Vinylene carbonate and vinylene trithiocarbonate as electrolyte additives for lithium ion battery

Vinylene carbonate (VC) and vinylene trithiocarbonate (VTC) are studied as electrolyte additives in two kinds of electrolytes: (1) propylene carbonate (PC) and diethyl carbonate (DEC) (1:2 by weight) 1 mol dm−3 LiPF6; (2) ethylene carbonate (EC) and DEC (1:2 by weight) 1 mol dm−3 LiPF6. Characterization is performed by cyclic voltammetry, impedance spectroscopy, scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and half cell tests. Cyclic life is better in either electrolyte with VC than either electrolyte with/without VTC. SEM shows VC and VTC both form well developed passivation films on the graphite anode, but the films with VTC are thicker than with VC. EIS shows the VTC films have significantly higher charge transfer resistance. The VTC film in PC fails to protect against exfoliation. XPS indicates VTC has different reaction pathways in PC relative to EC. In EC/DEC, VTC forms polymeric C–O–C-like components and sulfide species (C–S–S–C, S and C–S–C). In PC/DEC, VTC does not form polymeric species, instead forming a film mainly containing LiF and Li2S. It appears that a thinner polymeric film is preferential. The specific data herein are of interest, and the general conclusions may help development of improved additives for enhanced Li-ion battery performance.