Design of Electrolyte Using Deep Eutectic Solvents for High‐Performance Rechargeable Nickel‐Iodine Batteries

Abstract Rechargeable nickel‐ion batteries (RNiBs) have attracted significant attention because of their high volumetric density, low cost, environmental friendliness, and easy recyclability. In this study, a rechargeable nickel‐iodine battery using a rational design of a deep eutectic solvent (DES) electrolyte based on a conversion reaction mechanism is first demonstrated. The rechargeable Ni‐I 2 battery with the DES electrolyte delivered a specific capacity of 201 mAh g −1 with a coulombic efficiency of 82.5% over 65 cycles at a current density of 0.3 A g −1 . The energy storage mechanism can be attributed to I + /I − redox chemistry, which has been validated by ex situ Raman, X‐ray photoelectron spectroscopy (XPS) and X‐ray absorption spectroscopy (XAS). The study provides an avenue for exploring rechargeable nickel‐ion batteries with DES electrolytes based on the conversion reaction mechanism.