Interfacial Chemistry Design for Hybrid Lithium‐Ion/Metal Batteries Under Extreme Conditions

The storage behavior of Li ions in the anode limits the energy density of full cell. Storing entirely as Li ions sacrifices energy density while storing entirely as Li metal shortens cycle life. The hybrid behavior maximizes both energy density and lifespan through good anode candidate and interface engineering. In this work, Li ions storage is tailored in carbon film (CF) as a hybrid Li‐ion/metal to reduce Li metal consumption at low N/P ratios. A series of weakly solvating electrolytes are screened to enhance the Li intercalation ability of the CF anode while inducing highly reversible Li metal plating/stripping. Among them, 1 m LiFSI‐THF‐0.5 wt.%LiNO3 electrolyte achieves a low interfacial energy barrier, allowing the CF anode not only to have the highest intercalation capacity of 236.5 mAh g−1, but also to exhibit excellent cycling stability and high Coulombic efficiency, even at fast charging and low temperature. The NCM811||CF full cell with a low N/P ratio of 0.5 delivers a capacity of 527.3 mAh g−1 at 25 °C, and 381.5 mAh g−1 at −20 °C, achieving energy densities of 312.6 and 223.7 Wh kg−1, respectively. 100 mAh pouch cell can be cycled stably over 500 cycles, with a capacity retention of 83.0%. Weakly solvating electrolyte derived from tetrahydrofuran has low interface energy, enabling solvated‐Li+ co‐intercalate into the carbon film and inducing the formation of a robust SEI film with inorganic rich. Carbon film anode achieves ultra‐high Li intercalation capacity of 236.5 mAh g−1 at 0–0.1 V and reversible cycling of hybrid lithium‐ion/metal batteries over 1000 cycles.