Facile Electrode Additive Stabilizes Structure of Electrolytic MnO2 for Mild Aqueous Rechargeable Zinc-Ion Battery
Authors: Duan Qiaohui , Duan Qiaohui 
Published: July 2022

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:
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