Reversible Na15Sn4 alloy compensation for hard carbon anodes to enhance the initial coulombic efficiency in sodium-ion full cells

Abstract

An effective sodium compensation strategy employs a Na₁₅Sn₄ alloy as a dynamic sodium reservoir paired with hard carbon (HC) anodes, undergoing reversible dealloying at low potentials (<0.5 V vs. Na⁺/Na) to release active Na ions, thereby compensating for irreversible sodium losses during the initial cycles. The full-cell configurations with NaSn@HC in the Na₃V₂(PO₄)₃ cathode system achieve an ICE of 90.1%, outperforming conventional hard carbon anodes by more than 50%.