Manganese-Based Proton Reservoir Trigger Proton Diversion Effect for Ultrahigh-Capacity Aqueous Zinc-Ion Batteries.

Abstract

MnO₂, a prominent manganese-based cathode material, has been used extensively in aqueous zinc-ion batteries (ZIBs). However, Zn²⁺ intercalation in MnO₂ faces multiple obstacles, primarily due to the electrostatic interaction between Zn²⁺ and the skeleton, the coverage of by-product Zn₄SO₄ (OH)₆·xH₂O (ZSH) on the cathode, and the preferential occupation by H⁺ of the active sites. Here, we introduce MnOOH into K⁺-doped α-MnO₂ (KMO) to produce an ultrahigh-capacity KMO-MnOOH cathode. The MnOOH can transform into the active material β-MnO₂ via the in situ release of protons. The β-MnO₂ with the 1^*1 tunnel structure shows the strong adsorption for H⁺ and unique tunnels that allow for rapid migration of H⁺, resulting in the diversion of protons originally intercalated into KMO. This "proton diversion effect" leads to sufficient active sites in KMO that accelerate Zn²⁺ transport kinetics. The released protons from MnOOH can reduce the by-products ZSH, facilitating rapid Zn²⁺ migration and deep Zn²⁺ intercalation. Accordingly, the KMO-MnOOH cathode exhibits an ultrahigh specific capacity (645.6 mA h g^-1 at 0.3 A g^-1) and an excellent cycling stability (239.3 mA h g^-1 at 2 A g^-1 after 950 cycles). This work provides new insights into the regulation of H⁺/Zn²⁺ intercalation for high-performance Zn//MnO₂ batteries.