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Novel Insights into Energy Storage Mechanism of Aqueous Rechargeable Zn/MnO₂ Batteries with Participation of Mn².

ABSTRACT: Aqueous rechargeable Zn/MnO₂ zinc-ion batteries (ZIBs) are reviving recently due to their low cost, non-toxicity, and natural abundance. However, their energy storage mechanism remains controversial due to their complicated electrochemical reactions. Meanwhile, to achieve satisfactory cyclic stability and rate performance of the Zn/MnO₂ ZIBs, Mn²⁺ is introduced in the electrolyte (e.g., ZnSO₄ solution), which leads to more complicated reactions inside the ZIBs systems. Herein, based on comprehensive analysis methods including electrochemical analysis and Pourbaix diagram, we provide novel insights into the energy storage mechanism of Zn/MnO₂ batteries in the presence of Mn²⁺. A complex series of electrochemical reactions with the co-participation of Zn²⁺, H⁺, Mn²⁺, SO₄^2-, and OH^- were revealed. During the first discharge process, co-insertion of Zn²⁺ and H⁺ promotes the transformation of MnO₂ into Zn_xMnO₄, MnOOH, and Mn₂O₃, accompanying with increased electrolyte pH and the formation of ZnSO₄·3Zn(OH)₂·5H₂O. During the subsequent charge process, Zn_xMnO₄, MnOOH, and Mn₂O₃ revert to α-MnO₂ with the extraction of Zn²⁺ and H⁺, while ZnSO₄·3Zn(OH)₂·5H₂O reacts with Mn²⁺ to form ZnMn₃O₇·3H₂O. In the following charge/discharge processes, besides aforementioned electrochemical reactions, Zn²⁺ reversibly insert into/extract from α-MnO₂, Zn_xMnO₄, and ZnMn₃O₇·3H₂O hosts; ZnSO₄·3Zn(OH)₂·5H₂O, Zn₂Mn₃O₈, and ZnMn₂O₄ convert mutually with the participation of Mn²⁺. This work is believed to provide theoretical guidance for further research on high-performance ZIBs.

SUBMITTER: Huang Y

PROVIDER: S-EPMC7770901 | biostudies-literature |

REPOSITORIES: biostudies-literature

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