Polymer Chain‐Guided Ion Transport in Aqueous Electrolytes of Zn‐Ion Batteries

Abstract As a promising candidate for next‐generation energy storage devices, Zn metal battery excels with their good safety, high specific capacity, and economic attractiveness. However, it still suffers from a narrow electrochemical window, notorious dendrite formation, and sluggish Zn ion transfer. Aqueous electrolyte engineering has been regarded as an effective way to improve these. It is shown that by adding sodium polystyrene sulfonate (PSS) polymers into a dilute 1 m Zn(OTf) 2 aqueous electrolyte, compact water shells with stronger hydrogen bonding and more ordered structures are formed around the polymer chains. As a result, a fast transport channel to the zinc ions is provided. The PSS chains also protect the zinc electrode from directly contacting the water molecules and thus suppress water decomposition. With these merits, a Zn//Cu cell demonstrates a high coulombic efficiency of ≈99% after 1500 h cycling. Meanwhile, a record‐high cumulative Zn plating capacity of 10 000 mA h cm −2 is obtained using a Zn||Zn cell. In addition, the Zn//C@V 2 O 5 full cell achieves almost 100% capacity retention after 1000 cycles. This work provides a new strategy for designing advanced electrolyte systems excelling in ion transport kinetics.