Novel high-performance anodic materials for lithium ion batteries: two-dimensional Sn-X (X = C, Si, and Ge) alloy monolayers.

Lithium-ion batteries (LIBs) have always been the focus of researchers for energy storage applications. Here, the first-principles density functional theory method was used to explore the possibility of using stanene derived structures as LIB anodes. And such two-dimensional structures are similar to graphene or stanene, but half of the Sn atoms are replaced by group-IV atoms to form new structures, which are called Sn-X (X = C, Si, and Ge). Our calculation results showed that the optimized structure, lattice constant and other parameters are consistent with those reported in previous studies. Meanwhile, we found out that the semiconductor properties of pristine Sn-X transform into metal properties after the adsorption of Li. Then, by calculating the adsorption concentration of Li ions on the Sn-X monolayers, we found that these kinds of materials can meet the requirements of battery anodes very well, not only in terms of their open-circuit voltage, but also storage capacity. For Sn-Si and Sn-Ge, their theoretical capacities can be as high as 1095.78 mA h g (LiSn-Si) and 840.88 mA h g (LiSn-Ge). At last, based on the investigation of their diffusion path, Sn-X has been found to have high charge and discharge rates because of its low barrier. By reason of the foregoing, 2D Sn-X monolayers will be excellent battery anodes.