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

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.