A new all‑Manganese flow battery (all‑MFB) as non‑aqueous hybrid redox‑flow battery is reported. The discharged active material [Cat]₂[Mn^IICl₄] (Cat = organic cation) utilized in both half‑cells supports a long cycle life. The reversible oxidation of [Mn^IICl₄]^2– to [Mn^IIICl₅]^2– at the positive electrode and manganese metal deposition from [Mn^IICl₄]^2– at the negative electrode give a cell voltage of 2.59 V. Suitable electrolytes were prepared and optimized, followed by a characterization in static battery cells and in a pumped flow‑cell. Several electrode materials, solvents and membranes were tested for their feasibility in the all‑MFB. An electrolyte consisting of [EMP]₂[MnCl₄] and some solvent g-butyrolactone was cycled 500 times, both in a static as well as a flow‑cell, over a period of two months, with coulombic efficiencies up to 83 %. With the electrolytes prepared in this work, energy densities up to 74 Wh L^–1 are possible, exceeding the VRFB benchmark system, using solely the cheap and abundant element manganese as the active material. Although further optimizations are necessary, this system describes a new and promising setup towards sustainable stationary energy storage. 

Advanced Energy Materials 2021, 11, 2101261.