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UBC Theses and Dissertations

Investigation of capacity fade in flat-plate rechargeable alkaline MnO₂/Zn cells Mehta, Sean


The rechargeable alkaline manganese dioxide-zinc (RAM™) battery system has been difficult to commercially develop in the past due to irreversible phase formation and progressive and cumulative capacity fade. This system has many advantages however, such as low cost and environmentally sustainable materials, long shelf life, moderate energy density, and safety. A flat-plate architecture was developed and investigated in half and full-cell apparatuses with the goal of understanding and improving cumulative capacity fade in the electrolytic manganese dioxide (EMD) cathode. Two types of cathode current collectors (CCs) were developed, a thin film foil CC and an expanded metal mesh CC and used to assess the effect of various additives over 30+ cycles under various operating conditions. Conductive carbon black (Super C65) and graphite (KS44) additives were shown to improve cell performance at 15 wt. % KS44 graphite providing an electrically conductive network between adjacent EMD particles. In addition, other chemical additives (BaSO₄, Sr(OH)₂•8H₂O, Ca(OH)₂, and Bi₂O₃) were investigated at 5 wt. % with Bi₂O₃ providing a reproducible improvement over a control recipe. Mechanical stability of the cathode electrode and pressure application were significant causes of cell failure. Slow rates of discharge, and shallow depth of discharge (DOD) charge/discharge protocols reduced capacity fade by limiting electrochemically irreversible phase formation such as Mn₂O₃, Mn₃O₄, Zn₂MnO₄, and Mn(OH)₂. Analytical characterization techniques including Scanning Electron Microscopy/ Energy Dispersive X-Ray Spectroscopy (SEM/EDS), X-Ray Photoelectron Spectroscopy (XPS), Powder X-Ray Diffraction (XRD), and Potentiostatic Electrochemical Impedance Spectroscopy (PEIS) were used to provide supporting evidence indicating that the main causes of capacity fade are linked to the cathode electrode’s mechanical properties, increased cell resistance, and progressive and irreversible phase formation.

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