Electrochemical Studies of Metal Phthalocyanines as Alternative Cathodes for Aqueous Zinc Batteries in “Water-in-Salt” Electrolytes

Aqueous zinc batteries are emerging technologies for energy storage, owing to their high safety, high energy, and low cost. Among them, the development of low-cost and long-cycling cathode materials is of crucial importance. Currently, Zn-ion cathodes are heavily centered on metal-based inorganic materials and carbon-based organic materials; however, the metal–organic compounds remain largely overlooked. Herein, we report the electrochemical performance of metal phthalocyanines, a large group of underexplored compounds, as alternative cathode materials for aqueous zinc batteries. We discover that the selection of transition metal plays a vital role in affecting the electrochemical properties. Among them, iron phthalocyanine exhibits the most promising performance, with a reasonable capacity (~60 mAh g−1), a feasible voltage (~1.1 V), and the longest cycling (550 cycles). The optimal performance partly results from the utilization of zinc chloride “water-in-salt” electrolyte, which effectively mitigates material dissolution and enhances battery performance. Consequently, iron phthalocyanine holds promise as an inexpensive and cycle-stable cathode for aqueous zinc batteries.