<i>In Situ</i> Confined Co₅Ge₃ Alloy Nanoparticles\nin Nitrogen-Doped Carbon Nanotubes for\nBoosting Lithium Storage

Abstract

Ge-based materials\nhave garnered much attention in lithium-ion\nbatteries (LIBs) for their high theoretical capacity, but these materials\nsuffer from huge volume changes and serious pulverization, which cause\ninsufficient lithium storage performance. Herein, a composite composed\nof Co₅Ge₃- and nitrogen-doped carbon nanotube\n(Co₅Ge₃/N-CNT) was successfully synthesized\nusing ZIF-67 and GeO₂ as precursors. There are interactions\nbetween the Co₅Ge₃ alloy nanoparticles and carbon\nnanotubes in the growth process, in which the Co₅Ge₃ alloy nanoparticles were confined <i>in situ</i> in N-CNTs and the <i>in situ</i> growth of N-CNTs was\nboosted in the existence of the Co₅Ge₃ catalyst.\nDensity functional theory calculations revealed that the electronic\nconductivity of the Co₅Ge₃ alloy is much higher\nthan that of Ge and the Li⁺ interaction energy of the former\nis lower than that of the latter. In addition, the interconnected\ncarbon nanotubes not only offer Li⁺ diffusion pathways\nand electronic networks but also increase electronic conductivity.\nImportantly, carbon nanotubes and Co metal have a synergistic effect\nof buffering volume charge of Ge in the process of Li⁺ intercalation/deintercalation.\nAs expected, the Co₅Ge₃/N-CNT composite demonstrated\na high reversible capacity of 853.7 mA h g^–1 at\n2 A g^–1 after 1500 cycles and attractive rate performance\nof up to 10 A g^–1.