Lithium insertion into self-organized mesoscopic TiO2 (anatase) electrodes

Self-organized nanocrystalline anatase films were prepared by a sol–gel technique with subsequent hydrothermal growth of crystals in basic solutions. Hydrothermal treatment at 190–230°C leads to the formation of compact films with narrow pore size distribution. Materials prepared at higher temperatures show more open structure with lower specific surface area. The electrochemical activity of the self-organized electrodes decreases with decreasing specific surface area. Ordered electrodes showed higher insertion capacity by ca. 15% compared to those of non-ordered electrodes with the same specific surface area. Insertion coefficients, x, exceeding 0.5 were observed for very thin (0.2 mg/cm2) self-organized films with specific surface area higher than 60 m2/g. However, these values were not reproduced for thicker films. The insertion rate depends on the inserted charge with a maximum at x∼0.1. It indicates that only a part of the total electrode–electrolyte interface is available for charge transfer reaction. The total insertion capacity is therefore affected by propagation of the electrochemically active surface within the film.