Abstract:

In this study, K⁺ incorporated into δ-MnO₂ (K-δ-MnO₂) are prepared by a facile redox method and applied as cathodes in aqueous zinc ion batteries (AZIBs). The pre-intercalated K⁺ acting as structure stabilizing "pillars" allows the tune of the lattice space of MnO₂ and promotes the diffusion kinetics of Zn²⁺ in the tunnel structure. Additionally, cations introduce shallow donor levels that enhance hosts' electronic conductivity and activate additional active sites. Besides, the co-intercalating water screens the intercalation between the intercalated Zn ions and the MnO₂ cathode, resulting in faster intercalation processes. The as-prepared K-δ-MnO₂ as cathode materials for AZIBs shows a relatively high capacity (401.3 mAh/g at 0.3 A/g) and an impressive cycling stability (83.2% retention after 1200 cycles at 3 A/g), while an inferior cyclability is observed for the pristine δ-MnO₂. The energy storage mechanism is clarified as H⁺/Zn²⁺ coinsertion/extraction via an ex-situ XRD characterization. With the combination of CNT, the composite electrode of K-?δ?-MnO₂/CNT displays better cycling stability (98.6% retention after 1200 cycles at 3 A/g). The K-δ-MnO₂ prepared by the facile redox method, which is simple and easy upscaling from the laboratory to industry, shows great potential as the cathode for AZIBs with good electrochemical performance.

Key words: pre-intercalation, δ-MnO₂, CNT, zinc ion batteries