A voltage-decoupled Zn-Br₂ flow battery for large-scale energy storage

The flow battery represents a highly promising energy storage technology for the large-scale utilization of environmentally friendly renewable energy sources. However, the increasing discharge power of rechargeable battery results in a higher charge voltage due to its coupling relationship in charge-discharge processes, intensifying the burden of renewable energy power systems. Herein, we proposed a voltage-decoupled Na⁺-conducting Zn-Br₂ flow battery (U_d-Na-ZBFB). Within a pH-regulation strategy, both neutral Zn/Zn²⁺ and alkaline Zn/Zn(OH)₄²⁻ negative redox couples are integrated into one device, so as to increase discharge voltage a 0.5 V theoretical increase while remains a low charge voltage. The proof-of-concept U_d-Na-ZBFB demonstrates an unprecedented voltage characteristic, achieving a discharge voltage of up to 2.18 V while maintaining a remarkably low charge voltage of 1.78 V at a current density of 20 mA cm⁻². Benefiting from the high discharge voltage, the peak power density of U_d-Na-ZBFB reaches 580 mW cm⁻², nearly twice higher than the traditional ZBFB. Besides, the U_d-Na-ZBFB cycling operates for 45 h with excellent stability and resilience. With the “cycle-to-stage” operational mode, battery state of U_d-Na-ZBFB can be completely recovered after a long-term operation stage with several cycles, which electrolyte utilization efficiency of one stage is up to 41 %. This work offers a brand-new utilization pattern for high-power rechargeable battery that possesses a great potential in energy storage application scenes.