Towards high-performance zinc anode for zinc ion hybrid capacitor: Concurrently tailoring hydrodynamic stability, zinc deposition and solvation structure via electrolyte additive

Aqueous zinc ion hybrid capacitors (AZICs) represent an emerging class of cost-effective energy storage devices with both high energy and power densities. However, the exploration of advanced AZICs commonly encounters the performance deterioration issue induced by dendritic zinc deposition and parasitic reactions. Moreover, the frequent operations of AZICs at high rates can particularly trigger hydrodynamic instability at the vicinity of the zinc anode, which would further aggravate the growth of zinc dendrites. Here, a typical aqueous binder of sodium carboxymethyl cellulose (CMC) is introduced as an electrolyte additive in AZICs. The CMC additive is inclined to adsorb onto the (101) facet of zinc, which intriguingly leads to dendrite-free (101) plane-dominated zinc deposition. Besides, the interaction of CMC with Zn2+ alters the solvation structure, which gives rise to suppressed water-induced side reactions. More intriguingly, the CMC additive with a moderate concentration can constrain the hydrodynamic instability at a large reaction flux without compromising the ionic conductivity. Benefitting from the above favorable features, the strategy of adding CMC electrolyte additive, which significantly promotes the cyclic stability of the zinc anode at not only low but also high rates, has implications for further promoting the comprehensive performance of AZICs.