Two-electron conversion nitroxide radicals-based electrode synergistically enhancing charge storage in water-in-salt electrolyte

Abstract

Water-in-salt electrolytes (WISEs) are attractive in aqueous batteries due to their non-flammability, environmental friendliness, and wide electrochemical stability window. Stable nitroxide radicals with fast electron transfer rate and good cycling stability are promising electrode materials applied for WISEs, while their limited conductivity and high solubility in electrolytes are still challenges. Here, porous carbon with high specific area is used as conductive substrate for the deposition of 4-amino-TEMPO (TEMPO = 2,2,6,6-tetramethylpiperidine-1-oxyl), and MXene nanosheets are employed as their conductive binder to construct freestanding electrode with “hyacinth bean-like” structure. Nitroxide radicals undergo a two-step two-electron reversible redox reaction and MXene exhibits pseudocapacitive ion intercalation, leading to synergistically enhanced discharge capacity in WISE (19.8 m LiCl). The incorporated redox active nitroxide radicals in MXene/porous carbon-TEMPO electrode boost the surface pseudocapacity and the rationally designed three-dimensional structure further facilitates the ions diffusion and electrons transfer, endowing the composite electrode with fast charge storage kinetic. This work provides a promising potential for the design and fabrication of high-performance aqueous batteries.