Anode-free Zn-I batteries without fear of Zn loss: Hybrid energy-storage mechanism and dynamic capacity compensation.

Anode-free zinc (Zn) batteries (AFZBs) are promising in delivering high energy density at high Zn utilization. However, the limited availability and inevitable loss of Zn pose challenges such as reduced lifespan and inadequate stability to AFZBs. Herein, copper iodide (CuI) is introduced as a conversion-electrode material on the Cu current collector of an AFZB, composing a hybrid energy storage mechanism and forming an anode-free Zn-I battery (AFZIB). The Cu collector serves as a dual substrate for Zn deposition/stripping (Zn + 2e ↔ Zn) and a CuI conversion reaction (ZnI + 2Cu ↔ 2CuI + Zn + 2e), realizing a hybrid energy-storage mechanism. Notably, the conversion reaction of CuI in situ-generated stores Zn, dynamically compensating the Zn loss and consequent capacity loss. This hybrid mechanism endows the AFZIB with excellent cycling stability, with no capacity decay even after 3000 cycles. Even when constructed with a high-mass-loading cathode (15 mg cm), the AFZIB exhibits a capacity retention rate of 78.5 % after 300 cycles. This study effectively addresses the inevitable Zn loss and subsequent capacity degradation in conventional AFZBs and provides new insights for their further development.