Electrolyte lithium hexafluorophosphate synthesis technology -Lithium - Ion Battery Equipment
In 1990, Japan's sony company successfully developed the first generation of lithium-ion batteries. Because of its comprehensive performance superior to existing Ni/Cd batteries and Ni/M(H) batteries, and no memory effect and no environmental pollution, lithium-ion batteries quickly occupied the secondary battery market. The research on its core material lithium hexafluorophosphate (LipF6) has always been a hot spot in the industry. In this paper, the research status of LipF6 will be analyzed and reviewed, and its development prospects will be prospected.（Lithium - Ion Battery Equipment）
1. Research status of lithium hexafluorophosphate
The main synthesis methods of LipF6 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.
1.1 Gas-solid reaction method
The gas-solid reaction method is one of the earlier synthetic methods. The method is to react porous lithium fluoride (LiF) solids or LiF nanoparticles after anhydrous hydrogen fluoride (HF) treatment with phosphorus pentafluoride (pF5) gas under high temperature and high pressure conditions to directly obtain the product LipF6 solid. The advantages are that the process is simple, easy to operate, and the equipment requirements are not high, but it has not been used in industrial production so far. The fundamental reason is the difficulty of mass transfer, which is an important problem that this method is difficult to overcome. As the reaction progresses, the surface of the LiF solid phase will gradually be covered by the relatively dense LipF6 product, which hinders the diffusion of pF5 gas into the interior, resulting in incomplete reaction and serious product "inclusion" phenomenon. Therefore, this method is difficult to obtain high-purity products, and the yield is also low. Although many people have done a lot of exploratory research on this, it is still not well resolved.
1.2 Ion exchange method
The sodium, potassium, ammonium and organic amine salts of hexafluorophosphoric acid are relatively stable, and are convenient for purification by various methods. The so-called ion exchange method is a method in which LipF6 is prepared by ion exchange reaction with these stable hexafluorophosphate high-purity compounds and lithium-containing compounds in an organic solvent. Commonly used lithium salts include lithium chloride, lithium bromide, lithium perchlorate, lithium nitrate and lithium acetate. Solvents generally use low-boiling organic compounds, such as acetonitrile, ethylene carbonate (EC), diethyl carbonate (DEC) and dicarbonate. Methyl ester (DMC), etc., solvents with higher boiling points are rarely used to prevent decomposition of the product during drying of the lithium hexafluorophosphate complex.
The advantage of the ion exchange method is that the reaction is simple, and there is no pF5 in the raw material, so the raw material cost is lower than other methods. The disadvantage is that it requires high hexafluorophosphate and lithium content, which invisibly increases the procedures and costs of raw material purification. In addition, the conversion of hexafluorophosphate as one of the important reactants is not complete, and the product purity is not high. Although many people have studied this method, it is still in the laboratory stage, and it will take time for industrial application.
1.3 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 method: inorganic solvent method and organic solvent method.
1.3.1 Inorganic solvent method
(1) HF solvent method
In the method, LiF is first dissolved in anhydrous HF, and then high-purity pF5 gas is introduced for the reaction. After the reaction, the HF is removed, and the LipF6 product is obtained after separation and drying. Since the reaction is carried out in the liquid phase, the method has many advantages such as fast reaction speed, good mass transfer and heat transfer effect, easy control of the reaction, high conversion rate, and high product purity, so industrial production is quickly realized. Although this method has shortcomings such as high energy consumption, harsh anhydrous conditions and equipment corrosion, after the long-term efforts of scientific research and engineering and technical personnel, the method has been perfected day by day and has become a mainstream industrialized method recognized in the industry.
1. Research status of lithium hexafluorophosphate
The main synthesis methods of LipF6 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.
1.1 Gas-solid reaction method
The gas-solid reaction method is one of the earlier synthetic methods. The method is to react porous lithium fluoride (LiF) solids or LiF nanoparticles after anhydrous hydrogen fluoride (HF) treatment with phosphorus pentafluoride (pF5) gas under high temperature and high pressure conditions to directly obtain the product LipF6 solid. The advantages are that the process is simple, easy to operate, and the equipment requirements are not high, but it has not been used in industrial production so far. The fundamental reason is the difficulty of mass transfer, which is an important problem that this method is difficult to overcome. As the reaction progresses, the surface of the LiF solid phase will gradually be covered by the relatively dense LipF6 product, which hinders the diffusion of pF5 gas into the interior, resulting in incomplete reaction and serious product "inclusion" phenomenon. Therefore, this method is difficult to obtain high-purity products, and the yield is also low. Although many people have done a lot of exploratory research on this, it is still not well resolved.
1.2 Ion exchange method
The sodium, potassium, ammonium and organic amine salts of hexafluorophosphoric acid are relatively stable, and are convenient for purification by various methods. The so-called ion exchange method is a method in which LipF6 is prepared by ion exchange reaction with these stable hexafluorophosphate high-purity compounds and lithium-containing compounds in an organic solvent. Commonly used lithium salts include lithium chloride, lithium bromide, lithium perchlorate, lithium nitrate and lithium acetate. Solvents generally use low-boiling organic compounds, such as acetonitrile, ethylene carbonate (EC), diethyl carbonate (DEC) and dicarbonate. Methyl ester (DMC), etc., solvents with higher boiling points are rarely used to prevent decomposition of the product during drying of the lithium hexafluorophosphate complex.
The advantage of the ion exchange method is that the reaction is simple, and there is no pF5 in the raw material, so the raw material cost is lower than other methods. The disadvantage is that it requires high hexafluorophosphate and lithium content, which invisibly increases the procedures and costs of raw material purification. In addition, the conversion of hexafluorophosphate as one of the important reactants is not complete, and the product purity is not high. Although many people have studied this method, it is still in the laboratory stage, and it will take time for industrial application.
1.3 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 method: inorganic solvent method and organic solvent method.
1.3.1 Inorganic solvent method
(1) HF solvent method
In the method, LiF is first dissolved in anhydrous HF, and then high-purity pF5 gas is introduced for the reaction. After the reaction, the HF is removed, and the LipF6 product is obtained after separation and drying. Since the reaction is carried out in the liquid phase, the method has many advantages such as fast reaction speed, good mass transfer and heat transfer effect, easy control of the reaction, high conversion rate, and high product purity, so industrial production is quickly realized. Although this method has shortcomings such as high energy consumption, harsh anhydrous conditions and equipment corrosion, after the long-term efforts of scientific research and engineering and technical personnel, the method has been perfected day by day and has become a mainstream industrialized method recognized in the industry.
