Temperature Effect on the Behavior of a Lithium Titanate Electrode

Resumo

The effect of temperature (over the–15 to +60°С range) on the insertion of lithium into Li₄Ti₅O₁₂ is systematically studied. At a current of ~1.2 С, as the temperature decreased the capacity decreased, polarization increased, the range of compositions corresponding to nonequilibrium solid solutions widened, and the slope of the galvanostatic curves’ linear segment corresponding to the Li₄ + δTi₅O₁₂–Li_7–δTi₅O₁₂ twophase system increased. The decrease in capacity with decreasing temperature can be explained by the fact that, up to the moment of the abrupt change in the potential, at moderate current values, the diffusion layer’s thickness drops to a value smaller than the material particles’ size. In this case, the capacity’s temperature dependence corresponds to that of lithium’s solid-state diffusion. The latter is described by the Arrhenius equation with the activation energy of ~35 kJ/mol in the temperature range from–15 to +18°С; at higher temperatures the capacity is practically temperature-independent. The polarization of the anodic and cathodic processes is practically identical; it decreases linearly as the temperature increases with a proportionality coefficient of ~2.5 mV/K.