Reconstruction of LiF-Rich Interfaces through a Lithium Formate Additive for Anode-Free Lithium Metal Batteries

Anode-free lithium metal batteries (AFLMBs) offer high energy density and enhanced safety due to no excess lithium (Li) in the anode. Nevertheless, Li dendrite growth and dead Li formation rapidly consume the limited active Li in AFLMBs, resulting in a low Coulombic efficiency (CE) and accelerated battery capacity deterioration. Herein, a Li reservoir is established by incorporating lithium formate (CHLiO₂) into both the cathode and anode as a Li salt additive for interface reconstruction, which improves the cycling stability of AFLMBs. Density functional theory calculation confirms that CHLiO₂ exhibits relatively lower lowest unoccupied molecule orbital (LUMO) energies and higher highest occupied molecular orbital (HOMO) energies compared to the carbonate electrolyte solvents. The integration of CHLiO₂ significantly promotes the reconstruction of LiF-rich interfaces and effectively prevents continuous electrolyte decomposition, which contributes to uniform Li deposition and suppresses active Li consumption. After the introduction of the CHLiO₂ additive, the Cu||NCM811 cell retains an average CE of 97.3% during 40 cycles. This study provides a simple yet effective methodology to supply an extra Li source and reconstruct LiF-rich interfaces for extending the cycling life of AFLMBs.