Dual-inorganic-rich artificial interphase for sodium metal batteries

Abstract

Sodium metal batteries have gained attention as ideal alternatives to lithium-ion batteries, but the poor compatibility of metallic Na anodes in conventional ester-based electrolytes presents a pivotal challenge. To tackle this issue, a dual-inorganic-rich artificial layer is engineered via the spontaneous reaction of PCl₅ with Na, resulting in a Na₃P- and NaCl-rich interphase on metallic Na (PCI-Na). In the dual-inorganic-rich interphase, NaCl featuring electronic insulation and a low diffusion barrier can effectively prevent continuous electrolyte decomposition and mitigate the formation of "hot spots" for Na deposition. In addition, Na₃P with high interfacial energy and good sodiophilicity helps suppress the dendrite formation and promote uniform sodium plating. As a result, symmetric cells of PCI-Na cycle for nearly 500 h at 1 mA cm⁻² and 2 mAh cm⁻², outlasting the bare sodium counterpart. Furthermore, when paired with Na₃V₂(PO₄)₃, full cells of PCI-Na||Na₃V₂(PO₄)₃ cycle stably for 1000 cycles at 5 C, with a capacity retention of 82.3%. The full cells also work well at subzero temperatures, thus indicating that designing dual-inorganic-rich artificial interphase opens up new possibilities for practical sodium metal batteries.