Membrane‐Free Zn/MnO₂ Flow Battery for Large‐Scale Energy Storage

Abstract

The traditional Zn/MnO2 battery has attracted great interest due to its low cost, high safety, high output voltage, and environmental friendliness. However, it remains a big challenge to achieve long‐term stability, mainly owing to the poor reversibility of the cathode reaction. Different from previous studies where the cathode redox reaction of MnO2/MnOOH is in solid state with limited reversibility, here a new aqueous rechargeable Zn/MnO2 flow battery is constructed with dissolution–precipitation reactions in both cathodes (Mn2+/MnO2) and anodes (Zn2+/Zn), which allow mixing of anolyte and catholyte into only one electrolyte and remove the requirement for an ion selective membrane for cost reduction. Impressively, this new battery exhibits a high discharge voltage of ≈1.78 V, good rate capability (10C discharge), and excellent cycling stability (1000 cycles without decay) at the areal capacity ranging from 0.5 to 2 mAh cm‐2. More importantly, this battery can be readily enlarged to a bench scale flow cell of 1.2 Ah with good capacity retention of 89.7% at the 500th cycle, displaying great potential for large‐scale energy storage.

Opportunities of Aqueous Manganese‐Based Batteries with Deposition and Stripping Chemistry

“…In addition, it was confirmed that protons help promote the dissolution of MnO 2 in the discharge process and reduce the cell overpotential. [ 78 ] This work demonstrated exciting features of the cathode Mn 2+ /MnO 2 deposition/stripping charge storage mechanism and the importance of electrolyte management for the development of the Mn‐based batteries.…”

“…Therefore, further research is needed to improve the overall electrochemical performance and lower the cost of the conventional MnO 2 ‐Zn flow battery. In these regards, Cui and coworkers [ 78 ] developed a membrane‐free MnO 2 ‐Zn flow battery by circulating the single electrolyte, instead of the separated catholyte and anolyte in the conventional flow battery, through one tank without using the relatively expensive ion selective membrane (Figure 5b). The membrane‐free MnO 2 ‐Zn flow battery was conducted by the cathode Mn 2+ /MnO 2 reactions on carbon felt and the anode Zn 2+ /Zn reactions on Zn foil in the electrolyte of 1 m ZnSO 4 and 1 m MnSO 4 .…”

“…Owing to the remarkable advantages of low cost, good safety, high operation voltage, long lasting and reliable shelf life, high capacity, and energy density, the Mn‐based batteries with the cathode Mn 2+ /MnO 2 chemistry are promising for next‐generation large‐scale energy storage. [ 76,78 ] Figure 7 a shows a conceptual schematic of the representative future grid‐scale energy storage based on the rechargeable Mn‐based batteries with the Mn 2+ /MnO 2 chemistry. By virtue of integrating renewable yet intermittent energy resources such as solar, wind and hydro‐electricity into electrical grid, the centralized Mn‐based battery system with capacity of MWh can be used to power individual households, factories, buildings, and transportations like electric vehicles.…”

“…Reproduced with permission. [ 78 ] Copyright 2020, John Wiley and Sons. Inset (right) is a digital photograph of the prototype lab‐scaling‐up MnO 2 ‐Zn flow battery with capacity of ≈2000 mAh.…”

“…Using a new full cell chemistry of manganese dioxide‐hydrogen gas (MnO 2 ‐H 2 ) battery as an example, it achieved high cathode specific capacity and ultrastable cycling performance (10 000 cycles). This study evoked significant research interest in the exploration of the cathode Mn 2+ /MnO 2 deposition/stripping chemistry to combine with a variety of anode chemistries, creating different Mn‐based batteries such as MnO 2 ‐Zn, [ 77–79 ] MnO 2 ‐Cu, [ 80,81 ] MnO 2 ‐Carbon, [ 82 ] and MnO 2 ‐Pb, [ 83 ] to name a few, with superb electrochemical performance. Although the development of the Mn 2+ /MnO 2 deposition/stripping chemistry is at its early stage, it presents great opportunities for the design of high‐performance Mn‐based batteries for practical large‐scale energy storage applications.…”