Cr2O5 as new cathode for rechargeable sodium ion batteries

Abstract

Chromium oxide, Cr2O5, was synthesized by pyrolyzing CrO3 at 350°C and employed as a new cathode in rechargeable sodium ion batteries. Cr2O5/Na rechargeable batteries delivered high specific capacities up to 310mAh/g at a current density of C/16 (or 20mA/g). High-resolution solid-state 23Na NMR both qualitatively and quantitatively revealed the reversible intercalation of Na ions into the bulk electrode and participation of Na ions in the formation of the solid-electrolyte interphase largely at low potentials. Amorphization of the electrode structure occurred during the first discharge revealed by both NMR and X-ray diffraction data. CrO3-catalyzed electrolyte degradation and loss in electronic conductivity led to gradual capacity fading. The specific capacity stabilized at >120mAh/g after 50 charge-discharge cycles. Further improvement in electrochemical performance is possible via electrode surface modification, polymer binder incorporation, or designs of new morphologies.