Study On Synthesis And Purification Of LiBOB

A novel lithium ion electrolyte salt LiBOB was compared with LiPF6. Because of the good stability, the pollution-free decomposition products, the high decomposition potential, the superior protection of aluminum current collector and participating in the SEI film formation, LiBOB became the most likely substitute of LiPF6as the commercial electrolyte of lithium-ion battery. The synthesis and purification methods of LiBOB were not perfect at present and needed further improvement.LiBOB was synthesized by oxalic acid, boric acid and different lithium sources in this paper. TG-DTA measurement was used to analyze the characteristics of the synthesis process and to determine the properties of the products under different temperatures. Based on the TG-DTA results and the physical and chemical properties of the raw materials, the synthesis method was improved. LiBOB was synthesized by stepwise heating and characterized by XRD, FTIR, and electrochemical tests in order to select the proper lithium sources. The purification method of LiBOB was improved by comparing several purification methods and the corresponding yields. The optimum solvents for purification were also determined by checking the physical properties of common organic solvents. The performance of the self-made LiBOB was evaluated from the conductivity of the electrolyte, Dissolution, water content, cycle performance of LiFePO4. The following conclusions were made:(1)LiBOB was synthesized by solid-state stepwise heating method. The improved method can overcome the shortcomings that oxalic acid could easily volatile at120℃as a source of oxalate. LiBOB existed stable from240℃to300℃. The decomposition temperature was about310℃.(2)XRD measurement, ICP analysis, yield detection and the electrochemical performance test of lithium manganese battery were used to determine the effect of lithium sources on the properties of LiBOB. It was found that LiBOB contained more impurity phases and could not meet the requirements of the electrolyte with Li2C2O4as the lithium source. The yield of LiBOB was very low with CH3COOLi·2H2O as the lithium source. When Li2CO3and LiOH were used as the lithium sources, LiBOB showed higher purity, better phase composition, higher yield and could be used as the electrolyte.(3) By comparing the effect of different purification methods on the yield of LiBOB, a novel purification method was proposed and pure LiBOB product could be obtained in short time with higher yield, higher purification efficiency. Using the improved solid state synthesis method and the improved purification method, the reaction time was greatly decreased and the yield was increased compared with the traditional method. The total yield were as high as74.1%and72.7%, respectively with LiOH.H20and Li2CO3as lithium sources. The organic solvents were selected as:(a) acetonitrile and acetone whose boiling points were81.8℃and56.5℃respectively;(b) toluene and P-xylene whose boiling points were110.8℃and138.5℃.(4)The conductivity of LiBOB in organic solvents was proportional to the Dissolution of LiBOB. It was higher in y-BL, AN and other mixed solvents. The solubility of LiBOB in the mixed organic solvent of EC/PC/DMC was up to1mol/L(5) LiFePO4showed better cycle performance in the electrolyte of self-made LiBOB rather than in the lectrolyte of commercial LiBOB at low rate. But the high-rate performance of LiFePO4in the electrolyte of self-made LiBOB was inferior to that in the electrolyte of commercial of LiBOB.