New insight into the reaction mechanism for exceptional capacity of ordered mesoporous SnO₂ electrodes via synchrotron-based X-ray analysis

Tin oxide-based materials, operating via irreversible conversion and reversible alloying reaction, are promising lithium storage materials due to their higher capacity. Recent studies reported that nanostructured SnO₂ anode provides higher capacity beyond theoretical capacity based on the alloying reaction mechanism; however, their exact mechanism remains still unclear. Here, we report the detailed lithium storage mechanism of an ordered mesoporous SnO₂ electrode material. Synchrotron X-ray diffraction and absorption spectroscopy reveal that some portion of Li₂O decomposes upon delithiation and the resulting oxygen reacts with Sn to form the SnO_x phase along with dealloying of Li_xSn, which are the main reasons for unexpected high capacity of an ordered mesoporous SnO₂ material. This finding will not only be helpful in a more complete understanding of the reaction mechanism of Sn-based oxide anode materials but also will offer valuable guidance for developing new anode materials with abnormal high capacity for next generation rechargeable batteries.