UC Berkeley

Over the last decade, Na-ion batteries have been extensively studied as low-cost alternatives to Li-ion batteries for large-scale grid storage applications; however, the development of high-energy positive electrodes remains a major challenge. Materials with a polyanionic framework, such as Na superionic conductor (NASICON)-structured cathodes with formula NaxM2(PO4)3, have attracted considerable attention because of their stable 3D crystal structure and high operating potential. Herein, a novel NASICON-type compound, Na4MnCr(PO4)3, is reported as a promising cathode material for Na-ion batteries that deliver a high specific capacity of 130 mAh g−1 during discharge utilizing high-voltage Mn2+/3+ (3.5 V), Mn3+/4+ (4.0 V), and Cr3+/4+ (4.35 V) transition metal redox. In addition, Na4MnCr(PO4)3 exhibits a high rate capability (97 mAh g−1 at 5 C) and excellent all-temperature performance. In situ X-ray diffraction and synchrotron X-ray diffraction analyses reveal reversible structural evolution for both charge and discharge.