Multiphase artificial interphase layer enabled long-life and dendrite-free sodium metal batteries

Sodium metal anodes have received considerable attention due to their high theoretical capacity, low reduction potential, and natural abundance in sodium batteries. Nevertheless, uneven sodium ion (Na+) deposition accelerates uncontrolled dendrite growth and an unstable solid electrolyte interphase (SEI) layer hinders Na+ diffusion, which eventually leads to short circuits and potential safety hazards. Herein, a multiphase artificial interphase layer composed of sodium bismuth alloy (BiNa3) and sodium chloride (NaCl) is applied to improve the interface stability of sodium metal anodes. Theoretical calculations and experimental results demonstrate that the BiNa3 alloy with good sodiophilic properties can function as nucleation sites to lower the nucleation barrier, induce uniform Na+ flux, and guide dendrite-free Na deposition. Meanwhile, a NaCl compound with high ionic conductivity can lower the Na+ diffusion barrier and improve diffusion kinetics. As a result, the assembled symmetric cells with a sodium metal anode modified by using a multiphase artificial interphase layer exhibit a remarkable cycling performance of 1200 h with a low overpotential of 20 mV at 3 mA cm-2 and 3 mA h cm-2. The full battery assembled with the Na3V2(PO4)3 cathode retains an ultrahigh capacity of 99 mA h g-1 even after 1000 cycles at 5C. The design strategy for a multiphase artificial interphase layer can provide insight into developing high-performance and dendrite-free sodium metal batteries. A multiphase artificial interphase layer can induce homogeneous deposition of Na+ and promote rapid transport of Na+. Therefore, the BiCl3-Na anode achieves uniform dendrite-free deposition and improves electrochemical performance.