Lithium ion battery composite diaphragm and preparation method and application thereof

Abstract

The invention discloses a lithium ion battery composite diaphragm and a preparation method and an application thereof, belonging to the technical field of lithium ion batteries. The composite diaphragm comprises a polyolefin microporous membrane, a polymer microsphere based coating on one side surface of the polyolefin microporous membrane, and an inorganic ceramic-based coating on the other side surface of the polyolefin microporous membrane. The lithium ion battery composite diaphragm has good air permeability, liquid retaining capability and high-temperature resistance and can remarkably improve the security and the circulation property of the battery. The melting point or softening point of the polymer microsphere-based coating in the composite diaphragm is 90-140 DEG C, and when the temperature of the battery is increased, the polymer microsphere based coating is molten or swelled within a short time, then the apertures of the polyolefin microporous membrane are blocked rapidly, the thermal turn-off effect of the diaphragm is achieved, a lithium ion conveying channel is cut off, and short circuit inside the battery is prevented; meanwhile as ceramic grains inside the inorganic ceramic-based coating have the high-temperature resistance property, the polyolefin microporous membrane is effectively prevented from shrinkage, and the situation that positive and negative films directly come into contact to cause short circuit of the battery.

Description

Technical field [0001] The invention specifically relates to a lithium ion battery composite diaphragm, and also relates to a preparation method and application of the composite diaphragm, and belongs to the technical field of lithium ion batteries. Background technique [0002] The battery separator refers to a thin layer of porous material between the positive and negative electrodes of the battery. It is a very critical part of the battery and has a direct impact on the safety and cost of the battery. It needs to have high ion permeability and good mechanical strength, and long-term stability to the chemicals and solvents used in the system such as the battery electrolyte. In the battery, the separator must completely isolate the cathode and anode electrodes, but at the same time allow the electrolyte to permeate, and it must also have lasting elasticity. [0003] At present, the traditional battery separator is a porous organic polymer film, and the typical organic separator i...

AI Technical Summary

Problems solved by technology

However, the use of polyolefin microporous membranes in battery separators mainly has the following problems: (1) polyolefins, as non-polar materials, have poor affinity with highly polar electrolytes, that is, the diaphragm has poor liquid retention capacity; (2) polyolefins Microporous membranes are mostly made by mechanical stretching, or by organic solvent extraction after mechanical stretching, and then heat setting. The membrane has a shape memory effect. When the temperature is high, the diaphragm tends to restore the membrane before stretching. shape, enhanced heat shrinkability

The main reason for the safety hazards of lithium-ion batteries is that the irreversible electrochemical side reactions of the batteries produce thermal runaway.

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