Synthesis and electrochemical evaluation of an amorphous titanium dioxide derived from a solid state precursor

Titanium oxides are an important class of lithium–ion battery electrodes owing to their good capacity and stability within the cell environment. Although most Ti(IV) oxides are poor electronic conductors, new methods developed to synthesize nanometer scale primary particles have achieved the higher rate capability needed for modern commercial applications. In this report, the anionic water stable titanium oxalate anion [TiO(C2O4)2]2− was isolated in high yield as the insoluble DABCO (1,4-diazabicyclo[2.2.2]octane) salt. Powder X-ray diffraction studies show that the titanium dioxide material isolated after annealing in air is initially amorphous, converts to N-doped anatase above 400 °C, then to rutile above 600 °C. Electrochemical studies indicate that the amorphous titanium dioxide phase within a carbon matrix has a stable cycling capacity of ∼350 mAh g−1. On crystallizing at 400 °C to a carbon-coated anatase the capacity drops to 210 mAh g−1, and finally upon carbon burn-off to 50 mAh g−1. Mixtures of the amorphous titanium dioxide and Li4Ti5O12 showed a similar electrochemical profile and capacity to Li4Ti5O12 but with the addition of a sloping region to the end of the discharge curve that could be advantageous for determining state-of-charge in systems using Li4Ti5O12.