Electrochemical properties of spherical hollow composite powders with various Li₄Ti₅O₁₂/SnO₂ ratios prepared by spray pyrolysis

Li₄Ti₅O₁₂-SnO₂ composite powders with different Li₄Ti₅O₁₂/SnO₂ ratios and comprising hollow and sphere particles are prepared by an ultrasonic spray pyrolysis process. The composite powders exhibit mixed-crystal structures consisting of Li₄Ti₅O₁₂ and SnO₂ phases with no impurities being present, irrespective of their Li₄Ti₅O₁₂/SnO₂ ratios. The composite powders with low concentrations of SnO₂ contained SnO₂ nanocrystals several tens of nanometers in size, which are uniformly distributed in the Li₄Ti₅O₁₂ matrix. Complete necking between the SnO₂ nanocrystals results in an increase in the electrical conductivity of the composite powder with a high concentration of SnO₂ (Li₄Ti₅O₁₂/SnO₂ = 0.4/0.6). These composite powders exhibit a high initial charge capacity of 730 mAh g^-1 and good cyclability even at a high charge-and-discharge rate of 700 mA g^-1 for voltages between 0.1 and 2.5 V. In addition, it retained 70% of its initial capacity after 60 cycles. The initial charge capacities of this composite powder are 572, 399, and 303 mAh g^-1 at the extremely high charge-and-discharge rates of 3500, 7000, and 14000 mA g^-1, respectively.