Understanding the Role of Manganese Sulfate As an Electrolyte Additive for Aqueous Zinc Ion Battery
Authors: Kim Chaewon , Cui Chenglin , Kim Ji Man 
Published: December 2024

As energy demand escalates, there is a concurrent rise in the utilization of fossil fuels, exacerbating environmental challenges. To solve this challenge and achieve sustainable development, extensive research into renewable energy options is being conducted. Unlike conventional energy sources, renewable energies like solar and wind power exhibit fluctuations. Thus, effective utilization of these sources necessitates the development of energy storage systems to ensure a reliable and consistent energy supply. Among them, rechargeable batteries have been regarded as the most favorable candidate for energy storage systems because of their long cycle life, low pollution, portability and high efficiency. Of these, lithium-ion batteries (LIBs) have long held sway in the commercial rechargeable battery market, thanks to their high energy density and extended cycle life. However, several limitations obstruct their further progress. The safety concerns arising from toxic, volatile, and flammable electrolytes pose a significant challenge. Additionally, rising lithium prices can be another obstacle. These challenges have spurred researchers to investigate alternative batteries characterized by low cost, high safety, and extended cycle life. One such promising option is the aqueous zinc-ion battery (AZIB), garnering significant interest owing to its notable benefits, including high capacity and the low redox potential of zinc metal. Moreover, the stability of zinc metal in water, in contrast to the highly reactive nature of lithium, enables the use of aqueous electrolytes, enhancing safety considerably. Among various cathode materials for ZIBs, manganese-based options stand out for their high capacity, suitable working voltage, and excellent theoretical capacity, positioning them as compelling choices. However, the MnO2 electrode often suffers from capacity degradation over cycling, primarily due to manganese dissolution. Previous studies suggest that the role of Mn2+ additive in electrolytes is that it inhibits the dissolution of manganese cathode based on Le Chatelier's principle. However, gaining a comprehensive understanding of the inhibition mechanism has been challenging due to the presence of manganese species not only in the electrolyte but also in the cathode material.
In this paper, we use a simplified cell design to address this limitation. Prior to qualitative analysis, we manipulate three distinct factors to optimize conditions for subsequent experiments. Under the set conditions, qualitative analysis can be conducted using X-ray diffractometry (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and infrared spectroscopy. Furthermore, to assess their impact on electrochemical properties, cyclic voltammetry (CV) and Galvanostatic Charge/Discharge (GCD) tests are performed. This discovery is noteworthy as it challenges conventional understanding. Previous research suggested that adding Mn2+ to the electrolyte enhances cycle stability by preventing manganese dissolution. Our findings laid the groundwork for uncovering the role of the Mn2+ additive.
[1] M.H. Alfaruqi, V. Mathew, J. Gim, S. Kim, J. Song, J.P. Baboo, S.H. Choi, J. Kim, Electrochemically induced structural transformation in a γ-MnO2 cathode of a high capacity zinc-ion battery system, Chem. Mater. 27 (2015) 3609-3620
[2] K. Lu, B. Song, Y. Zhang, H. Ma, J. Zhang, Encapsulation of zinc hexacyanoferrate nanocubes with manganese oxide nanosheets for highperformance rechargeable zinc ion batteries, J. Mater. Chem. A. 5 (2017) 23628-23633