A multi-stage fiberized dry electrode plate and a preparation method thereof, and a battery

Abstract

This invention relates to a multi-stage fibrous dry electrode sheet, its preparation method, and a battery. The preparation method includes the following steps: uniformly mixing active materials, conductive agents, and binders in a certain proportion and then performing fibrosis treatment to obtain a primary electrode mixture; granulating the primary electrode mixture to obtain electrode mixture particles; uniformly mixing the electrode mixture particles with conductive agents and binders and then performing re-fibrosis treatment to obtain a next-stage electrode mixture; repeating the above steps to perform N re-fibrosis treatments on the primary electrode mixture to obtain an N+1 stage electrode mixture; performing a single rolling press on the N+1 stage electrode mixture to obtain an electrode film; and bonding the electrode film with a current collector and performing a second rolling press to obtain the multi-stage fibrous dry electrode sheet. Compared with the prior art, this invention achieves uniform dispersion among the mixtures through multi-stage fibrosis and the addition of conductive agents and binders in small amounts and multiple times, resulting in electrode sheets with superior electrochemical and mechanical properties.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and in particular relates to a multi-stage fibrous dry electrode sheet and its preparation method, as well as a battery. Background Technology

[0002] In lithium-ion battery electrode manufacturing, the key performance characteristics of lithium-ion batteries primarily depend on the electrode manufacturing process. Currently, electrode manufacturing processes are mainly divided into wet and dry methods, with the wet method currently accounting for the largest share. The disadvantages of the wet method include the use of toxic organic solvents such as N,N-dimethylpyrrolidone (NMP). During manufacturing, NMP can cause problems such as excessive water content, leading to issues like battery swelling and rapid performance degradation during cycling. Furthermore, the evaporation and recovery of solvents during manufacturing result in significant energy consumption, increasing production costs.

[0003] Based on the aforementioned issues, the preparation of battery electrodes using a solvent-free dry process is of significant research importance. The key feature of dry electrode technology is that it completely eliminates the use of solvents during the preparation process, directly processing active materials and related additives into electrode sheets. Dry processes not only reduce production costs and environmental pollution but also enable the production of thicker electrode sheets.

[0004] Existing methods for preparing dry electrode films employ single-stage fiberization. For example, CN114725320A discloses a method for preparing dry electrode sheets, which involves preparing a first mixture at a first temperature; preparing a second mixture containing a non-fibrillated binder at a second temperature; applying shear force to the second mixture to fiberize it, thereby obtaining a third mixture; preheating the third mixture; applying preforming pressure in multiple directions to the preheated third mixture to prepare a preformed self-supporting electrode film; subjecting the preformed self-supporting electrode film to hot rolling thinning to prepare a self-supporting electrode film; and feeding the prepared self-supporting electrode film and carbon-coated foil into a roller mill to obtain a dry electrode sheet.

[0005] However, incomplete single-stage fiberization of the aforementioned binder leads to deterioration of mechanical properties. During the single mixing and fiberization process, the binder is unable to form a dense and stable fiber network, resulting in a decrease in the mechanical properties of the electrode film. During rolling, stress concentration can easily cause cracks, affecting the electrode's processing performance. Secondly, due to differences in density and surface energy among the active material, conductive agent, and binder, the active particles and conductive agent are not evenly dispersed. This inhomogeneity will significantly affect the electrochemical performance of the electrode. Summary of the Invention

[0006] The purpose of this invention is to overcome at least one of the defects of existing single-fiber membranes, such as uneven mixing and dispersion, poor mechanical properties and electrochemical properties, and to provide a multi-stage fiberized dry electrode sheet, its preparation method and battery.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] The first aspect of this invention provides a method for preparing a multi-stage fibrous dry electrode sheet, characterized by comprising the following steps:

[0009] S1: The active material, conductive agent and binder are mixed evenly in proportion and then subjected to fiberization treatment to obtain the primary electrode mixture;

[0010] S2: Granulate the primary electrode mixture obtained in S1 to obtain electrode mixture particles. After uniformly mixing the electrode mixture particles with conductive agent and binder, perform re-fiberization treatment to obtain the next stage electrode mixture.

[0011] S3: Repeat the above steps to perform N refiberization treatments on the primary electrode mixture to obtain N+1 primary electrode mixture.

[0012] S4: Roll the N+1 grade electrode mixture obtained in S3 once to obtain the electrode film;

[0013] S5: After bonding the electrode film obtained in S4 with the current collector, a second rolling process is performed to obtain a multi-stage fiberized dry electrode sheet.

[0014] Further, in step S1, the mass ratio of the active material, conductive agent, and binder is (90-99):(0.1-5):(0.1-5).

[0015] Furthermore, in step S1, the amount of adhesive added is not less than 1 wt% of the total mass of the mixture.

[0016] Further, in step S1, the active material is any one or more of lithium iron phosphate, sodium iron pyrophosphate, lithium manganese oxide, lithium cobalt oxide, lithium manganese iron phosphate, lithium nickel manganese cobalt oxide, lithium nickel cobalt aluminum oxide, graphite, silicon suboxide, nano-silicon, and lithium titanate.

[0017] Further, in step S1, the conductive agent is any one or more of conductive carbon black, carbon nanotubes, acetylene black, and carbon fiber.

[0018] Further, in step S1, the adhesive is any one or more of polytetrafluoroethylene, polyvinylidene fluoride, styrene-acrylic rubber, polyethylene glycol-fumarate, or polyacrylonitrile.

[0019] Furthermore, in step S1, the mixing method is stirring.

[0020] Furthermore, the stirring temperature is -50 to 18°C, the stirring speed is 300 to 3000 rpm, and the stirring time is 5 to 150 minutes.

[0021] Further, in step S1, the fiberization process is performed using any one or more of the following: a high-speed air jet mill, a screw extruder, a ball mill, and a shearing machine.

[0022] Furthermore, when ball milling is used for the fiberization treatment, the milling speed is 300-500 rpm and the milling time is 5-15 min. Preferably, the fiberization is carried out by ball milling at 400 rpm for 10 min.

[0023] Furthermore, in step S2, the granulation method is at least one of a pelletizer or a crusher.

[0024] Furthermore, in step S2, the diameter of the electrode mixture particles is 50-100 μm.

[0025] Further, in steps S2 and S3, the mass ratio of the electrode mixture particles, conductive agent, and binder is (90-99):(0.1-5):(0.1-5). This mass ratio can be the same as or different from the mass ratio in step S1.

[0026] Furthermore, in steps S2 and S3, the refiberization process is performed using any one or more of a high-speed air jet mill, a screw extruder, a ball mill, and a shearing machine, preferably a ball mill.

[0027] Furthermore, in step S3, N is any integer from 2 to 5, such as 2, 3, 4, 5, and N is preferably 3.

[0028] Furthermore, in step S4, the process of the first rolling is as follows: at 50-95°C, the rolling is performed multiple times and the gap between the rollers is gradually shortened to <500μm.

[0029] Furthermore, in step S5, the secondary rolling process is as follows: at 70-180℃, the gap between the rollers is adjusted to ≤100μm, and thermal bonding is performed.

[0030] Furthermore, in step S5, the current collector is a metal foil.

[0031] A second aspect of the present invention provides a multi-stage fibrous dry electrode sheet, which is prepared by the above-described preparation method.

[0032] A third aspect of the present invention provides a battery in which the above-mentioned dry-process electrode sheet is used as a positive electrode sheet or a negative electrode sheet.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) This invention achieves uniform dispersion of active material, conductive agent and binder through multi-level fiberization and small-scale multiple addition of conductive agent and binder, forming a multi-scale fiber network structure, which can solve the problem of high electrode resistance caused by the agglomeration of conductive agent particles in the preparation process of existing dry electrodes, and the resulting electrode sheet has better electrochemical and mechanical properties.

[0035] (2) The primary electrode mixture obtained by the present invention through fibrosis treatment initially possesses a three-dimensional network structure, exhibiting certain adhesion and self-support. Only active materials, conductive agents, and binders need to be added during the process, avoiding the addition of other film-forming functional aids that could adversely affect battery performance.

[0036] (3) This invention, through a multi-stage refiberization process, repeatedly cycles through electrode mixing and granulation, the addition and mixing of conductive agents and binders, and fibrillation treatment, to obtain dry-processed electrode sheets with higher tensile strength. The key technology lies in the following: the binder added initially undergoes more fibrillation cycles, resulting in a higher degree of fibrillation and smaller fiber diameter. The binder added later undergoes fewer fibrillation cycles, resulting in a larger fiber diameter. The interlacing of fibers of different sizes forms a multi-layered network structure, providing stronger tensile strength and improving the stability of the battery during charging and discharging.

[0037] (4) In the refiberization process, the present invention adds conductive agents and binders to the dry-mixed particles in small amounts multiple times through granulation and fiberization, thereby preparing electrode sheets with uniformly dispersed conductive agents. The key technologies are: on the one hand, through granulation and crushing, large-sized conductive agent clusters are broken up by mechanical force, avoiding local agglomeration of conductive agents; on the other hand, during the multiple fiberization process, the conductive agents added in batches are uniformly coated by fiber networks of different sizes, inhibiting the reagglomeration of conductive agents. Attached Figure Description

[0038] Figure 1 This is a process flow diagram of the dry electrode sheet in this invention.

[0039] Figure 2 This is a scanning electron microscope image of the dry electrode sheet prepared in Example 1 of the present invention. Detailed Implementation

[0040] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0042] As used herein, the terms "and / or," "or / and," and "and / or" encompass any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. It should be noted that when at least three items are connected using at least two conjunctions selected from "and / or," "or / and," and "and / or," it should be understood that, in this application, the technical solution undoubtedly includes solutions connected by "logical AND," and also undoubtedly includes solutions connected by "logical OR."

[0043] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0044] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0045] This document only specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0046] Unless otherwise specified, the temperature parameters in this application may be either constant temperature processing or processing within a certain temperature range. The constant temperature processing allows temperature fluctuations within the precision range controlled by the instrument, such as ±5℃, ±4℃, ±3℃, ±2℃, or ±1℃.

[0047] In this document, the term "suitable" as used in phrases such as "suitable combination," "suitable method," and "any suitable method" refers to the ability to implement the technical solution of this application, solve the technical problem of this application, and achieve the expected technical effect of this application.

[0048] In this application, terms such as "further," "even further," and "particularly" are used to describe purposes and indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0049] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0050] In the description of the application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0051] Unless otherwise specified, all preparations and tests described herein took place at 25°C.

[0052] The terms “comprising,” “including,” “containing,” “having,” “comprising,” or other variations thereof are intended to cover non-closed inclusion, and no distinction is made between these terms. The term “comprising” means that other steps and ingredients may be added without affecting the final result. The compositions and methods / processes of the present invention comprise, consist of, and substantially consist of the essential elements and limitations described herein, as well as any additional or optional ingredients, components, steps, or limitations described herein. No distinction is made between the terms “efficacy,” “performance,” “effect,” and “potency” herein.

[0053] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions.

[0054] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, but sequentially is preferred.

[0055] The lithium cobalt oxide and conductive carbon black used were from Kelude New Energy Technology Co., Ltd., and the polytetrafluoroethylene dispersion resin FR203 used was produced by Shanghai Huayi Sanaifu New Materials Co., Ltd.

[0056] Unless otherwise specified, the reagents, methods, instruments, and equipment used in this invention are conventional in the art. Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0057] Example 1:

[0058] This embodiment provides a method for preparing a multi-stage fibrous dry electrode sheet, such as... Figure 1 As shown, the specific steps include:

[0059] (1) Weigh lithium cobalt oxide, conductive carbon black and polytetrafluoroethylene dispersion resin in a mass ratio of 98:1:1 and add them to a high-speed mixer. Mix them for 10 minutes at a stirring speed of 1200 rpm and a stirring temperature of 5℃ to obtain an electrode premix. Then, put the electrode premix into a ball mill and ball mill it for 10 minutes at 400 rpm to obtain a primary electrode mixture.

[0060] (2) The primary electrode mixture is re-fiberized once, and each re-fiberization step is performed as follows: The primary electrode mixture is fed into a granulator, and the diameter of the granulated electrode mixture particles is 75±25μm. The electrode mixture particles, conductive carbon black, and polytetrafluoroethylene dispersion resin are weighed at a mass ratio of 98:1:1 and added to a high-speed mixer. The mixture is stirred and mixed for 10 minutes at a stirring speed of 1200rpm and a stirring temperature of 5℃ to obtain an electrode premix. The electrode premix is ​​then fed into a ball mill and ball-milled at 400rpm for 10 minutes to obtain the next primary electrode mixture. After the primary electrode mixture undergoes one re-fiberization, the secondary electrode mixture is obtained.

[0061] (3) The secondary electrode mixture is subjected to the first roller pressing. After multiple roller pressings at 80°C, the gap between the rollers is gradually shortened to 100 micrometers to obtain the electrode film.

[0062] (4) After the dry film is bonded to the aluminum foil, it is thermally laminated by roller pressing to obtain the dry electrode sheet, wherein the thermal lamination temperature is 120°C and the roller spacing is 100 micrometers.

[0063] Figure 2 This is a SEM image of the dry-processed electrode sheet prepared in this embodiment. The image shows PTFE fibers, conductive graphite, and the active material lithium cobalt oxide. Under the multi-stage fiberization process, lithium cobalt oxide is uniformly dispersed in the fiber network. The PTFE fibers exhibit various fiber sizes under the multi-stage fiberization treatment: the finer fibers have a diameter of 10-30 nm, with conductive graphite densely distributed on the fine fibers to form a conductive network; the coarser fibers have a diameter of 30-50 nm, providing mechanical strength to the electrode sheet.

[0064] Example 2:

[0065] This embodiment provides a method for preparing a multi-stage fibrous dry electrode sheet, including the following steps:

[0066] (1) Weigh lithium cobalt oxide, conductive carbon black and polytetrafluoroethylene dispersion resin in a mass ratio of 98:1:1 and add them to a high-speed mixer. Mix them for 10 minutes at a stirring speed of 1200 rpm and a stirring temperature of 5℃ to obtain an electrode premix. Then, put the electrode premix into a ball mill and ball mill it for 10 minutes at 400 rpm to obtain a primary electrode mixture.

[0067] (2) The primary electrode mixture is re-fiberized twice, with each re-fiberization step performed as follows: The primary electrode mixture is fed into a granulator, and the granulated electrode mixture particles have a diameter of 75±25μm. The electrode mixture particles, conductive carbon black, and polytetrafluoroethylene dispersion resin are weighed at a mass ratio of 99:0.5:0.5 and added to a high-speed mixer. The mixture is stirred and mixed for 10 minutes at a stirring speed of 1200 rpm and a stirring temperature of 5℃ to obtain an electrode premix. The electrode premix is ​​then fed into a ball mill and ball-milled at 400 rpm for 10 minutes to obtain the next primary electrode mixture. After the primary electrode mixture undergoes two re-fiberizations, the tertiary electrode mixture is obtained.

[0068] (3) The secondary electrode mixture is subjected to the first roller pressing. After multiple roller pressings at 80°C, the gap between the rollers is gradually shortened to 100 micrometers to obtain the electrode film.

[0069] (4) After the dry film is bonded to the aluminum foil, it is thermally laminated by roller pressing to obtain the dry electrode sheet, wherein the thermal lamination temperature is 120°C and the roller spacing is 100 micrometers.

[0070] Example 3:

[0071] This embodiment provides a method for preparing a multi-stage fibrous dry electrode sheet, including the following steps:

[0072] (1) Weigh lithium cobalt oxide, conductive carbon black and polytetrafluoroethylene dispersion resin in a mass ratio of 98:1:1 and add them to a high-speed mixer. Mix them for 10 minutes at a stirring speed of 1200 rpm and a stirring temperature of 5℃ to obtain an electrode premix. Then, put the electrode premix into a ball mill and ball mill it for 10 minutes at 400 rpm to obtain a primary electrode mixture.

[0073] (2) The primary electrode mixture was re-fiberized three times, with each re-fiberization step performed as follows: The primary electrode mixture was fed into a granulator, and the granulated electrode mixture particles had a diameter of 75±25μm. The electrode mixture particles, conductive carbon black, and polytetrafluoroethylene dispersion resin were weighed at a mass ratio of 99.33:0.33:0.33 and added to a high-speed mixer. The mixture was stirred and mixed for 10 minutes at a stirring speed of 1200 rpm and a stirring temperature of 5℃ to obtain an electrode premix. The electrode premix was then fed into a ball mill and ball-milled at 400 rpm for 10 minutes to obtain the next primary electrode mixture. After the primary electrode mixture underwent three re-fiberizations, a quaternary electrode mixture was obtained.

[0074] (3) The secondary electrode mixture is subjected to the first roller pressing. After multiple roller pressings at 80°C, the gap between the rollers is gradually shortened to 100 micrometers to obtain the electrode film.

[0075] (4) After the dry film is bonded to the aluminum foil, it is thermally laminated by roller pressing to obtain the dry electrode sheet, wherein the thermal lamination temperature is 120°C and the roller spacing is 100 micrometers.

[0076] Example 4:

[0077] This embodiment provides a method for preparing a multi-stage fibrous dry electrode sheet, including the following steps:

[0078] (1) Weigh lithium cobalt oxide, conductive carbon black and polytetrafluoroethylene dispersion resin in a mass ratio of 98:1:1 and add them to a high-speed mixer. Mix them for 10 minutes at a stirring speed of 1200 rpm and a stirring temperature of 5℃ to obtain an electrode premix. Then, put the electrode premix into a ball mill and ball mill it for 10 minutes at 400 rpm to obtain a primary electrode mixture.

[0079] (2) The primary electrode mixture was re-fiberized four times, with each re-fiberization step performed as follows: The primary electrode mixture was fed into a granulator, and the granulated electrode mixture particles had a diameter of 75±25μm. The electrode mixture particles, conductive carbon black, and polytetrafluoroethylene dispersion resin were weighed at a mass ratio of 99.5:0.25:0.25 and added to a high-speed mixer. The mixture was stirred and mixed for 10 minutes at a stirring speed of 1200 rpm and a stirring temperature of 5℃ to obtain an electrode premix. The electrode premix was then fed into a ball mill and ball-milled at 400 rpm for 10 minutes to obtain the next primary electrode mixture. After the primary electrode mixture underwent four re-fiberizations, a fifth-stage electrode mixture was obtained.

[0080] (3) The secondary electrode mixture is subjected to the first roller pressing. After multiple roller pressings at 80°C, the gap between the rollers is gradually shortened to 100 micrometers to obtain the electrode film.

[0081] (4) After the dry film is bonded to the aluminum foil, it is thermally laminated by roller pressing to obtain the dry electrode sheet, wherein the thermal lamination temperature is 120°C and the roller spacing is 100 micrometers.

[0082] Comparative Example 1:

[0083] The preparation method of the dry electrode in this comparative example includes the following steps:

[0084] (1) Weigh lithium cobalt oxide, conductive carbon black and polytetrafluoroethylene dispersion resin in a mass ratio of 96:2:2 and add them to a high-speed mixer. Mix them for 10 minutes at a stirring speed of 1200 rpm and a stirring temperature of 5℃ to obtain an electrode premix. Then, put the electrode premix into a ball mill and ball mill it for 10 minutes at 400 rpm to obtain a primary electrode mixture.

[0085] (2) The primary electrode mixture is subjected to the first rolling press, and after multiple rolling presses at 80°C, the gap between the rollers is gradually shortened to 100 micrometers to obtain the electrode film.

[0086] (3) After the dry film is bonded to the aluminum foil, the dry electrode is obtained by heat bonding by roller pressing, wherein the heat bonding temperature is 120°C and the roller spacing is 100 micrometers.

[0087] Comparative Example 2:

[0088] The preparation method of the dry electrode in this comparative example includes the following steps:

[0089] (1) Weigh lithium cobalt oxide, conductive carbon black and polytetrafluoroethylene dispersion resin in a mass ratio of 98:1:1 and add them to a high-speed mixer. Mix them for 10 minutes at a stirring speed of 1200 rpm and a stirring temperature of 5℃ to obtain an electrode premix. Then, put the electrode premix into a ball mill and ball mill it for 10 minutes at 400 rpm to obtain a primary electrode mixture.

[0090] (2) The primary electrode mixture is subjected to the first rolling press, and after multiple rolling presses at 80°C, the gap between the rollers is gradually shortened to 100 micrometers to obtain the electrode film.

[0091] (3) After the dry film is bonded to the aluminum foil, the dry electrode is obtained by heat bonding by roller pressing, wherein the heat bonding temperature is 120°C and the roller spacing is 100 micrometers.

[0092] Comparative Example 3:

[0093] The preparation method of the dry electrode in this comparative example includes the following steps:

[0094] (1) Weigh lithium cobalt oxide, conductive carbon black and polytetrafluoroethylene dispersion resin in a mass ratio of 99:0.5:0.5 and add them to a high-speed mixer. Mix them for 10 minutes at a stirring speed of 1200 rpm and a stirring temperature of 5℃ to obtain an electrode premix. Then, put the electrode premix into a ball mill and ball mill it for 10 minutes at 400 rpm to obtain a primary electrode mixture.

[0095] (2) The primary electrode mixture is subjected to the first roller pressing, and after multiple roller pressings at 80°C, the gap between the rollers is gradually shortened to 100 micrometers to obtain the electrode film.

[0096] (3) After the dry film is bonded to the aluminum foil, the dry electrode is obtained by heat bonding by roller pressing, wherein the heat bonding temperature is 120°C and the roller spacing is 100 micrometers.

[0097] Comparative Example 4:

[0098] The preparation method of the dry electrode in this comparative example includes the following steps:

[0099] (1) Weigh lithium cobalt oxide, conductive carbon black and polytetrafluoroethylene dispersion resin in a mass ratio of 99:0.5:0.5 and add them to a high-speed mixer. Mix them for 10 minutes at a stirring speed of 1200 rpm and a stirring temperature of 5℃ to obtain an electrode premix. Then, put the electrode premix into a ball mill and ball mill it for 10 minutes at 400 rpm to obtain a primary electrode mixture.

[0100] (2) The primary electrode mixture was re-fiberized three times, with each re-fiberization step performed as follows: The primary electrode mixture was fed into a granulator, and the granulated electrode mixture particles had a diameter of 75±25μm. The electrode mixture particles, conductive carbon black, and polytetrafluoroethylene dispersion resin were weighed at a mass ratio of 99:0.5:0.5 and added to a high-speed mixer. The mixture was stirred and mixed for 10 minutes at a stirring speed of 1200 rpm and a stirring temperature of 5℃ to obtain an electrode premix. The electrode premix was then fed into a ball mill and ball-milled at 400 rpm for 10 minutes to obtain the next primary electrode mixture. After the primary electrode mixture underwent three re-fiberizations, a quaternary electrode mixture was obtained.

[0101] (3) The secondary electrode mixture is subjected to the first roller pressing. After multiple roller pressings at 80°C, the gap between the rollers is gradually shortened to 100 micrometers to obtain the electrode film.

[0102] (4) After the dry film is bonded to the aluminum foil, it is thermally laminated by roller pressing to obtain the dry electrode sheet, wherein the thermal lamination temperature is 120°C and the roller spacing is 100 micrometers.

[0103] Comparative Example 5:

[0104] The preparation method of the dry electrode in this comparative example includes the following steps:

[0105] (1) Weigh lithium cobalt oxide, conductive carbon black and polytetrafluoroethylene dispersion resin in a mass ratio of 98:1:1 and add them to a high-speed mixer. Mix them for 10 minutes at a stirring speed of 1200 rpm and a stirring temperature of 5℃ to obtain an electrode premix. Then, put the electrode premix into a ball mill and ball mill it for 10 minutes at 400 rpm to obtain a primary electrode mixture.

[0106] (2) The primary electrode mixture was re-fiberized three times, with each re-fiberization step performed as follows: The primary electrode mixture was fed into a granulator, and the granulated electrode mixture particles had a diameter of 150±25μm. The electrode mixture particles, conductive carbon black, and polytetrafluoroethylene dispersion resin were weighed at a mass ratio of 99.33:0.33:0.33 and added to a high-speed mixer. The mixture was stirred and mixed for 10 minutes at a stirring speed of 1200 rpm and a stirring temperature of 5℃ to obtain an electrode premix. The electrode premix was then fed into a ball mill and ball-milled at 400 rpm for 10 minutes to obtain the next primary electrode mixture. After the primary electrode mixture underwent three re-fiberizations, a quaternary electrode mixture was obtained.

[0107] (3) The secondary electrode mixture is subjected to the first roller pressing. After multiple roller pressings at 80°C, the gap between the rollers is gradually shortened to 100 micrometers to obtain the electrode film.

[0108] (4) After the dry film is bonded to the aluminum foil, it is thermally laminated by roller pressing to obtain the dry electrode sheet, wherein the thermal lamination temperature is 120°C and the roller spacing is 100 micrometers.

[0109] The present invention performs the following tests on the dry electrode samples of the above-prepared embodiments and comparative examples.

[0110] (1) First-efficiency test: Nine groups of electrode sheets were taken from Examples 1-4 and Comparative Examples 1-5, with 5 samples in each group, and assembled into button batteries for first-efficiency testing. The assembly and testing process of the button batteries is as follows: CR2032 button batteries were assembled in a glove box. The positive electrode used was the dry electrode sheet prepared in this patent, the negative electrode used was a lithium metal sheet (thickness 200μm, diameter 15.8mm, brand: KELUD), the electrolyte used was LiPF6 (in DMC, EC, EMC with VC, brand: Adamas), and the separator used was a polypropylene separator (brand: Celgard). After the assembled batteries were left to stand for 12 hours, they were clamped in the battery testing system for testing. A constant current charging mode was used, and the charging capacity Q was recorded. C and discharge capacity Q D The formula for calculating the initial charge / discharge efficiency is: Initial efficiency = Discharge capacity / Charge capacity * 100%. The test results are taken as the average value.

[0111] (2) Mechanical property test: Nine groups of electrode films were taken from Examples 1-6 and Comparative Examples 1-3, with 3 samples in each group. The tensile strength of the electrode films was tested using 15mm wide specimens, with an initial distance of 80mm between the clamps of the tensile testing machine and a test speed of 3mm / min.

[0112] The test results are shown in Table 1 below.

[0113] Table 1 Summary of Performance Test Results

[0114] Example 1 91.22 1.992 Example 2 92.25 2.383 Example 3 93.32 2.588 Example 4 92.47 2.631 Comparative Example 1 89.12 1.583 Comparative Example 2 88.56 1.294 Comparative Example 3 86.77 0.512 Comparative Example 4 86.31 0.375 Comparative Example 5 90.52 1.857

[0115] Comparing the data from Examples 1-4 and Comparative Example 1, it can be seen that using a multi-stage fiberization process to prepare dry-process electrodes in the positive electrode raw material system can improve the initial efficiency and tensile strength of the battery. Compared to the single-stage fiberization process used in Comparative Example 1, Examples 1-4, while maintaining the same total amount of active material, conductive agent, and binder, achieved a certain improvement in initial efficiency and tensile strength using a multi-stage fiberization process. This indicates that multiple fiberizations and multiple additions of conductive agent and binder are beneficial to the dispersion of conductive agent and the reinforcement of the fiber network. In Examples 1-4, as the number of refiberizations increased from 1 to 4, the tensile strength increased with the number of refiberizations, indicating that the entanglement of fiber structures of different scales in the fiber network is beneficial to strengthening the tensile properties of the electrode film. However, the initial efficiency of the battery showed a trend of first increasing and then decreasing, with the highest initial efficiency achieved after 3 refiberizations.

[0116] Comparing the data from Example 3 and Comparative Examples 1-4, it can be seen that when the binder content in the primary electrode mixture is 0.5%, even with multiple fiberization processes, the initial efficiency of the final dry electrode is slightly reduced, and the tensile strength of the resulting dry membrane decreases sharply. This indicates that there is a minimum requirement of 1% binder addition when preparing the primary electrode mixture to provide a basic fiber network to support the dry membrane. Below 1%, the strength and quantity of the fibers are insufficient to maintain stable battery operation.

[0117] Comparing Example 3 and Comparative Example 5, it can be seen that when the particle size of the granulated particles increases, the initial efficiency and tensile strength of the battery both decrease. This indicates that the large-particle-size electrode mixture particles affect its mixing with the binder and conductive agent, thus having an adverse effect on battery performance.

[0118] In summary, this invention utilizes a multi-stage fibrosis dry process to mix active materials, conductive agents, and binders to form electrodes. First, the primary electrode mixture obtained through fibrosis treatment initially possesses a three-dimensional network structure, exhibiting certain adhesion and self-support. Second, through multi-stage re-fiberization steps, repeatedly cycling the electrode mixture granulation, adding and mixing conductive agents and binders, and undergoing fibrosis treatment, the tensile strength of the dry-processed electrode sheet is improved, enabling the production of dry-processed electrodes with higher tensile strength. Third, during the re-fiberization process, conductive agents and binders are added repeatedly in small amounts to the dry-processed mixture particles, resulting in electrodes with uniformly dispersed conductive agents and inhibiting the re-agglomeration of the conductive agents.

[0119] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a multi-stage fibrous dry electrode, characterized in that, Includes the following steps: S1: The active material, conductive agent and binder are mixed evenly in proportion and then subjected to fiberization treatment to obtain the primary electrode mixture; S2: Granulate the primary electrode mixture obtained in S1 to obtain electrode mixture particles. Mix the electrode mixture particles with a conductive agent and a binder evenly and then perform a re-fiberization treatment to obtain the next stage electrode mixture. The diameter of the electrode mixture particles is 50-100 μm. S3: Repeat step S2 to perform N refiberization treatments on the primary electrode mixture to obtain N+1 primary electrode mixtures, where N≥2; S4: Roll the N+1 grade electrode mixture obtained in S3 once to obtain the electrode film; S5: After bonding the electrode film obtained in S4 with the current collector, perform a second rolling process to obtain a multi-stage fiberized dry electrode sheet. In step S1, the mass ratio of the active material, conductive agent, and binder is (90~99):(0.1~5):(0.1~5), and the amount of binder added is not less than 1 wt% of the total mass of the mixture. In steps S2 and S3, the mass ratio of the electrode mixture particles, conductive agent and binder is (90~99):(0.1~5):(0.1~5).

2. The method for preparing a multi-stage fibrous dry electrode sheet according to claim 1, characterized in that, In step S1, the active material is any one or more of lithium iron phosphate, sodium iron pyrophosphate, lithium manganese oxide, lithium cobalt oxide, lithium manganese iron phosphate, lithium nickel manganese cobalt oxide, lithium nickel cobalt aluminum oxide, graphite, silicon suboxide, nano-silicon, and lithium titanate. The conductive agent is any one or more of conductive carbon black, carbon nanotubes, acetylene black, and carbon fiber. The adhesive is any one or more of polytetrafluoroethylene, polyvinylidene fluoride, styrene-acrylic rubber, polyethylene glycol-fumarate, or polyacrylonitrile.

3. The method for preparing a multi-stage fibrous dry electrode sheet according to claim 1, characterized in that, In step S1, the mixing method is stirring, the stirring temperature is -50~18 ℃, the stirring speed is 300-3000 rpm, and the stirring time is 5~150 min; The fiberization process is performed using one or more of the following: high-speed air jet mill, screw extruder, ball mill, and shear mill.

4. The method for preparing a multi-stage fibrous dry electrode sheet according to claim 1, characterized in that, In step S2, the granulation method is at least one of a pelletizer or a crusher.

5. The method for preparing a multi-stage fibrous dry electrode sheet according to claim 1, characterized in that, The refiberization process is performed using one or more of the following: high-speed air jet mill, screw extruder, ball mill, and shear mill.

6. The method for preparing a multi-stage fibrous dry electrode sheet according to claim 1, characterized in that, N is any integer from 2 to 5.

7. The method for preparing a multi-stage fibrous dry electrode sheet according to claim 1, characterized in that, In step S4, the process of the first rolling is as follows: at 50~95 ℃, the rolling is performed multiple times and the gap between the rollers is gradually shortened to <500 μm.

8. The method for preparing a multi-stage fibrous dry electrode sheet according to claim 1, characterized in that, In step S5, the secondary rolling process is as follows: at 70~180 ℃, the gap between the rollers is adjusted to ≤100 μm, and thermal bonding is performed; The current collector is a metal foil.

9. A multi-stage fibrous dry electrode, characterized in that, It is prepared by the preparation method described in any one of claims 1-8.

10. A battery, characterized in that, The dry electrode sheet as described in claim 9 can be used as the positive electrode sheet or the negative electrode sheet.

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