A flame-retardant lithium battery separator and its preparation method

Abstract

The present invention discloses a flame-retardant lithium battery separator and a preparation method thereof, relating to the technical field of battery separators. When preparing the flame-retardant lithium battery separator of the present invention, hexachlorocyclotriphosphazene and daidzein are polymerized and coated on the surface of phase change microcapsules to obtain modified phase change microcapsules; 1,7-dichloro-1,1,3,3,5,5,7,7-octamethyltetrasiloxane and phenolphthalein are polymerized and grown on pretreated bamboo powder to obtain pre-modified bamboo powder; the pre-modified bamboo powder and sodium hydroxide are reacted to obtain modified bamboo powder; polypropylene and N,N-dimethylallylamine are reacted to obtain pre-modified polypropylene; the pre-modified polypropylene and 3-chloro-1-propanethiol are reacted to obtain modified polypropylene; the modified polypropylene, modified phase change microcapsules, modified bamboo powder and azobisisobutyronitrile are formulated into a spinning solution, and the flame-retardant lithium battery separator is prepared by electrospinning. The flame-retardant lithium battery separator prepared by the present invention has excellent flame retardancy, thermal stability, ionic conductivity and mechanical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of battery separators, and particularly to a flame-retardant lithium battery separator and a preparation method thereof. Background Art

[0002] Lithium-ion batteries have been widely used in many fields due to their excellent energy and power density, relatively high working voltage, and outstanding cycle life, such as portable electronic devices, electric vehicles, military applications, etc. The battery separator, as a core component of the lithium-ion battery, plays a crucial role. It not only prevents the short-circuit problem caused by the direct contact between the positive and negative electrodes of the battery, but also provides a necessary channel for the migration of lithium ions, thus ensuring that the battery can complete normal charge and discharge. However, commercial polyolefin separators have disadvantages such as poor electrolyte wettability, poor thermal stability, and flammability, which pose safety hazards to the use of lithium-ion batteries and limit the further development of lithium-ion batteries. Therefore, it is necessary to improve the polyolefin battery separator to enhance the flame-retardant and thermal stability performance of the battery separator, thereby improving the safety of lithium-ion batteries. Summary of the Invention

[0003] The purpose of the present invention is to provide a flame-retardant lithium battery separator and a preparation method thereof to solve the problems existing in the prior art.

[0004] To solve the above technical problems, the present invention provides the following technical solutions:

[0005] A preparation method of a flame-retardant lithium battery separator, the preparation method of the flame-retardant lithium battery separator includes the following preparation steps:

[0006] (1) Mix phase change microcapsules, triethylamine, and acetonitrile in a mass ratio of 1:(0.2 - 0.3):(20 - 22) evenly, ultrasonically disperse for 30 - 40 min, under the stirring conditions of 45 - 55 °C and 200 - 300 r / min, uniformly dropwise add a reaction solution 6 - 8 times the mass of the phase change microcapsules within 15 min. After the dropping is completed, continue to stir and react for 6 - 8 h, filter, wash with anhydrous ethanol and deionized water 3 - 5 times each, and dry at 60 - 70 °C under vacuum conditions for 9 - 11 h to obtain modified phase change microcapsules;

[0007] (2)Mix 1,7-dichloro-1,1,3,3,5,5,7,7-octamethyltetrasiloxane and N,N-dimethylacetamide evenly according to the mass ratio of 1:(7 - 8) to prepare a siloxane solution; mix the pretreated bamboo powder, phenolphthalein, triethylamine, and N,N-dimethylacetamide evenly according to the mass ratio of 1:(2 - 3):(0.06 - 0.08):(18 - 22), and under the stirring conditions of 50 - 60 °C and 200 - 300 r / min, dropwise add the siloxane solution which is 7 - 8 times the mass of the bamboo powder evenly within 30 min. After the dropping is completed, continue stirring and reacting for 1 - 2 h, filter, wash with anhydrous ethanol and deionized water 3 - 5 times each, and dry under vacuum conditions at 65 - 75 °C for 9 - 11 h to obtain pre-modified bamboo powder; mix the pre-modified bamboo powder and the sodium hydroxide aqueous solution with a concentration of 0.5 mol / L evenly according to the mass ratio of 1:(40 - 50), ultrasonicate at 70 - 80 °C for 1 - 2 h, filter, wash with the hydrochloric acid aqueous solution with a concentration of 0.5 mol / L 3 - 5 times, and then wash with deionized water until the filtrate is neutral, and dry under vacuum conditions at 65 - 75 °C for 9 - 11 h to obtain modified bamboo powder;

[0008] (3)Mix the pre-modified polypropylene and xylene evenly according to the mass ratio of 1:(20 - 24), stir at 70 - 80 °C and 100 - 120 r / min for 20 - 30 min, add 3-chloro-1-propanethiol which is 0.2 - 0.3 times the mass of the pre-modified polypropylene, continue stirring and reacting for 2 - 3 h, add deionized water with the same volume as xylene and mix evenly, let it stand for layering, take the organic phase and dry under vacuum conditions at 60 - 70 °C for 10 - 12 h to obtain modified polypropylene;

[0009] (4)By mass, weigh 98 - 102 parts of modified polypropylene, 4 - 5 parts of modified phase change microcapsules, 6 - 7 parts of modified bamboo powder, 0.6 - 0.8 parts of azobisisobutyronitrile, and 660 - 700 parts of dimethyl sulfoxide; mix the modified polypropylene, modified phase change microcapsules, modified bamboo powder, and dimethyl sulfoxide evenly, stir at 10 - 30 °C and 100 - 200 r / min for 50 - 60 min, let it stand for 4 - 5 h, add azobisisobutyronitrile and mix evenly to prepare a spinning solution; add the spinning solution into a syringe, then install the syringe on an electrospinning instrument for electrospinning, stack it on the receiving plate to form a fiber membrane with a thickness of 18 - 20 μm, let it stand at 72 - 78 °C for 35 - 45 min, and dry under vacuum conditions at 55 - 65 °C for 8 - 10 h to obtain a flame-retardant lithium battery separator.

[0010] As an optimization, for the preparation method of the reaction solution to be used in step (1): Add hexachlorocyclotriphosphazene and daidzein according to the molar ratio of 1:(3 - 4) to acetonitrile which is 10 - 12 times the mass of hexachlorocyclotriphosphazene to prepare the reaction solution to be used.

[0011] As an optimization, the type of the phase change microcapsules in step (1) is PCM 37, which is purchased from Dongguan Shengbang High Polymer Materials Co., Ltd.

[0012] As an optimization, the preparation method of the pre-modified bamboo powder in step (2) is as follows: Mix 1,7-dichloro-1,1,3,3,5,5,7,7-octamethyltetrasiloxane and N,N-dimethylacetamide evenly according to the mass ratio of 1:(7~8) to prepare a siloxane solution; Mix the pretreated bamboo powder, phenolphthalein, triethylamine, and N,N-dimethylacetamide evenly according to the mass ratio of 1:(2~3):(0.06~0.08):(18~22), and under the stirring conditions of 50~60°C and 200~300 r / min, uniformly dropwise add a siloxane solution 7~8 times the mass of the bamboo powder within 30 min. After the dropping is completed, continue stirring and reacting for 1~2 h, filter, wash with anhydrous ethanol and deionized water 3~5 times each, and dry at 65~75°C for 9~11 h under vacuum conditions to obtain the pre-modified bamboo powder.

[0013] As an optimization, the preparation method of the pretreated bamboo powder is as follows: Mix triethoxysilane and anhydrous ethanol evenly according to the mass ratio of 1:(20~24), adjust the pH to 5.8~6.2 with a hydrochloric acid aqueous solution with a concentration of 1.5 mol / L, and stir at 15~35°C and 200~300 r / min for 18~22 min to prepare a silane hydrolysis solution; Mix the bamboo powder and anhydrous ethanol evenly according to the mass ratio of 1:(30~40), ultrasonically disperse for 30~40 min, add a silane hydrolysis solution 14~16 times the mass of the bamboo powder, and stir and react at 65~75°C and 200~300 r / min for 3~4 h, filter, wash with anhydrous ethanol 3~5 times, and dry at 65~75°C for 9~11 h under vacuum conditions to obtain the pretreated bamboo powder.

[0014] As an optimization, the particle size of the bamboo powder is 300 mesh, which is purchased from Huamo (Shandong) Biotechnology Co., Ltd.

[0015] As an optimization, the preparation method of the pre-modified polypropylene in step (3) is as follows: Add polypropylene, N,N-dimethylallylamine, and dicumyl peroxide into a high-speed mixer according to the mass ratio of 100:(2~3):(0.4~0.6), mix at 800~1000 r / min for 5~7 min, and then place it in a screw extruder for extrusion granulation. Set the screw speed of the extruder during granulation to 85~95 r / min, and the screw temperature is: the first section is 170~172°C, the second section is 180~182°C, the third section is 188~190°C, and the fourth section is 184~186°C to obtain the pre-modified polypropylene.

[0016] As an optimization, the molecular weight of the polypropylene is 100,000.

[0017] As an optimization, the process parameters of the electrospinning described in step (4) are as follows: the pushing rate of the spinning solution is set to 0.50 - 0.52 mL / h, the spinning voltage is 16 - 18 kV, the receiving distance is 9 - 11 cm, the spinning temperature is 20 - 30 °C, and the air humidity is 46% - 50%.

[0018] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0019] When preparing the flame - retardant lithium - battery separator, the present invention polymerizes and coats hexachlorocyclotriphosphazene and daidzein on the surface of the phase - change microcapsule to obtain modified phase - change microcapsules; reacts bamboo powder with triethoxysilane chloride to obtain pretreated bamboo powder; polymerizes and grows 1,7 - dichloro - 1,1,3,3,5,5,7,7 - octamethyltetrasiloxane and phenolphthalein on the pretreated bamboo powder to obtain pre - modified bamboo powder; reacts the pre - modified bamboo powder with sodium hydroxide to obtain modified bamboo powder; reacts polypropylene with N,N - dimethylallylamine to obtain pre - modified polypropylene; reacts the pre - modified polypropylene with 3 - chloro - 1 - propanethiol to obtain modified polypropylene; formulates a spinning solution with the modified polypropylene, the modified phase - change microcapsules, the modified bamboo powder, and azobisisobutyronitrile, and prepares the flame - retardant lithium - battery separator by electrospinning.

[0020] First, the P - Cl bond on hexachlorocyclotriphosphazene reacts with the hydroxyl group on daidzein, so that hexachlorocyclotriphosphazene and daidzein polymerize and coat on the surface of the phase - change microcapsule to obtain modified phase - change microcapsules; introduce hexachlorocyclotriphosphazene and daidzein on the surface of the modified phase - change microcapsules; the introduction of hexachlorocyclotriphosphazene can improve the flame - retardant performance of the flame - retardant lithium - battery separator, and the deoxybenzoin structure in daidzein can increase the char - forming rate during polymer combustion, reduce the heat release amount and the release amount of volatile combustibles, further improving the flame - retardant performance of the flame - retardant lithium - battery separator; the carbon - carbon double bond in daidzein can react with the mercapto group introduced on the side chain of the modified polypropylene molecule under the catalysis of azobisisobutyronitrile to form a cross - linked network structure, inhibiting the relative movement of the polypropylene molecular chain and enhancing the mechanical properties of the flame - retardant lithium - battery separator; during the use of a lithium battery, it is easy to generate overheating inside the lithium battery due to charge and discharge, and the separator is prone to shrinkage or even rupture after heating, resulting in direct contact between the positive and negative electrodes inside the power supply and short - circuit, thus causing potential safety hazards in the battery; the phase - change microcapsule is an intelligent material that can intelligently adjust the temperature of the flame - retardant lithium - battery separator, effectively transfer heat or absorb heat when the ambient temperature changes, improving the thermal stability of the battery separator, and thus enhancing the safety of the lithium - ion battery.

[0021] Secondly, bamboo powder and triethoxysilane are reacted to obtain pretreated bamboo powder, and Si-Cl bonds are introduced onto the surface of the pretreated bamboo powder; the Si-Cl bonds on 1,7-dichloro-1,1,3,3,5,5,7,7-octamethyltetrasiloxane react with the hydroxyl groups on phenolphthalein and polymerize and grow on the pretreated bamboo powder to obtain pre-modified bamboo powder, and siloxane chains and phenolphthalein are introduced onto the modified bamboo powder; the introduction of siloxane chains can further improve the flame retardancy of the flame-retardant lithium battery separator; the phenolphthalein on the pre-modified bamboo powder is subjected to alkali treatment with sodium hydroxide, so that the lactone structure in phenolphthalein undergoes a ring-opening reaction to generate hydroxyl groups and carboxyl groups, introducing more polar groups, improving the affinity between the flame-retardant lithium battery separator and the electrolyte, and making the electrolyte wettability better, thereby improving the ionic conductivity of the flame-retardant lithium battery separator. In addition, the carboxyl groups generated on the modified bamboo powder can also combine with the quaternary ammonium salts generated on the side chains of the polypropylene molecules through positive and negative charges to form a cross-linked network structure, further improving the mechanical properties of the flame-retardant lithium battery separator.

[0022] Finally, N,N-dimethylallylamine is grafted onto the side chains of polypropylene molecules by means of melt grafting to obtain pre-modified polypropylene, and a tertiary amine structure is introduced onto the side chains of the pre-modified polypropylene molecules. The tertiary amine structure introduced onto the side chains of the pre-modified polypropylene molecules reacts with the chlorine atoms on 3-chloro-1-propanethiol to obtain modified polypropylene, and a quaternary ammonium salt structure is generated on the side chains of the modified polypropylene molecules, and a mercapto group is introduced at the same time; the introduction of the quaternary ammonium salt structure helps to improve the ionic conductivity of the flame-retardant lithium battery separator, and can also form a positive and negative charge structure with the carboxyl groups on the modified bamboo powder to enhance the mechanical properties; the mercapto groups introduced onto the side chains of the modified polypropylene molecules can react with the carbon-carbon double bonds on the modified phase change microcapsules to form a cross-linked network structure and improve the mechanical properties of the flame-retardant lithium battery separator. Specific embodiments

[0023] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0024] Example 1

[0025] A preparation method of a flame-retardant lithium battery separator, the preparation method of the flame-retardant lithium battery separator includes the following preparation steps:

[0026] (1) Add hexachlorocyclotriphosphazene and daidzein at a molar ratio of 1:3 into acetonitrile which is 10 times the mass of hexachlorocyclotriphosphazene to prepare a reaction solution to be reacted; Mix phase change microcapsules, triethylamine, and acetonitrile evenly at a mass ratio of 1:0.2:20, ultrasonically disperse for 30 min, and under the stirring conditions of 45 °C and 200 r / min, uniformly add dropwise the reaction solution to be reacted which is 6 times the mass of the phase change microcapsules within 15 min. After the dropwise addition is completed, continue to stir and react for 8 h, filter, wash 3 times with anhydrous ethanol and deionized water respectively, and dry at 60 °C for 11 h under vacuum conditions to obtain modified phase change microcapsules;

[0027] (2) Mix triethoxysilane and anhydrous ethanol evenly at a mass ratio of 1:20, adjust the pH to 5.8 with a hydrochloric acid aqueous solution with a concentration of 1.5 mol / L, and stir at 15 °C and 200 r / min for 22 min to prepare a silane hydrolysis solution; Mix bamboo powder and anhydrous ethanol evenly at a mass ratio of 1:30, ultrasonically disperse for 30 min, add the silane hydrolysis solution which is 14 times the mass of the bamboo powder, and stir and react at 65 °C and 200 r / min for 4 h, filter, wash 3 times with anhydrous ethanol, and dry at 65 °C for 11 h under vacuum conditions to obtain pretreated bamboo powder; Mix 1,7-dichloro-1,1,3,3,5,5,7,7-octamethyltetrasiloxane and N,N-dimethylacetamide evenly at a mass ratio of 1:7 to prepare a siloxane solution; Mix the pretreated bamboo powder, phenolphthalein, triethylamine, and N,N-dimethylacetamide evenly at a mass ratio of 1:2:0.06:18, and under the stirring conditions of 50 °C and 200 r / min, uniformly add dropwise the siloxane solution which is 7 times the mass of the bamboo powder within 30 min. After the dropwise addition is completed, continue to stir and react for 2 h, filter, wash 3 times with anhydrous ethanol and deionized water respectively, and dry at 65 °C for 11 h under vacuum conditions to obtain pre-modified bamboo powder; Mix the pre-modified bamboo powder and a sodium hydroxide aqueous solution with a concentration of 0.5 mol / L evenly at a mass ratio of 1:40, ultrasonically treat at 70 °C for 2 h, filter, wash 3 times with a hydrochloric acid aqueous solution with a concentration of 0.5 mol / L, and then wash with deionized water until the filtrate is neutral, and dry at 65 °C for 11 h under vacuum conditions to obtain modified bamboo powder;

[0028] (3) Polypropylene, N,N-dimethylallylamine, and diisopropylbenzene peroxide were added to a high-speed mixer at a mass ratio of 100:2:0.4, mixed at 800 r / min for 7 min, and then extruded and pelletized in a screw extruder. The screw speed of the extruder during pelletization was set at 85 r / min, and the screw temperatures were: 170 °C in the first section, 180 °C in the second section, 188 °C in the third section, and 184 °C in the fourth section to obtain pre-modified polypropylene; the pre-modified polypropylene and xylene were mixed evenly at a mass ratio of 1:20, stirred at 70 °C and 100 r / min for 30 min, 3-chloro-1-propanethiol 0.2 times the mass of the pre-modified polypropylene was added, and the stirring reaction continued for 3 h. Deionized water with the same volume as xylene was added and mixed evenly, allowed to stand and separate layers, and the organic phase was taken and dried at 60 °C under vacuum for 12 h to obtain modified polypropylene;

[0029] (4) By mass, 98 parts of modified polypropylene, 4 parts of modified phase change microcapsules, 6 parts of modified bamboo powder, 0.6 part of azobisisobutyronitrile, and 660 parts of dimethyl sulfoxide were weighed; the modified polypropylene, modified phase change microcapsules, modified bamboo powder, and dimethyl sulfoxide were mixed evenly, stirred at 10 °C and 100 r / min for 60 min, allowed to stand for 4 h, azobisisobutyronitrile was added and mixed evenly to prepare a spinning solution; the spinning solution was added to a syringe, and then the syringe was installed on an electrospinning instrument for electrospinning. The pushing rate of the spinning solution was set at 0.50 mL / h, the spinning voltage was 16 kV, the receiving distance was 9 cm, the spinning temperature was 20 °C, and the air humidity was 46%. A fiber membrane with a thickness of 18 μm was stacked on the receiving plate, allowed to stand at 72 °C for 35 min, and dried at 55 °C under vacuum for 10 h to obtain a flame-retardant lithium battery separator.

[0030] Example 2

[0031] A preparation method of a flame-retardant lithium battery separator, the preparation method of the flame-retardant lithium battery separator includes the following preparation steps:

[0032] (1) Hexachlorocyclotriphosphazene and daidzein were added to acetonitrile 11 times the mass of hexachlorocyclotriphosphazene at a molar ratio of 1:3.5 to prepare a reaction solution to be reacted; the phase change microcapsules, triethylamine, and acetonitrile were mixed evenly at a mass ratio of 1:0.25:21, ultrasonically dispersed for 35 min, and under stirring conditions at 50 °C and 250 r / min, the reaction solution to be reacted 7 times the mass of the phase change microcapsules was added dropwise uniformly within 15 min. After the addition was completed, the stirring reaction continued for 7 h, filtered, washed 4 times each with absolute ethanol and deionized water, and dried at 65 °C under vacuum for 10 h to obtain modified phase change microcapsules;

[0033] (2) Mix triethoxysilane and absolute ethanol evenly at a mass ratio of 1:22, adjust the pH to 6 with a hydrochloric acid aqueous solution with a concentration of 1.5 mol / L, stir at 25 °C and 250 r / min for 20 min to prepare a silane hydrolysis solution; mix bamboo powder and absolute ethanol at a mass ratio of 1:35, ultrasonically disperse for 35 min, add a silane hydrolysis solution 15 times the mass of the bamboo powder, stir and react at 70 °C and 250 r / min for 3.5 h, filter, wash 4 times with absolute ethanol, and dry at 70 °C for 10 h under vacuum conditions to obtain pretreated bamboo powder; mix 1,7-dichloro-1,1,3,3,5,5,7,7-octamethyltetrasiloxane and N,N-dimethylacetamide evenly at a mass ratio of 1:7.5 to prepare a siloxane solution; mix the pretreated bamboo powder, phenolphthalein, triethylamine, and N,N-dimethylacetamide evenly at a mass ratio of 1:2.5:0.07:20, and under the stirring condition of 55 °C and 250 r / min, uniformly dropwise add a siloxane solution 7.5 times the mass of the bamboo powder within 30 min. After the dropping is completed, continue to stir and react for 1.5 h, filter, wash 4 times with absolute ethanol and deionized water respectively, and dry at 70 °C for 10 h under vacuum conditions to obtain pre-modified bamboo powder; mix the pre-modified bamboo powder and a sodium hydroxide aqueous solution with a concentration of 0.5 mol / L evenly at a mass ratio of 1:45, ultrasonically treat at 75 °C for 1.5 h, filter, wash 4 times with a hydrochloric acid aqueous solution with a concentration of 0.5 mol / L, and then wash with deionized water until the filtrate is neutral, and dry at 70 °C for 10 h under vacuum conditions to obtain modified bamboo powder;

[0034] (3) Add polypropylene, N,N-dimethylallylamine, and diisopropylbenzene peroxide to a high-speed mixer at a mass ratio of 100:2.5:0.5, mix at 900 r / min for 6 min, and then place it in a screw extruder for extrusion granulation. Set the screw speed of the extruder during granulation to 90 r / min, and the screw temperatures are: 171 °C in the first section, 181 °C in the second section, 189 °C in the third section, and 185 °C in the fourth section to obtain pre-modified polypropylene; mix the pre-modified polypropylene and xylene evenly at a mass ratio of 1:22, stir at 75 °C and 110 r / min for 25 min, add 3-chloro-1-propanethiol ization of the pre-modified polypropylene, continue to stir and react for 2.5 h, add deionized water with the same volume as xylene and mix evenly, let it stand for layering, take the organic phase and dry at 65 °C for 11 h under vacuum conditions to obtain modified polypropylene;

[0035] (4)Weigh 100 parts of modified polypropylene, 4.5 parts of modified phase change microcapsules, 6.5 parts of modified bamboo powder, 0.7 part of azobisisobutyronitrile, and 680 parts of dimethyl sulfoxide by mass fraction; mix the modified polypropylene, modified phase change microcapsules, modified bamboo powder, and dimethyl sulfoxide evenly, stir at 20 °C and 150 r / min for 55 min, let stand for 4.5 h, add azobisisobutyronitrile and mix evenly to prepare a spinning solution; add the spinning solution into a syringe, then install the syringe on an electrospinning instrument for electrospinning. Set the pushing rate of the spinning solution to 0.51 mL / h, the spinning voltage to 17 kV, the receiving distance to 10 cm, the spinning temperature to 25 °C, and the air humidity to 48%. Stack a fiber membrane with a thickness of 19 μm on the receiving plate, let stand at 75 °C for 40 min, and dry at 60 °C for 9 h under vacuum conditions to obtain a flame-retardant lithium battery separator.

[0036] Example 3

[0037] A preparation method of a flame-retardant lithium battery separator, the preparation method of the flame-retardant lithium battery separator includes the following preparation steps:

[0038] (1)Add hexachlorocyclotriphosphazene and daidzein in a molar ratio of 1:4 to acetonitrile which is 12 times the mass of hexachlorocyclotriphosphazene to prepare a reaction solution to be reacted; mix the phase change microcapsules, triethylamine, and acetonitrile evenly according to a mass ratio of 1:0.3:22, ultrasonically disperse for 40 min, and under the stirring condition of 55 °C and 300 r / min, uniformly drop the reaction solution to be reacted which is 8 times the mass of the phase change microcapsules within 15 min. After the dropping is completed, continue to stir and react for 6 h, filter, wash 5 times each with absolute ethanol and deionized water, and dry at 70 °C for 9 h under vacuum conditions to obtain modified phase change microcapsules;

[0039] (2) Mix triethoxysilane and absolute ethanol evenly at a mass ratio of 1:24, adjust the pH to 6.2 with a hydrochloric acid aqueous solution with a concentration of 1.5 mol / L, stir at 35 °C and 300 r / min for 18 min to prepare a silane hydrolysis solution; mix bamboo powder and absolute ethanol at a mass ratio of 1:40, ultrasonically disperse for 40 min, add a silane hydrolysis solution 16 times the mass of the bamboo powder, stir and react at 75 °C and 300 r / min for 3 h, filter, wash 5 times with absolute ethanol, and dry at 75 °C for 9 h under vacuum conditions to obtain pretreated bamboo powder; mix 1,7-dichloro-1,1,3,3,5,5,7,7-octamethyltetrasiloxane and N,N-dimethylacetamide evenly at a mass ratio of 1:8 to prepare a siloxane solution; mix the pretreated bamboo powder, phenolphthalein, triethylamine, and N,N-dimethylacetamide evenly at a mass ratio of 1:3:0.08:22, and uniformly dropwise add a siloxane solution 8 times the mass of the bamboo powder within 30 min under stirring conditions at 60 °C and 300 r / min. After the dropping is completed, continue to stir and react for 1 h, filter, wash 5 times with absolute ethanol and deionized water respectively, and dry at 75 °C for 9 h under vacuum conditions to obtain pre-modified bamboo powder; mix the pre-modified bamboo powder and a sodium hydroxide aqueous solution with a concentration of 0.5 mol / L evenly at a mass ratio of 1:50, ultrasonically treat at 80 °C for 1 h, filter, wash 5 times with a hydrochloric acid aqueous solution with a concentration of 0.5 mol / L, and then wash with deionized water until the filtrate is neutral, and dry at 75 °C for 9 h under vacuum conditions to obtain modified bamboo powder;

[0040] (3) Add polypropylene, N,N-dimethylallylamine, and diisopropylbenzene peroxide to a high-speed mixer at a mass ratio of 100:3:0.6, mix at 1000 r / min for 5 min, and then place it in a screw extruder for extrusion granulation. Set the screw speed of the extruder during granulation to 95 r / min, and the screw temperatures are: 172 °C for the first section, 182 °C for the second section, 190 °C for the third section, and 186 °C for the fourth section to obtain pre-modified polypropylene; mix the pre-modified polypropylene and xylene evenly at a mass ratio of 1:24, stir at 80 °C and 120 r / min for 20 min, add 3-chloro-1-propanethiol 0.3 times the mass of the pre-modified polypropylene, continue to stir and react for 2 h, add deionized water with the same volume as xylene and mix evenly, let it stand for layering, take the organic phase and dry at 70 °C for 10 h under vacuum conditions to obtain modified polypropylene;

[0041] (4)Weigh 102 parts of modified polypropylene, 5 parts of modified phase change microcapsules, 7 parts of modified bamboo powder, 0.8 part of azobisisobutyronitrile, and 700 parts of dimethyl sulfoxide by mass fraction; mix the modified polypropylene, modified phase change microcapsules, modified bamboo powder, and dimethyl sulfoxide evenly, stir at 30 °C and 200 r / min for 50 min, let stand for 5 h, add azobisisobutyronitrile and mix evenly to prepare a spinning solution; add the spinning solution into a syringe, then install the syringe on an electrospinning instrument for electrospinning, set the pushing rate of the spinning solution to 0.52 mL / h, the spinning voltage to 18 kV, the receiving distance to 11 cm, the spinning temperature to 30 °C, and the air humidity to 50%, stack a fiber membrane with a thickness of 20 μm on the receiving plate, let stand at 78 °C for 35 min, and dry at 65 °C for 8 h under vacuum conditions to obtain a flame-retardant lithium battery separator.

[0042] Comparative Example 1

[0043] The difference between the preparation method of the flame-retardant lithium battery separator in Comparative Example 1 and that in Example 2 is that step (1) is not carried out, and step (4) is modified as follows: Weigh 100 parts of modified polypropylene, 6.5 parts of modified bamboo powder, 0.7 part of azobisisobutyronitrile, and 680 parts of dimethyl sulfoxide by mass fraction; mix the modified polypropylene, modified bamboo powder, and dimethyl sulfoxide evenly, stir at 20 °C and 150 r / min for 55 min, let stand for 4.5 h, add azobisisobutyronitrile and mix evenly to prepare a spinning solution; add the spinning solution into a syringe, then install the syringe on an electrospinning instrument for electrospinning, set the pushing rate of the spinning solution to 0.51 mL / h, the spinning voltage to 17 kV, the receiving distance to 10 cm, the spinning temperature to 25 °C, and the air humidity to 48%, stack a fiber membrane with a thickness of 19 μm on the receiving plate, let stand at 75 °C for 40 min, and dry at 60 °C for 9 h under vacuum conditions to obtain a flame-retardant lithium battery separator. The remaining steps are the same as those in Example 2.

[0044] Comparative Example 2

[0045] The preparation method of the flame-retardant lithium battery separator in Comparative Example 2 is different from that in Example 2 in that step (1) is not carried out, and step (4) is modified as follows: by mass, 100 parts of modified polypropylene, 4.5 parts of phase change microcapsules, 6.5 parts of modified bamboo powder, 0.7 part of azobisisobutyronitrile, and 680 parts of dimethyl sulfoxide are weighed; the modified polypropylene, phase change microcapsules, modified bamboo powder, and dimethyl sulfoxide are mixed evenly, stirred at 20 °C and 150 r / min for 55 min, allowed to stand for 4.5 h, azobisisobutyronitrile is added and mixed evenly to prepare a spinning solution; the spinning solution is added to a syringe, and then the syringe is installed on an electrospinning instrument for electrospinning. The spinning solution feeding rate is set to 0.51 mL / h, the spinning voltage is 17 kV, the receiving distance is 10 cm, the spinning temperature is 25 °C, and the air humidity is 48%. A fiber membrane with a thickness of 19 μm is stacked on the receiving plate, allowed to stand at 75 °C for 40 min, and dried at 60 °C for 9 h under vacuum conditions to obtain a flame-retardant lithium battery separator. The remaining steps are the same as those in Example 2.

[0046] Comparative Example 3

[0047] The preparation method of the flame-retardant lithium battery separator in Comparative Example 3 is different from that in Example 2 only in step (2). Step (2) is modified as follows: triethoxysilane chloride and absolute ethanol are mixed evenly at a mass ratio of 1:22, and the pH is adjusted to 6 with a 1.5 mol / L hydrochloric acid aqueous solution. Stir at 25 °C and 250 r / min for 20 min to prepare a silane hydrolysis solution; bamboo powder and absolute ethanol are mixed at a mass ratio of 1:35, ultrasonically dispersed for 35 min, 15 times the mass of the bamboo powder of the silane hydrolysis solution is added, and stirred and reacted at 70 °C and 250 r / min for 3.5 h, filtered, washed 4 times with absolute ethanol, and dried at 70 °C for 10 h under vacuum conditions to obtain pretreated bamboo powder; 1,7-dichloro-1,1,3,3,5,5,7,7-octamethyltetrasiloxane and N,N-dimethylacetamide are mixed evenly at a mass ratio of 1:7.5 to prepare a siloxane solution; the pretreated bamboo powder, phenolphthalein, triethylamine, and N,N-dimethylacetamide are mixed evenly at a mass ratio of 1:2.5:0.07:20. Under stirring conditions at 55 °C and 250 r / min, a siloxane solution 7.5 times the mass of the bamboo powder is added dropwise evenly within 30 min. After the addition is completed, continue to stir and react for 1.5 h, filter, wash 4 times with absolute ethanol and deionized water respectively, and dry at 70 °C for 10 h under vacuum conditions to obtain modified bamboo powder. The remaining steps are the same as those in Example 2.

[0048] Comparative Example 4

[0049] The preparation method of the flame-retardant lithium battery separator of Comparative Example 4 is different from that of Example 2 in that step (2) is not carried out, and step (4) is modified as follows: by mass, 100 parts of modified polypropylene, 4.5 parts of modified phase change microcapsules, 6.5 parts of bamboo powder, 0.7 part of azodiisobutyronitrile, and 680 parts of dimethyl sulfoxide are weighed; the modified polypropylene, modified phase change microcapsules, bamboo powder, and dimethyl sulfoxide are mixed evenly, stirred at 20 °C and 150 r / min for 55 min, left standing for 4.5 h, azodiisobutyronitrile is added and mixed evenly to prepare a spinning solution; the spinning solution is added to a syringe, and then the syringe is installed on an electrospinning instrument for electrospinning. The pushing rate of the spinning solution is set to 0.51 mL / h, the spinning voltage is 17 kV, the receiving distance is 10 cm, the spinning temperature is 25 °C, the air humidity is 48%, a fiber membrane with a thickness of 19 μm is stacked on the receiving plate, left standing at 75 °C for 40 min, and dried at 60 °C for 9 h under vacuum conditions to obtain a flame-retardant lithium battery separator. The remaining steps are the same as those in Example 2.

[0050] Comparative Example 5

[0051] The preparation method of the flame-retardant lithium battery separator of Comparative Example 5 is different from that of Example 2 in that step (3) is not carried out, and step (4) is modified as follows: by mass, 100 parts of polypropylene, 4.5 parts of modified phase change microcapsules, 6.5 parts of modified bamboo powder, 0.7 part of azodiisobutyronitrile, and 680 parts of dimethyl sulfoxide are weighed; the polypropylene, modified phase change microcapsules, modified bamboo powder, and dimethyl sulfoxide are mixed evenly, stirred at 20 °C and 150 r / min for 55 min, left standing for 4.5 h, azodiisobutyronitrile is added and mixed evenly to prepare a spinning solution; the spinning solution is added to a syringe, and then the syringe is installed on an electrospinning instrument for electrospinning. The pushing rate of the spinning solution is set to 0.51 mL / h, the spinning voltage is 17 kV, the receiving distance is 10 cm, the spinning temperature is 25 °C, the air humidity is 48%, a fiber membrane with a thickness of 19 μm is stacked on the receiving plate, left standing at 75 °C for 40 min, and dried at 60 °C for 9 h to obtain a flame-retardant lithium battery separator.

[0052] Test Example 1

[0053] Test of flame retardancy

[0054] Test method: According to GB / T2406-93, the examples and comparative examples are prepared into standard specimens, and the limiting oxygen index of the standard specimens is tested. The results are shown in Table 1.

[0055] Table 1

[0056]

[0057] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 5 in Table 1, it can be found that the flame-retardant lithium battery separator prepared by the present invention has good flame-retardant performance.

[0058] By comparison, the limiting oxygen index of Examples 1 to 3 is greater than that of Comparative Examples 1 to 2, indicating that the P-Cl bond on hexachlorocyclotriphosphazene reacts with the hydroxyl group on daidzein to polymerize hexachlorocyclotriphosphazene and daidzein and coat the surface of the phase change microcapsule to obtain modified phase change microcapsules; introducing cyclotriphosphazene and daidzein on the surface of the modified phase change microcapsules; the introduction of cyclotriphosphazene can improve the flame-retardant performance of the flame-retardant lithium battery separator, and the deoxybenzoin structure in daidzein can increase the char formation rate during polymer combustion, reduce the heat release amount and reduce the release amount of volatile combustibles, further improving the flame-retardant performance of the flame-retardant lithium battery separator.

[0059] By comparison, the limiting oxygen index of Examples 1 to 3 is greater than that of Comparative Example 4, indicating that bamboo powder and triethoxysilane chloride are reacted to obtain pretreated bamboo powder, and Si-Cl bonds are introduced on the surface of the pretreated bamboo powder; the Si-Cl bond on 1,7-dichloro-1,1,3,3,5,5,7,7-octamethyltetrasiloxane reacts with the hydroxyl group on phenolphthalein and polymerizes and grows on the pretreated bamboo powder to obtain pre-modified bamboo powder, and siloxane chains are introduced on the modified bamboo powder; the introduction of siloxane chains can further improve the flame-retardant performance of the flame-retardant lithium battery separator.

[0060] Test Example 2

[0061] Test of thermal stability

[0062] Test method: Cut the examples and comparative examples into circular specimens with a diameter of 1.9 cm, place them in a vacuum drying oven and treat them at 100 °C, 120 °C, and 140 °C for 0.5 h in turn, measure the diameter of the specimens after heat treatment, and calculate the thermal shrinkage rate of the specimens before and after heat treatment according to the diameters of the specimens before and after heat treatment. The thermal shrinkage rate = (area of the specimen before treatment - area of the specimen after treatment) / area of the specimen before treatment × 100%. The results are shown in Table 2.

[0063] Table 2

[0064]

[0065] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 5 in Table 2, it can be found that the flame-retardant lithium battery separator prepared by the present invention has good thermal stability.

[0066] By comparison, the thermal shrinkage rates of Examples 1 to 3 are less than that of Comparative Example 1, indicating that during the use of lithium batteries, overheating is likely to occur inside the lithium batteries due to charging and discharging. After the separator is heated, it is prone to shrinkage or even rupture, resulting in direct contact between the positive and negative electrodes inside the power supply and short circuit, thus triggering potential safety hazards of the battery; adding phase change microcapsules to the battery separator, the phase change microcapsules are a kind of intelligent material, which can intelligently adjust the temperature of the flame-retardant lithium battery separator. When the ambient temperature rises, it can effectively absorb heat, improve the thermal stability of the battery separator, and thus enhance the safety of lithium-ion batteries.

[0067] Test Example 3

[0068] Measurement of ionic conductivity

[0069] Test method: The ionic conductivities of the examples and comparative examples were measured by the alternating current impedance method. The separator was cut into circular specimens with a diameter of 18 mm, and stainless steel was used instead of the positive and negative electrode plates to assemble a blocking battery (stainless steel sheet / separator / stainless steel sheet). The bulk impedance was measured using an electrochemical workstation, the test frequency was 1×10 6 Hz - 1 Hz, the voltage was 10 mV, and the ionic conductivity was calculated according to the formula. Ionic conductivity = separator thickness / (bulk resistance × effective contact area) × 100%. The results are shown in Table 3.

[0070] Table 3

[0071]

[0072] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 5 in Table 3, it can be found that the flame-retardant lithium battery separator prepared by the present invention has good ionic conductivity.

[0073] By comparison, the ionic conductivities of Examples 1 to 3 are greater than those of Comparative Examples 3 to 4, indicating that bamboo powder and triethoxysilane chloride are reacted to obtain pretreated bamboo powder, and Si-Cl bonds are introduced on the surface of the pretreated bamboo powder; the Si-Cl bonds on 1,7-dichloro-1,1,3,3,5,5,7,7-octamethyltetrasiloxane react with the hydroxyl groups on phenolphthalein, and polymerization growth occurs on the pretreated bamboo powder to obtain pre-modified bamboo powder, and phenolphthalein is introduced on the modified bamboo powder; the phenolphthalein on the pre-modified bamboo powder is alkali-treated with sodium hydroxide to cause the ring-opening reaction of the lactone structure in phenolphthalein, generating hydroxyl groups and carboxyl groups, introducing more polar groups, improving the affinity between the flame-retardant lithium battery separator and the electrolyte, and making the wettability of the electrolyte better, thus improving the ionic conductivity of the flame-retardant lithium battery separator.

[0074] By comparison, the ionic conductivities of Examples 1 to 3 are greater than that of Comparative Example 5, indicating that N,N-dimethylallylamine is grafted onto the side chain of polypropylene molecules by melt grafting to obtain pre-modified polypropylene. A tertiary amine structure is introduced onto the side chain of the pre-modified polypropylene molecules, and the chlorine atom on 3-chloro-1-propanethiol reacts with the tertiary amine structure introduced onto the side chain of the pre-modified polypropylene molecules to obtain modified polypropylene, and a quaternary ammonium salt structure is generated on the side chain of the modified polypropylene molecules. The introduction of the quaternary ammonium salt structure helps to improve the ionic conductivity of the flame-retardant lithium battery separator.

[0075] Test Example 4

[0076] Testing of mechanical properties

[0077] Test method: The tensile strength of the examples and comparative examples was detected using an electronic universal testing machine. It was carried out according to the provisions of GB / T 1040.3-2006. Type 2 specimens with a width of 15 mm were used, the sample length was 130 mm, the initial distance between the clamps was 100 mm, and the test speed was 250 mm / min. The results are shown in Table 4.

[0078] Table 4

[0079]

[0080] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 5 in Table 4, it can be found that the flame-retardant lithium battery separator prepared by the present invention has good mechanical properties.

[0081] By comparison, the tensile strength of Examples 1 to 3 is greater than that of Comparative Examples 1 to 2, indicating that the P-Cl bond on hexachlorocyclotriphosphazene reacts with the hydroxyl group on daidzein to polymerize hexachlorocyclotriphosphazene and daidzein and coat the surface of the phase change microcapsules to obtain modified phase change microcapsules; daidzein is introduced onto the surface of the modified phase change microcapsules; the carbon-carbon double bond in daidzein can react with the mercapto group introduced onto the side chain of the modified polypropylene molecules under the catalysis of azobisisobutyronitrile to form a cross-linked network structure, inhibiting the relative movement of the polypropylene molecular chains and improving the mechanical properties of the flame-retardant lithium battery separator.

[0082] By comparison, the tensile strengths of Examples 1 to 3 are greater than those of Comparative Examples 3 to 4, indicating that pretreated bamboo powder is prepared by reacting bamboo powder with triethoxysilane chloride to introduce Si-Cl bonds on the surface of the pretreated bamboo powder; the Si-Cl bond on 1,7-dichloro-1,1,3,3,5,5,7,7-octamethyltetrasiloxane reacts with the hydroxyl group on phenolphthalein and polymerizes and grows on the pretreated bamboo powder to obtain pre-modified bamboo powder, and phenolphthalein is introduced onto the modified bamboo powder; the phenolphthalein on the pre-modified bamboo powder is treated with sodium hydroxide to cause the lactone structure in phenolphthalein to undergo a ring-opening reaction to generate hydroxyl and carboxyl groups. The carboxyl groups generated on the modified bamboo powder can combine with the quaternary ammonium salts generated on the side chains of polypropylene molecules through positive and negative charges to form a crosslinked network structure, further improving the mechanical properties of the flame-retardant lithium battery separator.

[0083] By comparison, the tensile strength of Examples 1 to 3 is greater than that of Comparative Example 5, indicating that N,N-dimethylallylamine is grafted onto the side chain of a polypropylene molecule by a melt grafting method to obtain pre-modified polypropylene, and a tertiary amine structure is introduced onto the side chain of the pre-modified polypropylene molecule. The tertiary amine structure introduced onto the side chain of the pre-modified polypropylene molecule reacts with the chlorine atom on 3-chloro-1-propanethiol to obtain modified polypropylene, and a quaternary ammonium salt structure is generated on the side chain of the modified polypropylene molecule, and a mercapto group is introduced at the same time; the quaternary ammonium salt structure can form positive and negative charge structures with the carboxyl groups on the modified bamboo powder to enhance the mechanical properties; the mercapto group introduced onto the side chain of the modified polypropylene molecule can react with the carbon-carbon double bond on the modified phase change microcapsule to form a crosslinked network structure, improving the mechanical properties of the flame-retardant lithium battery separator.

[0084] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be embraced within the present invention. Any reference signs in the claims should not be construed as limiting the claimed claim.

Claims

1. A flame-retardant lithium battery separator, characterized in that, The flame-retardant lithium battery separator is prepared by reacting pre-modified bamboo powder with sodium hydroxide to obtain modified bamboo powder; reacting pre-modified polypropylene with 3-chloro-1-propanethiol to obtain modified polypropylene; formulating a spinning solution with modified polypropylene, modified phase change microcapsules, modified bamboo powder, and azobisisobutyronitrile, and electrospinning to obtain it; The pre-modified bamboo powder is prepared by polymerizing and growing 1,7-dichloro-1,1,3,3,5,5,7,7-octamethyltetrasiloxane and phenolphthalein on pretreated bamboo powder; The pretreated bamboo powder is prepared by reacting bamboo powder with triethoxysilane chloride; The pre-modified polypropylene is prepared by reacting polypropylene with N,N-dimethylallylamine; The modified phase change microcapsules are prepared by polymerizing and coating hexachlorocyclotriphosphazene and daidzein on the surface of phase change microcapsules; 2. A preparation method of a flame-retardant lithium battery separator, characterized in that, The preparation method of the flame-retardant lithium battery separator includes the following preparation steps: (1) Mix phase change microcapsules, triethylamine, and acetonitrile in a mass ratio of 1:(0.2~0.3):(20~22) evenly, ultrasonically disperse for 30~40 min, under the stirring condition of 45~55 °C and 200~300 r / min, dropwise add the reaction solution 6~8 times the mass of the phase change microcapsules within 15 min at a uniform speed. After the dropping is completed, continue to stir and react for 6~8 h, filter, wash 3~5 times with anhydrous ethanol and deionized water respectively, and dry at 60~70 °C for 9~11 h under vacuum conditions to obtain modified phase change microcapsules; (2) Mix pre-modified bamboo powder and a 0.5 mol / L sodium hydroxide aqueous solution in a mass ratio of 1:(40~50) evenly, ultrasonically treat at 70~80 °C for 1~2 h, filter, wash 3~5 times with a 0.5 mol / L hydrochloric acid aqueous solution, and then wash with deionized water until the filtrate is neutral. Dry at 65~75 °C for 9~11 h under vacuum conditions to obtain modified bamboo powder; (3) Mix pre-modified polypropylene and xylene in a mass ratio of 1:(20~24) evenly, stir at 70~80 °C and 100~120 r / min for 20~30 min, add 3-chloro-1-propanethiol 0.2~0.3 times the mass of pre-modified polypropylene, continue to stir and react for 2~3 h, add deionized water with the same volume as xylene and mix evenly, let it stand for stratification, take the organic phase and dry at 60~70 °C for 10~12 h under vacuum conditions to obtain modified polypropylene; (4)Weigh 98 - 102 parts by mass of modified polypropylene, 4 - 5 parts of modified phase change microcapsules, 6 - 7 parts of modified bamboo powder, 0.6 - 0.8 parts of azobisisobutyronitrile, and 660 - 700 parts of dimethyl sulfoxide; mix the modified polypropylene, modified phase change microcapsules, modified bamboo powder, and dimethyl sulfoxide evenly, stir at 10 - 30 °C and 100 - 200 r / min for 50 - 60 min, let it stand for 4 - 5 h, add azobisisobutyronitrile and mix evenly to prepare a spinning solution; add the spinning solution into a syringe, then install the syringe on an electrospinning instrument for electrospinning, and stack a fiber membrane with a thickness of 18 - 20 μm on the receiving plate, let it stand at 72 - 78 °C for 35 - 45 min, and dry it at 55 - 65 °C for 8 - 10 h under vacuum conditions to obtain a flame-retardant lithium battery separator.

3. The preparation method of a flame-retardant lithium battery separator according to claim 2, characterized in that, The preparation method of the reaction solution to be used in step (1) is as follows: Add hexachlorocyclotriphosphazene and daidzein in a molar ratio of 1:(3 - 4) into acetonitrile which is 10 - 12 times the mass of hexachlorocyclotriphosphazene to prepare a reaction solution to be used.

4. The preparation method of a flame-retardant lithium battery separator according to claim 2, characterized in that, The model of the phase change microcapsules in step (1) is PCM 37.

5. The preparation method of a flame-retardant lithium battery separator according to claim 2, wherein, The preparation method of the pre-modified bamboo powder in step (2) is as follows: Mix 1,7 - dichloro - 1,1,3,3,5,5,7,7 - octamethyltetrasiloxane and N,N - dimethylacetamide evenly according to a mass ratio of 1:(7 - 8) to prepare a siloxane solution; mix the pretreated bamboo powder, phenolphthalein, triethylamine, and N,N - dimethylacetamide evenly according to a mass ratio of 1:(2 - 3):(0.06 - 0.08):(18 - 22), and under the stirring condition of 50 - 60 °C and 200 - 300 r / min, uniformly dropwise add the siloxane solution which is 7 - 8 times the mass of the bamboo powder within 30 min. After the dropping is completed, continue to stir and react for 1 - 2 h, filter, wash with anhydrous ethanol and deionized water 3 - 5 times each, and dry at 65 - 75 °C for 9 - 11 h under vacuum conditions to obtain the pre-modified bamboo powder.

6. The preparation method of a flame-retardant lithium battery separator according to claim 5, characterized in that, The preparation method of the pretreated bamboo powder is as follows: Mix triethoxysilane and anhydrous ethanol evenly according to a mass ratio of 1:(20 - 24), adjust the pH to 5.8 - 6.2 with a 1.5 mol / L hydrochloric acid aqueous solution, stir at 15 - 35 °C and 200 - 300 r / min for 18 - 22 min to prepare a silane hydrolysis solution; mix the bamboo powder and anhydrous ethanol according to a mass ratio of 1:(30 - 40), ultrasonically disperse for 30 - 40 min, add the silane hydrolysis solution which is 14 - 16 times the mass of the bamboo powder, stir and react at 65 - 75 °C and 200 - 300 r / min for 3 - 4 h, filter, wash with anhydrous ethanol 3 - 5 times, and dry at 65 - 75 °C for 9 - 11 h under vacuum conditions to obtain the pretreated bamboo powder.

7. The preparation method of a flame-retardant lithium battery separator according to claim 6, wherein The particle size of the bamboo powder is 300 mesh.

8. The preparation method of a flame-retardant lithium battery separator according to claim 2, wherein, The preparation method of the pre-modified polypropylene described in step (3) is as follows: Add polypropylene, N,N-dimethylallylamine, and dicumyl peroxide into a high-speed mixer according to a mass ratio of 100:(2-3):(0.4-0.6), mix at 800-1000 r / min for 5-7 min, and then place it in a screw extruder for extrusion granulation. Set the screw speed of the extruder during granulation to 85-95 r / min, and the screw temperatures are: the first stage is 170-172 °C, the second stage is 180-182 °C, the third stage is 188-190 °C, and the fourth stage is 184-186 °C to obtain the pre-modified polypropylene.

9. The preparation method of a flame-retardant lithium battery separator according to claim 8, wherein, The molecular weight of the polypropylene is 100,000.

10. The preparation method of a flame-retardant lithium battery separator according to claim 2, characterized in that, The process parameters of the electrospinning described in step (4) are: set the pushing rate of the spinning solution to 0.50-0.52 mL / h, the spinning voltage to 16-18 kV, the receiving distance to 9-11 cm, the spinning temperature to 20-30 °C, and the air humidity to 46%-50%.

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