LAUSR

Zn ion batteries (ZIB) have recently emerged to be a promising and rather cheap alternative to Li-ion batteries. However, the divalent charge of Zn limits the choice of cathode materials, whereas the choice of electrolyte is limited by hydrogen evolution reaction. Polymer cathodes have shown to be promising material for ZIB. In this paper we have studied in detail a Zn/polypyrrole battery in both aqueous and bio-ionic liquid-water mixture electrolytes. From in situ Raman spectroscopy it was observed that in aqueous solution Zn intercalation/deintercalation takes place by a two-step mechanism whereas a single-step mechanism for Zn storage was involved in bio-ionic liquid-water mixture electrolytes. The charge-discharge measurements showed a higher Zn storage capacity in the mixture of bio-ionic liquid-water electrolyte compared to the aqueous electrolyte. However with cycling, a capacity loss was observed. Post analysis of the polymer after cycling showed that a phase transformation has taken place in the polymer with Zn ions trapped in the polymer matrix which decreased the Zn storage capacity. Furthermore, the Zn anode showed formation of Zn nanoflakes from aqueous electrolytes which might lead to dendritic growth, whereas dendrite-free Zn nanoparticles were observed on using the bio-ionic liquid-water electrolyte.