Production of Lithium Hexafluorophosphate in China   

By Wen Lining, China Salt Industry Association

Lithium-ion batteries feature high voltage, high energy density, small self-discharge rate, good stability and environmental friendliness. Since they achieved industrial production in the 1990s, they have become one of fastest-growing energy sources. There are many types of electrolytes for lithium-ion batteries. Among them, lithium hexafluorophosphate (LiPF6) has the best performance and the largest consumption. It accounts for 50% to 70% of the total production cost of the Li-ion battery electrolyte. Therefore, the technical level, production capacity, output and price of LiPF6 to a large extent affect the development of the lithium-ion battery industry. At present, only a few companies in the world can commercially produce LiPF6 on a large scale.

1. Production methods

1) Traditional method

In the 1950s, American scientist J.H. Simmons proposed a preparation method for LiPF6. He let PF5 directly react with LiF in a nickel container to get LiPF6. The reaction went on under high temperature and pressure and did not use any solvents. Its main drawback is that it has a low yield and is difficult to achieve mass production. The reaction is a gas-solid reaction. The generated LiPF6 can completely cover LiF, preventing the reaction from going on. After more than 20 years of continuous improvement and development, a process using phosphorus pentachloride (PC15), lithium chloride (LiCl) and anhydrous hydrofluoric acid (HF) as raw materials to prepare LiPF6 has been industrialized. At present, most LiPF6 producers in the world use this method.
    The method has the following disadvantages: a) the reaction uses a large amount of highly corrosive anhydrous HF, so it requires the equipment to be highly resistant to corrosion; b) the reaction requires cryogenic conditions; c) the reaction has multiple steps and has a long process route. But its uses relatively cheap HF as one of raw materials, and the resulted impurities mostly leave the reaction system in the gas phase, so the purification process of LiPF6 is relatively simple.

2) Solution method

Lithium-ion batteries require high-purity LiPF6 as electrolyte. Early preparation methods cannot meet the requirement. Preparing LiPF6 in organic solvents can improve its purity. This method is expected to become the mainstream preparation method of LiPF6 in the future.
   The specific process of this method is as follows. LiF is first suspended in an organic solvent consisting of EC (ethylene carbonate), DEC (diethyl carbonate) and DME (ethylene glycol dimethyl ether) to form a uniform suspension. At the appropriate temperature, PF5 is piped into the suspension. After some time, LiPF6 can be generated. Although the reaction is also a solid - gas reaction, the resulted product LiPF6 can timely dissolve in the organic solvent, making the reaction interface continuously updated, so that the reaction can go on. The unreacted LiF and impurities are insoluble in the solvent and can be easily separated from the LiPF6 solution. The solvent is then vaporized and recovered using appropriate methods, so high-purity LiPF6 can be obtained. The method avoids the use of strong corrosive HF.

2. Production of LiPF6 in China and in the world

China, Japan and South Korea together occupy more than 95% of the global lithium-ion battery production, of which the proportion of China has increased year by year. In 2008, China became the world's largest producer of lithium-ion batteries. In 2009, the global total production of LiPF6 was about 2 400 tons, and China accounted for about half of the global demand for lithium-ion battery electrolytes and LiPF6. Due to the rapid development of the electric vehicle market, the global total production of LiPF6 reached 3 800 tons in 2010.
   Currently, major global LiPF6 producers are distributed in Japan, South Korea and China's Taiwan region (see Table 1). In Chinese mainland, Tianjin Jinniu Power Source Material Co Ltd, Guangzhou Tinci Materials Technology Co Ltd and Do-Fluoride Chemicals Co Ltd have ability to produce LiPF6 (see Table 2).

Table 1 Global leading producers of LiPF6
Producer    Capacity(t/a)    Remarks
Morita Chemical Industries Ltd (Japan)    1380    A 660 t/a facility in Japan and a 720 t/a facility in Zhangjiagang, China
Kanto Electro-chemical Corp  (Japan)    950    Sales in Japan
SUTER AKEMIFA (South Korea)    800    Sales in South Korea
Ulsan, South Korea    350    For Samsung
Formosa Plastics Group (Chinese Taiwan)    200    Currently 10 tons per month

Table 2 Major LiPF6 producers in China
Producer    Capacity (t/a)    Remarks
Tianjin Jinniu Power Source Material Co Ltd    250    For own use. Plan to expand the capacity to 400 t/a
Guangzhou Tinci Materials Technology Co Ltd    200    For own use. Plan to expand the capacity to 1 000 t/a
Do-Fluoride Chemicals Co Ltd    200    Plan to expand the capacity to 2 000 t/a
Total    650