In the present work, the cellulose-based materials were manufactured and used as components of electrochemical double layer capacitors (EDLCs). The preparation method of cellulose membranes as well as composite electrodes containing cellulose as a binder was presented. These materials were prepared using for the first time ionic liquid/dimethyl sulfoxide (IL/DMSO) mixture solvent. Obtained components displayed a uniform structure, thermal stability, and good electrochemical properties. The electrochemical performances of these materials were studied in 2-electrode EDLC cells by common electrochemical techniques as cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS). The composite electrodes were investigated in three types of electrolytes: aqueous, organic, and ionic liquids. The cellulose membranes were, however, soaked in an aqueous electrolyte and tested as hydrogel polymer electrolytes. All investigated materials show high efficiency in terms of specific capacity. The studied cellulose-based capacitors exhibited specific capacitance values in the range of 20–22 F g⁻¹, depending on the type of applied electrolyte.

Aqueous Zn‐metal battery (AZMB) is a promising candidate for future large‐scale energy storage with commendable capacity, exceptional safety characteristics, and low cost. Acetonitrile (AN) has been widely used as an effective electrolyte constituent to improve AZMBs’ performance. However, its functioning mechanisms remain unclear. In this study, we unveiled the critical roles of AN in AZMBs via comparative in situ electrochemical, gaseous, and morphological analyses. Despite its limited ability to solvate Zn ions, AN‐modulated Zn‐ion solvation sheath with increased anions and decreased water achieves a weakly‐solvating electrolyte. As a result, the Zn||Zn cell with AN addition exhibited 63 times longer cycle life than cell without AN and achieved a 4 Ah cm⁻² accumulated capacity with no H₂ generation. In V₂O₅||Zn cells, for the first time, AN suppressing CO₂ generation, elevating CO₂‐initiation voltage from 2→2.44 V (H₂: 2.43→2.55 V) was discovered. AN‐impeded transit and Zn‐side deposition of dissolved vanadium ions, known as “crosstalk,” ameliorated inhomogeneous Zn deposition and dendritic Zn growth. At last, we demonstrated an AN‐enabled high‐areal‐capacity AZMB (3.3 mAh cm⁻²) using high‐mass‐loading V₂O₅ cathode (26 mg cm⁻²). This study shed light on the strategy of constructing fast‐desolvation electrolytes and offered insights for future electrolyte accommodation for high‐voltage AZMB cathodes.