Protective NaSICON Interlayer between a Sodium–Tin Alloy Anode and Sulfide-Based Solid Electrolytes for All-Solid-State Sodium Batteries

This paper presents a suitable combination of different sodium solid electrolytes to surpass the challenge of highly reactive cell components in sodium batteries. The focus is laid on the introduction of ceramic Na3.4Zr2Si2.4P0.6O12 serving as a protective layer for sulfide-based separator electrolytes to avoid the high reactivity with the sodium metal anode. The chemical instability of the anode|sulfide solid electrolyte interface is demonstrated by impedance spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. The Na3.4Zr2Si2.4P0.6O12 disk shows chemical stability with the sodium metal anode as well as the sulfide solid electrolyte. Impedance analysis suggests an electrochemically stable interface. Electron microscopy points to a reaction at the Na3.4Zr2Si2.4P0.6O12 surface toward the sulfide solid electrolyte, which does not seem to affect the performance negatively. The results presented prove the chemical stabilization of the anode-separator interface using a Na3.4Zr2Si2.4P0.6O12 interlayer, which is an important step toward a sodium all-solid-state battery. Due to the applied pressure that is mandatory for battery cells with sulfide-based cathode composite, the use of a brittle ceramic in such cells remains challenging.