MXenes@Te as a composite material for high-performance aluminum batteries

The emerging two-dimensional (2D) materials, MXenes, play an important role in various fields of energy storage and exhibit excellent electrochemical performance. Herein, we prepared few-layered MXenes (F-Ti3C2Tx) and loaded Te on the surface of F-Ti3C2Tx by using a simple high-temperature evaporation method. In addition, the electrochemical performance of the aluminum battery with F-Ti3C2Tx as support material was studied. The initial charge/discharge specific capacities are 987/1096 mA h g−1 at 0.2 A g−1. An obvious discharge voltage plateau of about 1.3 V appears at various current densities. The specific capacity is about 258 mA h g−1 with MXenes@Te as the active material in the aluminum battery, which benefits from the excellent electronic conductivity of the MXenes and their 2D layered structure. Density functional theory calculations were carried out to explore the mechanism. Ti3C2O2@Te is more inclined to adsorb [AlCl4]− than Ti3C2O2. Furthermore, the valence change behavior of element Te was studied by using thermodynamic calculation (FactSage 7.1). X-ray photoelectron spectroscopy results show that when the battery is fully charged to 2.4 V element Te and Ti ions (Ti3+, Ti2+) are oxidized to Te4+ and Ti4+. In contrast to the charging process, the high-valence Te4+ and Ti4+ are reduced again during discharging. Element Te is reduced to lower-valence Te2− when the discharge voltage is lower than 0.6 V, and a higher charge voltage (2.56 V) is required for Te to be oxidized to Te6+.