Geometry-Guided Screening of Metal/Oxide Heterointerfaces Enables Superior Sodium Metal Batteries at -40 °C.

Despite their high theoretical energy density, sodium metal batteries (SMBs) remain limited by unstable interfacial chemistry and sluggish Na+ transport kinetics, particularly under ultralow-temperature conditions. Herein, guided by a geometry-driven design principle linking structural matching at metal/metal-oxide heterointerfaces with current density distribution, we identify a Y/Y2O3 heterostructure as an optimal surface modification layer and fabricate it on commercial aluminum foil via magnetron sputtering. The resulting Y/Y2O3 heterojunction, featuring a built-in electric field and moderate sodiophilicity, homogenizes Na+ flux, and directs reversible deposition. Meanwhile, the heterointerface facilitates PF6 - adsorption, directing interfacial reactions toward the generation of inorganic solid electrolyte interphase components, which contributes to improved interfacial stability under ultralow-temperature conditions. Consequently, the Y/Y2O3-modified current collector promotes highly reversible Na plating/stripping, enabling Na@Y/Y2O3@Al||Na3V2(PO4)3 full cells to retain robust cycling stability at -40 °C. The Y/Y2O3 heterointerface design provides an effective platform for enabling durable SMB operation under harsh ultralow-temperature conditions.