Nanointerface-driven pseudocapacitance tuning of TiO2 nanosheet anodes for high-rate, ultralong-life and enhanced capacity sodium-ion batteries

Titanium dioxide recently gained attention as sodium-ion battery anode material. However, its practical application is hindered by low specific capacity (~150 mAh/g), and mediocre cycling stability. Here we report for the first time, nanointerface-driven Na-ion intercalation pseudocapacitance tuning as a strategy to substantially improve the performance of TiO 2 anodes. This is achieved by tuning the crystal mismatch between anatase and bronze crystallites of hierarchical TiO 2 nanosheets. Hybrid TiO 2 nanosheets composed of ~10 nm sized anatase (~85%) and bronze (~15%) crystallites exhibited significantly higher pseudocapacitive Na-ion storage compared to phase-pure bronze and anatase TiO 2 nanosheets. High specific capacity of 290 mAh/g (~0.87 mol Na-ions) at a current density of 25 mA/g is obtained for this composition. Hybrid TiO 2 maintained a specific capacity of 120 mAh/g even at a high current density of 1 A/g. Coulombic efficiency (~100%) and cycling stability are outstanding, retaining 90% of the initial capacity after 2500 galvanostatic cycles. These electrochemical performances are noticeably superior to amorphous and crystalline TiO 2 reported earlier. Mechanistic studies proved Na-ion intercalation pseudocapacitance without considerable structural changes. Excellent electrochemical performance of dual-phase hierarchical TiO 2 nanosheets is credited to the superior Na-ion intercalation pseudocapacitance resulting from anatase-bronze nanointerfaces. The demonstrated strategy of nanointerface-driven pseudocapacitance tuning provides new opportunities for the designing of advanced Na-ion battery anodes.