Date of Completion

5-4-2018

Embargo Period

10-16-2018

Keywords

Li-ion batteries; Anode; Metal oxides; Conductivity; Conversion reaction; Doping

Major Advisor

William Mustain

Associate Advisor

Yu Lei

Associate Advisor

Richard Parnas

Associate Advisor

Michael Pettes

Associate Advisor

Luyi Sun

Field of Study

Chemical Engineering

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

In this thesis, various metal oxides have been investigated as innovative anode active materials for next generation Li ion batteries. Specifically, metal oxides have been proved to have higher specific and volumetric energy density than commercial graphitic anodes, wider operating voltage window and are environmentally friendly. However, pure metal oxides have been demonstrated to be characterized by poor reaction reversibility leading to high instability and short battery cycle life. It has been found that the key to achieving high reaction reversibility, or at least stabilizing the capacity, is to increase the inter-particle and/or intra-particle conductivity.

One effective strategy to increase the inter-particle conductivity is to mix or impregnating metal oxide active materials onto a carbon source. By synthesizing metal oxide materials with different carbon weight amount, a strong linkage between reaction reversibility and inter-particle electronic conductivity has been proved by means of the Van der Pauw method, rate capability, capacity retention and electrochemical impedance spectroscopy techniques. Moreover, effect of inter-particle electronic conductivity on the active material morphology during the electrochemical conversion reaction has been investigated by means of identical location TEM technique.

It is also shown that the intra-particle electronic conductivity can have a significant effect on capacity retention and reversibility. The intra-particle conductivity was controlled by synthesizing metal oxide active materials with Co and Na inclusions, significantly increasing capacity retention without modifying the reaction mechanism, as proved by a kinetic study involving Tafel slope analysis.

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