Glycerol-based electrolyte for sustainable low-rate zinc-ion batteries

The rapid expansion of renewable energy sources such as solar and wind demands safe, low-cost, and durable stationary energy storage technologies. In this context, aqueous zinc-ion batteries (ZIBs) have emerged as attractive alternatives to lithium-ion systems because they combine the abundance and geopolitical accessibility of zinc with the intrinsic safety of water-based electrolytes. Nevertheless, conventional aqueous electrolytes still suffer from major limitations, including parasitic hydrogen evolution, zinc corrosion, interfacial instability, and structural degradation of cathodes during long-term cycling, particularly under low-rate operating conditions. To address these challenges, we developed a sustainable low-temperature transition mixture (LTTM) electrolyte based on ZnSO4·7H2O and glycerol in a 1:10 molar ratio. Both components are inexpensive and widely available, with glycerol representing an abundant by-product of biodiesel production. A detailed physicochemical investigation linked the thermal properties of the mixture with ionic transport characteristics and electrochemical stability. Despite reduced transport kinetics compared with conventional aqueous ZnSO4 solutions, the LTTM exhibited a significantly widened electrochemical stability window, enabling highly reversible Zn plating/stripping at low current density (0.05 mA cm-2). Morphological characterization confirmed uniform zinc deposition on carbon substrates, while proof-of-concept full-cell tests using a Zn anode and zinc hexacyanoferrate cathode demonstrated stable cycling, coulombic efficiencies above 90%, and a specific capacity of 50.6 mAh g-1, comparable to standard aqueous electrolytes.