Enhancing capacity and transport kinetics of C@TiO₂core-shell composite anode by phase interface engineering

In nanocomposite electrodes, besides the synergistic effect that takes advantage of the merits of each component, phase interfaces between the components would contribute significantly to the overall electrochemical properties. However, the knowledge of such effects is far from being well developed up to now. The present work aims at a mechanistic understanding of the phase interface effect in C@TiO₂core-shell nanocomposite anode which is both scientifically and industrially important. Firstly, amorphous C, anatase TiO₂and C@anatse-TiO₂electrodes are compared. The C@anatase-TiO₂shows an obvious higher specific capacity (316.5 mAh g^-1at a current density of 37 mA g^-1after 100 cycles) and Li-ion diffusion coefficient (4.0 × 10^-14cm²s^-1) than the amorphous C (178 mAh g^-1and 2.9 × 10^-15cm²s^-1) and anatase TiO₂(120 mAh g^-1and 1.6 × 10^-15cm²s^-1) owing to the C/TiO₂phase interface effect. Then, C@anatase/rutile-TiO₂is obtained by a heat treatment of the C@anatase-TiO₂. Due to an anatase-to-rutile phase transformation and diffusion of C along the anatase/rutile phase interface, additional abundant C/TiO₂phase interfaces are created. This endows the C@anatase/rutile-TiO₂with further boosted specific capacity (409.4 mAh g^-1at 37 mA g^-1after 100 cycles) and Li-ion diffusion coefficient (3.2 × 10^-13cm²s^-1), and excellent rate capability (368.6 mAh g^-1at 444 mA g^-1). These greatly enhanced electrochemical properties explicitly reveal phase interface engineering as a feasible way to boost the electrochemical performance of nanocomposite anodes for Li-ion batteries.