二维钼基双过渡金属碳化物作为锂离子电池阳极材料的电化学性能研究

A Theoretical Study on the Electrochemical Performance of Two-Dimensional Mo-Based Double Transition Metal Carbide as Anode Material for Lithium-Ion-Batteries

二维过渡金属碳化物或氮化物(MXenes)作为一种新型二维材料,凭借其制备工艺简单、理化性能灵活可控、结构稳定性高等特点,受到了广泛关注。然而,大多数研究集中于单一过渡金属MXenes的性能,双过渡金属MXenes及其表面修饰结构对电化学性能的影响尚未被系统研究。因此,该文采用基于密度泛函理论的第一性原理计算方法,对35种Mo基有序双过渡金属MXenes的电化学性能进行了系统的评估,包括本征结构Mo_(2)MC_(2)(M=Sc、Ti、V、Zr、Nb、Hf、Ta)以及对应的4类修饰结构Mo_(2)MC_(2)T_(2)(T=H、O、F、OH)。计算结果表明,材料表面不同修饰基团对MXenes表面的吸附与锂原子扩散性能起着决定性作用;稳定吸附结构的容量在121~195mA·h/g之间,且本征与H修饰结构能够获得理想的开路电压(0.5~0.8V);同时本征结构表面极低的离子扩散势垒(0.03~0.06eV)能够大幅度提升锂离子电池的充放电效率。

As a new type of two-dimensional(2D)material,two-dimensional Mo-based double transition metal carbide or nitride(MXenes)has received extensive attentions because of its simple preparation process,flexible and controllable physical and chemical properties,and high structural stability.However,most studies have focused on the performance of mono-transition metal MXenes.The effect of double transition metal combinations and its surface modifications on electrochemical performances of MXenes have not been systematically reported.Therefore,in this study,the first-principles calculation method based on density functional theory was used to systematically evaluate the electrochemical performance of 35 Mo-based ordered double transition metal MXenes,including intrinsic structures Mo_(2)MC_(2)(M=Sc,Ti,V,Zr,Nb,Hf,Ta)and the corresponding four types of surface functionalized structures Mo_(2)MC_(2)T_(2)(T=H,O,F,OH).The calculation results show that different modification groups on the surface of the MXenes play a decisive role in both the adsorption of Li atom on the surface and the diffusion ability of lithium atoms.The theoretical capacity is in the range of 121~195mA·h/g,and the ideal OCV(0.5~0.8V)can be obtained by intrinsic and H-modified structures.At the same time,the extremely low ion diffusion barrier(0.03~0.06eV)of the intrinsic structures could greatly improve the charging or discharging rate of lithium ion batteries.