Improving reversibility and reducing overpotential of Cu–Zn battery with electrolyte engineering and cation-selective membrane

As an alternative battery system, Cu–Zn battery is attractive because the raw materials are inexpensive and non-toxic. However, traditional Cu–Zn battery is not rechargeable due to the limited reversibility and low stability caused by the shuttling of Cu²⁺ ions to the Zn anode. In this study, we have constructed reversible Cu–Zn batteries with a cation-selective membrane in a common ZnSO₄/Li₂SO₄ mixed electrolyte for both the catholyte and anolyte. The membrane allows the transfer of Li⁺ for the charge balance while suppressing the cross-over of Cu²⁺ ions, increasing the Coulombic efficiency of the battery. The effectiveness of the membrane and the stability of the battery are also found to be affected by the electrolyte concentration. Using 2 M ZnSO₄/2 M Li₂SO₄ electrolyte, the Cu–Zn battery can be cycled for more than 4000 cycles with a capacity limitation of 0.1 mAh cm^-2 at a current of 1 mA cm^-2 with stable voltages and Coulombic efficiency of about 99.5%.