Production process principle of lithium ion battery separator Lithium - Ion Battery Equipment

Briefly describe the production process and principle of lithium iron phosphate battery separator

Production process principle of lithium ion battery separator

The production process of lithium iron phosphate battery separator is mainly divided into dry process and wet process. The important steps and principles of dry and wet processes are as follows:

1. In the dry method, the polyolefin resin is first melted, extruded and blown to form a crystalline polymer film, and then subjected to crystallization heat treatment and annealing operations to obtain a highly oriented film structure, and then stretched at high temperature to test The crystalline cross section is separated to form a porous structure battery separator. The dry process can also be divided into uniaxial stretching and biaxial stretching.

2. Wet method The traditional wet method is mainly based on the phase inversion method, and in recent years, the TIPS thermally induced phase separation method is the main method. The principle is to mix crystalline polymers, thermoplastic polymers and small molecular chemical diluents with high boiling points (such as paraffin oil) to form a homogeneous solution at high temperature, and then reduce the solution temperature to cause solid-liquid phase separation of the mixture. Or liquid-liquid separation, after the small molecule chemical diluent is extracted and removed, a porous membrane of thermoplastic and crystalline polymers is formed.(Lithium - Ion Battery Equipment)

The many characteristics of the lithium iron phosphate battery separator and the difficulty in taking into account its performance indicators determine the high technical barriers to its production process and the difficulty in research and development. The production process of diaphragm includes many processes such as raw material formulation and rapid formulation adjustment, microporous preparation technology, and independent design of complete sets of equipment. Among them, the micropore preparation technology is the core of the preparation process of the lithium iron phosphate battery separator. According to the difference in the pore formation mechanism of the micropores, the separator process can be divided into two types: dry method and wet method.

Dry-process separators are divided into single-stretched and double-stretched according to the stretching orientation

The dry diaphragm process is the most commonly used method in the diaphragm preparation process. The process is to mix high molecular polymers, additives and other raw materials to form a uniform melt, and to form a lamellar structure under tensile stress during extrusion. Heat treatment of the lamellar structure A hard elastic polymer film is obtained, which is then stretched at a certain temperature to form slit-shaped micropores, and the microporous film is obtained after heat-setting. At present, the dry process mainly includes two processes of dry uniaxial stretching and biaxial stretching.

The dry single drawing process is as follows:

1) Feeding: raw materials such as PE or PP and additives are pretreated according to the formula, and then transported to the extrusion system.

2) Casting: The pretreated raw materials are melted and plasticized in the extrusion system, and then extruded from the die head, and the melt is casted to form a base film with a specific crystal structure.

3) Heat treatment: After heat treatment of the base film, a hard elastic film is obtained.

4) Stretching: The hard elastic film is cold-stretched and hot-stretched to form a nano-microporous membrane.

5) Slitting: Cut the nano-microporous membrane into finished membranes according to the customer's specifications.

The dry double drawing process is as follows:

1) Feeding: The raw materials such as PP and pore former are pretreated according to the formula and sent to the extrusion system.

2) Casting: PP casting sheets with high β crystal content and good β crystal morphology uniformity are obtained.

3) Longitudinal stretching: longitudinally stretching the cast sheet at a certain temperature, and making use of the characteristic that beta crystals are easily formed by tensile stress to form pores.



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