Lithium‐containing hybrid SEI layer enabling high mass loading and anode‐less sodium metal batteries

The continuous rupture and rebuilding of unstable solid electrolyte interphase layer during cycling would block Na+ diffusion and induce Na dendrite formation, ultimately limiting the practical application of high‐energy‐density sodium metal batteries. Herein, a hybrid SEI layer containing Li‐species is dexterously constructed on the surface of sodium metal anode. Li‐containing inorganic components (Li3N, LiF and Li2CO3) are introduced to stabilize the Na/electrolyte interface and enhance the mechanical and diffusion kinetic properties of the SEI layer, which can reduce the side reactions and gas generation, regulate Na+ flux during cycling and promote rapid Na+ migration for uniform dendrite‐free Na deposition. As a result, the constructed Na symmetric cells achieve low overpotential and long cycle life of 5900 h, 1800 h and 500 h at current densities of 3, 10 and 30 mA cm−2, respectively. Furthermore, the full cells paired with the Na3V2(PO4)3 cathode demonstrate high specific capacity and excellent cycle stability, even at an ultra‐high cathode loading of 39.3 mg cm−2 and a low N/P ratio (negative/positive electrode capacity ratio of 1.21).