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

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-I2 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.