Charge transport kinetics understanding and architecture design in thick electrodes for scalable high-energy/power batteries

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2023-12

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Replacing fossil fuels-powered vehicles with electric ones is an indispensable part of achieving carbon neutrality in the near future. Although the past decade has witnessed the unprecedented growth of the electric vehicle market, long endurance and fast-charging capacities are the two main challenges remaining. This asks for lithium-ion batteries, the heart part of the electric vehicle, with simultaneously high energy and high power. However, rate capabilities are often limited in practical high-loading electrodes, with their electrochemical behaviors governed by electrode architectures still elusive. In this dissertation, research efforts are focused on probing the charge transport limitations in high-loading battery electrodes, developing advanced electrode fabrication strategies to achieve high-energy/power electrodes, and understanding the architecture-related electrochemical properties via real-time structural and phase evolution characterization and numerical modelling. Chapter 1 introduces the essential electrochemical processes occurring within the battery electrode across diverse time and length scales. The complexity of a battery electrode system stems from the intertwined behaviors of electrons and lithium ions during charge storage. To unravel this, separate studies on electron and ion transport are executed to discern the pivotal step in thick electrodes. Electron transport kinetics are initially explored in thick electrodes embedded with conductive fillers of varying dimensionalities (Chapter 2). Their influence becomes pronounced when filler content is minimal. However, once the electrical percolation threshold is surpassed, further investigation into nanosheet-based electrodes reveals that ion transport within the electrolyte-saturated pores emerges as the rate-limiting factor (Chapter 3). Drawing insights from kinetic studies, the essential endeavor becomes the development of methodologies to engineer electrode architectures conducive to lithium-ion transport towards high energy/power densities. Magnetic templating is first introduced to craft low-tortuosity electrodes featuring vertically aligned nanosheets. In this context, the orientation of the nanosheets can be precisely manipulated, allowing for an in-depth investigation into the relationship between tortuosity and electrochemical properties (Chapter 4). Subsequently, a drying-based densification process is integrated with magnetic templating to attain vertically assembled nanosheets with compact packing (Chapter 5). On the other hand, bidirectional freeze-casting is amalgamated with compression/calendering-induced densification techniques to fabricate energy-dense, aligned battery electrodes with a high potential for scalability (Chapter 6).

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