A kind of polymer composite film and preparation method thereof and lithium ion battery

Abstract

The invention discloses a polymer composite membrane, a preparation method thereof and a lithium ion battery comprising the same. The polymer composite membrane includes a porous base film and a heat-resistant layer covering at least one surface of the porous base film. The closed cell temperature of the sub-heat-resistant layers increases sequentially; each sub-heat-resistant layer includes the first heat-resistant polymer material and / or the second heat-resistant polymer material, and each independently has a fiber network structure; the first heat-resistant The melting point of the polymer material is not less than 200°C; the melting point of the second heat-resistant polymer material is not less than 100°C. The polymer composite film softens in different temperature ranges by forming a multi-layer heat-resistant layer whose closed-cell temperature increases sequentially, so that it has a dynamic (staged) closed-cell behavior to adapt to the internal overheating of the battery. Furthermore, the thermal runaway of the separator caused by the perforation phenomenon can be effectively avoided, making the battery safer at high temperatures.

Description

technical field [0001] The invention relates to the field of lithium ion batteries, in particular to a polymer composite membrane and a preparation method thereof; the invention also includes a lithium ion battery using the aforementioned polymer composite membrane. Background technique [0002] Lithium-ion batteries are mainly composed of positive / negative electrode materials, electrolytes, separators and battery casing packaging materials. The separator is an important part of the lithium-ion battery, which is used to separate the positive and negative electrodes and prevent the internal short circuit of the battery; it allows the electrolyte ions to pass freely to complete the electrochemical charge and discharge process. The performance of the separator determines the interface structure and internal resistance of the battery, which directly affects the rate performance, cycle performance, and safety performance (high temperature resistance) of the battery. A separator w...

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Problems solved by technology

[0004] However, in the foregoing technical solutions, there is a large contradiction between the adhesion between the organic / inorganic composite layer and the porous base layer and the air permeability of the composite membrane.

This is because this organic / inorganic composite layer is formed by coating and relies on the gaps of inorganic particles to form voids. If you want to increase the porosity (permeability) of the organic / inorganic composite layer, you need to reduce the polymer bonding. However, due to the high glass transition temperature of the aforementioned polymer binder, its viscosity is not good. Once the amount of polymer binder is reduced, it will lead to poor bonding performance between the coating and the base layer. reduced, which in turn makes the high temperature thermal stability of this composite film worse

[0005] In addition, since the melting temperature of the high-temperature closed-cell material and the melting temperature of the substrate are basically in the same range, when the internal temperature of the lithium battery reaches this range due to a short circuit, etc., the high-temperature closed-cell material and the substrate will melt together. The pores between the particles are blocked, so that the battery stops reacting; however, when the internal temperature of the battery rises, overheating or local overheating usually occurs, and the molten composite film may be ruptured by high-temperature shock at this time, or may be caused by polymerization. The shrinkage of the material leads to the appearance of holes (referred to as porosity), which in turn leads to the occurrence of internal short circuits in the battery, resulting in thermal failure of the separator. This is also an important reason why the safety performance of lithium-ion batteries at high temperatures (above 160-180°C) has not been improved much. reason

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