This work focuses on the assessment, in terms of effectiveness, feasibility and sustainability, of three different procedures for the synthesis of vanadium-based mixed-acid electrolytes to be used in vanadium redox-flow batteries (VRFBs). Procedures considered consisted in: a) the mere mixing of suitable vanadium precursors (Electrolyte A); b) the chemical reduction of V2O5 by oxalic acid (Electrolyte B); c) the electrochemical reduction of V2O5 using a home-made “H-shaped” electrolysis cell (Electrolyte C). VRFB properties such as energy efficiency, mean charge–discharge voltages, cycle duration as well as stability and conductivity of the electrolyte were analysed and compared with the state-of-the-art. Experimental tests carried out on a laboratory scale VRFB battery comprised: thermal stability test, cyclic voltammetry, electrochemical impedance spectroscopy measurements and charge–discharge tests. A Life Cycle Assessment of the three electrolytes is also presented for benchmarking purposes. •Assessing sustainability of vanadium redox-flow battery electrolyte through advanced LCA tools (ISO 14040).•Sustainable experimental synthesis procedures of vanadium electrolytes.•Cradle-to-gate LCA comparison with local specific data.•Syntheses of mixed acid vanadium electrolytes for VRFB are compared in terms of effectiveness and sustainability.