Tris (pentafluorophenyl) phosphine: An electrolyte additive for high voltage Li-ion batteries

Tris (pentafluorophenyl) phosphine (TPFPP) is used as an electrolyte additive to improve the cycling performance of high voltage (~ 5 V) lithium-ion battery. The electrochemical behaviors and surface chemistry of LiNi0.5Mn1.5O4 are investigated via cyclic voltammetry, chronoamperometry, charge–discharge test, X-ray photoelectron spectroscopy, and theoretical computations. It is found that the cycling performance of the cell Li/LiNi0.5Mn1.5O4, using an electrolyte of 1.0 M LiPF6 in ethylene carbonate/dimethyl carbonate/diethyl carbonate (1/1/1, in volume), can be improved by adding TPFPP into the electrolyte. The theoretical calculations predict that TPFPP is preferably oxidized compared to the solvents. Electrochemical measurements and XPS analyses show that a protective film is formed on LiNi0.5Mn1.5O4 when TPFPP is used, which contributes to the cycling performance improvement of the cell.

► Significant improvement of cycling stability at 4.9 V with incorporation of TPFPP.
► Thinner surface layer formed on LiNi0.5Mn1.5O4 surface with TPFPP added electrolyte.
► More organic species formed on LiNi0.5Mn1.5O4 surface with TPFPP added electrolyte.
► Faster kinetics of Li-ion transport achieved with TPFPP containing electrolyte.