4‑(Trifluoromethyl)phenyl Isothiocyanate as a Bifunctional Additive for Regulating High-Temperature Performance of Lithium-High Nickel Batteries

Although nickel-rich cathode materials have been suggested as prospective advanced cathodes for more than 20 years, their poor cycling lifespan remains the main challenge in achieving stable cycling. Herein, we report the use of 4-(trifluoromethyl)phenyl isothiocyanate (FIC) to build cathode–electrolyte interphases (CEI) for stabilizing the Ni-rich cathode interfaces. Because the FIC additive involves an isothiocyanate (NCS) functional group, it is predicted that the electrochemical oxidation of FIC results in an NCS-functionalized CEI at the interface of the nickel-rich cathode, which is expected to constrain parasitic reactions. The electrochemical oxidation of FIC permits the buildup of NCS-functionalized CEI layers at 3.97 V (vs Li/Li⁺) without severe intervening of Li⁺ transport during the electrochemical processes. In cycling performance, the FIC-containing electrolytes experienced a remarkable improvement in retention at high-temperature cycling (89.1%), whereas the baseline electrolyte led to an enormous fading of the retention (70.3%). Further systematic microscopic and spectroscopic analyses indicate that less electrolyte decomposition and irreversible dissolution of transition metals are found at the interface of recovered electrodes by incorporating NCS-functionalized CEI layers.