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High-Entropy Stabilization as a Designing Tool for Li-Ion Electrodes
Title
High-Entropy Stabilization as a Designing Tool for Li-Ion Electrodes
Creator
Bandeira Jovino Marques, Otavio Jose
Date
2023
Description
High-Entropy oxides (HEOs) form a new class of materials where the configurational entropy plays the stabilizing role of multicomponent...
Show moreHigh-Entropy oxides (HEOs) form a new class of materials where the configurational entropy plays the stabilizing role of multicomponent systems at high temperatures. Recently, it raised much attention for energy storage applications, especially on Li-ion batteries, where the combination of several different elements in a single solid solution can synergistically act to overcome some of its main drawbacks, improving the battery’s performance. The entropy stabilization opens new boundaries on electrode’s design by increasing the compositional space available for different structures and compounds. Not long ago, the high-entropy oxide (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O demonstrated a big potential as anode material in Li-ion batteries. Its high capacity and long cycling stability raised a lot of questions about the role of the transition metals in the conversion reaction, and the configurational entropy contribution to the electrochemical reaction, further supporting the electrode’s stability. In order to investigate the structural evolution, the role of the multicomponent oxides and structures on the battery’s performance, and the entropic contribution to the electrode’s stability, this research proposes a systematic and robust methodology around the (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O high-entropy oxide (HEO). The project heavily relies on the EXAFS ability to determine the short-range structure and the chemical sensitivity to isolate the elemental contribution of the compound at different cycling and charging states. First, the role of different metallic cations on the electrochemical reaction mechanism of the HEO was analyzed by the change in local structure during different charging steps of a Li-ion battery (Chapter 3). Secondly, the entropy contribution and tunability effects on electrochemical performance were tested in a series of medium and high-entropy oxides derived from the seminal HEO. Mg, Co, Ni, Cu, and Zn were individually removed from the HEO’s composition at a time and tested as Li-ion electrode. Fe was also added to the HEO’s composition (HEO+Fe) in order to prove the tunability effects and entropy contribution (Chapter 4). Operando x-ray absorption spectroscopy (XAS) was used to capture the short lived phases and the transient nature of the conversion reaction, to explain the origins of the extra storage capacity encountered on entropy stabilized systems (Chapter 5). Finally, the role of the high-entropy oxide initial structure was investigated and compared, to check versatility of the elements that can be used on a high-entropy system (Chapter 6).
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