A novel rechargeable zinc–copper battery without a separator

Rechargeable zinc–copper batteries attract considerable interest due to their relatively-high theoretical energy density, low cost, and inherent safety. However, their practical applications are restricted by different factors, such as the need of a separator preventing copper ion crossover or zinc dendrite growth. In this work, a novel rechargeable zinc–copper battery concept is proposed where the electrolytes are made from hydrogels. One hydrogel is formulated such that it coordinates the copper ions but allows for unhindered transfer of sodium ions which are exchanged between the electrodes to maintain electro-neutrality. Hence, the battery does not need a separator but still can be repeatedly charged and discharged. Testing of the separator-less battery shows a maximum specific capacity of 280 mAh g−1 at a current density of 1 mA cm−2. Characterization of the battery components after 100 charge–discharge cycles reveals that there is no dendrite growth and the hydrogels inhibit copper ion crossover due to the coordination in the gel matrix. The battery can be easily bend indicating the potential as a flexible energy storage system.