A High-Rate Aqueous Proton Battery Delivering Power Below-78 °C via an Unfrozen Phosphoric Acid

The sluggish ion diffusion and electrolyte freezing with volumetric changes limit the low-temperature performance of rechargeable batteries. Herein, a high-rate aqueous proton battery (APB) operated at and below -78 degrees C via a 62 wt% (9.5 m) H3PO4 electrolyte is reported. The APB is a rocking-chair battery that operates with protons commuting between a Prussian blue cathode and an MoO3 anode. At -78 degrees C, the APB full cells exhibit stable cycle life for 450 cycles, high round-trip efficiency of 85%, and appreciable power performance. The APB delivers 30% of its room-temperature capacity even at -88 degrees C. The proton storage mechanism is investigated by ex situ synchrotron XRD, XAS, and XPS. The APB pouch cells demonstrate no capacity fading at -78 degrees C, and thus offers a safe and reliable candidate for high-latitude applications.