Unraveling the Charge Storage Mechanism of β-MnO2 in Aqueous Zinc Electrolytes

Lang Yuan Wu, Zhi Wei Li, Yu Xuan Xiang, Wen Di Dong, Hai Yang Wu, Ying Hong Xu, Zhen Xiao Ling, Munseok S. Chae, Daniel Sharon, Netanel Shpigel*, Xiao Gang Zhang*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

MnO2-based zinc-ion batteries have emerged as a promising candidate for next-generation energy storage systems. Despite extensive research on MnO2 electrodes, the charging mechanism in mildly acidic electrolytes remains debated. Most studies have focused on α-MnO2, and this study aims to shed light on the identity of the charge carrier in β-MnO2 and the role of the Mn2+ cations. By employing in situ EQCM-D measurements, along with ssNMR, XRD, TEM, and in situ pH monitoring, we demonstrated that the charging mechanism is primarily governed by proton de/intercalation. Compared to α-MnO2, with its larger 2 × 2 tunnels that accommodate hydronium ions, the β-phase has smaller 1 × 1 tunnels, permitting only the insertion of bare protons. During cycling, we observed the formation of new phases on β-MnO2 originating from the repetitive electrodeposition/dissolution of Mn2+. In addition, these phases can reversibly host hydronium ions, resulting in a mixed charging mechanism that involves the insertion of both H3O+ and H+.

Original languageEnglish
Pages (from-to)5801-5809
Number of pages9
JournalACS Energy Letters
DOIs
StateAccepted/In press - 2024

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© 2024 American Chemical Society.

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