Atomic Layer Deposition of Amorphous TiO2 on Carbon Nanotube Networks and Their Superior Li and Na Ion Storage Properties

Titanium dioxide is a promising anode material for lithium and sodium-ion batteries (LIBs, SIBs). Current research of TiO2 is mainly focused on the crystalline phase (anatase or rutile) with a battery-like diffusion mechanism. In the present work, it is aimed to demonstrate the advantages of amorphous titanium dioxide over crystalline ones for both Li and Na ion batteries. Amorphous TiO2 thin layers of different thicknesses are deposited on carbon nanotube (CNT) network/carbon fiber paper (CFP) substrates, forming the double-walled TiO2@CNT nanotubes. For comparison, the as-obtained amorphous TiO2@CNT/CFP samples are annealed to achieve anatase TiO2. It is shown that, as an anode of LIBs, the amorphous TiO2 shows better performance than the anatase one in terms of specific capacity, rate capacity, as well as cycling performance. The difference in the electrochemical property stems from their different charge-storage mechanisms; different from the diffusion-limited process in crystalline TiO2, the amorphous TiO2 stores charges via a fast surface-controlled capacitive process similar to the orthorhombic Nb2O5. Moreover, the amorphous TiO2@CNT/CFP electrodes are also confirmed to be suitable for SIBs.