Na-containing manganese-based cathode materials synthesized by sol-gel method for zinc-based rechargeable aqueous battery

Abstract Zinc-based rechargeable aqueous batteries are regarded as one of the most safe and inexpensive energy storage systems compared to the conventional rechargeable batteries with organic electrolytes. However, the limited cathode materials and the problem of associated metal ion dissolution restrict its practical application. Herein, the inexpensive novel cathode materials of Na-containing manganese-based composite of Na0.44MnO2/Mn2O3 and Na2/3Fe1/2Mn1/2O2 are designed and synthesized correspondingly by sol-gel methods combined with freeze-drying technique, and are applied in the zinc-based aqueous batteries for the first time. The secondary particles of Na0.44MnO2/Mn2O3 composite with a cubic box and the molecular sieve configurations are composed of nano primary particles with about 150∼300nm, and the obtained O3-Na2/3Fe1/2Mn1/2O2 at 850 °C (O3-NFM-850) appears to homogenous distribution with 3D solid block structure and platelet-shaped particles, while the spherical core-shell structure of P2-Na2/3Fe1/2Mn1/2O2 at 850 °C (P3-NFM-850-PVA) after dispersed by poly (vinyl alcohol) are linked to each other by amorphous carbon. Finally, the cathode of Na0.44MnO2/Mn2O3 and P3-NFM-850-PVA deliver the reversible capacities of 68.3 mAh g-1 and 42 mAh g-1 even after 200 cycles at 0.4 A/g respectively without capacity fading. Compared to the reported Na0.44MnO2, the increased capacity of Na0.44MnO2/Mn2O3 composite is attributed to the possible co-insertion of sodium ion and zinc ion for Na0.44MnO2 and the zinc ion insertion for Mn2O3 as well, indicating the synergetic energy storage for rechargeable hybrid aqueous battery and aqueous zinc ion battery. While the improved cyclic performance of Na2/3Fe1/2Mn1/2O2 is ascribed to the structural stability by Fe-doping and carbon-coating.