content of the weakly coordinated ion-conducting structural unit in the copolymer is less than 15 wt%.

2. The negative electrode binder according to claim 1, characterized in that, The negative electrode binder has a gel content of 10wt% to 60wt%; and / or, The weight-average molecular weight of the negative electrode binder is 300,000 Da to 1,200,000 Da; and / or, The molecular weight distribution index (PDI) of the negative electrode binder is 2.0–4.0; and / or, The glass transition temperature (Tg) of the negative electrode binder is -70℃ to 20℃; and / or, The ionic conductivity of the negative electrode binder is 1×10⁻⁶. -7 S / cm~1×10 -6 S / cm.

3. The negative electrode binder according to claim 1 or 2, characterized in that, The copolymer further includes crosslinking structural units; in the copolymer, the mass ratio of the aromatic vinyl-diene copolymer unit, the weakly coordinated ion-conducting structural unit, the acrylate flexible structural unit to the crosslinking structural unit is (70-90):(3-15):(16-25):(0.5-4).

4. The negative electrode binder according to claim 3, characterized in that, The cross-linked structural unit includes a siloxane-containing cross-linked structural unit.

5. The negative electrode binder according to claim 3, characterized in that, The aromatic ethylene-diene copolymer unit includes aromatic ethylene structural units and diene structural units, and the mass ratio of the aromatic ethylene structural units to the diene structural units is (15-30):(55-75).

6. The negative electrode binder according to claim 1, characterized in that, The lithium-containing anionic structural unit includes at least one of lithium carboxylate-based structural units and lithium sulfonate-based structural units; and / or... The acrylate structural unit containing polyether segments includes at least one of methacrylate structural units containing polyethylene glycol segments and acrylate structural units containing polyethylene glycol segments.

7. The negative electrode binder according to claim 6, characterized in that, The lithium salt-containing anionic structural unit includes at least one of lithium methacrylate, lithium acrylate, and lithium 2-acrylamide-2-methylpropanesulfonate; and / or, The acrylate structural unit containing polyether segments includes at least one of polyethylene glycol methyl ether methacrylate structural units and polyethylene glycol methyl ether acrylate structural units; and / or, The amide structural unit includes a lithium 2-acrylamido-2-methylpropanesulfonate structural unit; and / or, The nitrile structural unit includes at least one of an acrylonitrile structural unit and a methacrylonitrile structural unit.

8. The negative electrode binder according to claim 1, characterized in that, The acrylate flexible structural units include at least one of the following: ethyl acrylate structural units, n-propyl acrylate structural units, isopropyl acrylate structural units, n-butyl acrylate structural units, isobutyl acrylate structural units, n-pentyl acrylate structural units, isopentyl acrylate structural units, n-hexyl acrylate structural units, isohexyl acrylate structural units, n-heptyl acrylate structural units, isoheptyl acrylate structural units, n-octyl acrylate structural units, isooctyl acrylate structural units, 2-ethylhexyl acrylate structural units, n-nonyl acrylate structural units, n-decyl acrylate structural units, and lauryl acrylate structural units.

9. A negative electrode sheet, characterized in that, The negative electrode sheet includes the negative electrode binder as described in any one of claims 1 to 8.

10. A sulfide all-solid-state battery, characterized in that, Includes the negative electrode as described in claim 9.

Images