Integrated Uniformly Microporous C₄N/Multi-Walled Carbon Nanotubes Composite Toward Ultra-Stable and Ultralow-Temperature Proton Batteries

Benefiting from the proton's small size and ultrahigh mobility in water, aqueous proton batteries are regarded as an attractive candidate for high-power and ultralow-temperature energy storage devices. Herein, a new-type C₄N polymer with uniform micropores and a large specific surface area is prepared by sulfuric acid-catalyzed ketone amine condensation reaction and employed as the electrode of proton batteries. Multi-walled carbon nanotubes (MWCNT) are introduced to induce the in situ growth of C₄N, and reaped significantly enhanced porosity and conductivity, and thus better both room- and low-temperature performance. When coupled with MnO₂@Carbon fiber (MnO₂@CF) cathode, MnO₂@CF//C₄N-50% MWCNT full battery shows unprecedented cycle stability with a capacity retention of 98% after 11 000 cycles at 10 A g⁻¹ and even 100% after 70 000 cycles at 20 A g⁻¹. Additionally, a novel anti-freezing electrolyte (5 m H₂SO₄ + 0.5 m MnSO₄) is developed and showed a high ionic conductivity of 123.2 mS cm⁻¹ at -70 °C. The resultant MnO₂@CF//C₄N-50% MWCNT battery delivers a specific capacity of 110.5 mAh g⁻¹ even at -70 °C at 1 A g⁻¹, the highest in all reported proton batteries under the same conditions. This work is expected to offer a package solution for constructing high-performance ultralow-temperature aqueous proton batteries.