Improving the cyclability of sodium-ion cathodes by selection of electrolyte solvent

► Na1.8FePO4F/C composite material is prepared by a new mechanical-ceramic method. ► The local structure of NaxFePO4F electrodes were examined for the first time by XAS. ► The local changes from Na1.8FePO4F to NaFePO4F, and then to Na2FePO4F are small. ► Both Fe2+ and Fe3+ are in high spin configurations in NaxFePO4F electrodes. ► Capacity and capacity retention are improved by using NaPF6 electrolyte in EC:DEC.