Rational design of a carbonate-glyme hybrid electrolyte for practical anode-free lithium metal batteries

Rechargeable Li batteries are promising candidates for next-generation energy storage devices due to their high energy density. Electrolyte compositions profoundly impact their electrochemical performance. The carbonate-based electrolytes employed in conventional Li-ion batteries (LIBs) are highly corrosive to elemental Li. Glyme-based electrolytes generally possess better stability towards reduction, but they suffer from an early oxidation under 4 V/Li, mismatched with high-voltage cathodes. Most recently, fluorinated solvents and salts demonstrated a positive effect on the cyclic behaviour of Li anode, but the high cost hampers their application. Herein, we designed an economical carbonate-glyme hybrid electrolyte (CGHE) compatible with both elemental Li anode and Ni-rich cathode. The resulted Li battery cycled at 2C delivers a specific capacity of 99.2 mAh g⁻¹ after the 200^th cycle, almost four times higher than the baseline electrolyte with a remained capacity of 27 mAh g⁻¹. The hybrid electrolyte provides a capacity retention of 73 % at the 50^th cycle for the cell with no Li excess, while the cell with typical carbonate electrolyte ultimately failed within 45 cycles. The merits originate from the unique solvation structure of the designed electrolyte. In particular, diglyme solvates both Li-ions and film-forming additive, while carbonates dilute the mixture, enabling facile ion migrations.