Preparation method for multilayer micro-porous membrane of lithium ion battery

Abstract

The invention provides a preparation method for a multilayer micro-porous membrane of a lithium ion battery. The method comprises the following steps: taking polyolefin resin and auxiliary additive as raw materials, fusing and plastifying, thereby acquiring a flux; extruding by a die head and performing tape casting, thereby acquiring intermediate membranes; taking multiple coils of intermediate membranes and compounding by adopting a compounding device with a horizontal stretching function, thereby acquiring a compound intermediate; and performing annealing treatment under an effect of bidirectional micro-tension and longitudinally stretching, thereby acquiring the multilayer micro-porous membrane of the lithium ion battery. According to the invention, a compounding roll is heated in a compounding process of the intermediate membranes, the inner macromolecular structure crystallization of the intermediate membranes is further perfected, and meanwhile, the intermediate membranes horizontally extend under the effect of bidirectional micro-tension and the horizontal orientation degree is increased, so that the micro-pores of the prepared micro-porous membrane are uniform, the horizontal strength is promoted, the capacity of resisting against lithium dendrite puncture is effectively promoted, the micro-short circuit phenomenon is avoided and the micro-porous membrane is suitable for large-scale production. The multilayer micro-porous membrane prepared according to the invention is high in structure uniformity and is effective in promoting the safety of the battery.

Description

technical field [0001] The invention relates to the technical field of lithium ion batteries, in particular to a preparation method of a multilayer microporous membrane for lithium ion batteries. Background technique [0002] The lithium-ion battery separator is an important part of the lithium-ion battery. The microporous structure, physical properties, chemical properties, and thermal properties of the separator are closely related to the performance of the battery. Due to the high operating voltage of lithium-ion batteries, the high oxidation of positive electrode materials and the high reducibility of negative electrode materials, lithium-ion battery separator materials and high electrochemical activity positive and negative electrode materials should have excellent compatibility. Excellent stability, solvent resistance, ionic conductivity, electronic insulation, good mechanical strength, high heat resistance and fusing isolation. The physical and chemical properties of...

AI Technical Summary

Problems solved by technology

The composite rollers used in the existing composite equipment are composited at room temperature, and the gas between the layers cannot be removed in time when the product is composited, forming small air bubbles, and there are differences in the degree of bonding of the composite films of each layer, resulting in bubbles during the stretching process. Part of it cannot be stretched into holes, forming a "blind hole" area, and the degree of lamination of the film is different. When stretched under force, it will form a serious "neck shrinkage". Big

[0004] In addition, the micropores of the separator prepared by the dry uniaxial stretching process are slit-shaped structures, because only a high degree of longitudinal stretching occurs during the stretching process, resulting in higher longitudinal strength of the finished microporous membrane and higher transverse strength. Small, easy to be torn by mechanical force during battery assembly and battery use, or because the lithium dendrites generated on the negative electrode material side penetrate the separator to form a short circuit or micro short circuit, which is likely to cause safety problems

The dry biaxial stretching process adds a β crystal form modifier with nucleating effect to polypropylene, and utilizes the difference in density between different phases of polypropylene to form micropores during the stretching process through crystal transformation, which is used for production Single-layer PP film, but because of the transition from β crystal form to α crystal form during its preparation process, the structure of the micropores is not easy to control, the micropore structure is uneven, and the permeability is low

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