Duration: 24 months
Proton batteries are a new concept that could find Space as its most promising field of application. Differently from state-of-the-art rechargeable batteries, where the charge carrier is an alkali metal ion (e.g., Li+), the ionic charge carrier in proton batteries is the proton (H+). This feature enables them to meet most of the requirements for electrochemical energy storage devices listed under section 6.4 of ESA Technology Strategy. Namely, proton batteries can sustain nearly a million charge/discharge cycles, currents well above 50C, and they can work at temperatures below -70 °C. Moreover, the active materials employed for this kind of battery are stable and nonflammable. However, proton batteries have a limited energy density because the Prussian blue analogs currently used to prepare the positive electrodes rely on the reversible redox of iron and copper ions. This reaction occurs at relatively low potentials, limiting the cell potential to ~1 V. Even if this limitation was surpassed, the electrolyte employed for sustaining the redox reaction would not be able to sustain higher cell potentials. Indeed, to achieve a potential in the range of 3.2-3.7 V, typical values for modern Li-ion batteries, a new generation of both materials and electrolytes is needed.
We claim that the working potential of Prussian blue analogs can be improved with an approach still not found in the literature: substituting iron and copper with metal ions having redox transitions at higher potentials, such as nickel ions. Therefore, HI-PRO will develop proton batteries equipped with novel Prussian blue analogs based on nickel and other high-working-potential metal ions. Regarding the instability of standard electrolytes, our preliminary tests have shown that it can be circumvented by a novel approach: substituting aqueous acidic solutions with concentrated phosphoric acid solutions in oxidation-resistant organic solvents.
