High capacity hard carbon anodes for sodium ion batteries in additive free electrolyte

Electrochemical performance of hard carbon prepared from sugar pyrolysis was investigated against sodium anodes. Specific surface area and graphitization degree are determinant for achieving the highest reversible capacity ever reported (more than 300 mAh/g at C/10 after 120 cycles) with excellent rate capability. Such results were obtained using additive free EC:PC based electrolyte which appears to induce the formation of a more conducting solid electrolyte interphase (SEI) than that produced in the presence of 2% fluoroethylene carbonate (FEC).

► Microstructure of hard carbon is determinant for performance in sodium based cells. ► Additive free EC:PC based electrolyte promotes a suitable SEI. ► Optimized hard carbon yields 300 mAh/g after 120 cycles with good rate capability.