Stable Cycling of High-Voltage Lithium-Metal Batteries Enabled by High-Concentration FEC-Based Electrolyte

Functional electrolytes that are stable toward both Li-metal anode and high-voltage (>4 V vs Li/Li⁺) cathodes play a critical role in the development of high-energy density Li-metal batteries. Traditional carbonate-based electrolytes can hardly be used in high-voltage Li-metal batteries due to the dendritic Li deposits, low Coulombic efficiency, and anodic instability in the presence of aggressive cathodes. Herein, we design a concentrated dual-salt electrolyte that achieves high stability for both Li anodes and high-voltage cathodes of LiNi_0.5Mn_1.5O₄ (LNMO) and LiNi_0.7Co_0.15Mn_0.15O₂ (NCM). A Li||Cu cell in the designed electrolyte shows a high Coulombic efficiency of >98% in long-term plating/stripping for 900 cycles. Li||LNMO and Li||NCM cells achieve a capacity retention of 88.5% over 500 cycles and 86.2% over 200 cycles with a cutoff voltage of 4.9 and 4.3 V, respectively. The Li||LNMO full cell with a cathode areal capacity of 1.8 mAh/cm² and only 3× excess Li was fabricated, and it delivered a high capacity retention of 87.8% after 100 cycles. The reasons for the good cycling stability of the cells in a concentrated dual-salt electrolyte can be attributed to the reversible dendrite-free plating/stripping of a Li-metal anode and stable interfacial layers on both anode and cathode.