Modified diaphragm for lithium battery as well as preparation method and application of modified diaphragm

Abstract

The invention relates to a modified diaphragm for a lithium battery and a preparation method and application thereof, the modified diaphragm for the lithium battery comprises cellulose and / or a cellulose derivative and polydopamine located on the surface of the cellulose and / or the cellulose derivative, and the porosity of the modified diaphragm for the lithium battery is 50-80%; the polydopamine coating layer in the modified diaphragm for the lithium battery enables the diaphragm of the cellulose and / or the cellulose derivative to have a compact porous structure and high mechanical strength, so that the safety of the battery is improved, and the self-discharge of the battery is reduced; meanwhile, the contact between the diaphragm and an electrode as well as an electrolyte is tighter due to the polydopamine coating layer, so that the electrochemical performance of the battery is improved.

Description

technical field [0001] The invention belongs to the field of lithium battery materials, and relates to a diaphragm for modified lithium batteries, a preparation method and application thereof. Background technique [0002] At present, the separator commonly used in lithium-ion batteries is a polyolefin separator. The polyolefin separator will have closed cells at a temperature of about 130°C, and will melt when the temperature exceeds 160°C, resulting in direct contact between the positive and negative electrodes of the battery and a short circuit, which will cause the battery to catch fire. Or explosion, therefore, the safety performance of batteries assembled with polyolefin separators is low. [0003] CN110289382A discloses a preparation method of a lithium battery diaphragm and a lithium battery diaphragm. The lithium battery diaphragm is composed of a polymer substrate and silicate powder, wherein the mass percentage of the polymer substrate is 40wt% to 99.9wt %, the m...

AI Technical Summary

Problems solved by technology

Wherein the polymer substrate includes one or a combination of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene; CN209592166U discloses a novel high-performance composite polypropylene lithium battery diaphragm, including lithium battery The diaphragm body, the top of the lithium battery diaphragm body is bonded with a first composite polypropylene layer; the above lithium battery diaphragms are all made of polyolefin diaphragms; although the polyolefin diaphragms are coated with surface polymers and coated with composite inorganic particles Such methods can improve its wettability and thermal safety performance, but the above-mentioned methods will reduce the air permeability value of the diaphragm, reduce the tensile strength and increase the resistance value, and thus cannot meet the requirements for high-rate charge and discharge of power vehicles and tool products.

[0004] Cellulose has the characteristics of rich resources, environmental friendliness, low cost and some excellent properties, and has been widely used in various fields; the hydrophilic nature of cellulose itself makes it have good wettability, and it also has good thermal stability. No thermal shrinkage will occur below 300°C; however, the currently used cellulose separators have problems of large thickness, poor mechanical strength and too large pores, which limit their application

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