An improved dry electrode fabrication process for PTFE fiberized networks

Abstract

The application belongs to the technical field of lithium ion batteries, and particularly relates to a dry-process electrode preparation process for improving a PTFE fiberization network, which comprises the following steps: uniformly mixing an active material, a conductive agent and activated carbon through a mixer; adding a binder PTFE for secondary mixing; performing fiberization treatment on the above material; performing roller pressing on the fiberized powder to form a film, and compounding the film with a current collector to obtain a dry-process electrode. Through the preparation of the dry-process electrode, local stress concentration points can be formed in the mixing and fiberization processes, the shearing action on PTFE particles is improved, the PTFE particles are caused to deform and fiberize, the problem of low fiberization degree and poor mechanical performance in the process of preparing the dry-process electrode by the original fiber method is effectively improved, the ion resistance of the pole piece is lower, and the pole piece exhibits better electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a dry electrode preparation process for improving PTFE fibrous networks. Background Technology

[0002] Traditional lithium-ion battery manufacturing relies on wet coating processes, which suffer from high energy consumption, solvent pollution, and performance bottlenecks. To achieve green, low-cost, and high-performance battery production, dry electrode technology has emerged. This technology eliminates the need for solvents, using dry mixing and calendering to form films, significantly reducing manufacturing costs and improving electrode structural stability. Dry processes demonstrate key advantages, particularly in the development of high-energy-density and all-solid-state batteries.

[0003] Among the many dry processes reported, the PTFE fibrillation method is undoubtedly the most likely route to achieve commercialization and large-scale replacement of wet processes. The PTFE fibrillation method transforms the PTFE binder from powder to fiber by in-situ fiberizing, significantly increasing its specific surface area. This allows the active material inside the positive electrode to be bonded and fixed with a small amount of PTFE binder, ultimately achieving the film formation of the dry electrode.

[0004] The PTFE fibrillation method is generally suitable for large-particle-size active material particles. However, to improve the electrochemical performance of lithium-ion batteries, the demand for dry-process electrodes using small-particle-size active material particles is constantly increasing. Furthermore, in dry processes, mechanical equipment such as ball mills and planetary mixers often experience significant internal collision forces, which can cause secondary large-particle active material particles to break down into primary small particles. Preparing dry-process electrodes with small-particle-size active material particles is particularly difficult: firstly, PTFE requires shear force to function, but the shear force provided by PTFE due to the collision and compression of small particles is relatively small, making it difficult for PTFE to effectively complete fibrillation; secondly, bonding the same mass of small-particle material requires more binder. Since small-particle-size active material particles themselves provide less shear force to PTFE, and preparing dry-process electrodes requires even more PTFE, these factors collectively make the preparation of dry-process electrodes with small-particle-size active material particles more challenging. Summary of the Invention

[0005] The purpose of this invention is to provide an improved dry electrode fabrication process for PTFE fibrous networks to solve the problems mentioned in the background art.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a dry electrode preparation process for improving PTFE fibrous networks, comprising the following steps: Step 1: After mixing the active material particles, conductive agent, and activated carbon particles once, add the binder PTFE and mix again to obtain a mixture. Step 2: The mixture is subjected to fibrous treatment using ball milling to obtain a fibrous mixture; Step 3: Roll press the fibrous mixture into a film, and then combine it with a current collector to obtain a dry electrode.

[0007] Further, in step 1, the active material particles are at least one of lithium cobalt oxide, lithium iron phosphate, lithium manganese oxide, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0008] Furthermore, in step 1, the conductive agent is at least one of carbon nanotubes, acetylene black, conductive carbon black, and carbon fiber.

[0009] Furthermore, in step 1, the particle size D of the active material particles 50 The size ranges from 0.5 to 2 μm.

[0010] Furthermore, in step 1, the particle size D of the activated carbon particles 50 It is 5~10μm.

[0011] Furthermore, in step 1, both the primary and secondary mixing are carried out by stirring, with a stirring speed of 400~600 rpm and a time of 60~120 min.

[0012] Further, in step 1, the content of each component in the mixture, by weight percentage, is 81-91% active material particles, 2-3% conductive agent, 5-10% activated carbon particles, and 2-3% binder PTFE.

[0013] Furthermore, in step 2, the ball milling speed is 600~800 rpm and the ball milling time is 60~90 min.

[0014] Furthermore, in step 3, the rolling temperature is 80~95°C, and the rolling gap thickness decreases from 400μm to 100μm.

[0015] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: By introducing large-diameter activated carbon particles into small-diameter active material particles, the present invention can form local stress concentration points during mixing and fiberization, thereby increasing the shearing effect on PTFE particles, promoting deformation and fiberization of PTFE particles, effectively improving the problems of low fiberization degree and poor mechanical properties in the preparation of dry electrodes by the fibrillation method, and improving the processability of small-diameter single crystal materials; at the same time, the low friction coefficient of activated carbon particles makes them suitable as a lubricant, accelerating the rolling and thinning rate of dry electrodes; in addition, capacitive activated carbon particles achieve charging and discharging based on ion adsorption, exhibiting excellent rate performance, thus the electrode exhibits better mechanical and electrochemical properties. Attached Figure Description

[0016] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 These are optical microscope images of the fibrous mixtures in this invention; wherein, Figure 1 In the image, 'a' is an optical microscope photograph of the fibrous mixture in Comparative Example 1. Figure 1 b in the figure is an optical microscope photograph of the fibrous mixture in Example 1; Figure 2 These are electron microscope images of the fibrous mixtures in this invention; wherein, Figure 2 a and Figure 2 In the figures, b represents electron microscope images of the fibrous mixture in Comparative Example 1 at magnifications of 5000× and 20000×. Figure 2 c and Figure 2 In the figures, d represents electron microscope images of the fibrous mixture in Example 1 at magnifications of 5000× and 20000×. Figure 3 These are the cycle performance diagrams of Embodiment 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] The active material particles NCM811 used in this invention were purchased from BTR New Materials Group Co., Ltd.; the conductive agent was VGCF, purchased from Showa Denk Co., Ltd., Japan; and the activated carbon particles AC were purchased from Kuraray Co., Ltd., Japan.

[0019] Example 1: A dry electrode fabrication process for improving PTFE fibrous networks, comprising the following steps: Step 1: Add active material particles NCM811 (D 50 The active material particles (1.68 μm), conductive agent VGCF, and activated carbon particles AC (5.21 μm) were mixed once, and then binder PTFE was added for a second mixing to obtain a mixture. Both the first and second mixing were carried out in a double planetary mixer using a stirring method. The stirring speed for the first mixing was 400 rpm and the stirring time was 60 min. The stirring speed for the second mixing was 500 rpm and the stirring time was 60 min. The content of each component in the mixture, by weight percentage, is 91% active material particles, 2% conductive agent, 5% activated carbon particles, and 2% binder PTFE.

[0020] Step 2: Place the mixture from Step 1 into a ball mill and ball mill it at a speed of 600 rpm for 60 minutes to obtain a fibrous mixture. Step 3: Roll forming the fibrous mixture with a rolling temperature of 80°C and a roll gap thickness decreasing from 400μm to 100μm; then composite the rolled film material with a current collector to obtain a dry electrode.

[0021] Example 2: A dry electrode fabrication process for improving PTFE fibrous networks, comprising the following steps: Step 1: Add active material particles NCM811 (D 50 The active material particles (1.68 μm), conductive agent VGCF, and activated carbon particles AC (5.21 μm) were mixed once, and then binder PTFE was added for a second mixing to obtain a mixture. Both the first and second mixing were carried out in a double planetary mixer using a stirring method. The stirring speed for the first mixing was 500 rpm and the stirring time was 90 min. The stirring speed for the second mixing was 400 rpm and the stirring time was 90 min. The content of each component in the mixture, by weight percentage, was 86% active material particles, 2% conductive agent, 10% activated carbon particles, and 2% binder PTFE.

[0022] Step 2: Place the mixture from Step 1 into a ball mill and ball mill it at a speed of 750 rpm for 80 minutes to obtain a fibrous mixture. Step 3: Roll forming the fibrous mixture with a rolling temperature of 90°C and a roll gap thickness decreasing from 400μm to 100μm; then composite the rolled film material with a current collector to obtain a dry electrode.

[0023] Example 3: A dry electrode fabrication process for improving PTFE fibrous networks, comprising the following steps: Step 1: Add active material particles NCM811 (D 50 The active material particles (1.68 μm), conductive agent VGCF, and activated carbon particles AC (5.21 μm) were mixed once, and then binder PTFE was added for a second mixing to obtain a mixture. Both the first and second mixing were carried out in a double planetary mixer using a stirring method. The stirring speed for the first mixing was 600 rpm and the stirring time was 120 min. The stirring speed for the second mixing was 600 rpm and the stirring time was 120 min. The content of each component in the mixture, by weight percentage, is 85% active material particles, 3% conductive agent, 10% activated carbon particles, and 2% binder PTFE.

[0024] Step 2: Place the mixture from Step 1 into a ball mill and ball mill it at a speed of 800 rpm for 90 minutes to obtain a fibrous mixture. Step 3: Roll forming the fibrous mixture with a rolling temperature of 95°C and a roll gap thickness decreasing from 400μm to 100μm; then composite the rolled film material with a current collector to obtain a dry electrode.

[0025] Comparative Example 1: A dry electrode fabrication process, comprising the following steps: Step 1: Add active material particles NCM811 (D 50 The active material particles (1.68 μm) and conductive agent VGCF were mixed once, and then binder PTFE was added for a second mixing to obtain a mixture. Both the first and second mixing were carried out in a double planetary mixer using a stirring method. The stirring speed for the first mixing was 400 rpm and the stirring time was 60 min. During the second mixing, the stirring speed was 500 rpm and the stirring time was 60 min. The content of each component in the mixture, by weight percentage, is 91% active material particles, 7% conductive agent, and 2% binder PTFE.

[0026] Step 2: Place the mixture from Step 1 into a ball mill and ball mill it at a speed of 600 rpm for 60 minutes to obtain a fibrous mixture. Step 3: Roll forming the fibrous mixture with a rolling temperature of 80°C and a roll gap thickness decreasing from 400μm to 100μm; then composite the rolled film material with a current collector to obtain a dry electrode.

[0027] Comparative Example 2: A dry electrode fabrication process, comprising the following steps: Step 1: Add active material particles NCM811 (D 50The active material particles (1.68 μm), conductive agent VGCF, and activated carbon particles AC (5.21 μm) were mixed once, and then binder PTFE was added for a second mixing to obtain a mixture. Both the first and second mixing were carried out in a double planetary mixer using a stirring method. The stirring speed for the first mixing was 500 rpm and the stirring time was 90 min. The stirring speed for the second mixing was 400 rpm and the stirring time was 90 min. The content of each component in the mixture, by weight percentage, was 81% active material particles, 2% conductive agent, 15% activated carbon particles, and 2% binder PTFE.

[0028] Step 2: Place the mixture from Step 1 into a ball mill and ball mill it at a speed of 750 rpm for 80 minutes to obtain a fibrous mixture. Step 3: Roll forming the fibrous mixture with a rolling temperature of 90°C and a roll gap thickness decreasing from 400μm to 100μm; then composite the rolled film material with a current collector to obtain a dry electrode.

[0029] Comparative Example 3: A dry electrode fabrication process, comprising the following steps: Step 1: Add active material particles NCM811 (D 50 The active material particles (1.68 μm), conductive agent VGCF, and activated carbon particles AC (5.21 μm) were mixed once, and then binder PTFE was added for a second mixing to obtain a mixture. Both the first and second mixing were carried out in a double planetary mixer using a stirring method. The stirring speed for the first mixing was 600 rpm and the stirring time was 120 min. The stirring speed for the second mixing was 600 rpm and the stirring time was 120 min. The content of each component in the mixture, by weight percentage, is 76% active material particles, 2% conductive agent, 20% activated carbon particles, and 2% binder PTFE.

[0030] Step 2: Place the mixture from Step 1 into a ball mill and ball mill it at a speed of 800 rpm for 90 minutes to obtain a fibrous mixture. Step 3: Roll forming the fibrous mixture with a rolling temperature of 95°C and a roll gap thickness decreasing from 400μm to 100μm; then composite the rolled film material with a current collector to obtain a dry electrode.

[0031] The parameters of the dry electrode materials prepared in Examples 1-3 and Comparative Examples 1-3 were tested, and the experimental results are shown in Table 1. Wherein: Fiberization degree test: The powder morphology and fiberization degree after mixing were observed by optical microscope and SEM.

[0032] Tensile test: The two ends of the sample are fixed by a universal tensile testing machine and stretched. The reaction force and length change during the stretching process of the dry electrode are measured, and the tensile strength of the electrode is calculated.

[0033] Ion resistance testing: A symmetrical cell with dry electrodes was assembled at 25°C, and EIS testing was performed on the symmetrical cell using an electrochemical workstation. The amplitude of the EIS test was 10mV, and the test range was 1MHz~100mHz. The ionic resistance was calculated by solving the impedance spectrum using the equivalent circuit of the TLM model.

[0034] Electrochemical performance: At 25°C, a dry electrode pair lithium metal battery was assembled, and the electrochemical performance was tested using the LAND battery testing system (three cycles of activation at 0.1C, and the long-cycle test current density was 1 / 3C).

[0035] Table 1

[0036] Conclusion: The data in Table 1 show that the PTFE prepared in Examples 1 to 3 of this invention has a higher degree of fiberization and exhibits better mechanical and electrochemical properties.

[0037] from Figure 1 , Figure 2 As can be seen, compared with Comparative Example 1, due to the introduction of a certain amount of activated carbon in Example 1, the powder showed obvious agglomeration, higher degree of fiberization, better mechanical properties, lower ionic resistance, and significantly improved high-rate discharge capacity. Figure 3 As can be seen from the results, the dry electrode prepared in Example 1 has superior cycle performance.

[0038] Although increasing the activated carbon content helps improve the degree of fibrosis, when the amount of activated carbon added increases to 15 wt% (Comparative Example 2), the ionic resistance of the electrode increases, and the excessive amount of activated carbon added deteriorates the ion transport process inside the electrode; when the amount of activated carbon added increases to 20 wt% (Comparative Example 3), the activated carbon further affects the thermodynamic potential balance inside the electrode, and overcharging occurs during the first charge and discharge process. Therefore, the amount of activated carbon introduced should be appropriate.

[0039] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0040] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A dry electrode fabrication process for improving PTFE fibrous networks, characterized in that: Includes the following steps: Step 1: After mixing the active material particles, conductive agent, and activated carbon particles once, add the binder PTFE and mix again to obtain a mixture. Step 2: The mixture is subjected to fibrous treatment using ball milling to obtain a fibrous mixture; Step 3: Roll press the fibrous mixture into a film, and then combine it with a current collector to obtain a dry electrode; In step 1, the particle size D of the active material particles 50 The particle size D of activated carbon particles is 0.5~2μm. 50 It is 5~10μm.

2. The preparation process according to claim 1, characterized in that: In step 1, the active material particles are at least one of lithium cobalt oxide, lithium iron phosphate, lithium manganese oxide, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

3. The preparation process according to claim 1, characterized in that: In step 1, the conductive agent is at least one of carbon nanotubes, acetylene black, conductive carbon black, and carbon fiber.

4. The preparation process according to claim 1, characterized in that: In step 1, both the first and second mixing are carried out by stirring, with a stirring speed of 400~600 rpm and a time of 60~120 min.

5. The preparation process according to claim 1, characterized in that: In step 1, the content of each component in the mixture, by weight percentage, is 81-91% active material particles, 2-3% conductive agent, 5-10% activated carbon particles, and 2-3% binder PTFE.

6. The preparation process according to claim 1, characterized in that: In step 2, the ball milling speed is 600~800 rpm and the ball milling time is 60~90 min.

7. The preparation process according to claim 1, characterized in that: In step 3, the rolling temperature is 80~95°C, and the rolling gap thickness decreases from 400μm to 100μm.

8. The dry electrode prepared by the preparation process according to any one of claims 1 to 7.

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