Seeding a Gradient Solid-Electrolyte Interphase in Anode-Free Lithium Metal Batteries

Anode-free lithium metal batteries (AFLMBs), coupling lithiated cathodes and bare anode current collectors, deliver advantages in both energy density and safety. Nevertheless, AFLMBs suffer from a limited cycling life due to the parasitic reactions and vulnerable solid-electrolyte interphase (SEI). In this study, a chromium nitride nanofilm is coated on copper foil by a filtered cathodic vacuum arc (FCVA) to optimize Li deposition and participate in forming a gradient SEI. This gradient SEI has a LiF-rich surface and a CrF₃-rich middle layer, mitigating parasitic electrolyte decomposition by reducing electron leakage into the electrolyte. Meanwhile, the inner region of the SEI is predominately composed of Li₃N, which facilitates smooth Li⁺ transport and uniform Li deposition. Under lean-electrolyte conditions (1.75 g of Ah^-1), the anode-free pouch cell (0.72 Ah) achieves a high energy density of 453 Wh kg^-1. This work presents a scalable route to nanoscale lithiophilic coatings, advancing AFLMB technology toward practical application.