The Key Material Of Lithium Battery – Lithium Hexafluorophosphate
- Main components of lithium battery electrolyte
- The irreplaceability of lithium hexafluorophosphate
- Preparation process and application of lithium hexafluorophosphate
- Analysis and forecast of lithium hexafluorophosphate demand
Main components of lithium battery electrolyteLithium hexafluorophosphate is the most important part of the cost of the electrolyte, accounting for about 43% of the total cost of the electrolyte. The production technology threshold 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 the name of the soul of the electrolyte. As an electrolyte material, the overall performance is good, but the disadvantage is that the thermal stability is not good, and it is easy to deliquescence, so it needs to be stored at low temperature and isolated from the air.
The irreplaceability of lithium hexafluorophosphateLithium hexafluorophosphate has moderate ion transfer number, moderate dissociation constant, good oxidation resistance and good aluminum foil passivation ability in commonly used organic solvents, and can be matched with various positive and negative electrode materials, thus becoming a commercial lithium salt is the most important electrolyte used in batteries. Researchers are constantly trying to develop new lithium salts in order to replace lithium hexafluorophosphate, but so far they have not been successful. Therefore, it is expected that for a long period of time in the future, lithium hexafluorophosphate will still be the only electrolyte salt used on a large scale, and its uniqueness mainly depends on the three elements of lithium, phosphorus and fluorine. Lithium is the lightest alkali metal element and the metal element with the smallest molar mass. It is also the metal element with the lowest redox potential, the largest mass energy density, and the highest electrochemical equivalent. These characteristics determine that lithium is a high specific energy electrode material. Fluorine is the most electronegative element in nature and the most active element among non-metallic elements, and it is also the element with the highest standard electrode potential. The combination of fluorine and lithium constitutes an electrochemical reversible battery, with a maximum potential of 5.93V and the highest specific battery energy density. At the same time, the radii of lithium and fluorine are extremely small, making them suitable as electrode materials for lithium batteries. In addition, the association ability of hexafluorophosphate is poor, so the conductivity of its electrolyte is relatively high, which is higher than that of general inorganic lithium salts. Lithium hexafluorophosphate has strong electrochemical stability, and the stable voltage of the cathode reaches 5.1V, which is much higher than the 4.2V required by lithium-ion batteries. It does not corrode the current collector, and its comprehensive performance is stronger than other lithium salts.
Preparation process and application of lithium hexafluorophosphateLithium hexafluorophosphate is very unstable, decomposes at around 60°C, and is also prone to deliquescence. Generally, potassium hexafluorophosphate products should be 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 battery, the requirements for its purity, stability, and consistency are very high. At the same time, the production process of lithium hexafluorophosphate involves harsh working conditions such as low temperature, strong corrosion, no water and no dust, and the process is extremely difficult. The preparation methods of lithium hexafluorophosphate mainly include gas-solid reaction method, organic solvent method and hydrogen fluoride solvent method. At present, the mainstream lithium hexafluorophosphate preparation method at home and abroad is the hydrogen fluoride solvent method, which accounts for more than 80% of all industrial production methods. Large-scale enterprises such as Morita, Jinniu Chemical, DFD Chemical, and Jiangsu Jiujiujiu all adopt this method to achieve industrialization. Therefore, the hydrogen fluoride solvent method that realizes continuous and automatic production is mainly introduced.
Gas-solid reaction methodThe gas-solid reaction method is the earliest preparation method of lithium hexafluorophosphate, which was proposed by American scientists in 1950. The gas-solid reaction method preparation process mainly includes two steps:
LiF (solid) + HF (gas) → LiHF2 (solid) → LiF (porous) + HF (gas)
LiF (porous) + PF5 (gas) → LiPF6The synthesis method is simple to operate and carried out at high temperature and high temperature, but the generated lithium hexafluorophosphate will cover the surface of the corroded lithium to form a dense protective film, which prevents the further progress of the reaction, resulting in a large amount of unreacted lithium fluoride in the final product, the product purity is relatively low. If it is further purified, the process and cost will be increased, and the purity is not easy to guarantee. If porous LiF is used to react with high-purity PF5 gas, lithium hexafluorophosphate with a purity of 99.9% can be prepared, but the preparation cost is relatively high.