Rethinking sodium-ion anodes as nucleation layers for anode-free batteries

Abstract

Here we report a room-temperature sodium metal battery, where the sodium initially stored in a Na₃V₂(PO₄)₃ cathode is plated, upon charging, onto an aluminum current collector coated with a thin nucleation layer. To maximize the battery performance, conventional sodium-ion anode materials, including non-graphitized carbons and sodium-alloying metals, were evaluated as nucleation layers to facilitate stable electroplating of sodium metal. Among several materials studied, carbon black and bismuth showed the highest sodium plating–stripping coulombic efficiencies in half-cell testing, averaging 99.9% and 99.85%, respectively, over 50 cycles at 0.5 mA cm⁻². Building on these findings, anode-free cells with Na₃V₂(PO₄)₃ cathodes were assembled in a discharged state, demonstrating energy densities up to 318 W h kg⁻¹ at 0.25 mA cm⁻² (∼C/6), a first-cycle coulombic efficiency up to 92%, a stable discharge voltage at 3.35 V, an average round-trip energy efficiency of 98%, and a capacity retention of 82.5% after 100 cycles at 0.5 mA cm⁻² (∼C/3). With its unique performance highlighted in this work, the anode-free sodium battery emerges as a low-cost, high-performance option for stationary electric storage.