A novel methyl urea-based deep eutectic solvent for high-performance zin-ion batteries with polyaniline/graphene nanofiber composite cathode

In this study, we propose a new deep eutectic solvent (DES) based on methyl urea, together with Zn2+/Na+ dual cations, whose physicochemical properties have been successfully adjusted through the addition of co-solvents such as acetonitrile and water. The interaction between the constituents of electrolytes is thoroughly examined by using spectroscopic techniques. A cost-effective chemical approach is utilized to synthesize the polyaniline decorated graphene nanofiber (GPANi) as the cathode material. The performances of zinc anode and GPANi cathode and their compatibility in DES electrolyte are systematically investigated. The kinetics study of GPANi in DES electrolytes suggests its charge storage mechanism involves both battery-like and pseudocapacitive behavior. The Zn//GPANi device with DES electrolyte delivers the maximum energy density of 101 Wh kg−1 at a power density of 274 W kg−1 and an outstanding rate capability. In addition, the cell retains 78 % of its initial capacity after 1600 cycles at a high current density of 2 Ag−1. More significantly, our device with an operating voltage of 2.2 V can work consistently at −10 °C, which is usually not achievable for traditional aqueous electrolytes.