Er Dequan, Li Junwen, Naguib Michael, Gogotsi Yury, Shenoy Vivek B
Department of Materials Science and Engineering, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States.
ACS Appl Mater Interfaces. 2014 Jul 23;6(14):11173-9. doi: 10.1021/am501144q. Epub 2014 Jul 11.
Two-dimensional (2-D) materials are capable of handling high rates of charge in batteries since metal ions do not need to diffuse in a 3-D lattice structure. However, graphene, which is the most well-studied 2-D material, is known to have no Li capacity. Here, adsorption of Li, as well as Na, K, and Ca, on Ti3C2, one representative MXene, is predicted by first-principles density functional calculations. In our study, we observed that these alkali atoms exhibit different adsorption energies depending on the coverage. The adsorption energies of Na, K, and Ca decrease as coverage increases, while Li shows little sensitivity to variance in coverage. This observed relationship between adsorption energies and coverage of alkali ions on Ti3C2 can be explained by their effective ionic radii. A larger effective ionic radius increases interaction between alkali atoms, thus lower coverage is obtained. Our calculated capacities for Li, Na, K, and Ca on Ti3C2 are 447.8, 351.8, 191.8, and 319.8 mAh/g, respectively. Compared to materials currently used in high-rate Li and Na ion battery anodes, MXene shows promise in increasing overall battery performance.
二维（2-D）材料能够在电池中处理高电荷率，因为金属离子无需在三维晶格结构中扩散。然而，石墨烯作为研究最为深入的二维材料，已知其没有锂存储容量。在此，通过第一性原理密度泛函计算预测了锂以及钠、钾和钙在一种代表性的MXene——Ti3C2上的吸附情况。在我们的研究中，我们观察到这些碱金属原子根据覆盖度表现出不同的吸附能。随着覆盖度增加，钠、钾和钙的吸附能降低，而锂对覆盖度的变化几乎不敏感。在Ti3C2上观察到的碱金属离子吸附能与覆盖度之间的这种关系可以用它们的有效离子半径来解释。较大的有效离子半径会增加碱金属原子之间的相互作用，从而获得较低的覆盖度。我们计算得出Ti3C2上锂、钠、钾和钙的容量分别为447.8、351.8、191.8和319.8 mAh/g。与目前用于高倍率锂离子和钠离子电池负极的材料相比，MXene在提高电池整体性能方面显示出前景。
