Eliminating H2O/HF and regulating interphase with bifunctional tolylene-2, 4-diisocyanate (TDI) additive for long life Li-ion battery

Lithium-ion batteries (LIBs) featuring a Ni-rich cathode exhibit increased specific capacity, but the establishment of a stable interphase through the implementation of a functional electrolyte strategy remains challenging. Especially when the battery is operated under high temperature, the trace water present in the electrolyte will accelerate the hydrolysis of the electrolyte and the resulting HF will further erode the interphase. In order to enhance the long-term cycling performance of graphite/LiNi0.8Co0.1Mn0.1O2 (NCM811) LIBs, herein, Tolylene-2, 4-diisocyanate (TDI) additive containing lone-pair electrons is employed to formulate a novel bifunctional electrolyte aimed at eliminating H2O/HF generated at elevated temperature. After 1000 cycles at 25 °C, the battery incorporating the TDI-containing electrolyte exhibits an impressive capacity retention of 94% at 1 C. In contrast, the battery utilizing the blank electrolyte has a lower capacity retention of only 78%. Furthermore, after undergoing 550 cycles at 1 C under 45 °C, the inclusion of TDI results in a notable enhancement of capacity, increasing it from 68% to 80%. This indicates TDI has a favorable influence on the cycling performance of LIBs, especially at elevated temperatures. The analysis of the film formation mechanism suggests that the lone pair of electrons of the isocyanate group in TDI play a crucial role in inhibiting the generation of H2O and HF, which leads to the formation of a thin and dense interphase. The existence of this interphase is thought to substantially enhance the cycling performance of the LIBs. This work not only improves the performance of graphite/NCM811 batteries at room temperature and high temperature by eliminating H2O/HF but also presents a novel strategy for advancing functional electrolyte development.