What are the synthesis processes for lithium hexafluorophosphate?

Lithium hexafluorophosphate is the most important component of the electrolyte composition, accounting for about 43% of the total cost of the electrolyte. Lithium hexafluorophosphate is an inorganic substance with the chemical formula LiPF6, white crystal or powder. It is easily soluble in water, and also soluble in low concentrations of methanol, ethanol, acetone, carbonate and other organic solvents.

What are the synthesis processes of lithium hexafluorophosphate?

Lithium hexafluorophosphate synthesis process mainly includes gas-solid reaction method, hydrofluoric acid solvent method, organic solvent method, ion exchange method, etc. At present, large-scale industrial production mainly adopts hydrofluoric acid solvent method.

1、Gas-solid reaction method

American scientists proposed the gas-solid reaction method as early as in 1950, the method is the processed perforated LiF solid and PF5 gas directly reacted to generate LiPF6, the reaction is carried out at high temperature and high pressure, without the use of any solvents, the advantages of this method are fewer reaction steps, the operation is simple. The disadvantages of this method are that the reaction process needs to be protected by dry inert gas, so the sealing requirement of the reaction vessel is high, the reaction is only carried out on the surface of the solid, the LiF conversion efficiency is low, and a large amount of un-reacted LiF is left in the end, and the separation and purification is more complicated, and it is difficult to obtain high purity products. At present, this method is not in large-scale industrialized production, some laboratories are used.

2、Hydrofluoric acid solvent method

Lithium halide is dissolved in anhydrous hydrogen fluoride, and then pass into the high-purity PF5 gas reaction, generating lithium hexafluorophosphate crystals, and then after separation and drying to get lithium hexafluorophosphate products. The chemical formula of the reaction is as follows: 5HF + production of lithium hexafluorophosphate is one of the main methods.

3、Organic solvent method

Organic solvents used are mainly ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC) and so on. In this method, LiF solid is suspended in an organic solvent and then purified PF5 gas is passed through. The LiPF5 generated by the reaction is directly dissolved in the organic solvent, and the resulting solution can be directly used as an electrolyte for lithium-ion batteries. This method avoids the use of hydrogen fluoride, the production process will not be contaminated to the product, while reducing the danger, the operation is relatively safe, reducing the anti-corrosion requirements of the equipment; fast reaction speed, high purity of the product, the resulting electrolyte can also be used directly for lithium-ion batteries, with a high yield. The process is relatively simple and mild working conditions, less investment in equipment, no pollution in the production process. The disadvantage is that the reaction of raw materials and some organic solvents will be polymerization, decomposition and other reactions, it is difficult to obtain high purity products, applicable to the preparation of lithium hexafluorophosphate liquid solvent products.

4、Ion exchange method

It is the method to get lithium hexafluorophosphate by ion exchange reaction between hexafluorophosphate and lithium-containing compounds in organic solvents. According to the physical and chemical properties of lithium hexafluorophosphate, lithium hexafluorophosphate products should be avoided as much as possible to avoid heat, so as not to be unstable, heat decomposition, and easy to absorb moisture decomposition of water, the production of lithium hexafluorophosphate should be carried out as far as possible in the anhydrous environment, raw materials for the anhydrous treatment. The purity of the product prepared by this method is not high, lithium hexafluorophosphate is easy to absorb water, must use safe anhydrous solvent, the requirement of solvent is high, the relative cost of raw materials is also high.