Unlocking bipolar electrode-electrolyte solid-solid conversion in aqueous zinc-halogen batteries for high Zn utilization across various cell formats.

The increasing demand for high-energy-density batteries pushes practical aqueous Zn-based batteries. However, high Zn utilization achieved in coin symmetric cells is unable to translate to full cells, especially large pouch cells, due to the poor reversibility of Zn and capacity output of high-loading positive electrodes. Here, solid-solid interfacial conversion mechanisms via chelation at electrodes-electrolyte interfaces effectively suppress parasitic reactions being widely prevalent under traditional solid-liquid conversion mechanisms. Consequently, high Zn utilization ( ≥ 78.3%) is unified across coin symmetric, coin full and pouch full cells. The Zn | |I2 pouch cell (10 cm×10 cm) demonstrates a specific energy of 116.8 Wh kg-1 (based on total mass) and over 850 cycles (85.1% capacity retention) at 10 mA cm-2. Furthermore, solid-solid interfacial conversion mechanisms exhibit universality across halogen positive electrodes, advancing practical aqueous Zn | |halogen batteries.