Dry electrode films and their preparation methods, electrodes and batteries

Abstract

This application discloses a dry-process electrode film and its preparation method, as well as an electrode and a battery, belonging to the field of battery technology. The method includes: mixing and pulverizing polytetrafluoroethylene, an active material, and a conductive agent to obtain a pulverized mixture; subjecting the pulverized mixture to a first-stage airflow milling and shearing process to obtain a milled and sheared mixture; the first-stage shearing conditions include: airflow temperature of -10 to 10°C, airflow pressure of 0.7 to 0.9 MPa, and rotation speed of 8000 to 12000 rpm; subjecting the milled and sheared mixture to a second-stage airflow milling and shearing process to obtain a fibrous material; and subjecting the fibrous material to a second-stage fibrosis treatment to obtain a dry-process electrode film. This method can significantly improve the tensile strength of the electrode film, increase the electrode liquid absorption rate, and reduce the electrode resistivity.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more specifically, to a dry electrode film and its preparation method, an electrode, and a battery. Background Technology

[0002] Traditional lithium battery electrode preparation typically employs a coating method. First, binders, solvents, and conductive agents are mixed to form a conductive slurry. Then, electrode active materials are added in batches to form a uniform slurry. Finally, the slurry is uniformly coated onto a current collector using coating equipment. After drying, rolling, and slitting, the electrode sheet is formed. This method requires high precision in controlling the dispersion of the conductive agent, the viscosity of the slurry, and the coating equipment. It also results in low active material content in the electrode sheet, strict production process control, and the inability to produce thick electrode sheets. Furthermore, the solvent drying and solvent recovery processes are energy-intensive and costly, and are environmentally unfriendly.

[0003] To address the aforementioned issues, a dry electrode process has been developed. The main steps of this process involve uniformly mixing a conductive agent, binder, and electrode active material, followed by high-speed shearing to fiberize the PTFE binder into a fibrous network that binds the active material and conductive agent. Finally, further fiberization via rolling is used to create a self-supporting electrode membrane, which is then laminated onto the current collector to obtain a double-sided electrode. The fiberization step is the key step in the dry electrode process, requiring extremely high shearing forces to uniformly disperse and fiberize the PTFE. Mainstream methods include airflow shearing, high-speed stirring shearing, and ball milling shearing. However, conventional fiberization processes require high binder content (e.g., above 8 wt%), high requirements for the degree of binder fiberization, high equipment shearing forces, and high requirements for the uniformity of the mixture, resulting in long production times and making large-scale production difficult. The main reason for this contradiction is the special properties of PTFE, the binder required for this process. The electrode film forming process requires PTFE to be uniformly dispersed between the electrode materials and to form a nanoscale fiber network through shearing and stretching. The higher the molecular weight of PTFE, the easier the fiberization process is to occur. However, commercially available high molecular weight PTFE is often made into particles with a secondary particle size of 500 to 700 μm in order to avoid agglomeration during transportation. For positive electrode active materials with a particle size generally less than 30 μm and conductive agents with a nanoscale particle size, segregation is easily caused by uneven mixing during the mixing process, resulting in an uneven fiberization effect. Summary of the Invention

[0004] The main objective of this application is to provide a dry electrode membrane and its preparation method, as well as an electrode and a battery, to solve the problem of uneven mixing of polytetrafluoroethylene binder and low degree of fibrosis in the dry electrode process, which leads to low strength of the electrode membrane.

[0005] To achieve the above objectives, according to one aspect of this application, a method for preparing a dry electrode film is provided, the method comprising the following steps:

[0006] Step S1: Mix and pulverize the polytetrafluoroethylene material, electrode active material, and conductive agent to obtain a pulverized mixture;

[0007] Step S2: Perform a single airflow milling and shearing process on the pulverized mixture to obtain a milled and sheared mixture; wherein, the conditions for the single airflow milling and shearing process include: airflow temperature of -10℃ to 10℃, compressed airflow pressure of 0.7 to 0.9 MPa, and shearing speed of 8000 to 12000 rpm;

[0008] Step S3: Perform secondary airflow milling and shearing fiberization on the milled and sheared mixture to obtain fibrous material;

[0009] Step S4: Perform secondary fiberization on the fibrous material to obtain a dry electrode membrane.

[0010] Furthermore, the airflow temperature during the first airflow grinding and shearing process is -5℃ to 5℃; further, it is 0℃ to 5℃.

[0011] Furthermore, the airflow temperature for secondary airflow milling and shearing is 50℃~100℃, the compressed airflow pressure is 0.7~0.9MPa, and the shearing speed is 8000~12000rpm.

[0012] Furthermore, the airflow temperature for secondary airflow grinding and shearing is 60–100°C; further still, it is 70–100°C; and even further, it is 80–100°C.

[0013] Furthermore, the shearing speed of a single airflow milling shear is 10,000 to 11,000 rpm.

[0014] Furthermore, the shearing speed of the secondary airflow milling shear is 10,000 to 11,000 rpm.

[0015] Furthermore, the polytetrafluoroethylene material is a polytetrafluoroethylene dispersion resin with an average particle size of 400–600 μm, a molecular weight of 500,000–800,000, and a compression ratio of 100–3000.

[0016] Furthermore, the polytetrafluoroethylene dispersion resin is kept at -8℃ to -12℃ for 8 to 12 hours before mixing.

[0017] Further, the specific process of step S1 includes: mixing and pulverizing the electrode active material and the conductive agent to obtain powder A; mixing and pulverizing the heat-insulated polytetrafluoroethylene dispersion resin and powder A to obtain a pulverized mixture.

[0018] Furthermore, the electrode active material and conductive agent are mixed using a ball mill or a high-speed mixer with a rotation speed of 400–600 rpm.

[0019] Furthermore, the ball-to-material ratio of the ball mill is 1:(1-2).

[0020] Furthermore, the polytetrafluoroethylene dispersion resin and powder A are mixed using a dual-motion mixer or a three-dimensional motion mixer.

[0021] Furthermore, the mixing time of the polytetrafluoroethylene dispersion resin and powder A in the dual-motion mixer is 20–40 min.

[0022] Furthermore, the average particle size of the pulverized mixture is 8–12 μm.

[0023] Furthermore, the average particle size of the grinding and shearing mixture is 3–6 μm.

[0024] Furthermore, the first air jet milling shearing and / or the second air jet milling shearing are performed using an air jet mill.

[0025] Furthermore, the air jet mill is a fluidized bed air jet mill.

[0026] Furthermore, the secondary fiberization process employs a differential speed roller press for differential speed fiberization.

[0027] Furthermore, the differential roller press has a roller pressing temperature of 60℃~120℃ and a roller pressing speed ratio of 1:(1~1.5).

[0028] Furthermore, the weight ratio of the electrode active material to the conductive agent is (90-95):(0-5).

[0029] Furthermore, the weight ratio of powder A to the heat-insulated polytetrafluoroethylene dispersion resin is (95-99):(1-3).

[0030] Furthermore, the electrode active material includes a positive electrode active material and a negative electrode active material; wherein, the positive electrode active material is selected from at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt aluminum oxide, and manganese dioxide; and the negative electrode active material is selected from at least one of artificial graphite, natural graphite, lithium titanate, silicon-oxygen negative electrode material, and silicon-carbon.

[0031] Furthermore, the conductive agent is selected from at least one of conductive carbon black, graphite, graphene, carbon nanotubes, carbon fibers, acetylene black, and Ketjen black.

[0032] According to a second aspect of this application, a dry electrode membrane is provided, which is prepared by the above-described method for preparing a dry electrode membrane.

[0033] Furthermore, the dry electrode film has a thickness of 100–150 μm, a tensile strength of 0.2–0.4 MPa, and a compaction density of 2.50–3.30 g / cm³. 3 .

[0034] According to a third aspect of this application, a method for preparing a dry electrode is provided, the method comprising the following steps: rolling a dry electrode film onto at least one side of a current collector; wherein the dry electrode film is the aforementioned dry electrode film.

[0035] Furthermore, the rolling temperature is 0℃~100℃.

[0036] Furthermore, the current collector is selected from at least one of copper foil, carbon-coated copper foil, aluminum foil, nickel foil, stainless steel mesh, aluminum mesh, and nickel mesh.

[0037] According to a fourth aspect of this application, a battery is provided, comprising an electrode, a separator, and an electrolyte; the electrode is an electrode prepared by the above-described dry electrode preparation method.

[0038] This application provides a dry electrode film preparation method based on the phase transition temperature of the binder PTFE. It employs different temperature shearing methods: first, low-temperature high-speed shearing reduces the binder particle size to the nanometer scale, resulting in a more uniform distribution; then, high-temperature high-speed shearing further increases the binder's fibrous degree, leading to a higher tensile strength in the resulting electrode film, less binder usage, and reduced anisotropy after film formation. This method also breaks through the electrode thickness limit, enabling the production of electrodes with thicknesses ranging from 30 μm to 3 mm, and is applicable to various battery systems. Compared to traditional coating electrode processes, it eliminates the drying step, reduces electrode powder shedding, and allows for the production of thicker electrodes, meeting the manufacturing requirements of higher energy density battery cells. Attached Figure Description

[0039] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0040] Figure 1 A process flow diagram of the dry electrode film and electrode fabrication process according to an embodiment of this application is shown;

[0041] Figure 2 This shows a SEM image of the PTFE coating on the surface of the positive electrode active material before fiberization in Example 1 of this application;

[0042] Figure 3 SEM images of the PTFE fiberization effect in Embodiment 1 of this application are shown;

[0043] Figure 4 This paper shows a SEM image of the electrode film surface in Embodiment 1 of this application;

[0044] Figure 5The diagram shows a comparison of the longitudinal tensile strength of the electrode films of Embodiment 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 of this application;

[0045] Figure 6 The diagram shows a comparison of the transverse tensile strength of the electrode films of Embodiment 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 of this application;

[0046] Figure 7 A comparison graph showing the electrode resistivity of Embodiment 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 of this application is shown;

[0047] Figure 8 A comparison graph showing the electrode liquid absorption rate of Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 of this application is shown. Detailed Implementation

[0048] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0049] Existing technologies for PTFE binder fiberization typically employ methods such as airflow shearing, high-speed stirring shearing, and ball milling shearing. These methods require relatively high binder concentrations, such as 8 wt% or more, and the secondary particle size of the PTFE used is 500–700 μm. This results in uneven mixing with active materials and conductive agents, easily causing segregation and potentially leading to uneven fiberization, which in turn reduces the tensile strength and other properties of the dry electrode film. Therefore, this application, based on the phase transition temperature of the PTFE binder, specifically employs different temperature shearing methods to improve the mixing uniformity and fiberization degree of PTFE.

[0050] According to one aspect of this application, a method for preparing a dry electrode film is provided, the method comprising the following steps:

[0051] Step S1: Mix and pulverize the polytetrafluoroethylene material, electrode active material, and conductive agent to obtain a pulverized mixture;

[0052] Step S2: Perform a single airflow milling and shearing process on the pulverized mixture to obtain a milled and sheared mixture; wherein, the conditions for the single airflow milling and shearing process include: airflow temperature of -10℃ to 10℃, compressed airflow pressure of 0.7 to 0.9 MPa, and shearing speed of 8000 to 12000 rpm;

[0053] Step S3: Perform secondary airflow milling and shearing on the milled and sheared mixture to obtain fibrous material;

[0054] Step S4: Perform secondary fiberization on the fibrous material to obtain a dry electrode membrane.

[0055] The airflow temperature for the primary airflow grinding and shearing process described in this application is selected from any value or a range between any two of -10℃, -9℃, -8℃, -7℃, -6℃, -5℃, -4℃, -3℃, -1℃, 0℃, 1℃, 2℃, 3℃, 4℃, 5℃, 6℃, 7℃, 8℃, 9℃, and 10℃; the airflow temperature for the secondary airflow grinding and shearing process is selected from any value or a range between any two of 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, and 100℃; for example, the primary airflow grinding temperature is -5 to 10℃, further -5 to 5℃, further 0 to 5℃, and for example 0℃; the secondary airflow grinding temperature is 50 to 100℃, further 60 to 100℃, further 70 to 100℃, further 80 to 100℃, and for example 80℃.

[0056] The shearing speed of the first airflow milling shearing described in this application is any value or a range between any two of 8000 rpm, 8500 rpm, 9000 rpm, 9500 rpm, 10000 rpm, 10500 rpm, 11000 rpm, 11500 rpm, and 12000 rpm; for example, 10000 rpm; the shearing speed of the second airflow milling shearing is any value or a range between any two of 8000 rpm, 8500 rpm, 9000 rpm, 9500 rpm, 10000 rpm, 10500 rpm, 11000 rpm, 11500 rpm, and 12000 rpm; for example, 10000 rpm; the shearing speeds of the two shearing processes can be the same or different.

[0057] The dry electrode film preparation method provided in this application, based on the phase transition temperature of the binder PTFE (PTFE phase transition temperature is 19℃), employs different temperature shearing methods. First, the PTFE-containing mixture is subjected to low-temperature high-speed shearing, reducing the PTFE binder particle size from the micrometer level to the nanometer level, resulting in more uniform dispersion of the mixture. During this low-temperature high-speed shearing process, since the temperature is below the phase transition temperature, theoretically PTFE will not undergo significant fiberization. However, heat is generated during the shearing process. To achieve the desired fiberization effect, the aforementioned low-temperature high-speed shearing temperature is controlled between -10℃ and 1℃. 0℃ is suitable; since the shearing speed and the fiber shearing speed are similar, high-speed grinding and shearing are used to grind and shear conventionally used PTFE with a large particle size of micron to the nanoscale. After the PTFE is reduced to the nanoscale size, it is coated on the active material. This will greatly improve the uniformity of the mixing of various raw materials and make it more conducive to the subsequent fiberization of PTFE mixture. After the PTFE mixture is made into nanoscale, high-temperature and high-speed shearing is performed to make the degree of PTFE fiberization higher, the tensile strength of the electrode film is higher, the amount of binder used is less, and the anisotropy after film formation is also reduced.

[0058] This application uses a continuous dry rolling process to manufacture electrodes, eliminating the need for solvents and drying, thus reducing energy consumption. The electrode binder exists in a fibrous state, allowing for closer contact between the positive electrode active material and the conductive agent particles, increasing electrode compaction density, reducing electrode resistance, and lowering the electrode powder shedding rate. Furthermore, this application uses temperature control to regulate the PTFE binder particle size and degree of fibrosis, improving mixing uniformity, reducing the difficulty of electrode film formation, and increasing the tensile strength of the film.

[0059] In some embodiments, the polytetrafluoroethylene material is a polytetrafluoroethylene dispersion resin with an average particle size of 400-600 μm, a molecular weight of 500,000-8,000,000, and a compression ratio of 100-3000.

[0060] The improved method of this application mainly addresses the issue that commonly used high molecular weight PTFE is often processed into large particles with a secondary particle size of 500-700 μm to prevent agglomeration during transportation. Existing technologies often directly mix this large-particle PTFE with active materials and conductive agents, resulting in poor mixing between micron-sized PTFE and other nano-sized materials, thus affecting the degree of PTFE fiberization and the strength of the electrode film. By adopting the improved method of this application, micron-sized PTFE can be processed into nano-sized particles, further improving its dispersion uniformity.

[0061] In some embodiments, the polytetrafluoroethylene dispersion resin is kept at -8°C to -12°C for 8 to 12 hours before mixing; for example, at -10°C for 10 hours. The purpose of keeping the PTFE at the above temperatures before use is to prevent further agglomeration of the PTFE and increase its particle size, thus avoiding difficulties in subsequent powder mixing.

[0062] In some embodiments, step S1 specifically includes: mixing and pulverizing the electrode active material and the conductive agent to obtain powder A; mixing the heat-insulated polytetrafluoroethylene dispersion resin and powder A to obtain a pulverized mixture. This application can further improve the mixing uniformity through a stepwise mixing method.

[0063] In some embodiments, the electrode active material and the conductive agent are mixed using a ball mill or a high-speed mixer, with the high-speed mixer rotating at 400–600 rpm; the ball-to-material ratio of the ball mill is 1:(1–2); the polytetrafluoroethylene dispersion resin and powder A are mixed using a dual-motion mixer or a three-dimensional motion mixer; the mixing time in the dual-motion mixer is 20–40 min.

[0064] This application selects different mixing equipment and process conditions according to different mixtures, and improves the dispersibility and uniformity of each mixture in a targeted manner; when PTFE and powder A are mixed in a dual-motion or three-dimensional motion mixer, the mixing time is controlled as described above, such as 20 to 40 minutes, for example, 30 minutes; this can avoid excessive shearing, which would cause PTFE to fiberize before subsequent high-temperature and high-speed shearing, thus hindering the subsequent PTFE fiberization effect.

[0065] In some embodiments, the average particle size of the pulverized mixture is 8–12 μm; the average particle size of the milled and sheared mixture is 3–6 μm, for example, 3–4 μm. This application achieves a gradual reduction in particle size through pulverization and milling / shearing processes, which facilitates subsequent airflow milling / shearing processes.

[0066] In some embodiments, the first and / or second air jet milling shearing processes employ an air jet mill, such as a fluidized bed air jet mill. This application uses the aforementioned equipment for both grinding and shearing processes. Compared to a mixer or ball mill, the heat generated during the grinding process in an air jet mill is promptly carried away by the low-temperature airflow, preventing PTFE deformation, fiberization, and uneven distribution caused by localized heat accumulation within the equipment cavity. During the fiberization process, a high-temperature airflow (specifically, an airflow above the PTFE phase transition temperature, i.e., above 19°C) can be used to induce a phase transition in PTFE, promoting PTFE fiberization. Below 19°C, the PTFE molecular chain is a 13 / 6 helix; at 19°C, a phase transition occurs, and the molecules slightly unwind, forming a 15 / 7 helix, making it easier to fiberize.

[0067] In some embodiments, the secondary fiberization process employs a differential speed roller press for differential opening and fiberization; the roller pressing temperature can be 60°C to 120°C, and the roller pressing speed ratio can be 1:(1 to 1.5). Using the above roller pressing conditions, the PTFE mixture can be fully and completely fiberized to form an electrode film.

[0068] In some embodiments, the weight ratio of electrode active material to conductive agent is (90-95):(0-5), for example, 92:5; the weight ratio of powder A to polytetrafluoroethylene dispersion resin after heat preservation is (95-99):(1-5), for example, 98:2. This application controls the PTFE content to be between 1 and 5, which, when mixed with other components, results in better synergistic fiberization and avoids phenomena such as membrane cracking caused by excessive or insufficient PTFE content.

[0069] In some embodiments, the electrode active material includes a positive electrode active material and a negative electrode active material; wherein, the positive electrode active material is selected from at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt aluminum oxide, and manganese dioxide; the negative electrode active material is selected from at least one of artificial graphite, natural graphite, lithium titanate, silicon-oxygen anode material, and silicon-carbon. The electrode film preparation method of this application is applicable to both positive and negative electrode films, and other types of positive electrode active materials, negative electrode active materials, or conductive agents can also be selected according to actual needs.

[0070] The conductive agent used in this application mainly uses carbon nanotubes (CNTs) and graphite. Since carbon nanotubes and PTFE fibers have similar one-dimensional linear morphology, the two may have a synergistic effect, which can connect more active material particles and thus construct a more effective electron unblocking network. The role of graphite is that its layered structure has good lubricity, which can help the powder film thinning process.

[0071] According to a second aspect of this application, a dry electrode membrane is provided, which is prepared by the above-described method for preparing a dry electrode membrane.

[0072] In some embodiments, the thickness of the dry electrode film is 100–152 μm, for example 115–152 μm; the tensile strength is 0.15–0.4 MPa, for example 0.15–0.30 MPa; and even more specifically 0.15–0.25 MPa; the compaction density is 2.50–3.30 g / cm³. 3 For example, 2.50~3.0g / cm³ 3 .

[0073] The electrode film prepared by the method of this application has good PTFE dispersion, good uniformity and high degree of fibrosis, which improves the tensile strength and other mechanical properties of the electrode film, increases the compaction density of the electrode film, and thus improves the energy density of the battery; the method is also applicable to thicker electrode films.

[0074] According to a third aspect of this application, a method for preparing a dry electrode is provided, the method comprising the following steps: rolling a dry electrode film onto at least one side of a current collector; wherein the dry electrode film is the aforementioned dry electrode film.

[0075] In some embodiments, the temperature of the roller pressing during the application of the current collector is 0°C to 100°C; the current collector is selected from at least one of copper foil, carbon-coated copper foil, aluminum foil, nickel foil, stainless steel mesh, aluminum mesh, and nickel mesh.

[0076] The electrode film prepared by the method of this application can be coated on one or both sides of the positive electrode current collector or the negative electrode current collector, and other types of current collectors can be selected according to actual needs.

[0077] According to a fourth aspect of this application, a battery is provided, comprising an electrode, a separator, and an electrolyte; the electrode is an electrode prepared by the above-described dry electrode preparation method.

[0078] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0079] All raw materials and equipment used in the embodiments of this application are existing technologies and are commercially available.

[0080] Example 1

[0081] The preparation process of battery electrodes is as follows: Figure 1 As shown, it includes the following steps:

[0082] (1) PTFE insulation: The secondary particle size of PTFE is 570μm, the molecular weight is 7.7 million, and the compression ratio is 100~300; PTFE is kept at -10℃ for 10h;

[0083] (2) Premixing: Lithium iron phosphate (LFP), graphite, and carbon nanotubes were mixed uniformly in a ball mill at a ratio of 92:2:3 (ball ratio 1:1) at 500 rpm to obtain powder A. Powder A and the heat-insulated binder PTFE were then mixed in a double-motion mixer at a ratio of 98:2 for 30 min to obtain powder B, with an average particle size of 10.4 μm. The morphology of the PTFE-coated active material after mixing is as follows: Figure 2 As shown;

[0084] (3) Fiberization: Powder B was ground using a low-temperature airflow mill (airflow temperature 0℃, grinding pressure 0.70MPa, classifying wheel speed 10000rpm) to obtain powder C with an average particle size of 3.6μm; the effect of PTFE fiberization is as follows: Figure 3 As shown;

[0085] Powder C is then ground using a high-temperature airflow mill with an airflow temperature of 80℃, a grinding pressure of 0.90MPa, and a classifying wheel speed of 10000rpm to obtain powder D.

[0086] (4) Film Formation: Powder D is fibrousized and formed into a film using a multi-stage differential speed roller press. The roller press speed ratio is 1:1.5, and the temperature is 120℃ / 100℃ / 60℃, with each temperature being applied once to obtain the electrode film. The film thickness is 120μm, the tensile strength is 0.25MPa, and the compaction density is 2.90g / cm³. 3 ; membrane morphology as Figure 4 As shown;

[0087] (5) Applying current collector: After the diaphragm is formed, it is rolled into electrodes on both sides of the aluminum foil current collector at a rolling temperature of 50°C to obtain the positive electrode sheet.

[0088] Example 2

[0089] The difference between Example 2 and Example 1 is that the fiberization process in step (3) is different;

[0090] Fiberization: Powder B was ground in a low-temperature airflow mill with an airflow temperature of -10℃, a grinding pressure of 0.80MPa, and a classifying wheel speed of 10000rpm to obtain powder C with an average particle size of 4.1μm.

[0091] Powder C is then ground using a high-temperature airflow mill with an airflow temperature of 90℃, a grinding pressure of 0.90MPa, and a classifying wheel speed of 10000rpm to obtain powder D.

[0092] Example 3

[0093] Example 3 differs from Example 1 in that the fiberization process in step (3) is different;

[0094] Fiberization: Powder B was ground using a low-temperature airflow mill (model), with an airflow temperature of -5℃, a grinding pressure of 0.90MPa, and a classifying wheel speed of 10000rpm to obtain powder C, which has an average particle size of 3.2μm;

[0095] Powder C is then ground using a high-temperature airflow mill with an airflow temperature of 100℃, a grinding pressure of 0.90MPa, and a classifying wheel speed of 10000rpm to obtain powder D.

[0096] Example 4

[0097] The difference between Example 4 and Example 1 is that the fiberization process in step (3) is different;

[0098] Fiberization: Powder B was ground in a low-temperature airflow mill with an airflow temperature of 5°C, a grinding pressure of 0.90 MPa, and a classifying wheel speed of 10,000 rpm to obtain powder C with an average particle size of 4.0 μm.

[0099] Powder C is then ground using a high-temperature airflow mill with an airflow temperature of 70°C, a grinding pressure of 0.90 MPa, and a classifying wheel speed of 10,000 rpm to obtain powder D.

[0100] Example 5

[0101] The difference between Example 5 and Example 1 is that the fiberization process in step (3) is different;

[0102] Fiberization: Powder B was ground in a low-temperature airflow mill with an airflow temperature of 10℃, a grinding pressure of 0.90MPa, and a classifying wheel speed of 10000rpm to obtain powder C with an average particle size of 3.5μm.

[0103] Powder C is then ground using a high-temperature airflow mill with an airflow temperature of 60℃, a grinding pressure of 0.90MPa, and a classifying wheel speed of 10000rpm to obtain powder D.

[0104] Example 6

[0105] The difference between Example 6 and Example 1 is that the fiberization process in step (3) is different;

[0106] Fiberization: Powder B was ground in a low-temperature airflow mill with an airflow temperature of 3°C, a grinding pressure of 0.90 MPa, and a classifying wheel speed of 10,000 rpm to obtain powder C with an average particle size of 3.9 μm;

[0107] Powder C is then ground using a high-temperature airflow mill with an airflow temperature of 50°C, a grinding pressure of 0.90 MPa, and a classifying wheel speed of 10,000 rpm to obtain powder D.

[0108] Example 7

[0109] The difference between Example 7 and Example 1 is that the fiberization process in step (3) is different;

[0110] Fiberization: Powder B was ground in a low-temperature airflow mill with an airflow temperature of 0℃, a grinding pressure of 0.70MPa, and a classifying wheel speed of 8000rpm to obtain powder C with an average particle size of 5.4μm.

[0111] Powder C is then ground using a high-temperature airflow mill with an airflow temperature of 80℃, a grinding pressure of 0.90MPa, and a classifying wheel speed of 8000rpm to obtain powder D.

[0112] Example 8

[0113] The difference between Example 8 and Example 1 is that the fiberization process in step (3) is different;

[0114] Fiberization: Powder B was ground in a low-temperature airflow mill with an airflow temperature of 0℃, a grinding pressure of 0.70MPa, and a classifying wheel speed of 9000rpm to obtain powder C with an average particle size of 6.1μm.

[0115] Powder C is then ground using a high-temperature airflow mill with an airflow temperature of 80℃, a grinding pressure of 0.90MPa, and a classifying wheel speed of 9000rpm to obtain powder D.

[0116] Example 9

[0117] The difference between Example 9 and Example 1 is that the fiberization process in step (3) is different;

[0118] Fiberization: Powder B was ground in a low-temperature airflow mill with an airflow temperature of 0℃, a grinding pressure of 0.70MPa, and a classifying wheel speed of 11000rpm to obtain powder C with an average particle size of 5.0μm.

[0119] Powder C is then ground using a high-temperature airflow mill with an airflow temperature of 80℃, a grinding pressure of 0.90MPa, and a classifying wheel speed of 11000rpm to obtain powder D.

[0120] Example 10

[0121] The difference between Example 10 and Example 1 is that the fiberization process in step (3) is different;

[0122] Fiberization: Powder B was ground in a low-temperature airflow mill with an airflow temperature of 0℃, a grinding pressure of 0.70MPa, and a classifying wheel speed of 12000rpm to obtain powder C with an average particle size of 4.7μm.

[0123] Powder C is then ground using a high-temperature airflow mill with an airflow temperature of 80℃, a grinding pressure of 0.90MPa, and a classifying wheel speed of 12000rpm to obtain powder D.

[0124] Example 11

[0125] The difference between Example 11 and Example 1 is that the fiberization process in step (3) is different;

[0126] Fiberization: Powder B was ground in a low-temperature airflow mill with an airflow temperature of 0℃, a grinding pressure of 0.70MPa, and a classifying wheel speed of 10000rpm to obtain powder C with an average particle size of 5.6μm.

[0127] Powder C is then ground using a high-temperature airflow mill with an airflow temperature of 90℃, a grinding pressure of 0.90MPa, and a classifying wheel speed of 12000rpm to obtain powder D.

[0128] Example 12

[0129] The difference between Example 12 and Example 1 is that the active material in step (2) is a negative electrode active material;

[0130] Premixing: Artificial graphite and carbon nanotubes are mixed evenly in a ball mill at a ratio of 92:6 and a ball-to-material ratio of 1:1 at 500 rpm to obtain powder A. Powder A and the heat-insulated binder PTFE are mixed in a double-motion mixer at a ratio of 98:2 for 30 minutes to obtain powder B.

[0131] Comparative Example 1

[0132] The difference between Comparative Example 1 and Example 1 is that the PTFE was not subjected to low-temperature high-speed grinding and shearing treatment, but was directly subjected to high-temperature airflow grinding and fiberization.

[0133] (3) Fiberization: Powder B is fiberized by high-temperature air jet milling with air jet milling machine. The air jet temperature is 80℃, the milling pressure is 0.90MPa, and the classifying wheel speed is 10000rpm to obtain powder D.

[0134] Comparative Example 2

[0135] The difference between Comparative Example 2 and Example 1 is that in step (3), powder C is fiberized at room temperature;

[0136] Powder C was subjected to air jet milling at an air jet temperature of 20℃, a grinding pressure of 0.90MPa, and a classifying wheel speed of 10000rpm to obtain powder D.

[0137] Comparative Example 3

[0138] The difference between Comparative Example 3 and Example 1 is that the PTFE content in step (1) is 8 wt% and the PTFE in step (3) is not subjected to low-temperature high-speed grinding and shearing treatment but is fiberized at room temperature.

[0139] Lithium iron phosphate (LFP), graphite, and carbon nanotubes were mixed evenly in a ball mill at a ratio of 90:1:1 and a ball-to-material ratio of 1:1 at 500 rpm to obtain powder A. Powder A and the heat-insulated binder PTFE were then mixed in a dual-motion mixer at a ratio of 90:8 for 30 minutes to obtain powder B.

[0140] Powder B was fiberized by air jet milling in a low-temperature air jet mill at a temperature of 20°C, a grinding pressure of 0.90 MPa, and a classifying wheel speed of 10,000 rpm to obtain powder D.

[0141] Comparative Example 4

[0142] The difference between Comparative Example 4 and Example 1 is that step (3) did not involve low-temperature high-speed grinding and shearing of PTFE, but instead used room-temperature fiberization;

[0143] Powder B was ground using a low-temperature airflow mill at a temperature of 20°C, a grinding pressure of 0.90 MPa, and a classifying wheel speed of 10,000 rpm to obtain powder D.

[0144] Comparative Example 5

[0145] The difference between Comparative Example 5 and Example 1 is that the temperature at which powder B is subjected to airflow milling and shearing in step (3) is different;

[0146] Powder B was ground using a low-temperature airflow mill with an airflow temperature of 15°C, a grinding pressure of 0.70 MPa, and a classifying wheel speed of 10,000 rpm to obtain powder C.

[0147] Comparative Example 6

[0148] The difference between Comparative Example 6 and Example 1 is that the temperature at which powder B is subjected to airflow milling and shearing in step (3) is different;

[0149] Powder B was ground using a low-temperature airflow mill with an airflow temperature of 19°C, a grinding pressure of 0.70 MPa, and a classifying wheel speed of 10,000 rpm to obtain powder C.

[0150] The thickness, tensile strength, and compaction density of the electrode films prepared in Examples 1-12 and Comparative Examples 1-6 were tested. The tensile strength test method was based on Part 2 of GB / T 1040.2-2022 Determination of Tensile Properties of Plastics: Test Conditions for Molded and Extruded Plastics. The test results are shown in Table 1.

[0151] Electrochemical performance testing method: The resistivity of the obtained electrode film was tested using the Yuaneng Technology BER2300 electrode resistance meter.

[0152] The test method for liquid absorption rate is as follows: take a 10×3cm membrane and weigh it, and record the initial weight as m1. After weighing, immerse the membrane in the electrolyte for 2 hours, then use tweezers to remove it, wipe off the free electrolyte on the surface, weigh it, and record the weight as m2. Then the liquid absorption rate = (m2-m1) / m1.

[0153] The resistivity and liquid absorption rate of the prepared electrode were measured using the above method.

[0154] Table 1

[0155]

[0156] Table 1 shows that the electrode films prepared using the dry process in Examples 1-12 of this application have a thickness of 115-152 μm, a tensile strength of 0.15-0.22 MPa, and a compaction density of 2.65-2.90 g / cm³. 3 (Example 12 is a negative electrode with a compaction density of 1.76); tensile strength, resistivity, and liquid absorption rate are as follows: Figure 5 , Figure 6 , Figure 7 and Figure 8 As shown.

[0157] In Comparative Example 1, the PTFE was not subjected to low-temperature high-speed grinding and shearing beforehand. Instead, micron-sized PTFE was directly mixed with nano-sized active materials and conductive agents and then subjected to high-temperature airflow grinding. Due to the poor dispersibility and inhomogeneity of the PTFE mixture, the fiberization effect was even worse, resulting in an electrode film with a tensile strength of 0.14 MPa and a compaction density of 2.78 g / cm³. 3 The electrode films were prone to cracking or breakage, and the film surface showed obvious unevenly dispersed PTFE. Comparison shows that this application, by first preparing PTFE into nano-sized particles under low-temperature, high-speed grinding and shearing conditions, followed by high-temperature, high-speed grinding, shearing, and fiberization treatment, significantly promotes the uniformity of PTFE dispersion and improves the fiberization effect, resulting in a significantly improved tensile strength of the prepared film.

[0158] Comparative Example 2 involved fiberizing PTFE at room temperature. Due to an unsuitable fiberization temperature, a continuous electrode film could not be obtained, and the film experienced band breakage during thinning. This indicates that to achieve a good fiberization effect, the fiberization temperature must reach a certain value.

[0159] Comparative Example 3 had an excessive PTFE content, lacked low-temperature high-speed shearing of PTFE, and used room-temperature fiberization; cracks appeared during the membrane thinning process, which greatly reduced the tensile strength of the membrane.

[0160] Comparative Example 4 did not undergo low-temperature high-speed grinding and shearing treatment of PTFE and instead used room-temperature fiberization; during the film formation process, the powder was stuck and had no tensile strength.

[0161] Comparative Examples 5 and 6 involved low-temperature airflow milling at temperatures close to the phase transition temperature of PTFE. At these temperatures, during the process of converting PTFE from micron-sized to nano-sized particles, the heat generated during the shearing process caused some PTFE to become fibrous. This hindered the conversion of PTFE into nano-sized particles, resulting in poor dispersion and uniformity of the final PTFE, leading to poor PTFE fiber formation and consequently reducing the tensile strength of the membrane. The comparison shows that before PTFE fiberization, it is not only necessary to convert PTFE into nano-sized particles but also to avoid premature PTFE fiberization due to excessively high shear temperatures during the nano-particle conversion process. Therefore, the shear temperature during the PTFE nanoparticle conversion process must be strictly controlled.

[0162] like Figure 7 As shown, the electrode sheet represented by Example 1 has the lowest resistivity, at 9 mΩ, while the electrode sheet of Comparative Example 3 has the highest resistivity. The resistivity of the electrodes of Comparative Examples 2 and 3 is also at least twice that of Example 1. This indicates that the resistivity of the electrode prepared in Example 1 of this application, by first subjecting PTFE to low-temperature high-speed grinding and shearing to achieve nanoscale, is only about 30% of the resistivity of the electrode prepared using micron-scale PTFE.

[0163] like Figure 8 As shown, the electrode sheet represented by Example 1 has the highest liquid absorption rate, reaching over 225%. The liquid absorption rates of the electrode sheets in Comparative Examples 1, 2, and 3 decrease sequentially, with the liquid absorption rate of Comparative Example 1 only reaching about 65% of that of Example 1. This indicates that Example 1 of this application, by first subjecting PTFE to low-temperature high-speed grinding and shearing to achieve a nanoscale size, improves the liquid absorption rate of the prepared electrode by more than 35% compared to the electrode prepared directly using micron-sized PTFE.

[0164] The above demonstrates that the dry electrode film prepared using the method of this application can significantly improve its tensile strength, compaction density, etc., and also significantly reduce the resistivity of the dry electrode and increase the liquid absorption rate.

[0165] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those described herein.

[0166] The above description is merely an embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing a dry electrode film, characterized in that, The method includes the following steps: Step S1: Mix and pulverize the polytetrafluoroethylene material, electrode active material, and conductive agent to obtain a pulverized mixture; the average particle size of the polytetrafluoroethylene material is 400~600μm; Step S2: Perform a single air jet milling and shearing process on the pulverized mixture to obtain a milled and sheared mixture; wherein, the conditions for the single air jet milling and shearing process include: air jet temperature of -10℃ to 10℃, compressed air jet pressure of 0.7 to 0.9 MPa, the single air jet milling and shearing process uses an air jet mill, and the classifying wheel speed is 8000 to 12000 rpm; Step S3: The grinding and shearing mixture is subjected to secondary airflow grinding and shearing fiberization to obtain fibrous material; the conditions for the secondary airflow grinding and shearing include: airflow temperature of 50℃~100℃, compressed airflow pressure of 0.7~0.9MPa, the secondary airflow grinding and shearing uses an airflow mill, and the classifying wheel speed is 8000~12000rpm; Step S4: Perform secondary fiberization on the fiberized material to obtain a dry electrode membrane; wherein, the secondary fiberization is performed by differential speed roller press for differential opening fiberization, the roller pressing temperature of the differential speed roller press is 60℃~120℃, and the roller pressing speed ratio is greater than 1:1 and less than or equal to 1:1.

5.

2. The method for preparing the dry electrode film according to claim 1, characterized in that, The temperature of the airflow in the first airflow grinding and shearing process is -5℃ to 5℃; And / or, the temperature of the airflow in the secondary airflow grinding and shearing process is 60~100℃; And / or, the speed of the classifying wheel in the primary airflow milling shearing is 10000~11000 rpm; And / or, the polytetrafluoroethylene material is a polytetrafluoroethylene dispersion resin with a molecular weight of 500,000 to 8,000,000 and a compression ratio of 100 to 3,000.

3. The method for preparing the dry electrode film according to claim 1, characterized in that, The temperature of the airflow in the first airflow grinding and shearing process is 0~5℃; And / or, the temperature of the airflow used for secondary airflow grinding and shearing is 70~100℃.

4. The method for preparing the dry electrode film according to claim 1, characterized in that, The airflow temperature in the secondary airflow grinding and shearing process is 80~100℃, and the classifying wheel speed is 10000~11000rpm.

5. The method for preparing a dry electrode film according to claim 2, characterized in that, The specific process of step S1 includes: mixing and pulverizing the electrode active material and the conductive agent to obtain powder A; mixing and pulverizing the polytetrafluoroethylene dispersion resin after heat preservation and the powder A to obtain the pulverized mixture; And / or, the polytetrafluoroethylene dispersion resin is kept at -8°C to -12°C for 8 to 12 hours before mixing.

6. The method for preparing a dry electrode film according to claim 5, characterized in that, The electrode active material and the conductive agent are mixed using a ball mill or a high-speed mixer, wherein the high-speed mixer rotates at 400-600 rpm; and the ball-to-material ratio of the ball mill is 1:(1-2). And / or, the polytetrafluoroethylene dispersion resin and the powder A are mixed using a dual-motion mixer or a three-dimensional motion mixer; the mixing time in the dual-motion mixer is 20~40 min.

7. The method for preparing a dry electrode film according to any one of claims 1 to 3, characterized in that, The average particle size of the pulverized mixture is 8~12μm; And / or, the average particle size of the grinding and shearing mixture is 3~6μm.

8. The method for preparing a dry electrode film according to any one of claims 1 to 3, characterized in that, The air jet mill is a fluidized bed air jet mill.

9. The method for preparing a dry electrode film according to claim 5, characterized in that, The weight ratio of the electrode active material to the conductive agent is (90~95):(0~5), and the conductive agent is not 0; And / or, the weight ratio of the powder A to the polytetrafluoroethylene dispersion resin after heat preservation is (95~99):(1~5); And / or, the electrode active material includes a positive electrode active material and a negative electrode active material; wherein, the positive electrode active material is selected from at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt aluminum oxide, and manganese dioxide; and the negative electrode active material is selected from at least one of artificial graphite, natural graphite, lithium titanate, silicon-oxygen anode material, and silicon-carbon. And / or, the conductive agent is selected from at least one of conductive carbon black, graphite, graphene, carbon nanotubes and carbon fibers.

10. A dry electrode film, characterized in that, The dry electrode film is prepared by the method described in any one of claims 1 to 9.

11. The dry electrode film according to claim 10, characterized in that, The dry electrode film has a thickness of 100~152μm, a tensile strength of 0.15~0.4 MPa, and a compaction density of 2.50~3.30 g / cm³. 3 .

12. A method for preparing a dry electrode, characterized in that, The method for preparing the dry electrode includes the following steps: rolling a dry electrode film onto at least one side of a current collector; wherein the dry electrode film is the dry electrode film according to claim 10 or 11.

13. The method for preparing a dry electrode according to claim 12, characterized in that, The temperature of the roller pressing is 0℃~100℃; And / or, the current collector is selected from at least one of copper foil, aluminum foil, nickel foil, stainless steel mesh, aluminum mesh, and nickel mesh.

14. A battery, comprising electrodes, a separator, and an electrolyte; characterized in that, The electrode is prepared by the dry electrode preparation method according to claim 12 or 13.

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