A low internal resistance ultra-thin dry-process positive electrode and its preparation method

Abstract

This application discloses a method for preparing a low-internal-resistance, ultra-thin dry-process positive electrode in the field of chemical energy storage battery technology, comprising the following steps: S1. Mixing: Stirring and mixing the active material, binder, and conductive agent at a temperature of 10-20°C to obtain a powder; S2. Electrostatic spraying: In a high-voltage electrostatic environment, atomizing and spraying the granular powder onto the surface of a metal current collector under the action of compressed air to obtain a pole piece with a thickness of less than 80 μm; S3. Pole piece baking: High-temperature baking the sprayed pole piece; S4. Pole piece rolling: Differential hot pressing the baked pole piece to obtain a low-internal-resistance, ultra-thin dry-process pole piece with a thickness of less than 70 μm. By using a low-speed temperature-controlled mixing process and a differential hot pressing process to control the degree of binder fibrillation, combined with an electrostatic spraying method to prepare a low-internal-resistance electrode, the thickness of the positive electrode prepared by this method can be reduced to less than 70 μm, significantly improving the battery's rate performance.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical energy storage batteries, and in particular to a low-internal-resistance ultra-thin dry-process positive electrode and a preparation method thereof. Background Art

[0002] The electrode preparation process for lithium-ion batteries is crucial for performance and is categorized into two types: wet and dry processes. While the wet process is more mature, it suffers from high manufacturing costs and difficulties with solvent recovery. In contrast, the dry process eliminates the need for solvents, significantly reducing manufacturing costs.

[0003] At present, the principle of the mainstream dry electrode preparation technology is to transform the fibrillated binder such as PTFE from the triclinic system to the hexagonal system under high temperature environment, so that the molecular chain becomes soft and, under the action of external shear force, changes from agglomerates to fibrils, making it a network of adhesive active materials and conductive agents, and compounding with the collector under hot pressing treatment, and rolling into pole pieces. However, the degree of rolling that can be performed on the self-supporting film obtained by the fibrillation preparation process is limited. Especially for the positive electrode, when the thickness is thinned to a certain extent, continuous hot pressing will cause cracks and damage to the pole piece. The thickness of the dry positive electrode prepared by fibrillation is generally above 100um, which makes the electron / ion transmission path of the dry pole piece longer, resulting in poor pole piece rate performance.

[0004] Referring to the existing technology, dry electrode preparation is often optimized from the material side (such as patent CN 117790680A) and the process side (such as CN 117673248A). However, the dry electrodes prepared by these methods are usually thicker than 100 μm, have large internal resistance and poor rate performance, which cannot meet the needs of high-power lithium-ion batteries. Summary of the Invention

[0005] This invention aims to provide a low-internal-resistance, ultra-thin dry-process positive electrode and its preparation method. This method utilizes a low-speed temperature-controlled mixing process and a differential hot pressing process to control the degree of binder fibrillation, combined with an electrostatic spraying method to produce a low-internal-resistance electrode. This method can reduce the thickness of the positive electrode to less than 70 μm, significantly improving the battery's rate performance.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A method for preparing a low internal resistance ultra-thin dry-process positive electrode comprises the following steps:

[0008] S1. Mixing: Stir and mix the active material, binder and conductive agent at a temperature of 10-20°C to obtain a powder;

[0009] S2. Electrostatic spraying: In a high-voltage electrostatic environment, the granular powder is sieved and then atomized and sprayed onto the surface of the metal current collector under the action of compressed air to obtain a pole piece with a thickness of less than 80 μm.

[0010] S3. Pole sheet rolling: The baked pole sheet is subjected to differential hot pressing treatment to obtain a low internal resistance ultra-thin dry-process pole sheet with a thickness of less than 70um.

[0011] Working principle and beneficial effects of the present invention:

[0012] Currently, the mainstream dry-process electrode preparation technology is based on the principle of transforming fibrillated binders such as PTFE from triclinic to hexagonal crystals under high temperature, softening the molecular chains. Under the action of external shear force, the agglomerates are transformed into fibrils, forming a network of active materials and conductive agents. The fibrillated powder is then composited with the current collector under hot pressing and pressed into pole pieces. However, the initial film thickness of the fibrillated powder obtained by this preparation process is generally thick, and the degree of thinning by pressing is limited. The final pole piece thickness is usually thick, which makes the electron / ion transmission path longer and increases the degree of electrode polarization, seriously affecting the power performance of the battery.

[0013] This patented method achieves uniform mixing of powders without fibrillating the binder (temperature and shear force), preventing powder agglomeration. Sieving the powders produces uniform, small-particle powders. The resulting small-particle powders are then applied to the current collector via electrostatic spraying, resulting in an electrode sheet with a thinner initial thickness. The binder fibrillation level on the electrode sheet is relatively low, providing more room for rolling and thinning. During the differential hot pressing process, the high temperature and shear forces required for binder fibrillation are applied, resulting in a high degree of fibrillation. This further thins the electrode sheet, increases the bonding strength between the active material and the current collector, and reduces the contact resistance between the active material and the current collector. This method reduces the unevenness caused by powder agglomeration during electrostatic spraying and addresses the issue of insufficient bonding strength often encountered during electrostatic spraying. The resulting electrode sheet is thinner and has better rate performance.

[0014] Optimally, the active materials used are LiCoO2, LiMn2O4, LiFePO4, LiNi 1-x-y Co y Mn x O2 (NCM ternary material), LiNi 1-x-y Co y Al x O2 (NCA ternary material), LiM x Mn 2-x O4 (M is Fe or Co doping atom) is a positive electrode material for lithium-ion batteries, and the positive electrode material accounts for 90% to 98% of the mass.

[0015] Optimally, the binder used is one or more of polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), and the binder mass accounts for 1% to 5%.

[0016] Optimally, the conductive agent used is one or more of carbon nanotubes (CNTs), superconducting carbon black (SP), conductive graphite (KS-6), and Ketjen black (KB), and the mass proportion of the conductive agent is 1% to 5%.

[0017] Optimally, the S1 controls the stirring speed to be 200-800 r / min, and the mixing time is 10-30 min.

[0018] Optimally, the voltage of the S2 high-voltage static electricity is 50~90kV.

[0019] Optimally, the S2 atomization pressure is 0.2~0.4MPa, and the spray flow rate pressure is 0.3~0.6MPa.

[0020] Optimally, the speed differential ratio of the upper and lower rollers of S3 is controlled at above 3:1, and the hot pressing temperature is controlled at 80-150°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a scanning electron microscope image of the powder;

[0022] Figure 2 This is a comparison chart of the thickness of the pole piece;

[0023] Figure 3 This is a comparison chart of resistivity test;

[0024] Figure 4 This is a comparison chart of the magnification test. DETAILED DESCRIPTION

[0025] The following is further described in detail through specific implementation methods:

[0026] Example-1: Take 940g of lithium cobalt oxide (LCO), 30g of polytetrafluoroethylene (PTFE), and 30g of conductive carbon black (SP) and add them to a high-speed stirring device. Mix the materials at a speed of 600r / min, control the temperature at 15°C, and stir for 15min. Sieve the stirred powder with 2000 mesh. Use electrostatic spraying to adsorb the powder on aluminum foil. The voltage is 60kV, the atomization pressure is 0.3MPa, and the spray flow rate pressure is 0.4MPa. Use differential hot pressing for thinning and compounding. The differential speed ratio of the upper and lower rollers is controlled at 3:1. The hot pressing temperature is 120°C. The final positive electrode sheet loading is 2.86g / 100cm 2 , thickness is 67um.

[0027] Example-2: Take 940g of lithium cobalt oxide (LCO), 30g of polytetrafluoroethylene (PTFE), and 30g of conductive carbon black (SP) and add them to a high-speed stirring device. Mix the materials at a speed of 600r / min, control the temperature at 20°C, and stir for 15min. Sieve the stirred powder with 2000 mesh. Use electrostatic spraying to adsorb the powder on aluminum foil. The voltage is 60kV, the atomization pressure is 0.3MPa, and the spray flow rate pressure is 0.4MPa. Use differential hot pressing for thinning and compounding. The differential speed ratio of the upper and lower rollers is controlled at 3:1. The hot pressing temperature is 120°C. The final positive electrode sheet load is 2.86g / 100cm 2 , thickness is 70um.

[0028] Example-3: Take 940g of lithium cobalt oxide (LCO), 30g of polytetrafluoroethylene (PTFE), and 30g of conductive carbon black (SP) and add them to a high-speed stirring device. Mix the materials at a speed of 600r / min, control the temperature at 10°C, and stir for 15min. Sieve the stirred powder with 2000 mesh. Use electrostatic spraying to adsorb the powder on aluminum foil. The voltage is 60kV, the atomization pressure is 0.3MPa, and the spray flow rate pressure is 0.4MPa. Use differential hot pressing for thinning and compounding. The differential speed ratio of the upper and lower rollers is controlled at 3:1. The hot pressing temperature is 120°C. The final positive electrode sheet loading is 2.86g / 100cm 2 , thickness is 68um.

[0029] Comparative Example-1

[0030] 940g of lithium cobalt oxide (LCO) and 30g of conductive carbon black (SP) were added to a high-speed stirring device, the temperature was controlled at 70°C, and the premix was performed at a speed of 1200r / min for 15 minutes. 30g of polytetrafluoroethylene (PTFE) was added to the stirring device, and the binder was fiberized at a speed of 4000r / min for 20 minutes. The fiberized powder was hot-pressed into a self-supporting film and thinned to a surface loading of 4.26g / 100cm 2 The hot pressing temperature is 120° C. The self-supporting film and the current collector are composited by hot pressing to obtain a positive electrode sheet with a thickness of 105 μm.

[0031] Comparative Example-2

[0032] Take 940g of lithium cobalt oxide (LCO) and 30g of conductive carbon black (SP) and add them to a high-speed stirring device, control the temperature to 70°C, premix at a speed of 1200r / min, and stir for 15min. Add 30g of polytetrafluoroethylene (PTFE) to the stirring device, use a speed of 4000r / min to fiberize the binder, and stir for 20min. Use electrostatic spraying to adsorb the powder on the aluminum foil, the voltage is 60kV, the atomization pressure is 0.3MPa, and the spray flow rate pressure is 0.4MPa. Use hot pressing to compact the fiberized powder and the current collector, and the hot pressing temperature is 120°C. The final positive electrode sheet loading is 4.12g / 100cm 2 , thickness is 101um.

[0033] The powders, electrodes and soft-pack batteries prepared in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2 were subjected to electron microscope scanning, thickness, resistance and rate tests respectively. The results are as follows: Figures 1-4 shown.

[0034] The powders prepared in Example 1, Example 2, and Example 3 were uniformly dispersed, and the binder showed no obvious fiberization. The powders prepared in Comparative Example 1 and Comparative Example 2 showed obvious fiber filaments and powder agglomeration. The electrode sheets prepared in Example 1, Example 2, and Example 3 had thicknesses of 67.09, 68.36, and 69.61 μm, respectively, and resistances of 32.39, 34.87, and 33.55 mΩ, respectively. The electrode sheets in Comparative Example 1 and Comparative Example 2 had thicknesses of 105.43 and 101.49 μm, respectively, and resistances of 78.43 and 86.9 mΩ, respectively. This demonstrates that the electrode sheets prepared in the Examples have lower thickness and internal resistance, which is more conducive to the rate performance of the electrode sheets. The prepared soft-pack batteries were subjected to 1C, 5C, 10C, 20C and 40C discharge rate tests. The 40C rate capacity retention rates of the soft-pack batteries prepared in Example-1, Example-2 and Example-3 were 77.23%, 76.06% and 75.03% respectively. The 40C rate capacity retention rates of the soft-pack batteries prepared in Comparative Example-1 and Comparative Example-2 were 50.81% and 42.46% respectively.

Claims

1. A method for preparing a low internal resistance ultra-thin dry-process positive electrode, characterized by: The following steps are included: S1. Mixing: Stirring the active material, binder and conductive agent at a temperature of 10-20°C to obtain a powder; the stirring speed in S1 is controlled at 200-800 r / min, and the mixing time is 10-30 min; S2. Electrostatic spraying: In a high-voltage electrostatic environment, the granular powder is sieved and then atomized and sprayed onto the surface of the metal current collector under the action of compressed air to obtain a pole piece with a thickness of less than 80 microns; S3, electrode rolling: The baked electrode is subjected to differential hot pressing treatment to obtain a low internal resistance ultra-thin dry electrode with a thickness of less than 70 microns; the differential speed ratio of the upper and lower rollers of S3 is controlled at more than 3:1, and the hot pressing temperature is controlled at 80~150℃.

2. The method for preparing a low internal resistance ultra-thin dry-process positive electrode according to claim 1, characterized in that: The active materials used are LiCoO2, LiMn2O4, LiFePO4, LiNi 1-x-y Co y Mn x O2 (NCM ternary material), LiNi 1-x-y Co y Al x O2 (NCA ternary material), LiM x Mn 2-x O4, M is Fe and Co doped atoms for positive electrode materials used in lithium-ion batteries, and the mass proportion of positive electrode materials is 90%~98%.

3. The method for preparing a low internal resistance ultra-thin dry-process positive electrode according to claim 2, characterized in that: The binder used is one or more of polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), and the binder mass accounts for 1% to 5%.

4. The method for preparing a low internal resistance ultra-thin dry-process positive electrode according to claim 3, characterized in that: The conductive agent used is one or more of carbon nanotubes (CNTs), superconducting carbon black (SP), conductive graphite (KS-6), and Ketjen black (KB), and the mass proportion of the conductive agent is 1% to 5%.

5. The method for preparing a low internal resistance ultra-thin dry-process positive electrode according to claim 4, characterized in that: The voltage of the S2 high-voltage static electricity is 50~90kV.

6. The method for preparing a low internal resistance ultra-thin dry-process positive electrode according to claim 5, characterized in that: The S2 atomization pressure is 0.2~0.4MPa, and the spray flow rate pressure is 0.3~0.6MPa.

7. A positive electrode prepared according to the method for preparing a low internal resistance ultra-thin dry positive electrode according to any one of claims 1 to 6.

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