Nanoengineered aqueous-hydrotrope hybrid liquid electrolyte solutions for efficient zinc batteries across a wide...

Aqueous zinc metal batteries are ideal candidates for grid storage applications. However, their practical application is hindered by a narrow operating temperature range and a limited electrolyte electrochemical stability window, both of which can be attributed to the water activity. Here, to minimize water activity in the electrolyte solution, we introduce a nanoengineered approach in which the water molecules are confined within a hydrophilic-hydrophobic water solvation sheath. The hydrogen-bond interaction with the hydrophilic groups in the inner solvation layer effectively suppresses water decomposition, and the hydrophobic solvents in the outer solvation layer establish a repulsive effect against water molecules. As a proof of concept, a hydrophobic and non-polar hydrofluoroether cosolvent is introduced into a Zn-ion aqueous electrolyte solution and tested together with various fluorinated hydrotrope molecules to favour the compatibility of the cosolvent with water. By such a water confinement strategy, an average Zn plating/stripping reversibility of 99.92% is achieved for over 4,000 cycles at 2.0 mA cm^-2 and 2.0 mAh cm^-2 in a Zn||Cu coin cell configuration. When tested in a Zn||VOPO₄·2H₂O lab-scale cell configuration, the selected aqueous-hydrotrope hybrid electrolyte solution enables long-lasting and highly reversible battery performance across temperatures from -80 °C to +60 °C.