High Coulombic Efficiency Plating and Stripping of Sodium for Reservoir-Free Sodium Solid-State Batteries at Low Stack Pressure

“Anode-free” sodium solid-state batteries (SSBs) based on earth-abundant materials are promising candidates for next-generation energy storage devices. However, their deployment requires minimizing solid electrolyte|electrode interfacial resistances and forming a robust solid electrolyte|current collector interface. We demonstrate the dendrite-free deposition of sodium metal with >100 μm thickness, through a NaSICON (Na 3.4 Zr 2 Si 2.4 P 0.6 O 12 ) solid electrolyte, directly onto an aluminum current collector joined to the ceramic via a facile solid-state diffusion bonding method. Reversible sodium plating/stripping is achieved with Al|NaSICON laminates at a current density of 0.5 mA cm –2 for areal capacities of 1 and 3 mAh cm –2 under a stack pressure of ∼1 MPa. Long-term cycling is demonstrated over 300 cycles at 25 °C with an average Coulombic efficiency of >98%. Our work provides new insights into metal-ceramic contact and its influence on sodium nucleation and growth at solid|solid interfaces and suggests a path forward for the implementation of reservoir-free sodium SSBs.