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CN-122025998-A - Aramid fiber diaphragm and preparation method and application thereof

CN122025998ACN 122025998 ACN122025998 ACN 122025998ACN-122025998-A

Abstract

The invention provides an aramid fiber diaphragm, a preparation method and application thereof, wherein the preparation method comprises the steps of heating a meta-aramid fiber solution in an inert atmosphere, adding a pore-forming agent, carrying out ultrasonic dispersion to obtain a coating slurry, coating the coating slurry on the surface of a carrier to form a wet film, sequentially carrying out phase separation and solidification through at least two stages of coagulating baths to remove the pore-forming agent and strip the carrier to form a self-supporting aramid fiber base film with a through hole structure, wherein the primary coagulating bath is an N, N-dimethylacetamide aqueous solution with the temperature of 25-35 ℃, the volume ratio of N, N-dimethylacetamide to water is (65-75): (35-25), the secondary coagulating bath is an N, N-dimethylacetamide aqueous solution with the temperature of 20-30 ℃, the volume ratio of N, N-dimethylacetamide to water is (55-65): (35-45), carrying out two-stage heat setting on the self-supporting aramid fiber base film in an inert atmosphere, and carrying out two-stage heat setting to obtain the aramid fiber diaphragm, wherein the two-stage heat setting comprises the first stage temperature of 296-295 ℃ and the second stage temperature of 305-285 ℃.

Inventors

  • JIA DONGMIN
  • WAN CAIXIA
  • LI LIANGBIN
  • CUI KUNPENG
  • XIE MENGYU

Assignees

  • 中国科学技术大学

Dates

Publication Date
20260512
Application Date
20251229

Claims (10)

  1. 1. The preparation method of the aramid fiber diaphragm is characterized by comprising the following steps: Under inert atmosphere, heating meta-aramid solution, adding a pore-forming agent, and performing ultrasonic dispersion to obtain film slurry, wherein the pore-forming agent comprises an acidic pore-forming agent; Coating the coating slurry on the surface of a carrier to form a wet film, enabling the carrier of the wet film to sequentially pass through at least two stages of coagulating baths for phase separation and solidification, removing the pore-forming agent and stripping the carrier to form a self-supporting aramid fiber base film with a through hole structure, The first-stage coagulation bath is an N, N-dimethylacetamide aqueous solution with the temperature of 25-35 ℃, wherein the volume ratio of the N, N-dimethylacetamide to water is (65-75): (35-25); the second-stage coagulating bath is an N, N-dimethylacetamide aqueous solution with the temperature of 20-30 ℃, wherein the volume ratio of the N, N-dimethylacetamide to water is (55-65) (35-45); And carrying out bidirectional asynchronous stretching on the self-supporting aramid fiber base film in a solution atmosphere, drying, and carrying out two-stage heat setting under an inert atmosphere to obtain the aramid fiber diaphragm, wherein the two-stage heat setting comprises a first-stage setting temperature of 285-295 ℃ and a second-stage setting temperature of 296-305 ℃.
  2. 2. The method according to claim 1, wherein, The acidic pore-forming agent comprises at least one of boric acid, zinc borate and phosphoric acid.
  3. 3. The method according to claim 1, wherein, The meta-aramid is unmodified poly-m-phenylene isophthalamide, and the molecular weight of the meta-aramid is 28000-32000 g/mol; The solid content of the meta-aramid solution is 15 wt% -20 wt%, The addition amount of the pore-forming agent is 5wt% -20% wt%.
  4. 4. The method according to claim 1, wherein, The coagulation bath further comprises a third stage coagulation bath and a fourth stage coagulation bath, The third-stage coagulation bath is an N, N-dimethylacetamide aqueous solution at 15-25 ℃, wherein the volume ratio of the N, N-dimethylacetamide to water is (35-45): 65-55%; The fourth-stage coagulating bath is pure water at 15-20 ℃ or N, N-dimethylacetamide water solution at 15-20 ℃, wherein the volume ratio of N, N-dimethylacetamide to water is (5-15) (85-95).
  5. 5. The method according to claim 1, wherein, The stretching temperature of the bidirectional asynchronous stretching is 80-120 ℃, the longitudinal and transverse stretching rates are 1-10 mm/s, and the stretching multiplying power is 1.2-2 times.
  6. 6. The method according to claim 1, wherein, The thickness of the wet film is 10-25 mu m.
  7. 7. The aramid fiber diaphragm is characterized by having a nano through porous structure, wherein the porosity is 40-70%, and the pore size of the aramid fiber diaphragm accounting for more than 90% is 40+/-10 nm.
  8. 8. The aramid separator as claimed in claim 7, wherein, The performance of the aramid separator satisfies at least one of the following conditions: the air permeability per unit thickness is 14-41 s/mu m; the tensile strength is 40-70 MPa; the rupture temperature is 300-320 ℃; the tensile strength retention rate of the aramid fiber membrane is more than 80 percent under the environment of 100 ℃; and in the environment of 250 ℃, the thermal shrinkage rate of the aramid fiber diaphragm is 0-4%.
  9. 9. A secondary battery comprising a positive electrode, a negative electrode, an electrolyte and a battery separator, wherein, The battery diaphragm is positioned between the anode and the cathode, the electrolyte is filled in the gap between the battery diaphragm and the anode and the cathode, The battery diaphragm comprises the aramid diaphragm prepared by the preparation method according to any one of claims 1-6 or the aramid diaphragm according to any one of claims 7-8.
  10. 10. The secondary battery according to claim 9, wherein, The material of the positive electrode is any one of lithium nickel cobalt manganese oxide, lithium iron phosphate and nickel cobalt aluminum; The electrolyte is selected from any one of carbonate electrolyte, ether electrolyte and ionic liquid electrolyte; The material of the negative electrode is selected from any one of graphite, silicon-carbon composite material and lithium titanate.

Description

Aramid fiber diaphragm and preparation method and application thereof Technical Field The invention relates to the technical field of lithium ion battery diaphragms, in particular to an aramid fiber diaphragm and a preparation method and application thereof. Background Lithium ion batteries have been widely used in consumer electronics, electric vehicles, and energy storage systems due to their high energy density advantage. However, the thermal runaway problem faced in practical application is always a major safety challenge, and accidents such as fire and explosion are easy to initiate. The battery separator is used as an ion conduction barrier between the positive electrode and the negative electrode in the battery, and the safety of the battery is directly determined by the thermal stability of the battery separator. At present, commercial Polyethylene (PE) and polypropylene (PP) separators have certain ion permeability, but the materials are insufficient in intrinsic heat resistance, the rupture temperature is low (generally lower than 165 ℃) and significant heat shrinkage (the shrinkage rate is often more than 10%) occurs at 130 ℃, so that the requirement of a high specific energy battery on heat resistance is difficult to meet. In the prior art, the safety of the diaphragm is mainly improved by a composite modification technology such as coating a heat-resistant layer, and the like, although the heat shrinkage can be restrained to a certain extent, the fundamental problem of poor heat resistance of the base film is not solved, and under the extreme or long-term high-temperature condition, the safety improvement effect is limited, so that the urgent requirement of a high-specific-energy battery on the high safety can not be fundamentally met. In recent years, meta-aramid (PMIA) has been a focus of research on battery separators due to its inherent high melting point and good intrinsic flame retardant properties (oxygen index LOI > 28). However, the existing PMIA separator still has significant defects in performance, which restricts its practical application. For example, PMIA separators prepared based on conventional wet phase separation processes are generally large in pore size and uneven in distribution, which are prone to aggravation of self-discharge of batteries, uneven deposition of lithium ions and induction of growth of lithium dendrites, thereby increasing internal short circuit risks, and meanwhile, such separators are obvious in thermal shrinkage at 170 ℃ and prone to occurrence of fusion closed pores at 250 ℃ to form dense non-porous regions, resulting in sudden reduction of porosity and deterioration of thermal stability. In addition, unmodified pure PMIA separators often have insufficient mechanical properties and are difficult to meet the mechanical strength requirements of battery assembly and cycling. Disclosure of Invention Accordingly, a primary object of the present invention is to provide an aramid separator, and a preparation method and application thereof, so as to at least partially solve at least one of the above-mentioned technical problems. In order to achieve the above purpose, the technical scheme of the invention is as follows: In one aspect of the present invention, there is provided a method for preparing an aramid separator, comprising: under inert atmosphere, heating meta-aramid solution, adding a pore-forming agent, and performing ultrasonic dispersion to obtain film slurry, wherein the pore-forming agent comprises an acidic pore-forming agent; Coating the film slurry on the surface of a carrier to form a wet film, enabling the carrier containing the wet film to sequentially pass through at least two stages of coagulating baths for phase separation and solidification, removing pore-forming agents and stripping the carrier to form the self-supporting aramid fiber base film with a through hole structure, The first-stage coagulation bath is an N, N-dimethylacetamide aqueous solution with the temperature of 25-35 ℃, wherein the volume ratio of the N, N-dimethylacetamide to water is (65-75): (35-25); the second-stage coagulating bath is an N, N-dimethylacetamide aqueous solution with the temperature of 20-30 ℃, wherein the volume ratio of the N, N-dimethylacetamide to water is (55-65) (35-45); And carrying out two-way asynchronous stretching on the self-supporting aramid fiber base film, and carrying out two-section heat setting under an inert atmosphere to obtain the aramid fiber diaphragm, wherein the two-section heat setting comprises a first section setting temperature of 285-295 ℃ and a second section setting temperature of 296-305 ℃. In another aspect of the invention, an aramid fiber diaphragm is provided, which has a nano through porous structure, the porosity is 40-70%, and the pore size of the aramid fiber diaphragm, which accounts for more than 90%, is 40+/-10 nm. In still another aspect of the present invention, there is provided a secondary battery includin