Boosted H+ Intercalation Enables Ultrahigh Rate Performance of the δ-MnO2 Cathode for Aqueous Zinc Batteries

H+ intercalation, as a critical battery chemistry, enables electrodes' high rate performance due to the fast diffusion kinetics of H+. In this work, more water molecules are introduced into δ-MnO2 by the protonation of δ-MnO2 with abundant oxygen vacancies. Benefiting from the structure with a close arrangement of water molecules in interlayers, the Grotthuss transport of proton is achieved in the energy storage of the δ-MnO2 cathode. As a result, the δ-MnO2 cathode exhibits an ultrahigh rate performance with a capacity of 368.1 mAh g–1 at 0.5 A g–1 and 83.4 mAh g–1 at 50 A g–1, which has a capacity retention of 73% after 1100 cycles at 10 A g–1. The study of the storage mechanism reveals that the Grotthuss intercalation of proton predominates the storage process, which empowers the cathode with high rate performance.