Hierarchical core-shell structured CoZn-MOFs derived materials anode with raspberry-like shape for high-performance lithium storage

Abstract

Significant progress had been made in various fields with transition metal oxide electrode materials, particularly in battery materials where structural control played a crucial role in enhancing their electrochemical properties. Therefore, this study aimed to investigate the potential of a raspberry-like hierarchical core-shell structure derived from Co–Zn MOF as anode materials by varying concentration of reaction solution in hydrothermal method. The hierarchical raspberry-like hollow shell structure was beneficial to expose more active sites and reduced the diffusion distance of Li+ to the internal electroactive sites, improving the overall electrical conductivity of the electrode by full contact with carbon. Carbon nanotubes were incorporated into more suitable core-shell structure. They were uniformly coated the hollow sphere and filled inside of that to form a carbon skeleton. Specifically, the carbon nanotubes inside of the hollow sphere supported the shell not to collapse. This mitigated volume expansion during the cycling process, maintains structure stability, and allowed for rearrangement to occur during cycling to achieve a high specific capacity. Furthermore, the carbon nanotubes inside and outside of the hollow sphere created a high-density interface that enhanced interfacial polarisation and accelerated the rate of Li+ passage during cycling. These effects had resulted in an improvement in the material's performance. It is noteworthy that the specific capacity attains 1050 mAh g-1 when exposed to a current density of 0.2 A g-1. Notably, even after conducting 500 cycles at a current density of 0.5 A g-1, the specific capacity remains stable at 652 mAh g-1.