Engineering Interfaces to Control Phase Transformations in Lithium-Based Battery Components

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Quinterocortes, Francisco Javier
McDowell, Matthew T.
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Lithium-ion batteries are used in a broad range of applications from consumer electronics to electric vehicles. These applications are driving demand for increased battery capacity and improved safety. In this thesis, we investigate and engineer key battery components that can push battery performance to meet demand.This thesis presents several strategies to increase the energy density of lithium-based batteries. The first strategy presented here is the use of lithium metal anodes. Lithium metal has the highest specific capacity of any anode material for lithium batteries, but its use in conventional batteries is associated with fire hazards due to its interaction with the liquid electrolyte. To overcome this challenge, we replace liquid electrolytes with solids. In the first part of this thesis, we use operando synchrotron X-ray imaging and analysis to study the interfacial phenomena between lithium metal and the solid electrolyte and uncover the role of protection layers, contact area and currentconstriction.The second strategy presented in this thesis is the use of alloying anode materials, such as germanium or silicon, instead of lithium metal. These materials offer lower capacity but are deemed safer than lithium metal. Alloying materials, however, undergo phase transformations that induce large volume changes and fracture, limiting their stability. In the second part of this thesis, we present an operando synchrotron X-ray examination of a germanium alloying anode at the single particle level to reveal the evolution of strain and stress across a sharp interface during lithiation of the material. Lastly, we present an engineering strategy to replace commercially-used current collectors with lighter and more cost-effective alternatives. This effort requires stabilizing the interface between new current collector materials and liquid electrolytes. Anode current collectors in commercial batteries are made of copper and comprise around 10 % of the weight and cost of the battery while being an electrochemically inactive component. In the last part of this thesis, we develop new stabilized current collector materials resulting in improved energy density and reduced cost.The work presented in this thesis highlights the importance of understanding and controlling interfaces in lithium-based batteries, and it also provides important insight that can guide the development of the next generation of safe, high-capacity batteries.
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