Lithium battery diaphragm and preparation method thereof

Abstract

The invention discloses a lithium battery diaphragm and a preparation method, and belongs to the technical field of a battery diaphragm and a manufacturing method. The lithium battery diaphragm is a three-layer composite diaphragm, a track etch membrane is used as a base material, a high-temperature-resisting layer is compounded on the track etch membrane, a hot closed layer is compounded on the high-temperature-resisting layer, the high-temperature-resisting layer can resist the high temperature of more than 200 DEG C, and a melting point of the hot closed layer is 100 to 130 DEG C. The method comprises the following steps of blade coating the high-temperature material on the track etch membrane, and standing the track etch membrane; and quickly blade coating the hot closed material at a molten state outside the high-temperature-resisting material, and continuously solidifying the material at the room temperature to obtain the lithium battery diaphragm. The composite diaphragm is heated to 200 DEG C, the track etch membrane layer is basically molten, the high-temperature-resisting layer still can form a film, so that high heat stability can be realized; and moreover, in the charging and discharging process, even when the organism bottom membrane is molten, the high-temperature-resisting layer still can maintain the completeness of the diaphragm, the large-area positive / negative electrode short-circuit phenomenon can be prevented, and the safety of the battery can be improved.

Description

technical field [0001] The invention belongs to the technical field of battery separators and manufacturing methods, in particular to a lithium battery separator and a preparation method thereof. Background technique [0002] In the lithium-ion battery positive electrode, separator, electrolyte, and negative electrode composition mechanism, the cost of the lithium battery separator accounts for about 1 / 3 of the battery cost. The separator is an electrically insulating film with a porous structure, which is the key inner layer component of the lithium-ion battery. Its main function is to separate the positive and negative poles of the battery to prevent short circuit from direct contact between the two poles; it has the function of allowing ions to pass through freely, and can also block the current conduction in the battery by closing the pores when the battery is overheated. The performance of the separator determines the interface structure and internal resistance of the b...

AI Technical Summary

Problems solved by technology

However, this type of diaphragm has many shortcomings: PE and PP have high crystallinity and low polarity, and the electrolyte uses a highly polar organic solvent. Therefore, the affinity between the diaphragm and the electrolyte is not good, and it is almost impossible to Swelled by the electrolyte, that is, most of the electrolyte exists in the pores in liquid form, so the electrolyte is prone to leakage; the porosity is low, and because PP and PE have no solvent at room temperature, the separator can only be prepared by melt stretching at present , the stretching method not only requires extremely high equipment, but also it is difficult to obtain a high-porosity film (the porosity of the PP film does not exceed 50%, and the maximum porosity of the PE film can only reach 60%), resulting in high film resistance; The temperature performance is limited, usually lower than 150°C, which reduces the safety of lithium batteries; in order to further increase the specific energy of lithium-ion batteries, it is necessary to reduce the thickness of the film, which reduces the liquid absorption rate of the film with a two-dimensional pore structure, and at the same time affects safety

[0005] Ordinary nuclear pore membranes cannot be directly used as lithium battery separators

In order to ensure the safety of the battery, it is necessary for the diaphragm material to automatically close the pores above 100°C, and at the same time maintain a good film-forming state and certain insulating properties at higher temperatures (above 200°C). Single-layer nuclear pore membranes cannot meet such requirements