Ca-Zr co-doping enabled electrochemical reversibility of O3-type NaCrO2 for sodium-ion batteries with high-voltage characteristics.

• Ca-Zr co-doped Na 0.94 Ca 0.03 Cr 0.97 Zr 0.03 O 2 sample was prepared by a facile solid-state reaction. • Ca-Zr co-doping was innovatively adopted to improve the structural reversibility at high cutoff voltage. • Na 0.94 Ca 0.03 Cr 0.97 Zr 0.03 O 2 exhibits excellent electrochemical performance in the voltage range of 1.5–3.8 V. O3-type NaCrO 2 has been researched as a promising cathode material for sodium-ion batteries (SIBs), however, it suffers from serious irreversible phase transitions when charged to 3.8 V, thereby resulting in a severe decline of reversible capacity. To improve the structural stability, small amounts of Ca2+ and Zr4+ ions are introduced into the O3-type NaCrO 2 via a facile solid-state reaction in this work. In the voltage range of 1.5–3.8 V, O3-type Na 0.94 Ca 0.03 Cr 0.97 Zr 0.03 O 2 delivers ∼ 120 mAh g−1 with a capacity retention of 64.6% after 500 cycles and a reversible capacity of 76 mAh g−1 at 20C, much better than those of O3-type NaCrO 2. The improved performance of O3-type Na 0.94 Ca 0.03 Cr 0.97 Zr 0.03 O 2 is attributed to the better structural reversibility and electrochemical reaction kinetics at the high charge cutoff voltage enabled by Ca and Zr co-doping. Our findings benefit the development of cathode materials with high energy density and high cycling stability for SIBs. [ABSTRACT FROM AUTHOR]