Modified epoxidized styrene butadiene rubber (SBR) binder as well as preparation method and application thereof

Abstract

The invention relates to a modified epoxidized styrene butadiene rubber (SBR) binder and a preparation method and application thereof. The adhesive is prepared from epoxidized SBR (Styrene Butadiene Rubber), TPU (Thermoplastic Polyurethane) and modified gas-phase SiO2 according to the mass ratio of (89 to 94.5): (5 to 10): (0.5 to 1). An epoxy group on an epoxidized SBR molecular chain forms a dynamic ion transmission channel by changing a local structure and charge distribution, so that the ionic conductivity is improved; the modified gas-phase SiO2 is physically adsorbed with a polar group in an epoxidized SBR molecular chain through residual silicon hydroxyl on the surface, and meanwhile, an organic long chain introduced by a silane coupling agent is physically entangled with the epoxidized SBR molecular chain, so that the surface of the epoxidized SBR is coated with the modified gas-phase SiO2, the Van der Waals force among particles is reduced, the distance is increased, and agglomeration is inhibited; the dispersity is improved. The binder solves multiple challenges of binder dispersion, interface bonding, ion conduction and thermal stability faced by a dry method electrode process.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to modified epoxy-oxidized styrene-butadiene rubber (SBR) binders, their preparation methods, and applications. Background Technology

[0002] In the field of lithium-ion battery manufacturing technology, high-expansion anode materials (such as silicon-based anodes and graphite composites) have become a key research direction for improving battery performance due to their advantages such as high specific capacity. However, current electrode fabrication processes face many bottlenecks, which severely restrict the full utilization of the performance of high-expansion anode materials and the further improvement of the overall performance of lithium-ion batteries.

[0003] Existing electrode fabrication processes are mainly divided into wet processes and traditional dry processes, both of which have obvious drawbacks.

[0004] In wet processing, the process is highly dependent on solvents such as water or N-methylpyrrolidone. The drying stage in electrode preparation consumes enormous amounts of energy, exceeding 300 kWh / ton of electrode, which undoubtedly increases production costs and energy consumption. Furthermore, the solvent recovery rate of less than 85% not only wastes resources but may also cause environmental pollution. More critically, solvent residue significantly increases electrode resistance, typically exceeding 35%, thereby affecting the battery's charge / discharge efficiency and energy density.

[0005] Traditional dry-process technology also faces a series of problems that urgently need to be addressed. First, the dispersion uniformity index (D90 / D10) of styrene-butadiene rubber (SBR) powder is greater than 5, indicating uneven distribution of SBR powder within the electrode material. This can easily lead to inconsistencies in the internal structure of the electrode, affecting the stability of battery performance. Second, the hot-pressing temperature window is narrow, only effective within the range of 80℃-95℃. When the temperature exceeds 150℃, SBR degrades, with a molecular weight decrease of over 40%, resulting in a significant reduction in adhesion. Below 80℃, the adhesive fails, with a peel strength below 10 N / m, failing to guarantee the integrity of the electrode structure. Furthermore, the interfacial bonding force between the electrode and the current collector is insufficient, below 15 N / m. During battery cycling, the interfacial peel rate reaches as high as 30%, severely impacting the battery's cycle life. Finally, electrodes prepared by traditional dry processes have low ionic conductivity, less than 0.8 mS / cm, which greatly limits the rate performance of the battery and cannot meet the requirements of high-power applications.

[0006] In summary, existing electrode fabrication processes cannot meet the application requirements of high-expansion negative electrode materials in lithium-ion batteries. There is an urgent need to develop a new binder and negative electrode preparation method to overcome the above-mentioned defects and promote the further development of lithium-ion battery technology. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a modified epoxy-oxidized styrene-butadiene rubber (SBR) binder, its preparation method, and its application. This invention effectively solves problems such as uneven binder dispersion, narrow hot-pressing window, weak interfacial bonding, and low ionic conductivity in traditional dry processes, and significantly improves the structural stability, thermal stability, and ion transport efficiency of the electrode.

[0008] To achieve the above objectives, in a first aspect, the present invention provides a modified epoxy-oxidized styrene-butadiene rubber (SBR) adhesive, wherein the modified epoxy-oxidized SBR adhesive comprises epoxy-oxidized SBR, thermoplastic polyurethane (TPU), and modified fumed silica (SiO2) in a mass ratio of 89-94.5:5-10:0.5-1; the molecular chain of the epoxy-oxidized SBR contains epoxy groups.

[0009] The epoxy groups form dynamic ion transport channels by changing the local structure and charge distribution of the epoxy-based SBR molecular chain, thereby improving the ionic conductivity of the modified epoxy-based SBR binder.

[0010] The silanol groups remaining on the surface of the modified fumed SiO2 undergo physical adsorption with the polar groups in the epoxy-based SBR molecular chain. Simultaneously, the long organic chains introduced by the silane coupling agent physically entangle with the epoxy-based SBR molecular chain, causing the modified fumed SiO2 to coat the surface of the epoxy-based SBR. This reduces the van der Waals forces between the epoxy-based SBR particles, increases the interparticle spacing, and inhibits particle aggregation, thereby improving the dispersibility of the modified epoxy-based SBR binder.

[0011] Preferably, when the modified epoxy-based SBR binder is applied to the negative electrode sheet, the epoxy groups on the epoxy-based SBR undergo a ring-opening reaction with the hydroxyl groups on the surface of the copper foil current collector to form covalent bonds. At the same time, the TPU molecular chains and the epoxy-based SBR molecular chains intertwine to form a physical entanglement structure, preventing slippage between the epoxy-based SBR molecular chains and the TPU molecular chains. Furthermore, the modified gaseous SiO2 forms chemical bonds with the copper foil current collector through the functional groups introduced by the silane coupling agent, synergistically enhancing the interfacial bonding force between the electrode and the current collector and improving the structural stability of the electrode.

[0012] The TPU molecular chains form a three-dimensional network skeleton through physical cross-linking points formed by hard segment microregions. The three-dimensional network skeleton and the elastic network formed by the epoxy-oxidized SBR in the three-dimensional network skeleton constitute an epoxy-oxidized SBR-TPU dual network structure, which improves the thermal stability of the modified epoxy-oxidized SBR adhesive.

[0013] Meanwhile, the modified fumed SiO2 exhibits low agglomeration and can be uniformly dispersed in the electrode slurry to form a three-dimensional network structure. This, in conjunction with the epoxy-modified SBR-TPU dual network structure, provides a continuous channel for ion transport and improves the ionic conductivity of the modified epoxy-modified SBR binder. The three-dimensional network framework provides the main transport channel for ion transport, while the elastic network, through elastic deformation, mitigates volume changes in the active material, maintaining the porous structure within the negative electrode sheet and providing a buffer space for ion transport within the three-dimensional framework.

[0014] Preferably, the epoxy grafting rate of the epoxy-oxidized SBR is 1.0 mmol / g-1.5 mmol / g;

[0015] The silane coupling agent is one or more of γ-aminopropyltriethoxysilane KH550 or γ-(2,3-epoxypropoxy)propyltrimethoxysilane KH560.

[0016] Secondly, the present invention provides a method for preparing the modified epoxy-oxidized styrene-butadiene rubber (SBR) adhesive described in the first aspect above, the preparation method comprising:

[0017] Styrene-butadiene rubber (SBR) emulsion and glycidyl methacrylate (GMA) containing epoxy groups were stirred and mixed at room temperature, and then heated to 55℃-70℃ to carry out a constant temperature grafting reaction, so that the epoxy groups in the GMA were grafted onto the SBR molecular chain to obtain an epoxy-modified SBR emulsion.

[0018] The epoxy-based SBR emulsion was spray-dried to obtain reactive epoxy-based SBR powder.

[0019] The epoxy-oxidized SBR powder, thermoplastic polyurethane (TPU), and modified fumed silica (SiO2) in a mass ratio of 89-94.5:5-10:0.5-1 are dry-mixed. The modified SiO2 is physically adsorbed onto the polar groups in the epoxy-oxidized SBR molecular chain through residual silanol groups on its surface. At the same time, the organic long chains introduced by the silane coupling agent are physically entangled with the epoxy-oxidized SBR molecular chain, thereby uniformly coating the surface of the epoxy-oxidized SBR, inhibiting the agglomeration of the epoxy-oxidized SBR particles, and obtaining a uniformly dispersed modified epoxy-oxidized SBR binder.

[0020] Preferably, the SBR emulsion is prepared by emulsion polymerization of styrene and butadiene in a mass ratio of 35-45:55-65;

[0021] The amount of GMA added is 2.5wt%-4wt% of the solid content in the SBR emulsion; wherein the solid content in the SBR emulsion is 30wt%-40wt%.

[0022] Preferably, the silane coupling agent is one or more of γ-aminopropyltriethoxysilane KH550 or γ-(2,3-epoxypropoxy)propyltrimethoxysilane KH560.

[0023] Thirdly, the present invention provides a negative electrode sheet, the negative electrode sheet comprising the modified epoxy-oxidized styrene-butadiene rubber (SBR) binder described in the first aspect above, or comprising the modified epoxy-oxidized SBR binder prepared by the preparation method described in the second aspect above.

[0024] Fourthly, the present invention provides a method for preparing the negative electrode sheet described in the third aspect above, the method comprising:

[0025] The negative electrode active material, conductive agent and modified epoxy-oxidized styrene-butadiene rubber (SBR) binder in a mass ratio of 90-94:2-4:4-6 were dry-stirred to ensure uniform dispersion of each component and obtain a homogeneous mixture.

[0026] The mixture is rolled and stretched to form a self-supporting membrane;

[0027] Under conditions of 80℃-90℃ and 2MPa-5MPa, the self-supporting membrane and copper foil current collector are subjected to hot pressing and shaping treatment for 20s-40s, which melts the TPU in the modified epoxy-based SBR binder and initially builds a three-dimensional network skeleton, and flows and fills the gaps of the negative electrode active material. At the same time, it penetrates into the surface micropores of the copper foil current collector and softens the epoxy-based SBR in the modified epoxy-based SBR binder. Meanwhile, the TPU and the epoxy-based SBR molecular chains intertwine to form a physical entanglement structure, thus obtaining the negative electrode preform.

[0028] Under conditions of 100℃-120℃ and 10MPa-15MPa, the negative electrode preform is subjected to hot-pressing anchoring treatment for 40s-80s, which causes the epoxy-oxidized SBR to flow and form a continuous elastic network in the three-dimensional mesh skeleton, thereby forming an epoxy-oxidized SBR-TPU dual network structure with the three-dimensional mesh skeleton. At the same time, the epoxy-oxidized SBR, relying on the skeleton formed by the TPU, penetrates into the surface micropores of the copper foil current collector, so that the epoxy groups on the epoxy-oxidized SBR and the hydroxyl groups on the surface of the copper foil current collector undergo ring-opening reaction to form covalent bonds. Simultaneously, the modified gaseous SiO2 in the modified epoxy-oxidized SBR binder forms chemical bonds with the copper foil current collector through the surface functional groups introduced by the silane coupling agent, thus completing the dual interface chemical anchoring.

[0029] The negative electrode preform after hot-pressing and anchoring is cooled to room temperature to allow the TPU to crystallize, thereby fixing the physical entanglement structure and the epoxy-based SBR-TPU dual network structure to obtain the negative electrode sheet.

[0030] Preferably, the negative electrode active material is a SiOx / C composite material, wherein the value of x ranges from 0.5 to 1.5, and C is one or more of graphite, carbon nanotubes, graphene, or amorphous carbon.

[0031] The conductive agent includes one or more of carbon nanotubes, conductive carbon black, Ketjen black, carbon fiber, or acetylene black.

[0032] The silane coupling agent is one or more of γ-aminopropyltriethoxysilane KH550 or γ-(2,3-epoxypropoxy)propyltrimethoxysilane KH560;

[0033] During the cooling process to room temperature, the cooling rate is 40℃ / s-60℃ / s.

[0034] Fifthly, the present invention provides an energy storage device, the energy storage device comprising: for lithium-ion batteries or lithium-ion capacitors; the energy storage device comprising the modified epoxy-oxidized styrene-butadiene rubber (SBR) binder described in the first aspect above, or comprising the modified epoxy-oxidized SBR binder prepared by the preparation method described in the second aspect above, or comprising the negative electrode sheet described in the third aspect above, or comprising the negative electrode sheet prepared by the preparation method described in the fourth aspect above.

[0035] The modified epoxy-oxidized styrene-butadiene rubber (SBR) binder provided by this invention comprehensively solves the bottleneck problem of traditional dry electrode processes through the synergistic effect of epoxy-oxidized SBR, TPU, and modified fumed silica (SiO2), achieving significant technical effects: the epoxy groups on the epoxy-oxidized SBR molecular chains form dynamic ion transport channels by changing the local molecular chain structure and charge distribution, thereby directly improving the ionic conductivity of the modified epoxy-oxidized SBR binder; the modified fumed silica (SiO2) physically adsorbs the residual silanol groups on the surface and physically entangles with the epoxy-oxidized SBR molecular chains through the introduction of organic long chains by silane coupling agents, synergistically coating the epoxy-oxidized SBR surface, significantly reducing the van der Waals forces between epoxy-oxidized SBR particles, increasing the particle spacing, fundamentally inhibiting particle agglomeration, and thus greatly improving the dispersion stability of the modified epoxy-oxidized SBR binder.

[0036] In summary, the modified epoxy-based SBR binder provided by this invention solves the problems of poor dispersibility, poor thermal stability, insufficient interfacial bonding force, and low ionic conductivity of traditional binders in dry electrode processes, providing a key material basis for the preparation of high-performance, long-life lithium-ion batteries. Attached Figure Description

[0037] Figure 1 A schematic diagram of the preparation process of the modified epoxy-oxidized styrene-butadiene rubber (SBR) adhesive provided in the embodiments of the present invention;

[0038] Figure 2 This is a schematic diagram of the preparation process of the negative electrode sheet provided in an embodiment of the present invention. Detailed Implementation

[0039] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0040] The reagents and materials used in the following examples and comparative examples are all commercially available conventional reagent products, or can be prepared by conventional methods. Where specific experimental steps or conditions are not specified in the examples, they were performed according to conventional experimental steps and conditions in the art. Unless otherwise specified, all equipment used is conventional equipment currently available in the art.

[0041] This invention provides a modified epoxy-oxidized styrene-butadiene rubber (SBR) adhesive, its preparation method, and its application.

[0042] The modified epoxy-oxidized styrene-butadiene rubber (SBR) provided by the present invention comprises epoxy-oxidized SBR, thermoplastic polyurethane (TPU), and modified fumed silica (SiO2) in a mass ratio of 89-94.5:5-10:0.5-1; the molecular chain of the epoxy-oxidized SBR contains epoxy groups.

[0043] Epoxy groups form dynamic ion transport channels by altering the local structure and charge distribution of the epoxy-oxidized SBR molecular chain, thereby improving the ionic conductivity of the modified epoxy-oxidized SBR binder.

[0044] The residual silanol groups on the surface of modified gaseous SiO2 undergo physical adsorption with the polar groups in the epoxy-based SBR molecular chain. At the same time, the organic long chains introduced by the silane coupling agent physically entangle with the epoxy-based SBR molecular chain, so that the modified gaseous SiO2 coats the surface of the epoxy-based SBR, thereby reducing the van der Waals forces between epoxy-based SBR particles, increasing the interparticle spacing and inhibiting particle agglomeration, thus improving the dispersibility of the modified epoxy-based SBR binder.

[0045] When the modified epoxy-based SBR binder is applied to the negative electrode sheet, the epoxy groups on the epoxy-based SBR undergo a ring-opening reaction with the hydroxyl groups on the surface of the copper foil current collector to form covalent bonds. At the same time, the TPU molecular chains and the epoxy-based SBR molecular chains intertwine to form a physical entanglement structure, preventing slippage between the epoxy-based SBR molecular chains and the TPU molecular chains. In addition, the modified gas-phase SiO2 forms chemical bonds with the copper foil current collector through functional groups introduced by the silane coupling agent, which synergistically enhances the interfacial bonding force between the electrode and the current collector and improves the structural stability of the electrode.

[0046] The TPU molecular chains form physical cross-linking points through hard segment microregions, constructing a three-dimensional network framework. The three-dimensional network framework and the elastic network formed by the epoxy-oxidized SBR in the three-dimensional network framework constitute an epoxy-oxidized SBR-TPU dual network structure, which improves the thermal stability of the modified epoxy-oxidized SBR adhesive.

[0047] Meanwhile, the modified fumed SiO2 has low agglomeration and can be uniformly dispersed in the electrode slurry to form a three-dimensional network structure. This, along with the synergistic effect of the epoxy-modified SBR-TPU dual network structure, provides a continuous channel for ion transport and improves the ionic conductivity of the modified epoxy-modified SBR binder. The three-dimensional network framework provides the main transport channel for ion transport, while the elastic network, through elastic deformation, alleviates the volume change of the active material and maintains the porous structure inside the negative electrode sheet, providing a buffer space for ion transport within the three-dimensional framework.

[0048] Specifically, epoxy-based SBR is formed by grafting glycidyl methacrylate (GMA) containing epoxy groups onto SBR. The double bonds in the GMA molecule can undergo a ring-opening reaction with the SBR molecular chain, introducing epoxy groups into the SBR molecular chain. Epoxy groups can alter the local structure and charge distribution of the SBR molecular chain, forming dynamic ion transport channels and improving ionic conductivity. Specifically, from a molecular structure perspective, the rigidity of epoxy groups alters the flexibility of the molecular chain, producing steric hindrance and affecting the stacking pattern of the molecular chain. From a charge distribution perspective, the electronegativity of the oxygen atoms in the epoxy groups induces polarization, and even produces conjugation effects and electron delocalization when unsaturated structures are adjacent, changing the surface charge properties of the molecular chain. For example, epoxy groups create more microscopic pores between epoxy-based SBR molecular chains, increasing ion transport channels. Simultaneously, epoxy groups alter the surface charge distribution of the molecular chain, enhancing interactions with ions, guiding the ordered arrangement of ions, and lowering the ion transport energy barrier. These changes combined can increase ion transport channels, lower ion transport energy barriers, and optimize ion transport dynamics, thereby increasing ion transport rate and ion conductivity.

[0049] As described above, epoxy-modified SBR introduces epoxy groups through GMA grafting. These epoxy groups possess certain chemical stability and high reactivity, enabling them to react chemically with the hydroxyl groups on the copper foil surface to form covalent bonds. Compared to traditional physical adsorption, covalent bonds provide a more stable and robust bonding force. This chemical bonding significantly enhances the adhesion strength between the binder and the copper foil, improving the interfacial bonding between the electrode and the current collector, and reducing the interfacial peeling rate during battery cycling. During electrode use, the excellent adhesion performance ensures a tight bond between the electrode active material and the copper foil current collector, effectively improving the structural stability of the electrode, preventing active material detachment, ensuring normal electrode operation, and extending battery cycle life. This demonstrates that the modified epoxy-modified SBR binder provided by this invention, through epoxy functionalization of SBR, enhances the bonding force between the binder and the electrode material, effectively improving the interfacial bonding between the electrode and the current collector, reducing the interfacial peeling rate, and solving the technical problems of insufficient interfacial bonding and high peeling rate between the electrode and the current collector when using traditional SBR.

[0050] TPU is a high-strength, high-toughness polymer material. Its molecular structure contains hard segments and soft segments. The hard segments are typically composed of diisocyanates and small-molecule chain extenders, exhibiting high thermal stability and strength. The soft segments are generally composed of polyethers or polyester polyols, giving TPU a certain degree of flexibility and elasticity. This unique molecular structure allows TPU to maintain stable performance over a wide temperature range. The hard segments in the TPU molecular chain form crystalline regions (hard segment microdomains) through microphase separation. These hard segment microdomains act as physical crosslinking points, providing a stable three-dimensional network framework for the entire adhesive system.

[0051] Furthermore, when epoxy-oxidized SBR is compounded with TPU, the TPU molecular chains and epoxy-oxidized SBR molecular chains intertwine and interpenetrate, forming a network structure. This network structure is a three-dimensional network structure formed by the spatial entanglement and interpenetration between the TPU and epoxy-oxidized SBR polymer chains. This network structure can effectively disperse the stress generated in the electrode during charging and discharging through stress transfer, preventing interfacial slippage between the epoxy-oxidized SBR and TPU molecular chains, enhancing the interfacial bonding force between the electrode and the copper foil current collector, and improving the electrode's resistance to volume expansion. Specifically, during electrode charging and discharging, when the electrode undergoes volume changes, the high strength of TPU can withstand significant external forces, preventing electrode structural damage, while its high toughness allows the electrode to quickly recover its original shape after deformation, reducing the likelihood of breakage. By improving the electrode's mechanical properties, TPU helps enhance the electrode's structural stability and extend its cycle life. That is, during the charging and discharging process, the tensile or shear stress generated by the volume change can be uniformly transferred between TPU and epoxy-based SBR through the physical entanglement structure, avoiding electrode breakage caused by local stress concentration.

[0052] Furthermore, when epoxy-oxidized SBR is compounded with TPU, the hard segments of TPU can form certain physical cross-links or interactions with the epoxy-oxidized SBR, enhancing the thermal stability of the entire adhesive system. At high temperatures, the hard segments of TPU can restrict the thermal motion of the epoxy-oxidized SBR molecular chains, reducing the degradation of the epoxy-oxidized SBR and ensuring adhesive performance. At low temperatures, the soft segments of TPU and the flexibility of the epoxy-oxidized SBR can maintain the adhesive's bonding effect, ensuring that the peel strength of the adhesive is not too low, thus widening the hot-pressing temperature window. Simultaneously, the epoxy-oxidized SBR also possesses a certain degree of elasticity, forming an elastic layer that can alleviate stress on the modified adhesive during use, maintain pore stability, facilitate ion transport, and improve ionic conductivity.

[0053] Specifically, in the modified epoxy-based SBR binder system, TPU and epoxy-based SBR form a synergistic mechanical and ion-conducting framework through a unique structural composite. Specifically, the hard segments in the aforementioned TPU molecular chain undergo microphase separation to form hard segment microregions. These hard segment microregions serve as physical cross-linking points, constructing a continuous and stable three-dimensional network framework. This framework not only endows the electrode with excellent macroscopic structural strength but also forms micron-sized channels with pore sizes between 0.2 and 0.5 μm, serving as the main channels for lithium-ion transport and laying the structural foundation for rapid ion migration.

[0054] Meanwhile, the epoxy-oxidized SBR molecular chains penetrate and anchor within the three-dimensional TPU framework, forming an elastic network. Together, they constitute an epoxy-oxidized SBR-TPU dual-network structure, improving the thermal stability of the modified epoxy-oxidized SBR binder. Furthermore, in this structure, the elastic network formed by the epoxy-oxidized SBR plays a crucial dynamic buffering role: during charging and discharging, when the negative electrode active material undergoes significant volume changes, this network effectively absorbs and dissipates stress through reversible elastic deformation, thereby maintaining the integrity and connectivity of the micropores within the electrode and ensuring a continuous buffer space for ion transport within the framework channels.

[0055] This dual-network structure achieves the synergistic function of "rigid skeleton maintaining unobstructed channels" and "elastic phase buffering volumetric strain", thereby jointly ensuring the ionic conductivity and structural stability of the electrode under high load and long cycle.

[0056] It should be noted that, in this invention, the modified gaseous SiO2 is obtained by modifying hydrophilic gaseous SiO2 using a silane coupling agent. Preferably, the silane coupling agent is one or more of γ-aminopropyltriethoxysilane (KH550) or γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH560).

[0057] Specifically, the core mechanism of modification lies in the reaction between the functional groups (such as alkoxy groups) at one end of the silane coupling agent and some of the silanol groups on the SiO2 surface. This reaction replaces some of the silanol groups with long organic chains, significantly reducing the number of polar groups on the surface and introducing steric hindrance. This fundamentally reduces the van der Waals forces and hydrogen bonds between particles, thus endowing the modified gaseous SiO2 with excellent low agglomeration properties. This characteristic ensures that the modified gaseous SiO2 can be uniformly dispersed in the electrode slurry, overlapping to form a through-hole three-dimensional network structure. This structure creates through-hole, continuous pores inside the electrode, providing continuous channels for lithium-ion transport and effectively improving ionic conductivity.

[0058] Meanwhile, the specific functional groups introduced at the other end of the silane coupling agent (such as the amino group of KH550 or the epoxy group of KH560) are key to achieving interfacial bonding. These functional groups can form stable chemical bonds with the oxides or hydroxyl groups on the surface of the copper foil current collector. In other words, the modified gaseous SiO2 forms stable chemical bonds (covalent or coordinate bonds) with the copper foil current collector through the surface functional groups introduced by the silane coupling agent. This effect is much stronger than physical adsorption and can resist the stress caused by volume changes during battery cycling, significantly enhancing the interfacial bonding force between the electrode and the current collector, thereby improving the stability of the electrode structure.

[0059] Furthermore, the modified fumed SiO2 undergoes physical adsorption with polar groups (such as carboxyl groups) in the epoxy-based SBR molecular chains through residual silanol groups on its surface, and also physically entangles with the epoxy-based SBR molecular chains through the introduction of organic long chains by silane coupling agents. Through these dual effects, the modified fumed SiO2 firmly coats the surface of the epoxy-based SBR particles. This coating effectively increases the interparticle spacing of the epoxy-based SBR, weakens the van der Waals forces between them, and inhibits the aggregation of epoxy-based SBR particles. This synergistically improves the dispersion uniformity of the modified epoxy-based SBR binder in the electrode slurry, jointly ensuring the integrity of the electrode structure and ion transport efficiency.

[0060] The epoxy grafting rate on the surface of the epoxy-modified SBR provided by this invention has a significant impact on the performance of the modified epoxy-modified SBR. When the epoxy grafting rate on the surface of the epoxy-modified SBR powder is less than 1.0 mmol / g, the number of epoxy groups available for chemical reactions on the surface of the epoxy-modified SBR powder is relatively small. When reacting with other substances, the lack of active sites prevents the formation of a sufficient number or strength of chemical bonds. This deficiency will seriously affect the performance of the material and reduce its reliability and stability in practical applications. When the surface epoxy grafting rate exceeds 1.5 mmol / g, the density of epoxy groups on the material surface is too high, and there are strong interaction forces between the epoxy groups (such as dipole-dipole interactions). Under high density, these interaction forces make it easier for the epoxy-modified SBR powder particles to attract and aggregate, thus forming agglomerates. Agglomeration will significantly change the structure and properties of the material surface, such as reducing the effective specific surface area of ​​the material and affecting its contact and reaction efficiency with other substances. Therefore, in this invention, preferably, the epoxy grafting rate of the epoxy-oxidized SBR is 1.0-1.5 mmol / g, and more preferably, the epoxy grafting rate of the epoxy-oxidized SBR is 1.2 mmol / g-1.4 mmol / g.

[0061] Preferably, the modified epoxy-oxidized SBR adhesive provided in this application has a TPU component that is polyester type, with a hardness of 80A-95A, tear strength >50kN / m, melt index of 20g / min-30g / min, and glass transition temperature Tg ≤-30℃.

[0062] The modified epoxy-based SBR binder provided by this invention achieves a significant improvement in interfacial bonding energy (simulated calculations show it can reach over 150 kJ / mol) by forming covalent bonds between its epoxy groups and copper foil. Simultaneously, the composite of TPU and epoxy-based SBR endows the binder with excellent thermal processing properties over a wide temperature range of 80℃-130℃, resulting in good flowability under heating conditions and ease of molding, thus significantly broadening its applicable processing temperature range.

[0063] The above analysis shows that the modified epoxy-based SBR binder provided by this invention, through the synergistic effect of epoxy-based SBR, TPU, and modified fumed SiO2, comprehensively solves the bottleneck problem of traditional dry electrode processes and achieves significant technical effects.

[0064] First, the interfacial bonding force and electrode structure stability are significantly enhanced.

[0065] When this binder is applied to the negative electrode sheet, the interfacial bonding force between the electrode and the copper foil current collector is fundamentally strengthened through the synergistic bonding and entanglement of epoxy-oxidized SBR, TPU and modified gaseous SiO2. This significantly improves the structural integrity and stability of the electrode during long-term charge-discharge cycles and effectively inhibits the shedding of active materials.

[0066] Second, the ionic conductivity was significantly improved.

[0067] This binder system significantly reduces the migration resistance of ions within the electrode by constructing a multidimensional ion transport path, enabling the electrode to exhibit excellent ionic conductivity and providing a key material basis for achieving high-rate performance and fast charge-discharge in batteries.

[0068] Third, thermal stability and processability are improved simultaneously.

[0069] The binder of this invention exhibits excellent thermal stability and can withstand higher processing and operating temperatures; at the same time, it has excellent dispersion uniformity in electrode slurry, which together broadens the electrode preparation process window, improves production yield and efficiency, and ensures the reliability of the electrode under harsh working conditions.

[0070] In summary, the binder of this invention effectively solves multiple challenges faced by high-expansion negative electrodes in dry electrode processes, such as binder dispersion, interfacial bonding, ion conduction, and thermal stability, providing a key material basis for the preparation of high-performance, long-life lithium-ion batteries.

[0071] The modified epoxy-based SBR binder proposed in this invention can be used in the fabrication of negative electrode sheets, and further in energy storage devices, such as lithium-ion batteries or lithium-ion capacitors. It can significantly improve the ion transport capacity, interfacial bonding force and thermal stability of the electrodes, providing strong support for high-performance battery systems and meeting the needs of various application scenarios.

[0072] This invention also provides a method for preparing the above-mentioned modified epoxy-based SBR binder, specifically, as follows: Figure 1 As shown, the preparation method mainly includes the following steps:

[0073] Step 110: Styrene-butadiene rubber (SBR) emulsion and glycidyl methacrylate (GMA) containing epoxy groups are stirred and mixed at room temperature, and then the temperature is raised to 55℃-70℃ to carry out a constant temperature grafting reaction, so that the epoxy groups in GMA are grafted onto the SBR molecular chain to obtain an epoxy-modified SBR emulsion.

[0074] Under heating conditions, the active sites in the SBR emulsion react chemically with GMA, causing epoxy groups to be grafted onto the SBR molecular chain, thereby endowing the SBR with epoxy functional properties. This grafting reaction is based on the interaction of active groups in a chemical reaction. At a certain temperature, the epoxy groups of GMA undergo a ring-opening reaction with specific groups (such as unsaturated bonds) on the SBR molecular chain, thereby introducing epoxy groups.

[0075] Specifically, if the stirring speed is too low, the solution will not mix sufficiently, which may lead to uneven local reactions. If the stirring speed is too high, excessive energy may be introduced, causing unnecessary side effects. Preferably, stirring and mixing at a speed of 100-400 rpm for 10 minutes is to ensure that the SBR emulsion and GMA are thoroughly and uniformly mixed to obtain a good reaction system foundation for subsequent grafting reactions.

[0076] To ensure a smooth temperature rise to the target temperature and avoid rapid heating leading to localized overheating, side reactions, and reduced grafting rate, the preferred heating rate of this invention is 2°C / min. After the mixture reaches 55°C-70°C, a isothermal reaction is initiated to graft epoxy groups onto the SBR. If the reaction temperature is too low, the reaction rate will be slow and incomplete; if the reaction temperature is too high, it may increase side reactions such as GMA self-polymerization, reducing the grafting rate. Simultaneously, if the reaction time is too short, grafting will be incomplete; if the reaction time is too long, it may increase the occurrence of side reactions, adversely affecting product performance. Preferably, to ensure the grafting reaction proceeds fully, allowing sufficient time for GMA to react with the active sites on the SBR molecular chain to achieve the expected grafting rate, the isothermal reaction time is 1.5h-3h.

[0077] Furthermore, preferably, in this invention, the SBR emulsion used is prepared by emulsion polymerization of styrene and butadiene in a mass ratio of 35-45:55-65. If the styrene proportion is less than 35%, the SBR emulsion will have insufficient adhesion, leading to a decrease in the peel strength of the prepared epoxy-modified SBR, which will affect the stability of the electrode structure when applied in the electrode. If the proportion exceeds 45%, the decreased elasticity will reduce the elongation at break, and the prepared epoxy-modified SBR will reduce the flexibility and impact resistance of the electrode when applied in the electrode. The solid content of the SBR emulsion selected in this invention is 30wt%-40wt%, which can balance drying energy consumption and emulsion viscosity. When the solid content is less than 30%, the drying energy consumption will increase, increasing production costs. If the solid content is greater than 50%, the emulsion viscosity will be relatively high, making it difficult to graft uniformly and affecting the modification effect. Furthermore, to control the grafting rate within the range of 1 mmol / g to 1.5 mmol / g, the amount of GMA added is based on the solid content mass of the SBR (not the total mass of the SBR emulsion). Specifically, the amount of GMA added is 2.5% to 4% of the solid content mass of the SBR. This amount ensures that an appropriate number of epoxy groups are introduced onto the SBR molecular chain. If the amount added is too low, the grafting rate will be low, and there will be no effective improvement in SBR performance. If the amount added is too high, it will not only increase production costs but may also lead to uneven grafting reactions or even side reactions, affecting product quality.

[0078] Epoxy functionalization introduces epoxy groups into the SBR molecular chain, providing active sites for further reactions with other substances containing active hydrogen groups, thereby improving the adhesion and compatibility of SBR with other polymers and broadening its application range.

[0079] Step 120: Spray dry the epoxy-oxidized SBR emulsion to obtain reactive epoxy-oxidized SBR powder.

[0080] The epoxy-based SBR emulsion is atomized into fine droplets using hot air. The water in the droplets evaporates rapidly under the action of hot air, causing the epoxy-based SBR emulsion to solidify into powder particles, namely epoxy-based SBR powder.

[0081] In the preparation process of modified epoxy-based SBR binders, the core technology lies in endowing the binder system with active chemical bonding function through molecular structure design and physical morphology control. Specifically, "reactivity" refers to the unique chemical ability of the epoxy groups introduced into the SBR molecular chain through grafting to react with the hydroxyl groups on the surface of the copper foil current collector, thereby forming a stable CO-Cu covalent interface layer. This reactivity is a decisive factor in strengthening the bonding force between the electrode and the current collector interface and the overall structural stability.

[0082] The spray drying step is a key process for achieving and maintaining the aforementioned reactivity. In the emulsion system before drying, the epoxy groups are shielded by the aqueous phase and subjected to hydrogen bonding, thus blocking their reaction sites and posing a risk of premature hydrolysis and deactivation. Through spray drying, the system undergoes a physical transformation from emulsion to powder. This process not only effectively eliminates the shielding effect of water on the epoxy groups, fully exposing their active sites, but more importantly, it immobilizes the highly reactive epoxy groups within the dried powder matrix, placing them in a stable kinetic dormant state, thereby avoiding unintended consumption during storage and slurry preparation.

[0083] Based on the above description, the technical path of the present invention can be summarized as follows: First, reactive epoxy functional groups are introduced into the SBR framework through chemical grafting; then, the active sites are physically exposed and stably encapsulated through spray drying; finally, during the electrode forming process, the activity is directionally triggered and forms a stable chemical bridge with the current collector, thereby realizing an essential improvement in the bonding mechanism from traditional physical adsorption to active chemical bonding.

[0084] In the spray drying process, the selection of inlet and outlet temperatures is crucial. If the inlet temperature is too low, moisture evaporation is slow, drying time is too long, and production efficiency is low. If the temperature is too high, it may cause adverse reactions such as thermal degradation of the epoxy-based SBR powder, affecting product quality. If the outlet temperature is too low, it may indicate that the moisture has not evaporated completely, resulting in excessively high powder moisture content. If the outlet temperature is too high, it may also cause problems such as thermal decomposition of the powder. Preferably, the spray drying equipment used is selected from either an open-type spray dryer or a closed-type spray dryer, with an inlet temperature of 170℃-190℃. Within this temperature range, the emulsion can be heated rapidly, and the moisture can evaporate quickly, ensuring drying efficiency. Preferably, the outlet temperature range is 75℃-85℃, which ensures that the powder is basically completely dried when it leaves the drying tower, while avoiding the adverse effects of excessively high temperatures on powder properties.

[0085] In this invention, the target particle size is D50 = 5 ± 0.5 μm powder. Within this particle size range, the powder has good flowability and dispersibility, which is beneficial for subsequent processing operations such as dry mixing. If the particle size is too large, the powder has poor flowability and is prone to agglomeration. If the particle size is too small, the powder is prone to flying, which can easily cause losses during processing and may affect the uniformity of the product.

[0086] In this invention, spray drying effectively removes moisture from the emulsion, reducing the water content from 60% to 0.8%. At the same time, it controls the particle size (D50 of 5±0.5μm) and flowability (angle of repose <35°) of the powder, ensuring the uniformity of the dry mix and providing a stable and high-performance SBR powder raw material for subsequent processing.

[0087] Step 130: Epoxylated SBR powder, thermoplastic polyurethane (TPU), and modified fumed silica (SiO2) in a mass ratio of 89-94.5:5-10:0.5-1 are dry-mixed. Mechanical force causes the TPU and epoxylated SBR molecular chains to intertwine, forming a physically entangled structure. The modified SiO2, through residual silanol groups on its surface, physically adsorbs onto the polar groups in the epoxylated SBR molecular chains. Simultaneously, the organic long chains introduced by the silane coupling agent physically entangle with the epoxylated SBR molecular chains, thus uniformly coating the epoxylated SBR surface and inhibiting the agglomeration of epoxylated SBR particles, resulting in a uniformly dispersed modified epoxylated SBR binder.

[0088] Epoxylated SBR powder, TPU, and modified fumed SiO2 are dry-mixed uniformly to form a modified epoxylated SBR binder. The mixing equipment can be any of a high-speed mixer, a precision mixer, or a V-type mixer; preferably, a V-type mixer is used. During the mixing process, the particles of different components collide and disperse, ultimately achieving a uniform distribution and forming a stable mixture.

[0089] Furthermore, during the mixing process, if the stirring speed is too low, the mixing efficiency will be low, the mixing time will be long, and the mixing may be uneven. If the speed is too high, the powder may fly away, causing losses. At the same time, excessive stirring may damage the powder structure. If the mixing time is too short, the mixing will also be insufficient. If the mixing time is too long, the improvement in mixing effect will not be significant, and the energy consumption will be increased. Preferably, in this application, the speed of the mixing equipment is 15 rpm-25 rpm, and the mixing time is 25 min-40 min.

[0090] Step 130 is actually the dry mixing process of each component. In order to control the temperature during the dry mixing process and prevent the powder temperature from rising due to heat generated by mechanical stirring, which could lead to powder agglomeration or performance changes, cooling water is used to maintain the mixing chamber at 25±5℃. Within this temperature range, the quality and stability of the modified binder can be guaranteed.

[0091] Furthermore, the modified fumed silica used in this application is obtained by modifying hydrophilic fumed silica with a silane coupling agent (such as KH550 or KH560). The amount of silane coupling agent used is typically 1 wt% to 3 wt% of the mass of the hydrophilic fumed silica. For example, for 100 g of hydrophilic fumed silica, 1 g to 3 g of KH550 or KH560 is used. Specifically, a method for preparing modified fumed silica is provided below, including the following steps:

[0092] (1) Preprocessing:

[0093] Hydrophilic vapor phase SiO2 is vacuum dried at 100℃-120℃ for 2h-4h to remove the water physically adsorbed on the surface of hydrophilic vapor phase SiO2, and dry SiO2 powder is obtained.

[0094] (2) Hydrolysis of silane coupling agents:

[0095] The silane coupling agent was dispersed in a mixed solvent of ethanol and water at a volume ratio of 9:1 and hydrolyzed by stirring at room temperature for 0.5-1 h to obtain a silane coupling agent hydrolysate solution. The concentration of the silane coupling agent hydrolysate solution was 1 wt%-5 wt%.

[0096] (3) Modification reaction:

[0097] Dry SiO2 powder is slowly added to a silane coupling agent hydrolysis solution and mechanically stirred at 60℃-80℃ for 4-6 hours to ensure that the SiO2 powder is fully decomposed and reacts with the silane coupling agent molecules to obtain modified SiO2 slurry.

[0098] (4) Post-processing:

[0099] The modified SiO2 slurry was separated by centrifugation or filtration and washed 2-3 times with anhydrous ethanol to remove physically adsorbed and unreacted silane coupling agents. Finally, the washed product was vacuum dried at 80℃-100℃ for 6-8 hours and then ground to obtain modified gaseous SiO2.

[0100] To facilitate the uniform dispersion of modified fumed SiO2 in the binder and maximize its reinforcing effect, preferably, the modified fumed SiO2 used in this invention has a specific surface area of ​​180 m². 2 / g-400m 2 / g, and more preferably, the specific surface area of ​​the modified gaseous SiO2 is 200m². 2 / g-300m 2 / g; preferably, the particle size D50 is between 10nm and 30nm, more preferably between 10nm and 20nm.

[0101] In addition to the above steps, to improve the uniformity of the modified epoxy-based SBR binder, making the powder more uniform and fine, and improving the powder quality and stability, the preparation method of the modified epoxy-based SBR binder also includes sieving. The modified epoxy-based SBR binder prepared after dry mixing is sieved to remove agglomerates. Preferably, to remove agglomerates larger than 75 μm, a 200-mesh sieve is used to sieve the dry-mixed modified epoxy-based SBR binder, ensuring that the residual agglomerates are less than 0.1%. The method for testing residual agglomerates is as follows: 100g of powder is sieved, the mass m of the substance on the sieve is weighed, and the residual rate is calculated using the following formula:

[0102] Residual rate = m / 100 * 100%.

[0103] Epoxylated SBR, as the main component, imparts basic elasticity and adhesion to the adhesive. TPU enhances the interface through molecular chain entanglement and, combined with its hard and soft segment structures, synergistically improves rigidity, wear resistance, and ion transport buffering capacity. Therefore, the addition of TPU synergistically enhances interfacial bonding and is mainly used to improve the rigidity and wear resistance of the product. If the proportion of TPU is too high, the product's elasticity may decrease; if the proportion is too low, the improvement effect on the product's rigidity and wear resistance will be insignificant. Modified fumed silica, as a nanofiller, can play a reinforcing and toughening role in the polymer. Its core function stems from the pre-treatment of the surface with silane coupling agents such as KH550 or KH560—the coupling agent is anchored to the SiO2 surface through Si-O-Si covalent bonds, reducing the number of silanol groups and exposing organic functional groups (such as amino or epoxy groups). On the one hand, it imparts low agglomeration to the particles through steric hindrance; on the other hand, it utilizes the physical adsorption of residual silanol groups on the surface with SBR molecular chains and the physical entanglement of organic long chains with SBR. This process allows SiO2 to uniformly coat SBR particles, inhibiting SBR agglomeration and promoting uniform dispersion of all components in equipment such as V-type mixers through mechanical force. This forms a stable mixture supported by a three-dimensional skeletal structure, providing continuous channels for ion transport. Ultimately, it enhances the electrode-current collector bonding force and structural stability through interfacial chemical bridging and physical entanglement. Insufficient SiO2 addition results in limited reinforcing effect; excessive addition may lead to uneven dispersion in the polymer, causing agglomeration and becoming stress defects, thus affecting the overall product performance. Therefore, to balance the product's elasticity, rigidity, wear resistance, and processing dispersibility, this application specifies the mass ratio of epoxy-oxidized SBR powder, thermoplastic polyurethane (TPU), and modified fumed SiO2 as 89-94.5:5-10:0.5-1.

[0104] Dry mixing ensures uniform mixing of epoxy-oxidized SBR, TPU, and hydrophilic fumed SiO2, fully leveraging the advantages of each component and improving the overall performance of the modified epoxy-oxidized SBR binder, such as increasing the material's strength and hardness, thus providing excellent raw materials for subsequent processing and use.

[0105] The modified epoxy-based SBR binder prepared by this invention can be applied to electrode sheets, such as negative electrode sheets, and further applied in energy storage devices, such as lithium-ion batteries or lithium-ion capacitors. It can significantly improve the ion transport capacity, interfacial bonding force and thermal stability of the electrode, providing strong support for high-performance battery systems and meeting the needs of various application scenarios.

[0106] This invention also provides a method for preparing a negative electrode sheet, specifically, as follows: Figure 2 As shown, the preparation method mainly includes the following steps:

[0107] Step 210: The negative electrode active material, conductive agent and modified epoxy-oxidized styrene-butadiene rubber (SBR) binder in a mass ratio of 90-94:2-4:4-6 are dry-stirred to make the components uniformly dispersed and form a three-dimensional conductive and ion transport network, so as to obtain a homogeneous mixture.

[0108] Step 210 is the dry mixing stage. The high shear force generated by the high-speed shear mixer breaks up the agglomeration between material particles of the negative electrode active material, conductive agent and modified epoxy-based SBR binder powder under the action of the high-speed rotating agitator, so that the particles of different components can fully contact each other and achieve a uniform mixing state.

[0109] In this application, the mass ratio of the negative electrode active material, conductive agent, and modified styrene-butadiene rubber (SBR) is 90-94:2-4:4-6. The negative electrode active material, as the main active material of the electrode, provides a carrier for lithium-ion insertion and extraction. Preferably, the negative electrode active material in this invention is a silicon-carbon negative electrode, specifically a SiOx / C composite material, where x ranges from 0.5 to 1.5, and C is one or more of graphite, carbon nanotubes, graphene, or amorphous carbon. The conductive agent's role is to construct a conductive network, improve the electrode's conductivity, and enable rapid electron conduction within the electrode. Insufficient addition results in an incomplete conductive network, increasing the electrode's internal resistance. Excessive addition occupies space in the active material, reducing electrode capacity. The modified SBR acts as a binder, bonding the negative electrode active material and conductive agent together and ensuring good adhesion between the electrode material and the current collector. Insufficient addition results in insufficient adhesion, making the electrode prone to detachment. Excessive addition increases the electrode's thickness and internal resistance, affecting lithium-ion transport.

[0110] In this invention, preferably, the conductive agent includes one or more of carbon nanotubes, conductive carbon black, Ketjen black, carbon fiber, or acetylene black.

[0111] Preferably, in order to generate sufficient high shear force to ensure thorough dispersion of the components, achieve uniform mixing in a short time, and meet the requirement that the mixing uniformity RSD is less than 3%, the speed of the high-speed shear mixer is preferably 1500 rpm-2500 rpm, and the time is 8 min-15 min during this stage. The method for testing the mixing uniformity is as follows:

[0112] 1. Sampling: Take 5 points (center + four corners) from the mixture, and weigh 1.0g of sample from each point.

[0113] 2. Testing: (1) Place the sample in a muffle furnace and burn it at 600℃ for 2 hours, then determine the ash content (conductive agent residue); (2) Dissolve the modified SBR with acetone, then filter out SiO2 and negative electrode active material, dry and weigh.

[0114] 3. Calculate the uniformity of mixing between the conductive agent and the modified SBR separately:

[0115] RSD = Standard deviation / Mean * 100%.

[0116] The smaller the RSD, the smaller the difference in the content of the corresponding components (conductive agent, modified SBR) at each sampling point, and the more uniform the mixing. If the uniformity of the conductive agent and the modified epoxy-based SB binder R is less than 3%, it means that the mixture obtained in step 210 meets the requirements for uniformity of mixing.

[0117] Step 220: The mixture is rolled and stretched to form a self-supporting membrane.

[0118] Specifically, the dry-mixed homogeneous mixture can be fed into a twin-roll calender. Between two relatively rotating rolls, the mixture is subjected to the squeezing and shearing forces of the rolls, while the heat from the rolls softens the mixture. Thus, under the combined action of pressure and temperature, the mixture is calendered into an electrode preform of a certain thickness and uniformity. The self-supporting film prepared by this invention has a thickness of 150±5μm. The calendering pressure is adjusted by the roll gap. According to the formula P=F / L (F is the hydraulic cylinder pressure, L is the roll length), the calendering pressure is controlled by adjusting the hydraulic cylinder pressure, thereby controlling the thickness and quality of the self-supporting film.

[0119] Specifically, the calendering temperature is 45℃-55℃, and the calendering pressure is 50N / m-100N / m. The dry mixture is calendered to form a film with a certain thickness, uniformity, and self-support, providing a suitable intermediate product for subsequent hot-pressing lamination with copper foil, ensuring the structural integrity and performance stability of the electrode.

[0120] Step 230: Under conditions of 80℃-90℃ and 2MPa-5MPa, the self-supporting membrane and copper foil current collector are subjected to hot pressing and shaping treatment for 20s-40s, so that the TPU in the modified epoxy-modified SBR binder melts and flows to fill the gaps of the negative electrode active material, and intertwines with the epoxy-modified SBR molecular chains in the modified epoxy-modified SBR binder to form a physical entanglement structure, thereby obtaining the negative electrode preform.

[0121] Step 230 is the pre-bonding stage, maintained at 80℃-90℃ and 2MPa-5MPa pressure for 20-40 seconds. This temperature is slightly higher than the softening point of TPU, allowing the TPU to melt and soften, and flow fully under pressure, filling the gaps between the negative electrode active material particles. This not only increases the contact area between the negative electrode active material particles, but also actively strengthens the conductive framework and mechanical integrity of the electrode through the physical entanglement structure formed by the TPU with the epoxy-based SBR molecular chains in the modified epoxy-based SBR binder. Simultaneously, this temperature and conditions ensure that the epoxy-based SBR remains elastic without violent flow, preserving an ideal structural basis for the subsequent anchoring stage.

[0122] Step 240: Under conditions of 100℃-120℃ and 10MPa-15MPa, the negative electrode preform is subjected to hot-press anchoring treatment for 40s-80s. This causes the epoxy groups on the epoxy-oxidized SBR to undergo a ring-opening reaction with the hydroxyl groups on the surface of the copper foil current collector to form covalent bonds. At the same time, it also causes the modified gaseous SiO2 in the modified epoxy-oxidized SBR binder to form chemical bonds with the copper foil current collector through the surface functional groups introduced by the silane coupling agent, thus completing the dual-interface chemical anchoring.

[0123] Step 240 is the anchoring stage, maintained at 100℃-120℃ and 10MPa-15MPa pressure for 40s-80s. This stage triggers dual interfacial chemical anchoring through higher temperature and pressure: on one hand, the epoxy-based SBR penetrates into the micropores of the copper foil current collector via the TPU framework, and the high temperature activates the epoxy groups on the epoxy-based SBR, causing them to undergo a ring-opening reaction with the hydroxyl groups on the surface of the copper foil current collector, forming stable -Cu-OC- covalent bonds; on the other hand, it also promotes the formation of chemical bonds between the modified fumed silica and the copper foil current collector through functional groups (such as amino and epoxy groups) introduced by the silane coupling agent on its surface. During this process, the polymer components in the modified epoxy-based SBR binder more easily penetrate into the micropores on the surface of the copper foil current collector under high pressure, thereby further enhancing the mechanical interlocking effect and firmly anchoring the self-supporting film to the copper foil.

[0124] The anchoring stage enables a strong chemical bond and mechanical anchoring between the self-supporting film and the copper foil, significantly improving the interfacial bonding strength between the electrode and the current collector, reducing the risk of electrode detachment during charging and discharging, and improving the cycle stability and service life of the electrode.

[0125] The core reason for employing a gradient hot-pressing process in this invention is the need to balance the flow and filling of TPU with the interfacial chemical reaction of epoxy-modified SBR. Directly applying high temperature and pressure would cause excessive TPU flow, damaging the established conductive network. Simultaneously, the epoxy-modified SBR might not have enough time to fully spread and bond at the interface due to the rapid reaction, ultimately leading to a decrease in interfacial bonding energy. The gradient process precisely matches the optimal action window for each component, ensuring the synergistic achievement of a stable electrode structure and a high-strength interface.

[0126] Step 250: Cool the hot-pressed negative electrode preform to room temperature to allow TPU to crystallize, thereby fixing the physical entanglement structure and obtaining the negative electrode sheet.

[0127] Specifically, the hot-pressed composite electrode is rapidly cooled to 20℃-30℃ using a water-cooling roller at a cooling rate of 40℃ / s-60℃ / s. This rapid cooling rate allows TPU and other components to crystallize quickly, resulting in high crystallinity. Through rapid cooling, the crystallinity of the electrode exceeds 80%, improving its mechanical strength and reducing volume changes and structural damage during charge and discharge, thus enhancing its cycle performance and lifespan. The crystallinity is tested using a differential scanning calorimeter (DSC) at 100℃-200℃ to obtain the actual enthalpy of fusion. Specifically, 10g of electrode is heated in a nitrogen atmosphere at a heating rate of 10℃ / min, according to the formula: Where, ΔH m It is the enthalpy of fusion; The theoretical enthalpy of fusion for 100% crystalline TPU is 130 J / g.

[0128] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0129] The SBR emulsions used below were all prepared by emulsion polymerization of styrene and butadiene in a mass ratio of 35-45:55-65. The modified fumed SiO2 used was prepared by the method described above. Specifically, the modified fumed SiO2 in Examples 1-3 was obtained by modifying hydrophilic fumed SiO2 with KH550, while the modified fumed SiO2 in Examples 4-5 was obtained by modifying hydrophilic fumed SiO2 with KH560.

[0130] Additionally, it should be noted that the modified fumed SiO2 particle size D50 refers to the median particle size of the modified fumed SiO2 material, which can be the median value sorted by volume, mass, or quantity. In this example, it is the median particle size sorted by quantity, representing the particle size of the modified fumed SiO2 particles that make up the top 50% of the quantity distribution. Particle size D50 is a well-known concept in the art. The particle size D50 of the material provided in the embodiments of the present invention can be determined using instruments and conventional methods known in the art. Specifically, in all embodiments of the present invention, a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK, is used to determine the particle size D50. Similarly, the above also applies to the hydrophilic fumed SiO2 in this example.

[0131] Example 1

[0132] 1. Preparation of modified epoxy-based SBR binder.

[0133] At room temperature, an SBR emulsion with a solid content of 35 wt% and GMA containing epoxy groups were stirred and mixed at 300 rpm for 10 min, and then the temperature was increased to 60 ℃ at 2 ℃ / min and the reaction was kept at a constant temperature for 2.5 h to obtain an epoxy-based SBR emulsion; wherein the amount of GMA containing epoxy groups added was 3% of the mass of the solid content of the SBR emulsion.

[0134] The epoxy-oxidized SBR emulsion was spray-dried to obtain epoxy-oxidized SBR powder.

[0135] Epoxylated SBR powder, thermoplastic polyurethane (TPU), and modified fumed SiO2 in a mass ratio of 92:7:1 were stirred at 20 rpm for 35 min in a V-type mixer. During the mixing process, the mixing chamber was kept at 25±5℃ with cooling water to finally obtain the modified epoxylated SBR binder.

[0136] 2. Preparation of modified gaseous SiO2.

[0137] Raw material: 100g of hydrophilic gaseous SiO2 (specific surface area approximately 220m²) 2 / g, D50 is about 12nm), KH550 (2g).

[0138] Preparation process:

[0139] Hydrophilic vapor phase SiO2 was vacuum dried at 110℃ for 3 hours.

[0140] 2g of KH550 was dispersed in a mixed solvent of 57g ethanol and 8g water, and hydrolyzed at room temperature for 45min to obtain a silane coupling agent hydrolysate solution with a concentration of 3wt%.

[0141] Dry SiO2 powder was added to a silane coupling agent hydrolysis solution and mechanically stirred at 70°C for 5 hours to obtain modified SiO2 slurry.

[0142] Modified SiO2 slurry was obtained by centrifugation, washing three times with anhydrous ethanol, vacuum drying at 90℃ for 7 hours, and grinding; the specific surface area was approximately 205 m² / g. 2 / g, with a particle size D50 of approximately 14nm.

[0143] 3. Using the modified epoxy-based SBR binder prepared above, prepare the negative electrode sheet.

[0144] The SiO2 / graphite composite material, conductive agent, and modified epoxy-based SBR in a mass ratio of 92:3:5 were stirred evenly in a high-speed shear mixer to obtain a mixture.

[0145] The mixture is calendered into a self-supporting film using a twin-roll calender.

[0146] At 90℃ and 3MPa, the self-supporting film and copper foil current collector were hot-pressed for 30s to melt the TPU and fill the gaps in the SiO2 / graphite composite material, thus obtaining the electrode preform.

[0147] The electrode preform was hot-pressed for 70 seconds at 100℃ and 15 MPa to allow the epoxy groups to undergo a ring-opening reaction with the hydroxyl groups on the surface of the copper foil current collector to form covalent bonds. Then it was cooled to room temperature to obtain the negative electrode.

[0148] Example 2

[0149] 1. Preparation of modified epoxy-based SBR binder.

[0150] At room temperature, an SBR emulsion with a solid content of 35 wt% and GMA containing epoxy groups were stirred and mixed at 400 rpm for 10 min, and then the temperature was increased to 55 ℃ at 2 ℃ / min and reacted at a constant temperature for 3 h to obtain an epoxy-based SBR emulsion; wherein the amount of GMA containing epoxy groups added was 2.5% of the mass of the solid content of the SBR emulsion.

[0151] The epoxy-oxidized SBR emulsion was spray-dried to obtain epoxy-oxidized SBR powder.

[0152] Epoxylated SBR powder, thermoplastic polyurethane (TPU), and modified fumed SiO2 in a mass ratio of 90:9:1 were stirred at 20 rpm for 30 min in a V-type mixer. During the mixing process, the mixing chamber was kept at 25±5℃ with cooling water to finally obtain the modified epoxylated SBR binder.

[0153] 2. Preparation of modified gaseous SiO2.

[0154] Raw material: 100g of hydrophilic gaseous SiO2 (specific surface area approximately 270m²) 2 / g, D50 is about 10nm), KH560 (1.5g).

[0155] Preparation process:

[0156] The steps are the same as in Example 1, except that KH560 is used as the coupling agent, and the dosage is 1.5g. The specific surface area of ​​the obtained modified gas phase is approximately 250m². 2 / g, with a particle size D50 of approximately 12nm.

[0157] 3. Using the modified epoxy-based SBR binder prepared above, prepare the negative electrode sheet.

[0158] The SiO2 / graphite composite material, conductive agent, and modified epoxy-based SBR in a mass ratio of 92:4:4 were stirred evenly in a high-speed shear mixer to obtain a mixture.

[0159] The mixture is calendered into a self-supporting film using a twin-roll calender.

[0160] At 85℃ and 5MPa, the self-supporting film and copper foil current collector were hot-pressed for 35s to melt the TPU and fill the gaps in the SiO2 / graphite composite material, thus obtaining the electrode preform.

[0161] The electrode preform was hot-pressed for 70 seconds at 110℃ and 15MPa to allow the epoxy groups to undergo a ring-opening reaction with the hydroxyl groups on the surface of the copper foil current collector to form covalent bonds. Then it was cooled to room temperature to obtain the negative electrode.

[0162] Example 3

[0163] 1. Preparation of modified epoxy-based SBR binder.

[0164] At room temperature, an SBR emulsion with a solid content of 30 wt% and GMA containing epoxy groups were stirred and mixed at 100 rpm for 10 min, and then the temperature was increased to 65 ℃ at 2 ℃ / min and reacted at a constant temperature for 2 h to obtain an epoxy-based SBR emulsion; wherein the amount of GMA containing epoxy groups added was 4% of the mass of the solid content of the SBR emulsion.

[0165] The epoxy-oxidized SBR emulsion was spray-dried to obtain epoxy-oxidized SBR powder.

[0166] Epoxylated SBR powder, thermoplastic polyurethane (TPU), and modified fumed SiO2 in a mass ratio of 91.5:8:0.5 were stirred at 25 rpm for 25 min in a V-type mixer. During the mixing process, the mixing chamber was kept at 25 ± 5 °C with cooling water to finally obtain the modified epoxylated SBR binder.

[0167] 2. Preparation of modified gaseous SiO2.

[0168] Raw material: 100g of hydrophilic gaseous SiO2 (specific surface area approximately 320m²) 2 / g, D50 is about 8nm), KH550 (3g).

[0169] Preparation process:

[0170] The steps are the same as in Example 1, except that the specific surface area of ​​the hydrophilic gaseous SiO2 is increased, the amount of KH550 is increased to 3g, and vacuum drying at 120℃ for 2h is performed to remove the physically adsorbed moisture on the surface of the hydrophilic gaseous SiO2. The specific surface area of ​​the obtained modified gaseous phase is approximately 295m². 2 / g, with a particle size D50 of approximately 10nm.

[0171] 3. Using the modified epoxy-based SBR binder prepared above, prepare the negative electrode sheet.

[0172] The SiO2 / graphene composite material, conductive agent, and modified epoxy-modified SBR in a mass ratio of 90:4:6 were stirred evenly in a high-speed shear mixer to obtain a mixture.

[0173] The mixture is calendered into a self-supporting film using a twin-roll calender.

[0174] At 80℃ and 4MPa, the self-supporting film and copper foil current collector were hot-pressed for 40s to melt the TPU and fill the gaps in the SiO2 / graphite composite material, thus obtaining the electrode preform.

[0175] The electrode preform was hot-pressed for 50 seconds at 120℃ and 10 MPa to allow the epoxy groups to undergo a ring-opening reaction with the hydroxyl groups on the surface of the copper foil current collector to form covalent bonds. Then it was cooled to room temperature to obtain the negative electrode.

[0176] Example 4

[0177] 1. Preparation of modified epoxy-based SBR binder.

[0178] At room temperature, an SBR emulsion with a solid content of 35 wt% and GMA containing epoxy groups were stirred and mixed at 200 rpm for 10 min, and then the temperature was increased to 60 ℃ at 2 ℃ / min and reacted at a constant temperature for 2.5 h to obtain an epoxy-based SBR emulsion; wherein the amount of GMA containing epoxy groups added was 2% of the mass of the solid content of the SBR emulsion.

[0179] The epoxy-oxidized SBR emulsion was spray-dried to obtain epoxy-oxidized SBR powder.

[0180] Epoxylated SBR powder, thermoplastic polyurethane (TPU), and modified fumed SiO2 in a mass ratio of 89:10:1 were stirred at 15 rpm for 35 min in a V-type mixer. During the mixing process, the mixing chamber was kept at 25±5℃ with cooling water to finally obtain the modified epoxylated SBR binder.

[0181] 2. Preparation of modified gaseous SiO2.

[0182] Raw material: 100g of hydrophilic gaseous SiO2 (specific surface area approximately 200m²) 2 / g, D50 is about 22nm), KH560 (1g).

[0183] Preparation process:

[0184] The steps are the same as in Example 1, except that a low specific surface area hydrophilic gaseous SiO2 is used, and the amount of KH560 is the minimum of 1g. In the final step, the washed product is vacuum dried at 100°C for 6 hours. The specific surface area of ​​the obtained modified gaseous phase is approximately 185 m² / g. 2 / g, with a particle size D50 of approximately 25nm.

[0185] 3. Using the modified epoxy-based SBR binder prepared above, prepare the negative electrode sheet.

[0186] SiO with a mass ratio of 94:2:4 0.5 The graphite composite material, conductive agent, and modified epoxy-based SBR are stirred evenly in a high-speed shear mixer to obtain a mixture.

[0187] The mixture is calendered into a self-supporting film using a twin-roll calender.

[0188] The self-supporting film and copper foil current collector were hot-pressed for 25 seconds at 85℃ and 2MPa, causing the TPU to melt and fill with SiO2. 0.5 / The gaps in the graphite composite material are used to obtain the electrode preform;

[0189] The electrode preform was hot-pressed for 40 seconds at 120℃ and 15 MPa to allow the epoxy groups to undergo a ring-opening reaction with the hydroxyl groups on the surface of the copper foil current collector to form covalent bonds. Then it was cooled to room temperature to obtain the negative electrode.

[0190] Example 5

[0191] 1. Preparation of modified epoxy-based SBR binder.

[0192] At room temperature, an SBR emulsion with a solid content of 40 wt% and GMA containing epoxy groups were stirred and mixed at 100 rpm for 10 min, and then the temperature was increased to 70 ℃ at 2 ℃ / min and the reaction was kept at a constant temperature for 1.5 h to obtain an epoxy-based SBR emulsion; wherein the amount of GMA containing epoxy groups added was 4% of the mass of the solid content of the SBR emulsion.

[0193] The epoxy-oxidized SBR emulsion was spray-dried to obtain epoxy-oxidized SBR powder.

[0194] Epoxylated SBR powder, thermoplastic polyurethane (TPU), and modified fumed SiO2 in a mass ratio of 94.5:5:0.5 were stirred at 15 rpm for 40 min in a V-type mixer. During the mixing process, the mixing chamber was kept at 25±5℃ with cooling water to finally obtain the modified epoxylated SBR binder.

[0195] 2. Preparation of modified gaseous SiO2.

[0196] Raw material: 100g of hydrophilic gaseous SiO2 (specific surface area approximately 420m²) 2 / g, D50 is about 15nm), KH550 (2.5g).

[0197] Preparation process:

[0198] The steps are the same as in Example 1, except that a high specific surface area hydrophilic gaseous SiO2 is used, the modification reaction temperature is adjusted to 60℃, and the reaction time is extended to 6 hours. The specific surface area of ​​the obtained modified gaseous phase is approximately 380 m² / s. 2 / g, with a particle size D50 of approximately 18nm.

[0199] 3. Using the modified epoxy-based SBR binder prepared above, prepare the negative electrode sheet.

[0200] SiO with a mass ratio of 94:3:3 1.5 The graphite composite material, conductive agent, and modified epoxy-based SBR are stirred evenly in a high-speed shear mixer to obtain a mixture.

[0201] The mixture is calendered into a self-supporting film using a twin-roll calender.

[0202] The self-supporting film and copper foil current collector were hot-pressed for 20 seconds at 90℃ and 2MPa to melt the TPU and fill it with SiO2. 1.5 / The gaps in the graphite composite material are used to obtain the electrode preform;

[0203] The electrode preform was hot-pressed for 80 seconds at 100℃ and 10 MPa to allow the epoxy groups to undergo a ring-opening reaction with the hydroxyl groups on the surface of the copper foil current collector to form covalent bonds. Then it was cooled to room temperature to obtain the negative electrode.

[0204] Example 6

[0205] The difference between Example 6 and Example 1 is that the preparation of modified gaseous SiO2 is different.

[0206] In Example 6, the modified gaseous SiO2 was prepared as follows:

[0207] Raw material: 100g of hydrophilic gaseous SiO2 (specific surface area approximately 240m²) 2 / g, D50 is about 28nm), KH560 (3g).

[0208] Preparation process:

[0209] The steps are the same as in Example 1, except that KH560 is used as the coupling agent, and the dosage is 3g. The modification reaction temperature is adjusted to 80℃. The specific surface area of ​​the obtained modified gas phase is approximately 220m². 2 / g, with a particle size D50 of approximately 32nm.

[0210] Example 7

[0211] The difference between Example 7 and Example 2 is that the preparation of modified gaseous SiO2 is different.

[0212] In Example 7, the modified gaseous SiO2 was prepared as follows:

[0213] Raw material: 100g of hydrophilic gaseous SiO2 (specific surface area approximately 300m²) 2 / g, D50 is about 9nm), a mixture of KH550 (1g) and KH560 (1g).

[0214] Preparation process:

[0215] The steps are the same as in Example 1, except that a mixture of two silane coupling agents is used, with a total dosage of 2g, and the stirring time during hydrolysis is 0.5h. The specific surface area of ​​the resulting modified gas phase is approximately 275m². 2 / g, with a particle size D50 of approximately 11nm.

[0216] Example 8

[0217] The difference between Example 8 and Example 3 is that the preparation of modified gaseous SiO2 is different.

[0218] In Example 8, the modified gaseous SiO2 was prepared as follows:

[0219] Raw material: 100g of hydrophilic gaseous SiO2 (specific surface area approximately 220m²) 2 / g, D50 is about 15nm), KH550 (2g).

[0220] Preparation process:

[0221] The steps are the same as in Example 1, except for the concentration of the silane coupling agent hydrolysis solution. 2g of KH550 is dispersed in a mixed solvent of 175g ethanol and 25g water, resulting in a silane coupling agent hydrolysis solution concentration of 1wt%. The resulting modified gas phase has a specific surface area of ​​approximately 200 m². 2 / g, with a particle size D50 of approximately 17nm.

[0222] Example 9

[0223] The difference between Example 9 and Example 4 is that the preparation of modified gaseous SiO2 is different.

[0224] In Example 9, the modified gaseous SiO2 was prepared as follows:

[0225] Raw material: 100g of hydrophilic gaseous SiO2 (specific surface area approximately 210m²) 2 / g, D50 is approximately 16nm), KH550 (2g)

[0226] Preparation process:

[0227] The steps are the same as in Example 1. The difference lies in the concentration of the silane coupling agent hydrolysis solution. 2g of KH550 is dispersed in a mixed solvent of 42g ethanol and 6g water, resulting in a silane coupling agent hydrolysis solution concentration of 4wt%. The resulting modified gas phase has a specific surface area of ​​approximately 190m². 2 / g, with a particle size D50 of approximately 18nm.

[0228] Example 10

[0229] The difference between Example 10 and Example 5 is that the preparation of modified gaseous SiO2 is different.

[0230] In Example 10, the modified gaseous SiO2 was prepared as follows:

[0231] Raw material: 100g of hydrophilic gaseous SiO2 (specific surface area approximately 280m²) 2 / g, D50 is approximately 12nm), KH560 (3g)

[0232] Preparation process:

[0233] Hydrophilic vapor phase SiO2 was vacuum dried at 100℃ for 4 hours.

[0234] 3g of KH560 was dispersed in a mixed solvent of 50g ethanol and 7g water, and hydrolyzed at room temperature for 1 hour with stirring.

[0235] A silane coupling agent hydrolysis solution with a concentration of 5 wt% was obtained.

[0236] Dry SiO2 powder was added to a silane coupling agent hydrolysis solution and mechanically stirred at 75°C for 4 hours to obtain modified SiO2 slurry.

[0237] Modified SiO2 slurry was separated by filtration, washed twice with anhydrous ethanol, vacuum dried at 80℃ for 8 hours, and then ground to obtain modified gaseous SiO2; the specific surface area of ​​which was approximately 260 m². 2 / g, with a particle size D50 of approximately 14nm.

[0238] Comparative Example 1

[0239] Negative electrode sheets were prepared using the conventional SBR dry process.

[0240] SBR and SiO in a mass ratio of 92:3:5 x / C composite material and conductive carbon black were stirred at a temperature of 20±2℃; the temperature before adding the binder was below 16℃; after adding unmodified conventional SBR, the mixture was mixed in a high-speed shear mixer at 20℃ and 2000rpm for 10min, and then sheared at 8000rpm under conditions of 50℃-150℃ to obtain the mixture.

[0241] The mixture was calendered into a self-supporting film with a thickness of 150±5μm using a two-roll calender (roll temperature 50℃).

[0242] The self-supporting film and copper foil were hot-pressed together in a single process on a hot press. The hot-pressing conditions were: temperature 95℃, pressure 5MPa, and time 1min.

[0243] Naturally cooled to room temperature, the traditional dry-process negative electrode sheet is obtained.

[0244] The parameters of the negative electrode sheets prepared in Examples 1-10 and / or Comparative Example 1 were tested, and the results are recorded in Table 1. The testing methods for each parameter are as follows:

[0245] Interfacial bonding forces (molecular dynamics simulation):

[0246] 1. Model building:

[0247] The SBR epoxy (-O-) / Cu(111) crystal interface model (Examples 1-10) and the "ordinary SBR fragment / Cu(111)" model (Comparative Example 1) were constructed using Materials Studio software; the force field was selected as COMPASS III, and the cutoff radius was set to...

[0248] 2. Simulation process:

[0249] Energy minimization → NVT ensemble equilibrium (298K, 1ns) → along the Z-axis / ps speed to separate two phases;

[0250] 3. Results Analysis:

[0251] Extract the force-displacement curve of the separation process and integrate to obtain the interfacial bonding energy:

[0252] E ad =∫Fdz / A

[0253] (A: Interface contact area).

[0254] Ionic conductivity:

[0255] 1. Sample preparation: Cut the electrode sheet into 10mm diameter circles and place them between two stainless steel blocking electrodes. No electrolyte needs to be injected. Assemble the 2032 button cell.

[0256] 2. AC impedance test: Using a Solartron 1260 electrochemical workstation and a constant temperature chamber (temperature chamber controlled ±0.5℃), the AC impedance spectrum of stainless steel / stainless steel battery open circuit voltage was tested at a constant temperature of 25℃, with a frequency range of 0.1Hz-1MHz and an amplitude of 10mA.

[0257] 3. Data processing:

[0258] The bulk resistance R1 is extracted by fitting the equivalent circuit model (R1(R2CPE)) using impedance spectrum fitting.

[0259] The ionic conductivity is calculated using the formula: σ=L / (R1×A) (L: electrode thickness (cm), A: electrode area (cm²) 2 )).

[0260] Electrode peel strength:

[0261] 1. Sample preparation: Cut electrode sheets of 1.5*15cm before and after rolling for later use. Prepare a thin steel plate with a length of 17cm and a width of 5cm. Attach a strip of double-sided tape to the center of the steel plate (ensure that the length of the double-sided tape is greater than the sample test length and the same width as the electrode sheet). Roll the plate flat with a roller. Attach the prepared electrode sheet to the double-sided tape and roll it flat again with a roller.

[0262] 2. Testing: Insert the steel plate with the attached electrode into the lower clamp and fix it horizontally. Insert the electrode without adhesive into the upper clamp and fix it at a 90° angle to the electrode in the lower clamp. Input the peel length and width, test force (50N), and peel speed (25cm / min) to start the test and obtain the peel strength curve and peel strength value. Perform the test 3 times and take the average value.

[0263] Hot-pressing temperature window: using the HST-H heat sealer (supports pressures from 0.05MPa to 0.7MPa).

[0264] 100-cycle capacity retention:

[0265] Half-cell capacity retention after 100 cycles, tested under the following conditions: voltage window of 0.005V-1.5V (vs. Li + / Li); discharge rate: 0.1C; lower limit of discharge voltage window: 0.005V.

[0266] Effective pore size distribution: measured by actual mercury porosimetry.

[0267] The purpose of measuring the effective aperture distribution is mainly threefold:

[0268] (1) Evaluation of ion transport efficiency: The appropriate pore size provides a channel for electrolyte wetting and lithium ion migration, which directly affects ion conductivity and rate performance.

[0269] (2) Verify the process effect: Verify whether the gradient hot pressing process and the "epoxylated SBR-TPU dual network" structure successfully constructed the ideal microstructure.

[0270] (3) Correlation with electrochemical performance: Correlation of pore size distribution data with electrochemical test results such as ionic conductivity and cycle performance provides microstructural explanation and evidence for performance improvement.

[0271] The test results for each parameter are recorded in Table 1 below.

[0272]

[0273]

[0274] Table 1

[0275] Based on the data in Table 1, comparing Examples 1-10 and Comparative Example 1, Examples 1-10 exhibit higher electrode peel strength, ionic conductivity, and capacity retention after 100 cycles, as well as a wider hot-pressing temperature window. This indicates that the modified epoxy-based SBR binder prepared in this application can significantly improve interfacial bonding, ion transport capacity, capacity retention, and thermal stability in the electrode.

[0276] The interfacial bonding energy of Examples 1-10 is also significantly better than that of Comparative Example 1, which indicates that the epoxy groups introduced by the adhesive provided in this application can form chemical bonds with the copper foil, significantly improving the interfacial bonding energy.

[0277] Furthermore, compared to Comparative Example 1, Examples 1-10 exhibit a smaller and more concentrated effective pore size distribution, with smaller and more concentrated main peaks. This is a result of precisely controlling the electrode microstructure through the "epoxylated SBR-TPU dual network" and modified fumed SiO2, which constructs a "highly efficient, stable, and durable" ion transport network. This is the fundamental reason why this invention surpasses traditional processes in ionic conductivity and cycle life. This also demonstrates that the binder prepared in this invention, when applied to the negative electrode sheet, forms an "epoxylated SBR-TPU dual network" structure through a gradient hot-pressing process. The main channels formed by the rigid TPU framework provide pathways for electrolyte wetting and lithium-ion migration. Simultaneously, the main channels formed by the rigid TPU framework and the buffer pores maintained by the elastic phase of the epoxylated SBR together constitute an optimized ion transport network, synergistically improving ionic conductivity and enhancing battery cycle performance.

[0278] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A modified epoxy-oxidized styrene-butadiene rubber (SBR) adhesive, characterized in that, The modified epoxy-based SBR binder comprises epoxy-based SBR, thermoplastic polyurethane (TPU), and modified fumed silica (SiO2) in a mass ratio of 89-94.5:5-10:0.5-1; the molecular chain of the epoxy-based SBR contains epoxy groups. The epoxy groups form dynamic ion transport channels by changing the local structure and charge distribution of the epoxy-oxidized SBR molecular chain, thereby improving the ionic conductivity of the modified epoxy-oxidized SBR binder. The silanol groups remaining on the surface of the modified fumed SiO2 undergo physical adsorption with the polar groups in the epoxy-based SBR molecular chain. Simultaneously, the long organic chains introduced by the silane coupling agent physically entangle with the epoxy-based SBR molecular chain, causing the modified fumed SiO2 to coat the surface of the epoxy-based SBR. This reduces the van der Waals forces between the epoxy-based SBR particles, increases the interparticle spacing, and inhibits particle aggregation, thereby improving the dispersibility of the modified epoxy-based SBR binder.

2. The modified epoxy-based SBR binder according to claim 1, characterized in that, When the modified epoxy-based SBR binder is applied to the negative electrode sheet, the epoxy groups on the epoxy-based SBR undergo a ring-opening reaction with the hydroxyl groups on the surface of the copper foil current collector to form covalent bonds. At the same time, the TPU molecular chains and the epoxy-based SBR molecular chains intertwine to form a physical entanglement structure, preventing slippage between the epoxy-based SBR molecular chains and the TPU molecular chains. In addition, the modified gaseous SiO2 forms chemical bonds with the copper foil current collector through the functional groups introduced by the silane coupling agent, synergistically enhancing the interfacial bonding force between the electrode and the current collector and improving the structural stability of the electrode. The TPU molecular chains form a three-dimensional network skeleton through physical cross-linking points formed by hard segment microregions. The three-dimensional network skeleton and the elastic network formed by the epoxy-oxidized SBR in the three-dimensional network skeleton constitute an epoxy-oxidized SBR-TPU dual network structure, which improves the thermal stability of the modified epoxy-oxidized SBR adhesive. Meanwhile, the modified fumed SiO2 exhibits low agglomeration and can be uniformly dispersed in the electrode slurry to form a three-dimensional network structure. This, in conjunction with the epoxy-modified SBR-TPU dual network structure, provides a continuous channel for ion transport and improves the ionic conductivity of the modified epoxy-modified SBR binder. The three-dimensional network framework provides the main transport channel for ion transport, while the elastic network, through elastic deformation, mitigates volume changes in the active material, maintaining the porous structure within the negative electrode sheet and providing a buffer space for ion transport within the three-dimensional framework.

3. The modified epoxy-based SBR binder according to claim 1, characterized in that, The epoxy grafting rate of the epoxy-oxidized SBR is 1.0 mmol / g-1.5 mmol / g; The silane coupling agent is one or more of γ-aminopropyltriethoxysilane KH550 or γ-(2,3-epoxypropoxy)propyltrimethoxysilane KH560.

4. A method for preparing the modified epoxy-oxidized styrene-butadiene rubber (SBR) adhesive according to any one of claims 1-3, characterized in that, The preparation method includes: Styrene-butadiene rubber (SBR) emulsion and glycidyl methacrylate (GMA) containing epoxy groups were stirred and mixed at room temperature, and then the temperature was raised to 55℃-70℃ to carry out a constant temperature grafting reaction, so that the epoxy groups in the GMA were grafted onto the SBR molecular chain to obtain an epoxy-modified SBR emulsion. The epoxy-based SBR emulsion was spray-dried to obtain reactive epoxy-based SBR powder. The epoxy-oxidized SBR powder, thermoplastic polyurethane (TPU), and modified fumed silica (SiO2) in a mass ratio of 89-94.5:5-10:0.5-1 are dry-mixed. The modified SiO2 is physically adsorbed onto the polar groups in the epoxy-oxidized SBR molecular chain through residual silanol groups on its surface. At the same time, the organic long chains introduced by the silane coupling agent are physically entangled with the epoxy-oxidized SBR molecular chain, thereby uniformly coating the surface of the epoxy-oxidized SBR, inhibiting the agglomeration of the epoxy-oxidized SBR particles, and obtaining a uniformly dispersed modified epoxy-oxidized SBR binder.

5. The preparation method according to claim 4, characterized in that, The SBR emulsion is prepared by emulsion polymerization of styrene and butadiene in a mass ratio of 35-45:55-65. The amount of GMA added is 2.5wt%-4wt% of the solid content in the SBR emulsion; wherein the solid content in the SBR emulsion is 30wt%-40wt%.

6. The preparation method according to claim 4, characterized in that, The silane coupling agent is one or more of γ-aminopropyltriethoxysilane KH550 or γ-(2,3-epoxypropoxy)propyltrimethoxysilane KH560.

7. A negative electrode sheet, characterized in that, The negative electrode sheet comprises the modified epoxy-oxidized styrene-butadiene rubber (SBR) binder according to any one of claims 1-3, or comprises the modified epoxy-oxidized SBR binder prepared by the preparation method according to any one of claims 4-6.

8. A method for preparing the negative electrode sheet according to claim 7, characterized in that, The preparation method includes: The negative electrode active material, conductive agent and modified epoxy-oxidized styrene-butadiene rubber (SBR) binder in a mass ratio of 90-94:2-4:4-6 were dry-stirred to ensure uniform dispersion of each component and obtain a homogeneous mixture. The mixture is rolled and stretched to form a self-supporting membrane; Under conditions of 80℃-90℃ and 2MPa-5MPa, the self-supporting membrane and copper foil current collector are subjected to hot pressing and shaping treatment for 20s-40s, which melts the TPU in the modified epoxy-based SBR binder and initially builds a three-dimensional network skeleton, and flows and fills the gaps of the negative electrode active material. At the same time, it penetrates into the surface micropores of the copper foil current collector and softens the epoxy-based SBR in the modified epoxy-based SBR binder. Meanwhile, the TPU and the epoxy-based SBR molecular chains intertwine to form a physical entanglement structure, thus obtaining the negative electrode preform. Under conditions of 100℃-120℃ and 10MPa-15MPa, the negative electrode preform is subjected to hot-pressing anchoring treatment for 40s-80s, which causes the epoxy-oxidized SBR to flow and form a continuous elastic network in the three-dimensional mesh skeleton, thereby forming an epoxy-oxidized SBR-TPU dual network structure with the three-dimensional mesh skeleton. At the same time, the epoxy-oxidized SBR, relying on the skeleton formed by the TPU, penetrates into the surface micropores of the copper foil current collector, so that the epoxy groups on the epoxy-oxidized SBR and the hydroxyl groups on the surface of the copper foil current collector undergo ring-opening reaction to form covalent bonds. Simultaneously, the modified gaseous SiO2 in the modified epoxy-oxidized SBR binder forms chemical bonds with the copper foil current collector through the surface functional groups introduced by the silane coupling agent, thus completing the dual interface chemical anchoring. The negative electrode preform after hot-pressing and anchoring is cooled to room temperature to allow the TPU to crystallize, thereby fixing the physical entanglement structure and the epoxy-based SBR-TPU dual network structure to obtain the negative electrode sheet.

9. The preparation method according to claim 8, characterized in that, The negative electrode active material is a SiOx / C composite material, wherein the value of x ranges from 0.5 to 1.5, and C is one or more of graphite, carbon nanotubes, graphene, or amorphous carbon. The conductive agent includes one or more of carbon nanotubes, conductive carbon black, Ketjen black, carbon fiber, or acetylene black. The silane coupling agent is one or more of γ-aminopropyltriethoxysilane KH550 or γ-(2,3-epoxypropoxy)propyltrimethoxysilane KH560; During the cooling process to room temperature, the cooling rate is 40℃ / s-60℃ / s.

10. An energy storage device, characterized in that, The energy storage device includes: for lithium-ion batteries or lithium-ion capacitors; the energy storage device includes the modified epoxy-oxidized styrene-butadiene rubber (SBR) binder according to any one of claims 1-3, or includes the modified epoxy-oxidized SBR binder prepared by the preparation method according to any one of claims 5-6, or includes the negative electrode sheet according to claim 7, or includes the negative electrode sheet prepared by the preparation method according to any one of claims 8-9.

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