Realizing a Rechargeable High‐Performance Cu–Zn Battery by Adjusting the Solubility of Cu2+

Rechargeable aqueous Zn‐based batteries show great potential for energy storage systems due to their good reliability, low cost, environmental friendliness, etc. However, the capacity of the most studied Mn‐, V‐, and Prussian blue analog‐based Zn‐ion batteries (the type with Zn2+ insertion) and the other type Zn‐based batteries without Zn2+ insertion (such as metal Ag and Ni or Co oxides/hydroxides) does not exceed 400 mAh g−1. Cu is a promising cathode with a high theoretical capacity of 844 mAh g−1 based on its unique two‐electron transfer process (Cu0 ↔ Cu2+), but Cu–Zn batteries have been impractical to recharge since they was invented by Daniell in 1836. By adjusting the solubility of Cu2+ in an alkaline solution, a rechargeable high‐performance Cu–Zn battery is achieved. A high specific capacity of 718 mAh g−1 is obtained for the prepared Cu clusters. Moreover, commercial Cu foil is explored for direct use as the cathode material and shows high capacity and stability through a simple self‐activation process. This rechargeable Cu–Zn battery is attractive for application due to its high capacity, simple synthesis method, environmental friendliness, and low cost.