Massaro Arianna, Pecoraro Adriana, Muñoz-García Ana B, Pavone Michele
Department of Chemical Sciences, University of Naples "Federico II", via Cintia 21, 80126 Naples, Italy.
Department of Physics "E. Pancini", University of Naples "Federico II", via Cintia 21, 80126 Naples, Italy.
J Phys Chem C Nanomater Interfaces. 2021 Feb 4;125(4):2276-2286. doi: 10.1021/acs.jpcc.0c10107. Epub 2021 Jan 21.
Na-ion batteries (NIBs) are emerging as promising energy storage devices for large-scale applications. Great research efforts are devoted to design new effective NIB electrode materials, especially for the anode side. A hybrid 2D heterojunction with graphene and MoS has been recently proposed for this purpose: while MoS has shown good reversible capacity as a NIB anode, graphene is expected to improve conductivity and resistance to mechanical stress upon cycling. The most relevant processes for the anode are the intercalation and diffusion of the large Na ion, whose complex mechanisms are determined by the structural and electronic features of the MoS/graphene interface. Understanding these processes and mechanisms is crucial for developing new nanoscale anodes for NIBs with high performances. To this end, here we report a state-of-the-art DFT study to address (a) the structural and electronic properties of heterointerfaces between the MoS monolayers and graphene, (b) the most convenient insertion sites for Na, and (c) the possible diffusion paths along the interface and the corresponding energy barrier heights. We considered two MoS polymorphs: 1T and 3R. Our results show that 1T-MoS interacts more strongly with graphene than 3R-MoS. In both cases, the best Na host site is found at the MoS side of the interface, and the band structure reveals a proper n-type character of the graphene moiety, which is responsible for electronic conduction. Minimum-energy paths for Na diffusion show very low barrier heights for the 3R-MoS/graphene interface (<0.25 eV) and much higher values for its 1T counterpart (∼0.7 eV). Analysis of structural features along the diffusion transition states allows us to identify the strong coordination of Na with the exposed S atoms as the main feature hindering an effective diffusion in the 1T case. These results provide new hints on the physicochemical details of Na intercalation and diffusion mechanisms at complex 2D heterointerfaces and will help further development of advanced electrode materials for efficient NIBs.
钠离子电池（NIBs）正成为大规模应用中颇具前景的储能装置。人们投入了大量研究精力来设计新型高效的NIB电极材料，尤其是负极材料。最近为此提出了一种由石墨烯和MoS组成的混合二维异质结：虽然MoS作为NIB负极已显示出良好的可逆容量，但预计石墨烯可提高导电性并增强循环时的抗机械应力能力。负极最相关的过程是大尺寸钠离子的嵌入和扩散，其复杂机制由MoS/石墨烯界面的结构和电子特性决定。理解这些过程和机制对于开发高性能的新型NIB纳米级负极至关重要。为此，我们在此报告一项前沿的密度泛函理论（DFT）研究，以探讨（a）MoS单层与石墨烯之间异质界面的结构和电子特性，（b）钠离子最适宜的嵌入位点，以及（c）沿界面的可能扩散路径和相应的能垒高度。我们考虑了两种MoS多晶型：1T和3R。我们的结果表明，1T-MoS与石墨烯的相互作用比3R-MoS更强。在这两种情况下，最佳的钠离子容纳位点都位于界面的MoS一侧，能带结构显示石墨烯部分具有合适的n型特性，这负责电子传导。钠离子扩散的最小能量路径表明，3R-MoS/石墨烯界面的能垒高度非常低（<0.25 eV），而其1T对应物的能垒高度则高得多（约0.7 eV）。对沿扩散过渡态的结构特征分析使我们能够确定，在1T情况下，钠离子与暴露的S原子的强配位是阻碍有效扩散的主要特征。这些结果为复杂二维异质界面上钠离子嵌入和扩散机制的物理化学细节提供了新线索，并将有助于高效NIBs先进电极材料的进一步开发。
