Xu Ke, Liao Ningbo, Zhang Miao, Xue Wei
College of Mechanical & Electrical Engineering, Wenzhou University, Wenzhou, 325035, P. R. China.
Nanoscale. 2020 Apr 7;12(13):7098-7108. doi: 10.1039/c9nr09352d. Epub 2020 Mar 19.
MoS is of great interest as an anode material of batteries due to its high theoretical reversible capacity; in particular, a defective MoS/graphene heterostructure exhibits excellent cycling stability. However, very little is known about the diffusion and ion storage mechanism at the atomistic level. To provide insights into the issue, we have developed and used first principles calculations and an atom intercalation/deintercalation algorithm to model the adsorption, diffusion, insertion and removal of Li, Na and Mg in pristine and defective MoS/graphene systems. First, the adsorption of Li, Na and Mg is generally more stable in the defective MoS/graphene structure. Mg and Li prefer to diffuse in the structure with disulfide defects, while Na prefers to diffuse in the molybdenum defective structure. Next, we found that the atomic configurations of both pristine and defective MoS/graphene are not restored to their original states after the insertion and removal of Li, Na and Mg, which is related to the irreversible capacity loss of the system. Furthermore, by excluding the amount of lithium atoms related to the unrestored sulfur atoms, an algorithm was proposed to calculate the reversible capacity and it was verified by experimental results. We have also demonstrated that the introduction of defects leads to significant increase in the theoretical capacities of the Na and Mg systems, however, decreasing the capacity retention rate of Mg.
由于其高理论可逆容量，二硫化钼作为电池的阳极材料备受关注；特别是，有缺陷的二硫化钼/石墨烯异质结构表现出优异的循环稳定性。然而，在原子层面上，关于扩散和离子存储机制的了解却非常少。为了深入了解这个问题，我们开发并使用了第一性原理计算和原子插层/脱层算法，对锂、钠和镁在原始和有缺陷的二硫化钼/石墨烯体系中的吸附、扩散、嵌入和脱除进行建模。首先，锂、钠和镁在有缺陷的二硫化钼/石墨烯结构中的吸附通常更稳定。镁和锂倾向于在具有二硫缺陷的结构中扩散，而钠则倾向于在钼缺陷结构中扩散。接下来，我们发现锂、钠和镁嵌入和脱除后，原始和有缺陷的二硫化钼/石墨烯的原子构型都没有恢复到原来的状态，这与体系的不可逆容量损失有关。此外，通过排除与未恢复的硫原子相关的锂原子数量，提出了一种计算可逆容量的算法，并通过实验结果进行了验证。我们还证明，缺陷的引入导致钠和镁体系的理论容量显著增加，然而，降低了镁的容量保持率。
