Toward Stable Sodium Metal Anode in Carbonate Electrolyte: A Compact, Inorganic Alloy Interface.

Development of the next generation high-energy-density, low-cost batteries will likely be fueled by sodium (Na) metal batteries due to their high capacity and earth-abundancy. However, their practical application is significantly plagued by the hyper-reactivity of Na metal, unstable solid electrolyte interphase (SEI) and dendritic Na growth, leading to continuous electrolyte decomposition, low Coulombic efficiency (CE), large impedance and safety concerns. Herein, we add a small amount of SnCl2 additive in a common carbonate electrolyte so that the spontaneous reaction between SnCl2 and Na metal enables in-situ formation of a Na-Sn alloy layer and a compact NaCl-rich SEI. Benefitted from this design, rapid interfacial ion transfer is realized and direct exposure of Na metal to the electrolyte is prohibited, which jointly achieve a non-dendritic deposition morphology and a markedly reduced voltage hysteresis in Na/Na symmetric cell for over 500 hours. The Na/SnCl2-added electrolyte/Na3V2(PO4)3 full cell exhibits high capacity retention over cycling and excellent rate capability (101 mAh/g at 10 C). This work can provide an easily-scalable and cost-effective approach for developing high-performance Na-metal batteries.