Fe Species Intercalation Confined by the Interlayer Environment of V2CTx MXene for Lithium-Ion Storage

This work successfully achieved pre-intercalation of Fe species in V2CTx MXene through an annealing method. The crystallographic structure, microscopic morphology, and functional groups of the samples before and after pre-intercalation were analyzed by XRD, SEM, and FTIR, and the electrochemical performance of MXene electrodes was studied. Research has shown that the interlayer spacing of pre-intercalated MXene increases with an increase in annealing temperature. The interlayer spacing of MXene annealed at 800 °C is 13.1% higher than that of the original MXene. However, the morphology of the samples was damaged by excessively high annealing temperatures, which also weakened the lithium-ion storage performance. In contrast, the cycling performance of MXene electrodes annealed at 400 °C showed the greatest improvement, reaching 71.65%. This is because iron species, acting as a pillar support structure, expand the interlayer spacing and broaden the transport channels for lithium ions. Meanwhile, high-temperature annealing generates more oxygen-containing functional groups, which provide additional active sites for lithium-ion transport, promote the kinetics of electrode reactions, and thus enhance its lithium-ion storage performance.