Aligned TiO₂nanotube/nanoparticle heterostructures with enhanced electrochemical performance as three-dimensional anode for lithium-ion microbatteries

A novel TiO2three-dimensional (3D) anode with an aligned TiO2nanotube/nanoparticle heterostructure (TiO2NTs/NPs) is developed by simply immersing as-anodized TiO2NTs into water and further crystallizing the TiO2NTs by post-annealing. The heterostructure, with its core in a tubular morphology and with both the outer and inner surface consisting of nanoparticles, is confirmed by FESEM and TEM. A reversible areal capacity of 0.126 mAh·cm-2is retained after 50 cycles for the TiO2NTs/NPs heterostructure electrode, which is higher than that of the TiO2NTs electrode (0.102 mAh·cm-2after 50 cycles). At the current densities of 0.02, 0.04, 0.06, 0.08, 0.10 and 0.20 mA·cm-2, the areal capacities are 0.142, 0.127, 0.117, 0.110, 0.104 and 0.089 mAh·cm-2, respectively, for the TiO2NTs/NPs heterostructure electrode compared to the areal capacities of 0.123, 0.112, 0.105, 0.101, 0.094 and 0.083 mAh·cm-2, respectively, for the the TiO2NTs electrode. The enhanced electrochemical performance is attributed to the unique microstructure of the TiO2NTs/NPs heterostructure electrode with the TiO2NT core used as a straight pathway for electronic transport and with TiO2NP offering enhanced surface areas for facile Li+ insertion/extraction. The results described here inspire a facile approach to fabricate a 3D anode with an enhanced electrochemical performance for lithium-ion microbattery applications.