Stable Na Metal Anode Enabled by a Reinforced Multistructural SEI Layer

Abstract Metallic sodium (Na) is one of the most promising anode candidates for next‐generation secondary batteries. The development of Na metal batteries with a high energy density and low cost is desirable to meet the requirements of both portable and stationary electrical energy storage. Unfortunately, several problems caused by the unstable Na metal anode severely hinder the practical applications of these batteries. Here reported is a facile but effective methodology to form a multistructural interphase layer containing a sodium fluoride‐rich solid electrolyte interphase (SEI) and crisscrossed Na 3 Sb bars on the Na electrode surface. The reinforced Na‐alloy network and chemically/electrochemically complementary SEI formation greatly improve the interphase strength and Na + conductivity. The well‐protected Na metal electrode in symmetric Na|Na cells is stable and dendrite‐free in the plating and stripping cycling processes with a negligible voltage divergence, even at a large current density of 5 mA cm −2 or with a high deposition capacity of 10 mAh cm −2 . Moreover, this anode is especially compatible with different cathodes and demonstrates outstanding cycle performance in the full cells. It is believed that this approach provides a practical solution toward stable Na metal anodes and related battery systems.