Defective BC2N as an Anode Material with Improved Performance for Lithium-Ion Batteries

Defect engineering can modify the physical and chemical properties of two-dimensional (2D) materials to advance their effectiveness for applications. Here, we have designed three kinds of single carbon vacancies (VC-I of BC2N-II as well as VC-III and VC-IV of BC2N-III) to systematically investigate their Li adsorption and diffusion performance based on DFT calculations. The electronic structure analysis shows that the existence of the defects plays a crucial role to tune the electronic properties and the performance of BC2N-II and BC2N-III monolayers toward the potential application as anodes of lithium-ion batteries (LIBs). Significantly, compared to the pristine BC2N-II and BC2N-III monolayers that can hardly adsorb Li atoms, defective BC2N monolayers greatly enhance the Li adsorption energy. In addition, the theoretical capacities of defective BC2N monolayers, especially for VC-I of BC2N-II (2256 mAh/g), are extremely high, but the energy barriers of Li transfer in the vicinity of the defective BC2N are relatively large, whereas for escaping defective sites, these levels are comparatively small. Considering the diffusion behavior of Li in the actual process of Li insertion in the anode of the LIBs, we further explored the adsorption and diffusion performance of Li on the modified VC-I monolayer with one Li atom occupying the most stable position (site H) of the defect. Remarkably, the Li can shuttle between the stable sites around the defects with energy barriers as low as 0.45 eV. The calculated voltages for all systems are all within the desired ranges of reported anode materials for LIBs. Our findings provide a theoretical guideline to design reasonable anode materials with defect for LIBs.