An All-Fluorinated Electrolyte Toward High Voltage and Long Cycle Performance Dual-Ion Batteries

The dual-ion battery (DIB) is a promising energy storage system that demonstrates high-power characteristics and fast-charging capability. However, conventional electrolytes are not compatible with the high-voltage graphite cathode and the reactive Li metal anode, thus leading to the poor cycle stability and low Coulombic efficiency of the DIB. Here, an all-fluorinated electrolyte is reported that can enable a highly stable operation of the graphite||Li DIB up to 5.2 V by forming robust and less-resistive passivation films on both electrodes to reduce side reactions. The electrolyte allows reversible PF₆^– anion insertion/extraction and Li⁺ cation plating/stripping in the graphite||Li battery, achieving stable cycling with 94.5% capacity retention over 5000 cycles at 500 mA g^–1, high capacity utilization of 91.8% of the available charge capacity at 50 C (5000 mA g^–1), and also minimal self-discharge. At a low temperature of 0 °C, this all-fluorinated electrolyte exhibits 97.8% of the room temperature reversible capacity, along with ≈100% capacity retention after more than 3000 cycles, at 5 C. This work sheds a new light on the development of fluorinated electrolytes for high voltage and long-lasting DIBs.