Hard Carbon–Sulfide Solid Electrolyte Interface in All-Solid-State Sodium Batteries

Hard carbon is a promising negative electrode material for sodium-ion batteries that operate at low potentials. However, reversible and high-capacity charging and discharging in all-solid-state sodium batteries with hard carbon electrodes using sulfide solid electrolytes have not been reported. This study reports that reductive decomposition of the sulfide solid electrolyte occurs at both the negative composite electrode and the interface between the negative electrode layer and the solid electrolyte layer. In the first cycle, the all-solid-state cell with a composite electrode containing a Na3PS4 solid electrolyte exhibited a large irreversible capacity of 561 mAh g−1 because of the reductive decomposition of Na3PS4 to Na2S and Na3P. The use of a Na3BS3 glass electrolyte with reduction stability can lead to the successful charging and discharging of all-solid-state cell that utilizes hard carbon. This glass electrolyte can serve as a solid electrolyte for the negative composite electrode and as a buffer layer between the negative electrode layer and the solid electrolyte layer. Hence, it can also help suppress the irreversible capacity of the cell to 122 mAh g−1.