Achieving Enhanced Cycle Stability in Zn–I2 Batteries with a Polyvinylpyrrolidone Binder

Abstract

Iodine (I2) is an attractive cathode for aqueous Zn batteries (AZBs) because of its high capacity, low cost, and environmental benignity. Nevertheless, the I2 dissolution and the shuttling effect of polyiodide during charge–discharge processes seriously hinder the cycle stability and practical application of Zn-I2 batteries. Herein, a water-soluble polyvinylpyrrolidone (PVP) polymer is proposed as a functional binder to address the above issues. The abundant polar groups in the PVP molecular chain serve as active sites, which can form a strong affinity with polyiodide ions, thereby effectively confining polyiodide species within the cathode. As a result, the PVP-based cathode achieves a capacity of 201 mAh g–1 at 0.1 A g–1 and retains 122 mAh g–1 at 5 A g–1, which significantly outperforms the conventional polytetrafluoroethylene (PTFE) binder-based cathode that only delivers 176 and 100 mAh g–1 under the same current densities, respectively. Moreover, a long cycling stability of 20,000 cycles at 5 A g–1 with 97 mAh g–1 capacity was achieved. This work not only provides an efficient and low-cost strategy to mitigate the iodine shuttle problem but also sheds insights into the design of multifunctional polymer binders for high-performance Zn-I2 batteries.