A high-temperature resistant polyimide composite separator and its preparation method

Abstract

The present invention discloses a high-temperature resistant polyimide composite separator. The composite separator comprises polyimide, a magnesium plastic reinforcing agent, a silane coupling agent, ceramic powder, an organosilicon wetting and dispersing agent, an isocyanate catalyst, and an organic solvent. By mass, the mass ratio of polyimide, the magnesium plastic reinforcing agent, the silane coupling agent, the ceramic powder, the organosilicon wetting and dispersing agent, the isocyanate catalyst, and the organic solvent is (93 parts - 94 parts):(3 parts - 5 parts):(1.5 parts - 2.5 parts):(14 parts - 16 parts):(1 part - 2 parts):(0.5 parts - 1 part):(565 parts - 603 parts). The polyimide composite separator of the present invention has good thermal stability, air permeability, and stretchability. Moreover, the mutual cooperation among the substances in the present invention can promote the increase of the crosslinking degree, thereby reducing the surface tension of the solution, and is particularly suitable for the preparation method of electrospinning.

Description

Technical Field

[0001] The present invention relates to the technical field of diaphragms, and particularly relates to a high-temperature resistant polyimide composite diaphragm and a preparation method thereof. Background Art

[0002] Nowadays, lithium-ion batteries have become the most commonly used energy devices for 3C products (computer, communication, consumer electronics). High capacity, stable charge and discharge performance, and a sufficiently long service life have always been the pursuits of engineers for lithium-ion batteries and the expectations of consumers. The diaphragm is the key to these pursuits and expectations.

[0003] Currently, the commonly used binder in diaphragms is mostly PVDF organic polymer. The PVDF organic polymer binder has good electrochemical stability and can form a gel electrolyte with the electrolyte to accelerate the migration of lithium ions. Although the water-solvent system PVDF is more environmentally friendly, under extreme conditions, its high-temperature resistance is still insufficient, resulting in a reduction in the performance of the diaphragm, thereby affecting the electrochemical performance and safety performance of the battery. Some research scholars have added polyimide and ceramic powder, which can improve the bonding strength between the diaphragm and the electrode sheet and the thermal stability of the diaphragm to a certain extent. However, there are still disadvantages such as uneven coating of the diaphragm, poor contact between ceramic powder particles, a decrease in the elasticity of the diaphragm due to the addition of ceramic powder, and easy brittle fracture, resulting in limited improvement in the electrochemical performance of the battery. Some research scholars have tried to use the electrospinning preparation method to promote the dispersion uniformity between particles through high voltage. However, due to the poor wettability of solid particles such as ceramic powder particles, the improvement effect of the diaphragm prepared by the electrospinning preparation method on the electrochemical performance of the battery is not significant. Summary of the Invention

[0004] Aiming at the problems in the prior art, the present invention discloses a high-temperature resistant polyimide composite diaphragm and a preparation method thereof. The composite diaphragm of the present invention includes polyimide and ceramic powder. The present invention can not only improve the bonding strength between the diaphragm and the electrode sheet, but also improve the thermal stability of the diaphragm while increasing the elasticity of the diaphragm, thereby reducing the occurrence of brittle fracture of the diaphragm, and enhancing the wettability of the ceramic powder. A composite diaphragm with more uniform distribution and better electrochemical performance is obtained through the electrospinning preparation method.

[0005] The present invention is realized through the following technical solutions:

[0006] A high-temperature resistant polyimide composite diaphragm provided by the present invention, the composite diaphragm comprises polyimide, a magnesium plastic reinforcing agent, a silane coupling agent, ceramic powder, an organosilicon wetting and dispersing agent, an isocyanate catalyst, and an organic solvent. By mass, the mass ratio of polyimide, magnesium plastic reinforcing agent, silane coupling agent, ceramic powder, organosilicon wetting and dispersing agent, isocyanate catalyst, and organic solvent is (93 parts - 94 parts):(3 parts - 5 parts):(1.5 parts - 2.5 parts):(14 parts - 16 parts):(1 part - 2 parts):(0.5 parts - 1 part):(565 parts - 603 parts).

[0007] In the above design of the present invention, polyimide has good thermal stability and bonding strength, and ceramic powder has certain mechanical properties; and due to the poor wettability and self-dispersibility of ceramic powder particles, and polyimide belongs to a polymer with a high viscosity, which further promotes the poor dispersibility of ceramic powder. Therefore, an organosilicon wetting and dispersing agent is added in the present invention. On the one hand, it can promote the wettability of ceramic powder, thereby improving the dispersibility of ceramic powder. On the other hand, it can also help reduce the viscosity of polyimide, thereby further promoting the more uniform mixing of ceramic powder and polyimide, and facilitating the reduction of the surface tension of the solution. We also further selected a plastic reinforcing agent, which can crosslink with polyimide to improve the tensile strength and toughness of the diaphragm. However, due to the strong hydrophilicity of the plastic reinforcing agent, the crosslinking reaction between the plastic reinforcing agent and polyimide may not be strong. Therefore, we selected a magnesium plastic reinforcing agent. A silane coupling agent of the same type as the organosilicon wetting and dispersing agent is beneficial to promoting the dissolution of the magnesium plastic reinforcing agent in the organic solvent, and magnesium is more likely to cooperate with the silane coupling agent, ceramic powder, and organosilicon wetting and dispersing agent, thereby promoting the dissolution of the magnesium plastic reinforcing agent, facilitating the crosslinking reaction between the plastic reinforcing agent and polyimide, and a catalyst with an isocyanate group is beneficial to the crosslinking reaction between the magnesium plastic reinforcing agent and polyimide. The isocyanate group has an unsaturated bond and high activity, and can serve as a bridge for the crosslinking of the magnesium plastic reinforcing agent and polyimide, and can improve the structural stability of the crosslinked magnesium plastic reinforcing agent and polyimide. The composite diaphragm prepared by this design not only has strong heat resistance and toughness, but also can reduce the occurrence of brittle fracture of the composite diaphragm.

[0008] As a further solution, the magnesium plastic reinforcing agent includes one or more of basic magnesium sulfate whiskers, magnesium hydroxide whiskers, magnesium carbonate whiskers, and magnesium borate whiskers. The magnesium plastic reinforcing agent has excellent reinforcing and toughening properties, can elastically bear large stress deformations, has a small expansion coefficient, and can better crosslink with polyimide under the cooperation of a silane coupling agent and an isocyanate catalyst, thereby improving the toughness of the diaphragm.

[0009] As a further embodiment, the silane coupling agent includes one or more of methyltriethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-(β-aminoethyl)aminopropyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-acryloxypropyltriethoxysilane, 3-methacryloxypropyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, allyltrimethoxysilane, allyltriethoxysilane, bis(2-hydroxyethyl)-3-aminopropyl-methoxysilane, N-hydroxymethyl-N-methylamine-propyltrimethoxysilane, hydroxymethyltriethoxysilane, triethoxysilylmethanol, N-(3-ethoxypropylsilyl)-4-hydroxybutyramide, N-(3-ethoxypropylsilyl)-glucosamide, 2,2-bis(3-ethoxypropylsilyl-methyl)-butanol, 2-carboxyethyltriethoxysilane.

[0010] As a further embodiment, the ceramic powder includes one or more of aluminum oxide, nano-silica, barium titanate, lead titanate zirconate, modified lead titanate zirconate, lead metaniobate, lead barium lithium niobate, lead lanthanum titanate zirconate, modified lead titanate, lead titanate-lead magnesium niobate, alumina, titanium dioxide.

[0011] As a further embodiment, the silicone wetting and dispersing agent includes one or more of BYKJET-9133, BYKJET-9142, BYKJET-9151, BYKJET-9152, DISPERBYK-167, DISPERBYK-190, DISPERBYK-191, and DISPERBYK-2200. It has a relatively small surface tension, which not only facilitates the wetting of the ceramic powder, thus promoting uniform dispersion among various substances, but also can be mutually fused with the silane coupling agent, thereby promoting the dissolution of the magnesium plastic enhancer in the mixed solution and facilitating the cross-linking reaction between the magnesium plastic enhancer and polyimide.

[0012] As a further embodiment, the isocyanate catalyst includes triphenylmethane triisocyanate. The acetate catalyst containing phenyl has an electron-withdrawing effect, thus forming an electron-withdrawing effect with the electrons in the magnesium plastic enhancer, making triphenylmethane triisocyanate more likely to serve as a bridge for the cross-linking reaction between the magnesium plastic enhancer and polyimide.

[0013] As a further embodiment, the organic solvent includes one of dimethylformamide and N-methylpyrrolidone.

[0014] The present invention also provides a method for preparing the composite separator.

[0015] As a further solution, the preparation method includes adding a diluted silane coupling agent to the magnesium plastic reinforcing agent, followed by stirring. Under ultrasonic conditions, an isocyanate catalyst, polyimide, ceramic powder, and an organosilicon wetting and dispersing agent are added to the mixture of the magnesium plastic reinforcing agent and the silane coupling agent. Then, the obtained product is dried. The dried product is dissolved in an organic solvent, and electrospinning is carried out on a base film. The distance between the syringe tip and the receiving surface of the base film is maintained at a certain distance, and the syringe is advanced at a certain speed to obtain a polyimide separator. The method of the present invention enables the substances to cooperate with each other, and on the premise of uniform dispersion, the crosslinking degree of polyimide and the plastic reinforcing agent increases, thereby reducing the excessive solution tension during electrospinning under high pressure, uniformly dispersing on the surface layer of the base film, and obtaining a separator with heat resistance, strength, certain tensile strength, and high viscosity.

[0016] As a further solution, the diluted silane coupling agent is diluted with absolute ethanol; the temperature of the stirring is 110°C - 130°C, and the time of the stirring is 25 min - 35 min; the conditions of the ultrasonic treatment are a frequency of 18 KHz - 20 KHz, and the time of the ultrasonic treatment is 20 min - 30 min; the time of the drying is 25 min - 35 min, and the temperature of the drying is 75°C - 85°C; the voltage of the electrospinning is 14 kV - 16 kV; the distance between the syringe tip and the receiving surface of the base film is 14 cm - 16 cm; the advancing speed of the syringe is 0.4 mL / h - 0.6 mL / h; the time of the electrospinning is 2.4 h - 2.6 h.

[0017] The features and beneficial effects of the present invention are as follows: The polyimide composite separator of the present invention has good thermal stability, air permeability, and stretchability. Moreover, the mutual cooperation among the substances in the present invention can promote the increase of the crosslinking degree, thereby reducing the solution tension, and is particularly suitable for the preparation method of electrospinning. Detailed implementation

[0018] To facilitate the understanding of a high-temperature resistant polyimide composite separator of the present invention, the composite separator of the present invention will be described more comprehensively below. Embodiments of the present invention are given, but the scope of the present invention is not limited thereby.

[0019] (1) Preparation method of polyimide: Diaminodiphenyl sulfone (DDS) and bisphenol A dianhydride (BPADA) are synthesized into polyimide at a molar ratio of 1:1 at 180°C. It is also possible to directly purchase existing polyimide drugs.

[0020] (2) Add the silane coupling agent diluted with ethanol to the magnesium plastic reinforcing agent, stir at 110°C - 130°C for 25 min - 35 min in a high-speed stirrer, pour it into an ultrasonic disperser, and ultrasonicate for 20 min - 30 min. Add isocyanate-based catalysts, polyimide powder, ceramic powder, and silicone-based wetting and dispersing agents at a frequency of 18 KHZ - 20 KHZ for cross-linking reaction. Dry the obtained product in an oven at 75°C - 85°C for 25 min - 35 min to obtain the dried product. Dissolve the dried product in NMP organic solvent and electrospin it in a high-voltage electrostatic field with a voltage of 14 Kv - 16 Kv. The distance from the syringe tip to the receiving surface is 14 cm - 16 cm, the advancing speed of the syringe is controlled at 0.4 mL / h - 0.6 mL / h, and the electrospinning time is 2.4 h - 2.6 h to prepare a heat-resistant polyimide separator.

[0021] Among them, the magnesium plastic reinforcing agent includes one or more of magnesium hydroxide whiskers, magnesium carbonate whiskers, magnesium borate whiskers, and basic magnesium sulfate whiskers.

[0022] The silane coupling agent includes one or more of methyltriethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-(β-aminoethyl)aminopropyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-acryloxypropyltriethoxysilane, 3-methacryloxypropyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, allyltrimethoxysilane, allyltriethoxysilane, bis(2-hydroxyethyl)-3-aminopropyl-methoxysilane, N-hydroxymethyl-N-methylamine-propyltrimethoxysilane, hydroxymethyltriethoxysilane, triethoxysilylmethanol, N-(3-ethoxypropylsilyl)-4-hydroxybutyramide, N-(3-ethoxypropylsilyl)-glucosamide, 2,2-bis(3-ethoxypropylsilyl-methyl)-butanol, and 2-carboxyethyltriethoxysilane.

[0023] The ceramic powder includes one or more of aluminum oxide, nano-silica, barium titanate, lead titanate zirconate, modified lead titanate zirconate, lead metaniobate, lead barium lithium niobate, lead lanthanum titanate zirconate, modified lead titanate, lead titanate - lead magnesium niobate, aluminum oxide, and titanium dioxide.

[0024] The silicone-based wetting and dispersing agent includes one or more of BYKJET-9133, BYKJET-9142, BYKJET-9151, BYKJET-9152, DISPERBYK-167, DISPERBYK-190, DISPERBYK-191, and DISPERBYK-2200.

[0025] Isocyanate catalysts include triphenylmethane triisocyanate.

[0026] We further compare the performance of the polyimide composite separator obtained in the present invention with other separators.

[0027] Example 1:

[0028] Add 2 g of methyltriethoxysilane diluted with absolute ethanol to 4 g of basic magnesium sulfate whiskers, stir at 120 °C for 30 minutes in a high-speed stirrer, pour it into an ultrasonic disperser, and ultrasonicate for 25 min. Add 0.5 g of catalyst triphenylmethane triisocyanate, 93.5 g of polyimide powder, 15 g of aluminum oxide, and 1.5 g of BYKJET-9133 at a frequency of 19 KHZ for cross-linking reaction. Dry the obtained product in an oven at 80 °C for 30 minutes to obtain the final product. Dissolve the final product in 565 g of NMP organic solvent, spin in a high-voltage electrostatic field with a voltage of 15 kV, the distance from the syringe tip to the receiving surface is 15 cm, the advancing speed of the syringe is controlled at 0.5 ml / h, and the electrospinning time is 2.5 hours to prepare a heat-resistant polyimide separator.

[0029] Example 2:

[0030] Add 2 g of vinyltriethoxysilane diluted with absolute ethanol to 4 g of magnesium hydroxide whiskers, stir at 120 °C for 30 minutes in a high-speed stirrer, pour it into an ultrasonic disperser, and ultrasonicate for 25 min. Add 0.5 g of catalyst triphenylmethane triisocyanate, 93.5 g of polyimide powder, 15 g of nano-silica, and 1.5 g of BYKJET-9142 at a frequency of 19 KHZ for cross-linking reaction. Dry the obtained product in an oven at 80 °C for 30 minutes to obtain the final product. Dissolve the final product in 565 g of NMP organic solvent, spin in a high-voltage electrostatic field with a voltage of 15 kV, the distance from the syringe tip to the receiving surface is 15 cm, the advancing speed of the syringe is controlled at 0.5 ml / h, and the electrospinning time is 2.5 hours to prepare a heat-resistant polyimide separator.

[0031] Example 3:

[0032] Add 2 g of hydroxymethyltriethoxysilane diluted with absolute ethanol to 4 g of magnesium carbonate whiskers, stir at 120 °C for 30 minutes in a high-speed stirrer, pour it into an ultrasonic disperser, and ultrasonicate for 25 min. Add 0.5 g of triphenylmethane triisocyanate, 93.5 g of polyimide powder, 15 g of barium titanate, and 1.5 g of DISPERBYK-167 at a frequency of 19 KHZ for cross-linking reaction. Dry the obtained product in an oven at 80 °C for 30 minutes to obtain the final product. Dissolve the final product in 565 g of NMP organic solvent and electrospin in a high-voltage electrostatic field with a voltage of 15 kV. The distance from the syringe tip to the receiving surface is 15 cm, the advancing speed of the syringe is controlled at 0.5 ml / h, and the electrospinning time is 2.5 hours to prepare a heat-resistant polyimide separator.

[0033] Example 4:

[0034] Add 2 g of allyltrimethoxysilane diluted with absolute ethanol to 4 g of magnesium borate whiskers, stir at 120 °C for 30 minutes in a high-speed stirrer, pour it into an ultrasonic disperser, and ultrasonicate for 25 min. Add 0.5% g of triphenylmethane triisocyanate, 93.5% g of polyimide powder, 15 g of titanium dioxide, and 1.5 g of DISPERBYK-191 at a frequency of 19 KHZ for cross-linking reaction. Dry the obtained product in an oven at 80 °C for 30 minutes to obtain the final product. Dissolve the final product in 565 g of NMP organic solvent and electrospin in a high-voltage electrostatic field with a voltage of 15 kV. The distance from the syringe tip to the receiving surface is 15 cm, the advancing speed of the syringe is controlled at 0.5 ml / h, and the electrospinning time is 2.5 hours to prepare a heat-resistant polyimide separator.

[0035] Comparative Example 1:

[0036] Dissolve 93.5% g of polyimide powder, 15 g of aluminum oxide, and 1.5 g of BYKJET-9133 in 565 g of NMP organic solvent and electrospin in a high-voltage electrostatic field with a voltage of 15 kV. The distance from the syringe tip to the receiving surface is 15 cm, the advancing speed of the syringe is controlled at 0.5 ml / h, and the electrospinning time is 2.5 hours to prepare a heat-resistant polyimide separator.

[0037] Comparative Example 2:

[0038] Add 2 g of methyltriethoxysilane diluted with absolute ethanol to 4 g of magnesium sulfate basic whiskers, stir at 120 °C for 30 minutes in a high-speed stirrer, pour it into an ultrasonic disperser, ultrasonicate for 25 min, and add 93.5% g of polyimide powder, 15 g of aluminum oxide and 1.5 g of BYKJET-9133 at a frequency of 19 KHZ to carry out a cross-linking reaction. Dry the obtained product in an oven at 80 °C for 30 minutes. Obtain the final product. Dissolve the final product in 565 g of NMP organic solvent, spin it in a high-voltage electrostatic field with a voltage of 15 kV, the distance from the syringe tip to the receiving surface is 15 cm, the advancing speed of the syringe is controlled at 0.5 ml / h, and the electrospinning time is 2.5 hours to prepare a heat-resistant polyimide separator.

[0039] Comparative Example 3:

[0040] Add 0.1 g of methyltriethoxysilane diluted with absolute ethanol to 4 g of magnesium sulfate basic whiskers, stir at 120 °C for 30 minutes in a high-speed stirrer, pour it into an ultrasonic disperser, ultrasonicate for 25 min, and add 0.5 g of catalyst triphenylmethane triisocyanate, 93.5 g of polyimide powder, 15 g of aluminum oxide and 1.5 g of BYKJET-9133 at a frequency of 19 KHZ to carry out a cross-linking reaction. Dry the obtained product in an oven at 80 °C for 30 minutes. Obtain the final product. Dissolve the final product in 565 g of NMP organic solvent, spin it in a high-voltage electrostatic field with a voltage of 15 kV, the distance from the syringe tip to the receiving surface is 15 cm, the advancing speed of the syringe is controlled at 0.5 ml / h, and the electrospinning time is 2.5 hours to prepare a heat-resistant polyimide separator.

[0041] Comparative Example 4:

[0042] Add 2 g of methyltriethoxysilane diluted with absolute ethanol to 2 g of magnesium sulfate basic whiskers, stir at 120 °C for 30 minutes in a high-speed stirrer, pour it into an ultrasonic disperser, ultrasonicate for 25 min, and add 0.5 g of catalyst triphenylmethane triisocyanate, 93.5 g of polyimide powder, 15 g of aluminum oxide and 1.5 g of BYKJET-9133 at a frequency of 19 KHZ to carry out a cross-linking reaction. Dry the obtained product in an oven at 80 °C for 30 minutes. Obtain the final product. Dissolve the final product in 565 g of NMP organic solvent, spin it in a high-voltage electrostatic field with a voltage of 15 kV, the distance from the syringe tip to the receiving surface is 15 cm, the advancing speed of the syringe is controlled at 0.5 ml / h, and the electrospinning time is 2.5 hours to prepare a heat-resistant polyimide separator.

[0043] Comparative Example 5:

[0044] Add 2 g of methyltriethoxysilane diluted with anhydrous ethanol to 6 g of magnesium sulfate basic whiskers, stir at 120 °C for 30 minutes in a high-speed stirrer, pour it into an ultrasonic disperser, ultrasonicate for 25 min, and add 0.5 g of triphenylmethane triisocyanate as a catalyst, 93.5 g of polyimide powder, 15 g of aluminum oxide and 1.5 g of BYKJET-9133 at a frequency of 19 KHZ for crosslinking reaction. Dry the obtained product in an oven at 80 °C for 30 minutes. Obtain the final product. Dissolve the final product in 565 g of NMP organic solvent, spin in a high-voltage electrostatic field with a voltage of 15 kV, the distance from the syringe tip to the receiving surface is 15 cm, the pushing speed of the syringe is controlled at 0.5 ml / h, and the electrospinning time is 2.5 hours to prepare a heat-resistant polyimide separator.

[0045] Comparative Example 6:

[0046] Add 2 g of methyltriethoxysilane diluted with anhydrous ethanol to 1 g of magnesium sulfate basic whiskers, stir at 120 °C for 30 minutes in a high-speed stirrer, pour it into an ultrasonic disperser, ultrasonicate for 25 min, and add 0.5% g of triphenylmethane triisocyanate as a catalyst, 93.5 g of polyimide powder, 15 g of aluminum oxide and 1.5 g of BYKJET-9133 at a frequency of 19 KHZ for crosslinking reaction. Dry the obtained product in an oven at 80 °C for 30 minutes. Obtain the final product. Dissolve the final product in 565 g of NMP organic solvent, spin in a high-voltage electrostatic field with a voltage of 15 kV, the distance from the syringe tip to the receiving surface is 15 cm, the pushing speed of the syringe is controlled at 0.5 ml / h, and the electrospinning time is 2.5 hours to prepare a heat-resistant polyimide separator.

[0047] Comparative Example 7:

[0048] Add 2 g of methyltriethoxysilane diluted with anhydrous ethanol to 6 g of magnesium sulfate basic whiskers, stir at 120 °C for 30 minutes in a high-speed stirrer, pour it into an ultrasonic disperser, ultrasonicate for 25 min, and add 0.5 g of triphenylmethane triisocyanate as a catalyst, 93.5 g of polyimide powder, 15 g of aluminum oxide and 1.5 g of BYKJET-9133 at a frequency of 19 KHZ for crosslinking reaction. Dry the obtained product in an oven at 80 °C for 30 minutes. Obtain the final product. Dissolve the final product in 700 g of NMP organic solvent, spin in a high-voltage electrostatic field with a voltage of 15 kV, the distance from the syringe tip to the receiving surface is 15 cm, the pushing speed of the syringe is controlled at 0.5 ml / h, and the electrospinning time is 2.5 hours to prepare a heat-resistant polyimide separator.

[0049] Comparative Example 8:

[0050] Add 2 g of methyltriethoxysilane diluted with absolute ethanol to 7 g of magnesium sulfate basic whiskers, stir at 120 °C for 30 minutes in a high-speed stirrer, pour it into an ultrasonic disperser, ultrasonicate for 25 min, and add 0.5 g of triphenylmethane triisocyanate as a catalyst, 93.5 g of polyimide powder, 15 g of aluminum oxide, and 1.5 g of BYKJET-9133 at a frequency of 19 KHZ to carry out a crosslinking reaction. Dry the obtained product in an oven at 80 °C for 30 minutes. Obtain the final product. Dissolve the final product in 700 g of NMP organic solvent, spin it in a high-voltage electrostatic field with a voltage of 15 kV, the distance from the syringe tip to the receiving surface is 15 cm, the advancing speed of the syringe is controlled at 0.5 ml / h, and the electrospinning time is 2.5 hours to prepare a heat-resistant polyimide separator.

[0051] Comparative Example 9:

[0052] Add 2 g of methyltriethoxysilane diluted with absolute ethanol to 4 g of magnesium sulfate basic whiskers, stir at 120 °C for 30 minutes in a high-speed stirrer, pour it into an ultrasonic disperser, ultrasonicate for 25 min, and add 0.5 g of triphenylmethane triisocyanate as a catalyst, 93.5 g of polyimide powder, 15 g of aluminum oxide, and 1.5 g of BYKJET-9133 at a frequency of 19 KHZ to carry out a crosslinking reaction. Dry the obtained product in an oven at 80 °C for 30 minutes. Obtain the final product. Dissolve the final product in 200 g of NMP organic solvent, spin it in a high-voltage electrostatic field with a voltage of 15 kV, the distance from the syringe tip to the receiving surface is 15 cm, the advancing speed of the syringe is controlled at 0.5 ml / h, and the electrospinning time is 2.5 hours to prepare a heat-resistant polyimide separator.

[0053] Comparative Example 10:

[0054] Add 2 g of methyltriethoxysilane diluted with absolute ethanol to 4 g of magnesium sulfate basic whiskers, stir at 120 °C for 30 minutes in a high-speed stirrer, pour it into an ultrasonic disperser, ultrasonicate for 25 min, and add 0.5 g of triphenylmethane triisocyanate as a catalyst, 93.5 g of polyimide powder, 15 g of aluminum oxide, and 1.5 g of BYKJET-9133 at a frequency of 19 KHZ to carry out a crosslinking reaction. Dry the obtained product in an oven at 80 °C for 30 minutes. Obtain the final product. Dissolve the final product in 300 g of NMP organic solvent, spin it in a high-voltage electrostatic field with a voltage of 15 kV, the distance from the syringe tip to the receiving surface is 15 cm, the advancing speed of the syringe is controlled at 0.5 ml / h, and the electrospinning time is 2.5 hours to prepare a heat-resistant polyimide separator.

[0055] We also tested the separators prepared in the examples and comparative examples, mainly including the following test methods:

[0056] (1) Thermal shrinkage of diaphragm. The test method shall refer to GB / T2027-2004.

[0057] (2) The tensile strength of the diaphragm. The test method shall refer to GB / T2040.3-2006.

[0058] (3) The puncture strength of the diaphragm. The test method shall refer to GB / T23318-2009.

[0059] (4) Viscosity of the final mixed solution. The detection method refers to GB / T5561-2012.

[0060] (5) The air permeability of the diaphragm. The testing method shall refer to GB / T36363-2018.

[0061] Verification results analysis

[0062] Table 1 Comparison of the diaphragms of the embodiments and comparative examples

[0063] - Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Comparative Example 8 Comparative Example 9 Comparative Example 10 Crosslinking degree / ρ 5.30％ 5％ 5％ 5.10％ - 1％ 1.80％ 3.60％ 2.50％ 3.60％ 2.70％ 2.50％ 5％ 5％ Heat shrinkage at 200 °C for 1 h 0.40％ 0.50％ 0.50％ 0.40％ 1.20％ 0.50％ 0.60％ 0.60％ 0.70％ 0.60％ 0.70％ 0.80％ 0.40％ 0.40％ Tensile strength / mp 96.8 95.8 96.1 96.2 60.5 76.9 82.3 90.6 89.5 90.9 89.5 88.8 91.4 91.6 Puncture strength / N 5.7 5.5 5.6 5.7 4.8 4.1 4.3 5.1 4.8 5.1 5 4.9 5.4 5.2 Viscosity of the mixed solution at 25 °C / pa.s 35.4 35.6 35.2 35.3 41.2 35.6 34.8 35.2 36.7 35.4 33.8 32.7 82.1 105.6 Air permeability value 175.3 170.4 173.5 173.3 150.4 174.6 176.3 173.5 173.6 175.8 204.2 206.3 131.5 128.3

[0064] We successfully obtained a polyimide composite diaphragm by an electrostatic spinning method. We tested the polyimide composite diaphragm prepared by the present invention, and the test results are shown in Table 1. We found that the performance of the composite diaphragm obtained by the present invention is better than that of the comparative example. It can be seen that the organic silicon wetting agent can not only promote the wettability of the ceramic powder, thereby improving the dispersibility of the ceramic powder in the polyimide, but also add a magnesium plastic reinforcing agent. In order to promote the cross-linking reaction between the magnesium plastic reinforcing agent and the polyimide, a silane coupling agent of the same type as the organic silane wetting agent is further added to promote the solubility of the magnesium plastic reinforcing agent, and cross-link with the polyimide under the action of the isocyanate catalyst. The isocyanate catalyst can serve as a bridge for the cross-linking of the magnesium reinforcing agent and the polyimide, thereby helping to improve the tensile strength and toughness of the composite diaphragm, and also overcome the brittle cracking of the diaphragm caused by solid particles such as ceramic powder. Through the mutual cooperation between the above substances, the electrostatic spinning method is adopted to successfully obtain a battery diaphragm with good air permeability, thermal stability and tensile strength.

[0065] We also further compared the traditional methods for preparing polyimide separators. As shown by Examples 1 - 4 and Comparative Example 1, it was found that the magnesium plastic enhancer in the present invention contributed to the combination of polyimide and ceramic powder, thereby reducing the thermal shrinkage of the separator, increasing the puncture strength and air permeability of the separator. We believe that this is related to the crosslinking of the magnesium plastic enhancer and polyimide. When the magnesium plastic enhancer and polyimide are crosslinked, the tension of the solution will be reduced, which promotes the uniform attachment of the mixed solution to the base film by electrospinning. In addition, the magnesium plastic enhancer can also enhance the tensile strength of the separator, thereby reducing the occurrence of brittle fracture of the separator and improving the safety performance of the battery.

[0066] On this basis, we further studied the influence of the interaction between substances in the present invention on the improvement degree of the performance of the battery separator, as shown by Examples 1 - 4 and Comparative Examples 2 - 10. When the addition amount of the magnesium plastic enhancer changes, it will directly affect the crosslinking of the magnesium plastic enhancer and polyimide. As shown by Comparative Examples 4 - 6, when the addition amount of the magnesium plastic enhancer is too much (Comparative Example 5) or too little (Comparative Examples 4 and 6), the degree of crosslinking will decrease. This may be because when the addition amount of the magnesium plastic enhancer is too little, the crosslinking is too low; while when the addition amount is too much, due to the relatively small amount of isocyanate catalysts, the crosslinking reaction cannot be fully completed, resulting in a decrease in the degree of crosslinking. In addition, we further found that isocyanate catalysts and silane coupling agents have a greater impact on the degree of crosslinking. As shown by Comparative Examples 2 - 3, when no isocyanate catalyst is added or the amount of silane coupling agent is reduced, it is not conducive to the reaction between the magnesium plastic enhancer and polyimide. We believe that this may be because the lack of isocyanate catalyst will lead to a straight-line decrease in the crosslinking degree of the magnesium plastic enhancer and polyimide due to the lack of bridging substances; while the reduction of the silane coupling agent will affect the solubility of the magnesium plastic enhancer and directly affect the crosslinking of the magnesium plastic enhancer and polyimide. Therefore, when the isocyanate catalyst or silane coupling agent is reduced or absent, the crosslinking of the magnesium plastic enhancer and polyimide decreases linearly, and the tensile strength, puncture strength and thermal shrinkage of the separator will all be affected.

[0067] We further found that the addition amount of the organic solvent directly affects the viscosity of the solution during electrostatic prevention, further affecting the surface tension of the solution, and thus affecting the air permeability value of the battery separator prepared by electrospinning. When the solution concentration is too high, the increase in viscosity will result in a lower air permeability value of the final separator; while when the concentration is too low, the viscosity decreases, resulting in a higher air permeability value of the separator, as shown in Comparative Examples 7-10. However, too high or too low air permeability value of the separator is not conducive to the performance of the separator. In summary, we further selected that the mass ratio of polyimide, magnesium plastic enhancer, silane coupling agent, ceramic powder, organosilicon wetting and dispersing agent, isocyanate catalyst, and organic solvent is (93 parts - 94 parts):(3 parts - 5 parts):(1.5 parts - 2.5 parts):(14 parts - 16 parts):(1 part - 2 parts):(0.5 parts - 1 part):(565 parts - 603 parts).

[0068] In summary, the preparation method of the present invention can obtain a battery separator with good air permeability, thermal stability and tensile strength.

[0069] It should be noted that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A high-temperature resistant polyimide composite separator, characterized in that, the composite separator comprises polyimide, magnesium plastic reinforcing agent, silane coupling agent, ceramic powder, organosilicon wetting and dispersing agent, isocyanate catalyst, and organic solvent. By mass, the mass ratio of polyimide, magnesium plastic reinforcing agent, silane coupling agent, ceramic powder, organosilicon wetting and dispersing agent, isocyanate catalyst, and organic solvent is (93 parts - 94 parts):(3 parts - 5 parts):(1.5 parts - 2.5 parts):(14 parts - 16 parts):(1 part - 2 parts):(0.5 parts - 1 part):(565 parts - 603 parts); the high-temperature resistant polyimide composite separator is prepared by the following method: adding the diluted silane coupling agent to the magnesium plastic reinforcing agent, then stirring, and adding the isocyanate catalyst, polyimide, ceramic powder, and organosilicon wetting and dispersing agent to the mixture of the magnesium plastic reinforcing agent and the silane coupling agent under ultrasound, and then drying the obtained product; dissolving the dried product in the organic solvent, and performing electrospinning on the base film. The distance between the syringe tip and the receiving surface of the base film is a certain distance, and the syringe is advanced at a certain speed to obtain the polyimide separator.

2. A high-temperature resistant polyimide composite separator according to claim 1, characterized in that, the magnesium plastic reinforcing agent includes one or more of basic magnesium sulfate whiskers, magnesium hydroxide whiskers, magnesium carbonate whiskers, and magnesium borate whiskers.

3. A high-temperature resistant polyimide composite separator according to claim 1, characterized in that, the silane coupling agent includes one or more of methyltriethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-(β-aminoethyl)aminopropyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-acryloxypropyltriethoxysilane, 3-methacryloxypropyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, allyltrimethoxysilane, allyltriethoxysilane, bis(2-hydroxyethyl)-3-aminopropyl-methoxysilane, N-hydroxymethyl-N-methylamine-propyltrimethoxysilane, hydroxymethyltriethoxysilane, triethoxysilylmethanol, N-(3-ethoxypropylsilyl)-4-hydroxybutyramide, N-(3-ethoxypropylsilyl)-glucosamide, 2,2-bis(3-ethoxypropylsilyl-methyl)-butanol, 2-carboxyethyltriethoxysilane.

4. A high-temperature resistant polyimide composite separator according to claim 1, characterized in that, the ceramic powder includes one or more of aluminum oxide, nano-silicon dioxide, barium titanate, lead titanate zirconate, modified lead titanate zirconate, lead metaniobate, lead barium lithium niobate, lead lanthanum titanate zirconate, modified lead titanate, lead titanate - lead magnesium niobate, aluminum oxide, and titanium dioxide.

5. A high-temperature resistant polyimide composite separator according to claim 1, characterized in that, The silicone-based wetting and dispersing agents include one or more of BYKJET-9133, BYKJET-9142, BYKJET-9151, BYKJET-9152, DISPERBYK-167, DISPERBYK-190, DISPERBYK-191, and DISPERBYK-2200.

6. A high-temperature resistant polyimide composite separator according to claim 1, characterized in that the isocyanate-based catalyst includes triphenylmethane triisocyanate.

7. A high-temperature resistant polyimide composite separator according to claim 1, characterized in that the organic solvent includes one of dimethylformamide and N-methylpyrrolidone.

8. A high-temperature resistant polyimide composite separator according to claim 1, characterized in that the diluted silane coupling agent is diluted with absolute ethanol; the temperature of the stirring is 110°C - 130°C, the time of the stirring is 25 min - 35 min; the conditions of the ultrasonic treatment are a frequency of 18 KHZ - 20 KHZ, the time of the ultrasonic treatment is 20 min - 30 min; the time of the drying is 25 min - 35 min, the temperature of the drying is 75°C - 85°C; the voltage of the electrospinning is 14 Kv - 16 Kv; the distance between the syringe needle tip and the receiving surface of the base film is 14 cm - 16 cm; the advancing speed of the syringe is 0.4 mL / h - 0.6 mL / h; the time of the electrospinning is 2.4 h - 2.6 h.