Topochemical synthesis of Mn ₂ O ₃ /TiO ₂ and MnTiO ₃ /TiO ₂ nanocomposites as lithium-ion battery anodes with fast Li ⁺ migration and giant pseudocapacitance via the mesocrystalline effect

Transition metal compounds are a promising substitute for graphite as lithium-ion battery (LIB) anodes. In this study, mesocrystalline Mn₂O₃/TiO₂ and MnTiO₃/TiO₂ nanocomposites were synthesized using a layered titanic acid H_1.07Ti_1.73O₄ (HTO) precursor. The β-MnOOH layer is intercalated into the interlayer of HTO by Mn²⁺-exchange treatment of H₂O₂-intercalated HTO, which includes ion-exchange of Mn²⁺ with H⁺ in the interlayer and oxidation of Mn²⁺ to the β-MnOOH layer by H₂O₂ in the interlayer space. Mesocrystalline Mn₂O₃/TiO₂ and MnTiO₃/TiO₂ nanocomposites with a platelike morphology were obtained by heat treatment of a sandwich layered HTO/β-MnOOH under air and H₂/Ar atmospheres, respectively. The electrochemical results suggest that the mesocrystalline Mn₂O₃/TiO₂ and MnTiO₃/TiO₂ nanocomposites show a synergistic effect for enhanced cycling stability and a mesocrystalline effect for enhanced discharge-charge specific capacity by improving the Li⁺ mobility and enhancing the pseudocapacitance of the mesocrystalline nanocomposites as LIB anode materials. The discharge-charge specific capacity of the mesocrystalline Mn₂O₃/TiO₂ nanocomposite is twice as high as that of the polycrystalline one caused by the mesocrystalline effect. Furthermore, the synergistic and mesocrystalline effects led to a stable large discharge-charge specific capacity of 710 mA h g^-1 for the mesocrystalline Mn₂O₃/TiO₂ nanocomposite. This work proposes a new concept to enhance the performance of anode materials for LIBs using mesocrystalline materials.