Spinel LiNi_0.5Mn_1.5O₄ (LNMO) is a promising high-voltage cathode material for the next generation lithium metal batteries because of its high operating voltage plateau (4.7 V vs. Li⁺/Li), high theoretical specific capacity (147 mAh/g), relatively low cost and environmentally benign properties. Despite promising, the commercialization of LNMO cathodes is hindered by its electrochemical instability using conventional carbonate electrolytes, resulting in lower Coulombic efficiency and poor cycling stability. Herein, we adopt an all-fluorinated electrolyte (AFE) with a wide electrochemical stability window for Li//LNMO cells. Compared to conventional carbonate electrolytes, AFE significantly improves the discharge capacity and rate performance of Li//LNMO cells at various cut-off voltages and temperatures, attributed to the formation of a robust cathode–electrolyte interphase (CEI) layer. Specifically, the resultant Li//AFE//LNMO cells deliver a discharge capacity of 131.7 mAh/g with 84.1% capacity retention after 250 cycles at a charge cut-off voltage of 4.9 V, while it sustains only 114.8 mAh/g with 81.9% capacity retention for the cell using a conventional carbonate electrolyte. The influence of charge/discharge rate and temperature on the performance is also evaluated. Overall, this study presents a facile approach to promote the commercialization of high-voltage LNMO cathodes.

Solid polymer electrolytes (SPEs) have attracted considerable attention for solid-state lithium-metal batteries (LMBs) with high energy density and enhanced safety for future applications. In this study, an SPE was developed based on a poly(ethyl acrylate) (PEA) polymer matrix with the vinylene carbonate (VC) additive (defined as PEA-VC) for high-voltage solid-state LMBs. Results show that introducing the VC additive into the PEA-based SPE leads to high lithium-ion conductivity (1.57 mS/cm at 22°C), a high lithium-ion transference number (0.73), and a wide electrochemical stability window (up to 4.9 V vs. Li/Li⁺). The remarkable compatibility of the PEA-VC SPE with lithium metal anodes and high-voltage cathodes was demonstrated in Li//Li symmetric cells (800 h lifetime at a current density of 0.1 mA/cm² at 22°C) and Li//LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) full cells (with a capacity retention of 77.8% after 100 cycles at 0.2C). The improved stability is attributed to the introduction of the VC additive, which helps form a robust cathode–electrolyte interphase, effectively suppressing parasitic interface side reactions. Overall, this study highlights the role of VC additives in high-voltage and solid-state LMBs, offering a general yet effective approach for addressing the interfacial instability issue through an additive-engineering strategy.