We are interested in synthesizing nano-structured materials and probing the effect of composition and size on the thermodynamics and kinetics when they are used as battery materials.
1. Understanding the mechanism of solid state conversion reactions
Nanoscale materials exhibit fast reaction rates due to high surface areas and short diffusion lengths that can significantly improve the power density of electrochemical devices such as rechargeable batteries. Theoretically, these nanomaterials are also expected to display effects beyond improved kinetics, including: 1) enhanced electrode cycle life due to improved mechanical properties; and 2) modified phase diagram behavior due to enhanced solid solution formation over phase separation. We are interested in understanding the effect of nanostructuring on complex battery reactions involving multiple solid state phases that underpin promising high energy-density battery chemistries. Previously, we have examined the reaction mechanism of Li/FeF3 – how the nanocomposite of LiF/Fe can reform iron fluoride upon lithium removal including the source of large hysteresis and rate limiting steps during structural transformation as well as the instability of the LiF/Fe nanocomposite. We are leveraging these mechanistic understandings to develop methods to improve reaction reversibility through manipulating reaction pathways and nanostructure design.
Understanding the reaction mechanisms of nanocomposite materials during battery operation can help us develop materials solutions to overcome the large hysteresis.
Thermodynamics and kinetics of the Li/FeF3 reaction by electrochemical analysis, P. Liu, J. Wang, W. Li, J. Liu, and J. Vajo, The Journal of Physical Chemistry C, (2012), 116 (10), 6467-6473.
2. Understanding the mechanism of solid state conversion reactions
We have leveraged the formation of the nanocomposite structure during the electrochemical cycling to fabricate nanoporous metals. The conversion reaction is conducted chemically with a reducing agent such as butyl lithium in hexane. Metal chlorides and bromides are used instead of fluorides to facilitate the removal of lithium salts from the metal/lithium salt nanocomposites with polar organic solvents. A wide variety of nanoporous metals have been synthesized. Several applications including catalysis and plasmonics are being explored.
A facile conversion reaction results in the formation of a variety of nanoporous metals.
A Scalable Synthesis Pathway to Nanoporous Metal Structures, Christopher Coaty, Hongyao Zhou, Haodong Liu, and Ping Liu, ACS Nano, (2018), DOI: 10.1021/acsnano.7b06667.