High-rate and high-safety paper-based lithium ion battery diaphragm as well as preparation method and application thereof

Abstract

The invention discloses a high-rate and high-safety paper-based lithium ion battery diaphragm as well as a preparation method and application thereof, and belongs to the technical field of lithium ion battery diaphragms. The lithium battery diaphragm is composed of paper, cellulose ester and inorganic micro-nano particles. Paper pulp fibers serve as raw materials, paper is prepared through a wet process, and then one face or two faces of the paper is / are coated with an inorganic micro-nano particle / cellulose ester solution to prepare the high-magnification lithium ion battery diaphragm. The high-rate and high-safety lithium ion battery diaphragm disclosed by the invention has excellent thermal dimensional stability, electrolyte wettability, stable high-rate cycle performance and high-temperature closed-cell cycle performance, and has huge application potential in the field of lithium ion batteries.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery separator technology, specifically relating to a high-rate and high-safety lithium-ion battery separator, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries are widely used in electric vehicles, electronic products, and other fields due to their high energy density and long lifespan. The separator, as a key component of lithium-ion batteries, largely determines their performance.

[0003] Currently, commercially available separators are mainly polyolefin separators, such as polyethylene, polypropylene, and their composites. Polyolefin separators have hydrophobic surfaces and poor wettability to the electrolyte, which severely affects the electrochemical performance of the assembled lithium-ion battery. Chinese patent CN 107369802 A discloses a method for preparing a cellulose-coated lithium-ion battery separator, comprising: taking appropriate amounts of water-soluble cellulose derivatives and polyvinyl alcohol to prepare uniform aqueous solutions, mixing and stirring them evenly; adding appropriate amounts of nanocellulose to the uniformly mixed aqueous solution to prepare a uniform aqueous suspension, stirring for a period of time until the system is homogeneous; coating the uniformly mixed coating onto the surface of the polyolefin separator, then quickly placing it in an anhydrous ethanol bath for a period of time, and finally drying it under vacuum to obtain the cellulose-coated lithium-ion battery separator. This patent improves the hydrophobicity problem of the polyethylene separator surface, resulting in a coated separator with excellent performance.

[0004] However, the above patents do not consider the thermal stability of the battery separator. According to existing publicly available research reports, commercial polyolefin separators can experience thermal runaway due to internal short circuits caused by thermal melting and shrinkage at high temperatures, potentially leading to fires or explosions in lithium-ion batteries, posing a safety hazard. As lithium-ion batteries develop towards larger sizes and higher energy densities, their safety has received widespread attention. Therefore, high thermal stability, safety, and good affinity with the electrolyte are crucial for achieving safe and high-performance lithium-ion batteries. Summary of the Invention

[0005] To address the above shortcomings, this invention provides a method for preparing a high-rate and high-safety lithium-ion battery separator. The prepared paper-based lithium battery separator exhibits excellent high-rate cycle performance and thermal stability. The specific technical solution is as follows: A method for preparing a high-rate and high-safety lithium-ion battery separator involves first wet-processing pulp fibers, followed by a coating process to produce the high-rate and high-safety lithium-ion battery separator. The specific preparation steps include: (1) Preparation of pulp fiber: The fiber pulp is mechanically ground to different degrees of beating using an ultra-micro pulverizer to obtain pulp fiber; (2) Paper preparation: Pulp fibers are added to water and then dispersed by a fiber standard dissociator to prepare a pulp fiber suspension of a certain concentration. Paper is then prepared by wet papermaking process. (3) Preparation of cellulose ester: Microcrystalline cellulose was dried at 100-110°C for 10-12 h, and then added to a round-bottom flask containing pyridine and mixed evenly; the temperature was raised to 90-110°C, and then acyl chloride was added and reacted for 1-2 h to obtain a reaction solution; the reaction solution was added dropwise to ethanol and centrifuged to obtain a precipitate; for further purification, the precipitate was dissolved in tetrahydrofuran, and then precipitated in 5 times the volume of ethanol, and centrifuged to obtain a precipitate. The dissolution-precipitation-separation operation was repeated 2-3 times; finally, the precipitate was dried at 45-60°C for 10-12 h to obtain cellulose ester; (4) Preparation of cellulose ester / inorganic micro / nanoparticle blend: Dissolve cellulose ester in tetrahydrofuran, add inorganic micro / nanoparticles, and stir at room temperature for a certain time to obtain cellulose ester / inorganic micro / nanoparticle blend. (5) The cellulose ester / inorganic micro-nano particle blend liquid is coated onto the paper surface by a coating machine, and then quickly immersed in an ethanol solution to obtain a composite film; (6) The composite membrane is dried at a certain temperature for a certain time to obtain a high-rate and high-safety paper-based lithium battery separator.

[0006] Preferably, in the above preparation method, the pulp fiber is natural pulp fiber.

[0007] Preferably, in the above preparation method, the pulp fiber beating degree is 50~80°SR.

[0008] Preferably, in the above preparation method, the pulp suspension contains pulp fibers with a mass fraction of 0.10~2.00wt%.

[0009] Preferably, in the above preparation method, the basis weight of the paper is 20~60 g / m². 2 .

[0010] Preferably, in the above preparation method, the acyl chloride is one or more of stearoyl chloride, oleoyl chloride, and linolenic acid chloride.

[0011] Preferably, in the above preparation method, in step (3), the ratio of microcrystalline cellulose, pyridine, and acyl chloride is 1g:40~60mL:10~14mL.

[0012] Preferably, in the above preparation method, in step (4), the mass percentage concentration of cellulose ester dissolved in tetrahydrofuran is 5%~20%.

[0013] Preferably, in the above preparation method, in step (4), the weight ratio of cellulose ester and inorganic micro / nano particles is 1:1 to 8, and the inorganic micro / nano particles are one or more of tin dioxide, zinc oxide, kaolin, montmorillonite, lithium carbonate, barium carbonate, strontium carbonate, etc.

[0014] Preferably, in the above preparation method, in step (4), the stirring time is 10-60 min and the stirring speed is 500-1500 rpm.

[0015] Preferably, in the above preparation method, the inorganic micro / nano particles have a particle size of one or more of the range of 50 to 5000 nm.

[0016] Preferably, in the above preparation method, the drying temperature of the composite film is 60~80°C.

[0017] Preferably, in the above preparation method, the drying time of the composite membrane is 1-3 hours; based on the weight of the dried composite membrane, the basis weight of the cellulose ester / inorganic micro / nano particle coating on the diaphragm is 1-20 g / m². -2 .

[0018] On the other hand, the present invention also provides a high-rate and high-safety lithium-ion battery separator, which is prepared by the above-described preparation method.

[0019] On the other hand, the present invention also provides the application of the above-mentioned high-rate and high-safety lithium-ion battery separator in the preparation of lithium-ion batteries.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The lithium-ion battery separator prepared by this invention combines polymer materials and inorganic materials, and has good thermal dimensional stability, interfacial compatibility, excellent high-rate cycling performance, and closed-cell performance at high temperatures. It can significantly improve the safety of the battery and has great application potential in the field of lithium-ion batteries.

[0021] 2. The lithium battery separator of the present invention contains a large number of polar ester groups (-COO-) and hydroxyl groups (-OH) on the cellulose ester molecular chain. These groups have good affinity with common organic electrolyte solvents (such as ethylene carbonate and dimethyl carbonate); the good wettability of the cellulose ester / inorganic micro / nano particle coating reduces the contact resistance between the electrode and the separator, which is beneficial to lithium ion concentration. The rapid transport of lithium ions enhances the battery's rate performance. Simultaneously, cellulose ester is a thermoplastic polymer; at normal temperatures, the cellulose ester membrane is rigid with a uniform microporous structure, allowing lithium ions to pass through smoothly. When the temperature rises to its thermal pore-closing initiation temperature, the cellulose ester polymer chains begin to soften and undergo macroscopic melting. This molten polymer flows and fills the microporous channels originally provided for ions, physically blocking these pores. The membrane itself does not shrink, exhibiting thermal dimensional stability, thus effectively cutting off the current and stopping or drastically slowing down the electrochemical reaction. This effectively prevents thermal runaway chain reactions, preventing battery combustion and explosion, and significantly improving battery safety. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 The 1H NMR spectrum of the cellulose ester prepared in Example 1 of this invention; Figure 2 The infrared spectra of the cellulose ester and microcrystalline cellulose prepared in Example 1 of this invention are shown below. Figure 3 This is a scanning electron microscope image of the battery separator prepared in Example 4 of the present invention before heating; Figure 4 This is a scanning electron microscope image of the battery separator prepared in Example 4 of the present invention after heating; Figure 5 This is a scanning electron microscope image of the battery separator prepared in Comparative Example 2 of the present invention before heating; Figure 6 This is a scanning electron microscope image of the battery separator prepared in Comparative Example 2 of the present invention after heating; Figure 7 This is a scanning electron microscope image of the battery separator prepared in Comparative Example 3 of the present invention before heating; Figure 8 This is a scanning electron microscope image of the battery separator prepared in Comparative Example 3 of the present invention after heating. Detailed Implementation

[0024] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. Unless otherwise defined, all technical terms used below have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of the present invention. Unless otherwise specifically stated, all raw materials, reagents, instruments, and equipment used in the present invention are commercially available or can be prepared by existing methods.

[0025] The fiber pulp used in the following examples and comparative examples is bleached bagasse sulfate pulp with a freeness of 18°SR, manufactured by Guangxi Zhuang Autonomous Region Yongkai Liujing Paper Industry Group Co., Ltd.

[0026] Example 1 A method for preparing a high-rate and high-safety lithium-ion battery separator, the specific preparation process of which includes: (1) Preparation of pulp fiber with a freeness of 55°SR: The pulp with a freeness of 18°SR is ground by mechanical grinding for 7000 revolutions to obtain pulp fiber with a freeness of 55°SR; (2) Paper preparation: Pulp fibers with a freeness of 55°SR are added to water and then dispersed using a fiber standard dissociator to prepare a pulp fiber suspension with a mass percentage concentration of 0.1%. Subsequently, a paper with a basis weight of 50 g / m³ is prepared by wet papermaking process. 2 Paper; (3) Preparation of cellulose ester: 1 gram of microcrystalline cellulose was dried at 105 °C for 12 h, and then added to a round-bottom flask containing pyridine (50 mL) and mixed thoroughly. The temperature was raised to 100 °C, and then stearoyl chloride (12.5 mL) was added and reacted for 1 h. The reaction solution was then added dropwise to ethanol (250 mL), and the precipitate was separated by centrifugation. To further purify the precipitate, it was dissolved in tetrahydrofuran, and then the precipitate was precipitated in 5 times its volume of ethanol. This operation was repeated 3 times. Finally, the sample was dried at 50 °C for 12 h to obtain cellulose ester; (4) Preparation of cellulose ester / tin dioxide particle blend: Dissolve 1g of cellulose ester in 10mL of tetrahydrofuran, add 1g of tin dioxide, stir at room temperature for 2h to obtain cellulose ester / tin dioxide particle blend; (5) The cellulose ester / tin dioxide particle blend was coated onto one side of the substrate material using a coating machine, and then immersed in ethanol for 10 min. (6) Drying: The composite membrane is dried at 60°C for 1 hour to obtain the battery separator. The basis weight of the cellulose ester / tin dioxide particle coating is 5.1 gm. -2 .

[0027] The hydrogen spectrum of the cellulose ester prepared in this embodiment is shown in the figure. Figure 1 Infrared spectrum (see) Figure 2 .

[0028] The thermal dimensional stability and electrolyte wettability of the high-rate lithium-ion battery separator prepared in this embodiment were tested. The test results showed that the separator did not shrink at 190°C and the contact angle of the electrolyte on the paper separator surface was 0.

[0029] This embodiment tests the constant current cycle charge-discharge performance of a lithium-ion battery separator on a Blue Electric Battery testing system. The 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 half-cell assembled with the lithium-ion battery separator prepared in this embodiment retains 90% of its capacity and achieves an average coulombic efficiency of 97% after 500 cycles at 5C.

[0030] Example 2 A method for preparing a high-rate and high-safety lithium-ion battery separator, the specific preparation process of which is as follows: (1) Preparation of pulp fiber with a freeness of 55°SR: The pulp with a freeness of 18°SR is ground by a mechanical grinder for 7000 revolutions to obtain pulp fiber with a freeness of 55°SR; (2) Paper preparation: Pulp fibers with a freeness of 55°SR are added to water and then dispersed using a fiber standard dissociator to prepare a pulp fiber suspension with a mass percentage concentration of 0.1%. Subsequently, a paper with a basis weight of 50 g / m³ is prepared by wet papermaking process. 2 Paper; (3) Preparation of cellulose ester: 1 gram of microcrystalline cellulose was dried at 105 °C for 12 h, and then added to a round-bottom flask containing pyridine (50 mL) and mixed thoroughly. The temperature was raised to 100 °C, and then stearoyl chloride (12.5 mL) was added and reacted for 1 h. The reaction solution was then added dropwise to ethanol (250 mL), and the precipitate was separated by centrifugation. To further purify the precipitate, it was dissolved in tetrahydrofuran, and then the precipitate was precipitated in 5 times its volume of ethanol. This operation was repeated 3 times. Finally, the sample was dried at 50 °C for 12 h to obtain cellulose ester; (4) Preparation of cellulose ester / tin dioxide particle blend: Dissolve 1g of cellulose ester in 10mL of tetrahydrofuran, add 2g of tin dioxide, and stir at room temperature for 2h; (5) The cellulose ester / tin dioxide particle blend was coated onto one side of the substrate material using a coating machine, and then immersed in ethanol for 10 min. (6) Drying: The composite membrane is dried at 60°C for 1 hour to obtain the target membrane. The basis weight of the cellulose ester / tin dioxide particle coating is 6.2 gm. -2 .

[0031] The thermal dimensional stability and electrolyte wettability of the high-rate lithium-ion battery separator prepared in this embodiment were tested. The results showed that the paper separator did not shrink at 190°C and the contact angle of the electrolyte on the paper separator surface was 0.

[0032] This embodiment tests the constant current cycle charge-discharge performance of a lithium-ion battery separator on a Blue Battery testing system. The 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 half-cell assembled with the lithium-ion battery separator prepared in this embodiment retains 89% of its capacity and achieves an average coulombic efficiency of 98% after 500 cycles at 5C.

[0033] Example 3 The preparation process of the high-rate lithium-ion battery separator described in this invention is as follows: (1) Preparation of pulp fiber with a freeness of 55°SR: The pulp with a freeness of 18°SR is ground by a mechanical grinder for 7000 revolutions to obtain pulp fiber with a freeness of 55°SR; (2) Paper preparation: Pulp fibers with a freeness of 55°SR are added to water and then dispersed using a fiber standard dissociator to prepare a pulp fiber suspension with a mass percentage concentration of 0.1%. Subsequently, a paper with a basis weight of 50 g / m³ is prepared by wet papermaking process. 2 Paper; (3) Preparation of cellulose ester: 1 g of microcrystalline cellulose was dried at 105 °C for 12 h, and then added to a round-bottom flask containing pyridine (50 mL) and mixed thoroughly. The temperature was raised to 100 °C, and then stearoyl chloride (12.5 mL) was added and reacted for 1 h. The reaction solution was then added dropwise to ethanol (250 mL), and the precipitate was separated by centrifugation. To further purify the precipitate, it was dissolved in tetrahydrofuran, and then the precipitate was precipitated in 5 times its volume of ethanol. This operation was repeated 3 times. Finally, the sample was dried at 50 °C for 12 h to obtain cellulose ester.

[0034] (4) Preparation of cellulose ester / tin dioxide particle blend: Dissolve 1g of cellulose ester in 10mL of tetrahydrofuran, add 3g of tin dioxide, and stir at room temperature for 2h; (5) The cellulose ester / tin dioxide particle blend was coated onto one side of the substrate material using a coating machine, and then immersed in ethanol for 10 min. (6) Drying: The composite membrane is dried at 60°C for 1 hour to obtain the target membrane. The coating basis weight is 6.5 gm. -2 The thermal dimensional stability and electrolyte wettability of the high-rate lithium-ion battery separator prepared in this embodiment were tested. The results showed that the paper separator did not shrink at 190°C and the contact angle of the electrolyte on the paper separator surface was 0.

[0035] This embodiment tests the constant current cycle charge-discharge performance of a lithium-ion battery separator on a Blue Electric Battery testing system. The 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 half-cell assembled with the lithium-ion battery separator prepared in this embodiment retains 95% of its capacity and achieves an average coulombic efficiency of 97% after 500 cycles at 5C.

[0036] Example 4 The preparation process of the high-rate lithium-ion battery separator described in this invention is as follows: (1) Preparation of pulp fiber with a freeness of 55°SR: The pulp with a freeness of 18°SR is ground by a mechanical grinder for 7000 revolutions to obtain pulp fiber with a freeness of 55°SR; (2) Paper preparation: Pulp fibers with a freeness of 55°SR are added to water and then dispersed using a fiber standard dissociator to prepare a pulp fiber suspension with a mass percentage concentration of 0.1%. Subsequently, a paper with a basis weight of 50 g / m³ is prepared by wet papermaking process. 2 Paper; (3) Preparation of cellulose ester: 1 g of microcrystalline cellulose was dried at 105 °C for 12 h, and then added to a round-bottom flask containing pyridine (50 mL) and mixed thoroughly. The temperature was raised to 100 °C, and then stearoyl chloride (12.5 mL) was added and reacted for 1 h. The reaction solution was then added dropwise to ethanol (250 mL), and the precipitate was separated by centrifugation. To further purify the precipitate, it was dissolved in tetrahydrofuran, and then the precipitate was precipitated in 5 times its volume of ethanol. This operation was repeated 3 times. Finally, the sample was dried at 50 °C for 12 h to obtain cellulose ester.

[0037] (4) Preparation of cellulose ester / tin dioxide particle blend: Dissolve 1g of cellulose ester in 10mL of tetrahydrofuran, add 4g of tin dioxide, stir at room temperature for 2h to obtain cellulose ester / tin dioxide particle blend; (5) The cellulose ester / tin dioxide particle blend was coated onto one side of the substrate material using a coating machine, and then immersed in ethanol for 10 min. (6) Drying: The composite membrane was dried at 60°C for 1 hour to obtain the target membrane. The basis weight of the cellulose ester / tin dioxide particle coating was 7.1 gm. -2 .

[0038] The thermal dimensional stability and electrolyte wettability of the high-rate lithium-ion battery separator prepared in this embodiment were tested. The results showed that the paper separator did not shrink at 190°C and the contact angle of the electrolyte on the paper separator surface was 0.

[0039] This embodiment tests the constant current cycle charge-discharge performance of a lithium-ion battery separator on a Blue Battery testing system. The 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 half-cell assembled with the lithium-ion battery separator prepared in this embodiment retains 87% of its capacity and achieves an average coulombic efficiency of 96% after 500 cycles at 5C.

[0040] The diaphragm from Example 4 was heated at 190°C for 30 minutes to obtain a closed-pore diaphragm. No dimensional shrinkage occurred after heating. Scanning electron microscope images of the diaphragm before and after heating are shown below. Figure 3 and Figure 4 The composite membrane pores close after heating, indicating that the battery separator of the present invention has obvious thermal pore-closing performance.

[0041] The thermal dimensional stability and electrolyte wettability of the heated high-rate lithium-ion battery separator were tested. The results showed that the paper separator did not shrink at 190℃ and the contact angle of the electrolyte on the paper separator surface was 0.

[0042] The heated high-rate lithium-ion battery separator was tested for its constant current cycle charge-discharge performance on a Blue Battery testing system. The lithium-ion battery separator was then assembled with a lithium anode and lithium iron phosphate (LiFePO4) cathode material to form a lithium-ion battery, and its electrochemical performance was tested. The half-cell assembled with the heated lithium-ion battery separator maintained 85% capacity and achieved an average coulombic efficiency of 96% after 500 cycles at 5C.

[0043] Example 5 The preparation process of the high-rate lithium-ion battery separator described in this invention is as follows: (1) Preparation of pulp fiber with a freeness of 62°SR: The pulp with a freeness of 18°SR is ground for 9500 revolutions by a mechanical grinder to obtain pulp fiber with a freeness of 62°SR; (2) Paper preparation: Pulp fibers with a freeness of 62°SR were added to water and then dispersed using a fiber standard dissociator to prepare a pulp fiber suspension with a mass percentage concentration of 0.2%. Subsequently, a paper with a basis weight of 40 g / m³ was prepared by wet papermaking process. 2 Paper; (3) Preparation of cellulose ester: 1 g of microcrystalline cellulose was dried at 105°C for 12 h, and then added to a round-bottom flask containing pyridine (50 mL) and mixed thoroughly. The temperature was raised to 100 °C, and then stearoyl chloride (12.5 mL) was added and reacted for 1 h. The reaction solution was then added dropwise to ethanol (250 mL), and the precipitate was separated by centrifugation. To further purify the precipitate, it was dissolved in tetrahydrofuran and then precipitated in 5 times its volume of ethanol. This process was repeated 3 times. Finally, the sample was dried at 50 °C for 12 h to obtain cellulose ester.

[0044] (4) Preparation of cellulose ester / strontium carbonate particle blend: Dissolve 1.5g of cellulose ester in 12mL of tetrahydrofuran, add 2g of strontium carbonate, and stir at room temperature for 0.5h; (5) The cellulose ester / strontium carbonate particle blend was coated onto one side of the matrix material using a coating machine, and then immersed in ethanol for 10 min. (6) Drying: The composite membrane is dried at 70°C for 1 hour to obtain the target membrane. The basis weight of the cellulose ester / strontium carbonate particle coating is 5.8 gm. -2 .

[0045] The thermal dimensional stability and electrolyte wettability of the high-rate lithium-ion battery separator prepared in this embodiment were tested. The results showed that the paper separator did not shrink at 190°C and the contact angle of the electrolyte on the paper separator surface was 0.

[0046] This embodiment tests the constant current cycle charge-discharge performance of a lithium-ion battery separator on a Blue Battery testing system. The 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 half-cell assembled with the lithium-ion battery separator prepared in this embodiment retains 91% of its capacity and achieves an average coulombic efficiency of 97% after 500 cycles at 5C.

[0047] Comparative Example 1 This comparative example uses Celgard as a control: A lithium-ion battery was assembled using the Celgard lithium-ion battery separator, along with a lithium anode and a lithium iron phosphate (LiFePO4) cathode material, and its electrochemical performance was tested. In this embodiment, the half-cell assembled with the lithium-ion battery separator maintained a capacity retention of 72% and achieved an average coulombic efficiency of 95% after 500 cycles at 5C.

[0048] Thermal dimensional stability and electrolyte wettability were tested on the Celgard lithium-ion battery separator. The results showed that the separator shrinkage rate was greater than 90% at 190℃, and the contact angle of the electrolyte on the separator surface was 40°. o .

[0049] Comparative Example 2 This comparative example differs from Example 4 in that it does not include step (3), and in step (4), cellulose propanesulfonate is used instead of cellulose ester. Otherwise, it is the same as Example 4.

[0050] The diaphragm of this comparative example was heated at 190°C for 30 minutes. Figure 5 and Figure 6 The images show scanning electron microscope (SEM) images of the diaphragm before and after heating. As can be seen from the images, the diaphragm in this comparative example does not have thermally closed-pore properties.

[0051] Comparative Example 3 This comparative example differs from Example 4 in that it does not include step (3), and in step (4), cellulose butyrate is used instead of cellulose ester. Otherwise, it is the same as Example 4.

[0052] The diaphragm of this comparative example was heated at 190°C for 30 minutes. Figure 7 and Figure 8 The images show scanning electron microscope (SEM) images of the diaphragm before and after heating. As can be seen from the images, the diaphragm in this comparative example does not have thermally closed-pore properties.

[0053] The thermal dimension tests for the above embodiments and comparative examples were as follows: the samples were cut into 1.8cm round pieces, placed in an oven and heated to 190℃, and kept at that temperature for 30 minutes; the electrolyte wettability was measured using a contact angle tester.

[0054] The lithium iron phosphate (LiFePO4) cathode material in the assembled lithium-ion batteries of the above embodiments and comparative examples is composed of 90% lithium iron phosphate, 5% PVDF, and 5% carbon black by mass percentage. The electrolyte is composed of LiPF6, ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC), with a weight ratio of 1:1:1. The concentration of LiPF6 in the electrolyte is 1M.

[0055] Table 1 shows the initial discharge capacity, capacity retention, average coulombic efficiency, thermal shrinkage at 190°C, and electrolyte wettability of the high-rate lithium-ion battery composite separators and Celgard lithium-ion battery separators prepared in Examples 1-5 and Comparative Example 1 after 500 cycles at a current density of 5C.

[0056] Table 1 Comparison of test performance of diaphragms

[0057] As shown in Table 1, compared with Comparative Example 1, the high-rate lithium-ion battery separators prepared in Examples 1-4 have higher initial discharge capacity, capacity retention rate, coulombic efficiency, thermal stability, and better wettability to electrolyte. At the same time, the battery separator of the present invention has obvious thermal pore-closing performance, the current is effectively cut off, the electrochemical reaction stops or slows down sharply, thereby effectively preventing the occurrence of thermal runaway chain reaction and improving the safety performance of the battery.

[0058] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for preparing a high rate and high safety lithium ion battery separator, characterized in that, The paper pulp fiber is firstly prepared by wet papermaking, and then a high-rate and high-safety lithium ion battery separator is prepared by a coating process; The specific preparation steps include: (1) preparing paper pulp fiber: the fiber slurry is mechanically ground by a super micro grinder to obtain paper pulp fiber; (2) preparing paper: the paper pulp fiber is dispersed in water to prepare a paper pulp fiber suspension, and then a paper is prepared by a wet papermaking process; (3) preparing cellulose ester: the microcrystalline cellulose is dried at 100-110°C for 10-12h, and then mixed with pyridine uniformly; the temperature is increased to 90-110°C, and then the acyl chloride is added to react for 1-2h to obtain a reaction solution; the reaction solution is dropped into ethanol, and centrifuged to obtain a precipitate; the precipitate is dried to obtain cellulose ester; (4) preparing cellulose ester / inorganic micro-nano particle blend: the cellulose ester is dissolved in tetrahydrofuran, and the inorganic micro-nano particle is added and stirred to obtain a cellulose ester / inorganic micro-nano particle blend; (5) the cellulose ester / inorganic micro-nano particle blend is coated on the surface of the paper by a coating machine, and then quickly immersed in an ethanol solution to obtain a composite film; the composite film is dried to obtain a high-rate and high-safety paper-based lithium ion battery separator.

2. The production method according to claim 1, characterized by, The paper pulp fiber is natural paper pulp fiber, and the beating degree of the paper pulp fiber is 50-80°SR.

3. The preparation method according to claim 1, characterized in that, In the step (2), the mass fraction of the pulp fibers in the pulp fiber suspension is 0.10-2.00 wt%; the grammage of the paper is 20-60 g / m 2 .

4. The method of claim 1, wherein, In step (3), the ratio of microcrystalline cellulose, pyridine and acyl chloride is 1g:40-60mL:10-14mL.

5. The preparation method according to claim 1, characterized in that, In step (3), the acyl chloride is one or more of stearoyl chloride, oleoyl chloride and linoleoyl chloride, the drying temperature of the precipitate is 45-60°C, and the drying time is 10-12h.

6. The preparation method according to claim 2, characterized in that, In step (4), the mass percentage concentration of the cellulose ester dissolved in tetrahydrofuran is 5%-20%.

7. The preparation method according to claim 2, characterized in that, In step (4), the weight ratio of the cellulose ester and the inorganic micro-nano particle is 1:1-8, and the stirring time is 10-60min; the inorganic micro-nano particle is one or more of tin dioxide, zinc oxide, kaolin, montmorillonite, lithium carbonate, barium carbonate and strontium carbonate, and the particle size of the inorganic micro-nano particle is 50-5000nm.

8. The preparation method according to claim 2, characterized in that, In the step (5), the drying temperature of the composite film is 60-80°C, the drying time is 1-3h, and the coating grammage is 1-20g / m -2 .

9. A high rate and high safety lithium ion battery separator, characterized by, The battery separator is prepared by the preparation method of any one of claims 1-8.

10. The high-rate and high-safety lithium ion battery separator of claim 9 in the preparation of a lithium ion battery.

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