18650 battery 3.7v 6000mah.An in-depth analysis of domestic reliance on imported lithium battery separator technology

　　As a major producer and consumer of lithium-ion batteries, my country has basically formed a complete industrial chain from mineral resources, battery materials and accessories to lithium-ion batteries and terminal application products. In recent years, my country's lithium-ion battery market has maintained rapid growth. The size of my country's lithium-ion battery market has increased from 27.7 billion yuan in 2011 to 85 billion yuan in 2015, with an average annual compound growth rate of 32.4%. Although my country's lithium-ion battery market is booming, our country is not a strong country in lithium-ion batteries. Let's talk about our shortcomings in terms of lithium-ion battery separators and aluminum-plastic films.

　　diaphragm

　　1. The role of lithium-ion battery separator

　　The separator is an important part of the lithium-ion battery. It is located between the positive and negative electrodes inside the battery, ensuring the passage of lithium ions while blocking electron transmission. The performance of the separator determines the interface structure, internal resistance, etc. of the battery, which directly affects the battery's capacity, cycle, safety performance and other characteristics. Excellent separators play an important role in improving the overall performance of the battery.

　　2. Lithium-ion battery requirements for separators

　　The requirements for separators for lithium-ion batteries include:

　　(1) It has electronic insulation and ensures mechanical isolation of the positive and negative electrodes;

　　(2) It has a certain pore size and porosity, ensuring low resistance and high ionic conductivity, and has good permeability to lithium ions; (3) It is resistant to electrolyte corrosion and has sufficient chemical and electrochemical stability. , this is because the solvent of the electrolyte is a highly polar organic compound;

　　(4) It has good electrolyte wettability and strong ability to absorb liquid and moisturize;

　　(5) High mechanical stability, including puncture strength, tensile strength, etc., but the thickness is as small as possible;

　　(6) Good spatial stability and flatness;

　　(7) Good thermal stability and automatic shutdown protection performance;

　　(8) The thermal shrinkage rate is small, otherwise it will cause short circuit and cause thermal runaway of the battery. In addition, power batteries usually use composite membranes, which have higher requirements for separators.

　　3. Lithium-ion battery separator classification

　　According to differences in physical and chemical properties, lithium battery separators can be divided into: woven membranes, non-woven membranes (non-woven fabrics), microporous membranes, composite membranes, separator paper, and rolled membranes. Although there are many types, commercial lithium battery separator materials so far mainly use polyethylene and polypropylene microporous films.

　　4. Lithium-ion battery separator technology

　　At present, the main methods for preparing lithium-ion battery separators include wet and dry methods. The wet method is also called the phase separation method or the thermally induced phase separation method. Liquid hydrocarbons or small molecular substances are mixed with polyolefin resins. After heating and melting, a uniform mixture is formed. The temperature is then cooled for phase separation, and the membrane is pressed to obtain a membrane. The sheet is heated to a temperature close to the melting point, biaxially stretched to orient the molecular chains, and finally kept warm for a certain period of time. The remaining solvent is eluted with volatile substances to prepare an interconnected microporous membrane. In the dry method, polyolefin resin is melted, extruded, and blown into a crystalline polymer film. After crystallization and annealing, a highly oriented multilayer structure is obtained, which is further stretched at high temperatures to peel off the crystalline surfaces. , forming a porous structure that can increase the pore size of the film.

　　The wet method and the dry method each have their own advantages and disadvantages. Among them, the wet method has small and uniform film pores and thinner films, but requires large investments, complex processes, and large environmental pollution; while the dry method is relatively simple, has high added value, and is environmentally friendly. However, the pore size and porosity are difficult to control, and the product is difficult to make thin.

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