Composite binder for dry-method electrode and preparation method and application thereof

Abstract

The invention discloses a composite binder for a dry-method electrode and a preparation method and application thereof, and relates to the technical field of battery preparation. The composite binder comprises polytetrafluoroethylene and an auxiliary binder, the auxiliary binder comprises a fluorine-containing polymer with crystallinity changing along with temperature, and the fluorine-containing polymer is a polymer which can form a molten state under a heating condition and can crystallize and form a fine spherocrystal structure after being cooled. The invention also provides a dry electrode, which comprises a positive active material, a conductive agent and a composite binder. According to the invention, a polymer with crystallinity adjustable along with temperature is creatively introduced as one of binder components to be compounded with polytetrafluoroethylene, and the crystallization behavior of the polymer, which can be regulated and controlled through processing conditions, is utilized to actively control the crystal form and size of the polymer in a composite fiber network; the auxiliary polymer forms a fine spherocrystal structure, and the structure cooperates with the PTFE fiber to construct a rigid-flexible three-dimensional bonding network structure.

Description

Technical Field

[0001] This invention relates to the field of battery manufacturing technology, specifically to a composite binder for dry electrode fabrication, its preparation method, and its application. Background Technology

[0002] With the rapid development of new energy vehicles and the large-scale energy storage market, increasingly stringent requirements have been placed on the energy density, power density, and manufacturing cost of lithium-ion batteries. To achieve higher energy density, high-nickel layered oxides (such as LiNi) are employed. 0.8 Co 0.1 Mn 0.1 O2 (NCM811) has become a clear technological path as a cathode material. However, the inherent problems of high-nickel materials, such as high surface alkalinity, sensitivity to moisture, and susceptibility to interfacial side reactions during cycling, severely restrict their commercial application lifespan and safety.

[0003] In electrode manufacturing processes, traditional wet coating techniques suffer from inherent drawbacks such as high energy consumption, low production efficiency, use of toxic organic solvents, and susceptibility to cracking during electrode drying, especially when fabricating thick electrodes with high areal loading. Therefore, solvent-free, low-energy dry electrode technology is considered a disruptive path for next-generation battery manufacturing. This technology typically utilizes fibrillated binders such as polytetrafluoroethylene (PTFE) to form a three-dimensional fiber network through mechanical shearing, directly bonding active materials and conductive agents, eliminating the need for slurry preparation and drying.

[0004] However, applying dry electrode technology to high-nickel cathode systems faces significant technical challenges. First, from a mechanical perspective, while PTFE can form a high-strength fiber network, it is brittle and lacks toughness. Under the crushing force of a high-load electrode and long-term electrochemical cyclic stress, the PTFE fiber network is prone to brittle fracture, leading to pulverization of the internal electrode structure and failure of the electronic conductivity network. Second, from an interfacial chemistry perspective, the large specific surface area and highly catalytically active surface of high-nickel materials cause violent side reactions upon contact with the electrolyte, generating HF gas and inducing transition metal dissolution, resulting in a continuous increase in interfacial impedance and rapid capacity decay. Although PTFE itself is chemically inert, its network is difficult to achieve complete and stable coating of highly active particle surfaces at the microscopic level. Finally, from the perspective of transport performance and process control, the long ion / electron transport paths in thick electrodes easily create transport bottlenecks. Existing dry processes rely on a passive and empirical approach to control the electrode microstructure, lacking proactive and precise control methods, making it difficult to simultaneously optimize the electrode's pore structure, conductive network, and interfacial state.

[0005] Therefore, there is a pressing technical contradiction in the existing technology: how to simultaneously solve the systemic problems faced by high-nickel materials in high-load thick electrodes, such as mechanical failure, interface instability and slow transport dynamics, without sacrificing the high efficiency and environmental protection advantages of dry electrodes.

[0006] To address the aforementioned challenges, while some studies have attempted to modify or compound binders, these efforts have largely remained at the level of simple physical mixing. They have failed to address fundamental aspects such as molecular chain structure and crystallization behavior, thus failing to design binder systems that can synergize with dry-process technology and actively regulate the multi-scale structure of the electrodes. Therefore, developing a novel composite binder suitable for high-nickel dry-process electrodes to achieve synergistic improvements in electrode mechanics, transport, and interfacial stability has become crucial for driving the industrial application of high-energy-density dry-process batteries. Summary of the Invention

[0007] The purpose of this invention is to at least solve one of the technical problems existing in the prior art, and to provide a composite binder for dry electrode, its preparation method and application, particularly relating to a composite binder system for high-nickel ternary material dry electrode, its preparation method and lithium-ion battery using the binder system. This invention is particularly suitable for solving the key technical problems faced by high areal load dry cathodes, such as mechanical reliability, interface stability and transport dynamics.

[0008] To address the problems of poor mechanical reliability, unstable electrochemical interfaces, and slow transport kinetics faced by existing dry electrode technologies, this invention provides a high-performance dry electrode binder system based on actively controlled crystallization behavior and its applications. This invention creatively introduces a temperature-tunable crystallinity polymer as one of the binder components, compounded with polytetrafluoroethylene (PTFE). The core lies in utilizing the polymer's temperature-tunable crystallization behavior. During the dry electrode preparation process, the polymer is first heated to a molten state, then rolled, with the rolling temperature controlled below the polymer's crystallization temperature. The molten polymer crystallizes to form a fine spherulite structure. This invention actively controls the crystal form and size of the polymer within the composite fiber network, enabling the auxiliary polymer to form a fine spherulite structure. This structure, in synergy with PTFE fibers, constructs a "rigid-flexible" three-dimensional binder network. PTFE fibers act as a rigid skeleton providing instantaneous strength, while the polymer with tunable crystal conformation acts as a flexible node, effectively dissipating stress through its plastic deformation. This significantly improves the crush resistance and structural durability of the high-load electrode under long-term cycling, fundamentally solving the problem of electrode pulverization. Furthermore, this composite network forms a uniform, dense, and porous coating structure at the microscopic level. This structure utilizes its porous nature to ensure sufficient electrolyte wetting and efficient lithium-ion transport. Ultimately, this invention achieves a simultaneous and proactive improvement in the mechanical strength, interfacial stability, and ion transport rate of dry-process electrodes within a single system, providing a crucial material foundation for manufacturing long-life, high-safety, and high-energy-density high-load dry-process lithium batteries.

[0009] The technical solution of the present invention is as follows: In a first aspect, the present invention provides a composite binder for dry-process electrodes. The composite adhesive includes polytetrafluoroethylene and an auxiliary adhesive; The auxiliary binder includes a fluoropolymer whose crystallinity changes with temperature. The fluoropolymer can form a molten state under heating conditions and crystallize to form a fine spherulite structure after cooling.

[0010] Optionally, the auxiliary binder is at least one of a poly(perfluoroalkoxy vinyl ether) copolymer, wherein the general structural formula of the poly(perfluoroalkoxy vinyl ether) copolymer is: R is at least one of -CF3, -CF2CF3, -CF2CF2CF3, and -CF2CF2CF2CF3, n = 500 to 10000, m = 500 to 10000, and the content of the perfluoroalkyl vinyl ether structural unit in the polyperfluoroalkoxy vinyl ether copolymer is 0.5 mol% to 12 mol; more preferably 3 mol% to 4 mol.

[0011] Optionally, the auxiliary binder is at least one of thermoplastic fluoroplastics, including perfluoroethylene propylene, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, ethylene-chlorotrifluoroethylene copolymer, and tetrafluoroethylene-perfluoroalkyl vinyl ether-hexafluoropropylene terpolymer.

[0012] Optionally, the auxiliary binder is at least one of the polyperfluoroalkoxy vinyl ether modified derivatives, including carboxyl-functionalized perfluoroalkoxy copolymers, anhydride-functionalized perfluoroalkoxy copolymers, sulfonic acid-functionalized perfluoroalkoxy copolymers, hydroxyl-functionalized perfluoroalkoxy copolymers, tetrafluoroethylene-perfluoromethyl vinyl ether copolymer derivatives containing crosslinkable side groups, tetrafluoroethylene-perfluoro(alkoxy vinyl ether)-perfluoro(ethyleneoxy)propyl vinyl ether copolymers, perfluoropolyethers, copolymers of tetrafluoroethylene and silicone-containing perfluorovinyl ethers, tetrafluoroethylene-perfluoromethyl vinyl ether copolymer-based block copolymers, and tetrafluoroethylene-perfluoromethyl vinyl ether copolymer-based star or hyperbranched polymers.

[0013] Optionally, the mass ratio of the polytetrafluoroethylene to the auxiliary binder is 1~2:1~2.

[0014] Secondly, the present invention provides a dry electrode, the dry electrode comprising a positive electrode active material, a conductive agent and the aforementioned composite binder; The composite binder forms a three-dimensional fiber network structure that encapsulates the positive electrode active material and the conductive agent. The polytetrafluoroethylene in the composite binder serves as the rigid skeleton of the three-dimensional fiber network structure, while the auxiliary binder in the composite binder serves as the flexible node of the three-dimensional fiber network structure.

[0015] Optionally, the mass ratio of the positive electrode active material, the conductive agent, and the composite binder is 92~94:4~6:1.5~2.5.

[0016] Thirdly, the present invention provides a method for preparing the aforementioned dry electrode, comprising the following steps: The positive electrode active material, conductive agent and composite binder are dry-mixed to obtain a mixture. The mixture is subjected to mechanical shearing to fibrillate the composite adhesive into a three-dimensional fiber network structure. The mixture after mechanical shearing is heated to a temperature higher than the melting temperature of the auxiliary binder in the composite binder, so that the auxiliary binder in the composite binder is in a molten state. The heated mixture is hot-rolled to form a dry electrode; wherein, in the hot-rolling process, the temperature of the rolling roller is lower than the crystallization temperature of the auxiliary binder.

[0017] Optionally, the heating temperature is 300℃~330℃, and the heating time is 5~15 minutes; The temperature of the rolling roller is 25℃~80℃, the gap between the rollers is 140μm~160μm, and the speed of the rolling roller is 0.4m / min~0.6m / min.

[0018] Fourthly, the present invention provides a lithium-ion battery, including a positive electrode, wherein the positive electrode is the dry electrode described above or a dry electrode obtained by the preparation method described above.

[0019] This invention has at least one of the following beneficial effects: 1. Significantly Enhanced Mechanical Properties: This invention constructs a "rigid skeleton-flexible crystalline region" composite fiber network through the compounding of an auxiliary binder and polytetrafluoroethylene (PTFE) and a subsequent rapid cooling process, which greatly improves the flexibility and tensile strength of the prepared electrode sheet. This structure can effectively dissipate stress, fundamentally solving the technical problem of easy "pulverization" of high-load dry-process electrodes during rolling and cycling, and greatly improving the cycle life and structural reliability of the battery.

[0020] 2. Revolutionary Improvement in Interface Stability: A dense and chemically inert composite fiber network formed with the participation of auxiliary binders constructs a highly efficient physicochemical barrier on the surface of positive electrode active materials such as highly active NCM811 particles. This composite fiber network not only physically blocks direct electrolyte erosion, but its superhydrophobicity also inhibits HF generation at the source and guides the formation of a stable LiF-rich interface film. This significantly reduces the increase in interface impedance and the dissolution of transition metals after long-term cycling, thereby ensuring high coulombic efficiency and cycle stability.

[0021] 3. Simultaneous Optimization of Transport Dynamics and Process Controllability: By regulating the crystallization behavior of the auxiliary binder, uniformly sized and rationally distributed nanoscale pores are created within the electrode, providing efficient channels for ion transport. Simultaneously, the robust network stabilizes the electronic conductivity pathway. This method elevates the compaction process of dry electrodes from empirical parameters to a "processing field" where the crystal structure can be actively controlled. It achieves precise design of the electrode's microstructure, simultaneously solving the transport bottleneck and process controllability issues of thick electrodes, laying the foundation for the large-scale manufacturing of high-performance, low-cost dry electrodes. Attached Figure Description

[0022] Figure 1 These are the X-ray diffraction spectra of the adhesives used in Embodiment 1 and Comparative Examples 1-2 of this invention; Figure 2 These are the stress-strain curves from the tensile tests of Embodiment 1 and Comparative Example 1 of the present invention; Figure 3These are SEM images of the fracture surfaces after tensile tests in Embodiment 1 and Comparative Example 1 of the present invention; Figure 4 These are contact angle tests and actual photographs of Embodiment 1 and Comparative Example 1 of the present invention; Figure 5 This describes the preparation process and microscopic SEM images of Example 1 of the present invention. Figure 6 These are actual pictures of Embodiment 1 of the present invention; Figure 7 These are surface SEM images of Embodiment 1 and Comparative Example 1 of the present invention; Figure 8 This is a comparison chart of the rate cycling performance of lithium half-cells in Embodiment 1 and Comparative Example 1 of the present invention. Figure 9 These are capacity-voltage curves of lithium half-cells in Embodiment 1 and Comparative Example 1 of the present invention at high rates. Figure 10 This is a comparison chart of long-cycle data of lithium half-cells under high load in Embodiment 1 and Comparative Example 1 of the present invention; Figure 11 This is a capacity retention test graph of Embodiment 1 and Comparative Example 1 after 200 cycles at a 0.5C rate. Detailed Implementation

[0023] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0024] An embodiment of the present invention provides a composite binder for dry electrode, the composite binder being composed of polytetrafluoroethylene and a crystallization-controllable auxiliary binder, the auxiliary binder being a fluoropolymer whose crystallinity changes with temperature, the fluoropolymer being able to form a molten state under heating conditions and crystallize to form a fine spherulite structure after cooling.

[0025] This invention creatively introduces a temperature-tunable crystallinity polymer as one of the binder components, compounded with polytetrafluoroethylene (PTFE). Its core lies in utilizing the polymer's crystallization behavior, which can be controlled by processing conditions, to actively control its crystal form and size within the composite fiber network through the thermo-mechanical field (such as rolling temperature and pressure) during dry electrode fabrication. Under specific process conditions (such as rapid cooling), the binder assists in forming fine spherulitic structures. This structure, in synergy with PTFE fibers, constructs a three-dimensional adhesive network that combines rigidity and flexibility.

[0026] In some embodiments, the auxiliary binder is at least one of a perfluoroalkoxy vinyl ether copolymer, wherein the general structural formula of the perfluoroalkoxy vinyl ether copolymer is: Wherein, R is at least one of -CF3, -CF2CF3, -CF2CF2CF3, and -CF2CF2CF2CF3, n=500~10000, m=500~10000, and the content of the perfluoroalkyl vinyl ether structural unit in the polyperfluoroalkoxy vinyl ether copolymer is 0.5 mol% to 12 mol%, with a preferred embodiment being 3 mol% to 4 mol%. Further, the auxiliary binder may be a direct analogue of polyperfluoroalkoxy vinyl ether, including at least one of tetrafluoroethylene-perfluoromethyl vinyl ether copolymer (PFA) (side chain -O-CF3), (side chain -O-CF2CF3), (side chain -O-CF2CF2CF3), and (side chain -O-CF2CF2CF2CF3).

[0027] In some embodiments, the auxiliary binder may be a thermoplastic fluoroplastic, including at least one of perfluoroethylene propylene (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), and tetrafluoroethylene-perfluoroalkyl vinyl ether-hexafluoropropylene terpolymer.

[0028] In some embodiments, the auxiliary binder may be a tetrafluoroethylene-perfluoromethyl vinyl ether copolymer modified derivative, including at least one of the following: carboxyl-functionalized perfluoroalkoxy copolymer, anhydride-functionalized perfluoroalkoxy copolymer, sulfonic acid-functionalized perfluoroalkoxy copolymer, hydroxyl-functionalized perfluoroalkoxy copolymer, tetrafluoroethylene-perfluoromethyl vinyl ether copolymer derivative containing crosslinkable side groups (such as vinyl groups), tetrafluoroethylene-perfluoro(alkoxyvinyl ether)-perfluoro(ethyleneoxy)propyl vinyl ether copolymer, perfluoropolyether (PFPE), copolymer of tetrafluoroethylene and silicone-containing perfluorovinyl ether, tetrafluoroethylene-perfluoromethyl vinyl ether copolymer-based block copolymer, and tetrafluoroethylene-perfluoromethyl vinyl ether copolymer-based star or hyperbranched polymer.

[0029] In some embodiments, the mass ratio of polytetrafluoroethylene to auxiliary binder is 1~2:1~2; preferably 1~1.5:1~1.5. More preferably 1~1.2:1~1.2.

[0030] Another embodiment of the present invention provides a dry electrode, wherein the above-mentioned composite binder is used to prepare the dry electrode, and the components of the dry electrode include a positive electrode active material, a conductive agent and the composite binder.

[0031] The composite binder forms a three-dimensional fiber network structure that encapsulates the positive electrode active material and the conductive agent. The polytetrafluoroethylene in the composite binder serves as the rigid skeleton of the three-dimensional fiber network structure, while the auxiliary binder in the composite binder serves as the flexible node of the three-dimensional fiber network structure.

[0032] The auxiliary binder of this invention works synergistically with PTFE fibers to construct a "rigid-flexible" three-dimensional bonding network. PTFE fibers act as a rigid skeleton, providing instantaneous strength, while the polymer with tunable crystal conformation serves as flexible nodes, effectively dissipating stress through plastic deformation, significantly improving the crush resistance and structural durability of the high-load electrode under long-term cycling. Furthermore, this composite network forms a uniform, dense, and porous coating structure at the microscopic level, utilizing its porous properties to ensure sufficient electrolyte wetting and efficient lithium-ion transport. Ultimately, this invention achieves simultaneous and proactive improvement in the mechanical strength, interfacial stability, and ion transport rate of dry-process electrodes within a single system, providing a crucial material foundation for manufacturing long-life, high-safety, and high-energy-density high-load dry-process lithium batteries.

[0033] In some embodiments, the mass ratio of the positive electrode active material, the conductive agent, and the composite binder is 92~94:4~6:1.5~2.5; preferably 92.5~93.5:4.5~5.5:1.8~2.2; more preferably 93:5:2.

[0034] Another embodiment of the present invention provides a method for preparing a dry electrode, comprising the following steps: The positive electrode active material, conductive agent and composite binder are dry-mixed to obtain a mixture. The mixture is subjected to mechanical shearing to fibrillate the composite adhesive into a three-dimensional fiber network structure. The mixture after mechanical shearing is heated to a temperature higher than the melting temperature of the auxiliary binder in the composite binder, causing the auxiliary binder in the composite binder to form a molten state. The heated mixture is hot-rolled to form a dry electrode; wherein, in the hot-rolling process, the temperature of the rolling roller is lower than the crystallization temperature of the auxiliary binder.

[0035] The preparation method of this invention involves first subjecting the mixture to mechanical shearing, causing PTFE and the auxiliary binder to undergo synergistic fibrillation to form a dense three-dimensional microfiber network that firmly encapsulates and connects the active material particles and the conductive agent; then heating the mixture to melt the auxiliary binder; and finally hot rolling, allowing the molten auxiliary binder to undergo a controllable cooling process from the molten state to below its crystallization temperature as it passes through the roller gap and is compacted into a film. This actively induces the auxiliary binder to form a favorable crystal structure, thereby simultaneously improving the mechanical strength, electrochemical interface stability, and ion transport capability of the dry electrode.

[0036] In some embodiments, the heating temperature is 300°C to 330°C, and the heating time is 5 to 15 minutes; The temperature of the rolling roller is 25℃~80℃, the gap between the rollers is 140μm~160μm, and the speed of the rolling roller is 0.4m / min~0.6m / min.

[0037] The "controlled cooling conditions" of this invention refer to controlling the temperature of the rolling mill rolls within a specific range during the hot rolling molding process. This allows the ether-containing perfluoropolymer component, molten from the mixture, to undergo a controlled cooling process from its molten state to below its crystallization temperature as it passes through the roll gap and is compacted into a film. This cooling rate is primarily achieved through the difference between the roll temperature and the initial temperature of the material. As a preferred embodiment, the controlled cooling conditions are achieved by setting the rolling mill roll temperature between 25°C and 80°C, more preferably between 40°C and 60°C. When the roll temperature is within this range, effective "rapid cooling" can be achieved, inducing the formation of fine spherulites; if the roll temperature is too high (e.g., >120°C), it approaches "slow cooling," which may lead to coarse crystals.

[0038] In some embodiments, "mechanical shearing action" refers to stirring the mixture. The stirring method includes: pre-mixing at a speed of 400 rpm to 600 rpm for 1 to 3 minutes to make the material initially uniform; then increasing the speed to 1500 rpm to 2500 rpm and continuing to mix for 10 to 20 minutes. Under this high-intensity shearing action, PTFE and the auxiliary binder undergo synergistic fibrillation to form a dense three-dimensional microfiber network, which firmly encapsulates and connects the active material particles and the conductive agent.

[0039] In some embodiments, the positive electrode active material comprises a high-nickel ternary material (LiNi). 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.8 Co 0.15 Mn 0.05O2, ultra-high nickel materials), lithium-rich manganese-based materials (xLi2MnO3·(1-x)LiMO3), lithium iron phosphate (LiFePO4), lithium manganese iron phosphate (LiMn x Fe 1-x PO4, and high-pressure spinel (LiNi) 0.5 Mn 1.5 At least one of the following: lithium manganese oxide (LiMn2O4), lithium spinel manganese oxide (LiMn2O4), sulfur-based cathode (S@C composite material), high-entropy oxide cathode, sulfide-compatible cathode (such as LiCoO2@LiNbO3 coating), and lithium manganese oxide (LiMnO2).

[0040] In some embodiments, the conductive agent is at least one of conductive carbon black, carbon nanotubes, or graphene.

[0041] Another embodiment of the present invention provides a lithium-ion battery, including a positive electrode, a negative electrode and a separator, wherein the positive electrode is the dry electrode described above or a dry electrode obtained by the preparation method described above.

[0042] Using the dry electrode of this invention as the positive electrode greatly improves the cycle life and structural reliability of the battery.

[0043] In some embodiments, the negative electrode of the battery is graphite, silicon carbide, or lithium metal, and the separator is at least one of polypropylene separator, polyethylene separator, or ceramic-coated separator.

[0044] The present invention will be further described in detail below with reference to specific embodiments, but the present invention is not limited to the following specific embodiments.

[0045] Example 1 A method for preparing a dry electrode includes the following steps: (1) Under dry conditions, weigh NCM811 positive electrode active material, conductive carbon black (SuperP) and composite binder in a mass ratio of 93:5:2. The composite binder is made by pre-mixing polytetrafluoroethylene (PTFE) and polyperfluoroalkoxy vinyl ether (PFA) in a dry weight ratio of 1:1 (i.e., PTFE and PFA each account for 1% of the total mass of the electrode).

[0046] (2) Place the above mixture into the sealed mixing tank of a high-speed mixer. First, premix at 500 rpm for 2 minutes to make the material initially uniform; then increase the speed to 2000 rpm and continue mixing for 15 minutes. Under this high-intensity shearing action, PTFE and PFA undergo synergistic fibrillation to form a dense three-dimensional microfiber network, which firmly encapsulates and connects the active material particles and the conductive agent.

[0047] (3) The mixed material is then heated to 310°C for 10 minutes. By heating the mixed material, the PFA in it is heated to a molten state.

[0048] (4) The heated mixture is evenly spread on a 20 μm thick aluminum foil current collector and then fed into a two-roll mill. The upper roller temperature is set to 50°C, the lower roller temperature is set to 50°C, the roller gap is adjusted to 150 μm, and the roller speed is controlled at 0.5 m / min. The material undergoes thermo-mechanical coupling when passing through the hot rollers. Since the roller temperature is much lower than the initial temperature of the mixture, the PFA component undergoes a process from the molten state to below its crystallization temperature when passing through the roller gap and being compacted into a film. Under this controlled cooling condition, the PFA component will crystallize and form a fine spherulite structure, ultimately producing an area loading of 45.2 mgcm. -2 A uniform, dense, and highly flexible self-supporting electrode sheet with a thickness of 125 μm.

[0049] A method for preparing a battery includes the following steps: The electrode sheet prepared above was used as the positive electrode, and a 14 mm diameter lithium metal sheet was used as the negative electrode. A Celgard 2325 polypropylene separator was used, and the cells were assembled into CR2032 coin cells in an argon-atmospheric glove box. Each cell was precisely injected with 80 μL of commercial electrolyte (1 M LiPF6 in EC / EMC / DMC, 2% VC), sealed, and allowed to stand for 3 hours to ensure full electrolyte wetting before electrochemical testing.

[0050] Example 2 A method for preparing a dry electrode includes the following steps: (1) Under dry conditions, weigh NCM811 positive electrode active material, conductive carbon black (SuperP) and composite binder in a mass ratio of 93:5:2. The composite binder is made by pre-mixing polytetrafluoroethylene (PTFE) and polyperfluoroalkoxy vinyl ether (PFA) in a dry weight ratio of 1.8:0.2.

[0051] The other steps are the same as in Example 1.

[0052] Example 3 A method for preparing a dry electrode includes the following steps: (1) Under dry conditions, weigh NCM811 positive electrode active material, conductive carbon black (SuperP) and composite binder in a mass ratio of 93:5:2. The composite binder is made by pre-mixing polytetrafluoroethylene (PTFE) and polyperfluoroalkoxy vinyl ether (PFA) in a dry weight ratio of 1.6:0.4.

[0053] The other steps are the same as in Example 1.

[0054] Example 4 A method for preparing a dry electrode includes the following steps: (1) Under dry conditions, weigh NCM811 positive electrode active material, conductive carbon black (SuperP) and composite binder in a mass ratio of 93:5:2. The composite binder is made by pre-mixing polytetrafluoroethylene (PTFE) and polyperfluoroalkoxy vinyl ether (PFA) in a dry weight ratio of 1.4:0.6.

[0055] The other steps are the same as in Example 1.

[0056] Example 5 A method for preparing a dry electrode includes the following steps: (1) Under dry conditions, weigh NCM811 positive electrode active material, conductive carbon black (SuperP) and composite binder in a mass ratio of 93:5:2. The composite binder is made by pre-mixing polytetrafluoroethylene (PTFE) and polyperfluoroalkoxy vinyl ether (PFA) in a dry weight ratio of 1.2:0.8.

[0057] The other steps are the same as in Example 1.

[0058] Example 6 A method for preparing a dry electrode includes the following steps: (1) Under dry conditions, weigh NCM811 positive electrode active material, conductive carbon black (SuperP) and composite binder in a mass ratio of 93:5:2. The composite binder is made by pre-mixing polytetrafluoroethylene (PTFE) and polyperfluoroalkoxy vinyl ether (PFA) in a dry weight ratio of 0.8:1.2.

[0059] The other steps are the same as in Example 1.

[0060] Example 7 A method for preparing a dry electrode includes the following steps: (1) Under dry conditions, weigh NCM811 positive electrode active material, conductive carbon black (SuperP) and composite binder in a mass ratio of 93:5:2. The composite binder is made by pre-mixing polytetrafluoroethylene (PTFE) and polyperfluoroalkoxy vinyl ether (PFA) in a dry weight ratio of 0.6:1.4.

[0061] The other steps are the same as in Example 1.

[0062] Example 8 A method for preparing a dry electrode includes the following steps: (1) Under dry conditions, weigh NCM811 positive electrode active material, conductive carbon black (SuperP) and composite binder in a mass ratio of 93:5:2. The composite binder is made by pre-mixing polytetrafluoroethylene (PTFE) and polyperfluoroalkoxy vinyl ether (PFA) in a dry weight ratio of 0.4:1.6.

[0063] The other steps are the same as in Example 1.

[0064] Example 9 A method for preparing a dry electrode includes the following steps: (1) Under dry conditions, weigh NCM811 positive electrode active material, conductive carbon black (SuperP) and composite binder in a mass ratio of 93:5:2. The composite binder is made by pre-mixing polytetrafluoroethylene (PTFE) and perfluoroethylene propylene (FEP) in a dry weight ratio of 1:1 (i.e., PTFE and FEP each account for 1% of the total mass of the electrode).

[0065] The other steps are the same as in Example 1.

[0066] Example 10 A method for preparing a dry electrode includes the following steps: (1) Under dry conditions, weigh NCM811 positive electrode active material, conductive carbon black (SuperP) and composite binder in a mass ratio of 93:5:2. The composite binder is made by pre-mixing polytetrafluoroethylene (PTFE) and perfluoropolyether (PFPE) in a dry weight ratio of 1:1 (i.e., PTFE and PFPE each account for 1% of the total mass of the electrode).

[0067] The other steps are the same as in Example 1.

[0068] Comparative Example 1 The difference from Example 1 is that PFA is not added; instead, PTFE is used as the sole binder. The specific preparation method is as follows: A method for preparing a dry electrode includes the following steps: (1) Under dry conditions, weigh NCM811 positive electrode active material, conductive carbon black (SuperP), and binder in a mass ratio of 93:5:2. The binder is composed of polytetrafluoroethylene (PTFE). Place the above mixture into the sealed mixing tank of a high-speed mixer. First, premix at 500 rpm for 2 minutes to make the material initially uniform; then increase the speed to 2000 rpm and continue mixing for 15 minutes.

[0069] (2) Spread the mixed material evenly on an aluminum foil current collector with a thickness of 20 μm, and then feed it into a two-roll mill. Set the temperature of the upper roller to 50°C, the temperature of the lower roller to 50°C, adjust the roller gap to 150 μm, and control the roller speed at 0.5 m / min to obtain the electrode sheet.

[0070] The electrode sheet prepared above was used as the positive electrode, and a 14 mm diameter lithium metal sheet was used as the negative electrode. A Celgard 2325 polypropylene separator was used, and the cells were assembled into CR2032 coin cells in an argon-atmospheric glove box. Each cell was precisely injected with 80 μL of commercial electrolyte (1 M LiPF6 in EC / EMC / DMC, 2% VC), sealed, and allowed to stand for 3 hours to ensure full electrolyte wetting before electrochemical testing.

[0071] Comparative Example 2 The difference from Example 1 is that PFA is replaced with PVDF, and PTFE and PVDF are used as composite binders. The specific preparation method is as follows: A method for preparing a dry electrode includes the following steps: (1) Under dry conditions, weigh NCM811 positive electrode active material, conductive carbon black (SuperP), and composite binder at a mass ratio of 93:5:2. The composite binder is made by pre-mixing polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) at a dry weight ratio of 1:1 (i.e., PTFE and PVDF each account for 1% of the total electrode mass). Place the above mixture into the sealed mixing tank of a high-speed mixer. First, pre-mix at 500 rpm for 2 minutes to make the material initially uniform; then increase the speed to 2000 rpm and continue mixing for 15 minutes.

[0072] (2) Spread the mixed material evenly on an aluminum foil current collector with a thickness of 20 μm, and then feed it into a two-roll mill. Set the temperature of the upper roller to 50°C, the temperature of the lower roller to 50°C, adjust the roller gap to 150 μm, and control the roller speed at 0.5 m / min to obtain the electrode sheet.

[0073] The electrode sheet prepared above was used as the positive electrode, and a 14 mm diameter lithium metal sheet was used as the negative electrode. A Celgard 2325 polypropylene separator was used, and the cells were assembled into CR2032 coin cells in an argon-atmospheric glove box. Each cell was precisely injected with 80 μL of commercial electrolyte (1 M LiPF6 in EC / EMC / DMC, 2% VC), sealed, and allowed to stand for 3 hours to ensure full electrolyte wetting before electrochemical testing.

[0074] Comparative Example 3 The difference from Example 1 is that PFA is replaced with TPU, and PTFE and TPU are used as composite binders. The specific preparation method is as follows: A method for preparing a dry electrode includes the following steps: (1) Under dry conditions, weigh NCM811 positive electrode active material, conductive carbon black (SuperP), and composite binder at a mass ratio of 93:5:2. The composite binder is made by pre-mixing polytetrafluoroethylene (PTFE) and thermoplastic polyurethane rubber (TPU) at a dry weight ratio of 1:1 (i.e., PTFE and TPU each account for 1% of the total electrode mass). Place the above mixture into the sealed mixing tank of a high-speed mixer. First, pre-mix at 500 rpm for 2 minutes to make the material initially uniform; then increase the speed to 2000 rpm and continue mixing for 15 minutes.

[0075] (2) Spread the mixed material evenly on an aluminum foil current collector with a thickness of 20 μm, and then feed it into a two-roll mill. Set the temperature of the upper roller to 50°C, the temperature of the lower roller to 50°C, adjust the roller gap to 150 μm, and control the roller speed at 0.5 m / min to obtain the electrode sheet.

[0076] The electrode sheet prepared above was used as the positive electrode, and a 14 mm diameter lithium metal sheet was used as the negative electrode. A Celgard 2325 polypropylene separator was used, and the cells were assembled into CR2032 coin cells in an argon-atmospheric glove box. Each cell was precisely injected with 80 μL of commercial electrolyte (1 M LiPF6 in EC / EMC / DMC, 2% VC), sealed, and allowed to stand for 3 hours to ensure full electrolyte wetting before electrochemical testing.

[0077] Comparative Example 4 The difference from Example 1 is that the mixed materials were not heated, i.e., step (3) was not performed, and the PFA was not heated to a molten state. The specific method is as follows: The active material (NCM811), conductive agent (Super P), and composite binder (PTFE and PFA in a 1:1 mass ratio, each accounting for 1%) used in this comparative example are exactly the same as in Example 1, with the same types and proportions (93:5:2). The mixing process (2000 rpm, 15 minutes) is also the same as in Example 1. The only difference is the rolling process: the mixed material is calendered through a pair of room temperature (approximately 25°C) rolling rollers without any active heating of the rollers. Under these conditions, the cooling process experienced by the material as it passes through the roller gap is passive and uncontrolled. The PFA component cannot undergo "controlled cooling" from the molten state, making it difficult to form the fine and perfect crystalline structure induced by the thermo-mechanical field upon which this invention relies. The battery assembly is also exactly the same as in Example 1.

[0078] Comparative Example 5 The difference from Example 1 is that the temperature of both the upper and lower rollers is 140°C during rolling, while the other steps are the same as in Example 1.

[0079] Experimental results show that if the rolling temperature is too high, the molten PFA cools slowly, resulting in coarse PFA crystals.

[0080] Comparative Example 6 The difference from Example 1 is that the temperature of both the upper and lower rollers is 10°C during rolling, while the other steps are the same as in Example 1.

[0081] Experimental results show that excessively low roller temperature will affect the rolling effect, affect the molecular vibration of PTFE, harden the electrode sheet, make it difficult to roll and thin it, and may even cause edge cracks.

[0082] Testing and Analysis: 1. SEM images and physical product images: Figure 5 This describes the preparation process and microscopic SEM images of Example 1. Figure 6 These are actual pictures of Embodiment 1 of the present invention. Figure 7 These are surface SEM images of Embodiment 1 and Comparative Example 1 of the present invention, derived from... Figure 7 It can be seen that when PFA is added, no obvious anisotropy is generated during the rolling process, and the binder fibers in the membrane do not have obvious directionality, making the whole membrane more uniform. This indicates that the internal stress generated during the rolling process is well released. In contrast, the membrane with only PTFE added has very obvious fiber directionality. In the direction perpendicular to fiber elongation, the tensile strength of the membrane is significantly weakened, and it cannot even meet the requirements for roll-to-roll fabrication.

[0083] 2. X-ray diffraction pattern: Figure 1 The X-ray diffraction spectra of the adhesives used in Example 1 and Comparative Examples 1-2 are shown. First, the peak positions of PFA and PTFE are basically similar, but the peak intensities are much weaker, indicating that the crystallinity of PFA is much lower than that of PTFE. Therefore, it cannot form fibrillated long fibers and cannot be used alone. Similarly, TPU and PvDF also cannot form fibrillated fibers.

[0084] 3. Mechanical properties: (1) Mechanical properties of the electrode sheets prepared in Examples 1-10 and Comparative Examples 1-6 were tested. The specific methods included cutting the prepared electrode sheets into standard dumbbell-shaped specimens and testing their tensile strength and elongation at break using a universal tensile testing machine to characterize the mechanical properties and toughness of the binder network.

[0085] The results are shown in Table 1 and... Figure 2 ,in, Figure 2The curve “PTFE:PFA-3” corresponds to Example 1. Figure 2 The curve “PTFE-2” corresponds to scale 1.

[0086] Table 1 The results showed that the elongation at break of the electrode sheet in Example 1 reached 10.2%, which was more than 80% higher than that in Comparative Example 1. Specifically, as shown below... Figure 2 As shown, the tensile strength of the electrode sheet in Example 1 reached 203 kPa, which is more than 40% higher than that in Comparative Example 1. This indicates that the composite binder system of the present invention significantly improves the flexibility and mechanical strength of the electrode compared with a single PTFE binder.

[0087] The elongation at break and tensile strength of Comparative Examples 2 and 3 were significantly lower than those of Example 1, indicating that using PTFE with PVDF and TPU as composite binders cannot effectively improve the flexibility and mechanical strength of the electrodes.

[0088] The electrode sheet prepared in Comparative Example 4 exhibited significant brittleness, with an elongation at break (approximately 7%) significantly lower than that of Example 1 (10.2%), and only slightly better than that of Comparative Example 1 with pure PTFE. This indicates that PFA, without undergoing effective thermo-mechanical coupling to form a crystalline network, cannot fulfill its "flexible ligament" function. Similarly, in Comparative Example 5, due to excessively high roller temperature, the molten PFA cooled slowly, resulting in coarse crystal formation and thus diminishing the effect on improving the electrode's flexibility and mechanical strength. In Comparative Example 6, due to excessively low roller temperature, the molten PFA cooled rapidly, resulting in the formation of uniformly sized spherulites, further diminishing the effect on improving the electrode's flexibility and mechanical strength.

[0089] (2) SEM of fracture surface after tensile test: Dumbbell-shaped specimens were used for the electrode sheets in Example 1 and Comparative Example 1, with a neck width of 2 mm and a length of 25 mm. A universal tensile testing machine was used with a 5 mm minimum tensile strength. -1 The device was stretched at a certain speed, and the stretching data was collected. Then, SEM was used to observe the fracture surface.

[0090] Figure 3 These are SEM images of the fracture surfaces after tensile tests in Example 1 and Comparative Example 1. The fracture surface images show that the fracture surface with added PFA does not have many cracks, while the sample containing only PTFE has more cracks at the fracture surface. The morphology also confirms that adding PFA improves the tensile strength of the dry electrode.

[0091] 4. Wettability: The electrolyte wettability of the electrode sheets in Examples 1-9 and Comparative Examples 1-6 was tested using a contact angle meter. 2 μL of commercial electrolyte was dropped onto the surface of the electrode sheet, and the static contact angle was measured to evaluate the electrolyte wettability of the electrode.

[0092] The results are shown in Table 1 and... Figure 4 .

[0093] In Example 1, the electrolyte contact angle of the electrode plate is 6.8°, while in Comparative Example 1, the electrolyte contact angle of the electrode plate is 14°. (Specific details are as follows...) Figure 4 As shown, the composite binder of the present invention significantly improves the electrolyte wetting performance of the electrode compared with a single PTFE binder.

[0094] In Comparative Example 4, the electrolyte contact angle of the electrode sheet was approximately 7°, which is between that of Example 1 (6.8°) and Comparative Example 1 (14°). This indicates that the addition of PFA slightly improved wettability, but uncrystallized PFA could not maximize this advantage by forming a regular microstructure.

[0095] 5. Electrochemical performance: (1) Rate performance: The rate performance of the NCM811||Li half cell assembled above was tested.

[0096] The half-cells assembled in Example 1 and Comparative Example 1 were subjected to charge-discharge tests at current densities of 0.1C, 0.2C, 0.5C, and 1C. The results are as follows: Figure 8 As shown. By Figure 8 As can be seen, in Example 1, even at a high rate of 1C, the reversible capacity can still release more than 140 mAh g. -1 Comparative Example 1, however, exhibits a reversible capacity of <120 mAh g at a high rate of 1C. -1 This indicates that the electrode of the present invention has excellent high-rate performance.

[0097] The half-cell assembled in Comparative Example 4 has a discharge specific capacity of approximately 100 mAh g at a 1C rate. -1 Although superior to Comparative Example 1 (<120 mAh g), -1 However, it is significantly inferior to Example 1 (142.3 mAhg). -1 This indicates that whether PFA is crystallized or not affects the rate capability of the battery.

[0098] (2) Polarization characteristics: The polarization characteristics of the NCM811||Li half-cell assembled above were tested.

[0099] The charge-discharge curves of the half-cells assembled in Example 1 and Comparative Example 1 at a 1 C rate are shown below. Figure 9 As shown, the voltage difference between the charge and discharge platforms in Example 1 is significantly smaller than that in Comparative Example 1, indicating that it has faster reaction kinetics and lower polarization.

[0100] The half-cell assembled in Comparative Example 4 had a charge-discharge plateau polarization voltage of 0.158 V at a rate of 0.5C, which is greater than 0.125 V in Example 1, indicating that whether or not PFA is crystallized will affect the polarization characteristics of the battery.

[0101] (3) Cyclic performance: The rate performance of the NCM811||Li half-cell assembled above was tested.

[0102] Using the prepared electrode as the positive electrode and the lithium metal sheet as the negative electrode, CR2032 coin cells were assembled in an argon-protected glove box. Charge-discharge cycle tests were conducted on a Newway battery testing system with a test voltage range of 3.0-4.3V to obtain battery capacity, coulombic efficiency, and cycle life data. The half-cells assembled in Example 1 and Comparative Example 1 were charged and discharged at current densities of 0.33C, 0.5C, and 1C, respectively.

[0103] like Figure 11 As shown, the battery in Comparative Example 1 retained approximately 82% of its capacity after 200 cycles at 0.5C, which is lower than the 88.2% in Example 1.

[0104] (4) High load test: The NCM811||Li half-cell assembled above was subjected to a high areal load cycle test at an areal load of 100 mg cm⁻¹. -2 Cyclic tests were conducted at a 0.2C rate.

[0105] The results are as follows Figure 10 As shown. By Figure 10 As can be seen, the battery using the composite binder in Example 1 can cycle stably for more than 50 cycles under this ultra-high load, while the battery in Comparative Example 1 short-circuited after 30 cycles, indicating that the present invention effectively improves the structural stability and cycle life of the high-load electrode.

[0106] The battery in Comparative Example 4 was at 100 mg cm⁻¹ -2 While the failure cycle count (approximately 35-40 weeks) under surface load was better than that of Comparative Example 1 (approximately 35 weeks), it was far from reaching the level of Example 1 (>50 weeks).

[0107] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A composite binder for dry-process electrodes, characterized in that, The composite adhesive includes polytetrafluoroethylene and an auxiliary adhesive; The auxiliary binder includes a fluoropolymer whose crystallinity changes with temperature. The fluoropolymer is a polymer that can form a molten state under heating conditions and crystallize to form a fine spherulitic structure after cooling.

2. The composite adhesive according to claim 1, characterized in that, The auxiliary binder is at least one of a poly(perfluoroalkoxy vinyl ether) copolymer, and the general structural formula of the poly(perfluoroalkoxy vinyl ether) copolymer is: Wherein, R is at least one of -CF3, -CF2CF3, -CF2CF2CF3, and -CF2CF2CF2CF3, n = 500 to 10000, m = 500 to 10000, and the content of the perfluoroalkyl vinyl ether structural unit in the polyperfluoroalkoxy vinyl ether copolymer is 0.5 mol% to 12 mol.

3. The composite adhesive according to claim 1, characterized in that, The auxiliary binder is at least one of thermoplastic fluoroplastics, including perfluoroethylene propylene, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, ethylene-chlorotrifluoroethylene copolymer, and tetrafluoroethylene-perfluoroalkyl vinyl ether-hexafluoropropylene terpolymer.

4. The composite adhesive according to claim 1, characterized in that, The auxiliary binder is at least one of the polyperfluoroalkoxy vinyl ether modified derivatives, including carboxyl-functionalized perfluoroalkoxy copolymers, anhydride-functionalized perfluoroalkoxy copolymers, sulfonic acid-functionalized perfluoroalkoxy copolymers, hydroxyl-functionalized perfluoroalkoxy copolymers, tetrafluoroethylene-perfluoromethyl vinyl ether copolymer derivatives containing crosslinkable side groups, tetrafluoroethylene-perfluoro(alkoxy vinyl ether)-perfluoro(ethyleneoxy)propyl vinyl ether copolymers, perfluoropolyethers, copolymers of tetrafluoroethylene and silicone-containing perfluorovinyl ethers, tetrafluoroethylene-perfluoromethyl vinyl ether copolymer-based block copolymers, and tetrafluoroethylene-perfluoromethyl vinyl ether copolymer-based star or hyperbranched polymers.

5. The composite adhesive according to claim 1, characterized in that, The mass ratio of polytetrafluoroethylene to auxiliary binder is 1~2:1~2.

6. A dry electrode, characterized in that, The dry electrode comprises a positive electrode active material, a conductive agent, and the composite binder as described in any one of claims 1 to 5; The composite binder forms a three-dimensional fiber network structure that encapsulates the positive electrode active material and the conductive agent. The polytetrafluoroethylene in the composite binder serves as the rigid skeleton of the three-dimensional fiber network structure, while the auxiliary binder in the composite binder serves as the flexible node of the three-dimensional fiber network structure.

7. The dry electrode according to claim 6, characterized in that, The mass ratio of the positive electrode active material, conductive agent and composite binder is 92~94:4~6:1.5~2.

5.

8. The method for preparing the dry electrode according to any one of claims 6 to 7, characterized in that, Includes the following steps: The positive electrode active material, conductive agent and composite binder are dry-mixed to obtain a mixture. The mixture is subjected to mechanical shearing to fibrillate the composite adhesive into a three-dimensional fiber network structure. The mixture after mechanical shearing is heated to a temperature higher than the melting temperature of the auxiliary binder in the composite binder, so that the auxiliary binder in the composite binder is in a molten state. The heated mixture is hot-rolled to form a dry electrode; wherein the temperature of the rolling roller in the hot-rolling process is lower than the crystallization temperature of the auxiliary binder.

9. The preparation method according to claim 8, characterized in that, The heating temperature is 300℃~330℃, and the heating time is 5~15 minutes; The temperature of the rolling roller is 25℃~80℃, the gap between the rollers is 140μm~160μm, and the speed of the rolling roller is 0.4m / min~0.6m / min.

10. A lithium-ion battery, comprising a positive electrode, characterized in that, The positive electrode is the dry electrode according to any one of claims 6 to 7 or the dry electrode obtained by the preparation method according to any one of claims 8 to 9.

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