Integrated Uniformly Microporous C 4 N/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 C 4 N 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 C 4 N, and reaped significantly enhanced porosity and conductivity, and thus better both room- and low-temperature performance. When coupled with MnO 2 @Carbon fiber (MnO 2 @CF) cathode, MnO 2 @CF//C 4 N-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 H 2 SO 4  + 0.5 m MnSO 4 ) is developed and showed a high ionic conductivity of 123.2 mS cm -1 at -70 °C. The resultant MnO 2 @CF//C 4 N-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.