Na3P interphase reduces Na nucleation energy enabling stable anode-less sodium metal batteries

Sodium metal batteries (SMBs) are rising as viable alternatives to lithium-ion systems due to their superior energy density and sodium's relative abundance. However, SMBs face significant impediments, particularly the exceedingly high negative-to-positive capacity ratios (N/P ratios) which severely encumber energy density and hinder their practical application. Herein, a novel nucleophilic Na3P interphase on aluminum foil has been designed to significantly lower the nucleation energy barrier for sodium atom deposition, resulting in a remarkable reduction of nucleation overpotential and efficient mitigation of dendritic growth at high sodium deposition of 5 mA h cm−2. The interphase promotes stable cycling in anode-less SMB configurations with a low N/P ratio of 1.4 and high cathode mass loading of 11.5 mg cm−2, and demonstrates a substantial increase in high capacity retention of 92.4% after 500 cycles even under 1 C rate condition. This innovation signifies a promising leap forward in the development of high-energy-density, anode-less SMBs, offering a potential solution to the longstanding issues of cycle stability and energy efficiency.