(Invited) Interface Engineering in Transition-Metal Oxide Electrode Materials for Sodium Ion Batteries

Sodium ion batteries (SIBs) are attractive alternative energy storage technology to lithium-ion batteries due to its low-cost. There has been growing attention in developing new electrode materials for sodium ion batteries. Compared to lithium ion batteries, SIBs suffer from more issues in long-term stability, resulted from the sluggish kinetics, large volume change due to the much larger Na+ ion (~ two times the size of Li+) as well as multiple phase transitions upon cycling. Several approaches to enhance the electrode performance have been explored such as doping, nanostructuring, and carbon coating. Here, we will discuss our recent work on developing advanced electrode materials for SIBs through interfacial engineering. We have developed a coaxial core-shell nanostructured negative composite electrode composed of carbon nanotube (CNT) as the core and TiO2@MoO2@C as shells. The 1D tubular nanostructure can effectively reduce ion diffusion path, increase electrical conductivity, accommodate the stress due to volume change upon cycling, and provide additional interfacial active sites for enhanced charge storage and transport properties. Significantly, a synergistic effect between TiO2 and MoO2 nanostructures is investigated through ex-situ solid state nuclear magnetic resonance. We also developed multi-phased transition metel oxide positive electrodes, which exhibits enhanced capacity and cycling stability.