Electrochemical properties of crystalline polymorphs of MnO2 in aluminum and zinc metal batteries

Author

Subhadip Pal, CUNY City CollegeFollow

Date of Award

2019

Document Type

Thesis

Department

Mechanical Engineering

First Advisor

Robert J. Messinger

Keywords

batteries, aluminium, zinc, aqueous, ionic salt, MnO2

Abstract

The widespread use of non-renewable fossil fuels has led to societal problems like global warming and climate change. Electrochemical energy storage can enable the integration of renewable energy sources that are inherently intermittent (solar, wind, etc.) into the electric grid, though major advances in cost, cycle life, and safety are necessary to have a global impact on the energy landscape. Both aluminium (Al) and zinc (Zn) metals are earth abundant, low-cost, safe, and exhibit high coulombic capacities, which make them promising electrode materials for “beyond lithium-ion” battery chemistries. However, the electrochemical feasibility and charge storage mechanisms of alternative Al and Zn battery systems, particularly when paired low-cost positive electrode materials, must be investigated.

In this thesis, high-energy-density aluminium and zinc metal batteries that employ low-cost and safe manganese dioxide (MnO₂) as positive electrode materials (“cathodes”) are investigated using ionic liquid and aqueous electrolytes. Two crystalline polymorphs of MnO₂ are used: birnessite (δ-MnO₂), a layered structure, and todorokite, a seldomly studied structure composed of large tunnels. For the Al batteries, two electrolyte were used: an ionic liquid containing aluminium chloride and 1-ethyl-3-methylimidazolium chloride ionic liquid (AlCl₃/Emim[Cl]), and aqueous aluminium triflate. For the Zn batteries, aqueous zinc sulfate (non-alkaline) was used. The batteries were characterized electrochemically by galvanostatic and cyclic voltammetry tests while the electrode and electrolytes materials were studied by X-ray diffraction and nuclear magnetic resonance (NMR) spectroscopic measurements. Al-MnO₂ batteries using choloraluminate-containing ionic liquid electrolytes are shown to be unsuitable for rechargeable redox electrochemistry, exhibiting large capacity fade, likely due to chemical and/or electrochemical instability of MnO₂ in the electrolyte. Aqueous Al-MnO₂ batteries showed far more promise, exhibiting reversible electrochemical behaviour in cyclic voltammograms. The underlying charge storage mechanism appears independent of the crystalline polymorph, likely linked to proton intercalation, and requires further study. Aqueous (non-alkaline) Zn-todorokite batteries also demonstrated reversible electrochemical behaviour and thus show promise as a rechargeable battery technology. The precise role of protons and water (e.g., hydration of zinc ions) should be clarified in future investigations. Overall, this work lays part of the scientific foundation towards using and understanding crystalline MnO₂ polymorphs as positive electrode materials for aqueous Al and Zn-ion batteries.

Recommended Citation

Pal, Subhadip, "Electrochemical properties of crystalline polymorphs of MnO2 in aluminum and zinc metal batteries" (2019). CUNY Academic Works.
https://academicworks.cuny.edu/cc_etds_theses/874