Directing the uniform and dense Li deposition via graphene-enhanced separators for high-stability Li metal batteries

Lithium (Li) has been widely studied as a next-generation anode material owing to its high theoretical capacity (3860 mAh g(-1)) and lowest negative potential (-3.04 V vs. SHE). However, the practical applications of Li-metal batteries (LMBs) are hindered by uncontrolled Li deposition during the charging/discharging process and low Coulombic efficiency. Among the numerous strategies, surface optimization of polymer separators with functional nanomaterials, especially graphene, has achieved significant progress in both academic and industrial fields. In this study, we elucidate how the graphene-enhanced separator (GES) improves the electrochemical reversibility of Li deposition/dissolution and consequently extends the cyclability of LMBs. When the GES is employed in Li|Cu cells, a dense Li layer forms between the graphene layer and Cu current collector after multiple Li deposition/dissolution cycles. Furthermore, when the graphene-modified current collector (GMCC) is employed, Li dendrites predominantly grow on the graphene surface and migrate toward the separator, alleviating the risk of separator puncture. The Li|Cu cell with GES demonstrates a higher cycle stability and Coulombic efficiency under high current conditions (similar to 99 % at 4 mA cm (-2)) than the Li|Cu and Li|GMCC cells. Moreover, anode-free cells paired with the GES exhibited high capacities and consistent cycle performances under both lowand high-current conditions.