Fast-Charging and High Volumetric Capacity Anode Based on Co3 O4 /CuO@TiO2 Composites for Lithium-Ion Batteries.

This paper presents an investigation of anodic TiO2 nanotube arrays (TNAs), with a Co3 O4 /CuO coating, for lithium-ion batteries (LIBs). The coated TNAs are investigated using various analytical techniques, with the results clearly suggesting that the molar ratio of Co3 O4 /CuO in the TiO2 nanotubes substantially influences its battery performance. In particular, a cobalt/copper molar ratio of 2:1 on the TNAs (Co2 Cu1 @TNAs) features the best LIBs anode performance, exhibiting high reversible capacity and enhanced cycling stability. Noticeably, Co2 Cu1 @TNAs achieve excellent rate capability even after quite a high current density of 20.0 A g-1 (≈25 C, where C corresponds to complete discharge in 1 h) and superior volumetric reversible capacity of ≈3330 mA h-1  cm-3 . This value is approximately seven times higher than those of a graphite-based anode. This outstanding performance is attributed to the synergistic effects of Co2 Cu1 @TNAs: 1) the structural advantage of TNAs, with their large amount of free space to accommodate the large volume expansion during Li+ insertion/extraction and 2) the optimized ratio of Co3 O4 and CuO in the composite for improved capacity. In addition, no binder or conductive agent is used, which is partly responsible for the overall improved volumetric capacity and electrochemical performance.