A lithium ion battery separator with thermal stability and a preparation method thereof

Abstract

The application discloses a lithium ion battery diaphragm with thermal stability and a preparation method thereof, and belongs to the technical field of lithium battery diaphragms. The method comprises the following steps: polyvinylidene fluoride is stirred and mixed in N-methyl pyrrolidone to obtain a preliminary slurry; boehmite powder is placed in the preliminary slurry, stirred and mixed, and ultrasonic treatment is conducted to obtain a final slurry; the final slurry is scraped and coated onto a glass plate and dried to form a shape; and the dried coating layer is peeled off from the glass plate to obtain the lithium ion battery diaphragm. The application can simply and economically obtain a novel diaphragm for a lithium ion battery and is easy to be mass-produced industrially. The diaphragm has effectively improved thermal stability, can effectively inhibit the thermal runaway risk of a lithium ion battery in the case of fire and the like, and reduces personnel casualties and property losses.

Description

Technical Field

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

[0002] Lithium-ion batteries have achieved rapid development in the field of electric vehicles in recent years due to their advantages such as high energy and volume density, large output voltage, minimal memory effect and long cycle life. They have also become the mainstream type of new energy storage technology in various countries around the world, and have been used in a large number of engineering practices at the user, grid and power supply levels.

[0003] However, the frequent occurrence of spontaneous combustion of lithium-ion power batteries and fires in large-scale energy storage power stations has hindered the continued popularization of lithium-ion batteries and raised concerns about their safety. How to improve the safety of lithium-ion batteries while ensuring their high energy density and power characteristics, and achieve the simultaneous development of electrochemical performance and battery safety, has become an important research topic for lithium-ion batteries.

[0004] Existing commercial polyolefin lithium-ion battery separators suffer from defects such as low porosity, poor electrolyte wettability, and low melting point. These defects result in high resistance, low ionic conductivity, and flammability, hindering lithium-ion permeability and selectivity, limiting effective ion transport, and promoting dendritic crystal growth. Furthermore, the tendency of commercial polyolefin lithium-ion battery separators to burn and shrink at high temperatures, causing short circuits at the positive and negative electrode contacts, poses a significant safety risk. Summary of the Invention

[0005] Technical problem solved: To address the above-mentioned technical problems, this invention provides a thermally stable lithium-ion battery separator and its preparation method, which effectively improves the thermal stability of the lithium-ion battery separator and can effectively suppress the risk of thermal runaway caused by fire in the event of an accident or other incident involving lithium-ion batteries, thereby reducing personal injury and property damage.

[0006] Technical solution: A method for preparing a thermally stable lithium-ion battery separator, comprising the following steps: S1. Polyvinylidene fluoride is placed in N-methylpyrrolidone and stirred to obtain a preliminary slurry; S2. Place boehmite powder into the preliminary slurry, stir and mix, and then sonicate to obtain the final slurry; S3. Apply the final slurry to the glass plate and then dry it to shape; S4. Peel the dried and shaped coating off the glass plate to obtain the lithium-ion battery separator.

[0007] Preferably, the volume of the N-methylpyrrolidone is 3-5 mL.

[0008] Preferably, the mass of the polyvinylidene fluoride is 2~2.5g.

[0009] Preferably, the stirring speed in S1 is 200~300 r / min, and the stirring time is 2~4 h.

[0010] Preferably, the mass ratio of boehmite powder to polyvinylidene fluoride is 1:1.

[0011] Preferably, the stirring speed in step S2 is 100~150 r / min, and the stirring time is 2~4 h.

[0012] Preferably, the ultrasonic treatment in S2 has a power of 100~150W, a temperature of 25~30℃, and a time of 10~15min.

[0013] Preferably, the drying temperature in step S3 is 45~50℃ and the drying time is 18~30h.

[0014] Preferably, the drying in step S3 is carried out in a vacuum environment.

[0015] The thermally stable lithium-ion battery separator prepared by the above method.

[0016] Beneficial effects: In addressing the risk of thermal runaway in lithium-ion batteries, this invention effectively improves the thermal stability of lithium-ion battery separators, ensuring that they do not melt or shrink in a 200°C environment for 20 minutes. The electrolyte wetting rate of the lithium-ion battery separator prepared by this invention is much higher than that of commercial PP separators; The lithium-ion battery separator prepared by this invention, when assembled into a full cell, can stably cycle for more than 60 cycles at a 1C rate, and the discharge specific capacity is stably maintained above 130mAh / g. The lithium-ion battery separator prepared by this invention can effectively suppress the risk of thermal runaway caused by fire in lithium-ion batteries in the event of accidents, thereby reducing personal injury and property loss. Attached Figure Description

[0017] Figure 1 This is a comparison of the heat shrinkage of the lithium-ion battery separator prepared by this invention and a commercial PP separator after 20 minutes in environments of 180°C and 200°C, respectively. Figure 2 This invention describes the long-cycle performance of a full cell assembled with a lithium-ion battery separator at a 1C rate. Detailed Implementation

[0018] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. All raw materials are commercially available products, wherein the purity of polyvinylidene fluoride (PVDF) is 99.7%; the purity of N-methylpyrrolidone (NMP) is ≥99%; and the purity of boehmite powder is 99.5%. Example 1

[0019] This embodiment provides a method for preparing a lithium-ion battery separator, the method is as follows: Step 1: Use a pipette to transfer 4 mL of N-methylpyrrolidone into a 10 mL reagent bottle; Part 2: Weigh 2g of polyvinylidene fluoride and place it in a reagent bottle containing N-methylpyrrolidone. Stir with a magnetic stirrer until completely dissolved to obtain a preliminary slurry. The stirring speed is 200~300r / min and the stirring time is 2 hours. Step 3: Weigh 2g of boehmite powder at a mass ratio of 1:1 with polyvinylidene fluoride and place it in the preliminary slurry. Stir with a magnetic stirrer and sonicate until evenly dispersed to obtain the final slurry. The stirring speed is 150r / min, the stirring time is 3 hours, the power of sonication is 150W, the temperature is controlled at 25℃, and the sonication time is 15 minutes. Step 4: After the final slurry is coated onto the glass plate, it is placed in a vacuum drying oven and dried at 45°C in a vacuum environment for 24 hours to form the final product. Step 5: Remove the glass plate and peel off the coating to obtain a lithium-ion battery separator.

[0020] Assemble all batteries Battery Assembly Method: Prepare a lithium sheet, a spacer, and a spring sheet. First, place the spring sheet and spacer sequentially from bottom to top in the negative electrode shell of the CR2032 battery. Then, place the pure lithium sheet on top of the spacer, ensuring the spring sheet and spacer are aligned. Next, place the lithium-ion battery separator prepared in Example 1 directly above the lithium sheet and drip in organic electrolyte to completely wet the separator. Finally, place the positive electrode sheet on top of the separator and cover it with the positive electrode shell. Seal the battery using a battery packaging machine to form a CR2032 button cell. This battery can stably cycle for more than 60 cycles at a 1C (170mA / g) rate, and its discharge specific capacity remains at 130mAh / g. Its long-cycle performance is as follows: Figure 2 As shown, the full cell assembled with the separator prepared by the present invention exhibits low discharge capacity decay and long-term cycle stability.

[0021] Comparative Example 1 This comparative example uses commercially available PP diaphragm.

[0022] The diaphragms of Example 1 and Comparative Example 1 were placed in environments of 180°C and 200°C for 20 minutes each, respectively. The results are as follows: Figure 1As shown, the separator prepared by the present invention does not melt or shrink in an environment of 200°C for 20 minutes, which effectively improves the thermal stability of the lithium-ion battery separator. This can effectively suppress the risk of thermal runaway caused by fire in the event of an accident or other incident involving the lithium-ion battery, thereby reducing personal injury and property damage.

Claims

1. A method for preparing a thermally stable lithium-ion battery separator, characterized in that, The steps include the following: S1. Polyvinylidene fluoride is placed in N-methylpyrrolidone and stirred to obtain a preliminary slurry; S2. Place boehmite powder into the preliminary slurry, stir and mix, and then sonicate to obtain the final slurry; S3. Apply the final slurry to the glass plate and then dry it to shape; S4. Peel the dried and shaped coating off the glass plate to obtain the lithium-ion battery separator.

2. The method for preparing a thermally stable lithium-ion battery separator according to claim 1, characterized in that, The volume of the N-methylpyrrolidone is 3-5 mL.

3. The method for preparing a thermally stable lithium-ion battery separator according to claim 1, characterized in that, The mass of the polyvinylidene fluoride is 2~2.5g.

4. The method for preparing a thermally stable lithium-ion battery separator according to claim 1, characterized in that, The stirring speed in S1 is 200~300 r / min, and the stirring time is 2~4 h.

5. The method for preparing a thermally stable lithium-ion battery separator according to claim 1, characterized in that, The mass ratio of boehmite powder to polyvinylidene fluoride is 1:

1.

6. The method for preparing a thermally stable lithium-ion battery separator according to claim 1, characterized in that, The stirring speed in S2 is 100~150 r / min, and the stirring time is 2~4 h.

7. The method for preparing a thermally stable lithium-ion battery separator according to claim 1, characterized in that, The ultrasonic treatment in S2 has a power of 100~150W, a temperature of 25~30℃, and a time of 10~15min.

8. The method for preparing a thermally stable lithium-ion battery separator according to claim 1, characterized in that, The drying temperature in S3 is 45~50℃, and the drying time is 18~30h.

9. The method for preparing a thermally stable lithium-ion battery separator according to claim 1, characterized in that, The drying in step S3 is carried out in a vacuum environment.

10. A thermally stable lithium-ion battery separator prepared by the method of claim 1.

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