Composite binder, method for preparing the same, electrode sheet, and secondary battery

Abstract

The application provides a composite binder and a preparation method thereof, an electrode sheet and a secondary battery. The composite binder comprises, in terms of weight parts, 90-97% of a polymer binder, 1-5% of a conductive material, 1-5% of solid electrolyte particles and 0.3-1% of an interface coupling agent; the mass ratio of the solid electrolyte particles to the conductive material is (1-1.5):1; the aspect ratio of the conductive material is greater than or equal to 1500; the conductive material comprises oxygen-containing functional groups; and the viscosity of the composite binder in a solution with a solid content of 5-25% is 2500-20000 mpa.s. The composite binder provided by the application is prepared by compounding the polymer binder, the conductive material, the solid electrolyte particles and the interface coupling agent, and the mass ratio of the solid electrolyte particles to the conductive material, the aspect ratio of the conductive material and the oxygen-containing functional groups of the conductive material are controlled, so that the cycle stability and structural integrity of the electrode sheet are improved, and the cycle performance, rate performance and initial efficiency of the secondary battery are improved.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery technology, and particularly relates to a composite binder and its preparation method, electrode sheet, and secondary battery. Background Technology

[0002] Secondary batteries (such as lithium-ion batteries) have been widely used in portable electronic devices, electric vehicles, and energy storage systems due to their high energy density, long cycle life, and environmental friendliness. However, as application scenarios continue to demand higher energy and power densities, existing secondary batteries still suffer from low initial coulombic efficiency, significant cycle capacity decay, and insufficient rate performance in practical applications, making it difficult to meet higher performance requirements.

[0003] As a core component of rechargeable batteries, the structural stability and electrochemical performance of electrodes directly determine the overall performance of the battery. Existing electrodes are prone to microstructural degradation during long-term charge-discharge processes, leading to increased interfacial impedance and decreased utilization efficiency of active materials, which in turn affects the battery's initial coulombic efficiency, cycle stability, and rate performance.

[0004] Therefore, there is an urgent need to develop a secondary battery that can effectively improve initial coulombic efficiency, cycle stability, and rate performance. Summary of the Invention

[0005] One objective of this invention is to provide a composite binder to solve the problems of poor initial coulombic efficiency, cycle stability, and rate performance of existing secondary batteries; a second objective is to provide a method for preparing the composite binder; a third objective is to provide an electrode sheet; and a fourth objective is to provide a secondary battery.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A composite adhesive, by weight, comprises: 90-97% polymer adhesive, 1-5% conductive material, 1-5% solid electrolyte particles, and 0.3-1% interfacial coupling agent; the mass ratio of the solid electrolyte particles to the conductive material is (1-1.5):1.

[0008] The conductive material has an aspect ratio ≥1500, and the conductive material includes oxygen-containing functional groups; the composite binder has a viscosity of 2500-20000 mPa·s in a solution with a solid content of 5-25%.

[0009] Based on the above-mentioned technical means, the composite binder has excellent mechanical properties, electron and ion transport properties and interfacial bonding stability, which can improve the cycle performance, rate performance and first efficiency of secondary batteries.

[0010] Further, by weight, the composite binder comprises: 90-96.7% polymer binder, 1.5-4.5% conductive material, 1.5-4.5% solid electrolyte particles, and 0.3-0.7% interfacial coupling agent; the mass ratio of the solid electrolyte particles to the conductive material is (1.1-1.3):1.

[0011] Based on the above technical means, the electron and ion transport paths inside the electrode sheet are made continuous, and the stress caused by the volume change of the active material in the electrode sheet is also effectively buffered, thereby improving the structural integrity, interface stability and cycle life of the electrode sheet.

[0012] Furthermore, the particle size Dv50 of the conductive material is ≤1.5 μm; and / or,

[0013] The particle size Dv50 of the solid electrolyte particles is 20-500 nm.

[0014] Based on the above technical means, while ensuring the film-forming and adhesion functions of the composite binder, the electron-ion synergistic transport capability is significantly improved, and the interfacial instability caused by the volume change of the active material is mitigated, thereby improving the integrity of the electrode, cycle life and the applicability of thick electrodes.

[0015] Furthermore, the interface coupling agent includes a dispersant and / or a coupling agent; the weight-average molecular weight of the dispersant is 500-10000, and the weight-average molecular weight of the coupling agent is ≤500.

[0016] Based on the above technical means, a more continuous micro-network structure can be formed inside the electrode sheet, making it less likely for conductive materials and solid electrolyte particles to agglomerate or settle during mixing, coating and drying, and maintaining interface integrity even under cyclic volume changes.

[0017] Furthermore, the polymer binder comprises at least one of polyisobutylene, styrene-ethylene-butene-styrene block copolymer, polyacrylic acid copolymer, polyimide, polyamide-imide, polyurethane, polyurea, styrene-butadiene rubber, and styrene-acrylic rubber; and / or,

[0018] The conductive material includes at least one of carbon nanotubes, conductive carbon fibers, silicon nanowires, and metal nanowires. Preferably, the average diameter of the carbon nanotubes is <10 nm, and the specific surface area of ​​the carbon nanotubes is >280 m². 2 / g; and / or,

[0019] The solid electrolyte particles include at least one of sulfide solid electrolyte particles, halide solid electrolyte particles, and oxide solid electrolyte particles; and / or,

[0020] The interface coupling agent includes at least one of polyisobutylene and its derivatives, polydimethylsiloxane and its derivatives, polyimide and its derivatives, alkylsilane coupling agents, and titanate coupling agents with a weight average molecular weight of 500-10000.

[0021] Based on the above technical means, the electron transport, lithium-ion transport and mechanical support inside the electrode sheet can be improved simultaneously, thereby effectively suppressing electrode sheet cracking, pulverization and impedance increase, and thus ensuring the cycle stability and rate performance of the secondary battery.

[0022] Furthermore, the oxide solid electrolyte particles include at least one of garnet-type solid electrolyte, NASICON-type solid electrolyte, and perovskite-type solid electrolyte.

[0023] Based on the above technical means, the oxide solid electrolyte particles can form a more stable dispersion and bonding state with conductive materials and interface coupling agents while ensuring ion conduction capacity. This improves the continuity of electron / ion transport and the stability of electrode structure in the electrode, thereby reducing polarization, suppressing cracking and pulverization, and improving the cycle life and rate performance of secondary batteries.

[0024] A second aspect of the present invention provides a method for preparing a composite adhesive, comprising the following steps:

[0025] 1) By weight, the raw materials including the polymer binder, conductive material, solid electrolyte particles and interfacial coupling agent are dispersed in a solvent to obtain a mixed slurry;

[0026] 2) The mixed slurry is subjected to high-pressure homogenization to obtain the composite adhesive; wherein the pressure of the high-pressure homogenization is 40-120 MPa.

[0027] By using the above-mentioned technical means, the components are uniformly coupled at the microscale, which can suppress the local enrichment of conductive materials and solid electrolyte particles and reduce interfacial impedance. This allows the composite binder to simultaneously possess excellent mechanical properties, electron and ion transport properties, and interfacial bonding stability, thereby improving the cycle performance, rate performance, and first-time efficiency of the secondary battery.

[0028] Further, in step 1), the dispersion includes stirring dispersion, wherein the stirring speed is 1000-2000 rpm and the stirring time is 20-30 min; and / or,

[0029] The pressure of the high-pressure homogenization process is 60-90 MPa; and / or,

[0030] The high-pressure homogenization process is repeated 2-5 times; and / or,

[0031] The discharge temperature after the high-pressure homogenization treatment is ≤40℃, preferably 30-35℃; and / or,

[0032] The solvent includes at least one of the following: n-decane, hexane, heptane, cyclohexane, toluene, xylene, fluoroether, octyl acetate, isobutyl isobutyrate, dimethyl carbonate, ethylene carbonate, dimethylformamide, N,N-dimethylacetamide, triethyl phosphate, N-methylpyrrolidone, and deionized water.

[0033] Based on the above technical means, a uniform and stable composite binder system is formed by polymer binder, conductive material, solid electrolyte particles and interface coupling agent, thereby providing a continuous bonding interface and transmission channel for the electrode.

[0034] A third aspect of the present invention provides an electrode sheet comprising the composite binder described in the first aspect above, or a composite binder prepared by the preparation method described in the second aspect above.

[0035] A fourth aspect of the present invention provides a secondary battery comprising the electrode sheet described in the first aspect above.

[0036] The beneficial effects of this invention are:

[0037] The composite binder provided by this invention combines a polymer binder, conductive material, solid electrolyte particles, and interfacial coupling agent in a defined weight ratio, and controls the mass ratio of solid electrolyte particles to conductive material, the aspect ratio and oxygen-containing functional group characteristics of the conductive material, and the viscosity range of the composite binder in the corresponding solution. This enables the simultaneous construction of a composite system with synergistic effects of electron transport, ion transport, and interfacial bonding in the bonding network, and improves the dispersibility, film-forming properties, and mechanical compatibility of each component. This reduces the transport bottleneck and interfacial impedance in high-load silicon-based anodes and thick electrodes, alleviates structural cracking and interfacial instability caused by cycling volume changes, and improves the cycling stability and structural integrity of the electrode sheet, thereby enhancing the cycle performance, rate performance, and first-efficiency of the secondary battery. Attached Figure Description

[0038] Figure 1 This is a SEM image of the composite adhesive of Example 1 of the present invention at a magnification of 20K;

[0039] Figure 2 This is a SEM image of the composite adhesive of Example 1 of the present invention at a magnification of 50K. Detailed Implementation

[0040] The embodiments of the present invention will be described below with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention and not for limiting the scope of protection of the present invention.

[0041] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0042] To further improve the initial coulombic efficiency, cycle stability, and rate performance of secondary batteries, the inventors studied existing secondary batteries and found that the reasons for their poor performance were: the binders used in existing electrode sheets (such as polymer binders) are intrinsically electronic and ion insulators and cannot effectively conduct electrons or active ions; although high-strength polymer binders (such as PVDF) can provide high initial bonding force, they have poor ductility and cannot adapt to the volume expansion of silicon particles; while high-toughness polymer binders (such as SBR) have ductility but insufficient strength and are prone to breakage during cycling, leading to electrode structure failure.

[0043] Therefore, the inventors attempted to introduce conductive and ion-conducting materials into polymer binders while balancing their strength and toughness.

[0044] Based on this, the first aspect of the present invention provides a composite adhesive, which, by weight, comprises: 90-97% polymer adhesive, 1-5% conductive material, 1-5% solid electrolyte particles, and 0.3-1% interfacial coupling agent; the mass ratio of solid electrolyte particles to conductive material is (1-1.5):1.

[0045] The conductive material has an aspect ratio ≥1500 and includes oxygen-containing functional groups; the composite binder has a viscosity of 2500-20000 mPa·s in a solution with a solid content of 5-25%.

[0046] It should be noted that the aspect ratio of a conductive material refers to the geometric measurement of its microstructure in scanning electron microscopy (SEM) or transmission electron microscopy (TEM) images. Length refers to the maximum measurable distance between any two points on the outer boundary of the conductive material; diameter refers to the lateral dimension of the conductive material on a cross-section perpendicular to the length direction, typically taken as the average width or equivalent diameter in that direction. The aspect ratio is simply the ratio of the length value to the diameter value.

[0047] In this invention, the solvent used to test the viscosity of the composite adhesive is n-decane.

[0048] For example, the composite adhesive comprises, by weight, 90%, 91%, 92%, 93%, 94%, 95%, 96%, or 97% of the polymer adhesive, or a range of any two of these values.

[0049] For example, the composite adhesive comprises, by weight, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5% of conductive material, or a range of any two of these values.

[0050] For example, the composite binder comprises, by weight, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5% of solid electrolyte particles, or a range of any two of these values.

[0051] For example, the composite adhesive comprises, by weight, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1% of the interfacial coupling agent, or a range of any two of these values.

[0052] For example, the mass ratio of solid electrolyte particles to conductive material is 1:1, 1.05:1, 1.1:1, 1.15:1, 1.2:1, 1.25:1, 1.3:1, 1.35:1, 1.4:1, or 1.5:1, or a range of any two of these values.

[0053] For example, the aspect ratio of the conductive material is 1500, 1550, 1600, 1650, 1700, 1750, 1800, 1850, 1900, 1950 or more, or a range consisting of any two of these values.

[0054] For example, the viscosity of the composite adhesive in a solution with a solid content of 5-25% is 2500, 5000, 10000, 15000 or 20000, or a range of any two of these values.

[0055] The composite binder provided by this invention possesses excellent mechanical properties, electron and ion transport properties, and interfacial bonding stability, which can improve the cycle performance, rate performance, and first-efficiency of secondary batteries. The reason is as follows:

[0056] On the one hand, the polymer binder forms a continuous flexible framework and transfers adhesion and deformation buffering capacity between active materials (positive or negative electrode active materials). A high aspect ratio conductive material with oxygen-containing functional groups forms an interparticle-connected electronic conduction network within this framework. Solid electrolyte particles are embedded around the electronic framework as dispersed nodes, providing an active interface for ion migration. An interfacial coupling agent stably binds these different phases through interfacial interactions. These substances give the composite binder a composite network that combines mechanical support, electronic conduction, and ion-assisted transport functions. On the other hand, under the above formulation, the polymer binder, as the main phase, ensures that the composite system still uses a continuous polymer network as its basic framework, thereby maintaining the slurry processing. The composite binder enhances the encapsulation, extensibility, and dry film integrity of the battery. High aspect ratio conductive materials, even at low addition levels, can form a conductive framework across scales within the polymer binder. The addition of solid electrolyte particles creates locally dispersed ion-transporting active nodes in the binder phase. Simultaneously, limiting the mass ratio of solid electrolyte particles to conductive materials allows for the formation of a mutually interlocking ion-electron synergistic bifunctional network within the composite binder. Within the aforementioned range, the amount of interfacial coupling agent transforms the stress transfer between high-modulus particles (conductive material and solid electrolyte particles) and the flexible polymer (polymer binder) from an abrupt interface to a gradient interface, thereby suppressing local delamination and crack initiation, achieving a balance between interfacial stability and system integrity. Furthermore, by controlling the solid content and viscosity of the composite binder within a processable window, the conductive material undergoes directional deagglomeration in the shear field while maintaining effective length, resulting in high dispersion uniformity of the solid electrolyte particles. This ensures good continuity of the bifunctional network in both the in-plane and thickness directions after subsequent film formation. The synergistic effect of these two aspects improves the cycle performance, rate performance, and first-efficiency of the secondary battery.

[0057] In one specific embodiment, the composite binder, by weight, comprises: 90-96.7% polymer binder, 1.5-4.5% conductive material, 1.5-4.5% solid electrolyte particles, and 0.3-0.7% interfacial coupling agent; the mass ratio of solid electrolyte particles to conductive material is (1.1-1.3):1. With the content and proportion of each component controlled within the above range, the composite binder maintains good dispersibility, homogenization, and film-forming properties, while also forming an electron-ion synergistic transport network in the electrode sheet, thereby reducing interfacial impedance, mitigating polarization, and improving rate performance. Simultaneously, the interfacial coupling agent, together with an appropriate solid electrolyte particle / conductive material ratio, inhibits agglomeration and stress concentration, making the electrode sheet less prone to cracking, pulverization, or detachment during repeated charge-discharge cycles, thus improving the cycle stability, rate performance, and initial efficiency of the secondary battery.

[0058] In one specific embodiment, the particle size Dv50 of the conductive material is ≤1.5μm. Controlling the particle size Dv50 of the conductive material to 1.5μm or less makes it easier for the conductive material to be sheared and homogeneously dispersed in the slurry, thereby constructing a continuous electronic conduction framework.

[0059] For example, the particle size Dv50 of the conductive material is 1.5 μm, 1.49 μm, 1.48 μm, 1.47 μm, 1.46 μm, 1.45 μm, 1.44 μm, 1.43 μm, 1.42 μm, 1.41 μm or less, or a range consisting of any two of these values.

[0060] In one specific embodiment, the particle size Dv50 of the solid electrolyte particles is 20-500 nm. A particle size Dv50 of 20-500 nm makes it easier for the solid electrolyte particles to be embedded between the polymer binder and the conductive network, forming high-density ion nodes.

[0061] For example, the particle size Dv50 of the solid electrolyte particles is 20nm, 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm or 500nm, or a range of any two of these values.

[0062] In one specific embodiment, the interfacial coupling agent includes a dispersant and / or a coupling agent; the weight-average molecular weight of the dispersant is 500-10000, and the weight-average molecular weight of the coupling agent is ≤500. The weight-average molecular weight of the dispersant, controlled at 500-10000, can form an adsorption layer or coating layer with a certain chain length on the particle surface, which can reduce van der Waals aggregation and bridging flocculation between particles, and inhibit the increase of system viscosity or phase separation. The weight-average molecular weight of the coupling agent is ≤500, typically a low molecular weight small molecule or oligomer, which facilitates rapid migration and directional adsorption onto the surface of inorganic particles (conductive materials and solid electrolyte particles), subsequently forming chemical bonds or strong coordination with the particle surface through its polar or reactive groups, while simultaneously constructing an interfacial transition layer with the polymer binder.

[0063] For example, the weight-average molecular weight of the dispersant is 500, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000 or 10000, or a range of any two of these values.

[0064] For example, the weight-average molecular weight of the coupling agent is 500, 490, 480, 470, 460, 450, 440, 430, 420, 410 or less, or a range of any two of these values.

[0065] To further improve the mechanical properties, electron and ion transport properties, and interfacial bonding stability of composite binders, the specific types of polymer binders, conductive materials, solid electrolyte particles, and interfacial coupling agents can be controlled.

[0066] In one specific embodiment, the polymer binder includes at least one selected from polyisobutylene, styrene-ethylene-butene-styrene block copolymer, polyacrylic acid copolymer, polyimide, polyamide-imide, polyurethane, polyurea, styrene-butadiene rubber, and styrene-acrylic rubber. The aforementioned polymer binders are adaptable to both non-polar and polar systems and maintain the integrity of the electrode sheet when the active material expands in volume.

[0067] In one specific embodiment, the conductive material includes at least one of carbon nanotubes, conductive carbon fibers, silicon nanowires, and metal nanowires. The aforementioned conductive material is capable of constructing continuous electronic pathways within the constructed bonding network.

[0068] In one specific embodiment, the average diameter of the carbon nanotubes is <10 nm, and the specific surface area of ​​the carbon nanotubes is >280 m². 2 / g. With the average tube diameter and specific surface area controlled within the above range, carbon nanotubes have a higher aspect ratio and better penetration efficiency, thereby reducing the internal resistance of the electrode and improving the conductivity uniformity of thick electrodes.

[0069] For example, the average diameter of the carbon nanotubes is 1 nm, 3 nm, 5 nm, 7 nm, 9 nm or 9.9 nm, or a range of any two of these values.

[0070] For example, the specific surface area of ​​carbon nanotubes is 281 nm, 283 nm, 285 nm, 287 nm, 289 nm or above, or a range consisting of any two of these values.

[0071] In one specific embodiment, the solid electrolyte particles include at least one of sulfide solid electrolyte particles, halide solid electrolyte particles, and oxide solid electrolyte particles. These solid electrolyte particles form ion transport nodes within the polymer phase, mitigating the adverse effects of traditional binders on the migration of active ions.

[0072] In one specific embodiment, the interfacial coupling agent includes at least one of polyisobutylene and its derivatives, polydimethylsiloxane and its derivatives, polyimide and its derivatives, and alkylsilane coupling agents and titanate coupling agents with a weight-average molecular weight of 500-10000. The aforementioned interfacial coupling agent enhances the compatibility between the organic matrix and inorganic particles through flexible coating, wetting bridging, or chemical coupling, and inhibits agglomeration and interfacial debinding.

[0073] Preferably, when the system is a non-polar / weakly polar material system, the polymer binder is preferably one or more of the following: high molecular weight polyisobutylene (PIB), styrene-ethylene-butene-styrene block copolymer (SEBS), and styrene-butadiene rubber (SBR) with a weight-average molecular weight Mw ≥ 500,000 (compound component Mw ≥ 50,000). The solid electrolyte particles are preferably sulfide solid electrolytes (such as Li6PS5Cl, Li...). 10 GeP2S 12 The system uses one or more of the following: solid electrolytes (such as Li3InCl6, Li3YBr6, etc.). These materials are extremely sensitive to water, and the non-polar nature of this system ensures its structural stability. The preferred interfacial coupling agent is one or more of low molecular weight polyisobutylene (PIB) and low molecular weight polydimethylsiloxane (PDMS), with a weight-average molecular weight (Mw) strictly limited to 500-10000.

[0074] The solvent is preferably a low-polarity non-aqueous solvent, specifically selected from one or more of n-decane, hexane, heptane, cyclohexane, toluene, xylene, fluoroether, octyl acetate, and isobutyl isobutyrate, with n-decane being the most preferred.

[0075] Preferably, when the system is a polar material system for a liquid / semi-solid battery, the polymer binder is preferably one or more of polyacrylic acid (PAA) copolymers, polyimide (PI), polyamide-imide (PAI), polyurethane (PU), polyurea, styrene-butadiene rubber (SBR), and styrene-acrylic acid (SAR), with a weight-average molecular weight Mw ≥ 50,000. The solid electrolyte particles are preferably oxide solid electrolytes, specifically including one or more of lithium-containing garnet-type solid electrolytes (such as LLZO), NASICON-type solid electrolytes (such as LATP, LAGP), and perovskite-type solid electrolytes (such as LLTO). These oxide electrolytes exhibit excellent chemical stability in polar or aqueous environments and do not undergo severe hydrolysis. The interfacial coupling agent is preferably one or more of alkylsilane coupling agents (such as KH550, KH560), titanate coupling agents, or polyimide dispersants. For small molecule coupling agents, the molecular weight is strictly limited to ≤500; for polymeric dispersants, the weight-average molecular weight (Mw) is strictly limited to 500~10000.

[0076] The solvent is preferably a medium to high polarity solvent, specifically selected from one or more of esters (such as DMC, EC, etc.), N-methylpyrrolidone (NMP), and water.

[0077] In one specific embodiment, the oxide solid electrolyte particles include at least one of garnet-type solid electrolyte, NASICON-type solid electrolyte, and perovskite-type solid electrolyte. Garnet-type solid electrolytes have high chemical stability and good active ion migration channels, making them suitable for synergistically constructing stable interfaces with polymer binders; NASICON-type solid electrolytes rely on open three-dimensional lattice channels to form a relatively balanced ion transport network, which helps reduce ion migration resistance inside the electrode; perovskite-type solid electrolytes utilize their specific lattice sites and channel structures to improve ion migration efficiency, enabling the composite binder to maintain a relatively continuous ion supply during charging and discharging.

[0078] When the polymer binder, conductive material, solid electrolyte particles, interfacial coupling agent, and oxide solid electrolyte particles are mixtures of the aforementioned substances, the present invention does not specifically limit the proportion of each specific substance in the mixture.

[0079] A second aspect of the present invention provides a method for preparing a composite adhesive, comprising the following steps:

[0080] 1) By weight, the raw materials including polymer binder, conductive material, solid electrolyte particles and interfacial coupling agent are dispersed in a solvent to obtain a mixed slurry;

[0081] 2) The mixed slurry is subjected to high-pressure homogenization to obtain a composite binder; wherein the pressure of the high-pressure homogenization is 40-120MPa.

[0082] For example, the pressure of the high-pressure homogenization process is 40 MPa, 50 MPa, 60 MPa, 70 MPa, 80 MPa, 90 MPa, 100 MPa, 110 MPa or 120 MPa, or a range of any two of these values.

[0083] The preparation method of this invention solves the technical problem that traditional stirring processes cannot achieve complete deentanglement and uniform dispersion of fillers by controlling the extreme energy field of high-pressure homogenization. The synergistic effect of shear force and cavitation effect of high-pressure homogenization ensures that the conductive material and solid electrolyte particles form a microscopic interpenetrating network in the polymer matrix. At the same time, temperature control avoids process defects, and finally obtains an adhesive solution with synergistic electronic-ionic-mechanical properties.

[0084] Specifically, this process completely de-entangles the conductive materials under microscopic shearing through high-pressure homogenization, forming a through-network that significantly improves the tensile strength and peel strength of the composite adhesive film. High-pressure homogenization causes solid electrolyte particles to be uniformly embedded in the conductive material network, forming a super-stable mechanical structure similar to a "honeycomb sandwich," thereby creating dual electron-ion transport channels and reducing interfacial impedance. Furthermore, the super-stable mechanical structure of the "honeycomb sandwich" uniformly dissipates local stress, inhibiting electrode pulverization and crack propagation. Simultaneously, high-pressure homogenization causes the interfacial coupling agent to preferentially adsorb at the heterogeneous interface, thus forming a more uniform dispersion structure in the polymer adhesive. Through chemical bonding and physical entanglement, it eliminates the brittle delamination of the "inorganic-organic" interface, endowing the composite adhesive film with high toughness. In addition, the pressure of the high-pressure homogenization process is controlled between 40-120 MPa to ensure dispersibility while avoiding damage to the particle structure caused by high pressure (e.g., excessive pressure may shear the aspect ratio of the conductive material), and forces the conductive material and solid electrolyte particles to insert into the gaps between polymer chain segments under strong microscopic extrusion.

[0085] High-pressure homogenization allows the components to be uniformly coupled at the microscale, which can suppress the local enrichment of conductive materials and solid electrolyte particles and reduce interfacial impedance. This enables the composite binder to possess excellent mechanical properties, electron and ion transport performance, and interfacial bonding stability, thereby improving the cycle performance, rate performance, and first-time efficiency of secondary batteries.

[0086] The present invention does not specifically limit the equipment used for dispersion, including but not limited to one of the vacuum planetary mixers.

[0087] In one specific embodiment, step 1) involves dispersion by stirring, with a stirring speed of 1000-2000 rpm and a stirring time of 20-30 min. Controlling the stirring speed to 1000-2000 rpm and the stirring time to 20-30 min allows the conductive material, solid electrolyte particles, and interfacial coupling agent to fully expand and complete initial depolymerization in the solvent.

[0088] For example, the stirring speed for dispersion is 1000 rpm, 1200 rpm, 1400 rpm, 1600 rpm, 1800 rpm or 2000 rpm, or a range of any two of these values.

[0089] For example, the stirring time for dispersion is 20 min, 21 min, 22 min, 23 min, 24 min, 25 min, 26 min, 27 min, 28 min, 29 min or 30 min, or a range of any two of these values.

[0090] In one specific implementation, the pressure of the high-pressure homogenization process is 60-90 MPa.

[0091] For example, the pressure of the high-pressure homogenization process is 60 MPa, 63 MPa, 66 MPa, 69 MPa, 72 MPa, 75 MPa, 78 MPa, 81 MPa, 84 MPa, 87 MPa or 90 MPa, or a range of any two of these values.

[0092] In one specific implementation, the high-pressure homogenization process is repeated 2-5 times.

[0093] For example, the number of cycles of high-pressure homogenization is 2, 3, 4 or 5, or a range of any two of these values.

[0094] The pressure of the high-pressure homogenization process is set to 60-90 MPa and circulated 2-5 times to further refine and disperse the mixed slurry under high shear and instantaneous pressure drop.

[0095] In one specific embodiment, the discharge temperature after high-pressure homogenization is ≤40℃, preferably 30-35℃. Controlling the discharge temperature within this range can obtain a more stable dispersion, which is more conducive to improving the structural stability of solid electrolytes and conductive fiber materials.

[0096] For example, the discharge temperature after high-pressure homogenization is 40°C, 39°C, 38°C, 37°C, 36°C, 35°C, 34°C, 33°C, 32°C, 31°C or below, or a range of any two of these values.

[0097] In one specific embodiment, the solvent includes at least one of the following: n-decane, hexane, heptane, cyclohexane, toluene, xylene, fluoroether, octyl acetate, isobutyl isobutyrate, dimethyl carbonate, ethylene carbonate, dimethylformamide, N,N-dimethylacetamide, triethyl phosphate, N-methylpyrrolidone, and deionized water. These solvents can meet the dissolution / dispersion requirements of different polymer binders and also take into account the wettability of conductive materials and solid electrolyte particles, making it easier for the shear forces generated during high-pressure homogenization to be transmitted to the surfaces of each solid component.

[0098] A third aspect of the present invention provides an electrode sheet comprising the composite binder described in the first aspect, or the composite binder prepared by the method described in the second aspect. This electrode sheet exhibits excellent structural integrity, interfacial stability, cycle performance, and rate performance, thereby improving the cycle performance, rate performance, and first-efficiency of a secondary battery.

[0099] The aforementioned composite binder can be used only in the negative electrode of the battery, or only in the positive electrode of the battery, or in both the positive and negative electrodes of the battery. It is preferred to use it in the negative electrode, and more preferably in the silicon-doped negative electrode.

[0100] It should be clarified that the above-mentioned composite binder can be used alone in the electrode sheet of the battery, or it can be used in combination with other binders conventionally used in the art in the electrode sheet of the battery, and there are no particular limitations on this.

[0101] Generally, an electrode sheet includes an electrode current collector and an electrode coating (or electrode active layer) located on at least one side of the electrode current collector. Specifically, the electrode coating may be located on only one side of the electrode current collector, or the electrode coating may be provided on both opposite sides of the electrode current collector (i.e., on both the front and back surfaces of the electrode current collector).

[0102] Generally, the electrode coating also includes electrode active material, conductive agent and solid electrolyte. In the electrode coating, the mass percentage of electrode active material can be 70-94%, the mass percentage of composite binder can be 0.5-15%, the mass percentage of conductive agent can be 0.5-15%, and the mass percentage of solid electrolyte can be 5-20%.

[0103] Specifically, when the electrode sheet is a positive electrode sheet, the electrode current collector is a positive electrode current collector, the electrode coating is a positive electrode coating (or positive electrode active layer), and the electrode active material is a positive electrode active material.

[0104] The binder in the positive electrode coating can be the composite binder provided by this invention, or it can be combined with other conventional binders as the binder for the positive electrode coating. Other conventional binders include one or more of the following: polyvinylidene fluoride (PVDF), polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, etc.

[0105] The positive electrode active material can be a conventional positive electrode active material in the art. For example, the positive electrode active material can include a lithium-containing active material capable of lithium ion intercalation and deintercalation. It can be a lithium-containing active material commonly used in lithium-ion batteries, such as one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, ternary materials, etc. The ternary material can include lithium nickel cobalt manganese oxide (NCM) and / or lithium nickel cobalt aluminum oxide (NCA), but is not limited thereto. In other embodiments, the positive electrode active material can also be a sodium battery positive electrode material capable of sodium ion intercalation and deintercalation. It can be a positive electrode active material commonly used in sodium-ion batteries, such as one or more of transition metal oxide sodium battery positive electrode materials and / or Prussian blue sodium battery positive electrode materials.

[0106] The present invention may employ conventional positive current collectors in the art, for example, positive current collectors may include aluminum foil.

[0107] The positive electrode sheet of this invention can be prepared by conventional methods in the art, such as by coating. Specifically, the positive electrode active material, conductive agent, composite binder, and other components used to form the positive electrode active layer can be dispersed in a solvent, such as N-methylpyrrolidone (NMP), to prepare a positive electrode slurry. This slurry is then coated onto the surface of the positive electrode current collector, and after drying, rolling, and other processes, the positive electrode sheet is obtained. The coating, drying, and rolling processes involved are conventional operations in the preparation of positive electrode sheets using the coating method, and are not particularly limited thereto.

[0108] When the electrode sheet is a negative electrode sheet, the electrode current collector is a negative electrode current collector, the electrode coating is a negative electrode coating (or negative electrode active layer), and the electrode active material is a negative electrode active material.

[0109] In this invention, the binder in the negative electrode coating can be the composite binder provided in the embodiments of this invention, or any binder known in the art suitable for the negative electrode can be used or combined. For example, the binder in the negative electrode coating may include at least one of polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), tetrafluoroethylene and its copolymers, polyvinylidene fluoride and its copolymers, polyolefins and their copolymers (e.g., polyethylene, polypropylene, polyethylene-polyethylene glycol block copolymers, etc.), polyvinyl alcohol, polyurethane, polyvinyl chloride, polyvinylpyrrolidone, nitrile rubber, polyacrylic acid (PAA), and polyacrylates (such as sodium polyacrylate).

[0110] In addition, the negative electrode active material can be a conventional negative electrode active material in the art, such as graphite, but is not limited thereto.

[0111] The embodiments of the present invention may employ conventional negative electrode current collectors in the art, for example, negative electrode current collectors include copper foil.

[0112] In this embodiment of the invention, the negative electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the components used to form the negative electrode active layer, such as the negative electrode active material, conductive agent, and composite binder, can be dispersed in a solvent, such as water, specifically deionized water, to prepare a negative electrode slurry. This slurry is then coated onto the surface of the negative electrode current collector, and after drying, rolling, and other processes, the negative electrode sheet is obtained. The coating, drying, and rolling processes involved are conventional operations for preparing negative electrode sheets using the coating method, and are not particularly limited thereto.

[0113] Furthermore, the conductive agent in the electrode coating (positive electrode coating, negative electrode coating) can be a conventional conductive material in the art. For example, the conductive agent may include one or more of carbon black, carbon nanotubes (CNTs), acetylene black, graphene, Ketjen black, and carbon fiber. The solid electrolyte in the electrode coating can be a conventional electrolyte material in the art, such as one or more of sulfide electrolytes, halide electrolytes, and oxide electrolytes.

[0114] A fourth aspect of the present invention provides a secondary battery comprising the electrode sheet described in the third aspect above. This secondary battery exhibits excellent cycle performance, rate performance, and initial efficiency.

[0115] In this embodiment of the invention, the battery may be a liquid battery or a solid battery, specifically a lithium-ion secondary battery, but is not limited thereto.

[0116] Generally, a liquid secondary battery includes an electrolyte, a battery cell, and a casing for encapsulating the battery cell. The electrolyte is injected into the battery cell within the casing. The battery cell includes a positive electrode, a negative electrode, and a separator located between the positive and negative electrodes. The battery cell can be a stacked cell, meaning it is composed of alternating layers of positive electrode, separator, and negative electrode; or it can be a wound cell, meaning it is composed of stacked positive electrode, separator, and negative electrode layers wound together.

[0117] The electrolyte in this invention can be a conventional electrolyte in the art. For example, the electrolyte is a non-aqueous electrolyte, which may specifically include organic solvents, additives and electrolyte salts. Organic solvents include one or more of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC) and propylene carbonate (PC). Additives include, for example, fluoroethylene carbonate (FEC) and vinylene carbonate (VC). Electrolyte salts may include lithium salts, such as lithium hexafluorophosphate (LiPF6), but are not limited thereto.

[0118] Solid-state rechargeable batteries include battery cells and a casing for encapsulating the battery cells. The battery cell includes a positive electrode, a negative electrode, and a solid electrolyte membrane located between the positive and negative electrode. The battery cell can be a stacked battery cell, that is, the battery cell is composed of positive electrode, separator, and negative electrode layers stacked alternately.

[0119] In this invention, a separator or solid electrolyte membrane is used to separate the positive electrode and the negative electrode to prevent short circuits caused by contact between the positive electrode and the negative electrode. In the embodiments of this invention, conventional separators and solid electrolyte membranes in the art can be used. For example, the separator includes a polypropylene membrane, and the solid electrolyte membrane includes a sulfide electrolyte membrane. There are no particular limitations on this.

[0120] In this embodiment of the invention, the battery cell can be packaged using conventional housing materials in the art, such as flexible packaging materials like aluminum-plastic film, but is not limited thereto.

[0121] This invention can assemble components such as positive electrode, separator or solid electrolyte membrane and negative electrode into a secondary battery using conventional methods in the art. For example, positive electrode, separator and negative electrode can be stacked alternately to obtain a stacked cell (or wound into a wound cell using conventional winding process); then the cell is placed in a casing (outer packaging), and after conventional processes such as liquid injection (i.e., injection of electrolyte), sealing, formation and capacity testing, a liquid secondary battery is obtained.

[0122] The present invention will be further described below through specific embodiments.

[0123] Example 1

[0124] The composite binder in this embodiment comprises, by weight, 94% polymer binder, 2.5% conductive material, 3% solid electrolyte particles, and 0.5% interfacial coupling agent; the mass ratio of solid electrolyte particles to conductive material is (1-1.5):1. The polymer binder is polyisobutylene (PIB) with a weight average molecular weight of 800,000, the conductive material is carbon nanotubes (CNTs) with an aspect ratio of 2000 and an average diameter of 1.5 nm, the solid electrolyte particles are sulfide solid electrolytes (Li6PS5Cl) with a particle size Dv50 of 200 nm, and the interfacial coupling agent is polyisobutylene with a weight average molecular weight of 2000.

[0125] The method for preparing the composite adhesive in this embodiment includes the following steps:

[0126] 1) By weight, the raw materials including polymer binder, conductive material, solid electrolyte particles and interfacial coupling agent are stirred and dispersed in a solvent to obtain a mixed slurry. The stirring speed for stirring and dispersion is 1500 rpm, the stirring time is 25 min, and the solvent is n-decane.

[0127] 2) The mixed slurry was subjected to high-pressure homogenization to obtain the composite binder; the high-pressure homogenization pressure was 80 MPa, 3 cycles, and the discharge temperature was 32-35℃. The composite binder had a solid content of 6 wt% and a viscosity of 4820 mPa·s in n-decane solution. The SEM image of the composite binder at 20K magnification is shown below. Figure 1 The SEM image at 50K magnification is shown below. Figure 2 .

[0128] Examples 2-11 and Comparative Examples 1-14 are basically the same as Example 1, with differences shown in Tables 1A, 1B and 2.

[0129] Experimental Example 1

[0130] 1. Some parameters of the composite adhesives of the examples and comparative examples are shown in Tables 1A and 1B; the parameters of the preparation methods of the composite adhesives of the examples and comparative examples are shown in Table 2.

[0131] 2. Testing Methods

[0132] 1) The types and contents of each component in the composite adhesive, and the weight-average molecular weight or test method of the weight-average molecular weight of the interfacial coupling agent.

[0133] The weight-average molecular weight (Mw) of interfacial coupling agents (such as low molecular weight polyisobutylene, polydimethylsiloxane, polyimide dispersants, etc.) was determined by gel permeation chromatography (GPC).

[0134] The relative molecular mass of coupling agents (such as KH550, KH560, titanate coupling agents, etc.) is determined by the nominal value in the supplier's quality certificate or by the theoretical molecular weight calculated based on the chemical structural formula.

[0135] 2) Test methods for the aspect ratio and average diameter, specific surface area, presence of oxygen-containing functional groups, particle size Dv50 of conductive materials, and particle size Dv50 of solid electrolyte particles.

[0136] Average diameter and aspect ratio of conductive materials: Geometric measurements of the microstructure of conductive materials are performed in scanning electron microscopy (SEM) or transmission electron microscopy (TEM) images. Length refers to the maximum measurable distance between any two points on the outer contour boundary of the conductive material; diameter refers to the lateral dimension of the conductive material on a cross-section perpendicular to the length direction, typically taken as the average width or equivalent diameter in that direction. The aspect ratio is the ratio of the length value to the diameter value.

[0137] Whether the surface of a conductive material contains oxygen-containing functional groups was analyzed using X-ray photoelectron spectroscopy (XPS).

[0138] The test conditions are as follows: Instrument: XPS photoelectron spectrometer; X-ray source: Al Kα; Vacuum level: below 1×10⁻⁶ -8 Pa. By analyzing the C1s and O1s spectral peaks, the presence of hydroxyl (-OH), carbonyl (C=O), carboxyl (-COOH), ether bond (COC), and epoxy (CO) groups on the material surface is confirmed. When at least one of these oxygen-containing groups is detected on the surface, the conductive material is considered to contain oxygen-containing functional groups. Furthermore, Fourier transform infrared spectroscopy (FTIR) can also be used as an auxiliary characterization method.

[0139] The particle size Dv50 of conductive materials and solid electrolytes was determined using a laser particle size analyzer. The specific method is as follows: Instrument: Laser particle size analyzer; Dispersion medium: Anhydrous ethanol, isopropanol, water, or n-decane, selected according to the material system; Ultrasonic dispersion time: 5–15 min; The shading rate was controlled at 10%–20% during the test. For sulfide solid electrolytes: the test was conducted at a dew point ≤ -40℃, and xylene, n-decane, etc., were required as the dispersion medium.

[0140] Table 1A

[0141]

[0142] Table 1B

[0143]

[0144] Table 2

[0145]

[0146] Experimental Example 2

[0147] 1. The viscosity of the composite binder with a solid content of 6% in n-decane solution was tested for the composite binder of the examples and comparative examples; after the composite binder of the examples and comparative examples was prepared into negative electrode sheets, it was assembled into secondary batteries for performance testing. The results are shown in Tables 3A and 3B.

[0148] Preparation of negative electrode sheet: The negative electrode active material, conductive agent, and composite binder are dispersed in an appropriate amount of deionized water according to the following mass percentages: 75% silicon-doped active material, 15.5% solid electrolyte, 1.5% conductive agent, and 8% composite binder. The mixture is stirred at 1200 rpm for 2 hours using a vacuum planetary mixer to form a uniform negative electrode slurry. The negative electrode slurry is uniformly coated on a 6 μm thick copper foil current collector. After drying, rolling and slitting, the negative electrode sheet is obtained.

[0149] Preparation of secondary batteries: The positive electrode, solid electrolyte membrane and the above-mentioned negative electrode are stacked, packaged, isostatically pressed and formed to obtain the battery cell.

[0150] 2. Testing Methods

[0151] 1) Test methods for the solid content and viscosity of composite adhesives in n-decane solution.

[0152] Solid content was determined by drying and weighing method. 2-5g of slurry was dried at 120℃ to constant weight, and the mass before and after drying was recorded to calculate the solid content.

[0153] Viscosity was measured using a rotational viscometer, with rotor #3 selected at a speed of 12 rpm.

[0154] 2) Test methods for tensile strength and elongation at break of adhesive film

[0155] The composite adhesive to be tested was cast into a film using a polytetrafluoroethylene mold and then vacuum dried at 60℃ for 24 hours to completely remove the n-decane solvent, resulting in a homogeneous, independent adhesive film with a thickness of 100 μm. The film was then cut into dumbbell-shaped specimens of 10 mm × 70 mm. Uniaxial tensile mechanical tests were performed using a micro universal testing machine at 25℃ with a tensile speed of 50 mm / min, and the tensile strength (MPa) and elongation at break (%) were recorded.

[0156] 3) Test method for resistivity of negative electrode

[0157] Electrode resistivity was tested using the two-probe method.

[0158] 4) Cyclic performance testing methods

[0159] At 25℃ and 15MPa operating pressure, the capacitor was charged at a constant current rate of 0.33C to 4.25V, then charged at a constant voltage rate of 0.05C to 4.25V, and finally discharged at a discharge rate of 0.33C to 1.9V. This charge-discharge cycle was repeated 100 times. The discharge capacity Q1 at the first cycle and the discharge capacity Q at the 100th cycle were measured. 100 .

[0160] The capacity retention rate Q after 100 cycles is calculated using the following formula.

[0161] Capacity retention rate Q = Q 100 / Q1*100%.

[0162] 5) Test method for initial coulomb efficiency

[0163] After each battery was left to stand at 25°C for 4 hours, its first charge-discharge capacity was tested under an operating pressure of 15 MPa. The test conditions were: charging to 4.25V at 0.1C, constant voltage charging to 0.025C, then standing for 3 minutes, followed by discharging to 1.9V at 0.1C. The first charge capacity C0 and the first discharge capacity D0 were recorded from 1.9V to 4.25V, and the first coulombic efficiency was calculated based on D0 / C0.

[0164] 6) Test methods for initial peel strength and peel strength after 100 cycles

[0165] Initial peel strength: A 180° peel test (50 mm / min) was conducted using a tensile testing machine. The initial average peel force (N / m) was recorded when the negative electrode active layer peeled off from the negative electrode current collector.

[0166] Peel strength after 100 cycles: The empty battery cell after 100 cycles was disassembled in a high dew point environment, and the peel strength after long cycles was tested.

[0167] Table 3A

[0168]

[0169] Table 3B

[0170]

[0171] As shown in Tables 3A and 3B, compared with the comparative example, the secondary battery prepared by the composite binder of the embodiment has excellent cycle performance, rate performance and first-time efficiency.

[0172] The above embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention.

Claims

1. A composite adhesive, characterized in that, The composite binder comprises, by weight, 90-97% polymer binder, 1-5% conductive material, 1-5% solid electrolyte particles, and 0.3-1% interfacial coupling agent; the mass ratio of the solid electrolyte particles to the conductive material is (1-1.5):

1. The conductive material has an aspect ratio ≥1500, and the conductive material includes oxygen-containing functional groups; the composite binder has a viscosity of 2500-20000 mPa·s in a solution with a solid content of 5-25%.

2. The composite adhesive according to claim 1, characterized in that, The composite binder comprises, by weight, 90-96.7% polymer binder, 1.5-4.5% conductive material, 1.5-4.5% solid electrolyte particles, and 0.3-0.7% interfacial coupling agent; the mass ratio of the solid electrolyte particles to the conductive material is (1.1-1.3):

1.

3. The composite adhesive according to claim 1 or 2, characterized in that, The particle size Dv50 of the conductive material is ≤1.5μm; and / or, The particle size Dv50 of the solid electrolyte particles is 20-500 nm.

4. The composite adhesive according to any one of claims 1-3, characterized in that, The interface coupling agent includes a dispersant and / or a coupling agent; the weight-average molecular weight of the dispersant is 500-10000, and the weight-average molecular weight of the coupling agent is ≤500.

5. The composite adhesive according to any one of claims 1-4, characterized in that, The polymer binder comprises at least one of polyisobutylene, styrene-ethylene-butene-styrene block copolymer, polyacrylic acid copolymer, polyimide, polyamide-imide, polyurethane, polyurea, styrene-butadiene rubber, and styrene-acrylic rubber; and / or, The conductive material includes at least one of carbon nanotubes, conductive carbon fibers, silicon nanowires, and metal nanowires. Preferably, the average diameter of the carbon nanotubes is <10 nm, and the specific surface area of ​​the carbon nanotubes is >280 m². 2 / g; and / or, The solid electrolyte particles include at least one of sulfide solid electrolyte particles, halide solid electrolyte particles, and oxide solid electrolyte particles; and / or, The interface coupling agent includes at least one of polyisobutylene and its derivatives, polysiloxane and its derivatives, polyimide and its derivatives, alkylsilane coupling agents, and titanate coupling agents with a weight average molecular weight of 500-10000.

6. The composite adhesive according to claim 5, characterized in that, The oxide solid electrolyte particles include at least one of garnet-type solid electrolyte, NASICON-type solid electrolyte, and perovskite-type solid electrolyte.

7. A method for preparing the composite adhesive according to any one of claims 1-6, characterized in that, Includes the following steps: 1) By weight, the raw materials including the polymer binder, conductive material, solid electrolyte particles and interfacial coupling agent are dispersed in a solvent to obtain a mixed slurry; 2) The mixed slurry is subjected to high-pressure homogenization to obtain the composite adhesive; wherein the pressure of the high-pressure homogenization is 40-120 MPa.

8. The method for preparing the composite adhesive according to claim 7, characterized in that, In step 1), the dispersion includes stirring dispersion, wherein the stirring speed is 1000-2000 rpm and the stirring time is 20-30 min; and / or, The pressure of the high-pressure homogenization process is 60-90 MPa; and / or, The high-pressure homogenization process is repeated 2-5 times; and / or, The discharge temperature after the high-pressure homogenization treatment is ≤40℃, preferably 30-35℃; and / or, The solvent includes at least one of the following: n-decane, hexane, heptane, cyclohexane, toluene, xylene, fluoroether, octyl acetate, isobutyl isobutyrate, dimethyl carbonate, ethylene carbonate, dimethylformamide, N,N-dimethylacetamide, triethyl phosphate, N-methylpyrrolidone, and deionized water.

9. An electrode sheet, characterized in that, Includes the composite adhesive as described in any one of claims 1-6, or the composite adhesive prepared by the preparation method described in claim 7 or 8.

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

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