Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Major/Program

Mechanical Engineering

First Advisor's Name

Dr. Bilal El-Zahab

First Advisor's Committee Title

Committee Chair

Second Advisor's Name

Dr. Shekhar Bhansali

Second Advisor's Committee Title

Committee member

Third Advisor's Name

Dr. Zhe Cheng

Third Advisor's Committee Title

Committee member

Fourth Advisor's Name

Dr. Chunlei Wang

Fourth Advisor's Committee Title

Committee member

Keywords

composite gel polymer electrolytes, carbon nanotubes, lithium-iodide redox, electrode stability, anode protection, ionic conduction

Date of Defense

3-6-2020

Abstract

In lithium-oxygen (Li-O2) batteries, addressing challenges like electrode degradation, cell stability and electrolyte decomposition are key to creating more practical applications. Despite many attempts to minimize anode oxidation and cathode byproduct formation, the electrolyte remains the leading source for rapid capacity fading and poor cyclability in Li-O2batteries. Understanding the loss of functionality in electrolytes, carbon nanotube (CNT) fillers and redox mediators (RM), during cycling within Li-O2battery systems, could be the solution to prolonging battery lifetime. Determining the efficiency of these battery components and additives will push the medium towards lifelong, rechargeable and safe battery configurations.

Composite gel polymer electrolytes (cGPE) consisting of an acrylate-based polymer, tetraglyme based electrolyte, and glass microfibers provided a stable membrane for a dual-enhancement system consisting of (1) CNT loaded onto a porous carbon cloth at the cathode for oxygen inlet and (2) a lithium-iodide (LiI) RM to oxidize the Li-O2battery during charge, thus reducing overpotential.

Combining the battery performance improvements of the highly conductive CNT fillers, charge mediation of LiI RM, modified cycle capacities (500 mAhg-1to 100 mAhg-1) and ionic transport properties of glass microfibers, resulted in a superior 1763% increase in charge/discharge cyclability (CCD) for maximized cGPE (423 cycles) cells, when compared to the control GPE (24 cycles) cell. Results using in-situ electrochemical impedance spectroscopy (EIS), Raman spectroscopy and cyclic voltammetry (CV) revealed that the source of the improvement was the rate of lithium carbonate formation being reduced on the surface of the cathode. Operation using thin, multi-layered concentric CNT fillers with LiI RM decreased LixRCO3 (R- carbon and hydrogen groups) formation rates due to the decreased electrolyte and cathode decomposition rates. This stabilization during cycling helped prolong battery life to 401 cycles (in comparison to 75 cycles from other CNTs) by maintaining lower charge potential, since higher potentials have been associated with rapid cell deterioration.

In this dissertation, Li-O2battery cyclability was extended by improving ionic transportation in the electrolyte, and charge mediation and conductivity in the cathode from LiI RM and CNT fillers, respectively. These batteries provide a wealth of application primarily in electric vehicles, grid and consumer electronics.

Identifier

FIDC008905

ORCID

https://orcid.org/0000-0002-0424-1157

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