Rechargeable aqueous zinc-ion batteries (ZIBs) have attracted much attention recently due to the high abundance, low cost, high theoretical capacity up to 820 mAh g^-1 with multi-valent charge carrier, and compatibility with aqueous electrolyte of the zinc anode.[1] Especially, the introduction of neutral or mild acidic electrolyte greatly improves the reversibility of zinc anode compared to conventional alkaline ZIBs.[2] Among all the cathode candidates, MnO₂ is most attractive due to its relatively high energy density, low toxicity and low cost.[3] However, MnO₂ electrode suffers from capacity fading during cycling mainly due to Mn dissolution and structural change. The addition of Mn²⁺ into the mild acidic electrolyte is a common method to suppress Mn dissolution.[4] Other strategies like structural design and surface coatings are also developed to suppress Mn dissolution.[5, 6] Though the cycle performance still cannot meet the demand of application, as the irreversible formation of inactive ZnMn₂O₄ during cycles still requires to be tackled.

Here, we proposed Bi₂O₃ as a facile electrode additive in the electrode to suppress ZnMn₂O₄ formation and improve the cyclability of commercial electrolytic manganese dioxide (EMD). XRD, in-situ pH measurements and ICP tests suggest that inactive ZnMn₂O₄ is formed upon cycling due to the interaction between MnO₂ and zincate ions in the electrolyte from localized increase in pH, and Bi₂O₃ dissolves into the electrolyte in the presence of zincate ions and forms a complex with the zincate ions to suppress the reaction pathway. A high capacity of 269 mAh g^-1 is maintained at 100 mA g^-1 after 50 cycles with a capacity retention of 91.5% when EMD with 10 wt% of Bi₂O₃ is tested in ZnSO₄ electrolyte without Mn²⁺ additive. Combining both Bi₂O₃ electrode additive and Mn²⁺ electrolyte additive, EMD can maintain a stable capacity of 190 mAh g^-1 for 1000 cycles at 1000 mA g^-1 (about 3.3C). More characterizations are underway to further understand the role of Bi₂O₃ and the results will be shown during the meeting.

Reference:

[1] B. Tang, L. Shan, S. Liang, J. Zhou, Issues and opportunities facing aqueous zinc-ion batteries, Energy & Environmental Science, 12 (2019) 3288-3304.

[2] J. Hao, X. Li, X. Zeng, D. Li, J. Mao, Z. Guo, Deeply understanding the Zn anode behaviour and corresponding improvement strategies in different aqueous Zn-based batteries, Energy & Environmental Science, 13 (2020) 3917-3949.

[3] N. Zhang, X. Chen, M. Yu, Z. Niu, F. Cheng, J. Chen, Materials chemistry for rechargeable zinc-ion batteries, Chemical Society Reviews, 49 (2020) 4203-4219.

[4] H. Pan, Y. Shao, P. Yan, Y. Cheng, K.S. Han, Z. Nie, C. Wang, J. Yang, X. Li, P. Bhattacharya, Reversible aqueous zinc/manganese oxide energy storage from conversion reactions, Nature Energy, 1 (2016) 1-7.

[5] J. Huang, Z. Wang, M. Hou, X. Dong, Y. Liu, Y. Wang, Y. Xia, Polyaniline-intercalated manganese dioxide nanolayers as a high-performance cathode material for an aqueous zinc-ion battery, Nature communications, 9 (2018) 1-8.

[6] B. Wu, G. Zhang, M. Yan, T. Xiong, P. He, L. He, X. Xu, L. Mai, Graphene scroll‐coated α‐MnO₂ nanowires as high‐performance cathode materials for aqueous Zn‐ion battery, Small, 14 (2018) 1703850.