Solvation structure regulation of deep eutectic solvents: stabilization of the zinc anode in rechargeable zinc-air batteries

Deep eutectic solvents (DESs) are promising electrolytes for the rechargeable zinc-air batteries (RZABs) but suffer from the low transport rate of Zn ligand ion, high over-potential of Zn redox, and dendrite growth of Zn metal. Here, we report a novel water-free ZnCl 2 -based DES that achieves an effective regulation of the solvation structure of [ZnCl x ] 2− x by simply controlling the concentration of ZnCl 2 . The coexisting solvation structure of [ZnCl 4 ] 2− /[ZnCl 3 ] − exhibits proper de-solvation energy and a relatively high transport rate of the zinc ligand ions. This unique solvation structure strikes a balance between the transport flux of [ZnCl x ] 2− x and the electrochemical reaction rate of [ZnCl x ] 2− x , as well as promotes Zn (002) homo-epitaxial deposition, enabling a highly reversible Zn plating/stripping with long-term stability of ∼1000 h at an ultralow over-potential of 33 mV. Furthermore, the RZABs with 1.0 M ZnCl 2 in DES demonstrated an impressive 8.7-fold enhancement in discharge performance (9.6 mA h cm −2 ) compared to the conventional alkaline electrolytes (1.1 mA h cm −2 ). This work demonstrates a new direction to produce a wide range of DES electrolytes with high ion conductivity and stable cycling performance. A novel water-free ZnCl 2 -based DES that achieves an effective regulation of the solvation structure of [ZnCl x ] 2− x by simply controlling the concentration of ZnCl 2 was developed.