Physics

Electrode

Diffusion

Anode

Engineering

X-ray photoelectron spectroscopy

Physical chemistry

Power (physics)

Aqueous solution

Chemistry

Metallurgy

Materials science

Phosphoric acid

Prussian blue

Cathode

Proton

Battery (electricity)

Quantum mechanics

Electrolyte

Chemical engineering

Electrochemistry

Thermodynamics

Advanced Energy Materials

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 °C via a 62 wt% (9.5 m) H 3 PO 4 electrolyte is reported. The APB is a rocking‐chair battery that operates with protons commuting between a Prussian blue cathode and an MoO 3 anode. At −78 °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 °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 °C, and thus offers a safe and reliable candidate for high‐latitude applications.

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