Sodium All-Solid-State Batteries and the Electrolyte Question

Abstract

As the need for green energy storage increases, the development of solid-state sodium batteries is pushed forward. Main advantage towards lithium-ion batteries is that sodium is an element that is abundant and ubiquitous. Recent studies have developed sodium ion conducting solid electrolytes with a conductivity of 4∙10-2 S cm-1, which exceeds the ionic conductivity of lithium ion conductors at room temperature. As solid electrolytes are immobile, the possibility of using different electrolytes as separator and catholyte according to their useful properties presents itself. Nasicon (Na3.4Zr2Si2.4P0.6O12) material as a ceramic has a high ionic conductivity however lacks mechanical flexibility. Sulfur electrolytes such as Na2.9Sb0.9W0.1S4 predominate with their high elastic modulus and at the same time high ionic conductivity, however, show major electro-chemical instabilities in contact with the electrodes. The halide type electrolytes show their strength in term of stability, but have not reached relevant ionic conductivities yet. The combination of different electrolytes and the electrochemical implications are presented in this study. Chemical, electrochemical and mechanical stabilities are tested and monitored in full and symmetric sodium tin alloy cells.