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 ZnCl2-based DES that achieves an effective regulation of the solvation structure of [ZnClx]2-x by simply controlling the concentration of ZnCl2. The coexisting solvation structure of [ZnCl4]2-/[ZnCl3]- 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 [ZnClx]2-x and the electrochemical reaction rate of [ZnClx]2-x, as well as promotes Zn (002) homo-epitaxial deposition, enabling a highly reversible Zn plating/stripping with long-term stability of similar to 1000 h at an ultralow over-potential of 33 mV. Furthermore, the RZABs with 1.0 M ZnCl2 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 ZnCl2-based DES that achieves an effective regulation of the solvation structure of [ZnClx]2-x by simply controlling the concentration of ZnCl2 was developed.