The importance of electrical energystorage systems (EES), for a successful integration of intermittent renewable energy sources into the electrical grid is beyond dispute. [1][2][3][4] For mobile applications, lithium ion batteries (LIBs) with high energy density prevail. [2,5,6] Although many efforts focus on alternative chemical systems (e.g., multivalent Al, Mg, and Ca), it is hard to imagine that LIBs will disappear in the near future. [4,7] Yet, for large scale stationary EES, there is no such prevailing technology. Although other alternatives, like pumped hydro or fuel cells are available, batteries are amongst the most promising technologies for this purpose. [1,3,8] With the energy density being slightly less relevant, other redox active materials could be employed in large scale EES, i.e., redox-flow batteries (RFBs) with their very long cycle life and decoupled capacity, power and energy output. [2,9,10] Their benchmark is the allvanadium redox-flow battery (VRFB) with V II /V III and V IV / V V redox couples, [2] as well as a 15 000-20 000 charge/discharge cycles lifetime and an acceptable energy density of 25-35 Wh L −1 installed in up to 60 MWh capacity EES. [2,6] However, probably due to the high cost, a commercial breakthrough still has to come. [2,6,9] Considering abundancy and cost, few elements are suitable as redox active material in sustainable batteries. [4,11] Manganese is one of them and, therefore, finds application in LIB-cathode active materials (e.g., LiMn 2 O 4 or Li[Ni 0.8 Co 0.1 Mn 0.1 ]O 2 ) or in cathode materials of primary batteries (MnO 2 ). [5,12] However, to the best of our knowledge, only one battery system exclusively using manganese compounds at both electrodes is described, [13] i.e., Mn(acac) 3 acetonitrile (MeCN) solutions with the Mn II /Mn III couple at the negative and the Mn III /Mn IV couple at the positive electrode. Yet, with E cell of 1.1 V the system does not exploit the large potential range advantage of a non-aqueous electrolyte. Already the aqueous standard potential difference ΔE 0 of Mn 0 /Mn II and Mn II /Mn III redox couples amounts to an impressive 2.69 V. In addition, the Mn volumetric specific capacity is 7034.7 Ah L −1 (two-electron-process). It clearly exceeds that of zinc (5853.8 Ah L −1 ), which in the zinc A new all-Manganese flow battery (all-MFB) as a non-aqueous hybrid redox-flow battery is reported. The discharged active material [Cat] 2 [Mn II Cl 4 ] (Cat = organic cation) utilized in both half-cells supports a long cycle life. The reversible oxidation of [Mn II Cl 4 ] 2− to [Mn III Cl 5 ] 2− at the positive electrode and manganese metal deposition from [Mn II Cl 4 ] 2− at the negative electrode give a cell voltage of 2.59 V. Suitable electrolytes are prepared and optimized, followed by a characterization in static battery cells and in a pumped flow-cell. Several electrode materials, solvents, and membranes are tested for their feasibility in the all-MFB. An electrolyte consisting of [EMP] 2 [MnCl 4 ] and some solvent γ-butyrolactone is cycle...

The ionic liquid (IL) trihalogen monoanions [N2221][X3]− and [N2221][XY2]− ([N2221]+=triethylmethylammonium, X=Cl, Br, I, Y=Cl, Br) were investigated electrochemically via temperature dependent conductance and cyclic voltammetry (CV) measurements. The polyhalogen monoanions were measured both as neat salts and as double salts in 1‐butyl‐1‐methyl‐pyrrolidinium trifluoromethane‐sulfonate ([BMP][OTf], [X3]−/[XY2]− 0.5 M). Lighter IL trihalogen monoanions displayed higher conductivities than their heavier homologues, with [Cl3]− being 1.1 and 3.7 times greater than [Br3]− and [I3]−, respectively. The addition of [BMP][OTf] reduced the conductivity significantly. Within the group of polyhalogen monoanions, the oxidation potential develops in the series [Cl3]−>[BrCl2]−>[Br3]−>[IBr2]−>[ICl2]−>[I3]−. The redox potential of the interhalogen monoanions was found to be primarily determined by the central halogen, I in [ICl2]− and [IBr2]−, and Br in [BrCl2]−. Additionally, tetrafluorobromate(III) ([N2221]+[BrF4]−) was analyzed via CV in MeCN at 0 °C, yielding a single reversible redox process ([BrF2]−/[BrF4]−).

Ionic liquids (IL) are valuable in a variety of applications due to their high electrochemical stability and physical properties. Using the cation 1-methyl-3-octylimidazolium, [OMIM] + , the bromidostannate RTIL [OMIM][Sn +II Br 3 ], "undercooled melt" [OMIM][Sn +IV Br 5 ], and IL [OMIM] 2 [Sn +IV Br 6 ] were synthesized. The uncommon solid state structure of [SnBr 5 ] − was elucidated in the form of its RTIL salt. Additionally, the IL based on tribromine-monoanion [OMIM][Br 3 ] was used to dissolve metallic Sn, selectively resulting in the formation of [SnBr 3 ] − as confirmed by Raman spectroscopy. Subsequent cyclic voltammograms (CV) of [SnBr 3 ] − confirmed the deposition potential of metallic Sn and renewal of the polybromide [Br 3 ] − . The RTIL bromidostannates were stable compounds, making a selective electrochemical investigation of the deposition of metallic Sn(0) to Sn(+II)/Sn(+IV) redox process possible, via conductance and CV measurements. The CVs of the RTILs and of solutions in propylene carbonate had the redox couples of Sn(0)/