Freestanding Cathode Electrode Design for High-Performance Sodium Dual-Ion Battery

In this work, both advantages of sodium-ion batteries and dual-ion batteries have been combined in an innovated sodium-ion-based dual-ion battery (SDI) system using a Na metal film as anode and a freestanding meso-carbon microbead film (FS-MCMB) as cathode. FS-MCMB in SDI battery exhibited a superior working performance with the specific capacity of 83.6 mAh/g and a remarkable long-term stability over 300 cycles. The SDI battery with FS-MCMB exhibited an advantage of high mass density loading in the range of 2–7.5 mg cm^–2, which was equal to a comparable capacity of 78–83 mAh/g. The electrochemical impedance analysis indicated that FS-MCMB provided a superior permeability, resulting in facilitating electrolyte infiltration into MCMB structure. In-situ XRD and ex-situ Raman spectroscopy were utilized to characterize the intercalating/deintercalating process of PF₆^– anions into/out of MCMB during charging/discharging processes. Finally, theoretical calculations further confirmed the structural arrangement of PF₆^– anions in the graphite layers.