Date of Award

Winter 2-2017

Embargo Period

2-28-2017

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Materials Science and Engineering

Advisor(s)

Jay Whitacre

Abstract

With the proliferation of renewable energy sources, there has been a growing interest in battery chemistries for grid scale energy storage. Aqueous sodium ion batteries are particularly interesting for large scale energy storage because of their low cost and high safety, however, they tend to show poor long term stability. NaTi2(PO4)3 shows promise as an anode for these systems with excellent long term stability when cycled quickly. When cycled slowly, NaTi2(PO4)3 shows rapid capacity fade. The reasons for this rate depend capacity fade is poorly understood and is the topic of this document. It has been found that the products of the hydrogen evolution reaction, H2(g) and OH-, are the two largest contributors to capacity fade. High electrolyte pH caused by generation of OH- promotes dissolution of NTP during extend cycling, this is exacerbated when the pH increase above 11. The single greatest cause of apparent capacity fade for this material is loss of electrochemical surface area due to hydrogen gas entrapment within the porous structure of the electrode. Capacity lost in this manner can be recovered through reinfiltration of the electrode. The detrimental effects of gas entrapment within the electrode can be partially mitigated through compositing of the electrode with activated carbon and enhancing the wettability of the pores through addition of a surfactant to the electrolyte.

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