Composite lithium ion battery separator and preparation method therefor

Abstract

The invention discloses a composite lithium ion battery separator and a preparation method therefor. The composite lithium ion battery separator comprises non-woven fabric cloth used as the framework, and a composite film which is formed by a polymethyl methacrylate polymer mixed liquid on the non-woven fabric and equipped with a three-dimensional cross-linking network. The composite lithium ion battery separator adopts the non-woven fabric framework and the polymer-repaired composite structure, so that the power performance of the lithium ion battery is improved, and the safety performance of the lithium ion battery is enhanced; according to the preparation method for the composite lithium ion battery separator, the PMMA is taken as the polymer for dip-coating; a proper amount of cross-linking agent is added to the PMMA solution to trigger polymerization under a proper condition so as to form the three-dimensional cross-linking network, so that a certain framework effect is performed in the PMMA polymer, which is similar to the effect of reinforcing steel bars in reinforced concrete; and therefore, the mechanical strength of the separator is greatly improved, and the influences on the air permeability of the separator, the wettability of the electrolyte, and the like are reduced as well.

Description

technical field [0001] The invention relates to the technical field of battery diaphragm manufacturing, in particular to a composite lithium-ion battery diaphragm and a preparation method thereof. Background technique [0002] Lithium-ion battery is a rechargeable battery, it mainly relies on lithium ions to move between positive and negative electrodes to work. During the charging and discharging process, Li + Intercalation and deintercalation back and forth between two electrodes: when charged, Li + It is deintercalated from the positive electrode, inserted into the negative electrode through the electrolyte, and the negative electrode is in a lithium-rich state; the opposite is true during discharge. Batteries generally use materials containing lithium elements as electrodes, which are representatives of modern high-performance batteries. [0003] Today, the society has higher and higher requirements for lithium-ion batteries with high energy density and high power den...

AI Technical Summary

Problems solved by technology

At present, the most commonly used separators for lithium-ion batteries are still polyolefin separators, mainly polyethylene (PE) separators and polypropylene (PP) separators; polyolefin separators have many advantages, but they have low melting point and poor heat resistance, which lead to Disadvantages such as large thermal shrinkage rate and low membrane rupture temperature

[0004] With the gradual development of lithium-ion batteries to high energy density, high power density and high current charge and discharge, battery separators with better temperature resistance and higher membrane rupture temperature are required. Polyolefin separators can no longer meet the needs of future battery development.

In addition, because the polyolefin separator itself is non-polar, it cannot maintain good wettability with the polar electrolyte, so that the lithium ions dissolved in the electrolyte cannot shuttle between the positive and negative electrodes in a timely and smooth manner, resulting in the internal resistance of the battery. Increase, affecting the energy density of the battery and the full electrical performance of the large current

[0005] In view of the defects of polyolefin diaphragms, there have been three-layer composite diaphragms including PP / PE / PP, inorganic particles and heat-resistant organic coatings coated with polyolefin diaphragms to improve heat resistance, and non-woven fabrics modified with non-woven fabrics or inorganic particles. Woven separators, but these separators still have defects that cannot be ignored, such as PP / PE / PP still have poor heat resistance and electrolyte absorption performance; inorganic or organic coated polyolefin separators still have high cost, low porosity, battery Large internal resistance; simple non-woven fabrics have large pore sizes and uneven pore size distribution; modified non-woven fabrics have no high-temperature closed-cell performance and low strength

In addition, Chinese patent applications CN103022557A, CN102643450A, etc. mention the use of non-woven fabrics and polyvinylidene fluoride, polyacrylonitrile, polyether, etc. to prepare lithium-ion battery separators. The performance is poor, and there is no high-temperature closed-cell performance or the closed-cell temperature is too high, which cannot effectively protect the battery from short circuit; Chinese patent application CN102643450A mentions the use of PMMA-based polymers to coat non-woven fabrics, but the battery separator prepared by it has low strength and cannot be used alone For use, it usually needs to be copolymerized or blended with other high-strength polymers for use, and CN102690386A mentions the use of methyl methacrylate, butyl acrylate monomers and cross-linking agents such as polyethylene glycol dimethacrylate Copolymerize under the premise of azobisisobutyronitrile as an initiator to prepare cross-linked PMMA to improve mechanical properties, and it is only used in the modification of organic glass

This method is complex in process, high in cost, and requires an additional reaction device in the modification process, so it is difficult to apply to the lithium-ion battery diaphragm industry

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