Confined CoGe Alloy Nanoparticles in Nitrogen-Doped Carbon Nanotubes for Boosting Lithium Storage.

Ge-based materials have garnered much attention in lithium-ion batteries (LIBs) for their high theoretical capacity, but these materials suffer from huge volume changes and serious pulverization, which cause insufficient lithium storage performance. Herein, a composite composed of CoGe- and nitrogen-doped carbon nanotube (CoGe/N-CNT) was successfully synthesized using ZIF-67 and GeO as precursors. There are interactions between the CoGe alloy nanoparticles and carbon nanotubes in the growth process, in which the CoGe alloy nanoparticles were confined in N-CNTs and the growth of N-CNTs was boosted in the existence of the CoGe catalyst. Density functional theory calculations revealed that the electronic conductivity of the CoGe alloy is much higher than that of Ge and the Li interaction energy of the former is lower than that of the latter. In addition, the interconnected carbon nanotubes not only offer Li diffusion pathways and electronic networks but also increase electronic conductivity. Importantly, carbon nanotubes and Co metal have a synergistic effect of buffering volume charge of Ge in the process of Li intercalation/deintercalation. As expected, the CoGe/N-CNT composite demonstrated a high reversible capacity of 853.7 mA h g at 2 A g after 1500 cycles and attractive rate performance of up to 10 A g.