Reversible magnesium and aluminium ions insertion in cation-deficient anatase TiO2

In contrast to monovalent lithium or sodium ions, the reversible insertion of multivalent ions such as Mg 2+ and Al 3+ into electrode materials remains an elusive goal. Here, we demonstrate a new strategy to achieve reversible Mg 2+ and Al 3+ insertion in anatase TiO 2 , achieved through aliovalent doping, to introduce a large number of titanium vacancies that act as intercalation sites. We present a broad range of experimental and theoretical characterizations that show a preferential insertion of multivalent ions into titanium vacancies, allowing a much greater capacity to be obtained compared to pure TiO 2 . This result highlights the possibility to use the chemistry of defects to unlock the electrochemical activity of known materials, providing a new strategy for the chemical design of materials for practical multivalent batteries. Compared to monovalent lithium or sodium ions, the reversible insertion of multivalent ions into battery electrodes has proved challenging. An aliovalent doping strategy involving reversible Mg 2+ and Al 3+ insertion in anatase TiO 2 is now reported.