Aqueous zinc batteries (AZBs) are considered
promising candidates for large-scale energy storage systems because
of their low cost and high safety. However, currently developed AZB
cathodes always suffer from the intense charge repulsion of
multivalent-ion and complex multiphase electrochemistry, resulting
in an insufficient cycling life and impracticable high-sloping
discharge profile. Herein, we found that the synthesized ultrathin
Bi2O2Se nanosheets can effectively activate stable protons storage in
AZBs rather than large zinc ions. This proton-dominated cathode
provides an ultraflat discharge plateau (72% capacity proportion)
and exhibits long-term cyclability as 90.64% capacity retention after
2300 cycles at 1 A g−1. Further in situ synchrotron X-ray diffraction,
ex situ X-ray photoelectronic spectroscopy, and density functional
theory confirm the energy storage mechanism regarding the highly reversible proton insertion/extraction process. Benefiting
from the proton-dominated fast dynamics, reliable energy supply (>81.5% discharge plateau capacity proportion) is
demonstrated at a high rate of up to 10 A g−1 and in the frozen electrolyte below −15 °C. This work provides a potential
design of high-performance electrode materials for AZBs.