Quickly form stable cathode/electrolyte interface of LiNi0.5Mn1.5O4 (LNMO)/graphite high-voltage lithium ion cells by using tosylmethyl isocyanide (TosMIC) as electrolyte additive

Tosylmethyl isocyanide (TosMIC) is used as electrolyte additive to study the effect on the cycling performance of LiNi0.5Mn1.5O4 (LNMO)/graphite 5V lithium-ion cell. The constant current charge and discharge measurement results shows that the capacity retention rate of the cell containing 0.3 wt% TosMIC increases by 18% after 200 cycles, while 1.0 wt% TosMIC worsens the cycling performance of the cell. The decomposition product PF5 of electrolyte salt LiPF6 may interact with TosMIC to form TosMIC-PF5 complex. The results of surface and electrochemical analysis indicate that the complex can be oxidized at the cathode and reduced at the anode simultaneously prior to the solvent molecules of the electrolyte. Theoretical calculation further shows that TosMIC-PF5 can be oxidized to form a dimer (TosMIC-PF5)2 at 4.46V (vs. Li/Li+), which may be deposited on the LNMO cathode to help form a coating layer. This coating layer can be rapidly formed in the first cycle and can significantly alleviate the oxidation of the electrolyte, but it cannot inhibit the decomposition of excessive additive. Two proposed reduction reactions of TosMIC-PF5 occur at 1.66 V and 2.00 V (vs. Li/Li+). Unfortunately, the reduction of this additive has a negative impact on the cycling performance of the cell.