In Situ Confined Co₅Ge₃ Alloy Nanoparticles in Nitrogen-Doped Carbon Nanotubes for Boosting Lithium Storage

Abstract

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.