Designing materials to address important challenges, and understanding fundamental science to guide materials design.

Lithium-ion batteries have had a profound impact on our daily life, but their capacity is approaching the theoretical limits with narrow room to satisfy our unprecedented demand. Thus, battery chemistries beyond Li-ion need to be developed.

Li metal is the ultimate anode of choice due to its highest theoretical capacity (more than ten times the value of the state-of-art graphite) and lowest electrochemical potential among all the candidates. Despite five decades of research, there remained no workable solution to the challenges of the Li metal anode, the major two of which are its high reactivity and infinite relative volume change during cycling.

 

The high reactivity results in the formation of a surface passivation film on metallic Li, called the solid-electrolyte interphase (SEI), instantaneously inside the liquid electrolyte. While the significant interfacial fluctuation during cycling cracks the fragile SEI layer, locally enhancing the Li-ion flux to promote dendritic Li deposition, which could trigger internal short circuit and compromise battery safety. Moreover, the high-surface-area dendrites and the recurring SEI breakdown/repair bring about continuous side reactions, severely shortening the cycle life.

Correspondingly, my PhD research focuses on solving the key challenges of Li metal anode from the following perspectives: 

1) Minimizing the volume change by rationally-designed Li-scaffold composite. 

    Surface characterizations and modifications are explored to manipulate the scaffolds' wetting properties by molten Li. 

2) Control and homogenize the surface reactivity of Li via artificial SEI designs.

3) Exploring novel electrolyte additives to modify the SEI formation process and its fundamental understanding based on electrochemical, surface-sensitive and microscopy techniques. 

Solid-state battery is a promising research direction for next-generation energy storage technologies due to their significantly high energy density and reduced safety risks. My research on this exciting topic revolves around utilizing the unique properties of nanomaterials (surface Lewis acidity, etc.) to improve the ionic conductivity of solid polymer electrolytes, and interfacing solid electrolytes with Li metal anode and high-energy cathodes (Sulfur cathode, etc.).

© 2019 by Yayuan Liu

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