Dry electrode film, method of making same, and electrode sheet and battery

Abstract

The present application relates to the technical field of electrode preparation, and particularly relates to a dry electrode film, a preparation method thereof, an electrode sheet and a battery. The dry electrode film comprises: polymer@Si / C powder 70-90%, graphite 0-20%, conductive agent 3-12%, and polytetrafluoroethylene 4-8%, wherein the polymer@Si / C powder is a composite formed by polymer-coated silicon-carbon material. The silicon-carbon active core provides high specific capacity, the polymer intermediate functional layer realizes molecular-level interface anchoring, buffers local stress, and promotes the formation of a solid-state electrolyte interface film, the PTFE outer layer provides macro-mechanical support, maintains the integrity of the electrode, and is well combined with the current collector. By constructing a polymer coating layer on the surface of the silicon-carbon active particles, the present application forms strong hydrogen bonds / coordination effects, effectively inhibits particle pulverization during charging and discharging, promotes the continuous growth of the solid-state electrolyte interface film, improves the electrochemical performance, and realizes the unification of high capacity and long cycle.

Description

Technical Field

[0001] This invention relates to the field of electrode preparation technology, and more particularly to dry electrode films, their preparation methods, electrode sheets, and batteries. Background Technology

[0002] With the continued growth in demand for high-energy-density lithium-ion batteries from electric vehicles and large-scale energy storage, traditional graphite anodes are no longer sufficient to meet future performance requirements. Regarding the active materials of anode electrode materials, silicon-based materials are considered the most promising next-generation anode material system due to their ultra-high theoretical specific capacity (4200 mAh / g for elemental silicon). Currently, the industry commonly uses silicon-carbon composite materials (such as nano-silicon / porous carbon, SiOx / C, etc.) and often blends them with graphite to balance capacity, cycle stability, and cost. For the bonding system of electrode materials, functional polymers such as polyacrylic acid (PAA), carboxymethyl cellulose (CMC), or polyethylene oxide (PEO) are used. PAA, rich in carboxyl groups (–COOH), can form strong hydrogen bonds and even coordination interactions with the silicon surface, effectively buffering volume expansion and inhibiting particle pulverization during charge and discharge, and promoting the formation of a dense and stable solid electrolyte interphase (SEI) film, significantly improving initial coulombic efficiency and cycle life.

[0003] In terms of electrode fabrication processes, wet electrode technology is typically used, which involves dispersing active materials, conductive agents, and binders in water or NMP, coating them with copper foil, and then drying them at high temperatures. While this process is mature, it suffers from problems such as high solvent recovery costs, high energy consumption, and VOC emissions, and it is difficult to fabricate high-load, thick electrodes. In recent years, dry electrode technology has become an important direction for green battery manufacturing due to its advantages such as being solvent-free, having low energy consumption, compact equipment, and being suitable for thick electrodes. This technology uses high-speed shearing to cause polytetrafluoroethylene (PTFE) to undergo fibrillation, forming a three-dimensional fiber network that physically "weaves" the active materials and conductive agents into a self-supporting flexible membrane, which is then composited with the current collector.

[0004] It is worth noting that although dry electrode technology has the structural potential to construct multiphase composite systems, existing dry silicon-carbon anodes mostly employ a simple structure of a single PTFE network mixed with active powder, lacking a design concept for the orderly arrangement and hierarchical integration of different functional components at the microscale. Therefore, a truly "multilayer composite dry electrode" has not yet been achieved. Currently, although dry electrode technology has made initial progress, there are still significant technological gaps in constructing multilayer composite structures with clearly defined functional zones, specifically manifested in the following deficiencies: (1) Lack of microscale multilayer functional structure design. Existing dry electrodes usually simply mix silicon carbon, conductive agent and PTFE. All components are randomly distributed. This homogeneous mixing mode cannot achieve the partition optimization of functions such as interface stability, stress buffering and electronic / ion conduction, which limits the electrochemical performance of high silicon system. (2) High-performance interface binders (such as PAA) are difficult to integrate into dry multilayer systems. Although PAA can significantly improve the stability of silicon anode interface, its water solubility and non-fibrillation characteristics make it impossible for it to directly participate in dry film formation. If it is forcibly added to the dry mixing system, it will not only destroy the PTFE fiber network, but also cause the material to be loose and unable to form a film.

[0005] Currently, there is no effective method to precisely construct PAA on the surface of silicon-carbon particles in the form of a "functional layer" while being compatible with subsequent dry processes. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a dry electrode film and its preparation method, as well as an electrode sheet and a battery, so as to at least solve the problems that existing dry electrodes cannot integrate high-performance interface functional layers, and that high silicon content anodes have poor film formation properties and are prone to cracking under dry processes.

[0007] The following is a summary of this disclosure to provide a basic understanding of some aspects. This summary is not intended to identify key or important elements, nor is it intended to limit the implementation or any aspects of the claims. Furthermore, this summary provides a simplified overview of some aspects that can be described in more detail in other parts of this disclosure.

[0008] The present invention solves the above-mentioned technical problems through the following technical means: According to a first aspect of the present invention, an embodiment of the present invention provides a dry electrode membrane, the dry electrode membrane comprising the following raw materials in weight percentages: The polymer@Si / C powder comprises 70%–90% polymer, 0–20% graphite, 3%–12% conductive agent, and 4%–8% polytetrafluoroethylene. The polymer@Si / C powder is a composite material formed by polymer coating silicon-carbon material.

[0009] In some embodiments, the amount of polymer in the polymer@Si / C powder is 1% to 8% of the mass of the silicon-carbon material; and / or, the water content of the polymer@Si / C powder is ≤0.3wt%.

[0010] In some embodiments, the polymer is selected from at least one of polyacrylic acid, carboxymethyl cellulose, polyethylene oxide, polyvinylidene fluoride, polyimide, and polydopamine.

[0011] In some embodiments, the conductive agent is selected from at least one of conductive carbon black, carbon nanotubes, VGCF, graphene, and acetylene black.

[0012] According to a second aspect of the present invention, embodiments of the present invention provide a method for preparing a dry electrode film, the method comprising the following steps: To prepare polymer@Si / C powder, silicon carbon material is uniformly dispersed in deionized water to obtain silicon carbon slurry. Polymer is added to silicon carbon slurry and stirred at 25-60℃ for 2-6 hours. The resulting solid product is vacuum dried to obtain polymer@Si / C powder with a water content of less than 0.3wt%. Calendering film formation: According to the mass percentages of polymer@Si / C powder 70%–90%, graphite 0–20%, conductive agent 3%–12%, and polytetrafluoroethylene 4%–8%, the polymer@Si / C powder, graphite, conductive agent, and polytetrafluoroethylene are weighed and mixed. The mixture is ball-milled at 450–600 rpm for 10–30 min to obtain a mixed powder. The mixed powder is fed into a roller press and calendered at room temperature to 180℃ and a linear pressure of 0.5–3 MPa to form an electrode film.

[0013] In some embodiments, the solid content of the silicon carbide slurry is 5 to 20 wt%, and the mass of the polymer is 1% to 8% of the mass of the silicon carbide material.

[0014] In some embodiments, the polymer is selected from at least one of polyacrylic acid, carboxymethyl cellulose, polyethylene oxide, polyvinylidene fluoride, polyimide, and polydopamine; and / or, the conductive agent is selected from at least one of conductive carbon black, carbon nanotubes, VGCF, graphene, and acetylene black.

[0015] According to a third aspect of the present invention, an embodiment of the present invention provides an electrode sheet comprising a current collector and a dry electrode film as described in the first or second aspect, wherein the dry electrode film is attached to the surface of the current collector by hot pressing, and the current collector is a carbon-coated copper foil.

[0016] According to a fourth aspect of the present invention, an embodiment of the present invention provides a method for preparing an electrode sheet, wherein a dry electrode film and a current collector are stacked together and hot-pressed at a temperature of 80-150°C and a pressure of 1-3 MPa to obtain an electrode sheet.

[0017] According to a fourth aspect of the present invention, an embodiment of the present invention provides a battery comprising the electrode sheet as described in claim 8 or 9.

[0018] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages: (1) Existing dry electrode membranes are mostly random mixtures of active materials, conductive agents and PTFE, lacking a clear functional hierarchy; the dry electrode membrane of the present invention constructs a multi-layer composite structure with a silicon-carbon active core, an intermediate functional layer of polymer (e.g. PAA) coated on the silicon-carbon active core, and an outer layer of PTFE network. The silicon-carbon active core is used to provide high specific capacity, the intermediate functional layer of polymer (e.g. PAA) realizes molecular-level interface anchoring, buffers local stress and promotes the formation of a stable solid electrolyte interface membrane, and the stretchable skeleton of the outer layer of PTFE network provides macroscopic mechanical support, which can maintain the integrity of the electrode and combine well with the current collector.

[0019] (2) The dry electrode film of the present invention utilizes a polymer (e.g., polyacrylic acid, PAA) coating layer constructed on the surface of silicon-carbon active particles. This coating layer is rich in carboxyl functional groups, which can tightly bind with the hydroxyl groups on the surface of silicon particles through strong hydrogen bonds and ion-dipole interactions. This effectively buffers the huge volume expansion stress of silicon particles during lithium insertion and extraction, inhibits particle breakage and electrode structure pulverization, and promotes the formation of a dense and stable solid electrolyte interface (SEI). As a result, the electrochemical performance of the electrode is significantly improved. The reversible specific capacity of the fabricated negative electrode is above 620 mAh / g, the initial coulombic efficiency is 86.8%, and the capacity retention rate is 88.5% after 300 cycles, successfully achieving a balance between high capacity and long-term cycling stability.

[0020] (3) In the dry electrode film of the present invention, the polymer (e.g., polyacrylic acid, PAA) coating layer effectively enhances the cohesive force between particles, while the three-dimensional network formed by the fibrillation of PTFE during high-speed shearing provides a flexible mechanical skeleton. The synergistic effect of the two gives the resulting self-supporting electrode film excellent ductility and crack resistance, allowing for smooth continuous dry processing operations such as calendering and winding. Tests show that the peel strength of this electrode film after hot-pressing composite with copper foil current collector reaches 0.80-1.2 N / mm, the transverse tensile strength is 1.2-1.8 MPa, the longitudinal tensile strength is 1.4-1.9 MPa, and the elongation at break is 15-30%, significantly better than traditional dry silicon-carbon electrodes (peel strength is typically <0.5 N / mm, and it is prone to brittleness). Therefore, the electrode film of the present invention has excellent mechanical properties and is fully compatible with high-speed continuous dry production lines.

[0021] (4) The dry electrode membrane of the present invention can adjust the ratio of silicon carbon to graphite (silicon content 10-30 wt%) according to the energy density requirements, balancing performance and cost; the amount of polymer (e.g. PAA) is small (accounting for only 1-8% of the silicon carbon mass), and no expensive crosslinking agent or complex post-processing is required, the formulation is flexible and the cost is controllable.

[0022] (5) The dry electrode film of the present invention supports the design of thick electrode and high active material loading, which can significantly improve the energy density of battery. Thanks to the characteristics of solvent-free dry process, there is no drying stress inside the electrode and the structure is uniform, so that a self-supporting electrode film with a thickness of 50-200μm can be stably prepared, and its corresponding areal capacity can reach 3.5-6.0 mAh / cm².

[0023] (6) The method for preparing the dry electrode film of the present invention involves uniformly coating the silicon-carbon active material with a dilute polymer (e.g., PAA) solution in advance and thoroughly removing the moisture by vacuum drying. The polymer (e.g., PAA) is "pre-coated" on the particle surface in the form of a nanoscale functional layer, so that it can play an interfacial stabilizing role without relying on solvent in the subsequent dry mixing process, thus solving the problem that existing dry electrodes cannot integrate high-performance interfacial functional layers.

[0024] (7) The dry electrode film preparation method of the present invention is free of organic solvents throughout the entire process, is clean and environmentally friendly, and has low energy consumption. It eliminates the use of NMP solvent, and compared with the wet process, the overall energy consumption is reduced by about 30-50%. (8) The electrode sheet preparation method of the present invention involves stacking and hot-pressing the current collector and the dry electrode film. During the hot-pressing process, the PTFE fiber portion is embedded in the surface of the copper foil to form a firm bond, which avoids the problem of the active material on the current collector being loose and unable to form a film, and meets the requirements of continuous and large-scale production of dry electrodes. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the electrode sheet structure; Figure 2 This is a schematic diagram of the electrode preparation process. Detailed Implementation

[0026] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0027] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0028] The dry electrode membrane of the present invention comprises a multilayer composite structure with a silicon-carbon active core, an intermediate functional layer of polymer (e.g., PAA) coated on the silicon-carbon active core, and an outer layer of PTFE network. The silicon-carbon active core provides high specific capacity, the intermediate functional layer of polymer (e.g., PAA) enables molecular-level interface anchoring, buffers local stress, and promotes the formation of a stable solid electrolyte interface membrane, and the stretchable skeleton of the outer layer of PTFE network provides macroscopic mechanical support, which can maintain electrode integrity and bond well with the current collector.

[0029] Specifically, the dry electrode film of this invention comprises the following raw materials by mass percentage: 70%–90% polymer@Si / C powder, 0–20% graphite, 3%–12% conductive agent, and 4%–8% polytetrafluoroethylene. The polymer@Si / C powder is a composite formed by polymer coating silicon-carbon material, and the amount of polymer is 1%–8% of the mass of silicon-carbon material. To meet the requirements of subsequent dry processes, the water content of the polymer@Si / C powder needs to be controlled below 0.3 wt%. The silicon-carbon material is a conventional silicon-carbon anode material used in lithium-ion batteries, and no improvement has been made in this application. It is not specifically limited and can be obtained through commercial purchase. The polymer is selected from at least one of polyacrylic acid, carboxymethyl cellulose, polyethylene oxide, polyvinylidene fluoride, polyimide, and polydopamine. The conductive agent is selected from at least one of conductive carbon black, carbon nanotubes, VGCF, graphene, and acetylene black. The polymer is selected from at least one of polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polyimide (PI), and polydopamine (PDA), and the aforementioned polymers have the advantages shown in Table 1 for coating silicon carbide materials.

[0030] Table 1 Functional characteristics and advantages of polymers

[0031] The electrode sheet of the present invention includes a current collector and a dry electrode film. The dry electrode film is attached to the surface of the current collector by hot pressing. The current collector is a carbon-coated copper foil. A schematic diagram of the electrode sheet of the present invention is shown below. Figure 1 As shown. The combination of the dry electrode film preparation method and the electrode sheet preparation method of the present invention is as follows. Figure 2 As shown.

[0032] In the specific implementation: Example 1

[0033] The dry electrode film of this embodiment comprises the following raw materials by mass percentage: The composition of PAA@Si / C powder is 80%, graphite 5%, conductive agent 7%, and polytetrafluoroethylene 8%. The amount of polyacrylic acid in the PAA@Si / C powder is 5% of the mass of the silicon carbide material.

[0034] The dry electrode film preparation method in this embodiment is as follows: (1) Preparation of PAA@Si / C powder Silicon carbon material was uniformly dispersed in deionized water to obtain a silicon carbon slurry with a solid content of 10 wt%. Polyacrylic acid aqueous solution was slowly added to the silicon carbon slurry and stirred at 40°C for 4 hours to allow polyacrylic acid to be uniformly adsorbed on the surface of silicon carbon particles. The resulting solid product was vacuum dried to completely remove moisture until the water content was less than 0.3 wt%, thus obtaining PAA@Si / C powder, which was used as the active particles in step (2).

[0035] (2) Calendering film formation PAA@Si / C powder, graphite, conductive agent, and polytetrafluoroethylene were weighed and added to a ball mill for mixing. The mixture was ball milled at 480 rpm for 20 min. During the ball milling shearing process, PTFE underwent fibrillation, forming a continuous three-dimensional fiber network that encapsulated all active particles and conductive agent, resulting in a mixed powder. The mixed powder was then fed into a roller press and calendered at 100°C and a linear pressure of 1 MPa to form an electrode film. The thickness of the electrode film was controlled to be 80 μm. The surface of the electrode film was smooth and free of cracks. Example 2

[0036] The dry electrode film of this embodiment comprises the following raw materials by mass percentage: The composition of PAA@Si / C powder is 70%, graphite 20%, conductive agent 6%, and polytetrafluoroethylene 4%. The amount of polyacrylic acid in the PAA@Si / C powder is 1% of the mass of the silicon carbide material.

[0037] The dry electrode film preparation method in this embodiment is as follows: (1) Preparation of PAA@Si / C powder Silicon carbon material was uniformly dispersed in deionized water to obtain a silicon carbon slurry with a solid content of 5 wt%. Polyacrylic acid aqueous solution was slowly added to the silicon carbon slurry and stirred at 25°C for 6 h to allow polyacrylic acid to be uniformly adsorbed on the surface of silicon carbon particles. The resulting solid product was vacuum dried to completely remove moisture until the water content was less than 0.3 wt%, thus obtaining PAA@Si / C powder, which was used as the active particles in step (2).

[0038] (2) Calendering film formation PAA@Si / C powder, graphite, conductive agent, and polytetrafluoroethylene were weighed and added to a ball mill for mixing. The mixture was ball milled at 450 rpm for 30 min. During the ball milling shearing process, PTFE underwent fibrillation, forming a continuous three-dimensional fiber network that encapsulated all active particles and conductive agent, resulting in a mixed powder. The mixed powder was then fed into a roller press and calendered at room temperature and a linear pressure of 3 MPa to form an electrode film. The thickness of the electrode film was controlled to be 100 μm. The electrode film had a smooth surface and was free of cracks. Example 3

[0039] The dry electrode film of this embodiment comprises the following raw materials by mass percentage: The composition consists of 90% PAA@Si / C powder, 3% conductive agent, and 7% polytetrafluoroethylene. The amount of polyacrylic acid in the PAA@Si / C powder is 8% of the mass of the silicon carbide material.

[0040] The dry electrode film preparation method in this embodiment is as follows: (1) Preparation of PAA@Si / C powder Silicon carbon material was uniformly dispersed in deionized water to obtain a silicon carbon slurry with a solid content of 20 wt%. Polyacrylic acid aqueous solution was slowly added to the silicon carbon slurry and stirred at 60°C for 2 hours to allow polyacrylic acid to be uniformly adsorbed onto the surface of silicon carbon particles. The resulting solid product was vacuum dried to completely remove moisture until the water content was less than 0.3 wt%, thus obtaining PAA@Si / C powder, which was used as the active particles in step (2).

[0041] (2) Calendering film formation PAA@Si / C powder, graphite, conductive agent, and polytetrafluoroethylene were weighed and added to a ball mill for mixing. The mixture was ball milled at 600 rpm for 10 min. During the ball milling shearing process, PTFE underwent fibrillation, forming a continuous three-dimensional fiber network that encapsulated all active particles and conductive agent, resulting in a mixed powder. The mixed powder was then fed into a roller press and calendered at 180°C and a linear pressure of 0.5 MPa to form an electrode film. The thickness of the electrode film was controlled to be 50 μm. The electrode film had a smooth surface and was free of cracks. Example 4

[0042] The dry electrode film of this embodiment comprises the following raw materials by mass percentage: The composition of CMC@Si / C powder is 80%, graphite 3%, conductive agent 12%, and polytetrafluoroethylene 5%. The amount of carboxymethyl cellulose in the CMC@Si / C powder is 4% of the mass of the silicon-carbon material.

[0043] The dry electrode film preparation method in this embodiment is as follows: (1) Preparation of CMC@Si / C powder Silicon carbon material was uniformly dispersed in deionized water to obtain a silicon carbon slurry with a solid content of 10 wt%. A carboxymethyl cellulose aqueous solution was slowly added to the silicon carbon slurry and stirred at 40°C for 4 hours to allow the carboxymethyl cellulose to be uniformly adsorbed onto the surface of the silicon carbon particles. The resulting solid product was vacuum dried to completely remove moisture until the water content was less than 0.3 wt%, thus obtaining CMC@Si / C powder, which was used as the active particles in step (2).

[0044] (2) Calendering film formation Weigh out CMC@Si / C powder, graphite, conductive agent, and polytetrafluoroethylene and add them to a ball mill for mixing. Ball mill at 500 rpm for 20 min. During the ball milling shearing process, PTFE undergoes fibrillation to form a continuous three-dimensional fiber network that encapsulates all active particles and conductive agent, resulting in a mixed powder. The mixed powder is then fed into a roller press and calendered at 60℃ and a linear pressure of 1.5 MPa to form an electrode film. The thickness of the electrode film is controlled to be 80 μm. The electrode film has a smooth surface and is free of cracks. Example 5

[0045] The dry electrode film of this embodiment comprises the following raw materials by mass percentage: The composition consists of 80% PEO@Si / C powder, 2% graphite, 10% conductive agent, and 8% polytetrafluoroethylene. The amount of polyoxyethylene in the PEO@Si / C powder is 5% of the mass of the silicon-carbon material.

[0046] The dry electrode film preparation method in this embodiment is as follows: (1) Preparation of PEO@Si / C powder Silicon carbon material was uniformly dispersed in deionized water to obtain a silicon carbon slurry with a solid content of 15 wt%. Polyethylene oxide aqueous solution was slowly added to the silicon carbon slurry and stirred at 40°C for 4 hours to allow the polyethylene oxide to be uniformly adsorbed on the surface of the silicon carbon particles. The resulting solid product was vacuum dried to completely remove moisture until the water content was less than 0.3 wt%, thus obtaining PEO@Si / C powder, which was used as the active particles in step (2).

[0047] (2) Calendering film formation PEO@Si / C powder, graphite, conductive agent, and polytetrafluoroethylene were weighed and added to a ball mill for mixing. The mixture was ball milled at 500 rpm for 15 min. During the ball milling shearing process, PTFE underwent fibrillation, forming a continuous three-dimensional fiber network that encapsulated all active particles and conductive agent, resulting in a mixed powder. The mixed powder was then fed into a roller press and calendered at 100°C and a linear pressure of 1 MPa to form an electrode film. The thickness of the electrode film was controlled to be 80 μm. The electrode film had a smooth surface and was free of cracks. Example 6

[0048] The electrode sheet in this embodiment uses the dry electrode film prepared in Example 1. The preparation method of the electrode sheet in this embodiment is as follows: The dry electrode film of Example 1 was laminated with a carbon-coated copper foil with a thickness of 10 μm, and then hot-pressed at a temperature of 100°C and a pressure of 2 MPa to embed the PTFE fiber portion into the surface of the copper foil, thereby achieving an electrode sheet in which the dry electrode film and the carbon-coated copper foil are firmly bonded. Example 7

[0049] The electrode sheet in this embodiment uses the dry electrode film prepared in Example 2. The preparation method of the electrode sheet in this embodiment is as follows: The dry electrode film of Example 2 was laminated with a carbon-coated copper foil with a thickness of 10 μm, and then hot-pressed at a temperature of 110°C and a pressure of 2 MPa to embed the PTFE fiber portion into the surface of the copper foil, thereby achieving an electrode sheet in which the dry electrode film and the carbon-coated copper foil are firmly bonded. Example 8

[0050] The electrode sheet in this embodiment uses the dry electrode film prepared in Example 3. The preparation method of the electrode sheet in this embodiment is as follows: The dry electrode film of Example 3 was laminated with a carbon-coated copper foil with a thickness of 12 μm, and then hot-pressed at a temperature of 80°C and a pressure of 3 MPa to embed the PTFE fiber portion into the surface of the copper foil, thereby achieving an electrode sheet in which the dry electrode film and the carbon-coated copper foil are firmly bonded. Example 9

[0051] The electrode sheet in this embodiment uses the dry electrode film prepared in Example 4. The preparation method of the electrode sheet in this embodiment is as follows: The dry electrode film of Example 4 was laminated with a carbon-coated copper foil with a thickness of 11 μm, and then hot-pressed at a temperature of 150°C and a pressure of 1 MPa to embed the PTFE fiber portion into the surface of the copper foil, thereby achieving an electrode sheet in which the dry electrode film and the carbon-coated copper foil are firmly bonded. Example 10

[0052] The electrode sheet in this embodiment uses the dry electrode film prepared in Example 5. The preparation method of the electrode sheet in this embodiment is as follows: The dry electrode film of Example 5 was laminated with a carbon-coated copper foil with a thickness of 11 μm, and then hot-pressed at a temperature of 150°C and a pressure of 1 MPa to embed the PTFE fiber portion into the surface of the copper foil, thereby achieving an electrode sheet in which the dry electrode film and the carbon-coated copper foil are firmly bonded.

[0053] Performance testing: (1) The dry electrode films prepared in Examples 1-5 were subjected to tensile strength and peel strength tests. The tensile strength test was conducted in accordance with the corresponding content in GB13022-91. The results of the tensile strength and peel strength tests are shown in Table 2.

[0054] Table 2. Tensile strength and peel strength test results

[0055] (2) Batteries were prepared using the electrode sheets prepared in Examples 6 to 10, and charge-discharge tests were performed on the batteries prepared using each electrode sheet. Specifically, the mold half-cell was charged at 0.1C with a constant current to 1.5V, charged at a constant voltage to 0.05C, and discharged at 0.1C with a constant current to 0.05V. The test results are shown in Table 3.

[0056] (3) Batteries were prepared using the electrode sheets prepared in Examples 6 to 10, and the discharge capacity and cycle performance of the batteries prepared using each electrode sheet were tested. Specifically, at a temperature of 25±2℃, the first step was to charge the battery at 0.1C or a specified current until the termination voltage was 1.5V and the cutoff current was 0.01C, and then let it stand for 30 minutes; the second step was to discharge the battery at 0.1C until the final discharge voltage was 0.05V, and the discharge capacity was recorded, and then let it stand for 30 minutes; the first and second steps were repeated, and the cycle performance of the battery was tested after 300 cycles. The test results are shown in Table 3.

[0057] Table 3 Battery Test Results

[0058] The electrode sheet of this invention includes the dry-process electrode film. This dry-process electrode film, by constructing a polymer (e.g., PAA) coating layer on the surface of silicon-carbon active particles, forms strong hydrogen bonds / coordination interactions, effectively suppressing particle pulverization during charge and discharge, promoting the continuous growth of the solid electrolyte interface film, significantly improving electrochemical performance, and achieving a balance between high capacity and long cycle life. Therefore, the electrode sheet of this invention can be used as the negative electrode sheet in batteries.

[0059] The foregoing description includes examples from this specification. Of course, for the purposes of describing this specification, it is impossible to describe every conceivable combination of components or methods; however, those skilled in the art will understand that many other combinations and arrangements are possible. Therefore, this specification is intended to cover all such changes, modifications, and variations that fall within the spirit and scope of the appended claims. Furthermore, with regard to the use of the term "comprising" in the detailed description or claims, the term is intended to be inclusive in a manner similar to the term "including," as interpreted when "comprising" is used as a transitional word in the claims.

[0060] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A dry electrode film, characterized in that, The dry electrode film comprises the following raw materials by mass percentage: The polymer@Si / C powder comprises 70%–90% polymer, 0–20% graphite, 3%–12% conductive agent, and 4%–8% polytetrafluoroethylene. The polymer@Si / C powder is a composite material formed by polymer coating silicon-carbon material.

2. The dry electrode film according to claim 1, characterized in that, The amount of polymer in the polymer@Si / C powder is 1% to 8% of the mass of the silicon-carbon material; and / or, The water content of the polymer@Si / C powder is ≤0.3wt%.

3. The dry electrode film according to claim 1, characterized in that, The polymer is selected from at least one of polyacrylic acid, carboxymethyl cellulose, polyethylene oxide, polyvinylidene fluoride, polyimide, and polydopamine.

4. The dry electrode film according to claim 1, characterized in that, The conductive agent is selected from at least one of conductive carbon black, carbon nanotubes, VGCF, graphene, and acetylene black.

5. A method for preparing a dry electrode film, characterized in that, The preparation method includes the following steps: To prepare polymer@Si / C powder, silicon carbon material is uniformly dispersed in deionized water to obtain silicon carbon slurry. Polymer is added to silicon carbon slurry and stirred at 25-60℃ for 2-6 hours. The resulting solid product is vacuum dried to obtain polymer@Si / C powder with a water content of less than 0.3wt%. Calendering film formation: According to the mass percentages of polymer@Si / C powder 70%–90%, graphite 0–20%, conductive agent 3%–12%, and polytetrafluoroethylene 4%–8%, the polymer@Si / C powder, graphite, conductive agent, and polytetrafluoroethylene are weighed and mixed. The mixture is ball-milled at 450–600 rpm for 10–30 min to obtain a mixed powder. The mixed powder is fed into a roller press and calendered at room temperature to 180℃ and a linear pressure of 0.5–3 MPa to form an electrode film.

6. The method for preparing a dry electrode film according to claim 5, characterized in that, The solid content of the silicon carbide slurry is 5-20 wt%, and the mass of the polymer is 1%-8% of the mass of the silicon carbide material.

7. The method for preparing a dry electrode film according to claim 5, characterized in that, The polymer is selected from at least one of polyacrylic acid, carboxymethyl cellulose, polyethylene oxide, polyvinylidene fluoride, polyimide, and polydopamine; and / or, The conductive agent is selected from at least one of conductive carbon black, carbon nanotubes, VGCF, graphene, and acetylene black.

8. An electrode sheet, characterized in that, The electrode sheet includes a current collector and a dry electrode film as described in any one of claims 1-7, wherein the dry electrode film is attached to the surface of the current collector by hot pressing, and the current collector is a carbon-coated copper foil.

9. The method for preparing the electrode sheet according to claim 8, characterized in that, The dry electrode film and the current collector are stacked together and hot-pressed at a temperature of 80-150℃ and a pressure of 1-3MPa to obtain the electrode sheet.

10. A battery, characterized in that, Includes the electrode sheet as described in claim 8 or 9.

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