Nonflammable Organics/H₂O Hybrid Electrolyte with a High Organics Ratio toward Safe and Sustainable Aqueous Na/Zn Hybrid Batteries

Aqueous Zn-ion batteries (ZIBs) have acquired more and more attention owing to their intrinsically high safety, environmental friendliness, low cost, and high power density. However, Zn dendrite growth, side reactions, and cathode dissolution caused by the high activity of free water hamper the practical applications of ZIBs. In this work, we report an organics/H₂O hybrid aqueous electrolyte that is composed of 50 wt % polyethylene glycol (PEG), 10 wt % ethanol (EtOH), and 40 wt % H₂O to address these issues. This electrolyte has a combined merit of low cost, environmental friendliness, and safety, and it also ensures dendrite-free Zn stripping/plating and chemical/electrochemical stability of the manganese-based Prussian blue (Mn-PB) cathode. Daniell-type Na/Zn-ion cells assembled with Zn anode, Mn-PB cathode, and the above electrolyte exhibit long cycle life (61.1% after 9000 cycles at 5 C) and superior rate performance (56.6% retention at 50 C relative 0.5 C). Stable cycling is also realized for the pouch-type cell and cell group. Flammability tests indicate that both the electrolyte and the pouch cell with the electrolyte exhibit nonflammability. This work sheds light on the design of low-cost, safe, and sustainable electrolytes for aqueous Na/Zn hybrid batteries for sustainable energy storage.