RESUMEN
Graphene quantum dots have been widely studied owing to their unique optical, electrical, and optoelectrical properties for various applications in solar devices. Here, we investigate the optoelectronic properties of hexagonal and nitrogen-doped graphene quantum dots using the first-principles method. We find that doping nitrogen atoms to hexagonal graphene quantum dots results in a significant red shift toward the visible light range as compared to that of the pristine graphene quantum dots, and the doped nitrogen atoms also induce a clear signature of anisotropy of the frontier orbitals induced by the electron correlation between the doped nitrogen atoms and their adjacent carbon atoms. Moreover, time-dependent density functional theory calculations with the M06-2X functional and 6-311++G(d,p) basis set reproduce well the experimental absorption spectra reported recently. These results provide us with a novel approach for more systematic investigations on next-generation solar devices with assembled quantum dots to improve their light selectivity as well as efficiency.
RESUMEN
Lithium-ion batteries lay the foundation for satisfying the fast-growing demand of portable electronics and electric vehicles. However, due to the complexity of material syntheses, high fabrication temperature condition, and toxic gas emission, high volume manufacturing of lithium-ion batteries is still challenging. Here, we propose a modified coprecipitation method to synthesize Li1.0Ni0.6Mn0.2Co0.2O2 (NMC622-MCP) as a cathode material in a simple, cost-effective, and environmentally friendly approach. We demonstrate that the proposed method can be operated in a lower temperature environment, with respect to the requirement of conventional synthesis methods. Furthermore, only CO2 gas is emitted during synthesis. We also employed first-principles simulations to evaluate the crystallinity of the synthesized materials via X-ray diffractometer patterns. During charge/discharge processes, the obtained cathode materials induce outstanding electrochemical performance with a maximum specific capacity of up to 206.9 mAh g-1 at 0.05 C and a retention capacity of 83.22% after 100 cycles. Thus, the simple, cost-effective, environmentally friendly, and highly electrochemical performance of the newly acquired material envisages the modified coprecipitation method as a promising tool to manufacture cathode materials for lithium-ion batteries.
