Triggering anomalous capacity by nanoengineered ordered mesoporous structure for Co3O4 anode material in Li-ion rechargeable batteries

Abstract

Nanostructured engineering is one of the strategies for optimizing transition metal oxides as anode materials in lithium-ion batteries. Among them, mesoporous structures have received significant attention due to their intrinsic properties which are related to porous structure. This structure provides short Li-ion diffusion pathways and acts as a buffer for volume changes during electrochemical reactions, affecting various electrochemical properties and performances. One of the intriguing aspects of the mesoporous structure effect is that it sometimes triggers a negative fading. Herein, we observed that ordered mesoporous Co3O4 exhibits a higher reversible capacity and anomalous cycle behavior that capacity increases during cycling, known as a negative fading, compared to bulk Co3O4. Moreover, the observed capacity is even higher than its theoretical capacity. Mesoporous Co3O4 exhibits stable and more reversible conversion reactions, and even gradually activated electrolyte-derived surface layer formation/decomposition during cycling. Based on combined synchrotron-based X-ray analyses and electrochemical tests, we found the weaker Co-O and Co-Co bond strength in mesoporous material than those in the bulk material, gives rise to a more reversible conversion reaction during cycling. In addition, the distinctive structural properties of mesoporous leads to the further formation/decomposition of electrolyte-derived surface layer, resulting in the negative fading.