A method for preparing a separator for improving impact resistance of a battery

Abstract

The application relates to the technical field of diaphragms and discloses a diaphragm preparation method for improving the impact resistance of a battery; the method comprises the following operation steps: S1: (1) adding a barrier material and sodium alginate into deionized water respectively to obtain solution A and solution B; (2) uniformly mixing the solution A and the solution B, adding nanocellulose fibrils and the solution A, ultrasonic treating at a frequency of 80-100 kHz for 5-10 minutes, and then hydrothermally reacting at 70-80 DEG C for 5-6 hours to obtain nanocellulose fibrils coated with a barrier layer; S2: uniformly mixing modified polytetrafluoroethylene fillers and the nanocellulose fibrils coated with the barrier layer with polyolefin particles, melt plasticizing, low-temperature extruding, cooling and then performing shaping annealing to obtain a sheet-shaped polyolefin-based film; and S3: bidirectionally stretching the sheet-shaped polyolefin-based film, high-temperature shaping, cooling and then obtaining a diaphragm.

Description

Technical Field

[0001] This invention relates to the field of battery separator technology, specifically a method for preparing a separator to improve the impact resistance of a battery. Background Technology

[0002] In recent years, the new energy industry has gradually replaced traditional energy in many fields. Cars equipped with lithium batteries with high energy density and excellent cycle performance have entered thousands of households. However, during battery operation, unexpected collisions and compressions will bring huge challenges to lithium batteries. Instantaneous impacts can usually cause the battery to smoke, catch fire, or even explode.

[0003] When a battery is subjected to large-area compression, and the compression pressure reaches a certain level, one of the main reasons for battery fire and explosion is that the separator is compressed. During compression, the micropores are stretched and enlarged, causing the positive and negative electrode active materials to come into direct contact and short-circuit. Furthermore, because the separator becomes thinner, small lithium dendrites may also puncture it under strong compression. Therefore, there is an urgent need to develop a battery separator that can effectively prevent batteries from catching fire and exploding due to instantaneous impact. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a separator that improves the impact resistance of a battery, thereby solving the problems mentioned in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for preparing a separator to improve the impact resistance of a battery includes the following steps:

[0007] S1: (1) Add the barrier material and sodium alginate to deionized water to obtain solution A and solution B; (2) Mix solution A and solution B evenly, add nanocellulose filaments and solution A, sonicate at 100kHz for 5-10 minutes, and then hydrothermally react at 70-80℃ for 5-6 hours to obtain nanocellulose filaments coated with barrier layer;

[0008] S2: The modified polytetrafluoroethylene filler and the barrier layer coated nanocellulose filaments are uniformly mixed with polyolefin particles, melt-plasticized, low-temperature extruded, cooled and then shaped and annealed to obtain a sheet-like polyolefin base film.

[0009] S3: The sheet-like polyolefin-based film is biaxially stretched, high-temperature shaped, and cooled to obtain a diaphragm.

[0010] More preferably, the concentration of solution A is 1-2 wt%, and the concentration of solution B is 3 wt%; the raw material of the nanocellulose filaments coated by the barrier layer includes the following components: by mass parts, 70-120 parts of solution A, 15-30 parts of solution B, and 5-20 parts of nanocellulose filaments.

[0011] The raw materials of the sheet-like polyolefin-based film include the following components: by mass, 5-20 parts modified polytetrafluoroethylene, 5-30 parts of nanocellulose filaments coated with a barrier layer, and 80-100 parts of polyolefin particles.

[0012] In a more optimized configuration, in S2, the temperature for melting and plasticizing is 180~240℃; the temperature for low-temperature extrusion is 190~220℃; and the temperature for shaping and annealing is 100~120℃. In S3, the temperature for high-temperature shaping is 130~150℃.

[0013] A more optimized method for preparing the nanocellulose filaments is as follows: plant cellulose is added to a nitric acid solution and mixed evenly, reacted at 15~30℃ for 6~12 hours, the pH is adjusted to neutral, washed with deionized water, and dried to obtain oxidized cellulose; a 0.2wt% cellulose suspension is prepared, subjected to high-intensity microfluidic homogenization treatment, and dried to obtain nanocellulose filaments.

[0014] In a more optimized configuration, the concentration of the nitric acid solution is 1-2 wt%; the aspect ratio of the oxidized cellulose is 5-50; the pressure of the high-intensity microjets is 70-200 MPa; and the aspect ratio of the nanocellulose filaments is 50-1000.

[0015] More preferably, the barrier material includes one of guar gum and its derivatives, or gum arabic and its derivatives.

[0016] A more optimized method for preparing the modified polytetrafluoroethylene filler is as follows: (1) Add the coupling agent to anhydrous ethanol and mix, add polytetrafluoroethylene resin, glass fiber and graphite and stir for 1 to 1.5 hours to obtain a mixture; (2) Sinter the mixture at 300°C, then add it to zinc acetate ethanol solution, ball mill and mix for 50 to 60 minutes, and heat treat at 100 to 150°C for 4 to 5 hours to obtain zinc-polytetrafluoroethylene filler; (3) Add the zinc-polytetrafluoroethylene filler to anhydrous ethanol and mix evenly, add imidazole blend under ultrasonic conditions of 80 to 100W, wash with ethanol 1 to 2 times to obtain modified polytetrafluoroethylene filler.

[0017] In a more optimized form, the raw materials of the mixture include the following components: by mass parts, 85-95 parts polytetrafluoroethylene, 1-5 parts glass fiber, 1-5 parts graphite, and 0.1-0.3 parts coupling agent; the concentration of the zinc acetate ethanol solution is 0.26-0.42 wt%, the concentration of the zinc-polytetrafluoroethylene filler is 0.2-0.35 wt%, and the concentration of the imidazole blend is 4-6 wt%.

[0018] A more optimized method for preparing imidazole blends is as follows: (1) Potassium carbonate is added to DMF and mixed evenly, tannic acid and 5,6-dichlorobenzamide are added, heated at 130~140ºC for 16~18 hours, cooled to room temperature, and filtered to obtain filtrate; the filtrate is concentrated under reduced pressure, deionized water is added, and stirred in an ice-water bath for 1~2 hours, filtered, washed, dried and purified to obtain benzimidazole tannic acid; (2) Benzimidazole tannic acid and 2-methylimidazole are added to ethanol, mixed evenly, and dried to obtain imidazole blends.

[0019] In a more optimized form, the raw material for the benzimidazole tannic acid comprises the following components: 3-4 parts by mass of tannic acid, 0.2-0.4 parts by mass of potassium carbonate, and 0.3-0.5 parts by mass of 5,6-dichlorobenzimidazole; the mass ratio of 2-methylimidazole to benzimidazole tannic acid is (2-4):1.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] This invention employs high aspect ratio nanofibers of cellulose and modified polytetrafluoroethylene (PTFE) as fillers for polyolefin separator base membranes to enhance the tensile and impact strength of the separator, reduce the planar deformation of the separator when the battery is compressed, and minimize the deformation of the separator micropores. Fluorine in PTFE is a polar atom, and the density of fluorine substituents on the main chain is very high, making internal rotation difficult and resulting in high rigidity. In contrast, cellulose exhibits strong intermolecular interactions, and its six-membered pyran ring structure hinders internal rotation. Furthermore, the formation of intramolecular and intermolecular hydrogen bonds contributes to its high rigidity. Furthermore, the nanofibers with a large aspect ratio can intertwine within the base membrane, further enhancing its strength. Simultaneously, the nanofibers selected in this solution are coated with a barrier layer, which improves the strength of the cellulose fibers while providing good barrier performance. This prevents the separator from swelling and increasing the battery's internal resistance during normal use in the electrolyte. When the battery is subjected to impact or compression, the exposed cross-section of the cellulose fibers after being stretched and broken will rapidly absorb liquid and swell, increasing the separator thickness, reducing the distance between the positive and negative electrodes, and minimizing the risk of short circuits.

[0022] In the proposed method, polytetrafluoroethylene resin, glass fiber, and graphite are uniformly mixed and then calcined at 300°C to obtain modified polytetrafluoroethylene filler. Among them, glass fiber can improve the tensile strength and compressive strength of the separator, making the separator less prone to deformation or breakage during use. In addition, glass fiber has high thermal stability, which can improve the high temperature resistance of the powder, thereby improving the safety of the battery.

[0023] In this scheme, graphite is added to the modified polytetrafluoroethylene (PTFE) filler to improve the conductivity and mechanical properties of the separator, enhance battery safety, and reduce internal resistance. Because PTFE is highly hydrophobic, it is calcined at 300°C to roughen the surface of the modified PTFE filler or increase its porosity, providing more contact points with the electrolyte and improving wetting, thereby optimizing internal resistance. However, its effect is limited. To further improve separator performance, the scheme involves uniformly mixing PTFE resin, glass fiber, and graphite, calcining at 300°C, then ball-milling and heat-treating with zinc acetate solution to obtain zinc-PTFE. Zinc ions are then coated onto its surface, and 2-methylimidazole is added to coat the zinc-PTFE surface with a layer of MOFs (Metal-Oxide-Foil) material. This MOF material improves the hydrophobicity of PTFE and the impact resistance of the separator.

[0024] To further improve the wetting effect and impact resistance of the diaphragm, the proposed method involves mixing 2-methylimidazole and benzimidazole tannic acid in a certain proportion to form an imidazole mixture, which is then coordinated with zinc on zinc-polytetrafluoroethylene to obtain a modified polytetrafluoroethylene filler.

[0025] In this scheme, DMF is used as a solvent and potassium carbonate as a catalyst to induce a nucleophilic addition reaction between the hydroxyl groups on tannic acid and the halogens on 5,6-dichlorobenzamide to form ether bonds, yielding benzimidazole tannic acid. The rigid structure of benzimidazole can act as a ligand to form coordinate bonds with metal ions, thereby enhancing the mechanical strength and thermal stability of MOFs materials on the zinc-polytetrafluoroethylene surface. The active groups on tannic acid can improve the interfacial compatibility between the modified polytetrafluoroethylene filler, polyolefin particles, and the nanocellulose filaments coated with the barrier layer, as well as the wettability of the membrane, thus improving mechanical properties and reducing internal resistance. Detailed Implementation

[0026] In the following detailed embodiments, "parts" refers to parts by weight. The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] The preparation method of the imidazole blend is as follows: (1) 0.3 parts of potassium carbonate are added to DMF and mixed evenly, 3 parts of tannic acid and 0.4 parts of 5,6-dichlorobenzamide are added, heated at 140ºC for 18 hours, cooled to room temperature, and filtered to obtain filtrate; the filtrate is concentrated under reduced pressure, deionized water is added, stirred under ice-water bath for 2 hours, filtered, washed and dried to obtain crude product; the crude product and activated carbon are added to methanol and refluxed for 2 hours, filtered with diatomaceous earth, the filtrate is distilled under reduced pressure, stirred at room temperature for 2 hours, stirred under ice-water bath for 1 hour, filtered, washed 3 times with ice methanol, and dried at 60℃ to obtain benzimidazole tannic acid; (2) benzimidazole tannic acid and 2-methylimidazole are added to ethanol, mixed evenly, and dried to obtain imidazole blend; the mass ratio of 2-methylimidazole to imidazole tannic acid is 3:1.

[0028] Example 1: A method for preparing a separator to improve the impact resistance of a battery, comprising the following steps;

[0029] S1: (1) Add plant cellulose to a 2wt% nitric acid solution and mix evenly. React at 25°C for 10 hours, adjust the pH to neutral, wash with deionized water to remove residual acid and other impurities, and dry to obtain oxidized cellulose with an aspect ratio of (5~50); add oxidized cellulose to deionized water to prepare a 0.2wt% cellulose suspension, perform high-intensity micro-jet homogenization treatment under a pressure of 200MPa, and dry to obtain nanocellulose filaments with an aspect ratio of 50~1000;

[0030] (2) Hydroxypropyl guar gum and sodium alginate were added to deionized water to obtain 2wt% solution A and 3wt% solution B; (3) 40 parts of solution A and 30 parts of solution B were mixed evenly, 10 parts of nanocellulose filaments and 30 parts of solution A were added, and ultrasonic treatment was carried out at a frequency of 100kHz for 10 minutes. Then, hydrothermal reaction was carried out at 80℃ for 6 hours and dried to obtain nanocellulose filaments coated with barrier layer.

[0031] S2: (1) Add 0.2 parts of coupling agent to anhydrous ethanol and mix evenly. Add 90 parts of polytetrafluoroethylene resin, 3 parts of glass fiber and 3 parts of graphite and mix evenly for 1 hour. Dry to obtain a mixture. Calcine the mixture at 300°C for 2 hours and then ball mill it to obtain modified polytetrafluoroethylene filler.

[0032] (2) 10 parts of modified polytetrafluoroethylene filler and 15 parts of barrier layer-coated nanocellulose filaments are uniformly mixed with 80 parts of polypropylene particles (polypropylene particles, model: F5006, Yanshan Petrochemical), melt-plasticized, low-temperature extruded, cooled and then annealed to obtain sheet-like polypropylene base film; wherein, the melt-plasticization temperature is 220℃; the low-temperature extrusion temperature is 200℃; and the annealing temperature is 110℃.

[0033] S3: The sheet-like polyolefin-based film is biaxially stretched, high-temperature shaped, and cooled to obtain a diaphragm; the high-temperature shaped temperature is 150℃.

[0034] Example 2 is based on Example 1, except that in S1 (2), the concentration of solution A is 1 wt%, and the hydrothermal reaction is carried out at 40°C for 2 hours.

[0035] S1: (1) Plant cellulose is added to 1wt% nitric acid solution and mixed evenly. The mixture is reacted at 25°C for 10 hours. The pH is adjusted to neutral. The mixture is washed with deionized water to remove residual acid and other impurities. The mixture is then dried to obtain oxidized cellulose with an aspect ratio of (5~50). The oxidized cellulose is added to deionized water to prepare a 0.2wt% cellulose suspension. The suspension is subjected to high-intensity microfluidic homogenization treatment under a pressure of 200MPa and then dried to obtain nanocellulose filaments with an aspect ratio of 50~1000.

[0036] (2) Hydroxypropyl guar gum and sodium alginate were added to deionized water to obtain 1wt% solution A and 3wt% solution B; (3) 40 parts of solution A and 30 parts of solution B were mixed evenly, 10 parts of nanocellulose filaments and 30 parts of solution A were added, and ultrasonic treatment was carried out at a frequency of 100kHz for 10 minutes. Then, hydrothermal reaction was carried out at 40℃ for 2 hours and dried to obtain nanocellulose filaments coated with barrier layer.

[0037] S2: (1) Add 0.2 parts of coupling agent to anhydrous ethanol and mix evenly. Add 90 parts of polytetrafluoroethylene resin, 3 parts of glass fiber and 3 parts of graphite and mix evenly for 1 hour. Dry to obtain a mixture. Calcine the mixture at 300°C for 2 hours and then ball mill it to obtain modified polytetrafluoroethylene filler.

[0038] (2) 10 parts of modified polytetrafluoroethylene filler and 15 parts of barrier layer-coated nanocellulose filaments are uniformly mixed with 80 parts of polyolefin particles (polypropylene particles, model: F5006, Yanshan Petrochemical), melt-plasticized, low-temperature extruded, cooled and then annealed to obtain a sheet-like polyolefin base film; wherein, the melt-plasticization temperature is 220℃; the low-temperature extrusion temperature is 200℃; and the annealing temperature is 110℃.

[0039] S3: The sheet-like polyolefin-based film is biaxially stretched, high-temperature shaped, and cooled to obtain a diaphragm; the high-temperature shaped temperature is 150℃.

[0040] Example 3 is based on Example 1, except that the pressure of the high-intensity microfluidic homogenization treatment in S1 (1) is 5 to 20 MPa, and the aspect ratio of the nanocellulose filaments is 5 to 100.

[0041] S1: (1) Add plant cellulose to a 2wt% nitric acid solution and mix evenly. React at 25°C for 10 hours, adjust the pH to neutral, wash with deionized water to remove residual acid and other impurities, and dry to obtain oxidized cellulose with an aspect ratio of (5~50); add oxidized cellulose to deionized water to prepare a 0.2wt% cellulose suspension, perform high-intensity micro-jet homogenization treatment under a pressure of 20MPa, and dry to obtain nanocellulose filaments with an aspect ratio of 5~100;

[0042] (2) Hydroxypropyl guar gum and sodium alginate were added to deionized water to obtain 2wt% solution A and 3wt% solution B; (3) 40 parts of solution A and 30 parts of solution B were mixed evenly, 10 parts of nanocellulose filaments and 30 parts of solution A were added, and ultrasonic treatment was carried out at a frequency of 100kHz for 10 minutes. Then, hydrothermal reaction was carried out at 80℃ for 6 hours and dried to obtain nanocellulose filaments coated with barrier layer.

[0043] S2: (1) Add 0.2 parts of coupling agent to anhydrous ethanol and mix evenly. Add 90 parts of polytetrafluoroethylene resin, 3 parts of glass fiber and 3 parts of graphite and mix evenly for 1 hour. Dry to obtain a mixture. Calcine the mixture at 300°C for 2 hours and then ball mill it to obtain modified polytetrafluoroethylene filler.

[0044] (2) 10 parts of modified polytetrafluoroethylene filler and 15 parts of barrier layer-coated nanocellulose filaments were uniformly mixed with 80 polyolefin particles (polypropylene particles, model: F5006, Yanshan Petrochemical), melt-plasticized, low-temperature extruded, cooled and then annealed to obtain a sheet-like polyolefin base film; wherein, the melt-plasticization temperature was 220℃; the low-temperature extrusion temperature was 200℃; and the annealing temperature was 110℃.

[0045] S3: The sheet-like polyolefin-based film is biaxially stretched, high-temperature shaped, and cooled to obtain a diaphragm; the high-temperature shaped temperature is 150℃.

[0046] Example 4 is based on Example 1, except that in S2 (1), there are 80 parts of polytetrafluoroethylene resin, 15 parts of glass fiber, 10 parts of graphite, and 0.3 parts of coupling agent;

[0047] S1: (1) Add plant cellulose to a 2wt% nitric acid solution and mix evenly. React at 25°C for 10 hours, adjust the pH to neutral, wash with deionized water to remove residual acid and other impurities, and dry to obtain oxidized cellulose with an aspect ratio of (5~50); add oxidized cellulose to deionized water to prepare a 0.2wt% cellulose suspension, perform high-intensity micro-jet homogenization treatment under a pressure of 200MPa, and dry to obtain nanocellulose filaments with an aspect ratio of 50~1000;

[0048] (2) Hydroxypropyl guar gum and sodium alginate were added to deionized water to obtain 2wt% solution A and 3wt% solution B; (3) 40 parts of solution A and 30 parts of solution B were mixed evenly, 10 parts of nanocellulose filaments and 30 parts of solution A were added, and ultrasonic treatment was carried out at a frequency of 100kHz for 10 minutes. Then, hydrothermal reaction was carried out at 80℃ for 6 hours and dried to obtain nanocellulose filaments coated with barrier layer.

[0049] S2: (1) Add 0.3 parts of coupling agent to anhydrous ethanol and mix evenly. Add 80 parts of polytetrafluoroethylene resin, 15 parts of glass fiber and 10 parts of graphite and mix evenly for 1 hour. Dry to obtain a mixture. Calcine the mixture at 300°C for 2 hours and then ball mill it to obtain modified polytetrafluoroethylene filler.

[0050] (2) 10 parts of modified polytetrafluoroethylene filler and 15 parts of barrier layer-coated nanocellulose filaments are uniformly mixed with 80 parts of polyolefin particles (polypropylene particles, model: F5006, Yanshan Petrochemical), melt-plasticized, low-temperature extruded, cooled and then annealed to obtain a sheet-like polyolefin base film; wherein, the melt-plasticization temperature is 220℃; the low-temperature extrusion temperature is 200℃; and the annealing temperature is 110℃.

[0051] S3: The sheet-like polyolefin-based film is biaxially stretched, high-temperature shaped, and cooled to obtain a diaphragm; the high-temperature shaped temperature is 150℃.

[0052] Example 5 is based on Example 1, and the mixture is further modified after sintering;

[0053] S1: (1) Add plant cellulose to a 2wt% nitric acid solution and mix evenly. React at 25°C for 10 hours, adjust the pH to neutral, wash with deionized water to remove residual acid and other impurities, and dry to obtain oxidized cellulose with an aspect ratio of (5~50); add oxidized cellulose to deionized water to prepare a 0.2wt% cellulose suspension, perform high-intensity micro-jet homogenization treatment under a pressure of 200MPa, and dry to obtain nanocellulose filaments with an aspect ratio of 50~1000;

[0054] (2) Hydroxypropyl guar gum and sodium alginate were added to deionized water to obtain 2wt% solution A and 3wt% solution B; (3) 40 parts of solution A and 30 parts of solution B were mixed evenly, 10 parts of nanocellulose filaments and 30 parts of solution A were added, and ultrasonic treatment was carried out at a frequency of 100kHz for 10 minutes. Then, hydrothermal reaction was carried out at 80℃ for 6 hours and dried to obtain nanocellulose filaments coated with barrier layer.

[0055] S2: (1) Add 0.2 parts of coupling agent to anhydrous ethanol and mix evenly. Add 90 parts of polytetrafluoroethylene resin, 3 parts of glass fiber and 3 parts of graphite and mix evenly for 1 hour. Dry to obtain a mixture. Calcine the mixture at 300°C for 2 hours. After cooling, add it to 0.28wt% zinc acetate ethanol solution, ball mill and mix for 60 minutes. Heat treat at 120°C for 4 hours to obtain zinc-polytetrafluoroethylene filler. (2) Add zinc-polytetrafluoroethylene filler to anhydrous ethanol and mix evenly. Add imidazole blend under 100W ultrasonic conditions and sonicate for 8 minutes. Wash twice with ethanol to obtain modified polytetrafluoroethylene filler.

[0056] The concentration of zinc-PTFE filler was 0.32 wt%, and the concentration of imidazole blend was 4.8 wt%.

[0057] (3) 10 parts of modified polytetrafluoroethylene filler and 15 parts of barrier layer-coated nanocellulose filaments are uniformly mixed with 80 parts of polyolefin particles (polypropylene particles, model: F5006, Yanshan Petrochemical), melt-plasticized, low-temperature extruded, cooled and then annealed to obtain a sheet-like polyolefin base film; wherein, the melt-plasticization temperature is 220℃; the low-temperature extrusion temperature is 200℃; and the annealing temperature is 110℃.

[0058] S3: The sheet-like polyolefin-based film is biaxially stretched, high-temperature shaped, and cooled to obtain a diaphragm; the high-temperature shaped temperature is 150℃.

[0059] Comparative Example 1 is based on Example 1, except that the plant cellulose is not fibrillated;

[0060] S1: (1) Hydroxypropyl guar gum and sodium alginate were added to deionized water to obtain 2wt% solution A and 3wt% solution B; (2) 40 parts of solution A and 30 parts of solution B were mixed evenly, 10 parts of plant cellulose and 30 parts of solution A were added, and the mixture was ultrasonically treated at a frequency of 100kHz for 10 minutes, and then hydrothermally reacted at 80℃ for 6 hours. After drying, plant cellulose with barrier layer coating was obtained.

[0061] S2: (1) Add 0.2 parts of coupling agent to anhydrous ethanol and mix evenly. Add 90 parts of polytetrafluoroethylene resin, 3 parts of glass fiber and 3 parts of graphite and mix evenly for 1 hour. Dry to obtain a mixture. Calcine the mixture at 300°C for 2 hours and then ball mill it to obtain modified polytetrafluoroethylene filler.

[0062] (2) 10 parts of modified polytetrafluoroethylene filler and 15 parts of plant cellulose coated with barrier layer are uniformly mixed with 80 parts of polyolefin particles (polypropylene particles, model: F5006, Yanshan Petrochemical), melt-plasticized, low-temperature extruded, cooled and then annealed to obtain sheet-like polyolefin base film; wherein, the melt-plasticization temperature is 220℃; the low-temperature extrusion temperature is 200℃; and the annealing temperature is 110℃.

[0063] S3: The sheet-like polyolefin-based film is biaxially stretched, high-temperature shaped, and cooled to obtain a diaphragm; the high-temperature shaped temperature is 150℃.

[0064] Comparative Example 2 is based on Example 1, except that the nanocellulose filaments are not coated with a barrier layer;

[0065] S1: (1) Add plant cellulose to a 2wt% nitric acid solution and mix evenly. React at 25°C for 10 hours, adjust the pH to neutral, wash with deionized water to remove residual acid and other impurities, and dry to obtain oxidized cellulose with an aspect ratio of (5~50); add oxidized cellulose to deionized water to prepare a 0.2wt% cellulose suspension, perform high-intensity micro-jet homogenization treatment under a pressure of 200MPa, and dry to obtain nanocellulose filaments with an aspect ratio of 50~1000;

[0066] S2: (1) Add 0.2 parts of coupling agent to anhydrous ethanol and mix evenly. Add 90 parts of polytetrafluoroethylene resin, 3 parts of glass fiber and 3 parts of graphite and mix evenly for 1 hour. Dry to obtain a mixture. Calcine the mixture at 300°C for 2 hours and then ball mill it to obtain modified polytetrafluoroethylene filler.

[0067] (2) 10 parts of modified polytetrafluoroethylene filler and 15 parts of nanocellulose filaments were uniformly mixed with 80 parts of polyolefin particles (polypropylene particles, model: F5006, Yanshan Petrochemical), melt-plasticized, low-temperature extruded, cooled and then annealed to obtain a sheet-like polyolefin base film; wherein, the melt-plasticization temperature was 220℃; the low-temperature extrusion temperature was 200℃; and the annealing temperature was 110℃.

[0068] S3: The sheet-like polyolefin-based film is biaxially stretched, high-temperature shaped, and cooled to obtain a diaphragm; the high-temperature shaped temperature is 150℃.

[0069] Comparative Example 3 is based on Example 1, except that polytetrafluoroethylene is used directly as a filler;

[0070] S1: (1) Add plant cellulose to a 2wt% nitric acid solution and mix evenly. React at 25°C for 10 hours, adjust the pH to neutral, wash with deionized water to remove residual acid and other impurities, and dry to obtain oxidized cellulose with an aspect ratio of (5~50); add oxidized cellulose to deionized water to prepare a 0.2wt% cellulose suspension, perform high-intensity micro-jet homogenization treatment under a pressure of 200MPa, and dry to obtain nanocellulose filaments with an aspect ratio of 50~1000;

[0071] (2) Hydroxypropyl guar gum and sodium alginate were added to deionized water to obtain 2wt% solution A and 3wt% solution B; (3) Solution A and solution B were mixed evenly, nanocellulose filaments and solution A were added, ultrasonic treatment was performed at a frequency of 100kHz for 10 minutes, hydrothermal reaction was carried out at 80℃ for 6 hours, and dried to obtain nanocellulose filaments coated with barrier layer;

[0072] S2: 10 parts of polytetrafluoroethylene filler and 15 parts of barrier layer-coated nanocellulose filaments are uniformly mixed with 80 parts of polyolefin particles (polypropylene particles, model: F5006, Yanshan Petrochemical), melt-plasticized, low-temperature extruded, cooled, and then annealed to obtain a sheet-like polyolefin-based film; wherein, the melt-plasticization temperature is 220℃; the low-temperature extrusion temperature is 200℃; and the annealing temperature is 110℃.

[0073] S3: The sheet-like polyolefin-based film is biaxially stretched, high-temperature shaped, and cooled to obtain a diaphragm; the high-temperature shaped temperature is 150℃.

[0074] Comparative Example 4 is based on Example 1, except that no nanocellulose filaments are added;

[0075] S1: (1) Add 0.2 parts of coupling agent to anhydrous ethanol and mix evenly. Add 90 parts of polytetrafluoroethylene resin, 3 parts of glass fiber and 3 parts of graphite and mix evenly for 1 hour. Dry to obtain a mixture. Calcine the mixture at 300°C for 2 hours and then ball mill it to obtain modified polytetrafluoroethylene filler.

[0076] (2) 10 parts of modified polytetrafluoroethylene filler and 80 parts of polyolefin particles (polypropylene particles, model: F5006, Yanshan Petrochemical) are uniformly mixed, melt-plasticized, low-temperature extruded, cooled and then annealed to obtain sheet-like polyolefin base film; wherein, the melting and plasticizing temperature is 220℃; the low-temperature extrusion temperature is 200℃; and the annealing temperature is 110℃.

[0077] S2: The sheet-like polyolefin-based film is biaxially stretched, high-temperature shaped, and cooled to obtain a diaphragm; the high-temperature shaped temperature is 150℃.

[0078] Comparative Example 5 is based on Example 1, except that no modified polytetrafluoroethylene filler is added;

[0079] S1: (1) Add plant cellulose to a 2wt% nitric acid solution and mix evenly. React at 25°C for 10 hours, adjust the pH to neutral, wash with deionized water to remove residual acid and other impurities, and dry to obtain oxidized cellulose with an aspect ratio of (5~50); add oxidized cellulose to deionized water to prepare a 0.2wt% cellulose suspension, perform high-intensity micro-jet homogenization treatment under a pressure of 200MPa, and dry to obtain nanocellulose filaments with an aspect ratio of 50~1000;

[0080] (2) Hydroxypropyl guar gum and sodium alginate were added to deionized water to obtain 2wt% solution A and 3wt% solution B; (3) 40 parts of solution A and 30 parts of solution B were mixed evenly, 10 parts of nanocellulose filaments and 30 parts of solution A were added, and ultrasonic treatment was carried out at a frequency of 100kHz for 10 minutes, and then hydrothermal reaction was carried out at 80℃ for 6 hours to obtain nanocellulose filaments coated with barrier layer;

[0081] S2: 15 parts of barrier layer-coated nanocellulose filaments are uniformly mixed with 80 parts of polyolefin particles (polypropylene particles, model: F5006, Yanshan Petrochemical), melt-plasticized, low-temperature extruded, cooled, and then shaped and annealed to obtain a sheet-like polyolefin-based film; wherein, the melt-plasticization temperature is 220℃; the low-temperature extrusion temperature is 200℃; and the shaped and annealing temperature is 110℃;

[0082] S3: The sheet-like polyolefin-based film is biaxially stretched, high-temperature shaped, and cooled to obtain a diaphragm; the high-temperature shaped temperature is 150℃.

[0083] Comparative Example 6 is based on Example 1, except that nanocellulose filaments and modified polytetrafluoroethylene filler are not added;

[0084] S1: Polyolefin granules (polypropylene granules, model: F5006, Yanshan Petrochemical) are melt-plasticized, low-temperature extruded, cooled, and then annealed to obtain sheet-like polyolefin-based films; wherein, the melt-plasticization temperature is 220℃; the low-temperature extrusion temperature is 200℃; and the annealing temperature is 110℃.

[0085] S2: The sheet-like polyolefin-based film is biaxially stretched, high-temperature shaped, and cooled to obtain a diaphragm; the high-temperature shaped temperature is 150℃.

[0086] Comparative Example 7 is based on Example 5, but without the addition of imidazole tannins;

[0087] S1: (1) Add plant cellulose to a 2wt% nitric acid solution and mix evenly. React at 25°C for 10 hours, adjust the pH to neutral, wash with deionized water to remove residual acid and other impurities, and dry to obtain oxidized cellulose with an aspect ratio of (5~50); add oxidized cellulose to deionized water to prepare a 0.2wt% cellulose suspension, perform high-intensity micro-jet homogenization treatment under a pressure of 200MPa, and dry to obtain nanocellulose filaments with an aspect ratio of 50~1000;

[0088] (2) Hydroxypropyl guar gum and sodium alginate were added to deionized water to obtain 2wt% solution A and 3wt% solution B; (3) 40 parts of solution A and 30 parts of solution B were mixed evenly, 10 parts of nanocellulose filaments and 30 parts of solution A were added, and ultrasonic treatment was carried out at a frequency of 100kHz for 10 minutes. Then, hydrothermal reaction was carried out at 80℃ for 6 hours and dried to obtain nanocellulose filaments coated with barrier layer.

[0089] S2: (1) Add 0.2 parts of coupling agent to anhydrous ethanol and mix evenly. Add 90 parts of polytetrafluoroethylene resin, 3 parts of glass fiber and 3 parts of graphite and mix evenly for 1 hour. Dry to obtain a mixture. Calcine the mixture at 300°C for 2 hours. After cooling, add it to 0.28wt% zinc acetate ethanol solution, ball mill and mix for 60 minutes. Heat treat at 120°C for 4 hours to obtain zinc-polytetrafluoroethylene filler. (2) Add zinc-polytetrafluoroethylene filler to anhydrous ethanol and mix evenly. Add 2-methylimidazole under 100W ultrasonic conditions and sonicate for 8 minutes. Wash with ethanol twice to obtain modified polytetrafluoroethylene filler.

[0090] The concentration of zinc-PTFE filler was 0.32 wt%, and the concentration of 2-methylimidazole was 4.8 wt%.

[0091] (3) 10 parts of modified polytetrafluoroethylene filler and 15 parts of barrier layer-coated nanocellulose filaments are uniformly mixed with 80 parts of polyolefin particles (polypropylene particles, model: F5006, Yanshan Petrochemical), melt-plasticized, low-temperature extruded, cooled and then annealed to obtain a sheet-like polyolefin base film; wherein, the melt-plasticization temperature is 220℃; the low-temperature extrusion temperature is 200℃; and the annealing temperature is 110℃.

[0092] S3: The sheet-like polyolefin-based film is biaxially stretched, high-temperature shaped, and cooled to obtain a diaphragm; the high-temperature shaped temperature is 150℃.

[0093] Comparative Example 8 is based on Example 5, but the mixture was not calcined at 300°C;

[0094] S1: (1) Plant cellulose is added to nitric acid solution and mixed evenly. The mixture is reacted at 25°C for 10 hours. The pH is adjusted to neutral. The mixture is washed with deionized water to remove residual acid and other impurities. The mixture is then dried to obtain oxidized cellulose with an aspect ratio of (5~50). The oxidized cellulose is added to deionized water to prepare a 0.2wt% cellulose suspension. The suspension is subjected to high-intensity microfluidic homogenization treatment under a pressure of 200MPa and then dried to obtain nanocellulose filaments with an aspect ratio of 50~1000.

[0095] (2) Hydroxypropyl guar gum and sodium alginate were added to deionized water to obtain 2wt% solution A and 3wt% solution B; (3) 40 parts of solution A and 30 parts of solution B were mixed evenly, 10 parts of nanocellulose filaments and 30 parts of solution A were added, and ultrasonic treatment was carried out at a frequency of 100kHz for 10 minutes. Then, hydrothermal reaction was carried out at 80℃ for 6 hours and dried to obtain nanocellulose filaments coated with barrier layer.

[0096] S2: (1) Add 0.2 parts of coupling agent to anhydrous ethanol and mix evenly. Add 90 parts of polytetrafluoroethylene resin, 3 parts of glass fiber and 3 parts of graphite and mix evenly for 1 hour. Dry to obtain a mixture. Add the mixture to 0.28wt% zinc acetate ethanol solution, ball mill and mix for 60 minutes, and heat treat at 120℃ for 4 hours to obtain zinc-polytetrafluoroethylene filler. (2) Add zinc-polytetrafluoroethylene filler to anhydrous ethanol and mix evenly. Add imidazole blend under 100W ultrasonic conditions and sonicate for 8 minutes. Wash with ethanol twice to obtain modified polytetrafluoroethylene filler.

[0097] The concentration of zinc-PTFE filler was 0.32 wt%, and the concentration of imidazole blend was 4.8 wt%.

[0098] (3) 10 parts of modified polytetrafluoroethylene filler and 15 parts of barrier layer-coated nanocellulose filaments are uniformly mixed with 80 parts of polyolefin particles (polypropylene particles, model: F5006, Yanshan Petrochemical), melt-plasticized, low-temperature extruded, cooled and then annealed to obtain a sheet-like polyolefin base film; wherein, the melt-plasticization temperature is 220℃; the low-temperature extrusion temperature is 200℃; and the annealing temperature is 110℃.

[0099] S3: The sheet-like polyolefin-based film is biaxially stretched, high-temperature shaped, and cooled to obtain a diaphragm; the high-temperature shaped temperature is 150℃.

[0100] Testing experiment:

[0101] I. Battery manufacturing;

[0102] (1) Preparation of positive electrode sheet: The ternary active material NCM811, conductive carbon black, and binder PVDF were thoroughly mixed in NMP at a weight ratio of 92:4:4 to obtain a positive electrode slurry; the positive electrode slurry was coated on the current collector, dried, rolled, and die-cut to obtain the positive electrode sheet; the compaction density of the positive electrode active material layer was 3.4 g / cm³. 3 .

[0103] (2) Preparation of negative electrode sheet:

[0104] Artificial graphite (anode active material), SBR (binder), CMC (dispersant), and conductive carbon black were added to water at a weight ratio of 96:2:12:0.8 and thoroughly mixed to obtain a cathode slurry. The cathode slurry was coated onto a current collector, dried, rolled, and die-cut to obtain a cathode electrode sheet. The compacted density of the cathode active layer was 1.65 g / cm³. 3 .

[0105] (3) Preparation of electrolyte:

[0106] Acetyl carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 4:6 as a solvent, and lithium salt LiPF6 was selected as the solute with a concentration of 1 mol / L.

[0107] (4) The positive electrode, separator and negative electrode are stacked in sequence, and after being wound, the cell is obtained. It is placed in the battery casing and added to the electrolyte. After the processes of encapsulation, standing, formation and capacity testing, the sample lithium battery is obtained.

[0108] II. Internal resistance test method:

[0109] Under normal temperature conditions, the lithium batteries prepared in the examples and comparative examples were subjected to a first charge and discharge at a current of 0.33C. The charging was constant current and constant voltage charging, with a termination voltage of 4.2V, a cutoff current of 0.05C, and a discharge termination voltage of 2.5V. The lithium batteries were then left to stand for 12 hours. The batteries were then charged at a constant current and constant voltage at a current of 1C, with a termination voltage of 4.2V and a cutoff current of 0.05C. The batteries were then discharged at a current of 1C, with a discharge termination voltage of 2.5V. The discharge capacity Cb of the cell during the first cycle was recorded. The test object was adjusted to 50% SOC and discharged at a current of 1C for 18 seconds. The battery voltage U2 before discharge termination, the current I, and the battery voltage U1 after the battery voltage stabilized were recorded. The DC resistance R was calculated according to the formula R=(U2-U1) / A, as shown in Table 1.

[0110] III. Compression Test Method:

[0111] (1) Charge the prepared lithium battery to 4.2V at a constant current of 0.5C, and then charge it to 0.05C at a constant voltage. Place the lithium battery to be tested between the two extrusion plates of the extrusion tester, with the two large surfaces of the battery in contact with the extrusion plates. Ensure that the extrusion tester is in operation, and at the same time, pay attention to ensure that the battery does not experience external circuits during the experiment.

[0112] (2) Start the test equipment and squeeze the lithium battery at a speed of 5 mm / s. When the lithium battery is squeezed to 70% of its original size or the squeezing force reaches 30 kN, hold for 5 minutes, release the force, observe and record the changes of the lithium battery during the squeezing process, such as whether smoke, fire, explosion or other situations occur.

[0113] (3) If the lithium battery does not smoke, catch fire, or explode, continue to squeeze until the battery smokes, catches fire, or explodes. Record the limit compression size change rate and limit pressure of the battery at this time, as shown in Table 1.

[0114]

[0115] Table 1

[0116] Conclusions: The study found that in Example 2, the excessively thick barrier layer coating on the nanocellulose filaments, while beneficial for increasing the tensile strength of the separator in the planar direction, was detrimental to exposing the cellulose filaments when the separator was stretched, and also detrimental to the separator thickening when the battery was compressed; in Example 3, the relatively short length-to-diameter ratio of the cellulose filaments was detrimental to increasing the tensile strength of the separator in the planar direction; in Example 4, the slightly insufficient amount of polytetrafluoroethylene resulted in a decrease in the tensile strength of the separator in the planar direction.

[0117] Example 5, based on Example 1, further modified the mixture after sintering, and found that the battery performance was improved. In Comparative Examples 1 to 6, it was found that Comparative Example 2, based on Example 1, differed in that it did not coat the nanocellulose filaments with a barrier layer. Although the battery prepared as a separator had good compression resistance test results, its separator cellulose had absorbed liquid and swelled severely under normal battery conditions, resulting in excessive internal resistance and the battery could not be used normally.

[0118] Comparative Example 7, based on Example 5, did not include benzimidazole tannins; this reduced the impact resistance of the separator, thus leading to a decrease in battery performance. Comparative Example 8, based on Example 5, did not calcine the mixture at 300°C; this reduced the surface roughness of the modified polytetrafluoroethylene filler, resulting in poor wetting and a weaker composite effect with zinc ions, thereby affecting battery performance.

[0119] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for preparing a separator to improve the impact resistance of a battery, characterized in that: The following steps are included: S1: (1) Add the barrier material and sodium alginate to deionized water to obtain solution A and solution B; (2) Mix solution A and solution B evenly, add nanocellulose fibers and solution A, sonicate at a frequency of 80~100kHz for 5~10 minutes, and then hydrothermally react at 70~80℃ for 5~6 hours to obtain nanocellulose fibers coated with barrier layer; S2: The modified polytetrafluoroethylene filler and the barrier layer coated nanocellulose filaments are uniformly mixed with polyolefin particles, melt-plasticized, low-temperature extruded, cooled and then shaped and annealed to obtain a sheet-like polyolefin base film. S3: The sheet-like polyolefin-based film is biaxially stretched, high-temperature shaped, and cooled to obtain a diaphragm; The barrier material includes one of guar gum and its derivatives, and gum arabic and its derivatives; The modified polytetrafluoroethylene filler is prepared as follows: (1) The coupling agent is added to anhydrous ethanol and mixed, polytetrafluoroethylene resin, glass fiber and graphite are added and stirred for 1 to 1.5 hours to obtain a mixture; (2) The mixture is sintered at 200 to 300°C for 1 to 2 hours, cooled and then added to zinc acetate ethanol solution, ball milled and mixed for 50 to 60 minutes, and heat-treated at 100 to 150°C for 4 to 5 hours to obtain zinc-polytetrafluoroethylene filler; (3) Zinc-polytetrafluoroethylene filler is added to anhydrous ethanol and mixed evenly, imidazole blend is added under ultrasonic conditions of 80 to 100W, and ethanol is washed 1 to 2 times to obtain modified polytetrafluoroethylene filler; The preparation method of the imidazole blend is as follows: (1) Add potassium carbonate to DMF and mix evenly, add tannic acid and 5,6-dichlorobenzamide, heat at 130~140ºC for 16~18 hours, cool to room temperature, filter to obtain filtrate; concentrate the filtrate under reduced pressure, add deionized water, stir in an ice-water bath for 1~2 hours, filter, wash, dry and purify to obtain benzimidazole tannic acid; (2) Add benzimidazole tannic acid and 2-methylimidazole to ethanol, mix evenly, dry to obtain imidazole blend.

2. The method for preparing a separator to improve the impact resistance of a battery according to claim 1, characterized in that: The concentration of solution A is 1-2 wt%, and the concentration of solution B is 3 wt%. The raw material for the nanocellulose filaments coated by the barrier layer includes the following components: by mass parts, 70-120 parts of solution A, 15-30 parts of solution B, and 5-20 parts of nanocellulose filaments. The raw materials of the sheet-like polyolefin-based film include the following components: by mass, 5-20 parts of modified polytetrafluoroethylene filler, 5-30 parts of nanocellulose filaments coated with a barrier layer, and 80-100 parts of polyolefin particles.

3. The method for preparing a separator to improve the impact resistance of a battery according to claim 1, characterized in that: In S2, the melting and plasticizing temperature is 180~240℃; the low-temperature extrusion temperature is 190~220℃; the shaping and annealing temperature is 100~120℃; in S3, the high-temperature shaping temperature is 130~150℃.

4. The method for preparing a separator to improve the impact resistance of a battery according to claim 1, characterized in that: The method for preparing the nanocellulose filaments is as follows: plant cellulose is added to nitric acid solution and mixed evenly, reacted at 15~30℃ for 6~12 hours, pH is adjusted to neutral, washed with deionized water, and dried to obtain oxidized cellulose; A 0.2 wt% cellulose suspension was prepared, subjected to high-intensity microfluidic homogenization, and dried to obtain nanocellulose filaments.

5. The method for preparing a separator to improve the impact resistance of a battery according to claim 4, characterized in that: The concentration of the nitric acid solution is 1-2 wt%; the aspect ratio of the oxidized cellulose is 5-50; the pressure of the high-intensity microjet is 70-200 MPa; and the aspect ratio of the nanocellulose filaments is 50-1000.

6. The method for preparing a separator to improve the impact resistance of a battery according to claim 1, characterized in that: The raw materials of the mixture include the following components: by mass, 85-95 parts polytetrafluoroethylene, 1-5 parts glass fiber, 1-5 parts graphite, and 0.1-0.3 parts coupling agent; the concentration of the zinc acetate ethanol solution is 0.26-0.42 wt%, the concentration of the zinc-polytetrafluoroethylene filler is 0.2-0.35 wt%, and the concentration of the imidazole blend is 4-6 wt%.

7. The method for preparing a separator to improve the impact resistance of a battery according to claim 1, characterized in that: The raw materials of the benzimidazole tannic acid include the following components: by mass, 3-4 parts tannic acid, 0.2-0.4 parts potassium carbonate, and 0.3-0.5 parts 5,6-dichlorobenzimidazole; the mass ratio of 2-methylimidazole to benzimidazole tannic acid is (2-4):1.

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