Technical status of potassium hexafluorophosphate used as electrolyte for lithium batteries

　　Current technical status of potassium hexafluorophosphate used as electrolyte in lithium batteries. Research on lithium hexafluorophosphate (LiPF6), the core material of lithium battery electrolyte, has always been a hot spot in the industry. The synthesis methods of lithium hexafluorophosphate mainly include gas-solid reaction method, hydrogen fluoride (HF) solvent method, organic solvent method and ion exchange method. In industry, the hydrogen fluoride solvent method is the main method, followed by the organic solvent method.

　　Technical status of potassium hexafluorophosphate used as electrolyte for lithium batteries

　　1. Gas-solid reaction method

　　The gas-solid reaction method is one of the earlier synthesis methods. This method is to react porous lithium fluoride (LiF) solid or LiF nanoparticles treated with anhydrous hydrogen fluoride (HF) with phosphorus pentafluoride (PF5) gas under high temperature and high pressure conditions to directly prepare the product LiPF6 solid. Its advantages are simple process, easy operation, and low equipment requirements, but it has not been used in industrial production so far. The fundamental reason lies in the difficulty of mass transfer, which is an important problem that is difficult to overcome with this method.

　　2. Ion exchange method

　　The sodium, potassium, ammonium and organic amine salts of hexafluorophosphate are relatively stable and can be easily purified by various methods. The so-called ion exchange method is a method to prepare LiPF6 through ion exchange reaction using these stable high-purity hexafluorophosphates and lithium-containing compounds in organic solvents. Commonly used lithium salts include lithium chloride, lithium bromide, lithium perchlorate, lithium nitrate and lithium acetate.

　　3. Solvent method

　　In order to overcome the shortcomings of the gas-solid reaction method, the solvent method was developed. There are two types of solvent methods: inorganic solvent method and organic solvent method. Organic solvent method: The preparation process of the organic solvent method is similar to the hydrogen fluoride solvent method. The difference in its preparation is that the purity of the product prepared by the organic solvent is only 90%~95%. The product easily absorbs the organic solvent, and further removal is difficult and it is not easy to produce a solid. Lithium hexafluorophosphate.

　　At present, the synthesis technology for potassium hexafluorophosphate is relatively mature, but its technology diffusion speed has accelerated significantly and is showing a new trend. From a technical perspective, the development and application of new phosphorus sources is one of the trends in the development of hydrogen fluoride solvent method technology. Another new trend worth noting is that some domestic and foreign companies and research units have begun to develop technology for synthesizing lithium hexafluorophosphate using cheap inorganic lithium salts and hexafluorohydrogen salts. How to effectively reuse valuable substances in used batteries will be a problem in the future. Become one of the new hot spots.

　　The technical threshold for the production of lithium hexafluorophosphate is relatively high, especially the production of high-purity crystalline lithium hexafluorophosphate. It can be said that lithium hexafluorophosphate, as a cutting-edge material in the lithium battery industry, is worthy of being called the soul of the electrolyte. The nature of lithium hexafluorophosphate batteries is very unstable. It decomposes at around 60°C and is easily deliquescent. Generally, potassium hexafluorophosphate products are prepared in non-aqueous solvents such as anhydrous hydrogen fluoride and low alkyl ethers.

　　Moreover, if lithium hexafluorophosphate develops in the direction of lithium-ion batteries and power lithium batteries, its purity, stability, and consistency requirements are very high. At the same time, the production process of lithium hexafluorophosphate involves harsh working conditions such as low temperature, strong corrosion, and no water and dust, making the process extremely difficult. Therefore, it is expected that lithium hexafluorophosphate will remain the only electrolyte salt used on a large scale for a long time to come, and its uniqueness mainly depends on the three elements of lithium, phosphorus, and fluorine.

　　As the most basic material for lithium battery electrolyte production, lithium hexafluorophosphate is easily overlooked, but its particle size distribution and impurity content restrict the development of lithium batteries, especially the impurity content, such as sodium, potassium, iron and other metal elements, as well as sulfate, Nitrate, etc. are all required to be below one hundred thousandth (mass fraction), which forces the industry to invest more in the optimization of the production process of lithium hexafluorophosphate and its raw material purification technology.

　　Lithium hexafluorophosphate is the most important component of the electrolyte, accounting for approximately 43% of the total cost of lithium battery electrolyte. In the fluorine chemical industry, although traditional products have experienced a significant year-on-year decline, demand growth for high-end products has maintained a strong momentum. In particular, the production and sales of lithium hexafluorophosphate continue to maintain a good momentum. With the continued expansion of the new energy field in the future, lithium hexafluorophosphate is expected to usher in a continued explosion. In the future, other new lithium salts are expected to replace lithium hexafluorophosphate.

　　As a lithium-ion battery electrolyte, potassium hexafluorophosphate is mainly used in lithium-ion power batteries, lithium-ion energy storage batteries and other daily batteries. It is also an irreplaceable lithium-ion battery electrolyte in the near to medium term.

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