First-principles investigation of FeP@Graphene as anode material for sodium-ion batteries

Considerable efforts have been devoted to addressing volume changes and capacity degradation in conversion-type electrodes. While most studies have relied on experimental approaches, simulation-based investigations remain limited. Here, DFT was used to investigate FeP, a well-known conversion-type electrodes due to its low cost and high theoretical capacity. To address volume variation, FeP can be combined with graphene to form a composite. Stronger Na adsorption was observed between FeP and graphene, compared each material alone. For the insertion of Na between the composite materials, as the Na concentration increased, average adsorption energy and cluster volume exhibited distinct trends across three stages, with the middle range corresponding to a transition from intercalation to conversion. This transformation was further supported by PDOS analysis, which confirmed the formation of a new phase at a Na-to-FeP ratio of 0.286. Bader charge analysis also revealed a gain–loss–gain pattern in Fe charge, reinforcing the existence of a transitional stage between the two mechanisms. Na diffusion barrier was evaluated with CI-NEB, while the OCV and theoretical capacity were computed to further assess its electrochemical performance. Insights gained in this study offer a fundamental understanding of the intercalation-to-conversion transition and provide guidance for rational design of conversion-type anode materials.