Diphenyl Diselenide As SEI- Forming Additive for High Voltage LiCoO_2/Graphite Battery

摘要

Lithium-ion batteries are widely used due to its high energy density and long cycle life. Yet, there is a continuous demand for much higher energy density and power density to expand the application to the electric vehicles. As flagship electrode materials, LiCoO_2 (LCO) and graphite have been used. Higher operating voltage increases energy density, so researchers have conducted developments to raise final charging voltage. However, LCO/graphite battery suffers from capacity decay due to the destruction of electrolyte and cathode material at high voltage operation (>～4.3 V) and graphite-electrolyte reaction. There is a lot of researches about the solid electrolyte interface (SEI) to improve the battery performance. Electrolyte additive to make better SEI layer is one of the effective ways. In this study, diphenyl diselenide (Ph_2Se_2) is used as additive to improve battery performance. Changing the concentration of additive (0%, 0.1%, 0.2%, 0.4%), the electrochemical characteristics of the LCO/graphite cell were analyzed by cyclic voltammetry (CV), linear sweep voltammetry (LSV), field emission scanning electron microscope (FE-SEM), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). At high voltage operation (4.4 V), rate capability and cyclic stability of the cell with diphenyl diselenide were improved. It was presented that diphenyl diselenide decomposed in the LCO surface. As a result, the SEI layers including diphenyl diselenide prevent a collapse of LiCoO_2 crystal on the cathode and decrease the reaction of graphite with electrolyte on the anode.