Dextran: A Multifunctional and Universal Electrolyte Additive for Aqueous Zn Ion Batteries

Abstract The aqueous Zn ion battery (ZIB) is a potentially sustainable energy storage device. However, its performance is still far from satisfactory. Herein, it is demonstrated that a branched sugar, dextran, widely used in eyedrop products to relieve irritated eyes, is a multifunctional and universal electrolyte additive to enable high‐performance ZIBs. Experimental and theoretical results reveal that dextran has four functions: forming a surface protective layer to minimize side reactions, facilitating stepwise [Zn(H 2 O) 6 ] 2+ desolvation, preferably adsorbing on Zn(0002) planes to supply desolvated Zn 2+ and homogenizing electric field. These functions are universally observed in Zn(CF 3 SO 3 ) 2 , ZnSO 4 , Zn(ClO 4 ) 2 , and ZnCl 2 aqueous electrolytes. As demonstrations for practical applications, Zn anodes deliver Coulombic efficiency of 99.97% after 3400 cycles in an electrolyte with 50 mg mL ‒1 of dextran and cumulative plating capacity of 3400 mAh cm ‒2 at 5 mA cm ‒2 . Zn//V 2 O 5 full cells with a low negative/positive electrode capacity ratio of 2.18 can be stably cycled over 138 cycles at 1 A g ‒1 . Pouch full cells can work under mechanical bending conditions. Zn//polyaniline full cells can cycle steadily for 3000 cycles at 0.5 A g ‒1 at −10 °C. Dextran shows excellent potential as a low‐cost and non‐toxic electrolyte additive to enable safe and reliable ZIBs.