High-safety composite fiber diaphragm as well as preparation method and application thereof
By using a mixture of sepiolite and boron nitrogen to prepare a composite fiber separator, the thermal runaway problem of lithium-ion batteries under extreme conditions was solved, the safety and electrochemical performance of the battery were improved, and efficient electrolyte infiltration and mechanical strength were achieved.
Patent Information
- Application Number
- CN202510840453.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-23
- Publication Date
- 2025-09-26
AI Technical Summary
Existing lithium-ion battery separators are prone to thermal runaway due to local short circuits under extreme conditions, posing a safety hazard. Existing coated separators may still shrink under local high temperatures, leading to further short circuits and safety accidents.
A composite fiber diaphragm containing sepiolite and a boron-nitrogen mixture is used. The sepiolite and the boron-nitrogen mixture are connected by chemical bonds to form a uniform chemical structure, thereby improving the mechanical properties and thermal stability of the diaphragm and inhibiting side reactions and dendrite formation inside the battery.
The rate performance, long cycle life and safety performance of lithium batteries are significantly improved. The diaphragm maintains structural integrity at high temperatures and has good electrolyte wettability and electrochemical interface properties.
Smart Images
Figure CN120709654A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of lithium-ion batteries, and in particular relates to a high-safety composite fiber diaphragm and a preparation method and application thereof. Background Art
[0002] In recent years, with the rise of new energy vehicles (NEVs), a strategic emerging industry, power batteries with high energy density, excellent safety, and impressive range have garnered increasing attention. As one of the four key components of a battery, the separator primarily separates the positive and negative electrodes while allowing ions to pass freely. Its performance directly impacts the battery's capacity, cycling performance, and safety. Currently, the most commonly used battery separator is polyfiber. Polyethylene (PE) separators have a melting point of approximately 130°C, while polypropylene (PP) separators have a melting point of 150°C. Batteries can release significant amounts of heat when overcharged, overloaded, impacted, or squeezed. This can rapidly increase the internal temperature of the battery, causing the separator to shrink or melt, leading to contact between the positive and negative electrodes and an internal short circuit. This can ultimately lead to thermal runaway, potentially causing fire and explosion.
[0003] In order to improve the thermal stability and safety performance of the diaphragm, the current method is to coat the surface of the diaphragm with a heat-resistant layer to reduce the thermal shrinkage of the diaphragm and improve the safety of the battery, but this does not fundamentally solve the safety problem of the battery. Especially in extreme cases, after a short circuit occurs at a local location inside the battery, the local temperature will rise rapidly. The local heat can easily cause the temperature of the diaphragm at the corresponding location to rise to above 150°C. In this way, the coated diaphragm will also produce local thermal shrinkage and cause further short circuits, leading to thermal runaway and safety accidents. Sepiolite is light, cheap, and abundant in reserves. It has a nano-scale fiber structure, uniform pore size, high stability, large specific surface area, adjustable surface charge, strong adsorption capacity, high temperature resistance, and excellent rheological properties. It is widely used in environmental protection, building materials, medicine, chemical industry, energy and other fields. The boron-nitrogen mixture combines the characteristics of the two elements in chemical bonding and flame retardancy and can interact with the surface functional groups of sepiolite. Summary of the Invention
[0004] In order to solve the above technical problems, the present invention provides a high-safety composite fiber diaphragm and its preparation method and application. The high-safety fiber diaphragm has excellent performance, good electrolyte wetting performance, flame retardant properties, suitable mechanical strength, high ionic conductivity, stable electrochemical interface and excellent electrochemical stability, which greatly improves the rate performance, long cycle life and safety performance of lithium batteries.
[0005] To achieve the above-mentioned purpose, the present invention provides a high-safety composite fiber diaphragm, which is a fiber diaphragm containing sepiolite and a boron-nitrogen mixture.
[0006] Based on a general inventive concept, the present invention also provides a method for preparing a high-safety composite fiber diaphragm, comprising the following steps:
[0007] S1. Preparing a fiber slurry: adding a fiber material, a polymer additive, a boron-containing compound, and an inorganic sepiolite to a dispersion and stirring or pre-dissolving them in a solvent, adding a nitrogen-containing compound as a pH adjuster to adjust the pH to 3-10, and allowing the mixture to stand for more than 24 hours to obtain a fiber slurry;
[0008] S2. Making paper from the slurry: coating or filtering the fiber material obtained in step S1 to obtain a wet fiber composite nonwoven membrane;
[0009] S3. Post-processing: drying the wet high-security fiber composite non-woven membrane, and then rolling and winding it to obtain a high-security composite fiber separator.
[0010] Preferably, in step S1, the mass percentage of the fiber material is 0.2% to 80%, the mass percentage of the boron-containing compound is 0.1% to 90%, and the mass percentage of the polymer additive is 0.1% to 40%.
[0011] Preferably, the dispersion in step S1 includes one or more of water, ethanol, isopropanol and glycerol.
[0012] Preferably, the solvent in step S1 is one or more of acetone, tetrahydrofuran, N,N-dimethylformamide, and N,N-dimethylacetamide.
[0013] Preferably, the polymer additive in step S1 includes one or more of starch acetate, hydroxymethyl starch, sodium carboxymethyl cellulose, hydroxymethyl cellulose, gelatin, carrageenan, chitosan, chitin, polyvinyl alcohol, polyethylene oxide, polyacrylamide, polyvinyl pyrrolidone or water-soluble polyurethane, fluoropolymer, polyaryletherketone, polyimide, polymethyl methacrylate, and polyarylsulfoneamide.
[0014] Preferably, the fluorine-containing polymer comprises polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, fluorinated ethylene propylene, ethylene tetrafluoroethylene copolymer, ethylene trichlorofluoroethylene copolymer. The solvent used is one or more of acetone, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide.
[0015] Preferably, the boron-containing compound in step S1 comprises one or more boron-containing substances such as zinc borate, magnesium borate, lithium borate, sodium borate, boric acid, and borax.
[0016] Preferably, the nitrogen-containing compound in step S1 includes one or more organic or inorganic nitrogen-containing compounds such as ammonia water, ammonium chloride, ammonium salts, amino acids, urea, amides, pyridine, quinoline, and carbazole.
[0017] Preferably, the rolling intensity in step S3 is 0.1-60 MPa, and the rolling temperature is 20-100°C.
[0018] Based on a general inventive concept, this solution also provides an application of a high-safety composite fiber diaphragm in the preparation of power batteries and energy storage batteries.
[0019] Preferably, the full-fiber diaphragm has a thickness of 10 to 500 μm, a porosity of 30% to 95%, a mechanical tensile strength of 5 to 120 MPa, and a thermal shrinkage rate of less than 2% after standing at 150° C. for 2 hours.
[0020] The high safety mechanism of this scheme's high safety composite fiber diaphragm is:
[0021] This solution uses boron- and nitrogen-containing compounds to modify sepiolite fibers, and the final product is a diaphragm material, which can provide better electrochemical performance when paired with a liquid electrolyte. Nitrogen-containing compounds can not only use the lone pair of electrons on the nitrogen atom to form coordination with the electron-deficient boron element, but also nitrogen-containing compounds (both acidic substances such as ammonium chloride and alkaline substances such as ammonia water) can flexibly adjust the pH value of the slurry. Chemical bonds can be formed between boron-containing compounds and oxygen-containing functional groups on the surface of sepiolite, and the form of the bond between boron and oxygen-containing functional groups is affected by the pH value. The special structure of the boron element makes it tend to form a three-coordinate structure under acidic conditions and a four-coordinate structure under alkaline conditions.
[0022] This approach utilizes chemical bonds to bond a boron-nitrogen mixture to sepiolite. This chemical preparation process results in a more uniform element distribution and facilitates adjustments to the microstructure, ultimately impacting the physicochemical properties of the separator. This material not only improves the mechanical properties and thermal stability of the separator, but also reacts chemically with substances in the electrolyte during battery cycling. Boron and nitrogen participate in the formation of the electrolyte / electrode material interface, thereby suppressing side reactions and the formation of dendrites in the battery, thereby improving the battery's electrochemical performance, including cycle life and rate capability.
[0023] Compared with the prior art, the present invention has the following beneficial effects:
[0024] (1) After the boron-nitrogen mixture is compounded with sepiolite and fiber, it can better maintain the integrity of the structure under heating conditions. The battery separator prepared by the present invention has good electrolyte infiltration characteristics, high ionic conductivity and excellent electrochemical interface performance, which greatly improves the rate performance, long cycle life and safety performance of lithium batteries.
[0025] (2) The battery separator material can not only improve the mechanical properties and thermal stability of the separator. Boron and nitrogen elements can react chemically with substances in the electrolyte during the battery cycle. Boron and nitrogen elements participate in the formation of the electrolyte / electrode material interface, thereby inhibiting side reactions and the formation of dendrites in the battery, which is beneficial to the improvement of the battery's electrochemical performance such as cycle and rate. BRIEF DESCRIPTION OF THE DRAWINGS
[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.
[0027] Figure 1 This is a picture of the safety composite fiber diaphragm in Example 1;
[0028] Figure 2 This is a scanning electron microscope image of the cross section of the high-safety composite fiber diaphragm prepared in Example 1;
[0029] Figure 3 This is a comparison of the long-cycle performance of the batteries in Experimental Example 1. a is the long-cycle performance diagram of the fiber diaphragm prepared in Example 1, and b is the long-cycle performance diagram of the battery of the commercial polypropylene diaphragm. DETAILED DESCRIPTION
[0030] In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.
[0031] The following examples are provided to illustrate the present invention but are not intended to limit the scope of the present invention. Without departing from the spirit and substance of the present invention, modifications or substitutions made to the methods, steps or conditions of the present invention are within the scope of the present invention.
[0032] Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art; unless otherwise specified, the reagents used in the examples are commercially available.
[0033] Example 1
[0034] Preparation of high-safety composite fiber diaphragm
[0035] S1. Preparation of fiber slurry: 40 g fiber pulp, 1 g polyacrylamide, 10 g boric acid, and 8 g sepiolite were dispersed in 2 L deionized water and mechanically stirred. 10 g 20% ammonia water was added to adjust the pH to 8, and the mixture was allowed to stand for 24 h to obtain a uniform fiber slurry.
[0036] S2. Making paper from the slurry: The obtained fiber slurry is spread flat on a mold and filtered to obtain a wet fiber composite non-woven membrane.
[0037] S3. Post-treatment: The wet fiber non-woven membrane is dried in an oven at 75°C to remove excess moisture in the paper layer, and then rolled at 30 MPa and 60°C, and finally wound to obtain a high-safety composite fiber diaphragm with a thickness of 35 μm.
[0038] Among them, high-safety composite fiber diaphragms such as Figure 1 As shown in the scanning electron microscope image of the cross section of the high-safety composite fiber diaphragm, Figure 2 shown.
[0039] Example 2
[0040] Preparation of high-safety composite fiber diaphragm
[0041] S1. Preparation of fiber slurry: 50 g fiber pulp, 1 g polyvinyl alcohol, 10 g zinc borate, and 4 g sepiolite were dispersed in 2 L deionized water and mechanically stirred. 10 g 20 wt% urea solution was added to adjust the pH to 6.5, and the mixture was allowed to stand for 16 h to obtain a uniform fiber slurry.
[0042] S2. Making paper from the slurry: The obtained fiber slurry is spread flat on a mold and filtered to obtain a wet fiber composite non-woven membrane.
[0043] S3. Post-treatment: The wet fiber nonwoven membrane is dried in an oven at 75°C to remove excess moisture in the paper layer, and then rolled at 35 MPa and 55°C and finally wound to obtain a high-safety composite fiber diaphragm with a thickness of 35 μm.
[0044] Example 3
[0045] Preparation of high-safety composite fiber diaphragm
[0046] S1. Preparation of fiber slurry: 40 g fiber pulp, 1 g polyvinyl pyrrolidone, 10 g lithium borate, and 3 g sepiolite were dispersed in 2 L deionized water and mechanically stirred. 10 g of 20 wt% ammonium chloride solution was added to adjust the pH to 8.5, and the mixture was allowed to stand for 15 h to obtain a uniform fiber slurry.
[0047] S2. Making paper from the slurry: The obtained fiber slurry is spread flat on a mold and filtered to obtain a wet fiber composite non-woven membrane.
[0048] S3. Post-treatment: The wet fiber non-woven membrane is dried in an oven at 75°C to remove excess moisture in the paper layer, and then rolled at 38 MPa and 56°C and finally wound to obtain a high-safety composite fiber diaphragm with a thickness of 35 μm.
[0049] Example 4
[0050] Preparation of high-safety composite fiber diaphragm
[0051] S1. Preparation of fiber slurry: 40 g fiber pulp, 1 g polyurethane, 5 g sepiolite, and 10 g magnesium borate were dispersed in 2 L deionized water and mechanically stirred. 10 g of 20 wt% ammonia water was added to adjust the pH to 4.5, and the mixture was allowed to stand for 18 h to obtain a uniform fiber slurry.
[0052] S2. Making paper from the slurry: The obtained fiber slurry is spread flat on a mold and filtered to obtain a wet fiber composite non-woven membrane.
[0053] S3. Post-treatment: The wet fiber non-woven membrane is dried in an oven at 75°C to remove excess moisture in the paper layer, and then rolled at 42 MPa and 48°C to obtain a high-security composite fiber diaphragm with a thickness of 35 μm.
[0054] Comparative Example 1
[0055] Preparation of nitrogen-free composite fiber membranes
[0056] The nitrogen-containing compounds in step S1 are removed, and the remaining steps are the same as those in Example 1.
[0057] Comparative Example 2
[0058] Preparation of boron-free composite fiber membranes
[0059] The boron-containing compound in step S1 is removed, and the remaining steps are the same as those in Example 1.
[0060] Comparative Example 3
[0061] Preparation of Sepiolite-free Composite Fiber Diaphragm
[0062] The sepiolite in step S1 is removed, and the remaining steps are the same as those in Example 1.
[0063] Experimental Example 1
[0064] The battery performance of the above-mentioned embodiment and a commercial polypropylene separator was examined. The positive electrode, negative electrode, and separator were stacked in sequence and installed in a button cell (battery model 2016).
[0065] About 150 mL of an electrolyte containing 1 M lithium hexafluorophosphate (LiPF6) in a mixed solvent (ethylene carbonate: methyl ethyl carbonate (EC / EMC) volume ratio of 1:1) was injected into the above-mentioned battery, and aged according to a conventional method. The battery aluminum shell was sealed to obtain a lithium-ion battery.
[0066] 2) Battery long cycle test
[0067] The test method is as follows: at 25±5°C, the full battery is charged and discharged at a constant current density (0.5°C) to study the change in discharge capacity with the number of charge and discharge times.
[0068] The long cycle performance of the battery of Example 1 and commercial polypropylene separator is as follows Figure 3 As shown, the results show that the electrical properties of the composite fiber membrane prepared by this scheme are significantly better than those of commercial polypropylene membranes.
[0069] The thickness, porosity, electrolyte absorption rate, tensile strength, flame retardancy, conductivity and other properties of Examples 1 to 3, Comparative Examples 1 to 3 and commercial polypropylene separators were characterized. The results are shown in Table 1 below:
[0070] Table 1 Properties of Examples 1 to 3, Comparative Examples 1 to 3 and Commercial Polypropylene Diaphragms
[0071]
[0072] The above results show that:
[0073] The experimental results show that different elements and substances have different effects on the performance of the composite diaphragm. Comparing Example 1 with Comparative Example 1, it can be seen that nitrogen affects conductivity and flame retardancy; Example 2 and Comparative Example 2 show that boron has a slight effect on tensile strength and conductivity; Example 3 and Comparative Example 3 illustrate that sepiolite has different degrees of influence on the electrochemical properties, mechanical properties and flame retardancy of the composite diaphragm. Combining Example 1 with Comparative Examples 1 to 3, it can be seen that when conditions are suitable, the synergistic effect of the boron-nitrogen mixture and sepiolite can make the composite diaphragm perform well in many aspects. The above results show that the high-safety composite fiber diaphragm provided by this scheme has the advantages of high porosity, high electrolyte absorption, good thermal stability, excellent flame retardancy, and suitable mechanical strength, which meets the requirements of high-performance battery diaphragms. At the same time, the battery assembled with flame-retardant fibers has a very good capacity retention rate.
[0074] The above is only a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited to the above embodiment. For those skilled in the art, improvements and modifications obtained without departing from the technical concept of the present invention should also be considered as the scope of protection of the present invention.
Claims
1. A high-safety composite fiber diaphragm, characterized in that: The diaphragm is a fiber diaphragm containing sepiolite and a boron-nitrogen mixture.
2. A method for preparing a high-safety composite fiber diaphragm according to claim 1, characterized in that: The following steps are involved: S1. Preparing a fiber slurry: adding a fiber material, a polymer additive, a boron-containing compound, and an inorganic sepiolite to a dispersion and stirring, adding a nitrogen-containing compound as a pH adjuster to adjust the pH to 3-10, and standing for more than 24 hours to obtain a fiber slurry; S2. Making paper from the slurry: coating or filtering the fiber slurry obtained in step S1 to obtain a wet fiber composite nonwoven membrane; S3. Post-processing: drying the wet high-security fiber composite non-woven membrane, and then rolling and winding it to obtain a high-security composite fiber separator.
3. The preparation method according to claim 2, characterized in that In step S1, the mass percentage of the fiber material is 0.2% to 80%, the mass percentage of the boron-containing compound is 0.1% to 90%, and the mass percentage of the polymer additive is 0.1% to 40%.
4. The preparation method according to claim 2, characterized in that The dispersion in step S1 includes one or more of water, ethanol, isopropanol and glycerol.
5. The preparation method according to claim 2, characterized in that The polymer additive in step S1 includes one or more of starch acetate, hydroxymethyl starch, sodium carboxymethyl cellulose, hydroxymethyl cellulose, gelatin, carrageenan, chitosan, chitin, polyvinyl alcohol, polyethylene oxide, polyacrylamide, polyvinyl pyrrolidone or water-soluble polyurethane, fluoropolymer, polyaryletherketone, polyimide, polymethyl methacrylate, and polyarylsulfoneamide.
6. The preparation method according to claim 5, characterized in that The fluorine-containing polymer includes polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, fluorinated ethylene propylene, ethylene tetrafluoroethylene copolymer, and ethylene trichlorofluoroethylene copolymer.
7. The preparation method according to claim 2, characterized in that The boron-containing compound in step S1 includes one or more boron-containing substances such as zinc borate, magnesium borate, lithium borate, sodium borate, boric acid, and borax.
8. The preparation method according to claim 2, characterized in that The nitrogen-containing compound in step S1 includes one or more organic or inorganic nitrogen-containing compounds such as ammonia water, ammonium chloride, ammonium salt, amino acid, urea, amide, pyridine, quinoline, and carbazole.
9. The preparation method according to claim 2, characterized in that The intensity of the rolling in step S3 is 0.1-60 MPa, and the rolling temperature is 20-100°C.
10. Use of the high-safety composite fiber diaphragm according to claim 1 or the high-safety composite fiber diaphragm prepared by the preparation method according to any one of claims 2 to 9 in the preparation of power batteries and energy storage batteries.