Method of making flexible solid dry electrode sheet

Abstract

This invention provides a method for preparing a flexible solid-state dry electrode sheet. The method first mixes polytetrafluoroethylene (PTFE) with lithium trimethylsilanolate to obtain a first powder; then, an electrode active material and a conductive agent are added to the first powder and mixed to obtain a second powder; the second powder is then hot-rolled into a film and thinned by rolling to form an electrode film; finally, the electrode film is hot-pressed onto a current collector to obtain the flexible solid-state dry electrode sheet. This method modifies PTFE by adding lithium trimethylsilanolate, improving the adhesion of the binder and increasing mechanical strength. By controlling the amount of lithium trimethylsilanolate and PTFE, this invention results in an electrode sheet with good mechanical properties and viscoelasticity; furthermore, the adhesion of lithium trimethylsilanolate to the fiber surface provides a lithium-ion pathway, thereby increasing ionic conductivity.

Description

Technical Field

[0001] This invention relates to the field of electrode fabrication technology, and more particularly to a method for fabricating a flexible solid-state dry electrode. Background Technology

[0002] Dry electrode technology is highly environmentally friendly because it does not use any solvents in its production process. Lithium-ion batteries using this novel dry film-forming process are expected to significantly improve energy density and greatly reduce production costs compared to traditional liquid lithium-ion batteries. Polytetrafluoroethylene (PTFE) is a widely used binder; during the preparation process, PTFE particles are sheared and mixed to form adhesive fibrils that can tightly bond with conductive carbon and active materials.

[0003] However, PTFE has limited lithium-ion conductivity, and due to its limited viscoelasticity, it cannot guarantee sufficient interfacial adhesion between the active material and conductive carbon. This leads to the formation of voids in the active material during volume expansion / contraction, reducing battery capacity and cycle stability. Furthermore, through electrochemical reduction defluorination, PTFE can be readily converted into alkyl-type carbon, subsequently producing conductive sp... 2 Carbon forms a mixed conductive interface, which destabilizes the SEI layer by increasing its electronic conductivity.

[0004] In view of this, it is necessary to design a method for preparing flexible solid-state dry electrode sheets to solve the above problems. Summary of the Invention

[0005] To address the shortcomings of the prior art, the present invention aims to provide a method for preparing a flexible solid-state dry electrode sheet. This method uses lithium trimethylsilanolate to modify PTFE. By controlling the amount of lithium trimethylsilanolate and PTFE, the resulting electrode sheet has good mechanical properties and viscoelasticity. Furthermore, the adhesion of lithium trimethylsilanolate to the fiber surface can provide a lithium ion pathway, thereby increasing ionic conductivity.

[0006] To achieve the above objectives, the present invention provides a method for preparing a flexible solid-state dry electrode sheet, comprising the following steps:

[0007] S1. Polytetrafluoroethylene and lithium trimethylsilyl alcohol are mixed at a first rotation speed to obtain a first powder;

[0008] S2. Add electrode active material and conductive agent to the first powder obtained in step S1, and mix at the second speed for 10-30 minutes; then increase the speed to the third speed and continue mixing for 10-30 minutes to obtain the second powder.

[0009] S3. The second powder obtained in step S2 is hot-rolled into a film and rolled thinned to form an electrode film; then the electrode film is hot-pressed onto the current collector to obtain a flexible solid dry electrode sheet.

[0010] As a further improvement of the present invention, in step S1, the mass ratio of polytetrafluoroethylene to lithium trimethylsilanolate is polytetrafluoroethylene: lithium trimethylsilanolate = 4:(1-16).

[0011] As a further improvement of the present invention, in step S2, the mass ratio of the first powder, the electrode active material, and the conductive agent is first powder: electrode active material: conductive agent = 2:(91-95):(7-3).

[0012] As a further improvement of the present invention, the electrode active material is one of lithium iron phosphate, activated carbon, graphite, silicon, hard carbon, soft carbon, lithium manganese iron phosphate, ternary nickel cobalt manganese, lithium titanate, ternary nickel cobalt aluminum, and lithium cobalt oxide.

[0013] As a further improvement of the present invention, the conductive agent is any one or a mixture of several of VGCF, acetylene black, Super-P, carbon nanotubes, carbon fibers, Ketjen black, graphite conductive agent, and graphene.

[0014] As a further improvement of the present invention, the current collector is one of aluminum foil, etched aluminum foil, carbon-coated aluminum foil, and aluminum mesh.

[0015] As a further improvement of the present invention, in step S3, the second powder is rolled thinned to 50-500 μm, preferably to 100-200 μm.

[0016] As a further improvement of the present invention, in step S3, the hot rolling temperature is 60-200℃, preferably 80-120℃; the hot pressing temperature is 80-120℃, and the pressure is 5-30t; preferably, the hot pressing temperature is 80-100℃, and the pressure is 5-20t.

[0017] As a further improvement of the present invention, in step S3, the pressure of the roller during the thinning process is 5-40t, and the temperature is 40-120℃. Preferably, the pressure is 10-30t, and the temperature is 80-100℃.

[0018] As a further improvement of the present invention, the first rotational speed is 300-500 rpm, the second rotational speed is 600-800 rpm, and the third rotational speed is 2000-3000 rpm.

[0019] The beneficial effects of this invention are:

[0020] This invention provides a method for preparing flexible solid-state dry electrode sheets. The method uses lithium trimethylsilanolate to modify PTFE. By controlling the amount of lithium trimethylsilanolate and PTFE, the resulting electrode sheet has good mechanical properties and viscoelasticity. Furthermore, the adhesion of lithium trimethylsilanolate to the fiber surface can provide lithium ion pathways, thereby increasing ionic conductivity.

[0021] The flexible solid-state dry electrode sheet provided by this invention has a film thickness of ≥150μm and excellent mechanical properties. It can be used to assemble lithium batteries of any structure, exhibiting good structural adaptability and a wider range of applications, making it suitable for engineering production. Furthermore, the assembled battery is unaffected by the mechanical properties of the electrode sheet, ion diffusion, and interfacial impedance, possessing excellent mechanical and electrochemical properties. The flexible solid-state dry electrode sheet provided by this invention has significant practical value in the battery field. Attached Figure Description

[0022] Figure 1 The image shows a SEM image of the flexible solid-state dry electrode sheet prepared in Example 1.

[0023] Figure 2 SEM image of the flexible solid-state dry electrode sheet prepared for Comparative Example 1. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] It should also be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and / or processing steps closely related to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0026] Additionally, it should be noted that 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.

[0027] Please see Figure 1 As shown, the present invention provides a method for preparing a flexible solid-state dry electrode sheet, comprising the following steps:

[0028] S1. Polytetrafluoroethylene and lithium trimethylsilyl alcohol are mixed at a first rotation speed to obtain a first powder;

[0029] The mass ratio of polytetrafluoroethylene (PTFE) to lithium trimethylsilanolate is PTFE:lithium trimethylsilanolate = 4:(1-16). The first rotational speed is 300-500 rpm.

[0030] S2. Add electrode active material and conductive agent to the first powder obtained in step S1, and mix at the second speed for 10-30 minutes; then increase the speed to the third speed and continue mixing for 10-30 minutes to obtain the second powder.

[0031] The mass ratio of the first powder, the electrode active material, and the conductive agent is: first powder: electrode active material: conductive agent = 2:(91-95):(7-3).

[0032] The electrode active material is one of lithium iron phosphate, activated carbon, graphite, silicon, hard carbon, soft carbon, lithium manganese iron phosphate, ternary nickel cobalt manganese, lithium titanate, ternary nickel cobalt aluminum, and lithium cobalt oxide.

[0033] The conductive agent is any one or a mixture of several of the following: VGCF, acetylene black, Super-P, carbon nanotubes, carbon fibers, Ketjen black, graphite conductive agent, and graphene.

[0034] The second speed is 600-800 rpm, and the third speed is 2000-3000 rpm.

[0035] S3. The second powder obtained in step S2 is hot-rolled into a film and rolled thinned to form an electrode film; then the electrode film is hot-pressed onto the current collector to obtain a flexible solid dry electrode sheet.

[0036] The hot rolling temperature is 60-200℃, with a preferred temperature of 80-120℃.

[0037] The current collector is one of aluminum foil, etched aluminum foil, carbon-coated aluminum foil, or aluminum mesh.

[0038] In step S3, the rolling pressure during the thinning process is 5-40t, and the temperature is 40-120℃. Preferably, the pressure is 10-30t, and the temperature is 80-100℃.

[0039] The second powder is rolled thinned to 50-500 μm, preferably to 100-200 μm.

[0040] The hot-pressing temperature is 80-120℃ and the pressure is 5-30t; preferably, the hot-pressing temperature is 80-100℃ and the pressure is 5-20t.

[0041] This invention uses lithium trimethylsilanolate to modify PTFE. By controlling the amount of lithium trimethylsilanolate and PTFE, the resulting electrode sheet has good mechanical properties and viscoelasticity. Furthermore, lithium trimethylsilanolate adheres to the fiber surface, with PTFE as the main supporting structure. Lithium trimethylsilanolate can provide lithium ion pathways, thereby increasing ionic conductivity.

[0042] The preparation method of the flexible solid-state dry electrode sheet provided by the present invention will be described below with reference to specific embodiments.

[0043] Example 1

[0044] Example 1 provides a method for preparing a flexible solid-state dry electrode sheet, comprising the following steps:

[0045] Mix 1g PTFE and 1g lithium trimethylsilyl alcohol in a mixer at 300rpm for 10 minutes. Then add 95g LFP and 3g VGCF and mix at 600rpm for 10 minutes. Then increase the speed to 2000rpm and mix for 10 minutes. Then hot roll press to form a film, roll press to thin to 150um, and hot press composite onto carbon-coated aluminum foil to obtain a flexible solid dry electrode sheet.

[0046] Comparative Example 1

[0047] Compared with Example 1, the only difference in Comparative Example 1 is that trimethylsilyl alcohol lithium was not used. Specifically, the trimethylsilyl alcohol lithium in Example 1 was replaced with polytetrafluoroethylene. Other experimental parameters and conditions are basically the same as those in Example 1, and will not be repeated here.

[0048] Example 2

[0049] Example 2 provides a method for preparing a flexible solid-state dry electrode sheet, comprising the following steps:

[0050] Mix 1.6g PTFE and 0.4g lithium trimethylsilyl alcohol in a mixer at 300rpm for 10 minutes. Then add 91g LFP and 7g VGCF and mix at 600rpm for 10 minutes. After that, increase the speed to 2000rpm and mix for 10 minutes. Then hot roll press to form a film, roll press to thin it to 150um, and hot press it onto carbon-coated aluminum foil to obtain a flexible solid-state dry electrode sheet.

[0051] Example 3

[0052] Example 3 provides a method for preparing a flexible solid-state dry electrode sheet, comprising the following steps:

[0053] Mix 0.4g PTFE and 1.6g lithium trimethylsilyl alcohol in a mixer at 300rpm for 10 minutes. Then add 93g LFP and 5g VGCF and mix at 600rpm for 10 minutes. Then increase the speed to 2000rpm and mix for 10 minutes. Then hot roll press to form a film, roll press to thin to 150um, and hot press composite onto carbon-coated aluminum foil to obtain a flexible solid-state dry electrode sheet.

[0054] Comparative Examples 2-3

[0055] Compared with Example 1, the main difference between Comparative Examples 2 and 3 is that the mass ratio of polytetrafluoroethylene to lithium trimethylsilyl alcohol is changed, and the mass ratio of the first powder, electrode active material, and conductive agent is changed, as shown in Table 1 below. Other experimental parameters and conditions are basically the same as those in Example 1, and will not be repeated here.

[0056] For ease of comparison, the main process parameters of Examples 1-3 and Comparative Examples 1-3 are summarized in Table 1 below.

[0057] Table 1

[0058]

[0059] Figure 1 The image shows a SEM image of the flexible solid-state dry electrode sheet prepared in Example 1.

[0060] Figure 2 The image shows a SEM image of the flexible solid-state dry electrode sheet prepared in Comparative Example 1. It can be seen that both contain PTFE slender fibers and VGCF coarse fibers. Figure 1 The particles adhering to the surface are lithium trimethylsilanolate. The adhesion of lithium trimethylsilanolate to the surface can provide lithium-ion pathways, thereby increasing ionic conductivity. Figure 2 No obvious particles adhered to the surface.

[0061] Experimental characterization:

[0062] 1. Peel force test: A tensile tester was used at a strain rate of 1 mm / min. -1 Peeling measurements were performed on samples from Examples 1-3 and Comparative Examples 1-3 under the following conditions, and the test data are shown in Table 2.

[0063] 2. Ionic conductivity of lithium-ion batteries:

[0064] Based on the 2025 battery casing, a binder (a mixture of polytetrafluoroethylene and lithium trimethylsilyl alcohol) was pressed into a circular sheet with a diameter of 19 mm and a thickness of d. A stainless steel circular sheet with an area of ​​A, a binder sheet, and liquid electrolyte were used to assemble a stainless steel / stainless steel symmetrical battery. The impedance Rs was measured, and the ionic conductivity σ was calculated using the formula σ = d / (Rs × A). Samples from Examples 1-3 and Comparative Examples 1-3 were tested, and the test data are shown in Table 2.

[0065] 3. Cycle performance of lithium-ion batteries:

[0066] Using the LAND battery testing system, the prepared battery was charged at a constant current of 0.5C to 3.7V at 25℃, then charged at a constant voltage of 3.7V to a current of 0.05C, rested for 5 minutes, and then discharged at 0.5C to 2.5V. The resulting discharge capacity was recorded as the initial capacity C0. The above steps were repeated for the same battery, and the discharge capacity Cn of the battery after the 100th cycle was recorded. The battery capacity retention rate after each cycle is Pn = (Cn / C0) × 100%. The difference in cycle performance can be reflected by the battery capacity retention rate after a specific number of cycles.

[0067] The samples from Examples 1-3 and Comparative Examples 1-3 were tested, and the data are shown in Table 2.

[0068] Table 2

[0069]

[0070] As shown in the table above, the peeling forces of Examples 1-3 are all higher than those of Comparative Examples 1-3, indicating that the addition of lithium trimethylsilanolate can significantly increase the interfacial adhesion.

[0071] The ionic conductivity of Examples 1-3 was higher than that of Comparative Examples 1-3, indicating that the addition of lithium trimethylsilyl alcohol can significantly enhance the ion transfer rate.

[0072] The capacity retention rates of Examples 1-3 and Comparative Examples 1-3 increased with increasing amounts of lithium trimethylsilanolate, reaching a peak at a 1:1 ratio, indicating that appropriate addition of lithium trimethylsilanolate significantly enhances electrochemical stability. The capacity retention rate of Example 1 was higher than that of Examples 2 and Comparative Example 2. However, when the amount of lithium trimethylsilanolate was further increased (Comparative Example 3), the performance began to decline, indicating that a 1:1 ratio is optimal. This is because PTFE is crucial for maintaining the cathode structure, and the amount of PTFE cannot be too small. Compared to Comparative Example 2, the capacity retention rate of Comparative Example 3 decreased, indicating that adding too much lithium trimethylsilanolate is detrimental to stability; at this point, the amount of PTFE was insufficient to maintain structural stability.

[0073] It should be noted that the electrode active material, lithium iron phosphate, can be replaced by one of the following: activated carbon, graphite, silicon, hard carbon, soft carbon, lithium manganese iron phosphate, ternary nickel-cobalt-manganese, lithium titanate, ternary nickel-cobalt-aluminum, and lithium cobalt oxide. The conductive agent, VGCF, can be replaced by any one or a mixture of several of the following: acetylene black, Super-P, carbon nanotubes, carbon fibers, Ketjen black, graphite conductive agent, and graphene.

[0074] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a flexible solid-state dry electrode sheet, characterized in that, Includes the following steps: S1. Polytetrafluoroethylene and lithium trimethylsilyl alcohol are mixed at a first rotation speed to obtain a first powder; S2. Add electrode active material and conductive agent to the first powder obtained in step S1, and mix at the second speed for 10-30 minutes; then increase the speed to the third speed and continue mixing for 10-30 minutes to obtain the second powder. S3. The second powder obtained in step S2 is hot-rolled into a film and rolled thinned to form an electrode film; then the electrode film is hot-pressed onto the current collector to obtain a flexible solid dry electrode sheet.

2. The method for preparing a flexible solid-state dry electrode sheet according to claim 1, characterized in that, In step S1, the mass ratio of polytetrafluoroethylene to lithium trimethylsilanolate is polytetrafluoroethylene:lithium trimethylsilanolate = 4:(1-16).

3. The method for preparing a flexible solid-state dry electrode sheet according to claim 1, characterized in that, In step S2, the mass ratio of the first powder, the electrode active material, and the conductive agent is first powder: electrode active material: conductive agent = 2:(91-95):(7-3).

4. The method for preparing a flexible solid-state dry electrode sheet according to claim 1, characterized in that, The electrode active material is one of lithium iron phosphate, activated carbon, graphite, silicon, hard carbon, soft carbon, lithium manganese iron phosphate, ternary nickel cobalt manganese, lithium titanate, ternary nickel cobalt aluminum, and lithium cobalt oxide.

5. The method for preparing a flexible solid-state dry electrode sheet according to claim 1, characterized in that, The conductive agent is any one or a mixture of several of the following: VGCF, acetylene black, Super-P, carbon nanotubes, carbon fibers, Ketjen black, graphite conductive agent, and graphene.

6. The method for preparing a flexible solid-state dry electrode sheet according to claim 1, characterized in that, The current collector is one of aluminum foil, etched aluminum foil, carbon-coated aluminum foil, or aluminum mesh.

7. The method for preparing a flexible solid-state dry electrode sheet according to claim 1, characterized in that, In step S3, the second powder is rolled thin to 50-500 μm.

8. The method for preparing a flexible solid-state dry electrode sheet according to claim 1, characterized in that, In step S3, the temperature of hot-pressing composite is 80-120℃, and the pressure is 5-30t.

9. The method for preparing a flexible solid-state dry electrode sheet according to claim 1, characterized in that, In step S3, the pressure of the roller during the thinning process is 5-40t, and the temperature is 40-120℃.

10. The method for preparing a flexible solid-state dry electrode sheet according to claim 1, characterized in that, The first rotational speed is 300-500 rpm, the second rotational speed is 600-800 rpm, and the third rotational speed is 2000-3000 rpm.

Images