High-Voltage Cr4+/Cr3+ Redox Couple in Polyanion Compounds

Higher-voltage operation is crucial to increase the energy density of rechargeable batteries. Here we explored the Cr4+/Cr3+ redox couple in a polyanion framework for a high-voltage sodium battery cathode. An archetypal NASICON-phase Na3Cr2(PO4)3 exhibited a reversible redox activity at ca. 4.5 V versus Na/Na+, offering further scope for searching new high-voltage materials based on Cr4+/Cr3+ redox couple.