Evaluation of undoped and M-doped TiO2, where M = Sn, Fe, Ni/Nb, Zr, V, and Mn, for lithium-ion battery applications prepared by the molten-salt method

The molten-salt method was used to synthesize a series of transition-metal containing titanium dioxides. Some of the transition metals were found to substitute into the TiO2 lattice, such as (Ti0.9Fe0.1)O-2, (Ti0.9Zr0.1)O-2, (Ti0.9V0.1)O-2, and (Ti0.9Mn0.1)O-2, while others were formed as composite electrodes (in addition to relatively minor substitutions), namely 0.1SnO(2)-0.9TiO(2) and 0.05NiO-0.1Nb(2)O(5)-0.9TiO(2). Although identical synthesis-conditions were used the different transition metals yielded different phases. A comparative study of the electrodes relating surface area and composition (via X-ray photoelectron spectroscopy, XPS), and electrochemical behaviour is presented in this work. Among the substituted single phase electrodes, (Ti0.9Zr0.1)O-2 exhibited the best reversible capacity of similar to 160 mA h g(-1), at the end of the 60th cycle in the voltage range 1.0-2.6 V, with a capacity fade of 24% from the 2nd to the 60th cycle. Among the composite electrodes, 0.05NiO-0.1Nb(2)O(5)-0.9TiO(2) shows the best performance which is comparable to pure TiO2 but with a slower capacity-fade on extended cycling. The worst performing electrode is (Ti0.9V0.1)O-2 with a reversible capacity of only similar to 70 mA h g(-1) at the end of 70 cycles with a current density of 130 mA g(-1) in the voltage range 1.0-2.6 V and a capacity drop of 52% from the 2nd to the 70th cycle. The composite 0.1SnO(2)-0.9TiO(2) features the highest irreversible capacity-loss. Zr-substitution into TiO2 gives the best electrochemical performance.