【作者】 刘建文；

【导师】 李新海；

【作者基本信息】 中南大学 ， 电化学工程， 2009， 博士

【摘要】 当前,我国锂离子电池电解质盐的相关研究及产业化一直未取得突破,国内所需电解质锂盐因无国产能力全部依赖进口。究其原因主要是由于产品纯度要求高、生产危险性大、原材料制备困难、技术垄断度高等。目前,国外普遍采用氟化氢(HF)作原料生产电解质锂盐,在国内防腐工程领域水平较低的前提下,国内按照国外工艺开展产业化瓶颈多、难度极大。本研究论文采用全新方法制备三种常用电解质盐四氟硼酸锂(LiBF4).六氟磷酸锂(LiPF6).双草酸硼酸锂(LiBOB),解决了国外方法中一直沿用腐蚀性、强毒性试剂的致命缺点,为我国自行开发制备方法提供了重要思路,意义重大。本文首先研究了重要原材料——氟化锂(LiF)的制备新方法,分为湿法、固相法两种方法制备。湿法采用硝酸溶解锂碳酸锂(Li2CO3),用过量氟化铵(NH4F)沉淀出LiF,实验中采用原子吸收法对制备过程及主要优化条件进行监测,结果表明：最佳沉淀时间控制在3-5 h；最佳pH值在4.4-4.7之间；最佳Li+初始浓度在1.0mol·L-1～2.0 mol·L-1之间；最佳F-／Li+浓度比为1.5-2.5。固相法采用氯化锂(LiCl)和氟化氢铵(NH4HF)为原料,LiCl经萃淋树脂纯化得高纯无水LiCl,后经NH4HF干法合成LiF。实验中采用X射线衍射分析监测过程中控制条件,结果表明：固相法最佳合成温度在150℃-200℃之间；最佳合成时间为5 h-6 h；最佳原材料配比以2：1-3：1为宜。两种制备方法所制得LiF的杂质含量都控制在10 ug·g-1之内,制备产品纯度高。LiBF4制备采用的是乙腈(CH3CN)溶剂法。其中中间产物BF3的制备过程采用气相色谱-质谱联用技术(GC-MS-SIM)监测,结果表明最佳条件为：氟硼酸钠在500℃条件下加热3 h。BF3和自制高纯LiF在CH3CN溶剂中直接反应,反应完全后经过滤、溶解、冷却结晶、重结晶、真空干燥得最终产物。产物经傅立叶变换红外光谱(FT-IR)、X射线衍射(XRD)进行定性表征,原子吸收法(AAS)、离子色谱法(IC)进行定量分析,并通过了热重、微分热重分析(TG-DTG)(下同)。结果表明：通过乙腈溶剂法制备LiBF4的纯度高,产率达到70%以上,产物主要在103.50℃和300.06℃处有2个强分解峰,整体失重率在75%左右,优于一般商业用的LiBF4。本文提出了高纯五氟化磷(PF5)气体的制备新方法,分为纯固相法、六氟磷酸(HPF6)中间产物法两种方法制备。本文提出了四套PF5纯固相制备方法,其中采用GC-MS-SIM法重点研究了P2O5和CaF2固-固加热制备过程的最佳控制条件：P2O5和CaF2固-固相在质量比≥2：1时,于280℃条件下加热3 h。HPF6中间产物法制备PF5采用P2O5和无水HF为原料,实验中采用传统的硝酸灵法对反应过程中的液相进行分析,以及采用GC法对最终所得气体进行气相分析,结果表明：在无水HF过量60%的条件下反应4 h,然后用比理论计算值大35%-40%的发烟硫酸(H2SO4·SO3)对中间产物HPF6进行除水处理,再在150℃条件下加热中间产物40 min-50 min,最后对混合气体进行冷凝除杂,冷却介质为0℃冷却水,最终得到产品PF5。本文提出的两类方法所制备PF5纯度高,优于传统方法。本文还确定无水乙醚是PF5的最佳溶剂。LiPF6制备采用的是乙腈溶剂法和乙醚溶剂法。乙腈溶剂法采用自制高纯LiF和PF5在乙腈中直接反应,反应完全后经过滤、溶解、冷却结晶、重结晶、真空干燥得最终产物。乙醚溶剂法采用自制高纯LiF和PF5在乙醚中直接反应,反应完全后经溶解、取清液、常温加热蒸发、真空干燥得最终产物。通过本实验制备的LiPF6纯度高、产率大,在78.33℃和202.15℃处出现两个强分解峰,失重率分别为12.44%和80.38%,整体失重率为84%左右。其热分解性能优于一般商品用LiPF6。LiBOB制备采用的是乙腈溶剂法和固相法。乙腈溶剂法以硼酸(H3BO3)、碳酸锂(Li2CO3)、草酸(H2C2O4)为原料,采用P204萃淋树脂预处理锂源,后将反应物置于乙腈溶剂中直接反应,反应完全后经过滤、减压蒸发、乙二醇二甲醚再溶解、重结晶、真空干燥得最终产物。固相法采用Li2CO3、H3BO3、H2C2O4为原料,以XRD实时分析方法重点就固相合成中的关键控制因素——合成温度、合成时间、锂源、提纯溶剂、结晶方式进行了考察。结果表明：原料置于管式炉中于120℃反应4h,再升温至240℃加热4h反应,反应完全后经溶解、过滤、减压蒸发、乙酸乙酯再溶解、重结晶、真空干燥得最终产物。通过本实验制备的LiBOB纯度高、产率大,主要在381.65℃和444.18℃处有2个强分解峰,失重率分别为75%和10%,整体失重率在85%左右,热稳定性能优。本研究论文提出的有机溶剂法(包含乙腈溶剂法和乙醚溶剂法)可应用于三种盐的制备中,该方法彻底摒弃使用了传统方法中普遍采用的HF等强毒、强腐蚀性溶剂,反应过程对环境和最终产品无污染。纯固相法因反应过程中无水分干扰,对电解质盐制备有利,优势明显。更多还原

【Abstract】 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.更多还原