Effects of amorphous and crystalline MoO3 coatings on the Li-ion insertion behavior of a TiO2 nanotube anode for lithium ion batteries

Amorphous and crystalline MoO3 coatings are synthesized on anodic TiO2 nanotube arrays by electrodeposition, as a self-standing, binder-free anode material in Li-ion batteries for enhancing the Li-ion insertion performance. The amorphous MoO3 layer is uniform and conformal with a thickness of 10 nm, and is converted into crystalline nanoparticles via thermal treatment. Our results show that both the coated TiO2 nanotubes deliver much higher areal capacities than bare nanotubes or a dense crystalline alpha-MoO3 film, while the crystalline alpha-MoO3 coating greatly increases the areal capacity of TiO2 nanotubes compared to the amorphous. The results are obtained at 1340 mu A h cm(-2) initial capacity for nanotubes with a crystalline coating, 977 mu A h cm(-2) for those with an amorphous coating and 342 mu A h cm(-2) for the bare ones. The significant enhancement is due to a combination of MoO3 with high specific capacity and TiO2 nanotube arrays with large surface area allowing uniform MoO3 deposition and rapid ionic transfer. Crystalline alpha-MoO3 is better than amorphous MoO3 and the coating medium is discussed in terms of chemical state, crystal defects, capacitive contributions and the charge-discharge kinetics in coated TiO2 nanotube electrodes.