Towards higher energy density redox-flow batteries: imidazolium ionic liquid for Zn electrochemistry in flow environment

We present the first demonstration of an ionic liquid electrolyte under a realistic flow environment for applications in redox-flow batteries based on the Zn²⁺/Zn⁰ redox couple. An electrolyte mixture containing Zn(dca)₂ and 3wt% H₂O in 1-ethyl-3-methylimidazolium dicyanamide, [Emim][dca], ionic liquid was used to study the effects of Zn²⁺ concentration and flow rate on the Zn²⁺/Zn⁰ electrochemical performance as well as its impact on the morphology of the Zn deposit. An optimized Zn²⁺ concentration and flow rate were determined by using an in-house-designed 3D-printed flow-cell prototype. Surface characterization through SEM revealed that both the concentration and flow rate directly impact Zn morphology under flow conditions. The electrolyte mixture with a higher Zn(dca)₂ concentration (18mol%) showed favourable results; voltammetry showed higher peak current densities (100mA/cm² discharge current density) and more positive Zn electrodeposition potentials (-1.33V vs Ag/AgOTf) coupled with higher cycling efficiency (45±3%) compared to those obtained with the lower Zn concentration system (9mol%, -1.44V vs Ag/AgOTf, 48mA/cm² discharge current density and 33±3% cycling efficiency).