Nb-Doped Rutile TiO2: a Potential Anode Material for Na-Ion Battery

The electrochemical properties of the rutile-type TiO2 and Nb-doped TiO2 were investigated for the first time as Na-ion battery anodes. Ti1-xNbxO2 thick-film electrodes without a binder and a conductive additive were prepared using a sol-gel method followed by a gas-deposition method. The TiO2 electrode showed reversible reactions of Na insertion/extraction accompanied by expansion/contraction of the TiO2 lattice. Among the Ti1-xNbxO2 electrodes with x = 0-0.18, the Ti0.94Nb0.06O2 electrode exhibited the best cycling performance, with a reversible capacity of 160 mA h g(-1) at the 50th cycle. As the Li-ion battery anode, this electrode also attained an excellent rate capability, with a capacity of 120 mA h g(-1) even at the high current density of 16.75 A g(-1) (50C). The improvements in the performances are attributed to a 3 orders of magnitude higher electronic conductivity of Ti0.94Nb0.06O2 compared to that of TiO2. This offers the possibility of Nb-doped rutile TiO2 as a Na-ion battery anode as well as a Li-ion battery anode.