(2cf) Solid Electrolyte Interphase: Where Polymer Composites Meet Electrochemistry

Solid electrolyte interphase (SEI) is the key component that contributes to the success of graphite electrodes in lithium-ion batteries. It is a chemically distinct phase formed through a series of reduction reactions involving electrolytes and salts. By separating the direct contact between electrodes and electrolyte molecules, it auto-inhibits electrolyte reduction and enables a longer device life. Next-generation rechargeable lithium batteries targeting higher energy densities require the replacement of graphite electrodes with silicon and lithium metal. In contrast to the mild (~9%) volume change exhibited by graphite electrodes, the enormous volume change of silicon (~400%) and lithium metal anodes (~∞) calls for both electrochemical and mechanical stability in the SEI. Since the idea of SEI was first proposed in 1979, the primary constituents have been identified as organic polymers(oligomers) and inorganic nanocrystals. As a polymer composite soaked in concentrated electrolytes, the thermodynamic state of the SEI film, particularly under non-equilibrium conditions, requires further investigation to provide guidelines for rational design. My future research will be at the intersection of soft matter and electrochemistry, commencing with the following interrelated projects on modeling the Solid Electrolyte Interphase (SEI).

Aim #1 Extraction of the capacitance and resistance of SEI.

Due to the submicron scale thickness of SEI, it is difficult to directly measure the capacitance and resistance. The resistance of SEI is only accessible by fitting the complex impedance into simplified equivalent circuits. To facilitate the measurements, I propose to develop a predictive porous electrode theory based model to infer the capacitance and resistance from the Electrochemical Impedance Spectroscopy.

Aim #2 Breathing of Solid Electrolyte Interphase.

Solid electrolyte interphase(SEI) is known to consists of organic polymer and inorganic nanocrystals. But why does the SEI form condensation? And how does the SEI film respond to the concentration change and the lithium ion flow due to electrochemical reactions? Based on the current understanding of SEI composition, I propose to build a microscopic model of polymer nanocomposites to study thermodynamic properties of SEI under working conditions. Specifically, coarse grained simulation and field theory will be applied to sketch out the phase-diagram of the electrolyte-soaked SEI and the role of electrostatics in its thermodynamic properties. The hydrodynamics and electrochemical reactions will be further introduced to establish a dynamic field theory to simulate the deposition of Lithium in the confined region between SEI and substrate.

Aim #3 Rational design of electrolyte and additives.

Based on the Aim #2, I propose to design the SEI composition and structure by engineering the electrolyte composition and additives to generate the desired SEI composition. We will analyze the formation mechanism of existing electrolytes and leverage the computer assisted synthesis planning tools, such as Reaction Mechanism Generator and Machine Learning techniques, to speed up the electrolyte design.

Teaching Interests

As trained by both departments of Materials Science and Chemical Engineering, I’m interested in teaching the core courses such as thermodynamics, transport phenomena and material physics, as well as more specialized courses on the soft matter and electrochemical systems. I am also excited to develop specialized graduate level courses in areas related to my research, such as “Computational Materials: From Atomic scale to Mesoscale” which would have the goal of teaching students the principles and algorithms behind the molecular dynamics, phase-field model and field theoretic approach.
As a faculty member, I aspire to foster an inclusive and supportive environment that promotes scientific integrity and critical thinking. To achieve this, it is crucial to establish a diverse research group. Different life experiences and educational backgrounds have a significant impact on individuals’ values and thinking patterns. Embracing diversity will ultimately enhance critical thinking by bringing together a variety of perspectives and approaches. Furthermore, as a principal investigator, I prioritize equipping students with strong communication and writing skills in addition to research techniques. I firmly believe that communication and writing are the most effective ways to practice critical thinking. Therefore, emphasizing these skills is essential, not only to prepare students for the challenges they may face during graduate school but also to benefit the entire lab as a whole.