Analysis of the industrial preparation process of lithium hexafluorophosphate for 4LR44 battery

At present, the mainstream LiPF6 production enterprises in China mainly adopt the HF solvent method, but they have their own characteristics in the specific process. 1. Duofuduo Chemical Co., Ltd. Duofuduo Chemical Co., Ltd. invented a double-kettle HF solvent method to prepare LiPF6, and the process is shown in Figure 4. First, PCl5 is reacted with anhydrous HF to obtain a mixed solution of PF5 and anhydrous HF, and then an anhydrous HF solution of LiF is prepared, which is added to the mixed solution, and high-purity LiPF6 crystals are obtained through reaction, crystallization, separation, and drying.

Anhydrous HF and PCl5 react slowly at -20~-30℃ to generate PF5 and HCl gas, which enter the pressure regulating tank after cooling to -40℃. PF5 gas reacts with LiF-HF solution in the 1# reactor to obtain LiPF6, and the by-product HCl gas and excess PF5 and a small amount of nitrogen enter the 2# reactor, and PF5 continues to react with LiF to generate LiPF6. After the reaction is completed, HCl gas is discharged from the top of the 2# reactor. A small amount of HF gas mixed with it can be removed by deep condensation, and industrial hydrochloric acid solution is obtained through a double-pot two-stage absorption system. The residual liquid mixture in the reactor is transported to the crystallization tank, and the LiPF6 product is obtained by crystallization, washing and drying. The dried HF is refined in the recovery tower and then enters the LiF preparation kettle for recycling. Advantages of this preparation process: Using the principle of chemical equilibrium, a double-pot series circulation operation is introduced in the LiPF6 preparation process, so that the liquid lithium hydrogen fluoride and the gas PF5 can react fully, and the gas and liquid can react in a homogeneous manner. At the same time, the addition of lithium hydrogen fluoride can also play the role of air flow stirring, accelerate the reaction rate, and improve the element conversion rate. 2. LiPF6 preparation process of Tianci High-tech Materials Co., Ltd. Tianci High-tech Materials Co., Ltd. has developed a process for preparing alkali metal hexafluorophosphate. The process can be simply summarized as PF5 gas and LiF solution are metered and introduced into a microchannel reactor for mixing and reaction, and the reaction liquid is crystallized and dried to obtain LiPF6. First, LiF and anhydrous HF with a mass ratio of 1:4 are introduced to generate an HF solution of LiF, and then PF5 gas and LiF solution are respectively pumped into the microchannel mixer module by a metering pump for mixing (molar ratio of 1:1), the reaction time is 30s, and the reaction temperature is -10℃. The reaction product flows out of the reaction equipment after filtration, and after evaporation, crystallization, filtration, and heating and drying at 50℃, the LiPF6 product can be obtained, and the yield can reach 96.2%. Advantages of this preparation process: The microchannel reactor is used for mixing, the reaction time is shortened, the efficiency is significantly improved, and the need for additional equipment and leakage during transfer in conventional intermittent reactions is avoided, and the safety is improved. 3. LiPF6 preparation process of Jiujiujiu Technology Co., Ltd. Jiujiujiu Technology Co., Ltd. has developed a circulating closed reaction equipment, and the prepared LiPF6 is treated by atomization drying. The solvent and solute are easy to be effectively separated, with high separation efficiency and low energy consumption, and continuous and automated production can be achieved. The specific process is shown in Figure 5.

LiPF6 and other reaction products are transported to the dryer by a pump for atomization, and flow from the top of the dryer along the spraying direction from top to bottom. The temperature in the dryer gradually increases from top to bottom. During the flow of the solution, anhydrous HF gas is continuously separated from the solution until the solution contains no HF gas. The anhydrous HF gas flows out from the top of the dryer, part of which is passed into the PF5 reactor I, and the other part is passed into the anhydrous HF condenser I to form anhydrous HF liquid, which is returned to the reaction equipment III as a reaction solvent after metering. The anhydrous HF gas passed into the PF5 reaction equipment II reacts with PCl5 to obtain PF5 and HCl gas, and the reaction product in the reaction equipment II is slowly passed into the reaction equipment III to ensure that PF5 is excessive. Among them, HCl gas is collected in the tail gas absorption device to prepare hydrochloric acid. The utilization efficiency of each reaction product is high. The traditional LiPF6 production process is complicated, and the synthesis, crystallization and other links are dangerous, making it difficult to achieve continuous and automated production. This process provides a high-quality, high-safety and environmentally friendly LiPF6 production method. 4. Morita Chemical (Zhangjiagang) LiPF6 Preparation Process Morita Chemical's preparation process can be divided into the main links of high-purity raw material preparation, PF5 preparation and purification, LiPF6 preparation and crystallization. The anhydrous HF is distilled through a distillation tower to obtain high-purity anhydrous HF gas, and the HF gas is passed into a condenser to obtain HF liquid, which is passed into a PF5 reactor at a temperature of 172~182℃ and a pressure of 0.6~0.7MPa, and the PF5 and HCl gases obtained by the reaction and the excess HF gas are collected. The PF5 and HCl gases are passed into the LiF and HF liquid reaction equipment at a temperature of 30~35℃ and a pressure of 0.6~0.7MPa. The LiPF6 solution is obtained by reaction under the conditions of a mass ratio of LiF, HF liquid and PF5 of 1:(3~7):(6~12). The HCl gas is converted into hydrochloric acid through a tail gas recovery device, and the obtained LiPF6 solution is filtered and passed into a crystallization tank. When the temperature drops to -70~-80℃, LiPF6 crystals are precipitated and dried to obtain a crude LiPF6 product. The advantages of this preparation process: it overcomes the shortcomings of LiPF6 such as high impurity content and low purity, has a low production cost and is simple to operate. 5. LiPF6 preparation process of Shandong Shida Shenghua Chemical Group The process developed by the company mainly includes the preparation and purification process of LiPF6. LiPF6 solution is prepared by using PF5, LiF and anhydrous HF. After filtering out insoluble impurities, the LiPF6 solution is passed into a crystallization tank to evaporate HF gas. When the volume of the original solution is 1/3~2/3, it is condensed at -20~-40℃ and filtered to obtain crude LiPF6. Specific steps: 1000kg anhydrous HF and 50kg LiF are added to the reactor, the temperature is controlled at -5℃, and stirred fully. 405kg PCl5 and 195kg anhydrous HF are added to the stainless steel reactor, and a mixed gas of PF5 and HCl is prepared at about 120℃ and a pressure of 0.05~0.1MPa. After purification, it is transferred to a reactor containing LiF, and LiPF6 is obtained by reaction at a temperature of 5~10℃ and a pressure of 0.05~0.1MPa, and LiPF6 is purified. Advantages of this preparation process: simple process, low cost, and high purity of the obtained product. Industrialization status of lithium hexafluorophosphate in domestic enterprises Lithium hexafluorophosphate will still have a large application market for a long time in the future due to its excellent performance. Based on the expectation that the country will continue to support the development of the new energy industry, many domestic companies are increasing their R&D investment in the field of lithium hexafluorophosphate. Representative domestic companies include Duofuduo Chemical Co., Ltd., Bikang Co., Ltd., Guangzhou Tianci High-tech Materials Co., Ltd., Tianjin Jinniu Power Materials Co., Ltd. and Shandong Shida Shenghua Chemical Group. The specific production capacity is shown in Table 2.

The performance of lithium-ion batteries depends to a large extent on the performance of the electrolyte, especially the purity of the electrolyte. Therefore, in the future, manufacturers will not only increase investment in production equipment, but also continue to improve production processes and strengthen the training of operators. Domestic companies have strong professional technology and talent reserves in the field of fluorine chemicals. With the saturation of the lithium hexafluorophosphate market, they will expand into new energy fields with higher technical requirements and capital investment. According to the current development trend of the new energy field, the possible development trends in the future are inferred as follows: 1. Improvement of high-purity crystal production process. The improvement of high temperature, high voltage and other performance of batteries is greatly affected by the purity of lithium salts. As the major manufacturers have a deeper understanding of the preparation process of LiPF6, they should continue to improve and optimize the existing crystallization and purification processes, reduce the content of free HF and insoluble matter, improve product quality and reduce production costs. 2. More rational capacity planning. With the influx of social capital into the new energy vehicle industry, 4LR44 battery and LiPF6 have been vigorously developed, but the state's subsidies for electric vehicles have gradually decreased. Enterprises should speed up the improvement and optimization of existing production process technologies to improve product quality and reduce production costs. At the same time, in the future, they should combine national policies to avoid blindly expanding production capacity. 3. Development of new high-value-added fluorine-containing lithium salts. The new fluorine-containing lithium salts have good electrochemical properties and are stable to water and heat. New lithium salts with more application prospects include lithium difluorooxalate borate (LiODFB), lithium bis(trifluoromethylsulfonyl)imide (LiFSI) and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI). Although there are still certain bottlenecks in industrialization and application, it can be used as an additive to improve the performance defects of batteries in the short term, but in the long run, it is necessary to accelerate research and development efforts, especially in combination with new energy storage systems for supporting application development. 4. Research and development of fluorinated solvents (such as fluoroethylene carbonate, fluoroalkyl compounds, fluorophosphazenes, and fluorophosphates). Carbonate solvents with low boiling point and low flash point are important factors affecting battery safety. Most fluorinated solvents have the characteristics of good film stability, excellent high and low temperature performance, stable electrochemical performance, high flash point, and flame retardancy, which have great advantages in improving the performance of 4LR44 battery. Therefore, while developing new fluorinated lithium salts, it is also necessary to carry out the research and development of fluorinated solvents to fundamentally improve and enhance the performance of the electrolyte system. 5. Development of green technology. The current lithium salt production process will produce a large amount of fluorine-containing and lithium-containing waste liquid. In the future, the current process needs to be optimized and system integrated to improve the utilization rate of elements and atoms, and the waste liquid needs to be recycled and reused to improve the greenness of the process. With the continuous advancement of the national new energy vehicle development strategy, the demand for lithium-ion batteries and lithium salts will continue to grow. LiPF6 has strong advantages in comprehensive performance indicators and industrialization costs, and will continue to be an important lithium salt electrolyte for some time to come. In the future development, China's fluorine-containing enterprises should focus on improving and optimizing process technology, improving product quality and reducing production costs. At the same time, they should conduct in-depth research on the comprehensive recycling and utilization of LiPF6 resources to ensure the healthy, sustainable and stable development of my country's new energy industry.

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