High Areal-Capacity Aqueous Manganese-Based Batteries Enabled by Redox Mediators

Abstract

Aqueous manganese batteries based on deposition-dissolution of Mn 2+ /MnO 2 reactions have aroused great attention due to their intrinsic low cost, high potential, and high energy. 1, 2 However, the incomplete dissolution and exfoliated dead MnO 2 would inevitably lead to capacity loss and poor cyclability at high areal capacity application. 3, 4 Herein, we apply a redox mediator strategy to dissolve the accumulated MnO 2 via a spontaneous chemical reaction between redox mediators iodide and MnO 2 . 5,6 During the discharge process, the iodide (I – ) could react with the residual MnO 2 and be oxidized to I 3 – that could be further reduced back to I – on the electrode, continuing this process until fully dissolved the accumulated MnO 2 . We will discuss detailed reaction mechanisms verified by ex-situ UV-vis spectroscopy, scanning electron microscopy, and X-ray diffraction. The zinc-manganese (Zn-Mn) battery with iodide mediator showed improved cycling stability at 2.5 mAh cm –2 (400 vs. 100 cycles, static mode) and 15 mAh cm –2 (225 vs. 60 cycles, flow mode). Areal capacity is one of the most important parameters determining system energy for deposition-based batteries. 7 The Zn-Mn flow cell could demonstrate a high areal capacity application at 50 mAh cm –2 for 50 cycles. We will discuss how to expand this strategy to other manganese-based batteries and broaden the horizon of aqueous batteries. Acknowledgment This work is supported by a grant from the Research Grant Council of the Hong Kong Special Administrative Region, China (project no. C1002-21G). Reference W. Chen, G. Li, A. Pei, Y. Li, L. Liao, H. Wang, J. Wan, Z. Liang, G. Chen, H. Zhang, J. Wang and Y. Cui, Nat. Energy , 2018, 3 , 428-435. D. Chao, W. Zhou, C. Ye, Q. Zhang, Y. Chen, L. Gu, K. Davey and S.-Z. Qiao, Angew. Chem. Int. Ed. Engl. , 2019, 58 , 7823-7828. C. Liu, X. Chi, Q. Han and Y. Liu, Adv. Energy Mater. , 2020, 10 , 1903589. G. Liang, F. Mo, H. Li, Z. Tang, Z. Liu, D. Wang, Q. Yang, L. Ma and C. Zhi, Adv. Energy Mater. , 2019, 9 , 1901838. J. Lei, Y. Yao, Z. Wang and Y.-C. Lu, Energy Environ. Sci. , 2021, 14 , 4418-4426. J. Lei, Y. Yao, Y. Huang and Y.-C. Lu, ACS Energy Letters , 2022, DOI: 10.1021/acsenergylett.2c02524, 429-435. Y. Yao, J. Lei, Y. Shi, F. Ai and Y.-C. Lu, Nat. Energy , 2021, 6 (6) , 582–588.