A dry electrode film with a skeleton film support and a preparation method thereof

Abstract

The application relates to a skeleton film supported dry-method electrode film and a preparation method thereof, which comprises a porous skeleton film, wherein the porous skeleton film is an ultrathin bidirectional stretched porous polymer film and has high porosity; and dry-method electrode raw materials formed on the surface and pores of the porous skeleton film. Specifically, the porous skeleton film adopts an ultrathin bidirectional stretching process to form a high porosity structure, the pores and the surface of which provide uniformly distributed carriers for the dry-method electrode raw materials, reduce the amount of binder and enhance the binding force between the active material and the conductive agent. The dry-method electrode raw materials are embedded in the surface and pores of the skeleton film, three-dimensional conductive paths are formed by using the high specific surface area and pore structure of the skeleton film, the preparation process is simplified, and the problems of increased surface resistance and low efficiency caused by the traditional spraying process are avoided.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to a dry electrode film with a skeleton film support and its preparation method. Background Technology

[0002] The manufacturing processes for lithium-ion battery electrode sheets mainly include wet and dry processes. The dry process is a solvent-free electrode film preparation method, offering significant advantages over traditional wet processes in terms of environmental friendliness, cost control, and process simplification. This process involves directly mixing and pressing powders of active materials, conductive agents, and binders to form a self-supporting electrode film.

[0003] Despite the advantages mentioned above, the industrial application of dry electrode processes still faces the core challenge of insufficient binder dispersion. Due to the lack of a solvent medium, the binder is difficult to distribute uniformly in the mixed powder, leading to poor film formation, poor film thickness uniformity, and increased binder usage, ultimately affecting the conductivity and mechanical strength of the electrode sheet. Related patents provide a method for preparing dry electrode films, using a polymer film as a substrate and directly spraying dry electrode raw materials onto the substrate surface to form a dry electrode. However, this method produces dry electrode films with high surface resistance and low preparation efficiency. Therefore, existing dry electrode processes generally fall into a dilemma: to ensure the mechanical strength of the film after formation to adapt to roll-to-roll production, a high proportion (e.g., 2-5%) of inert binder must be added; however, a high proportion of binder inevitably covers active particles and blocks electron transport channels, thus deteriorating the internal resistance and rate performance of the electrode. Summary of the Invention

[0004] This application aims to solve the inherent technical contradiction in existing dry electrode processes, where a high proportion of binder must be added to ensure mechanical strength, but a high proportion of binder will deteriorate electrochemical performance.

[0005] A dry electrode membrane with a framework membrane support, comprising:

[0006] A porous framework membrane, wherein the porous framework membrane is an ultrathin biaxially stretched porous polymer membrane with high porosity; and

[0007] Dry electrode raw materials formed on the surface and in the pores of porous framework membranes.

[0008] The above-mentioned scheme optimizes the mechanical support and conductivity of dry electrode films by introducing a composite structure of porous framework membranes and dry electrode raw materials. Specifically, the porous framework membrane is formed with a high porosity structure using an ultrathin biaxial stretching process. Its pores and surface provide a uniformly distributed carrier for the dry electrode raw materials, reducing the amount of binder and enhancing the binding force between the active material and the conductive agent. The ultrathin biaxial stretching process endows the framework membrane with high porosity and nanoscale pore size, ensuring that the electrode raw materials fully fill the pores to improve the continuity of the conductive network, and preventing the electrode membrane from breaking due to insufficient mechanical strength through the physical support of the framework membrane. The dry electrode raw materials are embedded in the surface and pores of the framework membrane, utilizing the high specific surface area and pore structure of the framework membrane to form a three-dimensional conductive pathway, while simplifying the preparation process and avoiding the problems of increased surface resistance and low efficiency caused by traditional spraying processes.

[0009] The dry electrode membrane with a skeleton membrane support provided in this application can achieve the following technical effects:

[0010] 1. The porous framework membrane is formed with an ultra-thin biaxial stretching process to form a high porosity structure. Its pores and surface provide a uniformly distributed carrier for the dry electrode raw materials, reducing the amount of binder and enhancing the binding force between the active material and the conductive agent.

[0011] 2. The ultrathin biaxial stretching process endows the skeleton membrane with high porosity and nanoscale pore size, which not only ensures that the electrode raw materials fully fill the pores to improve the continuity of the conductive network, but also prevents the electrode membrane from breaking due to insufficient mechanical strength through the physical support of the skeleton membrane.

[0012] 3. The dry electrode material is embedded in the surface and pores of the skeleton film, and the high specific surface area and pore structure of the skeleton film are used to form a three-dimensional conductive path. At the same time, the preparation process is simplified and the problems of increased surface resistance and low efficiency caused by traditional spraying process are avoided. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of a dry negative electrode membrane with a single-layer skeleton membrane support provided in an embodiment of this application;

[0014] Figure 2 This is a schematic diagram of a dry negative electrode membrane with a double-layer porous framework membrane support provided in an embodiment of this application;

[0015] Figure 3 This is a schematic diagram of a dry anode membrane preparation apparatus with a single-layer skeleton membrane support provided in an embodiment of this application;

[0016] Figure 4 This is a schematic diagram of a dry anode membrane preparation apparatus with a double-layer porous framework membrane support provided in an embodiment of this application;

[0017] Figure 5This is a flowchart illustrating the fabrication process of a dry electrode film with a skeleton membrane support according to an embodiment of this application.

[0018] Figure 6 This is a schematic diagram of the structure of a porous framework membrane under an electron microscope according to an embodiment of this application;

[0019] Figure 7 This is a schematic diagram of the structure of a dry electrode film with a skeleton film support provided in an embodiment of this application under an electron microscope (magnification of 1000x);

[0020] Figure 8 This is a schematic diagram of the structure of a dry electrode film with a skeleton film support provided in an embodiment of this application under an electron microscope (magnification of 50,000x).

[0021] Explanation of reference numerals in the attached drawings: 1. Porous skeleton membrane; 2. Dry electrode raw material; 10. First skeleton membrane; 12. Second skeleton membrane; 3. Unwinding roller; 4. Electrostatic feeding device; 5. Hot roller; 100. Dry electrode membrane. Detailed Implementation

[0022] The following is in conjunction with the appendix Figure 1-8 This application provides a further detailed description of the dry electrode film with a skeleton film support and its preparation method.

[0023] In existing technologies, the manufacturing processes for lithium-ion battery electrode sheets mainly include wet and dry processes. The dry process involves directly mixing and pressing powders of active materials, conductive agents, and binders into shape. While this method offers advantages in terms of environmental friendliness and cost, it suffers from insufficient binder dispersion. Due to the lack of a solvent medium, the binder is difficult to distribute uniformly, resulting in poor film formation, uneven film thickness, and reduced conductivity. Related patents employ a method of spraying electrode raw materials onto the surface of a polymer substrate, but this method suffers from increased surface resistivity and low preparation efficiency.

[0024] To resolve the above issues, please refer to Figure 1 To address the core issue of uneven binder dispersion in dry processes, this application proposes a dry electrode membrane 100 supported by a skeleton membrane, comprising a porous skeleton membrane 1 and a dry electrode raw material 2.

[0025] The porous framework membrane 1 is an ultrathin, biaxially stretched, high-porosity porous membrane, and the dry electrode material 2 is formed on its surface and in its pores. More specifically, it can be formed on one side or both sides of the porous framework membrane 1. This application does not impose any limitations.

[0026] Compared to uniaxially stretched membranes, biaxially stretched membranes exhibit isotropic structures. During subsequent calendering and winding, the skeleton membrane can uniformly bear stress regardless of its direction, effectively preventing tearing caused by localized stress concentration. Uniaxially stretched membranes, on the other hand, have very low strength perpendicular to the stretching direction and are highly prone to breakage. Compared to other porous membranes, biaxially stretched ePTFE membranes maintain excellent flexibility and elongation at break (>15%) even at extremely high porosity (>80%), which is crucial for achieving high energy density and high reliability manufacturing.

[0027] The thickness of the porous framework membrane 1 ranges from 1 to 10 micrometers, and the thickness of the dry electrode membrane 100 supported by the framework membrane ranges from 50 to 300 micrometers. Preferably, the thickness of the dry electrode membrane 100 supported by the framework membrane ranges from 80 to 150 micrometers. The porous framework membrane 1 refers to a thin film with a through-pore structure prepared by a biaxial stretching process, and can be made from ePTFE, PTFE, PE, PVDF, or PP materials prepared by the biaxial stretching process. The biaxially stretched porous membrane refers to a polymer membrane with a uniform pore distribution formed by a biaxial stretching process, achieved through simultaneous longitudinal and transverse stretching, resulting in a three-dimensional interconnected pore structure within it.

[0028] Specifically, the biaxial stretching process creates uniformly distributed nanopores in the framework membrane. Subsequent electrode materials fill these pores and cover the surface under mechanical pressure. The porous structure of the framework membrane guides the conductive agent to form a continuous network, and the active material achieves charge transfer through contact with the pore walls. The framework membrane itself acts as a support, maintaining the structural integrity of the electrode membrane, while a trace amount of binder only needs to play a bonding role in localized areas. This composite structure replaces traditional solvent dispersion with physical intercalation, ensuring the continuity of the conductive pathway while avoiding the material waste and efficiency loss caused by spraying processes.

[0029] The porous framework membrane 1 has a thickness of 1-10 micrometers, a porosity of 60%-90%, a pore size of 50-500 nm, and a weight per square meter of 1-10 g. Preferably, the weight per square meter is 1-5 g; more preferably, the weight per square meter is 1-2 g.

[0030] Porosity refers to the proportion of pore volume to the total volume in a porous membrane. It can be controlled by adjusting the stretching ratio and heat treatment temperature. A porosity higher than 60% provides sufficient space for the active material. Pore diameter of 50-500 nm refers to the diameter range of the pore channels, which can be achieved by adjusting the stretching process parameters and the content of the pore-forming agent. This size range ensures that the electrode raw material particles effectively fill the pores. Weight per square meter of 1-10 g refers to the mass index of the membrane material per unit area, aiming to reduce the membrane's weight while maintaining mechanical strength.

[0031] It should be noted that: when the thickness of the skeletal membrane is <1 micrometer, the membrane is prone to rupture; when the thickness of the skeletal membrane is >10 micrometers, the active material loading decreases by 10%. When the porosity is <60%, the ion diffusion rate decreases by 30%; when the porosity is >90%, the mechanical strength is insufficient.

[0032] The porous framework membrane provided in this application still exhibits an elongation at break greater than 15% even at a porosity of 90%. Porosity refers to the percentage of pore (void) volume in a material relative to its total volume. Elongation at break refers to the percentage of length a material can extend before breaking in a tensile test, calculated as: [(length at break - original length) / original length] × 100%. It measures the ductility or toughness of a material—the higher the elongation, the "softer" the material or the better it resists brittle fracture.

[0033] The porous framework membrane 1 accounts for 0.5-2% of the mass of the dry electrode membrane 100. That is, this solution forms an encapsulated structure through a double-layer porous framework membrane 1, confining the dry electrode raw material 2 within the interlayer and pores. During calendering, the framework membrane and the electrode layer formed by the dry electrode raw material 2 achieve three-dimensional interlocking, effectively preventing interlayer delamination. Simultaneously, the specific mass ratio solves the problem of excessive binder addition in traditional dry processes to increase strength.

[0034] Porous framework membranes are composed of inert polymeric materials (such as ePTFE and PE) that do not participate in electrochemical reactions. If the mass percentage of the framework membrane is too low (<0.5%), it means that the framework itself is too thin or has too high porosity, resulting in insufficient absolute physical support. Under the high tension environment of high-speed roll-to-roll production, or in subsequent processes such as cell winding and extrusion, the electrode membrane still faces the risk of breakage or permanent deformation. In such cases, the introduction of the framework membrane is not effective and cannot fundamentally solve the problem of "easily broken tape".

[0035] If its mass percentage is too high (>2%), although the mechanical strength will be stronger, it will bring a significant negative impact: within the limited volume and mass of the electrode film, the more inert material there is, the less active material can be filled; the energy density of the battery (whether it is the mass energy density Wh / kg or the volume energy density Wh / L) directly depends on the proportion of active material, and too much skeleton will "dilute" the energy density of the electrode.

[0036] Specifically, by embedding the dry electrode material 2 into the surface, interlayer gaps, or pores of the double-layer porous framework membrane 1, the pore network of the porous framework membrane 1 promotes the uniform filling of the dry electrode material 2 during calendering. The double-layer structure forms a symmetrical support system, and the synchronous elongation of the upper and lower porous framework membranes 1 during hot pressing inhibits electrode layer cracking. Mass ratio control ensures that the porous framework membrane 1 provides the necessary mechanical strength while avoiding excessive polymer material that hinders the conductive contact between the electrode active materials.

[0037] In this application, the dry electrode raw material 2 comprises an active material and a conductive agent, and may also include a binder. Each component, by mass percentage, includes 1.0%-4.5% conductive agent and the balance being active material; when the binder is present, its mass percentage is greater than 0% and not higher than 0.5%. That is, the binder accounts for 0-0.5% of the mass of the dry electrode raw material 2. The conductive agent accounts for 1.0%-4.5% of the mass of the dry electrode raw material 2, and the active material accounts for 95.0-99.0% of the mass of the dry electrode raw material 2.

[0038] In the mass ratio control, the design purpose of a binder ratio of 0-0.5% is to reduce the negative impact of inactive components on electrode performance. The conductive agent ratio of 1-4.5% is used to balance conductivity and the proportion of active material, while the high proportion of active material (95.0-99.0%) is used to maximize electrode energy density. Through precise control of the ratio of conductive agent to active material in the mass ratio, the electrode film can maintain high electronic conductivity and structural stability while reducing the amount of binder used.

[0039] Among them, conductive agent refers to the substance used to improve the electronic conductivity of electrode material. Specifically, the conductive agent can be one or more combinations of carbon black, acetylene black, carbon nanotubes, graphene, and Ketjen black.

[0040] Active materials refer to the main materials that participate in electrochemical reactions. Active materials can be positive electrode active materials or negative electrode active materials. Positive electrode active materials are one or more combinations of lithium iron phosphate, ternary materials, and lithium titanate, while negative electrode active materials can be one or more combinations of graphite or silicon.

[0041] In a more preferred embodiment, the negative electrode active material includes, but is not limited to:

[0042] Carbon-based materials, such as one or a combination of natural graphite, artificial graphite, mesophase carbon microspheres (MCMB), hard carbon, soft carbon, graphene, and carbon nanotubes;

[0043] Alloy materials, such as silicon-based materials (e.g., nano-silicon, silicon suboxide), tin-based materials (e.g., nano-tin, tin oxide), germanium-based materials, and their oxides or alloys, or combinations thereof.

[0044] When the negative electrode active material is a material with significant volume change, the flexible support and mechanical constraint of the porous framework membrane of the present invention can significantly suppress the pulverization of the active material and greatly improve the cycle stability of the electrode.

[0045] Oxide materials, such as lithium titanate (LTO) and titanium niobate (TNO);

[0046] In the case of lithium metal, the porous framework membrane can serve as a three-dimensional main framework for lithium metal deposition, thereby suppressing lithium dendrite growth.

[0047] The binder is a polymeric material used to maintain the structural integrity of the electrode. The binder is one or a combination of PTFE, PVDF, and PEO, and it forms a three-dimensional network structure through fibrosis to enhance mechanical strength. Uniform mixing refers to achieving uniform dispersion of each component through mechanical stirring or high-speed shearing, avoiding stress concentration caused by localized binder aggregation. Compared to existing technologies, traditional dry processes suffer from insufficient mechanical strength of the electrode film due to uneven binder dispersion. This solution, however, achieves directional distribution of the binder during hot pressing by limiting the type and proportion of binder. In existing technologies, conductive agents typically need to be added at levels above 5% to ensure conductivity. This solution, by selecting a combination of highly conductive materials, can form an effective conductive network with a low addition amount of 1-4.5%, or even within the range of 1-2%.

[0048] In the subsequent fiberization process, the binder forms a network structure that runs through the entire electrode material, creating a stable conductive path between the active material and the conductive agent. The low proportion of binder ensures the self-support of the electrode while reducing the negative impact of inactive materials on energy density.

[0049] Those skilled in the art should understand that when the binder content is zero, the dry electrode film of the present invention can still be formed and maintain excellent mechanical strength. The mechanism is as follows: 1) It mainly relies on the physical anchoring and mechanical interlocking effect of the three-dimensional network structure of the porous skeleton film 1. Under the huge pressure of hot roll calendering, the dry electrode raw material 2 is forced and densely pressed into the pores of the skeleton film. The overall strength of the film is mainly provided by the skeleton film itself; 2) The hot pressing process promotes the interfacial bonding between particles. Under the action of temperature and high pressure of 80-120°C, the active material and conductive agent particles will undergo a certain degree of interfacial diffusion or local micro-sintering at the close contact point, forming effective interparticle cohesion and preventing powder shedding.

[0050] In other words, this invention introduces an ultra-thin skeleton to construct a "load-bearing keel" that runs through the entire electrode system from the outside. This "keel" bears the vast majority of the mechanical stress with a very small volume and mass.

[0051] In addition, in the above-mentioned single-layer skeleton membrane (such as Figure 1 Based on the optimization of basic mechanical support and electrochemical performance (as shown), in order to further pursue the ultimate mechanical strength and higher active material loading capacity (i.e., higher compaction density) to meet the more stringent requirements of the comprehensive performance of the electrode film in application scenarios, this application also provides a preferred embodiment of a sandwich-type double-layer skeleton.

[0052] Please see Figure 2 This application further proposes that the porous framework membrane 1 may include an assembly of a first framework membrane 10 and a second framework membrane 12, with the dry electrode material 2 located between the first framework membrane 10 and the second framework membrane 12 and within the pores included in the first framework membrane 10 and the second framework membrane 12. The first framework membrane 10 and the second framework membrane 12 have identical structures. This forms a sandwich structure. When a symmetrical "sandwich" structure is adopted, the synchronous constraint effect between the upper and lower parts further prevents the lateral escape of the powder, thus reliably ensuring the yield and performance consistency of the final product.

[0053] Please see Figure 3-5 ,in, Figure 5 In addition to the preparation process for the dry electrode film 100 provided in this application, this application further proposes a method for preparing a dry electrode film 100 with a skeleton film support, including the following steps:

[0054] S1: Provides a porous framework membrane 1.

[0055] The high porosity structure of the porous framework membrane 1 allows the dry electrode material 2 to be embedded in its surface and internal pores, reducing material agglomeration through physical constraint.

[0056] S2: The conductive agent, active material and binder are mixed evenly and then fiberized to form dry electrode raw material 2.

[0057] The binder is fiberized to form a three-dimensional network, achieving uniform bonding between powder particles under solvent-free conditions.

[0058] Among them, fiberization refers to the formation of a fiber network by the binder through mechanical shearing, which can be achieved by high-speed stirring or roller pressing equipment. This process enhances the bonding force between powders and improves the dispersion uniformity.

[0059] The 'fiberized dry electrode material' refers to the binder (such as PTFE) in the dry electrode material being stretched into a three-dimensional fiber network at the micron or even nanometer scale under the mechanical shear force of high-speed mixing or air jet milling. This network physically entangles, fixes, and disperses the active material and conductive agent particles. This in-situ formed fiber network structure is key to achieving effective bonding with ultra-low binder content and provides a structural basis for subsequent embedding into the framework membrane.

[0060] In a preferred embodiment, the fiberization step can be carried out using an air jet mill. The grinding gas of the air jet mill is preferably dry air or nitrogen, and its inlet pressure can be controlled in the range of 0.5 MPa to 1.2 MPa, and the feed rate can be controlled in the range of 0.5 kg / h to 10 kg / h. If an air jet mill with a classifier is used, its rotation speed can be set between 3000 rpm and 12000 rpm to achieve sufficient fiberization of the PTFE binder.

[0061] S3: The dry electrode material 2 is embedded into the porous skeleton membrane 1; in this embodiment, the dry electrode material 2 is uniformly applied to the porous skeleton membrane 1 by electrostatic feeding or airflow powder spreading.

[0062] S4: A dry electrode film can be obtained by calendering the composite structure using hot roll calendering technology. The thickness of the dry electrode film is between 50 and 300 micrometers.

[0063] Please see Figure 6 The image, displayed at high magnification, shows the microstructure of the original porous framework membrane 1, which serves as the "load-bearing backbone" of this invention. It is clearly visible that the framework membrane is composed of numerous interwoven micron or submicron-sized polymer fibers connected by nodes, forming a three-dimensional network structure with extremely high porosity and a large specific surface area. These abundant, interconnected pores provide ample space for the subsequent embedding and fixation of the dry electrode material 2, forming the structural basis for achieving highly active material loading and constructing a three-dimensional conductive / ion transport network.

[0064] In stark contrast to this Figure 7 This displays a surface electron microscope (SEM) image (1000x magnification) of the final dry electrode film 100 prepared according to the present invention. Figure 6 The open porous structure of the pure framework membrane is quite different. Figure 7 The surface exhibits a highly dense, uniform, and smooth state, with almost no visible pores, cracks, or particle agglomerations. This strongly demonstrates that the preparation method of this invention can achieve complete penetration and efficient filling of the porous framework membrane 1 by the dry electrode raw material 2. Under the enormous pressure of hot roller calendering, the loose powder is forcibly compacted, forming a continuous conductive network with close contact between the active material particles. This is the key structural guarantee for achieving low interfacial resistance and excellent electrochemical performance.

[0065] To further explore its microscopic binding mechanism, please refer to [link / reference]. Figure 8At a higher magnification (50,000x), the fine internal structure of the electrode film was revealed. Under this view, it can be clearly observed that larger active material particles (irregularly shaped lumps in the image) are tightly entangled, wrapped, and physically anchored by the microfiber network of the porous framework membrane 1. The originally independent fiber network underwent plastic reconstruction during the hot-pressing process, acting like countless microscopic "rivets" and "cables," firmly "riveting" and "binding" the discrete electrode material particles to the three-dimensional framework.

[0066] Hot roll calendering technology refers to applying temperature and pressure to materials using heated rollers, which can be achieved using a twin-roll calender. This technology promotes the formation of a dense interface between the skeleton film and the electrode raw material. During hot roll calendering, the temperature softens the skeleton film material, and the pressure forces the electrode raw material to fully contact the pores of the skeleton film, forming a continuous conductive path. This process, through the synergistic effect of the physical support of the skeleton film and hot pressing, improves the structural stability of the electrode film while reducing the amount of binder used. In a preferred embodiment, the roller temperature of the hot roll calendering can be controlled within the range of 80°C to 120°C, the applied linear pressure can be set within the range of 50-800 kN / m, for example, 500 kN / m, and the calendering speed can be controlled within 1-15 m / min, so that the dry electrode raw material 2 is compacted and penetrates into the pores and surface of the porous skeleton film 1, forming a mechanically interlocked structure.

[0067] The core technical mechanism of this invention lies in achieving 'in-situ plastic reconstruction and mechanical riveting' between the skeleton membrane and electrode raw material particles through a hot calendering process. At temperatures of 80-120°C, the microfiber network of the porous skeleton membrane (especially ePTFE) enters a highly elastic state, possessing plastic deformation capabilities. Simultaneously, under a linear pressure of 50-800 kN / m, the dry-process electrode raw material 2 is forcibly pressed into the pores and surface of the porous skeleton membrane 1. At this point, the plastic fiber network of the porous skeleton membrane 1 undergoes reconstruction, forming a tight physical encapsulation and mechanical riveting around the particles, firmly locking the discrete powder within the three-dimensional network. This physically interlocking structure fundamentally replaces the reliance on large amounts of binders in traditional technologies.

[0068] Compared to existing technologies, traditional dry processes rely on binder dispersibility, requiring increased binder dosage to maintain film strength, leading to decreased conductivity. Existing spray-coating processes suffer from insufficient interfacial contact between the substrate and electrode materials, resulting in increased sheet resistance. This method uses a porous framework membrane 1 to constrain the distribution of electrode materials, combined with hot-pressing to strengthen interfacial bonding, achieving high mechanical strength and low sheet resistance in the electrode film with low binder content.

[0069] Through the above technical solution, this application solves the problem of poor film formation caused by insufficient binder dispersion in dry electrode processes. It utilizes the porous structure of the skeleton film to improve the uniformity of electrode material distribution and reduce interfacial contact resistance. The hot-pressing process reduces the dependence of traditional dry processes on high binder content while avoiding the efficiency bottleneck of spraying processes, thus achieving efficient preparation of highly conductive electrode films.

[0070] It should be noted that when the porous framework membrane 1 includes a first framework membrane 10 and a second framework membrane 12, the following is adopted: Figure 4 The dry electrode film 100 is prepared using the provided equipment.

[0071] The beneficial effects of this application are illustrated below through examples and comparative examples.

[0072] Example 1: Preparation of a dry electrode film with a single-framework membrane support

[0073] ① Preparation of dry-process negative electrode membrane supported by a single-layer framework membrane

[0074] The ingredients are as follows:

[0075] Negative electrode active material: artificial graphite; conductive agent: Super P (conductive carbon black); binder: PTFE.

[0076] S11: Provide an ePTFE ultrathin porous skeleton membrane with a porosity of 85%, a basis weight of 1.6g per square meter, and a thickness of 1.2 micrometers, and wind the ePTFE ultrathin porous skeleton membrane onto the unwinding roller 3.

[0077] S12: 98.5g of negative electrode active material, 1.25g of conductive agent, and 0.25g of PTFE are mixed at high speed and then fiberized to prepare dry electrode raw material 2. After fiberization, the binder (such as PTFE) is stretched to form a three-dimensional fiber network structure. This network physically wraps, fixes, and connects micron-sized active material particles and nano-sized conductive agent particles, forming a structurally stable composite aggregate. It should be particularly noted that in this invention, since the macroscopic mechanical strength will be borne by the subsequently introduced skeleton membrane, only a very low content (e.g., 0.25%) of PTFE is needed for fiberization in this step. Its role has changed from providing structural support to forming only a preliminary microscopic electrical connection network between active particles.

[0078] S13: The ePTFE ultra-thin porous skeleton membrane wound on the unwinding roller 3 is unwound at a speed of 50m / min using an unwinding device. The dry electrode material 2 is uniformly applied to the ultra-thin porous skeleton membrane 1 by the electrostatic feeding device 4, so that it initially adheres and penetrates into its surface pores under the action of electrostatic force to achieve in-situ embedding.

[0079] S14: A dry negative electrode film with a single-layer skeleton film support is prepared by hot roll calendering technology. In this embodiment, a pair of hot rolls 5 extrudes and stretches the initially composite material, and the temperature range of hot roll calendering is 80-120°C, and the applied linear pressure range is 50-800kN / m, for example, 500kN / m.

[0080] The reason why the above-mentioned hot calendering technology can firmly embed the dry electrode material 2 into the ePTFE ultrathin porous skeleton membrane to form a dry electrode membrane with strong integrity and excellent mechanical properties is due to the unique microstructure of ePTFE and its response behavior under hot pressing.

[0081] First, the ePTFE membrane, as the substrate, has a microstructure formed through a biaxial stretching process. This microstructure consists of a three-dimensional network of nodes and axially aligned fibrous filaments. This 'ordered randomness' lays a crucial physical foundation for its subsequent structural reconstruction.

[0082] Secondly, during the hot pressing process at 80-120℃, the combined effect of temperature and pressure triggers a controllable evolution of the microstructure: on the one hand, this temperature range (especially when it is close to its glass transition temperature Tg of about 115℃) loosens the molecular chains of PTFE, reduces fiber rigidity, and the entire skeleton network enters a "highly elastic state" that is easy to plastically deform; on the other hand, the huge vertical extrusion force applied by the hot roller 5 forces these "softened" fiber networks to shrink in the Z-axis direction, and the original three-dimensional pores are flattened and reshaped.

[0083] Crucially, due to the inherent arrangement tendency of the fibers themselves, they do not collapse randomly; instead, they fold, entangle, extend, and wrap between the compacted active material and conductive agent particles, ultimately reconstructing from a highly porous independent skeleton into a physically dense, interlocked, and mutually locked composite load-bearing structure that is deeply integrated with the electrode particles.

[0084] ② Preparation of dry cathode film supported by monolayer framework film

[0085] The ingredients are as follows:

[0086] Positive electrode active material: lithium iron phosphate; conductive agent: carbon nanotubes; binder: PTFE.

[0087] S21: Provide an ePTFE ultrathin porous skeleton membrane with a porosity of 85%, a weight of 1.6g per square meter, and a thickness of 1.2 micrometers, and wind the ePTFE ultrathin porous skeleton membrane onto the unwinding roller 3.

[0088] S22: Dry electrode raw material 2 is prepared by high-speed mixing and fiberization of 98.5g positive electrode active material, 1g conductive agent and 0.5g PTFE.

[0089] S23: The ultra-thin porous skeleton membrane wound on the unwinding roller 3 is unwound at a speed of 50m / min using an unwinding device, and the dry electrode material 2 is fed in uniformly through the electrostatic feeding device 4, so that the dry electrode material 2 is embedded in the ultra-thin porous skeleton membrane 1 in situ.

[0090] S24: A dry cathode membrane with a single-layer skeleton membrane is prepared by hot roll calendering and multi-stage thinning. The temperature range of hot roll calendering is 80-120℃, and the applied linear pressure range is 50-800kN / m, for example, 500kN / m.

[0091] Example 2: Preparation of a dry electrode membrane supported by a double-layer porous framework membrane

[0092] ③ Preparation of dry-process negative electrode membrane supported by a double-layer porous framework membrane

[0093] The ingredients are as follows:

[0094] Negative electrode active material: artificial graphite, conductive agent: Super P, binder: PTFE.

[0095] S31: Provides an ultra-thin porous skeleton membrane 1 made of ePTFE, with a porosity of 85%, a basis weight of 1.6g per square meter, and a thickness of 1.2 micrometers. The porous skeleton membrane 1 is wound on the unwinding roller 3.

[0096] S32: Dry electrode raw material 2 is obtained by high-speed mixing and fiberization of 98.5g of negative electrode active material, 1.25g of conductive agent and 0.25g of PTFE.

[0097] S33: Using two sets of unwinding devices, the ePTFE ultra-thin porous skeleton membrane wound on the unwinding roller 3 is unwound at a speed of 50m / min. The dry electrode material 2 is uniformly applied between the two ePTFE ultra-thin porous skeleton membranes 1 through the electrostatic feeding device 4. The dry electrode material 2 is embedded in the ePTFE ultra-thin porous skeleton membrane in situ.

[0098] S34: A dry negative electrode membrane with a double-layer porous skeleton membrane is prepared by multi-stage thinning through hot roll calendering technology. The temperature range of hot roll calendering is 80-120℃, and the applied linear pressure range is 50-800kN / m, for example, 500kN / m.

[0099] ④ Preparation of dry cathode membrane supported by a double-layer porous framework membrane

[0100] The ingredients are as follows:

[0101] Positive electrode active material: lithium iron phosphate; conductive agent: carbon nanotubes; binder: PTFE.

[0102] The steps are as follows:

[0103] S41: Provides an ePTFE ultrathin porous skeleton membrane with a porosity of 85%, a basis weight of 1.6g per square meter, a thickness of 1.2 micrometers, and is wound on unwinding roller 3.

[0104] S42: Dry electrode raw material 2 is prepared by high-speed mixing and fiberization of 98.5g positive electrode active material, 1g conductive agent and 0.5g PTFE.

[0105] S43: Using two sets of unwinding devices, the ultra-thin porous skeleton membrane 1 wound on the unwinding roller (3) is unwound at a speed of 50 m / min. The dry electrode material 2 is uniformly applied between the two ultra-thin porous skeleton membranes 1 through the electrostatic feeding device 4. The dry electrode material 2 is embedded in the ultra-thin porous skeleton membrane 1 in situ.

[0106] S44: A dry cathode membrane with a double-layer porous skeleton membrane is prepared by multi-stage thinning through hot roll calendering technology. The temperature range of hot roll calendering is 80-120℃, and the applied linear pressure ranges from 50-800kN / m, for example, 500kN / m.

[0107] The double-layer skeleton membrane acts like a mold, constraining and squeezing the dry powder in the middle from both top and bottom during hot pressing, preventing the powder from escaping to both sides, thus achieving more efficient filling and higher compaction density. According to SEM cross-sectional analysis and porosity calculation, the filling rate is about 40% higher than that of the single-layer skeleton membrane.

[0108] To further verify the universality of the technical solution of the present invention and to explore the influence of the parameters of the skeleton film itself (such as basis weight and thickness) on the overall performance of the final electrode film, so as to determine the preferred technical range, the applicant conducted the experiments of Examples 3-6 below.

[0109] Example 3: Preparation of dry electrode film supported by a single-layer framework film

[0110] Unlike Example 1, the provided ePTFE ultrathin porous framework membrane has a porosity of 85%, a basis weight of 4.8 g per square meter, and a thickness of 3.6 micrometers.

[0111] Example 4: Preparation of a dry electrode film supported by a double-layer skeleton film

[0112] Unlike Example 2, the provided ePTFE ultrathin porous framework membrane has a porosity of 85%, a basis weight of 4.8 g per square meter, and a thickness of 3.6 micrometers.

[0113] Example 5: Preparation of a dry electrode film supported by a single-layer framework film

[0114] Unlike Example 1, the provided ePTFE ultrathin porous framework membrane has a porosity of 85%, a basis weight of 9.6 g per square meter, and a thickness of 7.2 micrometers.

[0115] Example 6: Preparation of a dry electrode film supported by a double-layer skeleton film

[0116] Unlike Example 2, the provided ePTFE ultrathin porous framework membrane has a porosity of 85%, a basis weight of 9.6 g per square meter, and a thickness of 7.2 micrometers.

[0117] Comparative Example 1

[0118] The preparation of self-supporting dry electrode films includes the separate preparation of self-supporting dry negative electrode films and self-supporting dry positive electrode films. Self-supporting dry electrode films refer to electrode films formed solely by the bonding of the electrode materials themselves, without relying on external supporting structures. During the preparation of such electrode films, sufficient binder is required to ensure that the electrode material particles are tightly bonded together to form a stable film structure. If the binder content is insufficient, the electrode film is prone to cracking and delamination during calendering, resulting in insufficient mechanical strength and failing to meet the requirements of practical applications.

[0119] ⑤ The preparation of the self-supporting dry negative electrode film is as follows:

[0120] Negative electrode active material: artificial graphite; conductive agent: Super P (conductive carbon black); binder: PTFE.

[0121] The steps are as follows:

[0122] S51: Dry electrode raw material is prepared by high-speed mixing of 97g of negative electrode active material, 1g of conductive agent and 2g of PTFE.

[0123] S52: Self-supporting dry negative films are directly prepared from dry electrode raw materials using hot roll calendering technology. The temperature range of hot roll calendering is 80-120℃, and the applied linear pressure ranges from 50-800kN / m, for example, 500kN / m. At high temperatures, PTFE can soften and flow, forming a uniform film structure through the calendering process.

[0124] ⑥ Preparation of self-supporting dry cathode film

[0125] raw material:

[0126] Positive electrode active material: lithium iron phosphate; conductive agent: carbon nanotubes; binder: PTFE.

[0127] The steps are as follows:

[0128] S61: Dry electrode raw material is prepared by high-speed mixing of 97g positive electrode active material, 1g conductive agent and 2g PTFE.

[0129] S62: Self-supporting dry positive electrode film is directly prepared using dry electrode raw materials through hot roll calendering technology, and the temperature range of hot roll calendering is 80-120℃, and the applied linear pressure range is 50-800kN / m, for example, 500kN / m.

[0130] In Comparative Example 1, a higher content of PTFE (2%) is required as a binder, mainly because the self-supporting dry electrode film lacks other effective mechanical support structures and requires sufficient binder to ensure the mechanical strength and stability of the electrode film.

[0131] In Comparative Example 1, to ensure the electrode film could withstand subsequent production and processing without external support, a PTFE binder with a mass percentage as high as 2% had to be used. However, this approach relying on a high binder content has the following fundamental drawbacks:

[0132] As a polymeric insulator, PTFE itself does not participate in electrochemical reactions. However, up to 2% PTFE inevitably coats the surface of active materials and conductive agent particles, forming an insulating layer. This significantly increases the interfacial resistance for electron transport and lithium-ion migration, leading to increased electrode internal resistance and deterioration in rate performance and cycle life.

[0133] This 2% inert binder occupies valuable mass and volume in the electrode film, directly "diluting" the proportion of active material and becoming a difficult bottleneck to overcome in improving battery energy density.

[0134] Therefore, Comparative Example 1 typically reproduces the technical contradiction that is prevalent in the prior art: in order to obtain the necessary 'mechanical strength' (provided by high binder content), 'electrochemical performance' and 'energy density' must be sacrificed.

[0135] To systematically verify the superiority of the 'skeleton-reinforced dry electrode film' proposed in this invention compared to existing technologies, and to quantitatively reveal its inherent synergistic technological effects, this application conducted key index tests covering electrical performance, mechanical performance, and process consistency on the negative and positive electrode films prepared in Examples 1 and 2 (using the technical solution of this invention) and Comparative Example 1 (using the solution of existing technology). Specific test methods and result analysis are as follows.

[0136] 1. Film surface resistance test (characterizing electrical properties):

[0137] Test objective: This indicator directly reflects the quality of the electronic conductive network constructed inside the electrode. Lower film surface resistance means a shorter and smoother electron transport path between active material particles, which is a key prerequisite for achieving high-rate performance and low internal resistance in batteries.

[0138] Test method: A four-probe tester was used to test the electrode film at room temperature (25℃) under a dry nitrogen atmosphere. To ensure the accuracy of the data, five different locations on the surface of each sample were randomly selected for measurement, and the average value was taken as the final film surface resistance value, which is recorded in Tables 1 and 2.

[0139] 2. Electrode film tensile strength test (characterizing mechanical properties):

[0140] Test Objective: This indicator characterizes the mechanical robustness of the electrode film. A high-strength electrode film can withstand the mechanical stress in subsequent high-speed automated production processes (such as slitting, winding, and stacking), and is not prone to breakage or micro-cracks. This is an important guarantee for ensuring product yield and cell safety.

[0141] Test method: A tensile testing machine was used to precisely cut the electrode film into strips with dimensions of 100mm × 15mm. The tensile rate was set to 50mm / min for testing until the strips broke. The maximum tensile strength was recorded. Five strips were tested for each group of samples, and the average value was recorded in Tables 1 and 2.

[0142] 3. Electrode film thickness and uniformity testing (characterizing process consistency):

[0143] Test objective: Measuring the average thickness and its deviation of the electrode film is a key parameter for evaluating the stability and uniformity of the electrode fabrication process. A smaller thickness deviation (standard deviation) means a more consistent loading of active material across the entire electrode area, which helps ensure the consistency of performance between individual cells and within the cell itself.

[0144] Test method: A high-precision digital thickness gauge was used. Nine points were evenly distributed along the transverse (TD) and longitudinal (MD) directions on each electrode film sample for measurement. The average value was calculated and recorded in Tables 1 and 2.

[0145] Table 1

[0146] Adhesive dosage negative electrode film thickness Negative electrode film surface resistance Electrode film strength Comparative Example 1 2.00％ 65μm 2.73mΩ 1.15Mpa Example 1 0.25％ 65μm 1.56mΩ 5.60 MPa Example 2 0.25％ 65μm 1.89mΩ 8.70 MPa Example 3 0.25％ 65μm 1.91mΩ 9.67 MPa Example 4 0.25％ 65μm 1.93mΩ 15.76 MPa Example 5 0.25％ 65μm 1.97mΩ 15.96 MPa Example 6 0.25％ 65μm 1.99mΩ 23.33 MPa

[0147] Table 2

[0148] Adhesive dosage Positive electrode film thickness Positive electrode film surface resistance Electrode film strength Comparative Example 1 2.00％ 95μm 195mΩ 0.81 MPa Example 1 0.25％ 95μm 145mΩ 3.92 MPa Example 2 0.25％ 95μm 156mΩ 6.09 MPa Example 3 0.25％ 95μm 163mΩ 8.41 MPa Example 4 0.25％ 95μm 172mΩ 14.23 MPa Example 5 0.25％ 95μm 181mΩ 14.69 MPa Example 6 0.25％ 95μm 188mΩ 21.36 MPa

[0149] Referring to Table 1, Comparative Example 1 and Example 1 are compared. Comparative Example 1 and Example 1 use the same negative electrode active material, the same type of conductive agent, and the same binder. In Example 1, an ultrathin porous framework membrane is added as a supporting framework, allowing for direct electrode membrane fabrication. Comparative Example 1 requires the raw materials to be mixed evenly, and to ensure successful membrane formation, a high-speed mixer is used for further fiberization, and a higher proportion of PTFE is added.

[0150] Referring to Table 2, Comparative Example 1 and Example 1 are compared. Comparative Example 1 and Example 1 use the same negative electrode active material, the same type of conductive agent, and the same binder. In Example 1, an ultrathin porous framework membrane is added as a supporting framework, allowing for direct fabrication of the electrode membrane. In Comparative Example 1, because more binder is needed to ensure successful film formation, the content of active material and conductive agent is reduced, thus decreasing the conductivity of the positive electrode membrane.

[0151] Furthermore, comparing Comparative Example 1 and Example 1, Example 1 showed that the lower proportion of binder reduced the blockage of the electronic pathway between the active material and the conductive agent, significantly lowering the surface resistance of both the negative and positive electrode films. In Example 1, the addition of an ultrathin porous framework film as a supporting skeleton greatly enhanced the strength of both the negative and positive electrode films. In contrast, the self-supporting negative electrode film prepared in Comparative Example 1 had lower strength and was prone to breakage during production.

[0152] Comparing Example 1 with Example 2, the main difference between Example 2 and Example 1 is that a double-layer porous framework membrane 1 is used as a support. As can be seen from the data in Tables 1 and 2, since the porous framework membrane is ultrathin and porous, it does not affect the electrochemical performance of the electrode membrane. The change in membrane surface resistance is very small, but the strength of the dry electrode membrane 100 can be greatly increased.

[0153] In addition, observation Figure 6 The electron microscope image of the porous framework membrane 1 shows that there are many micropores with a diameter of 50-500 nm on the surface of the porous framework membrane 1. The presence of these micropores allows the dry electrode material 2 to be embedded in situ into the porous framework membrane 1.

[0154] observe Figure 7-8 The electron microscope image of the dry electrode membrane 100 supported by the skeleton membrane shows that the dry electrode raw material 2 has been embedded in the porous skeleton membrane 1.

[0155] This technology can significantly reduce the binder content, and the active material content can be increased to up to 99.0%. Through in-situ embedding technology, the distribution of active material / conductive agent can be more uniform, reducing interfacial impedance.

[0156] Based on the above test results, and by comparing Example 2 and Example 1, it can be seen that the dry electrode film prepared by the method of the present application with a skeleton film has higher strength when a double-layer porous skeleton film is selected as the support; when a single-layer skeleton film is selected as the support, the surface resistance of the prepared negative electrode film and positive electrode film is relatively smaller compared with that of the double-layer porous skeleton film support.

[0157] Furthermore, based on the comparative analysis of the embodiments and comparative examples, it can be concluded that:

[0158] 1. Improved mechanical strength

[0159] Negative electrode membrane: The strength of Comparative Example 1 (self-supporting membrane) is only 1.15 MPa. However, Example 1, which uses the thinnest single-layer framework membrane, achieves a strength of 5.60 MPa, nearly 4.9 times that of the former. Using a double-layer framework membrane (Example 2) or a thicker framework membrane (Example 6), the strength can reach up to 23.33 MPa, an improvement of more than 20 times.

[0160] Positive electrode film: The strength of Comparative Example 1 is 0.81 MPa, which is also very low. The strength of Example 1 is 3.92 MPa (an improvement of about 4.8 times), and the strength of Example 6 can reach as high as 21.36 MPa (an improvement of more than 26 times).

[0161] This application fundamentally solves the core problems of traditional self-supporting dry electrode membranes, namely extremely low mechanical strength and "extremely easy breakage" during production, by introducing a porous skeleton membrane. This leap in strength makes it feasible to produce dry electrode membranes at high speed and on a large scale, using roll-to-roll technology.

[0162] The comparison between Comparative Example 1 and the Examples also demonstrates the rationality of a porous framework membrane mass percentage of 0.5-2%. This range means that a "load-bearing framework" spanning the entire electrode membrane can be constructed using only a very small amount of polymer material. Experimental data (as shown in Tables 1 and 2) prove this point:

[0163] Comparative Example 1 (0% skeleton): The strength is only 0.81-1.15 MPa, which is very fragile.

[0164] With the introduction of a very small amount of skeleton: In the examples, even with a very low basis weight of the skeleton membrane, the final strength can easily reach 3.92-5.60 MPa or higher, an improvement of 4-5 times. As the basis weight increases (still within 2% of the total mass), the strength can be further increased by more than 20 times.

[0165] 2. The electrode film surface resistance is significantly reduced, resulting in superior electrochemical performance. The negative electrode film: The surface resistance of Comparative Example 1 is 2.73 mΩ. In contrast, the resistance of Example 1 drops to 1.56 mΩ, a reduction of approximately 43%.

[0166] Positive electrode film: The surface resistivity of the film in Comparative Example 1 is 195 mΩ. In contrast, the resistivity of Example 1 drops to 145 mΩ, a reduction of approximately 26%.

[0167] It is commonly believed that adding an inert porous framework membrane increases resistance. However, data shows the opposite: the resistance is significantly reduced. The fundamental reason is that the framework membrane provides mechanical support, allowing the amount of PTFE used as a binder to be drastically reduced from 2.00% to 0.25% (an eight-fold reduction). Since the binder itself is non-conductive, this significant reduction in its amount avoids blocking or covering the electronic pathways between the active material and the conductive agent particles, thereby significantly reducing the internal resistance of the electrode and optimizing its electrochemical performance.

[0168] 3. The amount of binder used is significantly reduced, while the proportion of active materials is increased.

[0169] To achieve a strength sufficient for film formation, 2.00% PTFE binder must be added to Comparative Example 1.

[0170] In the embodiments of this application, due to the strong support of the skeleton membrane, the amount of PTFE used is only 0.25% or 0.5%.

[0171] This application's design successfully decouples the functions of "mechanical support" and "particle bonding." The skeleton membrane handles the former, allowing the binder to focus on its core function of "particle bonding," requiring only a small amount. This not only directly results in the aforementioned reduction in resistance but also means a decrease in the inactive "dead weight" within the overall electrode mass, allowing for a corresponding increase in the mass proportion of active material, thereby contributing to improved battery energy density.

[0172] 4. The structure is highly designable and its performance is adjustable.

[0173] Comparing Example 1 (single-layer film) and Example 2 (double-layer film), it can be seen that, under similar conditions, using a double-layer framework film can further significantly improve the strength of the electrode film (the negative electrode strength increases from 5.60 MPa to 8.70 MPa), while the film surface resistance only increases slightly.

[0174] Comparing Examples 1, 3, and 5 (or 2, 4, and 6), it can be seen that as the basis weight of the skeleton membrane increases, the strength of the electrode membrane also increases linearly.

[0175] The core inventive concept of this invention is:

[0176] (1) "Load-bearing keel" mechanism: This invention introduces an ultra-thin skeleton that accounts for less than 2% of the total mass, constructing a "load-bearing keel" that runs through the entire electrode system from the outside. This "keel" bears most of the mechanical stress, making the high proportion of binder (2-5%) that must be added in traditional processes to ensure film formation unnecessary. The amount of binder is drastically reduced to 0.5% or even 0%, thereby releasing a large number of conductive channels and active specific surface areas occupied by insulating binder, resulting in a significant reduction in electrode film surface resistance and a significant improvement in electrochemical performance.

[0177] (2) "Mechanical riveting" mechanism: During the subsequent hot rolling process (e.g., 80-120℃, 50-800kN / m), the temperature causes the polymer fibers (such as ePTFE) of the skeleton film to enter a "highly elastic state" that is easily plastically deformed, while the enormous pressure forces the dry electrode material 2 into the pore network of the skeleton film. At this time, the already "softened" skeleton fiber network will be reconstructed, wrapping, and locking the electrode particles in situ, forming countless microscopic "mechanical riveting points" after cooling. This powerful physical interlocking structure fundamentally replaces the reliance on chemical binders in traditional technology, ensuring excellent structural integrity and anti-powdering ability of the electrode film even when the binder content is zero.

[0178] Specifically: 1) Under the enormous pressure of hot roll calendering, the dry electrode material 2 is forcibly injected into the pore network of the porous framework membrane 1;

[0179] 1. At the same time, the temperature of 80-120℃ causes the polymer fibers of the skeleton membrane to enter a plastic and elastic state, which causes in-situ entanglement and wrapping around the particles. After cooling, countless microscopic "mechanical riveting points" are formed, which firmly anchor the particles in the three-dimensional network.

[0180] 2. After high-intensity compaction, a huge static frictional force is generated between the particles and between the particles and the skeleton fibers, forming a stable frictional self-locking structure, which further enhances the overall cohesion of the membrane and effectively prevents powder shedding. Therefore, this invention, by creatively utilizing the plastic behavior of porous skeleton membranes under hot pressing, achieves the function of completely replacing chemical binders with physical and mechanical interlocking, fundamentally solving the technical contradiction of the incompatibility between strength and electrical properties in traditional processes.

[0181] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A dry electrode membrane supported by a double-layer skeleton membrane, characterized in that, include: Porous framework membrane (1), wherein the porous framework membrane (1) is an ultrathin biaxially stretched porous ePTFE membrane; as well as The dry electrode material (2) is formed on the surface and in the pores of the porous framework membrane (1). The dry electrode material (2) and the porous framework membrane (1) form a mechanically interlocked structure. The thickness of the porous framework membrane (1) is 1-10 micrometers, the porosity is 60%-90%, and the pore size is 50-500nm. The dry electrode material (2) consists of active substances, conductive agents, and binders. The mass percentage of the binder is greater than or equal to 0% and not higher than 0.5%. The dry electrode membrane is a sandwich structure formed by two layers of porous framework membrane (1) and dry electrode material (2).

2. A dry electrode membrane with a double-layer skeleton membrane support according to claim 1, characterized in that: The porous framework membrane (1) accounts for 0.5% to 2% of the total mass of the dry electrode membrane; or The porous framework membrane (1) has a weight of 1-10 g per square meter; or The total thickness of the dry electrode film is between 50 micrometers and 300 micrometers.

3. The dry electrode membrane with a double-layer skeleton membrane support according to claim 2, characterized in that: Each component, by mass percentage, includes 1.0%-4.5% conductive agent and the balance active material.

4. The dry electrode membrane with a double-layer skeleton membrane support according to claim 1, characterized in that: The porous skeleton membrane (1) includes a first skeleton membrane (10) and a second skeleton membrane (12), and the dry electrode raw material (2) is located between the first skeleton membrane (10) and the second skeleton membrane (12) and in the pores included in the first skeleton membrane (10) and the second skeleton membrane (12).

5. A dry electrode membrane with a double-layer skeleton membrane support according to claim 3, characterized in that: The conductive agent is one or more of carbon black, acetylene black, carbon nanotubes, graphene, and Ketjen black. The active material is either a positive electrode active material or a negative electrode active material. The positive electrode active material is one or more of lithium iron phosphate, ternary materials, and lithium titanate, and the negative electrode active material is graphite, silicon, or a combination thereof. The adhesive is one or a combination of PTFE, PVDF, and PEO.

6. A method for preparing a dry electrode film with a double-layer skeleton film support as described in claim 1, characterized in that, include: A porous framework membrane (1) is provided, wherein the porous framework membrane (1) is an ultrathin biaxially stretched porous ePTFE membrane, the thickness of the provided porous framework membrane (1) is 1-10 micrometers, the porosity is 60%-90%, and the pore size is 50-500nm; the dry electrode raw material (2) comprises active material, conductive agent and binder, wherein the mass percentage of the binder is greater than or equal to 0% and not higher than 0.5%; A fiberized dry electrode material (2) is provided. Two unwinding devices are used to uniformly unwind the ePTFE ultrathin porous skeleton membrane wound on the unwinding roller (3). An electrostatic unloading device (4) uniformly applies the dry electrode material (2) between two ePTFE ultrathin porous skeleton membranes (1), embedding the dry electrode material (2) into the surface and pores of the porous skeleton membrane (1). Hot rolling is performed to form a mechanically interlocked structure between the dry electrode raw material (2) and the porous skeleton membrane (1) to prepare a dry electrode membrane supported by a double-layer skeleton membrane.

7. The method for preparing a dry electrode film with a double-layer skeleton film support according to claim 6, characterized in that: Each component, by mass percentage, includes 1.0%-4.5% conductive agent and the balance active material.

8. The method for preparing a dry electrode film with a double-layer skeleton film support according to claim 6, characterized in that: The step of providing the dry electrode raw material (2) includes: treating a mixture of binder, conductive agent and active material with an air jet mill at an inlet pressure of 0.5 MPa to 1.2 MPa to fibrose the binder.

9. The method for preparing a dry electrode film with a double-layer skeleton film support according to claim 6, characterized in that: The rolling temperature range is 80-120℃, and the applied linear pressure ranges from 50-800kN / m.

10. A method for preparing a dry electrode film with a double-layer skeleton film support according to any one of claims 6-9, characterized in that: The porous skeletal membrane (1) has a weight of 1-10 g per square meter; or The porous framework membrane (1) accounts for 0.5% to 2% of the total mass of the dry electrode membrane.

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