Polymer-coated paper-based lithium ion battery separator, preparation method and application thereof

Abstract

This invention discloses a polymer-coated paper-based lithium-ion battery separator, its preparation method, and its applications, belonging to the field of lithium-ion battery separator applications. The battery separator uses propionylated fiber paper as a substrate, coated with a copolymer containing photosensitive groups. This invention first prepares a polymer solution using DMF, DMAc, or THF as a solvent, and then fixes the polymer onto the propionylated paper using an impregnation coating method and a UV curing method, thus preparing polymer-coated paper-based battery separators with different surface microstructures. Compared with traditional polyolefin separators, the polymer-coated paper-based battery separator of this invention possesses excellent thermal dimensional stability, electrolyte wettability, and high Li- content. + Its high transference number and excellent cycle performance make it a promising candidate for applications in the lithium-ion battery field.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery separator applications, and relates to a polymer-coated paper-based lithium-ion battery separator, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries have attracted widespread attention from researchers due to their advantages such as high energy density, low self-discharge rate, high coulombic efficiency, long cycle life, and absence of memory effect. In the battery structure, the separator, as one of the main components, although not directly involved in electrochemical reactions, plays a crucial role in the overall electrochemical performance and long-term operational stability of the battery due to its interfacial properties. However, commercially available polyolefin separators have two inherent drawbacks: firstly, poor electrolyte wettability, leading to poor interfacial compatibility with the electrodes; and secondly, poor thermal stability, easily shrinking at high temperatures, thus posing safety hazards. In contrast, paper-based separators not only exhibit excellent electrolyte wettability and thermal stability, but the abundant hydroxyl groups on the cellulose surface also provide possibilities for functionalization modification, showing potential to replace polyolefin separators. However, the micron-sized pores of traditional paper-based separators are prone to causing battery short circuits; simultaneously, the abundant hydroxyl groups on the surface may induce side reactions during battery operation, thus limiting the long-term cycle stability of the battery. Although polymer coating can effectively adjust the pore size of paper-based separators and reduce hydroxyl-initiated side reactions to meet the needs of lithium-ion battery applications, the interlayer bonding strength between the coating and the paper substrate needs to be strengthened. Furthermore, the surface morphology of the coating affects the interfacial resistance and Li- ionization of the separator. + Ion transport affects the lifespan of membrane-assembled batteries. However, this issue has received little attention. Summary of the Invention

[0003] To address the above problems, this invention provides a polymer-coated paper-based lithium-ion battery separator, its preparation method, and its application. The polymer-coated paper-based lithium-ion battery separator is prepared by coating a polymer containing photosensitive groups onto propionylated paper using an impregnation coating method and a UV curing method.

[0004] The purpose of this invention is to provide a polymer-coated paper-based lithium-ion battery separator;

[0005] A second objective of this invention is to provide a method for preparing the above-mentioned polymer-coated paper-based lithium-ion battery separator;

[0006] A third objective of this invention is to provide the application of the aforementioned polymer-coated paper-based lithium-ion battery separator.

[0007] To achieve the objectives of this invention, the invention is implemented through the following technical solutions:

[0008] A polymer-coated paper-based lithium-ion battery separator is disclosed, employing a copolymer containing photosensitive groups for coating. By changing the solvent of the impregnation solution, the separator exhibits different surface microstructures. The polymer-coated paper-based lithium-ion battery separator comprises: a propionylated cellulose paper substrate; and a polymer coating covalently bonded to the surface of the substrate through a photocuring reaction; the polymer coating is formed from polymethyl methacrylate containing benzophenone groups.

[0009] The propionylated fiber paper is prepared from propionylated modified fibers; the modified fibers are obtained by propionylation modification of natural pulp fibers or renewable pulp fibers.

[0010] The polymer coating has a particulate surface morphology formed by the combined regulation of solvent and fiber swelling, wherein the solvent is N,N-dimethylformamide, N,N-dimethylacetamide or tetrahydrofuran.

[0011] The polymer coating has a coating amount of 2.15~4.52 g / m².

[0012] The method for preparing a polymer-coated paper-based lithium-ion battery separator involves using different solvents to prepare polymer solutions, which are then coated onto propionylated paper via impregnation coating and UV curing methods to obtain separators with different surface microstructures. The specific preparation steps are as follows:

[0013] (1) Preparation of propionylated fiber paper: Take 0.18 g of propionylated fiber with an oven-dry weight, add ethanol to dilute to 80 mL, stir at room temperature, filter the propionylated fiber suspension into paper, and obtain propionylated fiber paper.

[0014] (2) Preparation of polymer dip coating solution: Weigh polymethyl methacrylate powder containing benzophenone group as solute, add solvent, and stir at room temperature until the solute is completely dissolved to obtain polymer dip coating solution; the solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide or tetrahydrofuran;

[0015] (3) Impregnation and coating: Immerse the propionylated paper in the polymer solution, remove it after impregnation, and air dry it at room temperature;

[0016] (4) UV curing: Place the air-dried sample in a UV curing chamber, irradiate both sides of the diaphragm for the same time, the light wavelength is 365 nm, and the irradiation time is 40 min;

[0017] (5) Washing: Use the corresponding solvent to wash the sample to remove unreacted polymers;

[0018] (6) Drying: The washed sample is first air-dried at room temperature, and then dried to obtain a polymer-coated paper-based lithium-ion battery separator.

[0019] The specific preparation process of the propionylated modified fiber is as follows: the pulp fiber is beaten to a freeness of 90~92°SR; then 2.5 g of the pulp with an oven-dry weight is weighed and solvent is replaced so that the solvent in the pulp is N,N-dimethylformamide (DMF); the replaced pulp is dispersed in DMF (400 mL), and propionyl chloride and pyridine are added dropwise, wherein the molar ratio of propionyl chloride to fiber is 6:1; the molar ratio of pyridine to propionyl chloride is 3:1; and the reaction is carried out at 100 °C for 1 h to obtain propionylated modified fiber.

[0020] The specific preparation process of the propionylated fiber paper is as follows: Take 0.18 g of propionylated fiber with an oven-dry weight, add ethanol to dilute to 80 mL, stir at room temperature for 1 h, filter the propionylated fiber suspension into paper, and obtain propionylated fiber paper.

[0021] The specific preparation process of the benzophenone monomer is as follows: 4-hydroxybenzophenone (0.030 mol~0.040 mol) is poured into a 250 mL round-bottom flask, followed by the addition of dichloromethane (1.1 mol~1.5 mol) and triethylamine (0.035 mol~0.045 mol), and then methacryloyl chloride (0.040 mol~0.050 mol). The mixture is stirred at room temperature for 24 h, and then the reaction is stopped. After purification, it is dried in an oven at 40 ℃ for 24 h.

[0022] The specific preparation process of the polymethyl methacrylate containing benzophenone monomer is as follows: The prepared benzophenone monomer (0.15 g~0.18 g) and azobisisobutyronitrile (0.08 g~0.12 g) are mixed in DMF (30 mL), and then methyl methacrylate (2.8 mL~3.2 mL) is added. The reaction is carried out at 60 °C for 16 h under a N2 atmosphere. The sample is purified three times by dissolving in tetrahydrofuran (THF), precipitating with ethanol, and repeated centrifugation. The sample is then dried in an oven (40 °C) to obtain the final product (white powder).

[0023] The impregnation and coating process is as follows: the propionylated paper is immersed in the polymer solution for 1 minute, then removed and air-dried in a fume hood at room temperature;

[0024] The washing process is as follows: the sample in (4) is washed with the corresponding solvent to wash away the unreacted polymer on the sample for 5 h;

[0025] The drying conditions are: drying at 40℃ for 24 hours.

[0026] The modified fiber is obtained by modifying natural pulp fiber or renewable pulp fiber.

[0027] The propionylated modified fiber has a freeness of 90~92°SR and a degree of substitution of 1.6~1.8.

[0028] The UV curing process uses a UV lamp with a wavelength of 365 nm and an irradiation time of 38-42 min.

[0029] The coating amount of the prepared coated paper-based battery separator is 2.15~4.52 g / m³. 2 .

[0030] The concentration of the polymer dipping solution is 15-45 mg / mL.

[0031] The preparation method of the polymethyl methacrylate containing benzophenone groups is as follows: methyl methacrylate monomer and monomer containing benzophenone groups are copolymerized to obtain polymethyl methacrylate copolymer containing benzophenone groups.

[0032] The application of the polymer-coated paper-based lithium-ion battery separator in the preparation of lithium-ion batteries.

[0033] Compared with existing polyolefin lithium-ion battery separators, the advantages of this invention are as follows:

[0034] The polymer-coated paper-based lithium-ion battery separator prepared by this invention has good thermal stability (no dimensional shrinkage at 120°C), and the battery assembled with lithium iron phosphate cathode and lithium metal anode has excellent cycle performance, showing great application prospects in the field of lithium-ion battery separators (after 600 cycles at 1C, the capacity retention rate is close to 77%, and the average coulombic efficiency is 93.2%). Attached Figure Description

[0035] Figure 1 SEM images of polymer-coated paper-based lithium-ion battery separators using DMF, DMAc, and THF as solvents, respectively. Detailed Implementation

[0036] The present invention will be clearly described below with reference to specific embodiments. This is not intended to limit the present invention. Simple modifications to the methods, steps or conditions of the present invention still fall within the scope of the present invention and are protected by the present invention.

[0037] Unless otherwise specified, the techniques, reagents, and equipment used in the embodiments are all conventional techniques, reagents, and equipment well known to those skilled in the art. All reagents and materials used in the embodiments are commercially available.

[0038] The benzophenone monomer was prepared by the following method: 4-hydroxybenzophenone (0.030 mol–0.040 mol) was poured into a 250 mL round-bottom flask, followed by the addition of dichloromethane (1.1 mol–1.5 mol) and triethylamine (0.035 mol–0.045 mol), and then methacryloyl chloride (0.040 mol–0.050 mol) was slowly added dropwise. The mixture was stirred at room temperature for 24 h, and then the reaction was stopped. After purification, the product was dried in an oven at 40 °C for 24 h.

[0039] Example 1

[0040] The preparation method of the polymer-coated paper-based lithium-ion battery separator of the present invention is as follows:

[0041] S1. Preparation of propionylated modified paper: The pulp fibers were beaten to a freeness of 90°SR. 2.5 g of pretreated pulp (air-dry weight) was weighed and solvent-displaced to replace water with N,N-dimethylformamide (DMF). The displaced pulp was dispersed in DMF (400 mL), and propionyl chloride (molar ratio of propionyl chloride to fiber was 6:1) and pyridine (molar ratio of pyridine to propionyl chloride was 3:1) were added dropwise. The mixture was reacted at 100 °C for one hour to obtain propionylated modified fibers. 0.18 g of modified fibers (air-dry weight) was weighed and diluted with ethanol to 80 mL. The mixture was stirred at room temperature for 1 h. The propionylated fiber suspension was then filtered to form paper, yielding propionylated fiber paper.

[0042] S2. Preparation of the polymer dip-coating solution: 0.15 g of benzophenone monomer and 0.08 g of azobisisobutyronitrile (DIS) were mixed in DMF (30 mL), and then methyl methacrylate (3.0 mL) was added. The mixture was reacted at 60 °C for 16 h under a N2 atmosphere. The sample was purified three times by dissolving in tetrahydrofuran (THF), precipitating with ethanol, and centrifuging repeatedly. The sample was then dried in an oven (40 °C) to obtain the final product (white powder), which is polymethyl methacrylate containing benzophenone monomer.

[0043] Take 0.60 g of benzophenone-containing polymethyl methacrylate at oven-dry weight, add 20 mL of N,N-dimethylformamide, and stir at room temperature until the polymer dissolves to obtain a polymer solution with a concentration of 30 mg / mL. This polymer solution is the polymer dip coating solution.

[0044] S3. Impregnation and coating: Immerse the propionylated paper prepared in step S1 into the polymer impregnation solution prepared in S2, remove it after 1 minute, and place it in a fume hood to air dry at room temperature.

[0045] S4. UV curing: Place the sample from S3 in a UV curing chamber for reaction. The light wavelength is 365 nm and the irradiation time is 40 min for each side.

[0046] S5. Washing and Drying: Wash the ungrafted polymer from the membrane using N,N-dimethylformamide, air dry at room temperature, and then dry at 40℃ for 24 h to obtain a coating weight of 3.45 g / m. 2 Polymer-coated paper-based lithium-ion battery separator.

[0047] The thermal dimensional stability of the polymer-coated paper-based lithium-ion battery separator prepared in this embodiment was tested, and the results showed that it did not shrink at 120°C.

[0048] This embodiment tests the constant current cycle charge-discharge performance of a polymer-coated paper-based lithium-ion battery separator on a Blue Electric Battery testing system. The polymer-coated paper-based lithium-ion battery separator, along with a lithium anode and lithium iron phosphate (LiFePO4) cathode material, is assembled into a lithium-ion battery, and its electrochemical performance is tested. The LiFePO4 cathode material is prepared as follows: LiFePO4 (90 wt%), superP (5 wt%), and polyvinylidene fluoride (PVDF) (5 wt%) are dissolved in N-methyl-2-pyrrolidone (NMP) solvent, thoroughly mixed, coated onto aluminum foil, and dried to form the cathode. A 1M lithium hexafluorophosphate (LiPF6) solution of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) is used as the electrolyte, with a solvent mass ratio of 1:1:1. The half-cell assembled with the polymer-coated paper-based lithium-ion battery separator prepared in this embodiment maintained a capacity retention of 76.7% and an average coulombic efficiency of 93.2% after 600 cycles at 1C.

[0049] Example 2

[0050] The preparation method of the polymer-coated paper-based lithium-ion battery separator of the present invention is as follows:

[0051] S1. Preparation of propionylated modified paper: The pulp fibers were beaten to a freeness of 90°SR. 2.5 g of pretreated pulp (air-dry weight) was weighed and solvent-displaced to replace water with N,N-dimethylformamide (DMF). The displaced pulp was dispersed in DMF (400 mL), and propionyl chloride (molar ratio of propionyl chloride to fiber was 6:1) and pyridine (molar ratio of pyridine to propionyl chloride was 3:1) were added dropwise. The mixture was reacted at 100 °C for one hour to obtain propionylated modified fibers. 0.18 g of modified fibers (air-dry weight) was weighed and diluted with ethanol to 80 mL. The mixture was stirred at room temperature for 1 h. The propionylated fiber suspension was then filtered to form paper, yielding propionylated fiber paper.

[0052] S2. Preparation of the polymer dip-coating solution: 0.15 g of benzophenone monomer and 0.08 g of azobisisobutyronitrile (DIS) were mixed in DMF (30 mL), and then methyl methacrylate (3.0 mL) was added. The mixture was reacted at 60 °C for 16 h under a N2 atmosphere. The sample was purified three times by dissolving in tetrahydrofuran (THF), precipitating with ethanol, and centrifuging repeatedly. The sample was then dried in an oven (40 °C) to obtain the final product (white powder), which is polymethyl methacrylate containing benzophenone monomer.

[0053] Take 0.60 g of benzophenone-containing polymethyl methacrylate at oven-dry weight, add 20 mL of N,N-dimethylacetamide, and stir at room temperature until the polymer dissolves to obtain a polymer solution with a concentration of 30 mg / mL.

[0054] S3. Impregnation and coating: Immerse the propionylated paper prepared in step S1 into the polymer impregnation solution prepared in S2, remove it after 1 minute, and place it in a fume hood to air dry at room temperature.

[0055] S4. UV curing: Place the sample from S3 in a UV curing chamber for reaction. The light wavelength is 365 nm and the irradiation time is 40 min for each side.

[0056] S5. Washing and Drying: Wash the ungrafted polymer in the membrane with N,N-dimethylacetamide from the sample in S4, air dry at room temperature, and then dry at 40℃ for 24 h to obtain a coating weight of 2.86 g / m. 2 Polymer-coated paper-based lithium-ion battery separator.

[0057] The thermal dimensional stability of the polymer-coated paper-based lithium-ion battery separator prepared in this embodiment was tested, and the results showed that it did not shrink at 120°C.

[0058] This embodiment tests the constant current cycle charge-discharge performance of a polymer-coated paper-based lithium-ion battery separator on a Blue Electric Battery testing system. The polymer-coated paper-based lithium-ion battery separator, along with a lithium anode and lithium iron phosphate (LiFePO4) cathode material, is assembled into a lithium-ion battery, and its electrochemical performance is tested. The LiFePO4 cathode material is prepared as follows: LiFePO4 (90 wt%), superP (5 wt%), and polyvinylidene fluoride (PVDF) (5 wt%) are dissolved in N-methyl-2-pyrrolidone (NMP) solvent, thoroughly mixed, coated onto aluminum foil, and dried to form the cathode. A 1M lithium hexafluorophosphate (LiPF6) solution of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) is used as the electrolyte, with a solvent mass ratio of 1:1:1. The half-cell assembled with the polymer-coated paper-based lithium-ion battery separator prepared in this embodiment retained a capacity of 72.9% and achieved an average coulombic efficiency of 95.6% after 600 cycles at 11C.

[0059] Example 3

[0060] The preparation method of the polymer-coated paper-based lithium-ion battery separator of the present invention is as follows:

[0061] S1. Preparation of propionylated modified paper: The pulp fibers were beaten to a freeness of 90°SR. 2.5 g of pretreated pulp (air-dry weight) was weighed and solvent-displaced to replace water with N,N-dimethylformamide (DMF). The displaced pulp was dispersed in DMF (400 mL), and propionyl chloride (molar ratio of propionyl chloride to fiber was 6:1) and pyridine (molar ratio of pyridine to propionyl chloride was 3:1) were added dropwise. The mixture was reacted at 100 °C for one hour to obtain propionylated modified fibers. 0.18 g of modified fibers (air-dry weight) was weighed and diluted with ethanol to 80 mL. The mixture was stirred at room temperature for 1 h. The propionylated fiber suspension was then filtered to form paper, yielding propionylated fiber paper.

[0062] S2. Preparation of the polymer dip-coating solution: 0.15 g of benzophenone monomer and 0.08 g of azobisisobutyronitrile (DIBON) were mixed in DMF (30 mL), and then methyl methacrylate (3.0 mL) was added. The mixture was reacted at 60 °C for 16 h under a N2 atmosphere. The sample was purified three times by dissolving in tetrahydrofuran (THF), precipitating with ethanol, and centrifuging repeatedly. The sample was then dried in an oven (40 °C) to obtain the final product (white powder), which is polymethyl methacrylate containing benzophenone monomer.

[0063] Take 0.60 g of benzophenone-containing polymethyl methacrylate at oven-dry weight, add 20 mL of tetrahydrofuran, and stir at room temperature until the polymer dissolves to obtain a polymer solution with a concentration of 30 mg / mL.

[0064] S3. Impregnation and coating: Immerse the propionylated paper prepared in step S1 into the polymer impregnation solution prepared in S2, remove it after 1 minute, and place it in a fume hood to air dry at room temperature.

[0065] S4. UV curing: Place the sample from S3 in a UV curing chamber for reaction. The light wavelength is 365 nm and the irradiation time is 40 min for each side.

[0066] S5. Washing and Drying: Wash the ungrafted polymer from the membrane using tetrahydrofuran, air dry at room temperature, and then dry at 40°C for 24 hours to obtain a coating weight of 4.33 g / m. 2 Polymer-coated paper-based lithium-ion battery separator.

[0067] The thermal dimensional stability of the polymer-coated paper-based lithium-ion battery separator prepared in this embodiment was tested, and the results showed that it did not shrink at 120°C.

[0068] This embodiment tests the constant current cycle charge-discharge performance of a polymer-coated paper-based lithium-ion battery separator on a Blue Electric Battery testing system. The polymer-coated paper-based lithium-ion battery separator, along with a lithium anode and lithium iron phosphate (LiFePO4) cathode material, is assembled into a lithium-ion battery, and its electrochemical performance is tested. The LiFePO4 cathode material is prepared as follows: LiFePO4 (90 wt%), superP (5 wt%), and polyvinylidene fluoride (PVDF) (5 wt%) are dissolved in N-methyl-2-pyrrolidone (NMP) solvent, thoroughly mixed, coated onto aluminum foil, and dried to form the cathode. A 1M lithium hexafluorophosphate (LiPF6) solution of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) is used as the electrolyte, with a solvent mass ratio of 1:1:1. The half-cell assembled with the polymer-coated paper-based lithium-ion battery separator prepared in this embodiment maintained a capacity retention of 76.4% and an average coulombic efficiency of 93.4% after 600 cycles at 1C.

[0069] Example 4

[0070] The preparation method of the polymer-coated paper-based lithium-ion battery separator of the present invention is as follows:

[0071] S1. Preparation of propionylated modified paper: The pulp fibers were beaten to a freeness of 92°SR. 2.5 g of pretreated pulp (octane-dry weight) was weighed and solvent-displaced to replace water with N,N-dimethylformamide (DMF). The displaced pulp was dispersed in DMF (400 mL), and propionyl chloride (molar ratio of propionyl chloride to fiber was 6:1) and pyridine (molar ratio of pyridine to propionyl chloride was 3:1) were added dropwise. The mixture was reacted at 100 °C for one hour to obtain propionylated modified fibers. 0.18 g of modified fibers (octane-dry weight) was weighed and diluted with ethanol to 80 mL. The mixture was stirred at room temperature for 1 h. The propionylated fiber suspension was then filtered to form paper, yielding propionylated fiber paper.

[0072] S2. Preparation of the polymer dip-coating solution: 0.16 g of benzophenone monomer and 0.10 g of azobisisobutyronitrile (DIBON) were mixed in DMF (30 mL), and then methyl methacrylate (2.8 mL) was added. The mixture was reacted at 60 °C for 16 h under a N2 atmosphere. The sample was purified three times by dissolving in tetrahydrofuran (THF), precipitating with ethanol, and centrifuging repeatedly. The sample was then dried in an oven (40 °C) to obtain the final product (white powder), which is polymethyl methacrylate containing benzophenone monomer.

[0073] Take 0.30 g of benzophenone-containing polymethyl methacrylate at oven-dry weight, add 20 mL of N,N-dimethylformamide, and stir at room temperature until the polymer dissolves to obtain a polymer solution with a concentration of 15 mg / mL.

[0074] S3. Impregnation and coating: Immerse the propionylated paper prepared in step S1 into the polymer impregnation solution prepared in S2, remove it after 1 minute, and place it in a fume hood to air dry at room temperature.

[0075] S4. UV curing: Place the sample from S3 in a UV curing chamber for reaction. The light wavelength is 365 nm and the irradiation time is 40 min for each side.

[0076] S5. Washing and Drying: Wash the ungrafted polymer from the membrane using N,N-dimethylformamide, air dry at room temperature, and then dry at 40℃ for 24 h to obtain a coating weight of 2.15 g / m. 2 Polymer-coated paper-based lithium-ion battery separator.

[0077] The thermal dimensional stability of the polymer-coated paper-based lithium-ion battery separator prepared in this embodiment was tested, and the results showed that it did not shrink at 120°C.

[0078] This embodiment tests the constant current cycle charge-discharge performance of a polymer-coated paper-based lithium-ion battery separator on a Blue Electric Battery testing system. The polymer-coated paper-based lithium-ion battery separator, along with a lithium anode and lithium iron phosphate (LiFePO4) cathode material, is assembled into a lithium-ion battery, and its electrochemical performance is tested. The LiFePO4 cathode material is prepared as follows: LiFePO4 (90 wt%), superP (5 wt%), and polyvinylidene fluoride (PVDF) (5 wt%) are dissolved in N-methyl-2-pyrrolidone (NMP) solvent, thoroughly mixed, coated onto aluminum foil, and dried to form the cathode. A 1M lithium hexafluorophosphate (LiPF6) solution of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) is used as the electrolyte, with a solvent mass ratio of 1:1:1. The half-cell assembled with the polymer-coated paper-based lithium-ion battery separator prepared in this embodiment retained 71.2% of its capacity and achieved an average coulombic efficiency of 95.9% after 600 cycles at 1C.

[0079] Example 5

[0080] The preparation method of the polymer-coated paper-based lithium-ion battery separator of the present invention is as follows:

[0081] S1. Preparation of propionylated modified paper: The pulp fibers were beaten to a freeness of 92°SR. 2.5 g of pretreated pulp (octane-dry weight) was weighed and solvent-displaced to replace water with N,N-dimethylformamide (DMF). The displaced pulp was dispersed in DMF (400 mL), and propionyl chloride (molar ratio of propionyl chloride to fiber was 6:1) and pyridine (molar ratio of pyridine to propionyl chloride was 3:1) were added dropwise. The mixture was reacted at 100 °C for one hour to obtain propionylated modified fibers. 0.18 g of modified fibers (octane-dry weight) was weighed and diluted with ethanol to 80 mL. The mixture was stirred at room temperature for 1 h. The propionylated fiber suspension was then filtered to form paper, yielding propionylated fiber paper.

[0082] S2. Preparation of the polymer dip-coating solution: 0.18 g of benzophenone monomer and 0.12 g of azobisisobutyronitrile (DIBON) were mixed in DMF (30 mL), and then methyl methacrylate (3.2 mL) was added. The mixture was reacted at 60 °C for 16 h under a N2 atmosphere. The sample was purified three times by dissolving in tetrahydrofuran (THF), precipitating with ethanol, and centrifuging repeatedly. The sample was then dried in an oven (40 °C) to obtain the final product (white powder), which is polymethyl methacrylate containing benzophenone monomer.

[0083] Take 0.90 g of benzophenone-containing polymethyl methacrylate at oven-dry weight, add 20 mL of N,N-dimethylformamide, and stir at room temperature until the polymer dissolves to obtain a polymer solution with a concentration of 45 mg / mL.

[0084] S3. Impregnation and coating: Immerse the propionylated paper prepared in step S1 into the polymer impregnation solution prepared in S2, remove it after 1 minute, and place it in a fume hood to air dry at room temperature.

[0085] S4. UV curing: Place the sample from S3 in a UV curing chamber for reaction. The light wavelength is 365 nm and the irradiation time is 40 min for each side.

[0086] S5. Washing and Drying: Wash the ungrafted polymer in the membrane with N,N-dimethylformamide from the sample in S4, air dry at room temperature, and then dry at 40℃ for 24 h to obtain a coating weight of 4.52 g / m. 2 Polymer-coated paper-based lithium-ion battery separator.

[0087] The thermal dimensional stability of the polymer-coated paper-based lithium-ion battery separator prepared in this embodiment was tested, and the results showed that it did not shrink at 120°C.

[0088] This embodiment tests the constant current cycle charge-discharge performance of a polymer-coated paper-based lithium-ion battery separator on a Blue Electric Battery testing system. The polymer-coated paper-based lithium-ion battery separator, along with a lithium anode and lithium iron phosphate (LiFePO4) cathode material, is assembled into a lithium-ion battery, and its electrochemical performance is tested. The LiFePO4 cathode material is prepared as follows: LiFePO4 (90 wt%), superP (5 wt%), and polyvinylidene fluoride (PVDF) (5 wt%) are dissolved in N-methyl-2-pyrrolidone (NMP) solvent, thoroughly mixed, coated onto aluminum foil, and dried to form the cathode. A 1M lithium hexafluorophosphate (LiPF6) solution of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) is used as the electrolyte, with a solvent mass ratio of 1:1:1. The half-cell assembled with the polymer-coated paper-based lithium-ion battery separator prepared in this embodiment retained 74.4% of its capacity and achieved an average coulombic efficiency of 98.4% after 600 cycles at 1C.

[0089] Comparative Example 1

[0090] The difference between this comparative example and Example 1 is that the preparation method is as follows:

[0091] S1. Preparation of propionylated modified paper: The pulp fibers were beaten to a freeness of 90°SR. 2.5 g of pretreated pulp (air-dry weight) was weighed and solvent-displaced to replace water with N,N-dimethylformamide (DMF). The displaced pulp was dispersed in DMF (400 mL), and propionyl chloride (molar ratio of propionyl chloride to fiber was 6:1) and pyridine (molar ratio of pyridine to propionyl chloride was 3:1) were added dropwise. The mixture was reacted at 100 °C for one hour to obtain propionylated modified fibers. 0.18 g of modified fibers (air-dry weight) was weighed and diluted with ethanol to 80 mL. The mixture was stirred at room temperature for 1 h. The propionylated fiber suspension was then filtered to form paper, yielding propionylated fiber paper.

[0092] S2. Drying: The prepared propionylated paper was dried at 80℃ for 6 h to obtain a propionylated paper-based separator with a basis weight of 23.5 g / m³. 2 .

[0093] The thermal dimensional stability of the pure paper-based lithium-ion battery separator prepared in this comparative example was tested, and the results showed that it did not shrink at 120℃.

[0094] The constant current cycle charge-discharge performance of a pure paper-based lithium-ion battery separator was tested using a Blue Battery testing system. The pure paper-based lithium-ion battery separator was assembled with a lithium anode and a lithium iron phosphate (LiFePO4) cathode material to form a lithium-ion battery, and its electrochemical performance was tested. The LiFePO4 cathode material was prepared by dissolving LiFePO4 (90 wt%), superP (5 wt%), and polyvinylidene fluoride (PVDF) (5 wt%) in N-methyl-2-pyrrolidone (NMP) solvent, thoroughly mixing, coating onto aluminum foil, and drying to form the cathode. A 1M lithium hexafluorophosphate (LiPF6) solution of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) was used as the electrolyte, with a solvent mass ratio of 1:1:1. The half-cell assembled with the pure paper-based lithium-ion battery separator could only cycle 310 times at 1C.

[0095] Table 1 shows the capacity retention and average coulombic efficiency of polymer-coated paper-based lithium-ion battery separators and pure paper-based lithium-ion battery separators prepared in Examples 1-3 and Comparative Example 1 after 600 cycles at a current density of 1C.

[0096] Table 1 Comparison of test performance of diaphragms

[0097] project Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 <![CDATA[Capacity at 1°C (mAh g -1 )]]> 149.8 134.5 113.1 134.0 128.2 - Capacity retention rate (%) after 600 cycles 76.7 72.9 76.4 71.2 74.4 - Average Coulomb efficiency (%) 93.2 95.6 93.4 95.9 98.4 -

[0098] As shown in Table 1, the polymer-coated paper-based lithium-ion battery separators prepared in Examples 1-5 exhibit higher rate performance, and the assembled half-cells show better capacity retention and coulombic efficiency. The technical principle of this invention is as follows: First, the matrix of the polymer-coated paper-based lithium-ion battery separator is composed of propionylated pulp fibers. Propionylation modification reduces the number of hydroxyl groups in the pulp fibers, thus suppressing side reactions caused by hydroxyl groups to a certain extent. Furthermore, polymer coating increases the number of lithium-ion binding sites in the separator, promoting the binding of lithium ions. + Transmission rate, thereby inducing Li + Uniform deposition extends the lifespan of the separator-assembled battery. Simultaneously, the paper-based battery separator prepared using N,N-dimethylformamide as a solvent exhibits a surface microstructure rich in polymer particles. This morphology effectively reduces the surface roughness of the separator, resulting in better interfacial compatibility between the separator and the electrode, and also helps suppress the growth and penetration of lithium dendrites, thereby further improving the overall performance of the battery. Furthermore, through ultraviolet curing technology, the benzophenone units in the polymer can chemically react with the alkyl groups on the paper substrate surface, thereby fixing the polymer to the paper substrate surface via covalent bonds, improving the bonding strength between the coating and the paper substrate.

[0099] It should be understood that the above description of the preferred embodiments of the present invention is quite detailed, but it should not be considered as a limitation on the scope of patent protection of the present invention. The scope of patent protection of the present invention shall be determined by the appended claims.

Claims

1. A polymer-coated paper-based lithium-ion battery separator, characterized in that, include: A propionylated fiber paper substrate and a polymer coating formed by photocuring reaction and covalently bonded to the surface of the substrate; the polymer coating is formed of polymethyl methacrylate containing benzophenone groups.

2. The polymer-coated paper-based lithium-ion battery separator according to claim 1, characterized in that, The propionylated fiber paper is prepared from propionylated modified fibers; the modified fibers are obtained by propionylation modification of natural pulp fibers or renewable pulp fibers.

3. The polymer-coated paper-based lithium-ion battery separator according to claim 1, characterized in that, The polymer coating has a particulate surface morphology formed by the co-regulation of solvent and fiber, wherein the solvent is N,N-dimethylformamide, N,N-dimethylacetamide or tetrahydrofuran.

4. The polymer-coated paper-based lithium-ion battery separator according to claim 1, characterized in that, The polymer coating has a coating amount of 2.15-4.52 g / m².

5. A method for preparing a polymer-coated paper-based lithium-ion battery separator according to any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Preparation of propionylated fiber paper: Take 0.18 g of propionylated fiber with an oven-dry weight, add ethanol to dilute to 80 mL, stir at room temperature, filter the propionylated fiber suspension into paper, and obtain propionylated fiber paper; (2) Preparation of polymer dip coating solution: Weigh polymethyl methacrylate powder containing benzophenone group as solute, add solvent, and stir at room temperature until the solute is completely dissolved to obtain polymer dip coating solution; the solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide or tetrahydrofuran; (3) Impregnation and coating: Immerse the propionylated paper in the polymer solution, remove it after impregnation, and air dry it at room temperature; (4) UV curing: Place the air-dried sample in a UV curing chamber and turn on the UV lamp for curing; (5) Washing: Use the corresponding solvent to wash the sample to remove unreacted polymers; (6) Drying: The washed sample is first air-dried at room temperature, and then dried to obtain a polymer-coated paper-based lithium-ion battery separator.

6. The preparation method according to claim 5, characterized in that, The method for preparing propionylated fiber in step (1) includes: reacting natural pulp fiber or renewable pulp fiber with propionylating agent to obtain propionylated modified fiber.

7. The preparation method according to claim 5, characterized in that, The specific preparation method of the polymethyl methacrylate containing benzophenone groups in step (2) is as follows: the methyl methacrylate monomer and the monomer containing benzophenone groups are copolymerized to obtain the polymethyl methacrylate copolymer containing benzophenone groups.

8. The preparation method according to claim 5, characterized in that, The monomer of the benzophenone group is prepared by the following method: 0.030 mol to 0.040 mol of 4-hydroxybenzophenone is poured into a flask, 1.1 mol to 1.5 mol of dichloromethane and 0.035 mol to 0.045 mol of triethylamine are added, followed by slow dropwise addition of 0.040 mol to 0.050 mol of methacrylamide chloride. The mixture is stirred at room temperature for 24 h, and then the reaction is stopped. After purification, the product is dried.

9. The preparation method according to claim 5, characterized in that, The concentration of the polymer dip coating solution in step (2) is 15~45 mg / mL.

10. The preparation method according to claim 5, characterized in that, The UV curing time in step (4) is 40 min for each side.

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