CN-122026000-A - Preparation method of high-temperature-resistant crosslinked polystyrene/polyolefin composite lithium battery diaphragm

CN122026000ACN 122026000 ACN122026000 ACN 122026000ACN-122026000-A

Abstract

The invention belongs to the technical field of lithium ion battery materials, in particular to a preparation method of a high-temperature-resistant crosslinked polystyrene/polyolefin composite lithium battery diaphragm, which comprises the steps of blending and extruding a precursor solution containing polystyrene monomers, a polymerizable crosslinking agent and a photoinitiator with polyolefin, after longitudinal stretching, ultraviolet in-situ irradiation is carried out to form a crosslinked polystyrene network on the surface layer of the matrix, and then the composite membrane with a chemical bonding and physical interpenetrating double interface structure is constructed through transverse stretching, heat setting and plasma treatment. The dual combination mechanism of covalent bonding and physical interpenetrating is formed at the interface of polystyrene and polyolefin, so that the cooperative control of the formation process of a crosslinked network and the development of a micropore structure in space distribution and time progress is realized, the pore channel blockage and interface defect are avoided, the dimensional stability of the diaphragm in a high-temperature environment is ensured, and meanwhile, the high porosity and electrolyte infiltration are reserved.

Inventors

ZHOU YANPENG
ZHANG CHENGJIE
LI KAI
ZHU QUANYAO
KONG JINGJING

Assignees

深圳科瑞沃科技有限公司

Dates

Publication Date: 20260512
Application Date: 20260305

Claims (10)

1. The preparation method of the high-temperature-resistant crosslinked polystyrene/polyolefin composite lithium battery diaphragm is characterized by comprising the following steps of: polystyrene monomer, polymerizable cross-linking agent and photoinitiator are dissolved in a low-boiling point organic solvent to form a homogeneous precursor solution; Premixing the precursor solution and polyolefin resin particles according to a mass ratio of 1:4 to 1:9, and then feeding the mixture into a double-screw extruder under an inert atmosphere for melt blending, wherein the extrusion temperature is 180-220 ℃ to obtain a primary sheet; Uniaxially stretching the primary sheet longitudinally at 80 ℃ to 110 ℃ to form a uniaxially oriented sheet; immediately irradiating the uniaxially oriented sheet by an ultraviolet light source after the longitudinal stretching and before the transverse stretching is finished, so that the precursor component generates in-situ free radical copolymerization and crosslinking reaction on the surface layer of the sheet to form a crosslinked polystyrene network layer; transversely biaxially stretching the sheet subjected to ultraviolet irradiation treatment to form a mutually communicated micropore structure inside the polyolefin matrix, and simultaneously inducing the crosslinked polystyrene network layer and the polyolefin matrix to form a physical interpenetrating structure at the interface; performing heat setting on the biaxially stretched film material to stabilize the pore structure and remove residual volatile matters; Finally, carrying out plasma surface treatment on the film material after heat setting, introducing polar groups to improve electrolyte wettability, and winding to obtain the composite diaphragm; wherein the polymerizable crosslinking agent is an aromatic or alicyclic compound containing two or more vinyl functional groups, and the molecular structure of the polymerizable crosslinking agent comprises at least one substituent group with polarity similar to that of a polystyrene main chain.
2. The method for preparing the high-temperature-resistant crosslinked polystyrene/polyolefin composite lithium battery separator according to claim 1, wherein the low-boiling-point organic solvent is an aliphatic ketone or ester compound, which is completely volatilized in the melt blending process and does not remain in a final product.
3. The preparation method of the high-temperature-resistant crosslinked polystyrene/polyolefin composite lithium battery diaphragm is characterized in that ultraviolet light irradiation is performed in an inert atmosphere closed cavity with the oxygen content lower than 50ppm, an irradiation unit and a longitudinal stretching roller are integrated in the same cavity, the roller surface temperature is precisely controlled through heat conduction oil circulation, and the material is ensured to be in an optimal reaction temperature window.
4. The method for preparing a high temperature resistant crosslinked polystyrene/polyolefin composite lithium battery separator according to claim 1, wherein during the ultraviolet irradiation, polystyrene monomer and polymerizable crosslinking agent are crosslinked in situ on the surface layer of the polyolefin matrix, and the inside of the polyolefin matrix is kept in an uncrosslinked state; Meanwhile, in the melt blending and ultraviolet irradiation stage, tertiary carbon free radicals generated on the polyolefin main chain by shearing heat or trace oxygen are subjected to coupling reaction with vinyl groups in the polymerizable crosslinking agent, and C-C covalent bond connection is formed at the polyolefin-polystyrene interface.
5. The method for preparing the high-temperature-resistant crosslinked polystyrene/polyolefin composite lithium battery separator according to claim 1, wherein in the transverse stretching process, as the modulus of a crosslinked polystyrene network is higher than that of a polyolefin matrix, microscale stress gradient is generated at an interface, so that a polystyrene network chain segment is promoted to penetrate into the polyolefin to form a physical interpenetrating structure, and the physical interpenetrating structure realizes interface anchoring through Van der Waals force and local chain entanglement.
6. The method for preparing a high temperature resistant crosslinked polystyrene/polyolefin composite lithium battery separator according to claim 1, wherein the crosslinked polystyrene network layer maintains rigidity due to the fact that the glass transition temperature is higher than the heat setting temperature in the heat setting treatment process, and provides mechanical support for the microporous wall of the polyolefin matrix.
7. The method for preparing the high-temperature-resistant crosslinked polystyrene/polyolefin composite lithium battery diaphragm according to claim 1, wherein the plasma surface treatment is performed by adopting argon or nitrogen plasma, so that the surface of the crosslinked polystyrene layer is introduced with an oxygen-containing or nitrogen-containing polar group.
8. The method for preparing a high-temperature-resistant crosslinked polystyrene/polyolefin composite lithium battery separator according to claim 1, wherein the polyolefin resin is high-density polyethylene or polypropylene; when polypropylene is used, the machine direction stretching temperature is adjusted to 100 ℃ to 110 ℃.
9. The preparation method of the high-temperature-resistant crosslinked polystyrene/polyolefin composite lithium battery diaphragm, which is disclosed in claim 1, is characterized in that the polymerizable crosslinking agent is selected from divinylbenzene or 1, 4-divinyl cyclohexane, and the photoinitiator is selected from 2-hydroxy-2-methyl-1-phenyl-1-acetone.
10. The composite lithium battery separator manufactured by the manufacturing method according to any one of claims 1 to 9, wherein the separator comprises a porous polyolefin matrix and a crosslinked polystyrene functional layer coated on the surface of the porous polyolefin matrix, and the functional layer and the matrix are combined through a covalent bonding and physical interpenetrating dual mechanism.

Description

Preparation method of high-temperature-resistant crosslinked polystyrene/polyolefin composite lithium battery diaphragm Technical Field The invention belongs to the technical field of lithium ion battery materials, and particularly relates to a preparation method of a high-temperature-resistant crosslinked polystyrene/polyolefin composite lithium battery diaphragm. Background With the rapid development of new energy automobiles, large-scale energy storage systems and high-power portable electronic equipment, the safety, the cycle life and the thermal stability of lithium ion batteries become key constraint factors for industrial upgrading. The diaphragm is used as a lithium ion battery core component, has the functions of physically isolating an anode and a cathode, guaranteeing ion conduction and maintaining structural integrity, has the performance of directly determining a battery safety boundary and a working temperature window, has a low melting point (generally lower than 165 ℃) and is easy to thermally shrink and even melt to close pores under extreme working conditions such as high temperature, overcharging and the like, and causes potential safety hazards such as internal short circuit and thermal runaway, so that the novel composite diaphragm with high thermal stability, good electrolyte wettability and excellent mechanical strength is developed and becomes the core technical direction of the field. The prior art for improving the heat resistance of the diaphragm mostly adopts a strategy of introducing inorganic filler or organic polymer coating into a polyolefin matrix, wherein the high-temperature-resistant polymer coating method is widely focused due to strong process compatibility and good controllability, partial researches try to introduce polystyrene into a diaphragm system, and improve the thermal dimensional stability by utilizing a higher glass transition temperature (about 100 ℃) and a rigid chain structure of the polystyrene, but the conventional linear polystyrene has the problems of insufficient softening temperature, poor compatibility with a polyolefin substrate interface, large film forming brittleness and the like, and is difficult to achieve high porosity and ionic conductivity, and an interface micropore defect or stress concentration area is easily formed by a physical blending or simple coating mode due to polarity difference of the two, so that crack expansion is induced in the battery assembly or the cycle process, and the mechanical integrity and the safety redundancy of the diaphragm are reduced. The deep contradiction of the existing composite diaphragm technology is that the strong interface combination and the synergistic heat stabilization effect of the high-temperature resistant component and the matrix are difficult to realize through the molecular structure design on the premise of retaining the flexibility of the polyolefin matrix, the mature stretching pore-forming process and the low cost advantage, the diaphragm porosity is reduced, the electrolyte absorptivity is reduced and the ion transmission is deteriorated due to the simple increase of the polystyrene content or the increase of the coating thickness; The prior art route does not achieve a substantial balance between high heat resistance and high ionic conductivity/good processability, essentially due to thermodynamic incompatibility of the heat resistant polymer phase with the polyolefin continuous phase and structural conflict of kinetic processing window. Therefore, the invention provides a preparation method of a high-temperature-resistant crosslinked polystyrene/polyolefin composite lithium battery diaphragm. Disclosure of Invention In order to overcome the deficiencies of the prior art, at least one technical problem presented in the background art is solved. The technical scheme adopted for solving the technical problems is that the preparation method of the high-temperature-resistant crosslinked polystyrene/polyolefin composite lithium battery diaphragm comprises the following steps: Firstly, polystyrene monomer, a polymerizable cross-linking agent and a photoinitiator are dissolved in a low-boiling-point organic solvent according to a specific proportion to form a homogeneous-phase precursor solution; The polymerizable crosslinking agent is an aromatic or alicyclic compound containing two or more vinyl functional groups, the molecular structure of the polymerizable crosslinking agent at least comprises one substituent group with similar polarity to a polystyrene main chain so as to ensure good copolymerization tendency with a polystyrene chain segment in the subsequent film forming process, and the photoinitiator is a radical initiator with strong absorption at 365 nm of ultraviolet wavelength and good thermal stability, and decomposition products of the photoinitiator can be completely volatilized in the subsequent heat treatment without residual catalytic active substances. The precursor solutio