Cellulose-based lithium battery separator and method of making the same

Abstract

The application discloses a cellulose-based lithium battery diaphragm and a preparation method thereof, and relates to the technical field of battery diaphragms. In the preparation of the cellulose-based lithium battery diaphragm, polyaryletherketone is sulfonated with concentrated sulfuric acid to obtain modified polyaryletherketone; 6-chloro-1-hexene is grafted on cellulose to obtain modified cellulose; the modified cellulose and the modified polyaryletherketone are mixed to be electrospun and photopolymerized to obtain a pre-modified cellulose film; nonafluorohexyltrimethoxysilane is hydrolyzed and grafted to the surface of the pre-modified cellulose to obtain a modified cellulose film; lithium fluoride nanoparticles are prepared by reacting lithium hydroxide monohydrate and ammonium fluoride, and then the lithium fluoride nanoparticles are impregnated and coated on the surface of the modified cellulose film to obtain the cellulose-based lithium battery diaphragm. The cellulose-based lithium battery diaphragm prepared by the application has excellent swelling resistance, thermal stability and electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of battery separator technology, specifically to a cellulose-based lithium battery separator and its preparation method. Background Technology

[0002] Battery separators are a core component of electrochemical energy storage devices, responsible for isolating the positive and negative electrodes to prevent short circuits and constructing ion transport channels. Their performance directly determines the battery's safety, cycle life, and rate capability. Currently, commercially available separators are mainly made of petroleum-based materials such as polyolefins and ceramic coatings. Although they have mature manufacturing processes, they suffer from inherent defects such as poor environmental friendliness, high resource dependence, and insufficient interfacial stability in aqueous batteries, making it difficult to meet the dual demands of sustainability and high performance for next-generation batteries.

[0003] Cellulose, as the most abundant renewable biopolymer in nature, has unique advantages such as low cost, environmental friendliness, excellent mechanical flexibility, good chemical stability, and surface rich in active hydroxyl groups that can be functionalized. It has become a research hotspot for green alternative materials for battery separators and has shown broad application potential in lithium-ion battery systems. Summary of the Invention

[0004] The purpose of this invention is to provide a cellulose-based lithium battery separator and its preparation method, so as to solve the problems existing in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following solution: A cellulose-based lithium battery separator is prepared by sulfonating polyaryletherketone with concentrated sulfuric acid to obtain modified polyaryletherketone; grafting 6-chloro-1-hexene onto cellulose to obtain modified cellulose; mixing modified cellulose and modified polyaryletherketone and electrospinning-photopolymerizing to obtain a pre-modified cellulose membrane; hydrolyzing nonafluorohexyltrimethoxysilane and grafting it onto the surface of the pre-modified cellulose to obtain a modified cellulose membrane; and reacting lithium hydroxide monohydrate and ammonium fluoride to obtain lithium fluoride nanoparticles, which are then impregnated and coated onto the surface of the modified cellulose membrane. The polyaryletherketone is prepared by polymerizing 2,5-dihydroxybiphenyl, diallyl bisphenol A, and 4,4'-difluorobenzophenone.

[0006] A method for preparing a cellulose-based lithium battery separator, the method comprising the following preparation steps: (1) Mix polyarylether ketone and 98 wt% concentrated sulfuric acid at a mass ratio of 1:(28~32), stir and react at room temperature for 12~14h, add 8~10 times the volume of deionized water of 98 wt% concentrated sulfuric acid, let stand for 1~2h, filter, wash with deionized water until the pH of the washing water is 6~7, and vacuum dry at 75~85℃ for 22~24h to obtain modified polyarylether ketone; (2) Premodified cellulose, modified polyarylether ketone, photoinitiator, N,N-dimethylformamide, and anhydrous ethanol are mixed evenly in a mass ratio of 1:(2~2.6):(0.02~0.04):(12~14):(2.8~3.2), stirred and reacted at room temperature for 12~14h, the viscosity was adjusted to 1000~1500mPa·s with ethanol, vacuum degassing was performed at room temperature for 20~30min, the film was loaded into an electrospinning machine for electrospinning, the film was peeled off, vacuum dried at 40~50℃ for 2~3h, irradiated under a 365nm ultraviolet lamp for 4~6min under nitrogen protection, and vacuum dried at 65~75℃ for 12~14h to obtain a premodified cellulose membrane; (3) Weigh the pre-modified cellulose membrane and nonafluorohexyltrimethoxysilane at a mass ratio of 1:(0.1~0.3); hydrolyze the nonafluorohexyltrimethoxysilane to obtain a silane hydrolysate; immerse the pre-modified cellulose membrane in the silane hydrolysate, stir and react at room temperature for 5~7h, wash with anhydrous ethanol 2~4 times, and vacuum dry at 70~80℃ for 10~12h to obtain the modified cellulose membrane; (4) Mix deionized water, anhydrous ethanol, polyoxyethylene lauryl ether, and water-based adhesive in a mass ratio of 1:(0.9~1.1):(0.2~0.3):(0.3~0.4) until homogeneous. Stir and react at room temperature for 40~60 min. Add lithium fluoride nanoparticles at a mass ratio of 0.3~0.4 times that of deionized water and continue stirring for 50~70 min to obtain a coating slurry. Immerse the modified cellulose membrane in the coating slurry, let it stand for 20~40 s, pull it out at a speed of 1 cm / s, let it stand at room temperature for 10~12 h, and vacuum dry it at 35~45℃ for 4~5 h to obtain a cellulose-based lithium battery separator.

[0007] As an optimization, the preparation steps of the polyarylether ketone in step (1) are as follows: 2,5-dihydroxybiphenyl, diallyl bisphenol A, 4,4'-difluorobenzophenone, and anhydrous potassium carbonate are mixed evenly with sulfolane at a molar ratio of 1:(0.5~1.5):(1.5~2.5):(1.6~2.6) and sulfolane at 8~10 times the mass of 2,5-dihydroxybiphenyl and toluene at 4~5 times the mass of 2,5-dihydroxybiphenyl. Under nitrogen protection, the mixture is heated to 120~140℃ and refluxed with stirring for 2.5~3.5h. The mixture is then heated to 190~210℃ and stirred for another 5~6h. 20~30 times the volume of toluene in deionized water is added, the mixture is filtered, pulverized, washed 2~4 times with deionized water and ethanol respectively, and dried under vacuum at 100~110℃ for 23~25h to obtain polyarylether ketone.

[0008] As an optimization, the preparation steps of the pre-modified cellulose in step (2) are as follows: cellulose, 6-chloro-1-hexene, and triethylamine are weighed at a mass ratio of 1:(0.65~0.75):(0.75~0.85); 6-chloro-1-hexene and N,N-dimethylacetamide are mixed evenly at a mass ratio of 1:(7~9), and ultrasonicated at room temperature for 10~20 min to obtain a 6-chloro-1-hexene solution; cellulose and N,N-dimethylacetamide are mixed at a mass ratio of 1:(8~1) 0) Mix thoroughly and stir at room temperature for 2-3 hours. Add triethylamine and continue stirring for 20-40 minutes. Under nitrogen protection, add 6-chloro-1-hexene solution at -6 to -4°C over 30-40 minutes at a uniform rate, stirring for 20-30 minutes. Raise the temperature to room temperature and stir for 23-25 ​​hours. Pour the solution into deionized water to precipitate, filter, and wash 2-4 times with deionized water and anhydrous ethanol, respectively. Dry under vacuum at 55-65°C for 22-24 hours to obtain pre-modified cellulose. As an optimization, the cellulose was 30 nm × 2 μm in size and was purchased from Wuhan Huaxiang Kejie Biotechnology Co., Ltd.

[0009] As an optimization, the photoinitiator in step (2) is photoinitiator 1173, purchased from Nanjing Milan Chemical Co., Ltd.

[0010] As an optimization, the electrospinning process parameters in step (2) are: spinning voltage 16~18kv, pushing rate 2~4μL / min, receiving distance 14~16cm, and film thickness controlled at 20~30μm.

[0011] As an optimization, the hydrolysis of nonafluorohexyltrimethoxysilane in step (3) is as follows: mix nonafluorohexyltrimethoxysilane and anhydrous ethanol at a mass ratio of 1:(14~16), adjust the pH to 4~5 with acetic acid, stir at room temperature for 10~20 min, add 8~10 times the mass of deionized water of nonafluorohexyltrimethoxysilane, and continue stirring for 30~40 min to obtain silane hydrolysate.

[0012] As an optimization, the preparation steps of the lithium fluoride nanoparticles in step (4) are as follows: Lithium hydroxide monohydrate and ammonium fluoride with a molar ratio of 1:(1.05~1.15) are mixed evenly and added to anhydrous ethanol at 25~35 times the mass of lithium hydroxide monohydrate. The mixture is stirred at room temperature for 2.5~3.5h, centrifuged, and the precipitate is washed 2~4 times with anhydrous ethanol. The precipitate is then vacuum dried at 55~65℃ for 9~11h, placed in a muffle furnace and dried at 90~110℃ for 9~11h, and heated to 280~320℃ at a rate of 4~6℃ / min and calcined for 5~7h to obtain lithium fluoride nanoparticles.

[0013] As an optimization, the water-based adhesive used in step (4) is model TOB-LA133, purchased from Shenzhen Liyou New Energy Technology Co., Ltd.

[0014] Compared with the prior art, the beneficial effects achieved by the present invention are: First, polyaryletherketone (POG) is prepared by polymerizing 2,5-dihydroxybiphenyl, diallyl bisphenol A, and 4,4'-difluorobenzophenone. The PPG is then sulfonated with concentrated sulfuric acid to obtain modified PPG, and sulfonic acid groups are introduced onto the PPG. 6-chloro-1-hexene is grafted onto cellulose to obtain modified cellulose, and carbon-carbon double bonds capable of polymerizing with the modified PPG are introduced onto the cellulose. The modified cellulose and modified PPG are then mixed and electrospun-photopolymerized to obtain a pre-modified cellulose membrane. The sulfonic acid groups dissociate into -SO3 in the electrolyte. - Its negative charge sites can interact with Li + The formation of dynamic ion pairs enables rapid lithium-ion transport through site hopping, thereby enhancing the ion conductivity of the cellulose-based lithium battery separator. Simultaneously, polyaryletherketone (PAK) possesses high thermal stability and excellent mechanical properties, providing rigid support for the cellulose membrane to withstand high temperatures and electrolyte corrosion, thus ensuring good thermal stability. Through electrospinning, PAK and nanocellulose form a dense three-dimensional network structure, effectively dispersing absorbed moisture uniformly within the membrane. Strong intermolecular hydrogen bonding effectively controls membrane swelling, resulting in good dimensional stability and thus endowing the cellulose-based lithium battery separator with excellent swelling resistance.

[0015] Secondly, nonafluorohexyltrimethoxysilane is hydrolyzed and grafted onto the surface of pre-modified cellulose to obtain a modified cellulose membrane. The Si-OC covalent bond has high stability and will not be degraded by the electrolyte. The fluorine-containing long chain has low bond polarity and low surface energy, which can form a directional hydrophobic layer on the membrane surface, reducing the adsorption of moisture in the air by the separator and reducing the interaction between electrolyte molecules and the membrane surface, thereby further improving the swelling resistance of the cellulose-based lithium battery separator. At the same time, the fluorine group has strong chemical inertness and low reactivity with lithium dendrites, which can reduce the adhesion of "dead lithium" between dendrites and the separator and improve the cycle life of the battery.

[0016] Finally, lithium hydroxide monohydrate and ammonium fluoride were reacted to prepare lithium fluoride nanoparticles, which were then impregnated and coated onto the surface of a modified cellulose membrane to obtain a cellulose-based lithium battery separator. The LiF coating improved the separator's hydrophilicity and electrolyte absorption. The LiF-coated modified separator reduced electrolyte consumption during SEI membrane formation, and the improved hydrophilicity and electrolyte absorption also enhanced the LiF... +The cellulose nanoparticles migrate more easily and quickly inside the battery, resulting in a higher initial capacity. At the same time, as artificial SEI film nucleation sites, LiF nanoparticles preferentially combine with electrolyte reduction products during the first charge and discharge of the battery, inducing the formation of a denser SEI layer structure on the lithium anode surface. This inhibits the short circuit problem caused by lithium dendrite growth piercing the separator, extends the battery cycle life, prevents further reaction between the electrolyte and electrode materials, and reduces the consumption of electrolyte and electrode materials, thus endowing the cellulose-based lithium battery separator with excellent electrochemical performance. Attached Figure Description

[0017] Figure 1 The cycling performance of the cellulose-based lithium battery separators in Examples 1-3 and Comparative Examples 1-3 is shown. Detailed Implementation

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

[0019] Example 1: A method for preparing a cellulose-based lithium battery separator, the method comprising the following steps: (1) 2,5-Dihydroxybiphenyl, diallyl bisphenol A, 4,4'-difluorobenzophenone, and anhydrous potassium carbonate were mixed evenly with sulfolane (8 times the mass of 2,5-dihydroxybiphenyl) and toluene (4 times the mass of 2,5-dihydroxybiphenyl) in a molar ratio of 1:0.5:1.5:1.6. Under nitrogen protection, the mixture was heated to 120°C, refluxed, and stirred for 3.5 h. The mixture was then heated to 190°C and stirred for another 6 h. 20 times the volume of toluene was added to the mixture, which was then filtered, pulverized, washed twice with deionized water and ethanol, and dried under vacuum at 100°C for 25 h to obtain polyaryletherketone. Polyaryletherketone and 98 wt% concentrated sulfuric acid were mixed evenly in a mass ratio of 1:28 and stirred for 14 h at room temperature. 98 wt% concentrated sulfuric acid was added to the mixture. The modified polyarylether ketone was prepared by standing for 2 hours with 8 times the volume of concentrated sulfuric acid (wt%) in deionized water, filtering, washing with deionized water until the pH of the washing water was 6, and then vacuum drying at 75°C for 24 hours. (2) Weigh cellulose, 6-chloro-1-hexene, and triethylamine in a mass ratio of 1:0.65:0.75; mix 6-chloro-1-hexene and N,N-dimethylacetamide in a mass ratio of 1:7, and sonicate at room temperature for 20 min to prepare a 6-chloro-1-hexene solution; mix cellulose and N,N-dimethylacetamide in a mass ratio of 1:8, stir at room temperature for 3 h, add triethylamine, continue stirring for 40 min, and under nitrogen protection, add the 6-chloro-1-hexene solution at -6℃ over 40 min at a uniform rate, stir for 30 min, raise the temperature to room temperature, stir and react for 25 h, pour into deionized water to precipitate, filter, wash twice with deionized water and anhydrous ethanol respectively, and then at 5 Pre-modified cellulose was obtained by vacuum drying at 5℃ for 24 h. The pre-modified cellulose, modified polyaryletherketone, photoinitiator, N,N-dimethylformamide, and anhydrous ethanol were mixed evenly at a mass ratio of 1:2:0.02:12:2.8 and stirred at room temperature for 14 h. The viscosity was adjusted to 1000 mPa·s with ethanol and degassed under vacuum at room temperature for 30 min. The mixture was then loaded into an electrospinning machine for spinning at a spinning voltage of 16 kV, a push rate of 2 μL / min, a receiving distance of 14 cm, and a film thickness of 20 μm. The film was then peeled off, vacuum dried at 40℃ for 3 h, irradiated under a 365 nm UV lamp for 6 min under nitrogen protection, and vacuum dried at 65℃ for 14 h to obtain the pre-modified cellulose membrane. (3) Weigh the pre-modified cellulose membrane and nonafluorohexyltrimethoxysilane at a mass ratio of 1:0.1; mix the nonafluorohexyltrimethoxysilane and anhydrous ethanol at a mass ratio of 1:14, adjust the pH to 4 with acetic acid, stir at room temperature for 20 min, add deionized water at a mass ratio of 8 times that of nonafluorohexyltrimethoxysilane, and continue stirring for 40 min to obtain silane hydrolysate; immerse the pre-modified cellulose membrane in silane hydrolysate, stir at room temperature for 7 h, wash twice with anhydrous ethanol, and vacuum dry at 70 °C for 12 h to obtain modified cellulose membrane; (4) Lithium hydroxide monohydrate and ammonium fluoride with a molar ratio of 1:1.05 were mixed evenly and added to anhydrous ethanol at a mass of 25 times that of lithium hydroxide monohydrate. The mixture was stirred at room temperature for 3.5 h, centrifuged, and the precipitate was washed twice with anhydrous ethanol. The precipitate was then vacuum dried at 55 °C for 11 h, placed in a muffle furnace and dried at 90 °C for 11 h. The temperature was then increased to 280 °C at a rate of 4 °C / min and calcined for 7 h to obtain lithium fluoride nanoparticles. Deionized water, anhydrous ethanol, polyoxyethylene lauryl ether, and aqueous binder were mixed evenly at a mass ratio of 1:0.9:0.2:0.3. The mixture was stirred and reacted at room temperature for 60 min. Lithium fluoride nanoparticles at a mass of 0.3 times that of deionized water were added and stirred for another 70 min to obtain a coating slurry. The modified cellulose membrane was immersed in the coating slurry, allowed to stand for 40 s, and then pulled out at a speed of 1 cm / s. The membrane was allowed to stand at room temperature for 12 h and then vacuum dried at 35 °C for 5 h to obtain a cellulose-based lithium battery separator.

[0020] Example 2: A method for preparing a cellulose-based lithium battery separator, the method comprising the following steps: (1) 2,5-Dihydroxybiphenyl, diallyl bisphenol A, 4,4'-difluorobenzophenone, and anhydrous potassium carbonate were mixed evenly with sulfolane (9 times the mass of 2,5-dihydroxybiphenyl) and toluene (4.5 times the mass of 2,5-dihydroxybiphenyl) in a molar ratio of 1:1:2:2.1. Under nitrogen protection, the mixture was heated to 130°C, refluxed and stirred for 3 hours, then heated to 200°C and stirred for another 5.5 hours. 25 times the volume of toluene was added to the mixture, which was then filtered, pulverized, washed three times with deionized water and ethanol respectively, and dried under vacuum at 120°C for 24 hours to obtain polyaryletherketone. Polyaryletherketone and 98 wt% concentrated sulfuric acid were mixed evenly in a mass ratio of 1:30 and stirred at room temperature for 13 hours. 98 wt% concentrated sulfuric acid was then added to the mixture. The modified polyarylether ketone was prepared by standing for 1.5 hours with 9 times the volume of concentrated sulfuric acid (wt%) in deionized water, filtering, washing with deionized water until the pH of the washing water was 6.5, and then drying under vacuum at 80°C for 23 hours. (2) Weigh cellulose, 6-chloro-1-hexene, and triethylamine in a mass ratio of 1:0.7:0.8; mix 6-chloro-1-hexene and N,N-dimethylacetamide in a mass ratio of 1:8, and sonicate at room temperature for 15 min to prepare a 6-chloro-1-hexene solution; mix cellulose and N,N-dimethylacetamide in a mass ratio of 1:9, stir at room temperature for 2.5 h, add triethylamine, continue stirring for 30 min, and under nitrogen protection, add the 6-chloro-1-hexene solution at -5℃ over 35 min at a uniform rate, stir for 25 min, raise the temperature to room temperature, stir and react for 24 h, pour into deionized water to precipitate, filter, wash three times with deionized water and anhydrous ethanol respectively, and then at 60℃. Pre-modified cellulose was obtained by vacuum drying at ℃ for 23 h. The pre-modified cellulose, modified polyaryletherketone, photoinitiator, N,N-dimethylformamide, and anhydrous ethanol were mixed evenly at a mass ratio of 1:2.3:0.03:13:3 and stirred at room temperature for 13 h. The viscosity was adjusted to 1250 mPa·s with ethanol and degassed under vacuum at room temperature for 25 min. The mixture was then loaded into an electrospinning machine for spinning at a spinning voltage of 17 kV, a push rate of 3 μL / min, a receiving distance of 15 cm, and a film thickness of 25 μm. The film was peeled off and vacuum dried at 45 ℃ for 2.5 h. Under nitrogen protection, the film was irradiated under a 365 nm ultraviolet lamp for 5 min and vacuum dried at 70 ℃ for 13 h to obtain the pre-modified cellulose membrane. (3) Weigh the pre-modified cellulose membrane and nonafluorohexyltrimethoxysilane at a mass ratio of 1:0.2; mix the nonafluorohexyltrimethoxysilane and anhydrous ethanol at a mass ratio of 1:15, adjust the pH to 4.5 with acetic acid, stir at room temperature for 15 min, add deionized water at a mass ratio of 9 times that of nonafluorohexyltrimethoxysilane, and continue stirring for 35 min to obtain silane hydrolysate; immerse the pre-modified cellulose membrane in silane hydrolysate, stir at room temperature for 6 h, wash with anhydrous ethanol 3 times, and vacuum dry at 75℃ for 11 h to obtain modified cellulose membrane; (4) Lithium hydroxide monohydrate and ammonium fluoride with a molar ratio of 1:1.1 were mixed evenly and added to anhydrous ethanol at a mass of 30 times that of lithium hydroxide monohydrate. The mixture was stirred at room temperature for 3 hours, centrifuged, and the precipitate was washed three times with anhydrous ethanol. The precipitate was then vacuum dried at 60°C for 10 hours and placed in a muffle furnace to dry at 100°C for 10 hours. The temperature was then increased to 300°C at a rate of 5°C / min and calcined for 6 hours to obtain lithium fluoride nanoparticles. Deionized water, anhydrous ethanol, polyoxyethylene lauryl ether, and aqueous binder were mixed evenly at a mass ratio of 1:1:0.25:0.35 and stirred at room temperature for 50 minutes. Lithium fluoride nanoparticles at a mass of 0.35 times that of deionized water were added and stirred for another 60 minutes to obtain a coating slurry. The modified cellulose membrane was immersed in the coating slurry, allowed to stand for 3 seconds, and then pulled out at a speed of 1 cm / s. The membrane was allowed to stand at room temperature for 11 hours and then vacuum dried at 40°C for 4.5 hours to obtain a cellulose-based lithium battery separator.

[0021] Example 3: A method for preparing a cellulose-based lithium battery separator, the method comprising the following steps: (1) 2,5-Dihydroxybiphenyl, diallyl bisphenol A, 4,4'-difluorobenzophenone, and anhydrous potassium carbonate were mixed evenly with sulfolane (10 times the mass of 2,5-dihydroxybiphenyl) and toluene (5 times the mass of 2,5-dihydroxybiphenyl) in a molar ratio of 1:1.5:2.5:2.6. Under nitrogen protection, the mixture was heated to 140°C, refluxed, and stirred for 2.5 h. The mixture was then heated to 210°C and stirred for another 5 h. 30 times the volume of toluene was added to the mixture, which was then filtered, pulverized, washed four times with deionized water and ethanol, and dried under vacuum at 110°C for 23 h to obtain polyaryletherketone. Polyaryletherketone and 98 wt% concentrated sulfuric acid were mixed evenly in a mass ratio of 1:32 and stirred for 12 h at room temperature. 98 wt% concentrated sulfuric acid was added to the mixture. 10 times the volume of concentrated sulfuric acid (wt%) in deionized water were left to stand for 1 hour, filtered, washed with deionized water until the pH of the washing water was 7, and then vacuum dried at 85°C for 22 hours to obtain modified polyarylether ketone. (2) Weigh cellulose, 6-chloro-1-hexene, and triethylamine in a mass ratio of 1:0.75:0.85; mix 6-chloro-1-hexene and N,N-dimethylacetamide in a mass ratio of 1:9, and sonicate at room temperature for 10 min to prepare a 6-chloro-1-hexene solution; mix cellulose and N,N-dimethylacetamide in a mass ratio of 1:10, stir at room temperature for 2 h, add triethylamine, continue stirring for 20 min, and under nitrogen protection, add the 6-chloro-1-hexene solution at -4℃ over 30 min at a uniform rate, stir for 20 min, raise the temperature to room temperature, stir and react for 23 h, pour into deionized water to precipitate, filter, wash 4 times with deionized water and anhydrous ethanol respectively, and then in 6 Pre-modified cellulose was obtained by vacuum drying at 5℃ for 22 h. The pre-modified cellulose, modified polyaryletherketone, photoinitiator, N,N-dimethylformamide, and anhydrous ethanol were mixed evenly at a mass ratio of 1:2.6:0.04:14:3.2 and stirred at room temperature for 12 h. The viscosity was adjusted to 1500 mPa·s with ethanol and degassed under vacuum at room temperature for 20 min. The mixture was then loaded into an electrospinning machine for spinning at a spinning voltage of 18 kV, a push rate of 4 μL / min, a receiving distance of 16 cm, and a film thickness of 30 μm. The film was then peeled off, vacuum dried at 50℃ for 2 h, irradiated under a 365 nm UV lamp for 4 min under nitrogen protection, and vacuum dried at 75℃ for 12 h to obtain the pre-modified cellulose membrane. (3) Weigh the pre-modified cellulose membrane and nonafluorohexyltrimethoxysilane at a mass ratio of 1:0.3; mix the nonafluorohexyltrimethoxysilane and anhydrous ethanol at a mass ratio of 1:16, adjust the pH to 5 with acetic acid, stir at room temperature for 10 min, add 10 times the mass of deionized water of nonafluorohexyltrimethoxysilane, and continue stirring for 30 min to obtain silane hydrolysate; immerse the pre-modified cellulose membrane in silane hydrolysate, stir at room temperature for 5 h, wash with anhydrous ethanol 4 times, and vacuum dry at 80℃ for 10 h to obtain modified cellulose membrane; (4) Lithium hydroxide monohydrate and ammonium fluoride with a molar ratio of 1:1.15 were mixed evenly and added to anhydrous ethanol at a mass of 35 times that of lithium hydroxide monohydrate. The mixture was stirred at room temperature for 2.5 h, centrifuged, and the precipitate was washed 4 times with anhydrous ethanol. The precipitate was then vacuum dried at 65 °C for 9 h, placed in a muffle furnace and dried at 110 °C for 9 h. The temperature was then increased to 320 °C at a rate of 6 °C / min and calcined for 5 h to obtain lithium fluoride nanoparticles. Deionized water, anhydrous ethanol, polyoxyethylene lauryl ether, and aqueous binder were mixed evenly at a mass ratio of 1:1.1:0.3:0.4. The mixture was stirred and reacted at room temperature for 40 min. Lithium fluoride nanoparticles at a mass of 0.4 times that of deionized water were added and stirred for another 50 min to obtain a coating slurry. The modified cellulose membrane was immersed in the coating slurry, allowed to stand for 20 s, and then pulled out at a speed of 1 cm / s. The membrane was allowed to stand at room temperature for 10 h and then vacuum dried at 45 °C for 4 h to obtain a cellulose-based lithium battery separator.

[0022] Comparative Example 1: The preparation method of the cellulose-based lithium battery separator in Comparative Example 1 differs from that in Example 2 in that step (1) is omitted, and step (2) is changed to: cellulose, N,N-dimethylformamide and anhydrous ethanol are mixed evenly in a mass ratio of 1:13:3, stirred and reacted at room temperature for 13 h, the viscosity is adjusted to 1250 mPa·s with ethanol, vacuum degassing is performed at room temperature for 25 min, and then loaded into an electrospinning machine for spinning. The spinning voltage is 17 kV, the pushing rate is 3 μL / min, the receiving distance is 15 cm, and the membrane thickness is controlled at 25 μm. The membrane is peeled off, vacuum dried at 45 °C for 2.5 h, and vacuum dried at 70 °C for 13 h to obtain the cellulose membrane. The remaining steps are the same as in Example 2.

[0023] Comparative Example 2: The preparation method of the cellulose-based lithium battery separator in Comparative Example 2 differs from that in Example 2 in that step (3) is omitted, and the phrase "immersing the modified cellulose membrane in the coating slurry" in step (4) is changed to "immersing the pre-modified cellulose membrane in the coating slurry". The remaining steps are the same as in Example 2.

[0024] Comparative Example 3: The preparation method of the cellulose-based lithium battery separator in Comparative Example 3 differs from that in Example 2 in that step (4) is omitted, and "preparing a modified cellulose membrane" in step (3) is changed to "preparing a cellulose-based lithium battery separator". The remaining steps are the same as in Example 2.

[0025] Test Example 1 Thermal stability test Test method: The cellulose-based lithium battery separators of the examples and comparative examples were cut into standard samples of 20mm × 20mm. The original area A1 of the sample was recorded. The samples were placed in a vacuum drying oven at 120°C, 150°C, 180°C and 200°C for 0.5h respectively, and the area A2 of the sample was measured. The thermal shrinkage rate was calculated as (A1-A2) / A1×100%. The results are shown in Table 1.

[0026] Table 1 A comparison of the experimental data of Examples 1-3 and Comparative Examples 1-3 in Table 1 reveals that the cellulose-based lithium battery separator prepared by the present invention has good thermal stability.

[0027] By comparison, the heat shrinkage rates of Examples 1-3 are less than those of Comparative Example 1, indicating that polyaryletherketone (PAK) is prepared by polymerizing 2,5-dihydroxybiphenyl, diallyl bisphenol A, and 4,4'-difluorobenzophenone; modified PAK is prepared by sulfonating PAK with concentrated sulfuric acid; modified cellulose is prepared by grafting 6-chloro-1-hexene onto cellulose, introducing carbon-carbon double bonds that can polymerize with modified PAK; and pre-modified cellulose membrane is prepared by electrospinning and photopolymerizing the modified cellulose and modified PAK together. PAK has high thermal stability and good mechanical properties, which can provide high-temperature resistant rigid support for the cellulose membrane, thereby giving the cellulose-based lithium battery separator good thermal stability.

[0028] Test Example 2 Swelling resistance test Test method: The cellulose-based lithium battery separators of the examples and comparative examples were cut into standard strips of 10×5mm and vacuum dried at 80℃ for 24h. The original mass M1 and volume V1 were recorded. The strips were then immersed in deionized water for 2h. After removing the samples, the surface water was quickly wiped dry, and the mass M2 and volume V2 were recorded. The water absorption rate was calculated as (M2-M1) / M1×100%, and the swelling rate was calculated as (V2-V1) / V1×100%. The results are shown in Table 2.

[0029] Table 2 A comparison of the experimental data from Examples 1-3 and Comparative Examples 1-3 in Table 2 reveals that the cellulose-based lithium battery separator prepared by this invention exhibits excellent swelling resistance.

[0030] By comparison, the water absorption and swelling rates of Examples 1-3 were lower than those of Comparative Example 1, indicating that polyaryletherketone (PAK) was prepared by polymerizing 2,5-dihydroxybiphenyl, diallyl bisphenol A, and 4,4'-difluorobenzophenone; modified PAK was prepared by sulfonating PAK with concentrated sulfuric acid, and sulfonic acid groups were introduced onto PAK; modified cellulose was prepared by grafting 6-chloro-1-hexene onto cellulose, and carbon-carbon double bonds that can polymerize with modified PAK were introduced onto cellulose; modified cellulose and modified PAK were mixed and electrospun-photopolymerized to prepare a pre-modified cellulose membrane; through the electrospinning process, PAK and nanocellulose formed a tight three-dimensional network structure, which can effectively and uniformly disperse the absorbed water in the membrane, and the strong intermolecular hydrogen bond interaction can effectively control the swelling of the membrane, giving the composite membrane good dimensional stability, thus endowing the cellulose-based lithium battery separator with excellent swelling resistance.

[0031] By comparison, the water absorption rate and swelling rate of Examples 1-3 are less than those of Comparative Example 2, indicating that hydrolyzing nonafluorohexyltrimethoxysilane and grafting it onto the surface of pre-modified cellulose yields a modified cellulose membrane. The Si-OC covalent bond has high stability and will not be degraded by the electrolyte. The fluorine-containing long chain has low bond polarity and low surface energy, which can form a directionally arranged hydrophobic layer on the membrane surface, reducing the adsorption of moisture from the air by the separator and reducing the interaction between electrolyte molecules and the membrane surface, thereby improving the swelling resistance of the cellulose-based lithium battery separator.

[0032] Test Example 3 Electrochemical performance testing Test Method: The cellulose-based lithium battery separators, LiFePO4 cathodes, lithium metal anodes, and electrolytes from the examples and comparative examples were assembled into CR2032 coin batteries in an argon-filled glove box. The electrolyte was a 1.0M LiPF6 solution dissolved in a 1:1 mixture of ethylene carbonate and diethyl carbonate. Performance tests were conducted using a Newway three-electrode battery tester. The charge and discharge currents were both 1.5C, and the constant current discharge voltage window was 2.8V~4.2V. The battery cycle performance was tested after 100 charge and discharge cycles. The results are shown in Table 3.

[0033] Table 3 A comparison of the experimental data from Examples 1-3 and Comparative Examples 1-3 in Table 3 reveals that the cellulose-based lithium battery separator prepared by this invention exhibits excellent electrochemical performance.

[0034] By comparison, the capacity retention rates of Examples 1-3 are greater than those of Comparative Example 2, indicating that by hydrolyzing nonafluorohexyltrimethoxysilane and grafting it onto the surface of pre-modified cellulose to obtain a modified cellulose membrane, the chemical inertness of the fluorine group and its low reactivity with lithium dendrites can reduce the adhesion of "dead lithium" between dendrites and the separator, thereby improving the battery cycle life.

[0035] By comparison, the initial capacity and capacity retention rate of Examples 1-3 were greater than those of Comparative Example 3, indicating that the reaction of lithium hydroxide monohydrate and ammonium fluoride to prepare lithium fluoride nanoparticles, followed by impregnation and coating onto the surface of a modified cellulose membrane, yields a cellulose-based lithium battery separator. The LiF coating improves the separator's hydrophilicity and electrolyte absorption, reducing electrolyte consumption during SEI membrane formation. The improved hydrophilicity and electrolyte absorption also enhance the performance of the LiF-coated separator. +The cellulose nanoparticles migrate more easily and quickly inside the battery, resulting in a higher initial capacity. At the same time, as artificial SEI film nucleation sites, LiF nanoparticles preferentially combine with electrolyte reduction products during the first charge and discharge of the battery, inducing the formation of a denser SEI layer structure on the lithium anode surface. This inhibits the short circuit problem caused by lithium dendrite growth piercing the separator, extends the battery cycle life, prevents further reaction between the electrolyte and electrode materials, and reduces the consumption of electrolyte and electrode materials, thus endowing the cellulose-based lithium battery separator with excellent electrochemical performance.

[0036] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A cellulose-based lithium battery separator, characterized in that, The cellulose-based lithium battery separator is prepared by sulfonating polyaryletherketone with concentrated sulfuric acid to obtain modified polyaryletherketone; grafting 6-chloro-1-hexene onto cellulose to obtain modified cellulose; mixing modified cellulose and modified polyaryletherketone and electrospinning-photopolymerizing to obtain a pre-modified cellulose membrane; hydrolyzing nonafluorohexyltrimethoxysilane and grafting it onto the surface of the pre-modified cellulose to obtain a modified cellulose membrane; reacting lithium hydroxide monohydrate and ammonium fluoride to obtain lithium fluoride nanoparticles, and then impregnating and coating them onto the surface of the modified cellulose membrane. The polyaryletherketone is prepared by polymerizing 2,5-dihydroxybiphenyl, diallyl bisphenol A, and 4,4'-difluorobenzophenone.

2. A method for preparing a cellulose-based lithium battery separator, characterized in that, The preparation method of the cellulose-based lithium battery separator includes the following preparation steps: (1) Mix polyarylether ketone and 98 wt% concentrated sulfuric acid at a mass ratio of 1:(28~32), stir and react at room temperature for 12~14h, add 8~10 times the volume of deionized water of 98 wt% concentrated sulfuric acid, let stand for 1~2h, filter, wash with deionized water until the pH of the washing water is 6~7, and vacuum dry at 75~85℃ for 22~24h to obtain modified polyarylether ketone; (2) Premodified cellulose, modified polyarylether ketone, photoinitiator, N,N-dimethylformamide, and anhydrous ethanol are mixed evenly in a mass ratio of 1:(2~2.6):(0.02~0.04):(12~14):(2.8~3.2), stirred and reacted at room temperature for 12~14h, the viscosity was adjusted to 1000~1500mPa·s with ethanol, vacuum degassing was performed at room temperature for 20~30min, the film was loaded into an electrospinning machine for electrospinning, the film was peeled off, vacuum dried at 40~50℃ for 2~3h, irradiated under a 365nm ultraviolet lamp for 4~6min under nitrogen protection, and vacuum dried at 65~75℃ for 12~14h to obtain a premodified cellulose membrane; (3) Weigh the pre-modified cellulose membrane and nonafluorohexyltrimethoxysilane at a mass ratio of 1:(0.1~0.3); hydrolyze the nonafluorohexyltrimethoxysilane to obtain a silane hydrolysate; immerse the pre-modified cellulose membrane in the silane hydrolysate, stir and react at room temperature for 5~7h, wash with anhydrous ethanol 2~4 times, and vacuum dry at 70~80℃ for 10~12h to obtain the modified cellulose membrane; (4) Mix deionized water, anhydrous ethanol, polyoxyethylene lauryl ether, and water-based adhesive in a mass ratio of 1:(0.9~1.1):(0.2~0.3):(0.3~0.4) until homogeneous. Stir and react at room temperature for 40~60 min. Add lithium fluoride nanoparticles at a mass ratio of 0.3~0.4 times that of deionized water and continue stirring for 50~70 min to obtain a coating slurry. Immerse the modified cellulose membrane in the coating slurry, let it stand for 20~40 s, pull it out at a speed of 1 cm / s, let it stand at room temperature for 10~12 h, and vacuum dry it at 35~45℃ for 4~5 h to obtain a cellulose-based lithium battery separator.

3. The method for preparing the cellulose-based lithium battery separator according to claim 2, characterized in that, The preparation steps of the polyarylether ketone in step (1) are as follows: 2,5-dihydroxybiphenyl, diallyl bisphenol A, 4,4'-difluorobenzophenone, anhydrous potassium carbonate, and sulfolane (8-10 times the mass of 2,5-dihydroxybiphenyl) and toluene (4-5 times the mass of 2,5-dihydroxybiphenyl) are mixed evenly under nitrogen protection, heated to 120-140℃, refluxed and stirred for 2.5-3.5h, heated to 190-210℃ and stirred for another 5-6h, poured in 20-30 times the volume of toluene in deionized water, filtered, pulverized, washed 2-4 times with deionized water and ethanol respectively, and dried under vacuum at 100-110℃ for 23-25h to obtain polyarylether ketone.

4. The method for preparing the cellulose-based lithium battery separator according to claim 2, characterized in that, The preparation steps of the pre-modified cellulose in step (2) are as follows: Weigh cellulose, 6-chloro-1-hexene and triethylamine at a mass ratio of 1:(0.65~0.75):(0.75~0.85); Mix 6-chloro-1-hexene and N,N-dimethylacetamide at a mass ratio of 1:(7~9) evenly, and sonicate at room temperature for 10~20 min to obtain a 6-chloro-1-hexene solution; Mix cellulose and N,N-dimethylacetamide at a mass ratio of 1:(8~10) Mix the ingredients thoroughly and stir at room temperature for 2-3 hours. Add triethylamine and continue stirring for 20-40 minutes. Under nitrogen protection, add 6-chloro-1-hexene solution at -6 to -4°C over 30-40 minutes and stir for 20-30 minutes. Heat to room temperature and stir for 23-25 ​​hours. Pour the solution into deionized water to precipitate, filter, and wash 2-4 times with deionized water and anhydrous ethanol, respectively. Dry under vacuum at 55-65°C for 22-24 hours to obtain pre-modified cellulose.

5. The method for preparing the cellulose-based lithium battery separator according to claim 4, characterized in that, The cellulose has a size of 30 nm × 2 μm.

6. The method for preparing the cellulose-based lithium battery separator according to claim 2, characterized in that, The photoinitiator used in step (2) is photoinitiator 1173.

7. The method for preparing the cellulose-based lithium battery separator according to claim 2, characterized in that, The electrospinning process parameters in step (2) are: spinning voltage 16~18kV, push rate 2~4μL / min, receiving distance 14~16cm, and film thickness controlled at 20~30μm.

8. The method for preparing the cellulose-based lithium battery separator according to claim 2, characterized in that, The hydrolysis of nonafluorohexyltrimethoxysilane in step (3) is as follows: nonafluorohexyltrimethoxysilane and anhydrous ethanol are mixed evenly at a mass ratio of 1:(14~16), the pH is adjusted to 4~5 with acetic acid, stirred at room temperature for 10~20 min, deionized water with a mass of 8~10 times that of nonafluorohexyltrimethoxysilane is added, and the reaction is continued to be stirred for 30~40 min to obtain silane hydrolysate.

9. The method for preparing the cellulose-based lithium battery separator according to claim 2, characterized in that, The preparation steps of the lithium fluoride nanoparticles in step (4) are as follows: Lithium hydroxide monohydrate and ammonium fluoride in a molar ratio of 1:(1.05~1.15) are mixed evenly and added to anhydrous ethanol at 25~35 times the mass of lithium hydroxide monohydrate. The mixture is stirred at room temperature for 2.5~3.5h, centrifuged, and the precipitate is washed 2~4 times with anhydrous ethanol. The precipitate is then vacuum dried at 55~65℃ for 9~11h, placed in a muffle furnace and dried at 90~110℃ for 9~11h, and heated to 280~320℃ at a rate of 4~6℃ / min and calcined for 5~7h to obtain lithium fluoride nanoparticles.

10. The method for preparing the cellulose-based lithium battery separator according to claim 2, characterized in that, The water-based adhesive used in step (4) is model TOB-LA133.

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