Conductive PProDOT-Me2-capped Li4Ti5O12 microspheres with an optimized Ti3+/Ti4+ ratio for enhanced and rapid lithium-ion storage

Li4Ti5O12 (LTO) has attracted much attention for its use as an anode material within lithium-ion batteries (LIBs), owing to its excellent safety and outstanding cyclability. Unfortunately, the poor electronic conductivity of LTO greatly limits the rate capability of the LIBs and, therefore, its practical applications. The conductivity of LTO can be enhanced significantly through thermal treatment under hypoxic conditions to form oxygen vacancies. The defective LTO with oxygen vacancies has a much higher electric conductivity, owing to partial reduction of the Ti ions (from Ti4+ to Ti3+). Too many oxygen vacancies generated in the LTO will, however, also cause severe lattice distortion, inhibiting ionic transfer. In this study, we optimized the Ti3+/Ti4+ ratio of LTO by annealing it under various conditions. We also modified the surface of LTO with a thin layer of poly (dimethyl 3,4-propylenedioxythiophene) (PProDOT-Me-2) through in situ chemical polymerization. Studies of the surface morphology and chemical composition confirmed that PProDOT-Me-2 had been successfully capped on the LTO surface. Combining the effects of the optimal Ti3+/Ti4+ ratio and the surface modification with PProDOT-Me-2 resulted in the charge and ionic transport properties of LTO both improving significantly. Accordingly, the nanocomposites displayed greatly enhanced rate capabilities, relative to those of the unmodified material.