A method for improving the performance of a lithium ion battery separator

Abstract

This invention relates to the technical field of battery separator performance improvement methods, and proposes a method for improving the performance of lithium-ion battery separators. The method involves preparing a PVDF electrospun layer on the surface of a polyolefin separator, and adding sepiolite to the electrospun layer. Sepiolite can improve the uniformity and stability of PVDF distribution in the separator, enhance the wettability of the separator, and adsorb hydrofluoric acid in the electrolyte, inhibiting internal side reactions in the lithium-ion battery and improving the battery's cycle performance. The method includes the following steps: First, using electrospinning technology, a PVDF electrospun layer is prepared on the surface of the polyolefin separator, and sepiolite is added to the electrospun layer. The sepiolite needs to be modified beforehand. A certain amount of modified sepiolite is added to a certain amount of PVDF solution to prepare an electrospinning solution. After the electrospinning solution is prepared, the polyolefin separator is wound onto an electrospinning collector.

Description

Technical Field

[0001] This invention relates to the technical field of battery separator performance improvement methods, specifically to a method for improving the performance of lithium-ion battery separators. Background Technology

[0002] Under the trend of the new energy revolution, lithium-ion batteries have become the main new energy storage products. Lithium-ion battery separators play a key role in lithium-ion batteries, preventing internal short circuits between positive and negative electrodes and maintaining sufficient electrolyte. Polyolefin separators for lithium-ion batteries are widely used in commercial lithium-ion batteries due to their low cost, good mechanical and electrochemical stability. However, polyolefin separators have poor compatibility with the electrode interface. Usually, PVDF is coated on the surface of the separator to improve the stability of the separator-electrode interface. However, directly coating PVDF on polyolefin separators will block the separator pores, affect ion conduction, and is not conducive to improving the cycle life of lithium-ion batteries. In addition, PVDF has poor high temperature resistance, and the separator is prone to shrinkage at high temperatures, resulting in poor thermal stability, which limits the application of polyolefin separators in high-temperature lithium-ion batteries. Summary of the Invention

[0003] (a) Technical problems to be solved

[0004] To address the shortcomings of existing technologies, this invention provides a method for improving the performance of lithium-ion battery separators. This method involves preparing a PVDF electrospun layer on the surface of a polyolefin separator and adding sepiolite to the electrospun layer. Sepiolite can improve the uniformity and stability of PVDF distribution in the separator, the electrospun layer can enhance the wettability of the separator, and sepiolite can adsorb hydrofluoric acid in the electrolyte, suppressing internal side reactions in the lithium-ion battery and improving the battery's cycle performance.

[0005] (II) Technical Solution

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for improving the performance of a lithium-ion battery separator, comprising the following steps:

[0007] S1 employs electrospinning technology to prepare a PVDF electrospun layer on the surface of a polyolefin membrane. Sepiolite is then added to this electrospun layer. First, the sepiolite is modified by adding a certain amount of sepiolite powder to a certain amount of anhydrous ethanol and ultrasonically treating it for 10-20 minutes to obtain a sepiolite suspension with a concentration of (10-15) g / L. A certain amount of vinyltriethoxysilane is then added to a certain amount of anhydrous ethanol to obtain a vinyltriethoxysilane solution with a concentration of (100-200) g / L. This vinyltriethoxysilane solution is then added dropwise to the sepiolite suspension, followed by the addition of 25 wt% ammonia water to control the pH at 9-10. The mixed suspension is heated to 80-90℃ and reacted for 2-3 hours. The resulting product is washed with anhydrous ethanol and dried at 80-90℃ for 12-24 hours to obtain modified sepiolite.

[0008] S2 Then, a certain amount of PVDF is dissolved in N-dimethylamide to prepare a PVDF solution with a concentration of 8%-10%. The solution is stirred with a mixer at a speed of 500 r / min for 2-3 hours. A certain amount of modified sepiolite is added to a certain amount of PVDF solution, and the solution is stirred with a mixer at a speed of 200 r / min-500 r / min for 8-12 hours. After standing for 1-2 hours, the electrospinning solution is obtained.

[0009] S3 involves winding a polyolefin separator onto an electrospinning collector, placing the electrospinning solution into the syringe of an electrospinning machine for electrospinning, and controlling the spinning thickness to be between 1 μm and 2 μm to obtain a polyolefin separator with electrospinning. This polyolefin separator has high porosity and good thermal stability, and its cycle life at a high temperature of 60°C for lithium-ion batteries can be increased by more than 100%.

[0010] Furthermore, based on the aforementioned scheme, the diaphragm is suitable for PP and PE materials.

[0011] Furthermore, based on the aforementioned scheme, the separator is suitable for lithium batteries with positive electrode systems such as lithium iron phosphate, lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel manganese oxide.

[0012] (III) Beneficial Effects

[0013] Compared with the prior art, the present invention provides a method for improving the performance of lithium-ion battery separators, which has the following beneficial effects:

[0014] 1. In this invention, sepiolite is modified so that -Si(OC2Hs)3 in ethylenetriethoxysilane can be hydrolyzed and bonded to hydroxyl groups on inorganic materials, thereby improving the aggregation of inorganic materials. Furthermore, the organic functional groups in triethoxysilane have good compatibility with organic matrices, which can improve the dispersibility and compatibility of sepiolite with PVDF polymer matrix.

[0015] 2. In this invention, adding an appropriate amount of ammonia to sepiolite can accelerate the hydrolysis of ethylenetriethoxysilane. The OH bonds in ammonia can attack the Si atoms in ethylenetriethoxysilane, causing the oxyethoxy group to fall off. Ethylenetriethoxysilane is then converted into silanol, which undergoes dehydration condensation with the hydroxyl groups on sepiolite, accelerating the grafting of ethylenetriethoxysilane onto sepiolite and improving the uniformity and stability of the PVDF distribution in the separator, thereby improving the high-temperature stability of the lithium-ion battery.

[0016] 3. In this invention, electrospinning technology is used to prepare a PVDF electrospinning layer of composite ethylene triethoxysilane on the surface of a polyolefin separator, which can enhance the wettability of the separator, and sepiolite can adsorb hydrofluoric acid in the electrolyte, inhibit the internal side reactions of the lithium-ion battery, and improve the cycle performance of the battery. Attached Figure Description

[0017] Figure 1 The following is a comparison curve of the 60℃ 3C charge-discharge cycle performance of a 26650-3000mAh-3.2V battery prepared by electrospun polyolefin separator and ordinary polyolefin separator in the examples. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Example 1

[0020] Please see Figure 1A method for improving the performance of lithium-ion battery separators employs the following technical solution: First, sepiolite is modified by adding a certain amount of sepiolite powder to a certain amount of anhydrous ethanol and ultrasonically treating it for 10-20 minutes to obtain a sepiolite suspension with a concentration of (10-15) g / L. A certain amount of vinyltriethoxysilane is added to a certain amount of anhydrous ethanol to obtain a vinyltriethoxysilane solution with a concentration of (100-200) g / L. The vinyltriethoxysilane solution is then added dropwise to the sepiolite suspension, followed by the addition of 25 wt% ammonia water to control the pH value at 9-10. The mixed suspension is heated to 80-90℃ and reacted for 2-3 hours. The resulting product is washed with anhydrous ethanol and dried at 80-90℃ for 12-24 hours to obtain modified sepiolite. Then, a certain amount of PVDF is dissolved in N-dimethylamide to prepare a PVDF solution with a concentration of 8%-10%. The solution is stirred with a stirrer at a speed of 500 r / min for 2-3 hours. A certain amount of modified sepiolite is added to the PVDF solution, and the mixture is stirred with a stirrer at a speed of 200 r / min-500 r / min for 8-12 hours. After standing for 1-2 hours, an electrospinning solution is obtained. The polyolefin membrane is wound onto the electrospinning collector, and the electrospinning solution is placed into the syringe of the electrospinning machine for electrospinning. The spinning thickness is controlled at 1 μm-2 μm to obtain a polyolefin membrane with electrospinning. This polyolefin membrane has high porosity and good thermal stability, and the cycle life of lithium-ion batteries prepared at 60℃ can be increased by more than 1 times.

[0021] Example 2

[0022] First, 25g of sepiolite powder was added to 2L of anhydrous ethanol and stirred for 20 minutes at a stirring speed of 1500r / min to obtain a sepiolite suspension. 200g of vinyltriethoxysilane was added to 1.5L of anhydrous ethanol and stirred dropwise into the sepiolite suspension. 25wt% ammonia water was added dropwise to control the pH value to 9. The mixed suspension was heated to 80℃ and reacted for 3 hours. The resulting product was washed with anhydrous ethanol and dried at 80℃ for 24 hours to obtain modified sepiolite.

[0023] Then, 50g of PVDF was dissolved in 500g of N-dimethylamide to prepare a PVDF solution. The solution was stirred at 500r / min for 3h. 20g of modified sepiolite was added to the 500g PVDF solution, and the mixture was stirred at 500r / min for 8h. After standing for 2h, an electrospinning solution was obtained. A 16μm thick PE membrane was wound around an electrospinning collector. The electrospinning solution was placed into the syringe of an electrospinning machine for electrospinning. The spinning thickness was controlled at 1μm-2μm to obtain a polyolefin membrane with electrospinning. The membrane exhibited good thermal stability and ion conduction properties.

[0024] When the electrospun polyolefin separator prepared using this invention is used in 22650-3000mAh-3.2V lithium iron phosphate batteries, compared with ordinary 16μm thick PE separators, the capacity of the electrospun PE separator battery is 82% after 2000 3C charge-discharge cycles at 60℃, while the capacity of the ordinary PE separator battery is 80% after 1000 3C charge-discharge cycles at 60℃.

[0025] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for improving the performance of a lithium-ion battery separator, comprising the following steps: S1 uses electrospinning technology to prepare a PVDF electrospinning layer on the surface of a polyolefin membrane, and adds sepiolite to the electrospinning layer. First, the sepiolite is modified by adding a certain amount of sepiolite powder to a certain amount of anhydrous ethanol and ultrasonically treating it for 10-20 minutes to obtain a sepiolite suspension with a concentration of (10-15) g / L. A certain amount of vinyltriethoxysilane is added to a certain amount of anhydrous ethanol to obtain a vinyltriethoxysilane solution with a concentration of (100-200) g / L. The vinyltriethoxysilane solution is added dropwise to the sepiolite suspension, and 25wt% ammonia water is added dropwise to control the pH value at 9-10. The mixed suspension is heated to 80℃-90℃ and reacted for 2-3 hours. The obtained product is washed with anhydrous ethanol and dried at 80℃-90℃ for 12-24 hours to obtain modified sepiolite. S2 Then, a certain amount of PVDF is dissolved in N-dimethylamide to prepare a PVDF solution with a concentration of 8%-10%. The solution is stirred with a stirrer at a speed of 500 r / min for 2-3 hours. A certain amount of modified sepiolite is added to a certain amount of PVDF solution, and the solution is stirred with a stirrer at a speed of 200 r / min-500 r / min for 8-12 hours. After standing for 1-2 hours, the electrospinning solution is obtained. S3 involves winding a polyolefin separator onto an electrospinning collector, placing the electrospinning solution into the syringe of an electrospinning machine for electrospinning, controlling the spinning thickness to 1μm-2μm, and obtaining a polyolefin separator with electrospinning. This polyolefin separator has high porosity and good thermal stability, and its cycle life at 60℃ can be increased by more than 1 times in lithium-ion batteries. The separator is suitable for PP and PE materials.

2. The method for improving the performance of a lithium ion battery separator according to claim 1, characterized in that, The separator is suitable for lithium batteries with positive electrode systems such as lithium iron phosphate, lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel manganese oxide.

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