Multi-element binder for dry-method electrode as well as preparation method and application of multi-element binder

Abstract

The invention discloses a multi-element binder for a dry-method electrode as well as a preparation method and application of the multi-element binder, and belongs to the field of lithium ion battery positive electrode materials. The multi-element binder comprises polytetrafluoroethylene and MAV, and the MAV is prepared from the following raw materials: sodium carboxymethyl cellulose, polyacrylic acid and polyvinylpyrrolidone. The preparation method comprises the following steps: (1) dissolving sodium carboxymethyl cellulose, polyacrylic acid and polyvinylpyrrolidone in water to obtain MAV, drying, and crushing into powder; and (2) mixing polytetrafluoroethylene with MAV to obtain the multi-element binder for the dry-method electrode. The multi-element binder provided by the invention can achieve the effects of strong adhesion, excellent conductivity and excellent stability.

Description

A multi-element binder for dry electrodes, its preparation method and application Technical Field

[0001] This invention relates to lithium-ion battery cathode materials, and in particular to a multi-element binder for dry electrode fabrication, its preparation method, and its application. Background Technology

[0002] With global energy shortages and increasing environmental awareness, lithium-ion batteries have been widely used in portable electronic devices, electric vehicles, and other fields due to their high energy density and long cycle life. In the manufacturing process of lithium-ion batteries, the electrode fabrication process has a significant impact on battery performance. Traditional wet processes suffer from problems such as high organic solvent consumption, high drying energy consumption, and severe environmental pollution. Furthermore, wet processes limit the thickness of the electrode sheets, hindering energy density improvements and increasing production costs. In contrast, dry electrode processes offer advantages such as simplicity, low cost, and environmental friendliness, and have received widespread attention in recent years. Moreover, they pave the way for battery miniaturization because the absence of solvents increases the maximum threshold of effective mass load, allowing for the manufacture of electrodes with higher mass loads. Currently, dry electrode processes based on binder fiberization heavily rely on polytetrafluoroethylene (PTFE) due to its excellent fiberization properties, which enable the formation of composite materials through mechanical mixing of active materials, conductive additives, and PTFE.

[0003] In existing technologies, commonly used dry electrode binders employ a single PTFE, which presents significant drawbacks. Firstly, its low surface energy results in very weak adhesion to other materials, meaning that PTFE-based electrodes exhibit poor adhesion to current collectors. Furthermore, PTFE binds active materials and conductive additives through simple mechanical anchoring rather than strong chemical or electrostatic affinity. Therefore, when the electrode structure undergoes repeated charge-discharge cycles leading to volume changes, its internal bonding function may become unsustainable over time. Single PTFE binders also suffer from insufficient fiberization and weak adhesion, resulting in poor electrode conductivity and mechanical stability. Summary of the Invention

[0004] Objectives of the invention: The present invention aims to provide a multi-element binder for dry-process electrodes with strong adhesion, excellent conductivity, and excellent stability; another objective of the present invention is to provide a method for preparing the above-mentioned binder; a third objective of the present invention is to provide an application of the above-mentioned binder in dry-process electrodes.

[0005] Technical solution: The dry electrode multi-component binder of the present invention includes polytetrafluoroethylene and MAV, wherein the raw materials for preparing MAV include sodium carboxymethyl cellulose, polyacrylic acid, and polyvinylpyrrolidone.

[0006] Preferably, the mass ratio of polytetrafluoroethylene to MAV is 1-2:1, and the mass ratio of sodium carboxymethyl cellulose, polyacrylic acid, and polyvinylpyrrolidone is 5:3-7:3-7.

[0007] The preparation method of the multi-component binder of the present invention includes the following steps: (1) dissolving sodium carboxymethyl cellulose, polyacrylic acid and polyvinylpyrrolidone in water and drying to obtain MAV; (2) mixing polytetrafluoroethylene with MAV to obtain a multi-component binder for dry electrode.

[0008] The dissolution conditions in step (1) are stirring at 200-300 rpm for 2-4 hours at 140-160℃; the drying temperature is 100-120℃ and the drying time is 12-14 hours.

[0009] The application of the multi-component binder in dry electrode according to the present invention includes the following steps: mixing battery active material, conductive agent and multi-component binder, cutting, kneading and granulating and then hot pressing into film, and then hot pressing and compounding with current collector to obtain dry electrode.

[0010] The mass ratio of the active material, conductive agent, and multi-component binder is 9:0.3-0.6:0.3-0.6.

[0011] The active material is at least one of the following cathode materials: lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, ternary lithium nickel cobalt manganese, and lithium nickel cobalt aluminum manganese.

[0012] The conductive agent is at least one of carbon black, conductive graphite, acetylene black, Super P, graphene, carbon nanotubes, Ketjen black, and carbon fiber.

[0013] The current collector is at least one of aluminum foil, carbon-coated aluminum foil, and adhesive-coated aluminum foil.

[0014] The temperature for hot pressing to form a film is 90-120℃; the temperature for hot pressing to composite is 90-120℃.

[0015] Invention Principle: This invention aims to provide a multi-component binder for preparing dry-process electrodes. By adding a multi-component binder (MAV) containing sodium carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and polyvinylpyrrolidone (PVP) to PTFE, the dry-process electrode binder exhibits excellent adhesion, conductivity, and stability, further improving the energy density of the battery cell. CMC forms a three-dimensional network during dry mixing, binding the active materials and conductive agents, and improving the mixing uniformity of the dry powder, ensuring electrode strength. PAA, containing a large number of -COOH groups, can form stable hydrogen bonds with the -OH groups in the alumina coating, thus acting as a hydrogen-bonding binder to enhance the adhesion of the electrode sheet. PVP can form a robust, inorganic-rich solid electrolyte interphase (SEI) film, thereby improving lithium-ion conductivity and interfacial stability. In addition, by utilizing the synergistic effect of PAA and PVP, the material is first prevented from agglomerating due to the steric hindrance of PVP and the electrostatic repulsion of CMC, so that a more uniform and dense three-dimensional physical skeleton of PTFE can be formed after PTFE fibrillation. Then, PAA in the three-dimensional skeleton of PTFE simultaneously bonds the -OH bonds of the active material and the alumina coating on the current collector through the rich -COOH groups, improving the overall integrity. This can simultaneously improve the adhesion, peel strength and interface stability of the electrode, forming a physically-chemically stable interface, thereby improving the cycle stability of the cell.

[0016] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The peel strength of the dry electrode obtained by the multi-element binder prepared by this method is as high as 22-27 N / m, which is 69.2%-107.7% higher than that of the traditional single PTFE binder; (2) The dry electrode obtained by the multi-element binder has excellent electrical performance and good interface stability: the 1C first discharge efficiency can reach up to 154.2 mAh / g, which is 9.7% higher than that of the traditional single PTFE binder, and the capacity retention rate after 50 cycles can reach up to 97.6%, which is 6.0% higher than that of the traditional single PTFE binder; (3) The dry electrode obtained by the multi-element binder has good wettability with electrolyte and a contact angle of only 31°. Attached Figure Description

[0017] Figure 1 shows the contact angle between the dry electrode and the electrolyte obtained in Example 3; Figure 2 shows the charge-discharge curve of the button cell assembled with the dry electrode obtained in Example 3; Figure 3 shows the cycle stability of the button cell assembled with the dry electrode obtained in Example 3. Detailed Implementation

[0018] The technical solution of the present invention will be further described below with reference to the embodiments.

[0019] Example 1 The dry electrode multi-component binder described in this example includes polytetrafluoroethylene and MAV in a mass ratio of 1.5:1. The MAV includes sodium carboxymethyl cellulose, polyacrylic acid, and polyvinylpyrrolidone in a mass ratio of 5:3:7.

[0020] The preparation method of the dry electrode multi-element binder described in this embodiment includes the following steps: (1) Dissolve 5g CMC powder, 3g PAA and 7g PVP in 200ml distilled water, heat to 140℃ and stir at 200rpm for 2 hours to form a transparent viscous solution MAV, dry at 100℃ for 12 hours, and then pulverize into powder.

[0021] (2) Mix PTFE powder and MAV powder at a mass ratio of 1.5:1 to obtain a multi-component binder.

[0022] The application of the multi-component binder in the dry electrode described in this embodiment includes the following steps: lithium iron phosphate, conductive carbon black, and multi-component binder are mixed evenly in a mass ratio of 9:0.5:0.5, and then the mixture is sheared at high speed to obtain a fibrous material. After kneading and granulation, the mixture is hot-pressed at 100°C to form a film, and then hot-pressed with a carbon-coated aluminum foil current collector at 100°C to obtain a dry electrode.

[0023] Example 2

[0024] The preparation method of the dry electrode binder described in this embodiment includes the following steps: (1) Dissolve 5g CMC powder, 5g PAA and 7g PVP in 200ml distilled water, heat to 150℃ and stir at 210rpm for 2.5 hours to form a transparent viscous solution MAV, dry at 110℃ for 12 hours, and then pulverize into powder.

[0025] (2) Mix PTFE powder and MAV powder at a mass ratio of 2:1 to obtain a multi-component binder.

[0026] The application of the multi-component binder in the dry electrode described in this embodiment includes the following steps: lithium manganese iron phosphate, carbon nanotubes, and multi-component binder are mixed evenly in a mass ratio of 9:0.5:0.5, and then the mixture is sheared at high speed to obtain a fibrous material. After kneading and granulation, the material is hot-pressed into a film at 120°C, and then hot-pressed with a carbon-coated aluminum foil current collector at 120°C to obtain a dry electrode.

[0027] Example 3

[0028] The preparation method of the dry electrode binder described in this embodiment includes the following steps: (1) Dissolve 5g CMC powder, 5g PAA and 5g PVP in 200ml distilled water, heat to 160℃ and stir at 205rpm for 2 hours to form a transparent viscous solution MAV, dry at 120℃ for 12 hours, and then pulverize into powder.

[0029] (2) Mix PTFE powder and MAV powder at a mass ratio of 1.5:1 to obtain a multi-component binder.

[0030] The application of the multi-component binder in the dry electrode described in this embodiment includes the following steps: lithium iron phosphate, conductive carbon black, and multi-component binder are mixed evenly in a mass ratio of 9:0.5:0.5, and then the mixture is sheared at high speed to obtain a fibrous material. After kneading and granulation, the mixture is hot-pressed at 105°C to form a film, and then hot-pressed with a carbon-coated aluminum foil current collector at 105°C to obtain a dry electrode.

[0031] Example 4

[0032] The preparation method of the dry electrode multi-element binder described in this embodiment includes the following steps: (1) Dissolve 5g CMC powder, 5g PAA and 5g PVP in 200ml distilled water, heat to 130℃ and stir at 200rpm for 3 hours to form a transparent viscous solution MAV, dry at 100℃ for 12 hours, and then pulverize into powder.

[0033] (2) Mix PTFE powder and MAV powder at a mass ratio of 1:1 to obtain a multi-component binder.

[0034] The application of the multi-component binder in the dry electrode described in this embodiment includes the following steps: lithium iron phosphate, conductive carbon black, and multi-component binder are mixed evenly in a mass ratio of 9:0.5:0.5, and then the mixture is sheared at high speed to obtain a fibrous material. After kneading and granulation, the mixture is hot-pressed into a film at 110°C, and then hot-pressed with a carbon-coated aluminum foil current collector at 105°C to obtain a dry electrode.

[0035] Example 5 The preparation method of the dry electrode multi-element binder described in this example includes the following steps: (1) Dissolve 5g CMC powder, 7g PAA and 3g PVP in 200ml distilled water, heat to 130℃ and stir at 200rpm for 3 hours to form a transparent viscous solution MAV, dry at 100℃ for 12 hours, and then pulverize into powder.

[0036] (2) Mix PTFE powder and MAV powder at a mass ratio of 1.5:1 to obtain a multi-component binder.

[0037] The application of the multi-component binder in the dry electrode described in this embodiment includes the following steps: lithium iron phosphate, conductive carbon black, and multi-component binder are mixed evenly in a mass ratio of 9:0.5:0.5, and then the mixture is sheared at high speed to obtain a fibrous material. After kneading and granulation, the mixture is hot-pressed into a film at 110°C, and then hot-pressed with a carbon-coated aluminum foil current collector at 105°C to obtain a dry electrode.

[0038] The similarities between Example 6 and Example 3 will not be repeated here. The difference is that the amount of CMC powder, PAA and PVP added in step (1) is 5g, 3g and 7g respectively.

[0039] The similarities between Example 7 and Example 3 will not be repeated here. The difference is that the amount of CMC powder, PAA and PVP added in step (1) is 5g, 7g and 3g respectively.

[0040] Comparative Example 1 uses traditional single PTFE as a binder without adding any other substances.

[0041] The application steps of this binder in the dry electrode are the same as in Example (3).

[0042] Comparative Example 2: PTFE powder and CMC powder were mixed at a mass ratio of 1.5:1 to obtain a multi-component binder.

[0043] The application steps of this multi-component binder in the dry electrode are the same as in Example (3).

[0044] The similarities between Comparative Example 3 and Example 3 will not be repeated here. The difference is that the amount of PVP added in step (1) is 0.

[0045] The similarities between Comparative Example 4 and Example 3 will not be repeated here. The difference is that the amount of PAA added in step (1) is 0.

[0046] The similarities between Comparative Example 5 and Example 3 will not be repeated here. The difference is that in step (1), the amount of PAA and PVP added is 9g and 1g, respectively.

[0047] Using lithium metal as the counter electrode, Celgard 2500 as the separator, and 1 mol / L LiPF6 dissolved in a mixed solvent of EC / (ethylene carbonate) / DMC (dimethyl carbonate) / EMC (methyl ethyl carbonate) (volume ratio 1:1:1), coin cells were fabricated and tested. Coin cells were prepared using the dry-process electrodes obtained in each experiment and tested. The peel strength of the electrode was measured according to GB / T2792-1999, the contact angle between the electrolyte and the electrode was measured according to GB / T30447-2013 and GB / T23367-2022, and the 1C discharge capacity and capacity retention were tested according to GB / T 42161-2022. The results are shown in Table 1.

[0048] Table 1. Test Results of Various Button Cells Sample Peel Strength (N / m) Contact Angle (°) First Discharge at 1C (mAh / g) Capacity Retention after 50 Cycles (1C, %) Example 1 2 2 3 8 1 48.6 95.8 Example 2 2 3 3 6 1 49.2 95.3 Example 3 2 7 3 1 1 54.2 97.6 Example 4 2 5 3 4 1 51.7 94.7 Example 5 2 4 3 3 1 50.3 96.5 Example 6 2 3 3 7 1 47.1 96.0 Example 7 2 5 3 2 1 51.2 96.8 Comparative Example 1 1 3 5 3 1 40.6 92.1 Comparative Example 2 1 5 4 8 1 42.5 92.8 Comparative Example 3 2 0 4 2 1 43.5 94.5 Comparative Example 4 1 6 4 5 1 46.5 93.4 Comparative Example 5 1 9 4 0 1 4 8 94.9 Analysis of the data in Table 1 shows that the multi-element binder prepared using this method exhibits strong adhesion, excellent conductivity, and excellent stability. When used to fabricate a dry electrode and then assembled into a coin cell, the coin cell demonstrates good electrical performance. Specifically, under the same parameters, when the mass ratio of CMC, PAA, and PVP is 1:1:1 (Example 3), all performance parameters reach their optimal values. Compared with the comparative examples, Example 1 shows significant improvements in electrode peel strength, capacity, and cycle stability. This is attributed to the strong and elastic bonding network formed by PAA grafted onto the CMC, and the high-speed ion transport channels and stable interface provided by the grafted PVP.

[0049] Analysis of the experimental data from Comparative Example 1 and the various embodiments shows that the coin cell obtained with a single PTFE binder exhibits poor peel strength, electrolyte wettability, and conductivity. Introducing CMC as a binder and dispersant (Comparative Example 2) into the system improves the electrochemical performance of the coin cell due to its good dispersibility and certain hydrophilicity, which facilitates electrolyte wettability. However, the bonding strength still needs improvement. Furthermore, grafting PAA onto CMC (Comparative Example 3) significantly enhances the peel strength of the dry-process electrode composite sheet due to the formation of numerous hydrogen bonds, promoting tighter adhesion between particles. Simultaneously, the good elasticity of PAA buffers volume changes. Grafting PVP onto CMC (Comparative Example 4) demonstrates its excellent lithium affinity; the lone pair electrons in the C=O group can form pairing-dissociation channels with lithium ions, enhancing the lithium-ion transport capacity of the binder phase. Additionally, the amide groups in PVP help form a more stable SEI film on the electrode surface, reducing continuous electrolyte decomposition and thus improving battery cycle stability. Grafting PAA and PVP onto CMC simultaneously (Comparative Example 5) not only improves the battery's adhesion performance but also accelerates lithium-ion transport, exhibiting superior discharge capacity and cycle stability compared to other comparative examples. However, analysis of Comparative Example 5 and Example 3 reveals that the optimal mass ratio of CMC, PAA, and PVP is not 5:9:1.

[0050] Figure 1 shows the contact angle between the dry electrode obtained in Example 3 and the electrolyte. The angle is 31°, indicating that the electrolyte has good wettability with the dry electrode, which is beneficial to lithium-ion transport. As shown in Figures 2-3, the coin cell assembled using the dry electrode prepared by this method exhibits good charge-discharge efficiency and cycle stability at a 1C rate, and the capacity retention rate is still as high as 97.6% after 50 cycles.

Claims

1. A multi-element binder for dry-process electrodes, characterized in that, The multi-component binder includes polytetrafluoroethylene and MAV, and the raw materials for preparing MAV include sodium carboxymethyl cellulose, polyacrylic acid, and polyvinylpyrrolidone.

2. The multi-element binder for dry electrodes according to claim 1, characterized in that, The mass ratio of polytetrafluoroethylene to MAV is 1-2:1, and the mass ratio of sodium carboxymethyl cellulose, polyacrylic acid, and polyvinylpyrrolidone is 5:3-7:3-7.

3. A method for preparing the multi-component adhesive according to claim 1 or 2, characterized in that, Includes the following steps: (1) Dissolve sodium carboxymethyl cellulose, polyacrylic acid, and polyvinylpyrrolidone in water and dry to obtain MAV; (2) Mix polytetrafluoroethylene with MAV to obtain a multi-element binder for dry electrode.

4. The preparation method according to claim 3, characterized in that, The dissolution conditions described in step (1) are stirring at 200-300 rpm for 2-4 hours at 130-160℃; the drying temperature is 100-120℃ and the drying time is 12-14 hours.

5. The application of the multi-component binder as described in claim 1 or 2 in a dry electrode.

6. The application according to claim 5, characterized in that, Includes the following steps: Battery active materials, conductive agents, and multi-component binders are mixed, sheared, kneaded, granulated, and then hot-pressed into a film. This film is then hot-pressed and compounded with a current collector to obtain a dry electrode.

7. The application according to claim 6, characterized in that, The mass ratio of the active material, conductive agent, and multi-component binder is 9:0.3-0.6:0.3-0.

6.

8. The application according to claim 6, characterized in that, The active material is at least one of the following cathode materials: lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, ternary nickel cobalt manganese lithium, and nickel cobalt aluminum manganese lithium; the conductive agent is at least one of the following: carbon black, conductive graphite, acetylene black, Super P, graphene, carbon nanotubes, Ketjen black, and carbon fiber.

9. The application according to claim 6, characterized in that, The current collector is at least one of aluminum foil, carbon-coated aluminum foil, and adhesive-coated aluminum foil.

10. The application according to claim 6, characterized in that, The temperature for hot pressing to form a film is 90-120℃; the temperature for hot pressing to composite is 90-120℃.

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