Nanoscale sputtered buffer layers for in situ fabrication of thin sodium metal anodes

Abstract Sodium (Na) metal is a highly attractive anode material for next-generation batteries due to its natural abundance and low cost, but its practical use is limited by poor reversibility of the Na plating/stripping process and instability during cycling. Herein, metal thin-films (Ti, Ni, Ge and In) with different thicknesses are grown by magnetron sputtering to coat commercial stainless stell 316L current collectors, and the substrate-dependent Na plating/stripping characteristics are thoroughly explored. The results reveal that sodiophilic interphases can be achieved by in situ formation of M–Na (M = Ge, In) alloys. A controlled protocol is developed to electrochemically form ultrathin Ge–Na or In–Na alloy buffer layers in the first cycle prior to Na plating, serving as pillars for a stable subsequent Na metal deposition and boosting the buildup of a highly efficient thin Na metal anode. Among the tested materials, 50 nm thick In coatings exhibit the most stable long-term plating/stripping process. These findings demonstrate a simple and effective interfacial engineering strategy to enhance the performance of Na metal anodes, providing a pathway toward safer and long-lasting sodium metal batteries (SMBs).