Interfacial design principle of sodiophilicity-regulated interlayer deposition in a sandwiched sodium metal anode

Sodium (Na) metal anodes provide the base for the high specific energy of rechargeable Na batteries. However, non-uniform dendrite growth, volume change, and low Coulombic efficiency of Na metal anodes cause safety concerns and poor cyclability, hindering the practical applications of Na batteries. Herein, we proposed an interfacial design principle to construct sodiophilicity-regulated Na metal anodes. Through modeling the interfacial interaction that appears in a sodiated Sn-O-C system, we discovered and experimentally confirmed that the intermediate phases of Na2O and/or Na15Sn4 lower the nucleation overpotentials and guide the Na deposition because of the strong binding to Na metal. More importantly, the poor cyclability caused by the loss of sodiophilic sites can be dramatically improved by designing a strong interaction between sodiophilic agents and conducive scaffolds. Following the principle, we sandwiched SnO2 nanodots between reduced graphene oxide (rGO) layers to form a monolithic Na metal anode and pre-coated it with artificial solid electrolyte interphase (SEI). The resultant layered sandwich structure enables a unique interlayer Na deposition through the thickness direction, thereby leading to a stable SEI and enhanced cyclability. This interfacial principle provides a rational design basis for durable and efficient Na metal anodes.