Superior electrochemical performance of TiO2 sodium-ion battery anodes in diglyme-based electrolyte solution

Abstract Sodium-ion batteries are considered a promising alternative to lithium-ion batteries due to its low cost and potential applications for large-scale energy storage. In this work, we focus on improving the Na-ion storage electrochemical performance of TiO2 anodes by using diglyme-based electrolyte solutions. Significantly better performances are observed for the first time in diglyme-based electrolyte solution, as compared to conventional carbonate electrolyte solutions with and without additives such as fluoroethylene carbonate (FEC) and vinylene (VC). The best TiO2 electrode demonstrated a high specific capacity of 248 mA h g−1 at 25 mA g−1 current density, ∼100% coulombic efficiency, superior pseudocapacitive Na-ion storage, and good capacity retention on extended galvanostatic charge-discharge cycles. A full-cell assembled with TiO2 anode, Na3V2(PO4)3 cathode and NaPF6-diglyme electrolyte solution demonstrated an energy density as high as 440 W h kg−1. Superior electrochemical performance of TiO2 anodes in diglyme-based electrolyte is credited to the enhanced passivation and Na-ion conducting properties of polyether-based solid electrolyte interfaces (SEI) compared to polycarbonate-based counterparts. Carbon coating also resulted in the reduced decomposition of both diglyme and carbonate based electrolyte solutions. These results potentially encourage the use of ether-based electrolyte solutions for further improving the electrochemical performance and commercialization of rechargeable Na-ion batteries.