A composite flame-retardant diaphragm for lithium batteries and preparation method thereof

Abstract

This application provides a composite flame-retardant separator for lithium batteries and a method for preparing the same. The composite flame-retardant separator comprises a polypropylene separator body; a modified layer is disposed on either side of the polypropylene separator body; the modified layer comprises the following raw materials: polyimide, a flame retardant, alumina, and silica-modified PVA fibers; the silica-modified PVA fibers comprise the following raw materials: PVA, silica sol, ammonium polyphosphate, and silane polyethylene glycol carboxyl groups. By disposing the modified layer on the surface of the polypropylene separator body, the present application improves the separator's flame retardancy.

Description

Technical Field

[0001] The present application relates to the technical field of lithium batteries, and in particular to a composite flame-retardant diaphragm for lithium batteries and a preparation method thereof. Background Art

[0002] Lithium-ion batteries have the advantages of high energy density, long life, and no memory effect. They are widely used in fields such as mobile phones, laptops, and electric vehicles. The safety issues of lithium batteries mainly stem from thermal runaway caused by improper use, which in turn leads to fire safety accidents. Analyzing the source of thermal runaway, there are two main reasons that threaten battery safety. On the one hand, polyolefin separators and carbonate electrolytes have extremely poor thermal stability and are highly flammable. Once the battery is overheated (greater than 120°C), the separator will shrink rapidly, causing the positive and negative electrodes to directly contact each other, forming an internal short circuit, generating a large amount of Joule heat and triggering a domino-like chemical reaction inside the battery.

[0003] The safety of the diaphragm will have a great impact on the safety of the battery, and a high-safety diaphragm must have excellent heat resistance, no obvious shrinkage behavior at high temperatures, and preferably have flame retardant properties; however, the flame retardant efficiency of the diaphragm in related technologies is low.

[0004] Application Contents

[0005] The present application is made in view of the above-mentioned problems, and its object is to provide a composite flame-retardant separator for lithium batteries, which separator has excellent flame-retardant performance.

[0006] Specifically as follows, the first aspect of the present application provides a composite flame-retardant diaphragm for a lithium battery, comprising a polypropylene diaphragm body;

[0007] A modified layer is provided on either side of the polypropylene diaphragm body;

[0008] The modified layer includes the following preparation materials:

[0009] Polyimide, flame retardant, alumina and silica modified PVA fiber;

[0010] The silica-modified PVA fiber comprises the following preparation raw materials:

[0011] PVA, silica sol, ammonium polyphosphate and silane polyethylene glycol carboxyl.

[0012] According to one of the technical solutions of this application, at least the following beneficial effects are achieved:

[0013] The present application forms a composite diaphragm with excellent flame retardant properties by setting a modified layer on the surface of a polypropylene diaphragm; the raw materials for preparing the modified layer in the present application also include polyimide, flame retardant, ammonium polyphosphate and silane polyethylene glycol carboxyl groups, wherein the polyimide itself has high thermal stability and contains rich polar groups on the surface, thereby giving the modified layer excellent high-temperature resistance; the present application also uses silane polyethylene glycol carboxyl groups to modify ammonium polyphosphate, which can improve its dispersibility in the modified layer and facilitate the full dispersion of ammonium polyphosphate in the modified layer. As above, the silane polyethylene glycol carboxyl groups introduce carboxyl groups on the surface of ammonium polyphosphate, and the carboxyl groups interact with the amino residues on the surface of the polyimide, which can anchor the ammonium polyphosphate on the surface of the polyimide, which is beneficial to improving the flame retardant properties of the polyimide.

[0014] According to some embodiments of the present application, the modified layer is provided on both side surfaces of the polypropylene diaphragm body.

[0015] According to some embodiments of the present application, the modified layer includes the following raw materials in parts by weight:

[0016] 100 parts of polyimide, 5 to 7 parts of flame retardant, 2 to 4 parts of aluminum oxide and 12 to 14 parts of silicon dioxide modified PVA fiber.

[0017] According to some embodiments of the present application, the raw materials for preparing the modified layer further include a solvent.

[0018] According to some embodiments of the present application, the silica-modified PVA fiber includes the following preparation raw materials in parts by weight:

[0019] 100 parts of PVA, 10-20 parts of silica sol, 8-15 parts of ammonium polyphosphate and 1-2 parts of silane polyethylene glycol carboxyl.

[0020] According to some embodiments of the present application, the degree of polymerization of the PVA is 15K to 18K.

[0021] According to some embodiments of the present application, the raw materials for preparing the silica-modified PVA fiber also include a solvent.

[0022] According to some embodiments of the present application, the thickness of the polypropylene diaphragm body is 5 μm to 30 μm.

[0023] According to some embodiments of the present application, the flame retardant includes DOPO-melamine.

[0024] The molecular structure of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) contains biphenyl rings and phenanthrene ring structures, especially the side phosphorus groups introduced in the form of cyclic O=PO bonds, which have excellent flame retardant properties; and melamine forms a physical entanglement with the molecular chain of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, which can also play a partial toughening effect.

[0025] DOPO-melamine appears in the form of two-dimensional flakes with large size; ammonium polyphosphate mainly exists in the form of small particles; forming a point-surface combined flame retardant additive; at the same time, melamine can decompose as a gas source to release a large amount of gas to promote the rapid expansion of the carbon layer. The fluffy and porous structure causes a certain temperature gradient between the matrix and the surface of the carbon layer. The surface temperature of the diaphragm is much lower than the flame temperature, which slows down the possibility of further degradation of polyimide and release of combustible gas, while isolating the entry of external oxygen, thereby exerting a good flame retardant effect for a considerable period of time.

[0026] The expansion system composed of DOPO-melamine and ammonium polyphosphate decomposes to generate a large amount of NH3, water vapor and other gases when heated, which do not break through the carbon layer barrier. There is also a synergistic effect between DOPO-melamine and ammonium polyphosphate, which can give full play to the heat insulation, oxygen isolation and smoke suppression effects of the carbon layer, thereby improving the flame retardant properties of the diaphragm.

[0027] According to some embodiments of the present application, the raw materials for preparing the DOPO-melamine include DOPO-OH and melamine.

[0028] According to some embodiments of the present application, the molar ratio of DOPO-OH to melamine is 1:0.9 to 1.1.

[0029] According to some embodiments of the present application, the particle size of the aluminum oxide is 20 nm to 50 nm.

[0030] According to some embodiments of the present application, raw materials for preparing the silica sol include tetraethoxysilane and a catalyst.

[0031] The second aspect of the present application provides a method for preparing the composite flame-retardant separator for a lithium battery according to the first aspect of the present application, comprising the following steps:

[0032] Electrospinning is used to form a modified layer on at least one side of a polypropylene diaphragm body.

[0033] According to some embodiments of the present application, the method for preparing the silica-modified PVA fiber comprises the following steps:

[0034] Mixing silane polyethylene glycol carboxyl, ethanol and water and reacting them to prepare a first mixture;

[0035] The first mixture, ammonium polyphosphate and ethanol are mixed and reacted to prepare modified ammonium polyphosphate;

[0036] Mixing PVA and water to prepare a PVA solution;

[0037] Modified ammonium polyphosphate, PVA solution and silica sol were mixed and then electrospun.

[0038] According to some embodiments of the present application, the method for preparing the flame retardant comprises the following steps:

[0039] DOPO-OH, melamine and water are mixed and reacted.

[0040] According to some embodiments of the present application, the reaction temperature is 60°C to 80°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the present drawings or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present drawings. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0042] Figure 1 It is a schematic diagram of the cross-sectional structure in an embodiment of the present application.

[0043] Description of Figure Numbers:

[0044] 100. Polypropylene diaphragm body; 101. First modified layer; 102. Second modified layer.

[0045] The purpose, features and advantages of this drawing will be further described with reference to the accompanying drawings in conjunction with the embodiments. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is described and illustrated below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are merely used to explain this application and are not intended to limit this application. Based on the embodiments provided in this application, all other embodiments obtained by those of ordinary skill in the art without making any creative work are within the scope of protection of this application.

[0047] Obviously, the following descriptions are merely some examples or embodiments of the present application. Those skilled in the art can apply the present application to other similar scenarios without inventive effort. Furthermore, it is also understood that, although the effort involved in such a development process may be complex and lengthy, for those skilled in the art related to the content disclosed in the present application, changes in design, manufacturing, or production based on the technical content disclosed in the present application are merely conventional technical means and should not be construed as an insufficiency of the content disclosed in the present application.

[0048] However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters or repeated descriptions of substantially identical structures may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. Furthermore, the following description is provided to enable those skilled in the art to fully understand this application and is not intended to limit the subject matter recited in the claims.

[0049] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0050] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0051] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0052] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0053] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0054] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0055] The properties of some raw materials in this application are as follows:

[0056] Alumina, particle size 20nm~50nm.

[0057] The preparation method of DOPO-OH in this application consists of the following steps:

[0058] DOPO (CAS No.: 35948-25-5) and hydrogen peroxide (mass fraction 30%) were mixed and refluxed at 80°C for 6 hours. After the reaction was completed, solid-liquid separation was performed, and the solid phase was collected and dried at 100°C for 12 hours to prepare DOPO-OH.

[0059] DOPO-OH, melamine (the molar ratio of DOPO-OH to melamine is 1:1) and water (melamine) are mixed and reacted at 70°C for 5 hours. After the reaction is completed, the solid phase is collected by filtration and dried at 100°C for 12 hours to obtain DOPO-melamine.

[0060] Example 1

[0061] This embodiment is a composite flame retardant diaphragm for lithium batteries. The cross-sectional results are as follows: Figure 1 As shown, it includes a polypropylene diaphragm body 100 (Celgard2500, thickness of 25 μm);

[0062] A first modified layer 101 is provided on one side of the polypropylene diaphragm body 100;

[0063] The other side of the polypropylene diaphragm body 100 is provided with a second modified layer 102;

[0064] The first modified layer 101 and the second modified layer 102 are prepared using the same raw materials and methods;

[0065] The modified layers (i.e., the first modified layer and the second modified layer) include the following preparation materials:

[0066] 100 parts of polyimide (soluble polyimide, PY5006T, Suzhou Pinyu Optoelectronics Technology Co., Ltd.), 6 parts of flame retardant (DOPO-melamine), 3 parts of aluminum oxide, and 13 parts of silica-modified PVA fibers;

[0067] The preparation method of the composite flame-retardant separator for lithium batteries in this embodiment comprises the following steps:

[0068] S1. Preparation of modified slurry:

[0069] Polyimide, flame retardant, alumina, silica-modified PVA fiber and solvent (N,N-dimethylacetamide (DMAC) and methyl pyrrolidone (NMP) volume ratio of 8:2, solvent to polyimide mass ratio of 5:1) were mixed uniformly to prepare a modified slurry;

[0070] S2. Electrospinning the modified slurry onto the surfaces of both sides of a polypropylene separator (20 cm in width and 30 cm in length) to form a first modified layer and a second modified layer, respectively, to obtain a composite flame-retardant separator for a lithium battery.

[0071] The spinning parameters are:

[0072] The relative humidity was 40% and the injection speed was 0.1 mm / min;

[0073] The spinning voltage was 8 KV, the receiving distance was 15 cm, and the temperature was 25°C.

[0074] The silica-modified PVA fiber in this embodiment includes the following raw materials in parts by weight:

[0075] 100 parts of PVA, 18 parts of silica sol, 12 parts of ammonium polyphosphate (CAS No.: 68333-79-9, degree of polymerization of 30-50, purchased from Maclean, product number A875115) and 1.8 parts of silane polyethylene glycol carboxyl (Silane-PEG2000-COOH, Mw is 2000);

[0076] The preparation method of silica-modified PVA fiber in this embodiment consists of the following steps:

[0077] S1. PVA (PVA1799, degree of polymerization of 1.7K, degree of alcoholysis of 99%) was dissolved in water (dissolving temperature was 90°C, dissolving time was 3 hours) to prepare a PVA solution (mass fraction of the PVA solution was 12%).

[0078] TEOS (tetraethoxysilane), H3PO4, and H2O were mixed in a molar ratio of 1:0.01:11 and stirred at 25°C for 12 h to obtain SiO2 sol;

[0079] Silane polyethylene glycol carboxyl, ethanol and distilled water were mixed in a mass ratio of 20, 72 and 8, and stirred at 50° C. for 30 minutes to obtain a first mixture;

[0080] Then, the first mixture, ammonium polyphosphate and ethanol (the mass volume ratio of ammonium polyphosphate to ethanol is 1:3) are mixed, stirred at 60°C for 1 hour, ball milled to a D50 of 1 μm, solid-liquid separation is performed, and the solid phase is dried at 60°C for 4 hours to obtain modified ammonium polyphosphate.

[0081] The PVA solution, SiO2 sol and modified ammonium polyphosphate were mixed and stirred at 1000 r / min for 4 h to obtain an electrospinning solution.

[0082] S2. The electrospinning solution is spun in an electrospinning machine. The parameters of the spinning process are as follows:

[0083] The relative humidity was 40% and the spinning solution injection speed was 0.05 mm / min;

[0084] The spinning voltage was 17 kV, the receiving distance was 25 cm, and the temperature was 25°C.

[0085] After the spinning is completed, the spinning product is placed in an oven at 80°C for 2 hours to dry out the moisture to obtain silica-modified PVA fiber.

[0086] Example 2

[0087] This embodiment is a composite flame-retardant diaphragm for lithium batteries, which differs from Example 1 in that:

[0088] The modified layers (i.e., the first modified layer and the second modified layer) include the following preparation materials:

[0089] 100 parts of polyimide (soluble polyimide, PY5006T, Suzhou Pinyu Optoelectronics Technology Co., Ltd.), 5 parts of flame retardant (DOPO-melamine), 4 parts of aluminum oxide and 12 parts of silica-modified PVA fiber.

[0090] The silica-modified PVA fiber in this embodiment includes the following raw materials in parts by weight:

[0091] 100 parts of PVA, 20 parts of silica sol, 8 parts of ammonium polyphosphate (CAS No.: 68333-79-9, degree of polymerization of 30-50, purchased from Maclean, product number A875115) and 2 parts of silane polyethylene glycol carboxyl (Silane-PEG2000-COOH, Mw is 2000).

[0092] The preparation method of the diaphragm in this embodiment is carried out with reference to Example 1.

[0093] Example 3

[0094] This embodiment is a composite flame-retardant diaphragm for lithium batteries, which differs from Example 1 in that:

[0095] The modified layers (i.e., the first modified layer and the second modified layer) include the following preparation materials:

[0096] 100 parts of polyimide (soluble polyimide, PY5006T, Suzhou Pinyu Optoelectronics Technology Co., Ltd.), 7 parts of flame retardant (DOPO-melamine), 2 parts of aluminum oxide and 14 parts of silica-modified PVA fiber.

[0097] The silica-modified PVA fiber in this embodiment includes the following raw materials in parts by weight:

[0098] 100 parts of PVA, 10 parts of silica sol, 15 parts of ammonium polyphosphate (CAS No.: 68333-79-9, degree of polymerization of 30-50, purchased from Maclean, product number A875115) and 1 part of silane polyethylene glycol carboxyl (Silane-PEG2000-COOH, Mw is 2000).

[0099] The preparation method of the diaphragm in this embodiment is carried out with reference to Example 1.

[0100] Example 4

[0101] This embodiment is a composite flame-retardant diaphragm for lithium batteries, which differs from Example 1 in that:

[0102] The modified layers (i.e., the first modified layer and the second modified layer) include the following preparation materials:

[0103] 100 parts of polyimide (soluble polyimide, PY5006T, Suzhou Pinyu Optoelectronics Technology Co., Ltd.), 7 parts of flame retardant (DOPO-melamine), 4 parts of aluminum oxide and 14 parts of silica-modified PVA fiber.

[0104] The silica-modified PVA fiber in this embodiment includes the following raw materials in parts by weight:

[0105] 100 parts of PVA, 20 parts of silica sol, 15 parts of ammonium polyphosphate (CAS No.: 68333-79-9, degree of polymerization of 30-50, purchased from Maclean, product number A875115) and 2 parts of silane polyethylene glycol carboxyl (Silane-PEG2000-COOH, Mw is 2000).

[0106] The preparation method of the diaphragm in this embodiment is carried out with reference to Example 1.

[0107] Example 5

[0108] This embodiment is a composite flame-retardant diaphragm for lithium batteries, which differs from Example 1 in that:

[0109] The modified layers (i.e., the first modified layer and the second modified layer) include the following preparation materials:

[0110] 100 parts of polyimide (soluble polyimide, PY5006T, Suzhou Pinyu Optoelectronics Technology Co., Ltd.), 5 parts of flame retardant (DOPO-melamine), 2 parts of alumina and 12 parts of silica-modified PVA fiber.

[0111] The silica-modified PVA fiber in this embodiment includes the following raw materials in parts by weight:

[0112] 100 parts of PVA, 10 parts of silica sol, 8 parts of ammonium polyphosphate (CAS No.: 68333-79-9, degree of polymerization of 30-50, purchased from Maclean, product number A875115) and 1 part of silane polyethylene glycol carboxyl (Silane-PEG2000-COOH, Mw is 2000).

[0113] The preparation method of the diaphragm in this embodiment is carried out with reference to Example 1.

[0114] Comparative Example 1

[0115] This comparative example is a separator for lithium batteries, which differs from Example 5 in that:

[0116] The silica-modified PVA fiber in this comparative example includes the following raw materials in parts by weight:

[0117] 100 parts of PVA, 10 parts of silica sol and 8 parts of ammonium polyphosphate (CAS No.: 68333-79-9, degree of polymerization of 30-50, purchased from Maclean, product number A875115).

[0118] The preparation method of silica-modified PVA fiber in this comparative example consists of the following steps:

[0119] S1. PVA (PVA1799, degree of polymerization of 1.7K, degree of alcoholysis of 99%) was dissolved in water (dissolving temperature was 90°C, dissolving time was 3 hours) to prepare a PVA solution (mass fraction of the PVA solution was 12%).

[0120] TEOS (tetraethoxysilane), H3PO4, and H2O were mixed in a molar ratio of 1:0.01:11 and stirred at 25°C for 12 h to obtain SiO2 sol;

[0121] Ammonium polyphosphate was mixed with ethanol (the mass volume ratio of ammonium polyphosphate to ethanol was 1:3), stirred at 60°C for 1 hour, ball milled until D50 was 1 μm, solid-liquid separation was performed, and the solid phase was dried at 60°C for 4 hours to obtain modified ammonium polyphosphate.

[0122] The PVA solution, SiO2 sol and modified ammonium polyphosphate were mixed and stirred at 1000 r / min for 4 h to obtain an electrospinning solution.

[0123] S2. The electrospinning solution is spun in an electrospinning machine. The parameters of the spinning process are as follows:

[0124] The relative humidity was 40% and the spinning solution injection speed was 0.05 mm / min;

[0125] The spinning voltage was 17 kV, the receiving distance was 25 cm, and the temperature was 25°C.

[0126] After the spinning is completed, the spinning product is placed in an oven at 80°C for 2 hours to dry out the moisture to obtain silica-modified PVA fiber.

[0127] Comparative Example 2

[0128] This comparative example is a separator for lithium batteries, which differs from Example 5 in that:

[0129] The modified layers (i.e., the first modified layer and the second modified layer) include the following preparation materials:

[0130] 100 parts of polyimide (soluble polyimide, PY5006T, Suzhou Pinyu Optoelectronics Technology Co., Ltd.), 5 parts of flame retardant (DOPO-melamine), 2 parts of alumina and 12 parts of silica-modified PVA fiber.

[0131] The silica-modified PVA fiber in this comparative example includes the following raw materials in parts by weight:

[0132] 100 parts of PVA, 10 parts of silica sol and 1 part of silane polyethylene glycol carboxyl (Silane-PEG2000-COOH, Mw is 2000).

[0133] The preparation method of silica-modified PVA fiber in this comparative example consists of the following steps:

[0134] S1. PVA (PVA1799, degree of polymerization of 1.7K, degree of alcoholysis of 99%) was dissolved in water (dissolving temperature was 90°C, dissolving time was 3 hours) to prepare a PVA solution (mass fraction of the PVA solution was 12%).

[0135] TEOS (tetraethoxysilane), H3PO4, and H2O were mixed in a molar ratio of 1:0.01:11 and stirred at 25°C for 12 h to obtain SiO2 sol;

[0136] The PVA solution, SiO2 sol and silane polyethylene glycol carboxyl were mixed and stirred at 1000 r / min for 4 h to obtain the electrospinning solution.

[0137] S2. The electrospinning solution is spun in an electrospinning machine. The parameters of the spinning process are as follows:

[0138] The relative humidity was 40% and the spinning solution injection speed was 0.05 mm / min;

[0139] The spinning voltage was 17 kV, the receiving distance was 25 cm, and the temperature was 25°C.

[0140] After the spinning is completed, the spinning product is placed in an oven at 80°C for 2 hours to dry out the moisture to obtain silica-modified PVA fiber.

[0141] Comparative Example 3

[0142] This comparative example is a separator for lithium batteries, which differs from Example 5 in that:

[0143] DOPO-melamine was replaced by DOPO (equal mass).

[0144] Comparative Example 4

[0145] This comparative example is a separator for lithium batteries, which differs from Example 5 in that:

[0146] DOPO-melamine was replaced by melamine (equal mass).

[0147] Comparative Example 5

[0148] This comparative example is a separator for lithium batteries, which differs from Example 5 in that:

[0149] The silica-modified PVA fiber in this comparative example includes the following raw materials in parts by weight:

[0150] 100 parts of PVA and 10 parts of silica sol.

[0151] The preparation method of silica-modified PVA fiber in this comparative example consists of the following steps:

[0152] S1. PVA (PVA1799, degree of polymerization of 1.7K, degree of alcoholysis of 99%) was dissolved in water (dissolving temperature was 90°C, dissolving time was 3 hours) to prepare a PVA solution (mass fraction of the PVA solution was 12%).

[0153] TEOS (tetraethoxysilane), H3PO4, and H2O were mixed in a molar ratio of 1:0.01:11 and stirred at 25°C for 12 h to obtain SiO2 sol;

[0154] The PVA solution and SiO2 sol were mixed and stirred at 1000 r / min for 4 h to obtain an electrospinning solution.

[0155] S2. The electrospinning solution is spun in an electrospinning machine. The parameters of the spinning process are as follows:

[0156] The relative humidity was 40% and the spinning solution injection speed was 0.05 mm / min;

[0157] The spinning voltage was 17 kV, the receiving distance was 25 cm, and the temperature was 25°C.

[0158] After the spinning is completed, the spinning product is placed in an oven at 80°C for 2 hours to dry out the moisture to obtain silica-modified PVA fiber.

[0159] The performance of the diaphragms prepared in the above examples and comparative examples was tested, and the results are shown in Table 1. The test items are as follows:

[0160] Membrane rupture temperature:

[0161] The membrane rupture temperature is measured by the resistance mutation method, and the point where the resistance suddenly increases is the membrane rupture temperature;

[0162] LOI Test:

[0163] According to the ASTM D2863-23 test standard, the standard size of the specimen is 130 × 6.5 × 3.2 mm 3 ;.

[0164] Table 1

[0165]

[0166]

[0167] As can be seen from Table 1, the membrane rupture temperatures and LOI values of the separators in Examples 1 to 5 are high; they have excellent high temperature resistance and flame retardancy, which is beneficial to improving the safety performance of lithium batteries.

[0168] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A composite flame-retardant diaphragm for lithium batteries, characterized in that: including a polypropylene diaphragm body; A modified layer is provided on either side of the polypropylene diaphragm body; The modified layer includes the following preparation materials: Polyimide, flame retardant, alumina and silica modified PVA fiber; The silica-modified PVA fiber comprises the following preparation raw materials: PVA, silica sol, ammonium polyphosphate and silane polyethylene glycol carboxyl; The ammonium polyphosphate and the silane polyethylene glycol carboxyl group react to obtain carboxyl-modified ammonium polyphosphate; The flame retardant includes DOPO-melamine.

2. The composite flame-retardant separator for lithium batteries according to claim 1, characterized in that: The modified layer includes the following raw materials in parts by weight: 100 parts of polyimide, 5 to 7 parts of flame retardant, 2 to 4 parts of alumina and 12 to 14 parts of silica-modified PVA fiber; And / or, the raw materials for preparing the modified layer further include a solvent.

3. The composite flame-retardant separator for lithium batteries according to claim 1, characterized in that: The silica-modified PVA fiber comprises the following raw materials in parts by weight: 100 parts of PVA, 10-20 parts of silica sol, 8-15 parts of ammonium polyphosphate and 1-2 parts of silane polyethylene glycol carboxyl; And / or, the degree of polymerization of the PVA is 15K~18K; And / or, the raw materials for preparing the silica-modified PVA fiber further include a solvent.

4. The composite flame-retardant separator for lithium batteries according to claim 1, characterized in that: The thickness of the polypropylene diaphragm body is 5 μm to 30 μm.

5. The composite flame-retardant separator for lithium batteries according to claim 1, characterized in that: The raw materials for preparing the DOPO-melamine include DOPO-OH and melamine.

6. The composite flame-retardant separator for lithium batteries according to claim 5, characterized in that: The molar ratio of DOPO-OH to melamine is 1:0.9-1.

1.

7. The composite flame-retardant separator for lithium batteries according to claim 1, characterized in that: The particle size of the aluminum oxide is 20 nm to 50 nm.

8. The composite flame-retardant separator for lithium batteries according to claim 1, characterized in that: The raw materials for preparing the silica sol include tetraethoxysilane and a catalyst.

9. A method for preparing a composite flame-retardant separator for a lithium battery according to any one of claims 1 to 8, characterized in that: The following steps are involved: Electrospinning is used to form a modified layer on at least one side of a polypropylene diaphragm body.

10. The preparation method according to claim 9, characterized in that The preparation method of the silica-modified PVA fiber comprises the following steps: Mixing silane polyethylene glycol carboxyl, ethanol and water and reacting them to prepare a first mixture; The first mixture, ammonium polyphosphate and ethanol are mixed and reacted to prepare modified ammonium polyphosphate; Mixing PVA and water to prepare a PVA solution; Modified ammonium polyphosphate, PVA solution and silica sol were mixed and then electrospun.

11. The preparation method according to claim 9, characterized in that The preparation method of the flame retardant comprises the following steps: mixing DOPO-OH, melamine and water and reacting the mixture.

12. The preparation method according to claim 11, characterized in that The reaction temperature is 60°C to 80°C.

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