| In China research and industrialization on lithium-ion battery electrolyte salts has not been received advancement at present, lithium electrolyte salts all depend on import. They can not be made in China nowadays because of the requirements of high purity, the fatalness occurred in manufacturing, the difficulties of preparing raw material, and the highly monopolized techniques.The low level of the corruption-resist capacity of domestic industry, in addition to the highly monopolized core techniques, makes it rather difficult to industrialize this product by applying foreign techniques, which traditionally uses HF method. In this thesis, three frequently-used types of electrolyte salts (LiBF4, LiPF6, LiBOB)are prepared by adopting new preparation methods.As is known, the critical defect of the preparation method adopted by foreign companies is caused by the use of strong corrosive and virulent solvents. Our method will help solve this problem. Therefore, this method will be of great significance to the self-development of its preparation method.Novel preparation method of LiF is studied in this thesis. The preparation methods are sub-divided into two:the wet method and the solid phase method. As for the wet method, nitric acid is used to dissolve the Li2CO3;LiF is precipitated by using excessive NH4F;the whole preparation process is to be monitored under the atomic absorption method. The results show that the best precipitation time is 3-5h, the best pH value is 4.4～4.7,the best Li+ initial concentration is 1.0 mol·L-1～2.0 mol·L-1,and the best F-/Li+ ratio is 1.5～2.5. As for the solid phase method, LiCl and NH4HF are used as materials; high pure and anhydrous LiCl is obtained from purified LiCl by using extraction resin; and then LiF is synthesized from it through NH4HF.The key controlling condition is monitored by X-ray diffraction analysis. The results show that the best temperature for synthesis is 150℃～200℃,the best time for synthesis is 5 h-6 h and the best raw material ratio is 2:1-3:1.Under the above two preparation methods, the impurity content is below 10 ug·g-1.The purity of the prepared product is high. The CH3CN solvent method is adopted in the preparation of LiBF4. The preparation of the intermediate product BF3 is monitored by the GC-MS-SIM technique. The result shows that the best condition is sodium tetra-fluoroborate is to be heated at the temperature of 500℃for 3h. BF3 and the self-made high pure LiF will directly react in CH3CN solvent. The final product is to be obtained after the following process:filtration, dissolution, cooling crystallization, re-crystallization and vacuum drying. FT-IR, XRD are used to the qualitative analysis of final production, AAS,IC are used to quantitative analysis, and TG-DTG is used to thermal analysis.The results show that LiBF4 synthesized under the CH3CN solvent method is of high purity, and the yield rate is over 70%; the product has two strong decomposition peaks at the temperature of 103.50℃and 300.06℃; the overall weight-loss ratio is around 75%,which is better than commercially available LiBF4.Novel preparation method of high pure PF5 is initially proposed in this thesis. The new methods can be subdivided into pure solid phase method and HPF6 intermediate product method.4 sets of pure solid phase methods for PF5 are introduced in this thesis.Much attention is given to the research of the best controlling condition of the solid-solid heating preparation for P2O5 and CaF2 by using the GC-MS-SIM method. The best controlling condition is that solid P2O5 and CaF2 with the mass ratio of≥2:1 are heated at the temperature of 280℃for 3 h. As for the preparation of PF5 under the HPF6 intermediate product method, P2O5 and anhydrous HF are used as materials.The reaction process is to be analyzed by adopting the conventional nitron method; the final gas is to be analyzed by adopting the GC method. The results show that the reaction is lasted for 4 h under the condition of excessive anhydrous HF over 60%; dehydrate the HPF6 by using H2SO4·SO3 which should be 35%～40% more than the theoretical value;then heat the intermediate product under the temperature of 150℃for 40 min-50 min; condensate and decontaminate the mixed gas; the cooling medium is water with the temperature of 0℃;then obtain the final product PF5.PF5 prepared under the above two methods has high purity and better than that made under conventional method. We also confirm that ether is the best dissolvent for PF5.The CH3CN solvent method and the aether solvent method are adopted in the preparation of LiPF6 in this thesis. As for the CH3CN solvent method, self-made high pure LiF and PF5 will be directly reacted in the CH3CN solvent. After the reaction, the final product is to be obtained through the following process:filtration, dissolution, cooling crystallization, re-crystallization and vacuum drying. As for the aether solvent method, self-made high pure LiF and PF5 will be directly reacted in the aether solvent. After the reaction, the final product is to be obtained trough the following process:dissolution, clear solution absorbing, heating and evaporation under normal pressure, and vacuum drying. LiPF6 synthesized in this thesis has high purity and high yield rate.Two strong decomposition peaks appear at the temperature of 78.33℃and 202.15℃,and the weight-loss ratio are respectively 12.44% and 80.38%, and the overall weight-loss ratio is around 84%.Its thermal decomposition capacity is better than general commercially available LiPF6.The CH3CN solvent method and the solid phase method are adopted in the preparation of LiBOB in this thesis. As for the CH3CN solvent method, H3BO3, Li2CO3, H2C2O4 are used as materials. Firstly, lithium source is pre-processed by using P204 extraction resin; then put the reactants in the CH3CN solvent; after the reaction, the final product is to be obtained through the following processes:filtration, vaporization under low pressure, EGME re-dissolution, re-crystallization and vacuum drying. As for the solid phase method, Li2CO3,H3BC3,H2C2O4 are used as materials. Under the XRD on-time analysis method, such key controlling factors are to be investigated as synthesis temperature, synthesis time, lithium materials, purification solvents, and crystallization forms. The results show that materials are to be put into the pipe furnace and reacted under the temperature of 120℃for 4 h; and then elevate the temperature to 240℃and reacted in this condition for 4 h; after the reaction, the final product is to be obtained through the following processses:filtration, vaporization under low pressure, re-dissolution, re-crystallization and vacuum drying. LiBOB synthesized in this thesis has high purity and high yield rate. Two strong decomposition peaks appear at the temperature of 381.65℃and 444.18℃,and the weight-loss ratio are respectively 75% and 10% and the overall weight-loss ratio is around 85%.Its thermal decomposition capacity is good.Organic solvent method (including CH3CN solvent and aether solvent) proposed in this thesis can be applied in the preparation of three salts.This method abandons the conventionally-used strong corrosive and virulent solvents. The reaction process has no pollution to the environment and the final product. What's more, the reaction process of the pure solid phase method is free from the disturbing of water. Therefore, it benefits much the preparation of electrolyte salt and has obvious advantages. |
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