*4.1. Materials*

For the positive electrode preparation, manganese dioxide (AM, Manganese(IV) oxide, 99.9% (metals basis), 325 mesh powder, Alfa Aesar, Heysham, United Kingdom), Carbon black (CB, Carbon black, acetylene, 100% compressed, 99.9+%, Alfa Aesar, Heysham, United Kingdom), binder polymer (BP) and solvent were mixed in different combinations in a speed mixer (DAC 150.1 FVZ-K, Hauschild and Co.KG, Hamm, Germany) at 3000 rpm for 2 min. Subsequently, the positive electrode aqueous slurry was homogenized in a threeroll mill (EXAKT 80E, EXAKT Advanced Technologies GmbH, Norderstedt, Germany) with a final roll gap of 10 μm to control and unify the particle sizes. Due to the evaporation and security characteristics of the solvents, the non-aqueous slurries were homogenized for 30 min at least at 2000 rpm in a laboratory dissolver (DISPERMAT CN10, VMA-GETZMANN GmbH, Reichshof, Germany) instead of being processed in the three-roll mill. The slurry was coated with a doctor blade and 200 μm wet layer thickness on a stainlesssteel foil (1.4301/AISI 304, thickness 25 μm, TBJ Industrieteile GmbH, Leipzig, Germany). The AM mass loading was ~2.5–4.6 mg/cm−<sup>2</sup> and the electrode coating thickness ~40 μm (see Supplementary Figure S10). Afterwards, the coating was dried for 24 h at 40 ◦C. Then, 16 mm coins were used as positive electrodes. As the negative electrode, a 25 μm thick zinc foil with the diameter of 16 mm was used (zinc foil 99.95%, Goodfellow GmbH, Hamburg, Germany). The separator (18 mm diameter) was made of glass fibre filter (Whatman® GF/A, Cytiva Europe GmbH, Freiburg, Germany). For the electrolyte, zinc sulfate heptahydrate (AnalaR NORMAPUR® Reag. Ph.Eur., ACS for analysis, VWR International GmbH, Darmstadt, Germany) and manganese sulfate tetrahydrate (99%, metal basis, Alfa Aesar, Heysham, United Kingdom) were used. A zinc wire (99.9% pure zinc wire, Goodfellow GmbH, Hamburg, Germany) was used as the reference electrode. For the BP study, the following binders have been investigated:


For the slurry preparation, aqueous and non-aqueous binder solutions/suspensions were prepared: For the aqueous slurry preparation, DI-water and for the non-aqueous slurry preparation, methyl ethyl ketone (MEK, for NBR and CA) or dimethyl sulfoxide (DMSO, for PAN) were used. The binder preparations are listed in Table 2.

In order to evaluate the material shares of active material, conductive agent and binder polymer, different mixing ratios were tested. For this purpose, the PAN-based aqueous *LA133* was used exemplarily as the binder. The share combinations listed in Table 3 have been tested.

#### *4.2. Cell Assembly*

Cells were assembled using EL-Cell® ECC-Aqu experimental cells. A glass fibre separator with a diameter 18 mm was used. Two hundred μL of an aqueous electrolyte containing 2 M ZnSO4 and 0.1 M MnSO4 was used (pH~4). The zinc wire was used as the reference electrode in the EL-Cell® ECC-Aqu. As the current collector on the positive electrode, an 18 mm stainless steel coin was used. As the current collector on the negative electrode, an 18 mm copper coin was used. The cell setup is shown in Supplementary Figure S2.
