Electrolyte formulation to enable ultra-stable aqueous Zn-organic batteries

Aqueous zinc batteries (ZBs) possess great potential in energy storage due to their advantages in safety, low-cost and resource abundance. However, the commercialization of ZBs is plagued by the lacking of suitable cathode structures (or nano-textures) and their poor cycle life. The popular cathode materials of Mn or V based oxides suffer from the high solubility and toxicity of transition metals (TMs). It is highly required to develop robust TM-free organic cathodes with design flexibility and environmental benignity. Herein, 1,4,5,8-naphthalene diimide (NDI) layered molecules are proposed as cathode candidate for ZBs, and they are characterized by sufficient interconnection of nano-particles (for continuous electron transport) into porous network (for facilitated ion filtration). It enables the achievement of reversible redox of carbonyl function groups and a stable gravimetric capacity around 200 mAh g−1. The superior cycling and rate performance (at least 5000 cycles under 3 A g−1) benefits from the electrolyte formulation. The blending of Na2SO4 additive takes effect in terms of the cathode grain attenuation into ultrathin 2D nanosheets, pseudo-capacitance contribution enhancement and Zn anode smoothening.