Dynamic evolution of cathode-electrolyte interphase in lithium metal batteries with ether electrolytes

Abstract

High-voltage lithium (Li) metal batteries (HVLMBs) have attracted tremendous research interest in the past decade owing to their high energy densities. Electrode-electrolyte interphases in HVLMBs play critical roles in dictating their electrochemical performance. However, despite the intensive research on solid-electrolyte interphase (SEI) of Li anode, the cathode-electrolyte interphase (CEI) on high-voltage cathodes remains elusive. Herein, we report the formation and dynamic evolution of CEI on LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) cathodes in ether-based electrolytes. We reveal that the solvent-derived interphase predominates the initial CEI, which subsequently evolves into a Li fluoride (LiF)-rich CEI during cycling. Through solvent design, the weak-solvation electrolyte with branched ether solvents promotes the formation of a conformal CEI layer featuring the monodispersing LiF nanocrystals (∼8 nm), thereby enabling NMC811 cathodes to sustain up to 2,000 cycles. This work addresses the long-standing questions regarding CEI evolution and provides valuable guidance for the rational electrolyte design for HVLMBs.