Tin dioxide and phosphoric acid-treated tin dioxide powders have been prepared throughout annealing in air of a gel precursor within the 120-1100 degrees C temperature range. Polycrystalline tin dioxide samples with crystallite size between 3 and 59 nm were obtained. A tin phosphate-based shell is formed on the surface of tin dioxide particles that can be detected as SnP2O7 in the X-ray diffraction pattern after annealing at 1100 degrees C, and the surface properties are modified. A net improvement of the electrochemical performance and better capacity retention upon cycling is observed for high-temperature tin dioxide treated with phosphoric acid. (c) 2007 The Electrochemical Society.