Dry-method electrode film and preparation method therefor, electrode and battery

Abstract

The present application belongs to the technical field of batteries. Disclosed are a dry-method electrode film and a preparation method therefor, an electrode and a battery. The method of the present application comprises: mixing polytetrafluoroethylene, an active substance and an electrically conductive agent, and crushing same, so as to obtain a crushed mixture; subjecting the crushed mixture to primary airflow grinding and shearing, so as obtain a ground and sheared mixture, wherein conditions of the primary shearing comprise: the airflow temperature is -10 to 10°C, the airflow pressure is 0.7-0.9 MPa, and the rotation speed is 8000-12000 rpm; subjecting the ground and sheared mixture to secondary airflow grinding, shearing and fibration, so as to obtain a fibration material; and subjecting the fibration material to a secondary fibration treatment, so as to obtain a dry-method electrode film. The method of the present application can significantly improve the tensile strength of an electrode film, improve the liquid absorption rate of an electrode and reduce the resistivity of the electrode.

Description

Dry electrode membrane and preparation method thereof, electrode and battery

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 24, 2024, with application number 202411922353.7. The entire contents of the above application are incorporated by reference into this application.

[0002] Technical Field

[0003] The present application relates to the field of battery technology, and in particular to a dry electrode membrane and a preparation method thereof, an electrode and a battery.

[0004] Background Art

[0005] Traditional lithium battery electrodes are usually prepared by coating. First, the binder, solvent and conductive agent are configured into a conductive slurry, and then the electrode active material is added in batches to make a uniform slurry. Finally, it is evenly coated on the current collector through a coating equipment, and then dried, rolled and cut into electrodes.

[0006] Technical issues

[0007] The above method has high requirements on the dispersion of conductive agent, slurry viscosity control and coating equipment. The active material content of the electrode is low, the production process is strictly controlled, and thick electrodes cannot be produced. In addition, the solvent drying and solvent recovery processes consume a lot of energy and are costly, which is not environmentally friendly.

[0008] In order to solve the above-mentioned shortcomings, a dry electrode process has been developed. The main steps of this process are to mix the conductive agent, binder, and electrode active material evenly, and then fiberize the binder PTFE through high-speed shearing to form a fiber network, which binds the active material and the conductive agent, and finally further fiberize it through rolling to form a self-supporting electrode membrane and coat it on the current collector to obtain a double-sided electrode. Among them, the fiberization step is the key step of the dry electrode process. It is necessary to use a huge shear force to make the PTFE evenly dispersed and fiberized. The mainstream methods include air flow shearing, high-speed stirring shearing, ball milling shearing, etc. However, the conventional fiberization process requires a high binder content (such as more than 8wt%), a high degree of binder fiberization, high shear force requirements for the equipment, and high uniformity requirements for the mixture. The production time is long, and it is difficult to achieve large-scale production. The main reason for this contradiction is the special properties of PTFE, the binder required for this process. The electrode membrane formation of this process requires PTFE to be evenly dispersed between the electrode materials and to form a nano-fiber network through shearing and stretching. The higher the molecular weight of PTFE, the easier it is for the fiberization process to occur. However, the high-molecular-weight PTFE on the market needs to avoid agglomeration during transportation, and is often made into particles with a secondary particle size of 500~700μm. For positive electrode active materials with a particle size generally less than 30μm and conductive agents with nano-particle size, it is easy to cause segregation due to uneven mixing during the mixing process, resulting in uneven fiberization effect.

[0009] Technical Solutions

[0010] The present application provides a dry electrode membrane and its preparation method, electrode and battery to solve the problems of uneven mixing and low fiberization of polytetrafluoroethylene binder in the dry electrode process, which leads to low strength of the electrode membrane.

[0011] According to one aspect of the present application, a method for preparing a dry electrode membrane is provided, the method comprising the following steps:

[0012] Step S1: mixing and crushing a polytetrafluoroethylene material, an electrode active material, and a conductive agent to obtain a crushed mixture;

[0013] Step S2: performing a primary airflow grinding and shearing on the pulverized mixture to obtain a ground and sheared mixture; wherein the conditions for the primary airflow grinding and shearing include: an airflow temperature of -10°C to 10°C, a compressed airflow pressure of 0.7 to 0.9 MPa, and a shearing speed of 8000 to 12000 rpm;

[0014] Step S3: performing secondary airflow grinding and shearing fiberization on the ground and sheared mixture to obtain a fiberized material;

[0015] Step S4: performing secondary fiberization treatment on the fiberized material to obtain a dry electrode membrane.

[0016] Optionally, the air flow temperature during the primary air flow grinding and shearing is -5°C to 5°C; optionally 0 to 5°C.

[0017] Optionally, the air flow temperature of the secondary air flow grinding and shearing is 50° C. to 100° C., the compressed air flow pressure is 0.7 to 0.9 MPa, and the shearing speed is 8000 to 12000 rpm.

[0018] Optionally, the air flow temperature of the secondary air flow grinding and shearing is 60-100°C; optionally 70-100°C; further optionally 80-100°C.

[0019] Optionally, the shearing speed of the primary air flow grinding and shearing is 10000~11000 rpm.

[0020] Optionally, the shearing speed of the secondary air flow grinding and shearing is 10000~11000 rpm.

[0021] Optionally, the polytetrafluoroethylene material is a polytetrafluoroethylene dispersion resin having an average particle size of 400-600 μm, a molecular weight of 500,000-8 million, and a compression ratio of 100-3000.

[0022] Optionally, the polytetrafluoroethylene dispersion resin is kept at -8°C to -12°C for 8 to 12 hours before mixing.

[0023] Optionally, the specific process of step S1 includes: mixing and crushing the electrode active material and the conductive agent to obtain powder A; mixing and crushing the heat-insulated polytetrafluoroethylene dispersion resin and the powder A to obtain a crushed mixture.

[0024] Optionally, the electrode active material and the conductive agent are mixed using a ball mill or a high-speed mixer, and the rotation speed of the high-speed mixer is 400-600 rpm.

[0025] Optionally, the ball-to-material ratio of the ball mill is 1:(1~2).

[0026] Optionally, the polytetrafluoroethylene dispersion resin and the powder A are mixed using a double-motion mixer or a three-dimensional motion mixer.

[0027] Optionally, the mixing time of the polytetrafluoroethylene dispersion resin and the powder A in the double-motion mixer is 20 to 40 minutes.

[0028] Optionally, the average particle size of the pulverized mixture is 8-12 μm.

[0029] Optionally, the average particle size of the ground and sheared mixture is 3-6 μm.

[0030] Optionally, the first air flow milling and shearing and / or the second air flow milling and shearing adopts an air flow mill.

[0031] Optionally, the jet mill is a fluidized bed jet mill.

[0032] Optionally, the secondary fiberization treatment uses a differential speed roller press to perform differential speed fiberization.

[0033] Optionally, the rolling temperature of the differential roller press is 60°C~120°C, and the rolling speed ratio is 1:(1~1.5).

[0034] Optionally, the weight ratio of the electrode active material to the conductive agent is (90-95): (0-5).

[0035] Optionally, the weight ratio of powder A to the heat-insulated polytetrafluoroethylene dispersion resin is (95-99): (1-3).

[0036] Optionally, 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 oxide negative electrode material and silicon carbon.

[0037] Optionally, the conductive agent is selected from at least one of conductive carbon black, graphite, graphene, carbon nanotubes, carbon fibers, acetylene black and Ketjen black.

[0038] According to a second aspect of the present application, a dry electrode membrane is provided, which is prepared using the above-mentioned dry electrode membrane preparation method.

[0039] Optionally, 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 / cm 3 .

[0040] According to the third aspect of the present application, a method for preparing a dry electrode is provided, which comprises the following steps: rolling a dry electrode film onto at least one side of a current collector; wherein the dry electrode film is the above-mentioned dry electrode film.

[0041] Optionally, the rolling temperature is 0°C to 100°C.

[0042] Optionally, 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.

[0043] According to a fourth aspect of the present application, a battery is provided, comprising an electrode, a diaphragm and an electrolyte; the electrode is an electrode prepared by the above-mentioned dry electrode preparation method.

[0044] Beneficial effects

[0045] The technical solution of this application provides a method for preparing a dry electrode membrane. Based on the phase transition temperature of the binder PTFE, different temperature shearing methods are used. First, low-temperature high-speed shearing is performed to reduce the binder particle size to the nanometer level, making the distribution more uniform. Then, high-temperature high-speed shearing is performed to increase the degree of binder fiberization. The resulting electrode membrane has higher tensile strength, uses less binder, and reduces the anisotropy after film formation. This method also breaks through the electrode thickness limit and can produce electrodes with a thickness of 30μm to 3mm, and is suitable for different battery systems. Compared with the traditional coating electrode process, the drying step is eliminated, the powder loss rate of the electrode piece is reduced, and thick electrode pieces can be produced to meet the manufacturing needs of higher energy density battery cells.

[0046] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description.

[0047] BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The drawings that constitute part of this application are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an improper limitation on this application. In the drawings:

[0049] FIG1 shows a flow chart of the preparation process of the dry-process electrode membrane and electrode according to an embodiment of the present application;

[0050] FIG2 shows an SEM image of PTFE coated on the surface of the positive electrode active material before fiberization in Example 1 of the present application;

[0051] FIG3 shows a SEM image of the PTFE fiberization effect in Example 1 of the present application;

[0052] FIG4 shows a SEM image of the surface of the electrode membrane in Example 1 of the present application;

[0053] FIG5 shows a comparison of the longitudinal tensile strength of the electrode films of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 of the present application;

[0054] FIG6 shows a comparison of the transverse tensile strength of the electrode films of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 of the present application;

[0055] FIG7 shows a comparison of the electrode resistivity of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 of the present application;

[0056] FIG8 shows a comparison of the liquid absorption rates of electrodes of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 of the present application.

[0057] Modes for Carrying Out the Invention

[0058] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0059] In the related art, methods such as air flow shearing, high-speed stirring shearing, and ball milling shearing are usually used to fiberize PTFE binders. These methods require a relatively high amount of binder, such as more than 8wt%, and the secondary particle size of the PTFE used is 500-700μm. This is unevenly mixed with the active material and the conductive agent, which can easily cause segregation and may produce an uneven fiberization effect, thereby reducing the tensile strength and other properties of the dry electrode membrane. Therefore, based on the phase transition temperature of the binder PTFE, this application uses a targeted shearing method at different temperatures to improve the mixing uniformity and fiberization degree of PTFE.

[0060] According to one aspect of the present application, a method for preparing a dry electrode membrane is provided, the method comprising the following steps:

[0061] Step S1: mixing and crushing a polytetrafluoroethylene material, an electrode active material, and a conductive agent to obtain a crushed mixture;

[0062] Step S2: performing a primary airflow grinding and shearing on the pulverized mixture to obtain a ground and sheared mixture; wherein the conditions for the primary airflow grinding and shearing include: an airflow temperature of -10°C to 10°C, a compressed airflow pressure of 0.7 to 0.9 MPa, and a shearing speed of 8000 to 12000 rpm;

[0063] Step S3: performing secondary airflow grinding and shearing on the ground and sheared mixture to obtain a fiberized material;

[0064] Step S4: performing secondary fiberization treatment on the fiberized material to obtain a dry electrode membrane.

[0065] The air flow temperature of the primary air flow grinding and shearing in the present application is selected from any value among -10℃, -9℃, -8℃, -7℃, -6℃, -5℃, -4℃, -3℃, -1℃, 0℃, 1℃, 2℃, 3℃, 4℃, 5℃, 6℃, 7℃, 8℃, 9℃, 10℃, or any range between two thereof; the air flow temperature of the secondary air flow grinding and shearing is selected from any value among 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, or any range between two thereof; for example, the primary air flow grinding temperature is -5~10℃, optionally -5~5℃, further optionally 0~5℃, and for example 0℃; the secondary air flow grinding temperature is 50~100℃, optionally 60~100℃, further optionally 70~100℃, further optionally 80~100℃, and for example 80℃.

[0066] The shear speed of the primary air flow grinding and shearing in the present application is any value among 8000 rpm, 8500 rpm, 9000 rpm, 9500 rpm, 10000 rpm, 10500 rpm, 11000 rpm, 11500 rpm, 12000 rpm, or a range value between any two of them; for example, 10000 rpm; the shear speed of the secondary air flow grinding and shearing is any value among 8000 rpm, 8500 rpm, 9000 rpm, 9500 rpm, 10000 rpm, 10500 rpm, 11000 rpm, 11500 rpm, 12000 rpm, or a range value between any two of them; for example, 10000 rpm; the two shear speeds may be the same or different.

[0067] The preparation method of the dry electrode membrane provided in the present application is based on the phase transition temperature of the binder PTFE (PTFE phase transition temperature is 19°C) and adopts a shearing method at different temperatures. The PTFE-containing mixture is first subjected to low-temperature high-speed shearing to reduce the PTFE binder particle size from the micron level to the nanometer level, making the mixture more evenly dispersed. During this low-temperature high-speed shearing process, since the temperature is lower than the phase transition temperature, theoretically, the PTFE will basically not undergo fiberization. However, heat will be generated during the shearing process. If the preset fiberization effect is to be achieved, it is appropriate to control the above-mentioned low-temperature high-speed shearing temperature to -10~10°C. Since the shearing speed is similar to the shearing speed of fiberization, high-speed grinding and shearing are both adopted. Conventional PTFE with large micron-level particles can be ground and sheared to the nanometer level. After the PTFE is reduced to the nanometer size, it is coated on the active material. This greatly improves the uniformity of the mixing of the various raw materials and is more conducive to the subsequent fiberization of the PTFE mixture. After the PTFE mixture is made into the nanometer level, it is subjected to high-temperature high-speed shearing, which makes the PTFE fiberized to a higher degree, the tensile strength of the prepared electrode membrane is higher, the binder content is reduced, and the anisotropy after the membrane is formed is also reduced.

[0068] The present application uses continuous dry rolling to produce electrodes. The production process does not require the use of solvents and there is no drying process, which reduces production energy consumption. The present application allows the electrode binder to exist in a fibrous state, so that the positive electrode active material and the conductive agent particles are in closer contact, thereby increasing the electrode compaction density, reducing the electrode sheet resistance, and lowering the electrode sheet powder loss rate. The present application uses temperature to control the PTFE binder particle size and fiberization degree, thereby improving the uniformity of the mixture, reducing the difficulty of electrode membrane molding, and increasing the membrane tensile strength.

[0069] In some embodiments, the polytetrafluoroethylene material is a polytetrafluoroethylene dispersion resin having an average particle size of 400-600 μm, a molecular weight of 500,000-8 million, and a compression ratio of 100-3000.

[0070] The improved method of this application primarily addresses the problem of commonly used high-molecular-weight PTFE being manufactured into large secondary particles with a size of 500-700 μm to prevent agglomeration during transportation. In related art, this large-particle PTFE is often directly mixed with active materials and conductive agents, resulting in poor mixing of the micron-sized PTFE and other nano-sized materials, which in turn affects the PTFE's fiberization and electrode membrane strength. By employing the improved method of this application, micron-sized PTFE can be manufactured into nano-sized particles, further improving its dispersion uniformity.

[0071] In some embodiments, the polytetrafluoroethylene dispersion resin is kept at -8°C to -12°C for 8 to 12 hours, for example, at -10°C for 10 hours, before mixing. This is done to prevent further agglomeration of the PTFE, which would increase particle size and complicate subsequent powder mixing.

[0072] In some embodiments, the specific process of step S1 includes: mixing and crushing the electrode active material and the conductive agent to obtain a powder A; and mixing the heat-insulated polytetrafluoroethylene dispersion resin with the powder A to obtain a crushed mixture. The present application can further improve the mixing uniformity by using a stepwise mixing method.

[0073] In some embodiments, the electrode active material and the conductive agent are mixed using a ball mill or a high-speed mixer, the speed of the high-speed mixer is 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 double-motion mixer or a three-dimensional motion mixer; the mixing time in the double-motion mixer is 20~40 minutes.

[0074] The present application selects different mixing equipment and process conditions according to different mixed materials, and specifically improves the dispersion and uniformity of each mixture; when PTFE and powder A are mixed in a double-motion or three-dimensional motion mixer, the mixing time is controlled as mentioned above, 20 to 40 minutes, for example, 30 minutes; excessive shearing can be avoided, which causes the PTFE to fiberize before the subsequent high-temperature and high-speed shearing, which is not conducive to the subsequent PTFE fiberization effect.

[0075] In some embodiments, the average particle size of the pulverized mixture is 8-12 μm; the average particle size of the ground and sheared mixture is 3-6 μm, for example, 3-4 μm. The present application gradually reduces the particle size of the mixture through the pulverization and grinding and shearing processes, which facilitates the subsequent airflow grinding and shearing process.

[0076] In some embodiments, the first air flow grinding and shearing and / or the second air flow grinding and shearing adopts an air flow grinder; for example, a fluidized bed air flow mill is used. The present application adopts the above-mentioned equipment in the two grinding and shearing. Compared with a mixer or a ball mill, the heat generated by the air flow mill during the grinding process will be promptly carried away by the low-temperature air flow, avoiding the deformation, fiberization, and uneven distribution of PTFE caused by local heat accumulation in the equipment cavity. In the fiberization process, a high-temperature air flow (specifically, an air flow above the phase transition temperature of PTFE, i.e., above 19°C) can be used to cause the PTFE to undergo a phase change, thereby promoting the fiberization of PTFE. When the temperature is below 19°C, the PTFE molecular chain is a 13 / 6 helix. At 19°C, a phase change occurs, and the molecules are slightly untied to form a 15 / 7 helix, which is easier to fiberize.

[0077] In some embodiments, the secondary fiberization treatment utilizes a differential speed roller press for differential fiberization; the roller pressing temperature can be 60°C to 120°C, and the roller pressing speed ratio can be 1:(1-1.5). The above roller pressing conditions employed in this application enable the PTFE mixture to be fully and completely fiberized, thereby forming an electrode membrane.

[0078] In some embodiments, the weight ratio of the electrode active material to the conductive agent is (90-95):(0-5), for example, 92:5; the weight ratio of powder A to the insulated polytetrafluoroethylene dispersion resin is (95-99):(1-5), for example, 98:2. In this application, the PTFE content is controlled within a range of 1-5, and fiberization after mixing with other components achieves a more synergistic effect, avoiding cracks in the membrane caused by excessive or insufficient PTFE content.

[0079] 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; and the negative electrode active material is selected from at least one of artificial graphite, natural graphite, lithium titanate, silicon oxide negative electrode material, and silicon carbon. The electrode film preparation method of the present 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 may also be used according to actual needs.

[0080] The conductive agent in this application mainly uses carbon nanotubes (CNTs) and graphite. Since carbon nanotubes and PTFE fibers have similar one-dimensional linear morphologies, the two may produce a synergistic effect, connecting more active material particles, thereby building a more effective electron flow network. The role of graphite is that its lamellar structure has good lubricity, which can assist in the powder film thinning process.

[0081] According to a second aspect of the present application, a dry electrode membrane is provided, which is prepared using the above-mentioned dry electrode membrane preparation method.

[0082] 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; for example, 0.15-0.25; and the compacted density is 2.50-3.30 g / cm 3 , for example 2.50~3.0g / cm 3 .

[0083] The electrode membrane prepared by the method of the present application has good PTFE dispersion, good uniformity and high degree of fiberization, which improves the mechanical properties such as tensile strength of the electrode membrane, increases the compaction density of the electrode membrane, and thus increases the energy density of the battery; this method is also suitable for thicker electrode membranes.

[0084] According to the third aspect of the present application, a method for preparing a dry electrode is provided, which comprises the following steps: rolling a dry electrode film onto at least one side of a current collector; wherein the dry electrode film is the above-mentioned dry electrode film.

[0085] In some embodiments, the rolling temperature during the coating 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.

[0086] The electrode film prepared by the method of the present application can be coated on one side 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.

[0087] According to a fourth aspect of the present application, a battery is provided, comprising an electrode, a diaphragm and an electrolyte; the electrode is an electrode prepared by the above-mentioned dry electrode preparation method.

[0088] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0089] The raw materials and equipment used in the examples of this application are products of related technologies and are commercially available. Example 1

[0090] The preparation process of battery electrodes is shown in Figure 1 and includes the following steps:

[0091] (1) PTFE insulation: PTFE secondary particle size is 570 μm, molecular weight is 7.7 million, and compression ratio is 100-300; PTFE is kept at -10°C for 10 hours;

[0092] (2) Premixing: Lithium iron phosphate (LFP), graphite, and carbon nanotubes were mixed uniformly in a ball mill at a ratio of 92:2:3 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 placed in a double-motion mixer at a ratio of 98:2 and mixed for 30 minutes to obtain powder B, whose average particle size was 10.4 μm. The morphology of the PTFE-coated active material after mixing is shown in Figure 2.

[0093] (3) Fiberization: Powder B was ground with a jet mill at low temperature, with an air flow temperature of 0°C, a grinding pressure of 0.70 MPa, and a classifying wheel speed of 10,000 rpm to obtain powder C with an average particle size of 3.6 μm. The effect of PTFE fiberization is shown in Figure 3.

[0094] Powder C was then ground using a jet mill with high-temperature airflow at an airflow temperature of 80°C, a grinding pressure of 0.90 MPa, and a classifying wheel speed of 10,000 rpm to obtain powder D.

[0095] (4) Film formation: Powder D was pulverized and fiberized into a film using a multi-stage differential speed roller press with a speed ratio of 1:1.5 and a temperature of 120°C / 100°C / 60°C. The film was pressed once to obtain an electrode film with a thickness of 120 μm, a tensile strength of 0.25 MPa, and a compaction density of 2.90 g / cm 3 ;The morphology of the membrane is shown in Figure 4;

[0096] (5) Coating the current collector: After the membrane is formed, it is rolled into electrodes on both sides of the aluminum foil current collector at the same time. The rolling temperature is 50°C to obtain the positive electrode sheet. Example 2

[0097] The difference between Example 2 and Example 1 is that the fiberization process in step (3) is different;

[0098] Fiberization: Powder B was ground using a jet mill at low temperature at an air flow temperature of -10°C, a grinding pressure of 0.80 MPa, and a classifying wheel speed of 10,000 rpm to obtain powder C with an average particle size of 4.1 μm.

[0099] The powder C was then ground with a jet mill at high temperature, with an air flow temperature of 90°C, a grinding pressure of 0.90 MPa, and a classifying wheel speed of 10,000 rpm to obtain powder D|. Example 3

[0100] Example 3 is different from Example 1 in that the fiberization process in step (3) is different;

[0101] Fiberization: Powder B was ground with a jet mill (model) at low temperature with an air flow 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 3.2 μm.

[0102] Powder C was then ground using a jet mill with high-temperature airflow at an airflow temperature of 100°C, a grinding pressure of 0.90 MPa, and a classifying wheel speed of 10,000 rpm to obtain powder D. Example 4

[0103] The difference between Example 4 and Example 1 is that the fiberization process in step (3) is different;

[0104] Fiberization: Powder B was ground using a jet mill at low temperature with an air flow 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.

[0105] Powder C was then ground using a jet mill with high-temperature airflow at 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. Example 5

[0106] The difference between Example 5 and Example 1 is that the fiberization process in step (3) is different;

[0107] Fiberization: Powder B was ground with a jet mill at low temperature at an air flow temperature of 10°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 3.5 μm.

[0108] Powder C was then ground using a jet mill with high-temperature airflow at an airflow temperature of 60°C, a grinding pressure of 0.90 MPa, and a classifying wheel speed of 10,000 rpm to obtain powder D. Example 6

[0109] The difference between Example 6 and Example 1 is that the fiberization process in step (3) is different;

[0110] Fiberization: Powder B was ground using a jet mill at low temperature at an air flow 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.

[0111] Powder C was then ground using a jet mill with high-temperature airflow at 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. Example 7

[0112] The difference between Example 7 and Example 1 is that the fiberization process in step (3) is different;

[0113] Fiberization: Powder B was ground using a jet mill at low temperature with an air flow temperature of 0°C, a grinding pressure of 0.70 MPa, and a classifying wheel speed of 8000 rpm to obtain powder C with an average particle size of 5.4 μm.

[0114] Powder C was then ground using a jet mill with high-temperature airflow at an airflow temperature of 80°C, a grinding pressure of 0.90 MPa, and a classifying wheel speed of 8000 rpm to obtain powder D. Example 8

[0115] The difference between Example 8 and Example 1 is that the fiberization process in step (3) is different;

[0116] Fiberization: Powder B was ground using a jet mill at low temperature with an air flow temperature of 0°C, a grinding pressure of 0.70 MPa, and a classifying wheel speed of 9000 rpm to obtain powder C with an average particle size of 6.1 μm.

[0117] Powder C was then ground using a jet mill with high-temperature airflow at an airflow temperature of 80°C, a grinding pressure of 0.90 MPa, and a classifying wheel speed of 9000 rpm to obtain powder D. Example 9

[0118] The difference between Example 9 and Example 1 is that the fiberization process in step (3) is different;

[0119] Fiberization: Powder B was ground using a jet mill at low temperature with an air flow temperature of 0°C, a grinding pressure of 0.70 MPa, and a classifying wheel speed of 11,000 rpm to obtain powder C with an average particle size of 5.0 μm.

[0120] Powder C was then ground using a jet mill with high-temperature airflow at an airflow temperature of 80°C, a grinding pressure of 0.90 MPa, and a classifying wheel speed of 11,000 rpm to obtain powder D. 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 using a jet mill at low temperature with an air flow temperature of 0°C, a grinding pressure of 0.70 MPa, and a classifying wheel speed of 12,000 rpm to obtain powder C with an average particle size of 4.7 μm.

[0123] Powder C was then ground using a jet mill with high-temperature airflow at an airflow temperature of 80°C, a grinding pressure of 0.90 MPa, and a classifying wheel speed of 12,000 rpm to obtain powder D. Example 11

[0124] The difference between Example 11 and Example 1 is that the fiberization process in step (3) is different;

[0125] Fiberization: Powder B was ground using a jet mill at low temperature with an air flow temperature of 0°C, a grinding pressure of 0.70 MPa, and a classifying wheel speed of 10,000 rpm to obtain powder C with an average particle size of 5.6 μm.

[0126] Powder C was then ground using a jet mill with high-temperature airflow at an airflow temperature of 90°C, a grinding pressure of 0.90 MPa, and a classifying wheel speed of 12,000 rpm to obtain powder D. Example 12

[0127] The difference between Example 12 and Example 1 is that the active material in step (2) is a negative electrode active material;

[0128] Premixing: Artificial graphite and carbon nanotubes were mixed uniformly 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 were placed in a double-motion mixer at a ratio of 98:2 and mixed for 30 minutes to obtain powder B. Comparative Example 1

[0129] The difference between Comparative Example 1 and Example 1 is that the PTFE is not subjected to low-temperature high-speed grinding and shearing treatment, but is directly subjected to high-temperature airflow grinding and fiberization;

[0130] (3) Fiberization: Powder B was fiberized by high-temperature air flow grinding in an air flow grinder with an air flow temperature of 80°C, a grinding pressure of 0.90 MPa, and a classifying wheel speed of 10,000 rpm to obtain powder D. Comparative Example 2

[0131] The difference between Comparative Example 2 and Example 1 is that in step (3), the powder C is fiberized at room temperature;

[0132] Powder C was jet milled with a jet mill at an air flow temperature of 20°C, a grinding pressure of 0.90 MPa, and a classifying wheel speed of 10,000 rpm to obtain powder D. Comparative Example 3

[0133] The difference between Comparative Example 3 and Example 1 is that the PTFE content in step (1) is 8 wt% and in step (3) the PTFE is not subjected to low-temperature high-speed grinding and shearing treatment but is subjected to room-temperature fiberization;

[0134] Lithium iron phosphate (LFP), graphite, and carbon nanotubes were mixed uniformly in a ball mill at a ratio of 90:1:1 at 500 rpm to obtain powder A. Powder A and the heat-insulated binder PTFE were placed in a double-motion mixer at a ratio of 90:8 and mixed for 30 minutes to obtain powder B.

[0135] Powder B was subjected to air flow grinding and fiberization in a low-temperature air flow grinder at an air flow temperature of 20°C, a grinding pressure of 0.90 MPa, and a classifying wheel speed of 10,000 rpm to obtain powder D. Comparative Example 4

[0136] The difference between Comparative Example 4 and Example 1 is that in step (3), the PTFE is not subjected to low-temperature high-speed grinding and shearing treatment and is subjected to room-temperature fiberization;

[0137] Powder B was ground with a jet mill at low temperature at an air flow temperature of 20°C, a grinding pressure of 0.90 MPa, and a classifying wheel speed of 10,000 rpm to obtain powder D. Comparative Example 5

[0138] The difference between Comparative Example 5 and Example 1 is that the temperature of airflow grinding and shearing of powder B in step (3) is different;

[0139] Powder B was ground with a jet mill at low temperature at an air flow temperature of 15°C, a grinding pressure of 0.70 MPa, and a classifying wheel speed of 10,000 rpm to obtain powder C. Comparative Example 6

[0140] The difference between Comparative Example 6 and Example 1 is that the temperature of airflow grinding and shearing of powder B in step (3) is different;

[0141] Powder B was ground with a jet mill at low temperature at an air flow temperature of 19° C., a grinding pressure of 0.70 MPa, and a classifying wheel speed of 10,000 rpm to obtain powder C.

[0142] The thickness, tensile strength, and compacted density of the electrode films prepared in Examples 1 to 12 and Comparative Examples 1 to 6 were tested. The tensile strength test method was based on the test results in accordance with Part 2: Test Conditions for Molded and Extruded Plastics, part of GB / T 1040.2-2022 Plastics - Determination of Tensile Properties. The test results are shown in Table 1.

[0143] Electrochemical performance testing method: The resistivity of the obtained electrode film was tested using Yuanneng Technology BER2300 electrode resistance meter.

[0144] The test method for liquid absorption rate is: take a 10ⅹ3cm membrane and weigh it, record it as the front weight m1, soak the membrane in the electrolyte for 2 hours after weighing, then use tweezers to remove the free electrolyte on the surface and weigh it, record it as m2, then the liquid absorption rate = (m2-m1) / m1.

[0145] The resistivity and liquid absorption rate of the prepared electrode were tested using the above method.

[0146] Table 1

[0147]

[0148] The test data in Table 1 show that the electrode films prepared by the dry process of Examples 1 to 12 of the present application have a thickness of 115 to 152 μm, a tensile strength of 0.15 to 0.22 MPa, and a compaction density of 2.65 to 2.90 g / cm 3 (Example 12 is a negative electrode with a compaction density of 1.76); the tensile strength, resistivity, and liquid absorption rate are shown in Figures 5, 6, 7, and 8.

[0149] In the preparation method of Comparative Example 1, the PTFE was not subjected to low-temperature high-speed grinding and shearing first. Instead, the micron-sized PTFE was mixed with the nano-sized active material and conductive agent and then directly subjected to high-temperature airflow grinding. Due to the poor dispersion and unevenness of the PTFE mixture, the fiberization effect was even worse. The tensile strength of the electrode membrane prepared was 0.14 MPa; the compacted density was 2.78 g / cm 3 The electrode membrane is prone to cracking or breaking, and the membrane surface has obvious uneven dispersion of PTFE. By comparison, it can be seen that the present application can significantly promote the uniformity of PTFE dispersion and better fiberization effect by first preparing PTFE into nano-sized particles under low-temperature and high-speed grinding and shearing conditions, and then subjecting it to high-temperature and high-speed grinding and shearing fiberization treatment, thus significantly improving the tensile strength of the prepared membrane.

[0150] Comparative Example 2 used room temperature fiberization of PTFE. However, due to the inappropriate fiberization temperature, a continuous electrode membrane could not be obtained, and the membrane was broken during thinning. This indicates that to achieve a good fiberization effect for PTFE, the fiberization temperature must reach a certain value.

[0151] In Comparative Example 3, the PTFE content is too high, the PTFE is not subjected to low-temperature high-speed shearing, and room-temperature fiberization is adopted; cracks are formed during the thinning process of the diaphragm, which greatly reduces the tensile strength of the diaphragm.

[0152] In Comparative Example 4, the PTFE was not subjected to low-temperature high-speed grinding and shearing treatment and was subjected to room-temperature fiberization; during the film-forming process, the powder meshed and stuck, resulting in no tensile strength.

[0153] Comparative Examples 5 and 6 employ low-temperature airflow milling at a temperature close to the PTFE phase transition temperature. At this temperature, the PTFE undergoes partial fiberization due to heat generated during the shearing process during the production of nanoparticles from micron-sized particles. This hinders the effectiveness of the PTFE nanoparticles, resulting in poor dispersion and uniformity of the resulting PTFE, poor PTFE fiber quality, and reduced tensile strength of the diaphragm. This comparison demonstrates that prior to fiberization, not only must the PTFE be nanosized, but also premature fiberization during the nanoparticle production process, which could occur due to excessively high shear temperatures, must be avoided. Therefore, the shear temperature during the PTFE nanoparticle production process must be strictly controlled.

[0154] As shown in Figure 7, the electrode sheet represented by Example 1 has the lowest resistivity, at 9 mΩ. The electrode sheet of Comparative Example 3 has the highest resistivity. The electrode sheet resistivities of Comparative Examples 2 and 3 are also at least 2 times higher than that of Example 1. This shows that Example 1 of the present application, by first grinding and shearing PTFE at low temperature and high speed to reach the nanoscale, has an electrode resistivity of only about 30% of that of an electrode made with micron-sized PTFE.

[0155] As shown in Figure 8, the liquid absorption rate of the electrode sheet represented by Example 1 is the highest, reaching over 225%. The liquid absorption rates of the electrode sheets of Comparative Examples 1, 2, and 3 decrease in turn, and the liquid absorption rate of Comparative Example 1 is only about 65% of that of Example 1. This shows that the liquid absorption rate of the electrode prepared in Example 1 of the present application is more than 35% higher than that of the electrode prepared directly using micron-grade PTFE after first subjecting the PTFE to low-temperature high-speed grinding and shearing to the nanometer level.

[0156] The above description shows that the dry electrode membrane prepared by the method of the present application can significantly improve its tensile strength, compaction density, etc., and also significantly reduce the resistivity of the dry electrode and improve the liquid absorption rate.

[0157] It should be noted that the terms "first," "second," and the like 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 precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments of the application described herein can, for example, be implemented in an order other than that described herein.

Claims

1. A method for preparing a dry electrode membrane, comprising the following steps: Step S1: mixing and crushing a polytetrafluoroethylene material, an electrode active material, and a conductive agent to obtain a crushed mixture; Step S2: performing a primary airflow grinding and shearing on the pulverized mixture to obtain a ground and sheared mixture; wherein the conditions for the primary airflow grinding and shearing include: an airflow temperature of -10°C to 10°C, a compressed airflow pressure of 0.7 to 0.9 MPa, and a shearing speed of 8000 to 12000 rpm; Step S3: performing secondary airflow grinding and shearing fiberization on the ground and sheared mixture to obtain a fiberized material; Step S4: performing secondary fiberization treatment on the fiberized material to obtain a dry electrode membrane.

2. The method for preparing a dry electrode film according to claim 1, wherein: The air flow temperature during the primary air flow grinding and shearing is -5°C to 5°C; optionally 0°C to 5°C; And / or, the conditions for the secondary airflow grinding and shearing include: airflow temperature of 50° C. to 100° C., compressed airflow pressure of 0.7 to 0.9 MPa, and shearing speed of 8000 to 12000 rpm; Optionally, the air flow temperature of the secondary air flow grinding and shearing is 60-100° C.; optionally 70-100° C.; further optionally 80-100° C.; the shearing speed is 10000-11000 rpm; And / or, the shearing speed of the primary air flow grinding and shearing is 10000-11000 rpm; And / or, the polytetrafluoroethylene material is a polytetrafluoroethylene dispersion resin having an average particle size of 400-600 μm, a molecular weight of 500,000-8 million, and a compression ratio of 100-3000; Optionally, the polytetrafluoroethylene dispersion resin is kept at -8°C to -12°C for 8 to 12 hours before mixing.

3. The method for preparing a dry electrode film according to claim 2, wherein: The specific process of step S1 includes: mixing and crushing the electrode active material and the conductive agent to obtain powder A; mixing and crushing the heat-insulated polytetrafluoroethylene dispersion resin and the powder A to obtain the crushed mixture; Optionally, the electrode active material and the conductive agent are mixed using a ball mill or a high-speed mixer, and the rotation speed of the high-speed mixer is 400-600 rpm; Optionally, the ball-to-material ratio of the ball mill is 1:(1-2); Optionally, the polytetrafluoroethylene dispersion resin and the powder A are mixed using a double-motion mixer or a three-dimensional motion mixer; Optionally, the mixing time of the polytetrafluoroethylene dispersion resin and the powder A in the double-motion mixer is 20 to 40 minutes.

4. The method for preparing a dry electrode membrane according to any one of claims 1 to 3, wherein: The average particle size of the pulverized mixture is 8 to 12 μm; and / or, the average particle size of the ground and sheared mixture is 3 to 6 μm; And / or, the primary air flow grinding and shearing and / or the secondary air flow grinding and shearing adopts an air flow grinder; Optionally, the air flow mill is a fluidized bed air flow mill.

5. The method for preparing a dry electrode membrane according to any one of claims 1 to 4, wherein: The secondary fiberization treatment uses a differential speed roller press to perform differential speed fiberization; Optionally, the rolling temperature of the differential roller press is 60°C~120°C, and the rolling speed ratio is 1:(1~1.5).

6. The method for preparing a dry electrode membrane according to any one of claims 2 to 5, wherein: The weight ratio of the electrode active material to the conductive agent is (90-95): (0-5); and / or, the weight ratio of the powder A to the heat-insulated polytetrafluoroethylene dispersion resin 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 manganate, lithium cobalt oxide, lithium manganate, 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 oxide negative electrode material, and silicon carbon; And / or, the conductive agent is selected from at least one of conductive carbon black, graphite, graphene, carbon nanotubes, carbon fibers, acetylene black and Ketjen black.

7. A dry electrode membrane, wherein: The dry electrode membrane is prepared by the dry electrode membrane preparation method according to any one of claims 1 to 6.

8. The dry electrode membrane according to claim 7, wherein: The thickness of the dry electrode film is 100-152 μm, the tensile strength is 0.15-0.4 MPa, and the compaction density is 2.50-3.30 g / cm 3 .

9. A method for preparing a dry electrode, wherein: The method for preparing the dry electrode comprises 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 7 or 8.

10. The method for preparing a dry electrode according to claim 9, wherein: The temperature of the roller pressing is 0°C to 100°C; Optionally, 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.

11. A battery comprising an electrode, a separator and an electrolyte, wherein: The electrode is an electrode prepared by the dry electrode preparation method according to claim 9 or 10.

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