MXenes@Te作为高性能铝电池复合正极材料

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

新兴的二维材料MXenes在储能领域中发挥着重要作用,并展现了优异的电化学性能.本文中我们制备了二维层状MXenes(F-Ti_(3)C_(2)T_(x)),通过高温蒸镀法将Te单质负载在F-Ti_(3)C_(2)T_(x)的表面,以MXenes@Te作为铝电池正极,其首次充/放电比容量为987/1096 mAh g^(-1).在不同电流密度条件下,铝电池的放电电压平台稳定在1.3 V左右,当以MXenes@Te为活性材料计算时,铝电池的比容量为258 mAh g^(-1),这得益于MXenes材料优异的电导率及其二维层状结构.通过密度泛函理论探索了其机理,计算结果表明,Ti_(3)C_(2)O_(2)@Te比Ti_(3)C_(2)O_(2)更倾向于吸附[AlCl_(4)]^(-).此外,通过热力学计算(Factsage7.1)和X射线光电子能谱研究了元素Te的价态变化.研究结果表明,当铝电池充满至2.4 V时,单质Te和Ti离子(Ti^(3+),Ti^(2+))被氧化为Te^(4+)和Ti^(4+).在放电过程中,高价态的Te^(4+)和Ti^(4+)被重新还原为单质Te和Ti离子(Ti^(3+),Ti^(2+)).当放电电压低于0.6 V时,单质Te被还原为更低价态的Te^(2-),而要将单质Te氧化为Te^(6+),则需要更高的充电电压(2.56 V).

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-Ti_(3)C_(2)T_(x))and loaded Te on the surface of F-Ti_(3)C_(2)T_(x) by using a simple hightemperature evaporation method.In addition,the electrochemical performance of the aluminum battery with F-Ti_(3)C_(2)T_(x) as support material was studied.The initial charge/discharge specific capacities are 987/1096mAh g^(-1)at 0.2Ag^(-1).An obvious discharge voltage plateau of about 1.3V appears at various current densities.The specific capacity is about 258mAh 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.Ti_(3)C_(2)O_(2)@Te is more inclined to adsorb[AlCl_(4)]^(-) than Ti_(3)C_(2)O_(2).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 2.4V element Te and Ti ions(Ti^(3+),Ti^(2+))are oxidized to Te^(4+)and Ti^(4+).In contrast to the charging process,the high-valence Te^(4+)and Ti^(4+)are reduced again during discharging.Element Te is reduced to lower-valence Te^(2-)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 Te^(6+).