Microstructural design principles for stable interphases in alkali-metal and anode-free batteries




Wang, Yixian, Ph. D.

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The pursuit of reliable and high-energy storage devices with enhanced safety has attracted significant research interest in recent decades. Alkali metals like lithium and sodium have shown promise as anode materials but suffer from limitations such as dendrite growth and interfacial instability, which pose safety risks and hinder their widespread applications. To overcome these challenges, an anode-free battery (AFB) design offers increased energy density and enhanced safety. However, AFBs often experience rapid capacity decay due to the lack of a reservoir for active ion loss during cycling. Additionally, solid-state batteries utilizing non-flammable inorganic solid electrolytes address safety concerns and potentially provide higher energy density but face interfacial obstacles such as dendrite growth and unstable solid electrolyte interphase (SEI). This dissertation focuses on microstructural design of stable interphases to address the interfacial challenges and improve the performance of alkali-metal and anode-free batteries. To start with, electrochemically stable intermetallics are introduced as effective coating layers on copper foam current collectors, improving metal wetting and subsequent cycling. Unlike conventional alloys, the introduced intermetallics (Na₂Te and Na₂S) do not undergo reversible alloying – dealloying reactions that cause remarkable volumetric change, therefore enhancing mechanical integrity throughout the cycling process. Building upon this design strategy, the dissertation further investigates the application of intermetallic coatings in solid-state electrolyte systems. A thin layer of Li₂Te intermetallic coating is fabricated onto commercial copper foil current collectors, which significantly reduces the electrodeposition/electrodissolution overpotentials, improves Coulombic efficiency (CE), and enables stable cycling of anode-free all-solid-state batteries. Additionally, this dissertation introduces a novel metallurgical composite composed of ternary sodium-antimony-tellurium (NST) intermetallic, which demonstrates remarkable sodiophilic properties, effectively facilitating uniform sodium electrodeposition and electrodissolution for enhanced cycling stability. An anode-free cell consisting of an NST-coated current collector and Na₃V₂(PO₄)₃ (NVP) cathode demonstrates significantly improved cycling performance compared to using a baseline copper collector. In this dissertation, various state-of-the-art characterization techniques are utilized to investigate the microstructural evolution occurring at interfaces, offering new insights into the intricate connection between wetting behavior and electrochemical performance. Furthermore, multidimensional modelling and simulation approaches are employed to gain a further understanding of the underlying mechanisms.


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