Nano-silica electrolyte additive enables dendrite suppression in an anode-free sodium metal battery

Sodium (Na)-based batteries are being explored as a sustainable and cost-effective alternative to Lithium (Li)-ion batteries. In particular, an "anode-free" Na metal battery offers the possibility to match or even exceed the energy density of the incumbent Li-ion technology. Nevertheless, the present lifespan of these batteries is insufficient to render them suitable as an energy source for current electronic devices and grid systems. The main reason for this is the evolution and growth of Na metal dendrites during the charge-discharge process. In this study, we report a "nano-silica modified suspension electrolyte" that improves the average coulombic efficiency and cycling performance of anode-free Na metal batteries. The nano-silica additives increase the Na+ diffusion coefficient in the electrolyte by ∼1000-fold, thereby decreasing the nucleation overpotential and inhibiting the formation of Na metal dendrites. We demonstrate that a Na|Cu half-cell with the suspension electrolyte can cycle stably for over 500 cycles at ∼1 mA cm−2 current density and an aerial capacity of ∼2 mAh cm−2. When paired with an Na3V2(PO4)3 (NVP) cathode, the anode-free NVP|Cu full-cell device with the nano-silica infused electrolyte drastically outperformed the conventional electrolyte in terms of specific capacity retention and coulombic efficiency.