Date of Award

Spring 1-1-2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

First Advisor

Steven M. George

Second Advisor

Daniel S. Dessau

Third Advisor

Charles T. Rogers

Abstract

As the world consumes the dwindling supply of fossil fuels, an alternative to gasoline powered vehicles will become necessary. Lithium ion batteries (LIBs) are emerging as the dominant power source for portable electronics, and are seen as a promising energy source in the development of electric vehicles. Current LIB technology is not well suited for vehicles, increases in the energy density, power density and durability are needed before LIB are ready for widespread use in electric vehicles. LiCoO2 and graphite are the dominant cathode and anode active materials, respectively in LIBs. On the cathode side, instabilities in LiCoO2 can lead to the deterioration of the LIB. Decomposition of electrolyte on the graphite anode surface to form a solid-electrolyte interphase (SEI) consumes lithium from the cathode resulting in a lower battery capacity. Instabilities in the in the SEI can result in catastrophic battery failure. Previous studies have employed metal oxides films, typically grown with wet chemical techniques, to stabilize LiCoO2 and mitigate the formation of the SEI on graphite. The thicknesses of films grown with wet chemical techniques was typically ∼50-1000 Å. In order to achieve higher power densities, the particle size of LIB active materials is being scaled down. As active materials get smaller the mass contribution of a protective film can become a significant fraction of the total mass. Atomic layer deposition (ALD) has been used to grow ultra thin films of Al2O3 on LiCoO2 and graphite. By altering the interaction between the active material and the battery electrolyte it was possible to improve the stability of both LiCoO2 and graphite electrodes in LIBs. In the case of graphite, the Al2O3 film may be thought of as an artificial SEI. During the initial charge-discharge cycle of a LIB, the electrolyte decomposes on the anode to form the SEI. The formation of the SEI is believed to prevent further decomposition of the electrolyte on the anode surface. The SEI contains electrolyte decomposition products including Li2CO3, Li2O, LiOH, LiF and R-OLi. In order to grow a truly artificial SEI on the graphite anode, i.e. grow a film that mimics the SEI that forms during charge-discharge cycling, new ALD chemistries for the growth of Li2CO3 and LiOH have been developed. The ALD of an artificial SEI layer may limit lithium loss and improve the capacity stability during charge-discharge cycles.

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