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

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) (approximate to 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) (approximate to 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.