Enabling Low-Temperature Zinc–Bromine Microbatteries with an Additive-Free Electrolyte Design

Aqueous zinc–bromine microbatteries (Zn–Br₂ MBs) are promising energy storage devices for miniaturized electronic applications. However, their performance in low-temperature environments remains a challenge due to poor compatibility between antifreeze agents and complexing agents. In this work, we propose an additive-free electrolyte design to address this incompatibility from the source. An electrochemically active 7.5 m zinc bromide solution was found to have a low freezing point of −105 °C, while also inhibiting polybromide dissolution. Zn–Br₂ microbatteries using this electrochemically active electrolyte demonstrated excellent cycling stability, with over 10,000 cycles (99% capacity retention) at 25 °C and more than 2000 cycles (98% capacity retention) at −60 °C. Both experimental data and theoretical calculations demonstrate that low-temperature environments inhibit polybromide dissolution. This work addresses the issue of incompatibility between antifreeze and complexing agents, challenging the traditional reliance on organic complexing agents to prevent polybromide dissolution in Zn–Br₂ systems.