Zero-deformation winding lithium ion battery and preparation method thereof

Abstract

This invention relates to a zero-deformation wound lithium-ion battery and its preparation method. The preparation method is as follows: (1) Polyvinylidene fluoride (PVDF), deionized water, and wetting agent are mixed and stirred to obtain a PVDF suspension; ethylene carbonate is heated to completely melt into a liquid state and added to the PVDF suspension, and stirred evenly to obtain a mixed slurry; (2) The mixed slurry is placed in a spraying equipment and evenly sprayed onto one or both sides of the separator, and then dried to obtain a coated separator; (3) Positive electrode sheet and negative electrode sheet are prepared; (4) Positive electrode sheet, negative electrode sheet, and coated separator are wound to obtain a core; (5) The core is assembled, placed in a shell, baked, formed, aged, and capacity tested to obtain a lithium-ion battery. This invention sprays a mixture of PVDF suspension and liquid ethylene carbonate (EC) onto the separator, leaving internal expansion space for the battery, releasing the stress caused by electrode expansion, and preventing deformation of the battery cell.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a zero-deformation wound lithium-ion battery and its preparation method. Background Technology

[0002] Currently, lithium-ion square aluminum-cased batteries can be classified into two manufacturing processes: stacking and winding. Stacking involves cutting electrode sheets into individual pieces, then stacking the positive and negative electrode sheets together using a stacking machine to form a core. Winding involves winding the positive and negative electrode sheets and the separator onto a winding needle to form a core. Most companies in the industry currently use the winding process. However, the internal stress of the core has been a persistent problem for battery cell developers. Because the electrode sheets and separator are under tension during winding, the stress on both sides of the core increases after hot pressing. After charging and discharging, the positive and negative electrode sheets thicken again, and the stress at the corners of the core becomes even greater, leading to core deformation. This results in increased distance between the electrode sheets, excessive cell thickness, difficulty in lithium-ion insertion / extraction, increased internal resistance, and a sharp decline in electrical performance.

[0003] To control battery deformation, the following methods are generally used: first, adjusting the internal stress of the winding core by optimizing the winding tension; second, selecting active materials with less expansion during charging and discharging, and pre-baking the electrodes before use; and third, selecting separators with less thermal shrinkage, and pre-baking the separators before use. However, these methods only have a small optimization effect and the improvement is not significant. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a zero-deformation wound lithium-ion battery, which reserves internal expansion space within the battery and achieves zero deformation of the battery.

[0005] The technical solution adopted by this invention to solve the above problems is: a method for preparing a zero-deformation wound lithium-ion battery, comprising the following steps: (1) Preparation of mixed slurry: (a) Polyvinylidene fluoride (PVDF), deionized water, and wetting agent are mixed and stirred to obtain a PVDF suspension; (b) Heat ethylene carbonate EC until it is completely melted into a liquid state, add it to the PVDF suspension, stir evenly to obtain a mixed slurry; (2) The mixed slurry is placed in the spraying equipment and sprayed evenly onto one or both sides of the diaphragm, and then dried to obtain the coated diaphragm. (3) Prepare positive and negative electrode plates; (4) The positive electrode sheet, the negative electrode sheet, and the adhesive-coated diaphragm are wound together to obtain a core body; (5) The core is assembled, placed into the shell, baked, formed, aged and tested to obtain a lithium-ion battery.

[0006] Preferably, step (a) in step (1) specifically involves: grinding PVDF to a particle size of less than 1 μm to obtain PVDF powder, then mixing and stirring the PVDF powder, deionized water and wetting agent at a stirring speed of 25-30 rpm / min for revolution and 2500-3000 rpm / min for rotation, and stirring for 150-180 min to obtain a PVDF suspension.

[0007] Preferably, step (b) in step (1) specifically involves heating EC, which is solid at room temperature, to 50-100℃ until it is completely melted into a liquid state, then adding it to the PVDF suspension and stirring. The stirring speed is 25-30 rpm / min for revolution and 2500-3000 rpm / min for rotation, and the stirring time is 30-60 min to obtain a mixed slurry.

[0008] Preferably, the spraying amount in step (2) is 0.4~0.6 g / m³. 2 .

[0009] Preferably, the EC is 5% to 8% of the weight of PVDF.

[0010] Another object of the present invention is to provide a lithium-ion battery prepared by zero-deformation winding lithium-ion battery, which is prepared by the above-mentioned preparation method and includes a positive electrode, a negative electrode, and a separator placed between the positive electrode and the negative electrode. One or both sides of the separator are coated with a mixed slurry. The mixed slurry is a mixture of PVDF suspension and liquid ethylene carbonate EC. The PVDF suspension is a mixture of polyvinylidene fluoride (PVDF), deionized water, and a wetting agent.

[0011] Compared with the prior art, the advantages of the present invention are as follows: This invention relates to a lithium-ion battery core comprising a positive electrode, a negative electrode, and a separator placed between the positive and negative electrodes. The separator is uniformly coated on one or both sides with a mixed slurry, which is a mixture of PVDF suspension and liquid ethylene carbonate (EC). On one hand, the PVDF is distributed in particulate form on the separator, creating a certain thickness difference. On the other hand, during baking after cell assembly, the EC dissolves and volatilizes, thus reserving internal expansion space for the battery, releasing stress caused by electrode expansion, and controlling battery deformation and arching. Furthermore, EC itself is a solvent component of the subsequent electrolyte, so any residue will not affect the battery. In addition, by spraying the mixture of PVDF suspension and liquid ethylene carbonate (EC) onto the separator, this invention can prevent battery cell deformation and eliminate internal stress in the battery. Implementation

[0012] The present invention will be further described in detail below with reference to the embodiments. Example 1

[0013] Taking 48173170-120Ah as an example A method for fabricating a zero-deformation wound lithium-ion battery includes the following steps: (1) Preparation of mixed slurry: (a) PVDF is ground to a particle size of less than 1 μm to obtain PVDF powder. Then, 1000 g of PVDF powder, 10 kg of deionized water and 10 g of wetting agent (BYKLP-C 22136) are mixed and stirred at a stirring speed of 25 rpm / min for revolution and 3000 rpm / min for rotation, and the stirring time is 150 min to obtain PVDF suspension. (b) Heat 100g of ethylene carbonate EC to 100℃ until it is completely melted into a liquid state, add it to the PVDF suspension, and continue stirring at a speed of 25 rpm / min for revolution and 3000 rpm / min for 30 min to obtain a mixed slurry; (2) The mixed slurry is placed in the spraying equipment and sprayed evenly onto both sides of the diaphragm (polypropylene dry-process base film). The density of the sprayed surface is about 0.4 g / m. 2 After drying, a coated diaphragm is obtained; (3) Prepare positive electrode and negative electrode, wherein the positive electrode is: lithium iron phosphate (DY-1):SP:PVDF:CNT=96.4:1:1.8:0.8 (mass ratio), and the negative electrode is: graphite (fsn-1):SP:CMC:PAA=96:1.1:0.6:2.3 (mass ratio); (4) The positive electrode sheet, negative electrode sheet, and coated diaphragm are wound to obtain a core body. The initial winding tension of the positive electrode is 450g, the attenuation tension is 8g per turn, and the minimum tension is 200g. The initial winding tension of the negative electrode is 420g, the attenuation tension is 9g per turn, and the minimum tension is 180g. The initial tension of the diaphragm is 220g, the attenuation tension is 6g, and the minimum tension is 100g. (5) The core is assembled, placed into the shell, baked (temperature 105℃, time 48h, vacuum degree -95kpa), formed, aged and tested to obtain a lithium-ion battery, wherein the core thickness is 47.00mm. Example 2

[0014] Taking 48173150-100Ah as an example A method for fabricating a zero-deformation wound lithium-ion battery includes the following steps: (1) Preparation of mixed slurry: (a) PVDF is ground to a particle size of less than 1 μm to obtain PVDF powder. Then, 1000 g of PVDF powder, 10 kg of deionized water and 10 g of wetting agent (BYKLP-C 22136) are mixed and stirred at a speed of 30 rpm / min for revolution and 2800 rpm / min for rotation, and the stirring time is 160 min to obtain PVDF suspension. (b) Heat 100g of ethylene carbonate EC to 100℃ until it is completely melted into a liquid state, add it to the PVDF suspension, and continue stirring. The stirring speed is 30 rpm / min for revolution and 3000 rpm / min for rotation, and the stirring time is 30 min to obtain a mixed slurry. (2) The mixed slurry is placed in the spraying equipment and sprayed evenly onto both sides of the diaphragm (polypropylene dry-process base film). The density of the sprayed surface is about 0.4 g / m. 2 After drying, a coated diaphragm is obtained; (3) Prepare positive electrode and negative electrode, wherein the positive electrode is: lithium iron phosphate (Dongyangguang p321):SP:PVDF:CNT=96.4:1:1.8:0.8 (mass ratio), and the negative electrode is: graphite (Baichuan BC-SO5H):SP:CMC:PAA=96:1.1:0.6:2.3 (mass ratio); (4) The positive electrode sheet, negative electrode sheet, and coated diaphragm are wound to obtain a core body. The initial winding tension of the positive electrode is 450g, the attenuation tension is 8g per turn, and the minimum tension is 200g. The initial winding tension of the negative electrode is 420g, the attenuation tension is 9g per turn, and the minimum tension is 180g. The initial tension of the diaphragm is 220g, the attenuation tension is 6g, and the minimum tension is 100g. (5) The core is assembled, placed into the shell, baked (temperature 105℃, time 48h, vacuum degree -95kpa), formed, aged and tested to obtain a lithium-ion battery, wherein the core thickness is 47.00mm. Example 3

[0015] Taking 48200170-140Ah as an example A method for fabricating a zero-deformation wound lithium-ion battery includes the following steps: (1) Preparation of mixed slurry: (a) PVDF is ground to a particle size of less than 1 μm to obtain PVDF powder. Then, 1000 g of PVDF powder, 10 kg of deionized water and 10 g of wetting agent (BYKLP-C 22136) are mixed and stirred at a stirring speed of 30 rpm / min for revolution and 3000 rpm / min for rotation, and the stirring time is 160 min to obtain PVDF suspension. (b) Heat 100g of ethylene carbonate EC to 100℃ until it is completely melted into a liquid state, add it to the PVDF suspension, and continue stirring at a speed of 25 rpm / min for revolution and 2500 rpm / min for rotation, for a stirring time of 60 min to obtain a mixed slurry; (2) The mixed slurry is placed in the spraying equipment and sprayed evenly onto both sides of the diaphragm (polypropylene dry-process base film). The density of the sprayed surface is about 0.4 g / m. 2 After drying, a coated diaphragm is obtained; (3) Prepare positive and negative electrode sheets. The positive electrode sheet is: lithium iron phosphate (Leneng N3):SP:PVDF:CNT=96.6:1:1.8:0.6. The negative electrode sheet is: graphite (Baichuan BC-SO2):SP:CMC:PAA=96:3.1:0.6:2.1. (4) The positive electrode sheet, negative electrode sheet, and coated diaphragm are wound to obtain a core body. The initial winding tension of the positive electrode is 450g, the attenuation tension is 8g per turn, and the minimum tension is 200g. The initial winding tension of the negative electrode is 420g, the attenuation tension is 9g per turn, and the minimum tension is 180g. The initial tension of the diaphragm is 220g, the attenuation tension is 6g, and the minimum tension is 100g. (5) The core is assembled, placed into the shell, baked (temperature 105℃, time 48h, vacuum degree -95kpa), formed, aged and tested to obtain a lithium-ion battery, wherein the core thickness is 47.00mm.

[0016] Comparative Example 1 The only difference from Example 1 is that only the PVDF suspension is sprayed onto the diaphragm.

[0017] Comparative Example 2 The only difference from Example 1 is that liquid ethylene carbonate EC is sprayed onto the diaphragm.

[0018] The performance of the wound lithium-ion batteries obtained in Examples 1-3 and Comparative Examples 1-2 was tested as follows: (1) Internal resistance test: Use an internal resistance tester to test the internal resistance of the cell when it is fully charged.

[0019] (2) Thickness test: Use calipers to test the thickness of the core when it is fully charged.

[0020] (3) The lithium-ion battery was subjected to a room temperature cycle test with the following parameters: 1C 100% DOD charge-discharge cycle, cut-off voltage 3.65-2.5V, and 80% capacity retention rate at the end of the life cycle.

[0021] Table 1 Performance test results of wound lithium-ion batteries obtained in Examples 1-3 and Comparative Examples 1-2

[0022] As can be seen from the table above, spraying the mixture of PVDF suspension and liquid ethylene carbonate EC onto the diaphragm did not result in a significant increase in core thickness, low internal resistance, and excellent cycling performance at room temperature. Furthermore, the data from Example 1 and Comparative Examples 1-2 show that the cycling performance and core thickness change of the PVDF suspension / liquid ethylene carbonate EC mixture were significantly better than the expected results (the sum of the number of cycles and the sum of the core thickness change rates of the PVDF suspension and liquid ethylene carbonate EC mixtures alone), indicating that the effects of the PVDF suspension and liquid ethylene carbonate EC mixtures are not simply additive.

[0023] In addition to the above embodiments, the present invention also includes other embodiments. All technical solutions formed by equivalent transformation or equivalent substitution should fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a zero-deformation wound lithium-ion battery, characterized in that: Includes the following steps: (1) Preparation of mixed slurry: (a) Polyvinylidene fluoride (PVDF), deionized water, and wetting agent are mixed and stirred to obtain a PVDF suspension; (b) Heat ethylene carbonate EC until it is completely melted into a liquid state, add it to the PVDF suspension, stir evenly to obtain a mixed slurry; (2) The mixed slurry is placed in the spraying equipment and sprayed evenly onto one or both sides of the diaphragm, and then dried to obtain the coated diaphragm. (3) Prepare positive and negative electrode plates; (4) The positive electrode sheet, the negative electrode sheet, and the adhesive-coated diaphragm are wound together to obtain a core body; (5) The core is assembled, placed into the shell, baked, formed, aged and tested to obtain a lithium-ion battery.

2. The method for preparing a zero-deformation wound lithium-ion battery according to claim 1, characterized in that: Step (a) in step (1) specifically involves grinding PVDF to a particle size of less than 1 μm to obtain PVDF powder. Then, the PVDF powder, deionized water, and wetting agent are mixed and stirred at a stirring speed of 25-30 rpm / min for revolution and 2500-3000 rpm / min for rotation, with a stirring time of 150-180 min to obtain a PVDF suspension.

3. The method for preparing a zero-deformation wound lithium-ion battery according to claim 1, characterized in that: Step (b) in step (1) specifically involves heating EC, which is solid at room temperature, to 50-100℃ until it is completely melted into a liquid state, then adding it to the PVDF suspension and stirring. The stirring speed is 25-30 rpm / min for revolution and 2500-3000 rpm / min for rotation, and the stirring time is 30-60 min to obtain a mixed slurry.

4. The method for preparing a zero-deformation wound lithium-ion battery according to claim 1, characterized in that: In step (2), the spraying amount is 0.4~0.6 g / m². 2 .

5. The method for preparing a zero-deformation wound lithium-ion battery according to claim 1, characterized in that: The EC is 5% to 8% of the PVDF weight.

6. A lithium-ion battery prepared according to any one of claims 1-5 with zero deformation winding, characterized in that: It includes a positive electrode, a negative electrode, and a separator placed between the positive and negative electrode. One or both sides of the separator are coated with a mixed slurry. The mixed slurry is a mixture of PVDF suspension and liquid ethylene carbonate EC. The PVDF suspension is a mixture of polyvinylidene fluoride (PVDF), deionized water, and a wetting agent.

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