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Due to its adaptability in scaling up, a redox flow battery (RFB) is seen to be one of the finest options for large-scale electrical backup systems. As a result, it is feasible to create RFB systems that are both cost and performance effective. Recently, a zinc-manganese RFB that relies on Zn(s)/Zn2+(aq) and Mn2+(aq)/MnO2 redox couples has gained attention since both zinc and manganese are cheap, abundant, and eco-friendly. However, the reversibility of Mn2+(aq)/MnO2 at the positive electrode is limited by the formation of Mn3+ species upon charge/discharge (CD) cycling, resulting in severe capacity fading. Herein, this study examines the use of reducing agents as electrolyte additives to enhance the reversibility of the Mn2+(aq)/MnO2 reaction. Experimental results indicate that sulfuric acid and oxalic acid as additives can significantly improve the reversibility of the Mn2+(aq)/MnO2 reaction and the cycling stability of zinc-manganese RFBs. The acetate-based system demonstrates better reversible reaction than the sulfate-based system having more than 100 CD cycles at a current density of 10 mA/cm2. Coulombic efficiency (CE) is also seen to be higher than 90%. Overall, results lead to increased efficiency and cycling stability for zinc-manganese RFBs. [ABSTRACT FROM AUTHOR]

Due to its excellent reversibility and stability, dimethyl sulfoxide (DMSO) electrolyte is seen to be a promising nonaqueous electrolyte. Compared to aqueous Zn–MnO2 systems, ZIBs having DMSO electrolyte, and the manganese dioxide (MnO2) cathode display inferior rates and capacity performances. However, it is found that the addition of water can improve the performance of DMSO-based ZIBs, even a small amount of water. In this work, the effect of water on the performance of DMSO-based ZIBs is thoroughly investigated. Herein, the layer-type MnO2 (δ type, birnessite) is used as the main cathode material. Ex situ/operando X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS) and in situ X-ray absorption spectroscopy (XAS) results suggest that the existence of water in DMSO electrolytes can lead to changes occurring in the Zn2+ intercalated phase. Zn-birnessite when replaced by super-hydrated Zn-buserite provides a much improved solid-phase diffusion of Zn2+ and surface kinetics. The optimized battery yields the highest capacity of 224 mA h g−1 and can cycle over 2500 cycles. This discovery extends the understanding of wet nonaqueous electrolyte chemistry and paves the way towards the practical application of ZIBs. [ABSTRACT FROM AUTHOR]

Nonaqueous zinc-ion batteries (NZIBs) featuring manganese dioxide (MnO 2 ) cathodes position themselves as viable options for large-scale energy storage systems. Herein, we demonstrate the use of ammonium cation as a preintercalant to improve the performance of the δ-MnO 2 cathode in wet dimethyl sulfoxide based electrolytes. Employing in situ X-ray absorption spectroscopy, Raman spectroscopy, and synchrotron X-ray diffraction, we reveal that the integration of ammonium cations promotes the formation of NH-O-Mn networks. These networks are crucial for manipulating the distortion of the MnO 6 octahedral units during discharging, thereby mitigating charge disproportionation, which is a primary limitation to MnO 2 's charge-storage efficiency. The modified MnO 2 , through this idea, displays a notable improvement in capacity (∼247 mAh/g) and can pass charge-discharge cycles up to 500 cycles with a capacity retention of 85%. These findings underscore the potential of modified MnO 2 in advancing MnO 2 -based hosts for Zn-MnO 2 batteries, marking significant progress toward next-generation energy storage solutions.