Core/shell TiO2–MnO2/MnO2 heterostructure anodes for high-performance lithium-ion batteries

Abstract

Core/shell TiO₂–MnO₂/MnO₂ heterostructures were synthesized by combining an electrospinning technique with a hydrothermal reaction. To create the starting materials, porous TiO₂–carbon nanofibers were first prepared using a simple electrospinning technique followed by calcination. The porous structure in TiO₂–carbon nanofibers caused by the partial decomposition of polystyrene is beneficial to the diffusion of KMnO₄ from the outer surface into inner fibers to completely react with carbon and produce MnO₂ nanosheets. Some MnO₂ nanosheets in the TiO₂ core connect with other MnO₂ nanosheets surrounding the TiO₂ core to form core/shell TiO₂–MnO₂/MnO₂, which can enhance the stability of the structure. The large surface area of the resulting materials offers a sufficient electrode–electrolyte interface to promote the charge-transfer reactions, which yields a better rate capability. The porous structure of TiO₂–MnO₂/MnO₂ nanofibers not only facilitates Li-ion access, but also accommodates large volumetric expansion during the charging–discharging processes, resulting in an excellent cycle performance. As an anode, this material delivered a high reversible capacity of 891 mA h g⁻¹ at the first cycle and maintained the capacity of 888 mA h g⁻¹ after 50 cycles at the current density of 0.1 A g⁻¹; it also showed a remarkable rate capability of 2 A g⁻¹ while retaining a capacity of 185 mA h g⁻¹ after 500 cycles. Given their enhanced electrochemical performance, core/shell TiO₂–MnO₂/MnO₂ heterostructure nanofibers are promising anode candidates for lithium-ion batteries.