Degree

Doctor of Philosophy (PhD)

Department

Chemical Engineering

Document Type

Dissertation

Abstract

The realization of renewable energy is dependent on the advancement of multi-functional materials for energy storage devices. As an example, the substantial progress observed in Li-ion batteries is a result of the discovery and subsequent industrial commercialization of cathode materials such as LiFePO4 (LFP). Although these materials possess relatively high specific capacity (~170 mAh/g), their low room-temperature electronic conductivity has been identified as a limitation for future high-performance batteries. Metastable SrBO3, (SBO, B = Nb, Ta, Mo, etc.) perovskite nanoparticles (NPs) with metallic properties offer an alternative route to improve the room-temperature electronic conductivity of LFP cathodes. Therefore, this work aims to demonstrate how the optoelectronic properties of metastable SBO perovskite NPs can be leveraged for applications in advanced energy storage. The layered film architecture is taken advantage of in order to synergistically couple the metallic conduction of the SBO perovskite internal layer with the high Li-ion conductivity of the olivine top layer to obtain improved electrochemical performance.

Despite the recent attention, the synthesis of SBO NPs using traditional wet-chemical methods result in B-site cations stabilized in highly oxidized states (i.e. Nb5+, Ta5+, Mo6+, etc.), rather than the desired 4+ valency. These over-oxidized states, present as surface/bulk defect states, suppress the expected optoelectronic responses. For this reason, the engineering of these defect states to recover the optoelectronic properties of metastable SBO perovskites is the main objective of this work. To address this challenge, the facile oxygen-controlled CP/MSS method was developed. The low-pressure environment reduces the partial pressure of oxygen during the crystallization process which allows for the simultaneous intercalation of Sr ions and suppression of defect states. Finally, a reducing post-treatment allows for further inhibition of these defect states, which triggers a change in the powder color (white, insulating to colored, metallic). These findings highlight the potential application of these materials as conductive scaffolds that otherwise would not be possible with traditional solution-based methods. As a proof of concept, a LiFePO4 top layer is deposited onto these conductive SBO perovskites to demonstrate their potential application in Li-ion batteries. Incorporation of the conductive scaffold significantly improves the charge transport properties of LFP, highlighting the promising electrochemical potential of these engineered nanomaterials. Ultimately, this ability to modify the charge transport response using these conductive scaffold materials will contribute to the design/development of next-generation energy storage and conversion technology.

Committee Chair

Dorman, James

Available for download on Saturday, March 09, 2024

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