Solvent Regulating Ni–O Bond Improves the Cyclability of High-Voltage Ni-Rich Cathodes in Nonflammable Electrolytes

Abstract

The adoption of nickel (Ni)-rich cathodes in lithium (Li) batteries is well suited for electric vehicles and portable electronic devices due to their high energy density and potential for longevity. However, the intense interactions between the cathode and electrolyte compromise electrochemical stability and safety, particularly under elevated voltage conditions. In this study, a nonflammable electrolyte with a low salt concentration of 0.75 M, incorporating fluoroethylene carbonate (FEC) and trimethyl phosphate (TMP) solvents, is developed to improve the cyclability at high state of charge. The combination of theoretical calculations and experimental characterizations demonstrates that the covalency of nickel (Ni) and oxygen bond is alleviated, thereby effectively mitigating the catalytic activity of highly delithiated cathodes and suppressing oxidative decomposition of the electrolyte and rock-salt phase formation. Moreover, this electrolyte facilitates the formation of an inorganic-rich solid-electrolyte interphase (SEI) on the Li metal anode, thus enhancing its reversibility. Consequently, the electrolyte markedly enhances the cyclability, stability, and safety of NCM811-Li batteries. The findings provide a promising solution for addressing the pivotal challenges associated with high-voltage Ni-rich Li batteries.