Initial Coulombic Efficiency of Hard Carbon in All-Solid-State Sodium-Ion Battery

All-solid-state sodium ion batteries are highly sought after stationary energy storage systems which can integrate renewal energy into the existing power grid. Among different sodium-ion anodes, hard carbon has a low redox potential, reasonable capacity, and is low cost making it a good candidate in a large-scale format. However, the implementation of hard carbon is hindered by its low initial Coulombic efficiency (ICE) due to formation of solid electrolyte interphase and irreversible sodium trapping. In this study, hard carbon compatibility with a solid-state electrolyte and its initial Coulombic efficiency were studied in detail using X-ray photoemission spectroscopy, electrochemical impedance spectroscopy, and electron microscopy. Additionally, we exploit a method presodiate of the hard carbon to significantly improve the initial Coulombic efficiency. Consequently, the assembled all-solid-state sodium-ions battery with presodiated hard carbon exhibits a higher initial energy density with good reversibility.