A kind of polyolefin lithium battery diaphragm and preparation method thereof

Abstract

The invention discloses a polyolefin lithium battery diaphragm, which uses a porous polyolefin diaphragm as a substrate, and one or both sides of the polyolefin diaphragm are electrospun with modified polyethylene terephthalate (PET) fiber coating. Layer, the modified polyethylene terephthalate fiber is a composite fiber of inorganic oxide nanoparticles and polyethylene terephthalate. The present invention aims at the problem of low high-temperature integrity of existing polypropylene or polyethylene porous diaphragms, and the problems of existing electrospinning diaphragms such as uneven pore structure or composite structure, and provides a polyolefin lithium battery diaphragm that can withstand high temperature It can reach 250-260°C, which can effectively avoid the problem of material melting and closing cells under the extreme conditions of battery abuse. It has good high-temperature integrity and can greatly improve the thermal safety of batteries.

Description

technical field [0001] The invention belongs to the field of new energy materials, and in particular relates to a polyolefin lithium battery diaphragm and a preparation method thereof. Background technique [0002] Separator is the most critical material that determines the safety of lithium batteries. It is generally made of polypropylene or polyethylene by dry single drawing, dry double drawing or wet process. Under overcharge / overdischarge or other extreme conditions of improper use, the temperature inside the lithium battery will rise rapidly above the melting point of polyolefin, causing the diaphragm to fuse, the positive and negative electrodes to contact directly in a local area and short circuit, the battery to catch fire or explode. [0003] At present, the method to improve the lithium battery diaphragm is mainly to coat the surface of the diaphragm with an inert polymer binder (mainly polyvinylidene fluoride PVDF, vinylidene fluoride-hexafluoropropylene copolyme...

AI Technical Summary

Problems solved by technology

However, there are two problems with the direct use of electrospun membranes as battery separators. One is that the porosity of the separator is very high, with a typical value of 60-80%, resulting in a lower electronic isolation capability of the separator and serious battery self-discharge. The silk separator has not been directional stretched, and its general strength is only 5-20MPa, which is far lower than the 100MPa of the stretched traditional separator, which is difficult to meet the needs of battery manufacturing process and mechanical safety.

[0005] CN201510069176.7 discloses a composite lithium-ion battery diaphragm, which includes a non-woven fabric substrate layer, an electrospinning layer and a polymer porous coating. Specifically, non-woven fabric is used as the substrate to ensure the high porosity of the diaphragm and heat resistance; the electrospinning layer is set on the upper and lower surfaces of the non-woven fabric substrate, which reduces the pore size of the non-woven fabric and makes the pore size uniform; patent CN201510069135. silk layer, but the problems of self-discharge and strength of electrospun membranes are still not resolved

Patent CN201210128618.7 discloses a three-layer nanofiber composite lithium-ion battery membrane and its preparation technology. The second outer layer, the first outer layer and the second outer layer were prepared by electrospinning technology, and then hot-compressed with the middle layer to obtain a composite structure, but hot-pressed composite has a relatively large impact on the pore structure of the polymer porous substrate and porous coating. Moreover, hot-press lamination requires a larger thickness of the single-layer film, which does not conform to the current trend of thinner diaphragms

[0006] Patent CN201710142596.2 discloses a polymer composite lithium battery separator and its preparation method. The polymer composite lithium battery separator includes a base film and an inorganic particle coating coated on one or both sides of the base film, and the inorganic particle coating The surface of the coating is coated with at least one high temperature resin layer, and the coating is transferred to the base film by one of dip coating, gravure printing, spray coating, extrusion coating, electrospinning and transfer coating, but , the inorganic oxides in this structure are added in a physical way, and it is difficult to disperse

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