Hierarchical flower-like NiCo2O4@TiO2 hetero-nanosheets as anodes for lithium ion batteries

Abstract

Flower-like NiCo₂O₄ consisting of nanosheets are synthesized by hydrothermal technique and subsequently surface-modified with a TiO₂ ultrathin layer by a hydrolysis process at low temperature. It is found that NiCo₂O₄@TiO₂ exhibits superior electrochemical performances over NiCo₂O₄ in terms of rate capability and cyclability. After 60 cycles at 100 mA g⁻¹, NiCo₂O₄@TiO₂ showed 78% capacity retention compared with 57% for bare NiCo₂O₄. Analysis from the electrochemical measurements indicates that the improved electrochemical performances of NiCo₂O₄@TiO₂ might be attributed to a higher lithium diffusion rate, smaller charge-transfer resistance and more structural stability. Kelvin probe force microscopy measurements reveal that NiCo₂O₄@TiO₂ has a lower work function than those of the pristine one, which help to facilitate electron transfer in composites. In addition, the electric field between NiCo₂O₄ and TiO₂ resulting from the difference in work functions is also expected to enhance the electrochemical performances.