Date of Award
Doctor of Philosophy (PhD)
School of Materials Science and Engineering
Rajendra K Bordia
High specific energy/power is nearly always desirable in battery systems but it is especially important in batteries for electric vehicles. One approach for increasing the specific energy/power is to maximize the mass fraction of active materials. A straight forward approach to realize this is to make the electrodes as thick as possible. There are two main limitations for increasing electrode thickness. One is the need for active material with high electronic and ionic transport properties, and the other is rapid Li ion transport through the entire thickness of a porous electrode.
In the research described in this dissertation, lithium titanite (Li4Ti5O12, LTO) was chosen as a promising safe active material for lithium batteries. In spite of many advantages, this material suffers from low electronic and ionic conductivity, making it an unsuitable choice for manufacturing thick electrodes. In order to alleviate this problem, a thorough investigation of the effect of Mo doping on structure, electronic and ionic conductivity of LTO was conducted.
In order to facilitate rapid Li ion transport through the thickness of thick porous electrodes, a novel processing approach, freeze tape casting, was developed to make ordered anisotropic macro porous electrodes directly on the surface of a metal foil current collector. The effect of electrode processing parameters, microstructure and thickness on the electrochemical performance of the electrode was studied experimentally.
Finally, comprehensive numerically simulations were conducted to investigate the effect of electrode microstructure (specifically thickness and tortuosity) on Li-ion transport at different discharge rate (C-rate) for both normal and freeze tape cast electrodes in order to guide the design of optimal microstructure. Computer simulations show that freeze tape cast electrodes may be fully discharged up to 750 µm thickness at 1 C rate compared to 300 µm for normal tape cast electrodes with the same mass loading. Freeze tape cast electrodes also show stable maximum areal capacity for C rates about double the maximum C rates of their normal tape cast electrode counterparts with the same mass loading.
Azami Ghadkolai, Milad, "Engineered Porous Electrodes for High Performance Li-Ion Batteries" (2020). All Dissertations. 2623.