Electrochemical Analysis for Enhancing Interface Layer of Spinel Li4Ti5O12: p-Toluenesulfonyl Isocyanate as Electrolyte Additive.

An electrolyte additive, p-toluenesulfonyl isocyanate (PTSI), is evaluated in our work to overcome the poor cycling performance of spinel lithium titanate (Li4Ti5O12) lithium-ion batteries. We find that the cycling performance of a Li/Li4Ti5O12 cell with 0.5 wt % PTSI after 400 cycles is obviously improved. Remarkably, we also find that a solid electrolyte interface (SEI) film is formed about 1.2 V, which has higher potential to generate a stable SEI film than do carbonate solvents in the voltage range of 3.0-0 V. The stable SEI film derived from PTSI can effectively suppress the decomposition of electrolyte, HF generation, interfacial reaction, and LiF formation upon cycling. These observations are explained in terms of PTSI including SO3. The S═O groups can delocalize the nitrogen core, which acts as the weak base site to hinder the reactivity of PF5. Hence, HF generation and LiF formation are suppressed.