In Situ Confined Co5Ge3 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 Co5Ge3- and nitrogen-doped carbon nanotube (Co5Ge3/N-CNT) was successfully synthesized using ZIF-67 and GeO2 as precursors. There are interactions between the Co5Ge3 alloy nanoparticles and carbon nanotubes in the growth process, in which the Co5Ge3 alloy nanoparticles were confined in situ in N-CNTs and the in situ growth of N-CNTs was boosted in the existence of the Co5Ge3 catalyst. Density functional theory calculations revealed that the electronic conductivity of the Co5Ge3 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 Co5Ge3/N-CNT composite demonstrated a high reversible capacity of 853.7 mA h g-1 at 2 A g-1 after 1500 cycles and attractive rate performance of up to 10 A g-1.