Microgravimetric contributions of multivalent metal ions, water molecules and protons to the energy storage at the electrolyte/electrode interface of aqueous ion batteries

The aqueous battery employing multivalent metal ions as charge carriers is theoretically a high energy density electrochemical energy storage device due to the fact that it carries more charges. However, the storage mechanism of multivalent metal ions, especially Al3+ ions, in TiO2 materials has not been established.A new model associated with the contribution of multivalent metal ions, water molecules and protons in the charging/discharging process of the electrode is established in this work. The storage mechanism of aqueous Al3+ ion batteries is revealed from a new perspective by studying the relationship between the charge inside the TiO2 film and the mass at the interface. More importantly, a highlighted work is to reveal the changes in the amount of interfacial free water molecules and the hydration number of Al3+ ions due to the adsorption/desorption of hydrated ions during the charging/discharging process.The present work is of great significance for revealing the mechanism of multivalent cations on metal oxide surfaces in aqueous batteries, and meanwhile, the model established can also be extended to other fields such as supercapacitors, photovoltaics, and photocatalysis. The results obtained in this work may have an impact on the performance of energy storage batteries, especially the influence of the rearrangement of interface hydration ions and water molecules on the energy storage mechanism.