Exploring the Mechanism of Buffer Additive Enhanced Electrochemical Performance of Aqueous Zinc-Ion Battery by Integration of Spectroscopic and Non Spectroscopic Methods

Abstract

Aqueous zinc-ion batteries (AZIBs) are a promising alternative to lithium-ion systems for grid and portable energy storage due to their low cost, intrinsic safety, and use of abundant materials. Among cathode materials, manganese dioxide (MnO₂) offers high theoretical capacity and affordability, but suffers from rapid capacity fading linked to dissolution and interfacial instability. To address these challenges, this work examines the role of buffer additives (50 mM ammonium dihydrogen phosphate with 5 mM acetic acid) in modifying the electrochemical environment and performance of MnO₂-based cathodes. Galvanostatic cycling, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS) were employed to compare buffered and unbuffered electrolytes across two commercial electrolytic manganese dioxide samples (EMD-1 and EMD-10). In unbuffered cells, capacity decayed rapidly with cycling, accompanied by the progressive growth of interfacial resistance. In buffered electrolytes, capacity retention improved significantly, with higher coulombic efficiency and smoother long-term cycling trends. Cyclic voltammetry revealed that buffer-containing electrolytes moderated charge–discharge asymmetry, while EIS spectra indicated a shift toward diffusion-dominated behavior at later stages of cycling. Although the precise mechanisms remain to be resolved, these observations suggest that buffers mitigate dissolution and stabilize the local chemical environment, thereby altering the balance between interfacial and transport processes. Taken together, this thesis demonstrates that a simple buffer additive can enhance the durability of MnO₂ cathodes in AZIBs without compromising the intrinsic advantages of aqueous electrolytes. The findings provide an accessible route to improving the long-term stability of zinc-based batteries and highlight directions for future mechanistic study, including operando characterization and refined electrochemical modeling.