Cho, Kyu Taek
M.S. (Master of Science)
Department of Mechanical Engineering
Lithium-ion battery has been the most popular energy-storage system for stationary, portable, and transportation systems, but it faces challenging issues such as low energy density (i.e. short driving range), high system cost, durability and safety-related issues. In this study, we revisited "Aluminum-Air Battery", which is promising but could not get much attention, to find the breakthrough technologies to resolve those issues of conventional systems. The aluminum-air battery has excellent benefits such as aluminum metal is abundantly available in earth's crust, high energy density of 2.8 kWh/g which is about 7 times greater than Li-ion battery (0.38 kWh/kg), but due to (1) the side reaction between aluminum and water causing hydrogen gas evolution due to which battery cannot be recharged and (2) the formation of oxide film on the surface that inhibits electrochemical reaction at the surface resulting in much lower cell performance than theoretically expected performance. To eliminate side reaction completely, a non-aqueous electrolyte has been used in this research. It is known that the shape of the oxide film is determined by the force balance between electro-compressive due to potential difference between metal and oxide (film breaking force) and surface-tension of oxide (film forming force). Oxide film should be broken down to increase rate of electrochemical reaction and thereby to increase the performance of the battery. The electro-compressive force acting across oxide film is constant for a given oxide thickness. Hence surface tension of oxide film should be decreased to break the film. In this research, change in surface tension of oxide film and its dependence on aggressive ions in the electrolyte is investigated. Ionic liquid was made in varied ratios of cation ([EmIm]Cl) to anion (AlCl3) to check its effect on battery performance. Conductivity decreases from 16.2 mS/cm at 1:1 ratio to 14.6 mS/cm at 1:1.5 ratio as multi coordinated chloraluminite species formed at higher ratios of ionic liquid decrease mobility and thereby decrease conductivity of ionic liquid. More chloride in solution decreases surface tension of oxide and breaks the oxide film at much lower thickness. Hence there has been an increase in bare active surface area of aluminum which increased OCV measured by the cell from 0.45 V to 1.4 V, but also decreased conductivity and increased ohmic losses which reduced maximum current discharged from 5.8 mA/cm2 at 1:1 ratio to 3.4 mA/cm2 at 1:1.5 ratio of the ionic liquid. Change in surface morphology of aluminum anode for different ratios of the ionic liquid and exposure time of aluminum anode to ionic liquid is investigated using Scanning Electron Microscope. Chlorine adsorption density on aluminum surface has been calculated using Energy Disruptive X-ray spectroscopy (EDX) analysis. Chlorine adsorption density can be used to predict an optimal concentration of chlorine in the electrolyte to decrease the surface tension of oxide film to an optimal value. To conclude, this research aims towards understanding the formation, growth and breakdown of oxide film. In addition, it also intends to suggest the design guideline for chlorine concentration in electrolyte and exposure time of aluminum anode to the electrolyte. This will eventually enhance the performance and efficiency of the battery.
Mohammad, Abdul Kaleem, "Study of oxide film formed on aluminum electrode in aluminum-air battery" (2017). Graduate Research Theses & Dissertations. 5114.
Northern Illinois University
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