Date of Completion

1-30-2017

Embargo Period

1-30-2017

Keywords

Transmission electron microscopy, energy storage, lithium-ion batteries, lithiation, in-situ

Major Advisor

Prof. C. Barry Carter

Associate Advisor

Prof. S. Pamir Alpay

Associate Advisor

Prof. George A. Rossetti, Jr.

Field of Study

Materials Science and Engineering

Open Access

Open Access

Abstract

The world-wide effort to produce and use cleaner energy also necessitates more advanced energy storage capabilities. For example, clean sources of electricity, such as wind or solar, are intermittent and require load leveling. Electric vehicles require more energy- and power-dense batteries in order to truly compete with fossil-fuel-based combustion engines. Lithium-ion batteries (LIBs) currently dominate the secondary battery market. However, in order to build a better LIB, there is a clear need for a better understanding of the fundamentals of lithiation processes. Transmission electron microscopy (TEM) is unique in its ability to correlate structural data with chemical information; as such, in-situ TEM techniques can provide vital, fundamental data on alternative electrode materials that will support the development of advanced batteries. In general, lithium storage in a host material may be accomplished by one of two mechanisms. The first is intercalation of layered materials, which is minimally disruptive to the host structure at the cost of Li storage capacity. The second is alloying, which in many cases allows the uptake of several Li atoms per host atom, but rapid structural evolution and expansion occur during the reaction. MoS2 and Sn were the materials chosen for this work, to represent both Li storage mechanisms and to demonstrate the power of in-situ TEM experimentation for identifying atomic-scale processes that contribute to the lithiation of an electrode material. MoS2 is a layered material with a high specific capacity and excellent rate capability, while elemental Sn forms several intermetallics with Li, storing up to 4.25 Li atoms per Sn atom in its fully-lithiated phase. Solid-state half-cells were constructed inside the TEM using a holder designed to perform simultaneous scanning-tunneling microscopy (STM) and TEM. Li metal was used as the counter/reference electrode, with either MoS2 or Sn as the working electrode and solid Li2O on the surface of the Li metal acting as an electrolyte. Real-time observations of the structural evolution of the working electrode materials, as well as post mortem analysis, are presented and discussed.

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