The Research On High-voltage Electrolytes Electrochemical Performance

The chemical composition of electrolytes profoundly affects the cell performance in many aspects. At present, usually the commercial5V electrolyte consists of a fluorine-containing lithium salt and alkyl carbonate solvents, for example the lithium hexafluorophosphate (LiPF6)-ethylene carbonate (EC)/diethyl carbonate (DMC) electrolyte system。 However, the preferred salt, LiPF6, can undergo an autocatalytic decomposition into undesired products as PF5and HF. And to make matters worse, the HF could attack cathode material to make transitional metals dissolved.Lithium bis(oxalato)borate (LiBOB), as a halogen-free lithium salt, has been reported as a promising candidate for lithium-ion batteries with improved properties, such as good thermal stability, low cost and low susceptibility. Based on the recently development of LiBOB-based electrolyte, this paper mainly studies the application of high-voltage electrolyte with LiBOB. First, the LiBOB is chosen as the lithium salt, y-butyrolactone (GBL), sulfolane (SL) as well as carbonate (DMC) is chosen as supporting electrolyte solvent, constructed an novel electrolyte of1.0mol L-1LiBOB-SL/GBL/DMC. Through the use of computational chemistry and electrochemical testing methods, it indicates that SL solvent is the key reason for the improvement of electrochemical performance, which not only improves the stability of electrolyte system against oxidative decomposition, but also decreases the electrode polarization resistance. More than that,1.0mol L-1LiBOB-SL/GBL/DMC electrolyte shows good compatibilities with both intercalation hosts as LiNi0.5Mn1.5O4cathode and carbonaceous anode, indicating a good application foreground of the novel electrolyte. Then, with dimethyl sulfite (DMS) and GBL as mixed solvents, the electrochemical behavior of LiBOB is studied. It shows that LiBOB-GBL/DMS electrolyte has high oxidation potential (>5.3V), and satisfactory conductivities. The novel electrolyte exhibits not only excellent film-forming characteristics, but also low impedances of the interface films. Besides, when used in LiFeO4/Li and Li/MCMB cells, exhibits not only excellent film-forming characteristics, but also a more stable cycle performance at room temperature. Finally, the chemical properties of the novel lithium salt, LiBF2SO4, were calculated by quantum calculation, including the optimization of the structure, the oxidation potential and oxidative decomposition path.