Chitosan modified filter paper separators with specific ion adsorption to inhibit side reactions and induce uniform Zn deposition for aqueous Zn batteries

The electrochemical performance of Zn metal anode in aqueous batteries is serious challenged by side reactions and dendrite growth. Separators are important cell components, which directly interact with electrolyte species and present potential solutions to regulate Zn anode performance. Herein, we modify the conventional filter paper separators by coating chitosan on the fibers. The hydroxyl, amino and ether groups on chitosan allow preferential adsorptions of proton, zinc ion and sulfate in ZnSO4 aqueous electrolytes. Proton adsorption suppresses the proton activity, which inhibits corrosions and hydrogen evolution reactions at Zn electrode. The interactions of zinc ion and sulfate with chitosan regulate the ion transport manner and enlarge Zn2+ transference number, which ensures homogeneous Zn nucleation and growth. With the application of chitosan modified filter paper separators, the Zn electrode presents a long cycle life of 2900 h. A high coulombic efficiency of 99.6% is achieved. The chitosan modified separators also enhance the capacity retention of Zn||MnO2 batteries from 52.8% to 98.4% over 1000 cycles. Our work presents an effective separator regulation approach for high-performance aqueous Zn batteries.