Liquid Alloying Na-K for Sodium Metal Anodes.

The prospects of sodium (Na) metal batteries have been fatally plagued by interfacial Na dendrites, mainly affected by preferred nucleation on the metal anode and the steep gradient of Na ions in the electrolyte, leading to limited Coulombic efficiency and short lifespans. Herein, an electrochemically inert potassium-based Na-K alloy demonstrates a liquid alloying diffusion mechanism that enables dendrite-free Na anodes. The extremely small Na fluctuation and flexible Na-K bonds in the liquid alloy phase bring isotropic nucleation of Na upon electroplating/stripping, which is directly observed by in situ optical imaging. Spontaneously, serving as (de)sodiation buffer with faster electron/mass transportation, the liquid inertia also provides attenuated concentration distribution of Na. Significantly, a record capacity retention of approximately 100% is rendered when coupled with Na3V2(PO4)3 cathodes (ca. 2 mg cm-2) over 500 cycles at 10C, advancing the possibility of using liquid alloy for stable metal anodes beyond Na storage systems.