(6dq) Exploring the Solid-Electrolyte Interface and Interphase By Surface-Plasmon Resonance Spectroscopy

• Ph.D., Chemical Engineering, Florida State University (Supervisor: Dr. Daniel Hallinan), 2017
• M.S., Chemical Engineering, Florida State University, 2016
• M.S., Biomedical Engineering, Southeast University, 2012
• M.S., Advanced Materials, Ulm University (Germany), 2012
• B.S., Biomedical Engineering, Southeast University (China), 2009

Postdoc Training (Oak Ridge National Laboratory, supervisor: Dr. Jagjit Nanda)

• Probing the Nanoscale Heterogeneity of SEI on Silicon Thin-film Anode Using Tip Enhanced Raman Spectroscopy (TERS)
• Developing Solid Polymer Electrolyte for Non-aqueous Redox Flow Batteries

Research Interests:

The growing need for energy storage systems requires batteries with high power and energy density as well as longer life and improved safety. This calls for innovations in high energy density electrode materials as well as in design of robust and efficient charge transfer interfaces without electrolyte degradation or chemical side reactions. Charge transport across the solid electrode-liquid electrolyte interface (SLI) is believed to be one of the rate limiting steps. In lithium-ion batteries, the thermodynamic instability of the electrolyte at the SLI leads to formation of a passivation layer, commonly referred to as the solid-electrolyte interphase (SEI). Although the composition, morphology, and structure of SEI of lithium-ion batteries have been extensively studied, probing its evolution in situ at nanoscale is still challenging to a large extent. Surface-plasmon resonance (SPR) spectroscopy is promising to solve this challenge. SPR is the resonant oscillation of conduction electrons at the interface between negative and positive permittivity molecules stimulated by incident light. It includes surface-enhanced Raman spectroscopy (SERS) and tip-enhanced Raman spectroscopy (TERS). The prerequisite of employing SPR to probe the surface molecules is to have a highly ordered plasmonic nanostructured SPR substrate, which is extremely challenging.

In my Ph.D. research, I developed two interfacial self-assembly techniques to fabricate gold nanoparticles (Au NPs) into large area (cm²) monolayers, which ensured the formation of long-range ordered nanogap arrays. The local electromagnetic field is extremely intense within the metallic nanogap (<10 nm) due to the coupling effect among adjacent nanoparticles, which allows for probing the molecules at immediate vicinity of SLI (distance from the solid surface < 20 nm). The Au NP monolayers exhibit high SERS sensitivity even down to single-molecule level (enhancement factor > 10⁷). This allows for probing a broad range of trace electrolyte components, such as lithium hexafluorophosphate (LiPF₆), fluoroethylene carbonate (FEC), ethylene carbonate (EC) and diethyl carbonate (DEC), etc. The investigation of a commercial lithium-ion battery electrolyte (LiPF₆ in EC+DEC binary solvents) using SERS allows for the determination of the solvent coordination numbers, which ranges from 2 to 5, in sharp contrast to those calculated from bulk liquid electrolytes by standard confocal Raman and infra-red (IR) spectroscopy from 3 to 6.

SERS is promising to probe molecular fingerprints in nanoscale through sample plane. However, it lacks the nanoscale resolution within sample plane. This makes it extremely hard for getting spatial heterogeneity of the SEI, which can be only on the order of 10 nm. Tip Enhanced Raman Spectroscopy (TERS) combines SERS with atomic force microscopy (AFM), capable of providing the chemical vibrational information and topography of the sample in the nanometer spatial resolution simultaneously. My postdoc training is focused on using TERS to understand the SEI evolution on amorphous silicon (a-Si) thin film electrode. TERS analysis on cycled a-Si indicates that the nanometer scale SEI “islands” are unevenly distributed. Even for the same SEI “island”, the composition is different from point to point with inter-point distance smaller than 10 nm. The local chemical information studied by TERS is intrinsically different than that collected from the standard confocal Raman and IR spectroscopy.

My near future research involves in continually developing in operando SPR techniques based on SERS and TERS to understand the interfacial phenomenon in situ in energy storage units. The model systems of interest include the high voltage cathode/electrolyte interface, electrode/solid-state electrolyte interface, and electrode/polymer electrolyte interface. Such surface sensitive probing techniques can also be readily applied in water desalination, catalysis, corrosion, energy storage and ion distribution/transport through biological membranes, etc.

Teaching Interests:

Served as a teaching assistant for more than 4 years in chemical engineering department at FSU, I got rich hands-on experience in teaching and greatly enjoyed sharing my knowledge with the undergraduates. The core courses include ‘Mathematics in Chemical Engineering’, ‘Mass and Energy Balance’, ‘Process and Analysis Design’, and ‘Unit Operations Lab’, etc. I truly enjoyed mentoring students during recitation and office hour, helping with preparing the teaching materials and grading their homework. I see teaching more than an integral part of an academic career. I much look forward to having the opportunity to teach chemical engineering core course for undergraduate or graduate students.

Selected Publications (27 in total, with 10 first author publications and 2 filed patents)

1. Yang, G., Ivanov, I., Ruther, R., Sacci, Robert., Subjakova, V., Hallinan, D. T. & Nanda, J. (2018). Electrolyte Solvation Structure at Solid/liquid Interface Probed by Nanogap Surface-enhanced Raman Spectroscopy. ACS Nano (under review).
2. Ruther, Rose, Guang Yang, Frank M. Delnick, Zhijiang Tang, Michelle Lehmann, Tomonori Saito, Yujie Meng, Thomas A. Zawodzinski, and Jagjit Nanda (2018). Mechanically Robust, Sodium-Ion Conducting Membranes for Nonaqueous Redox Flow Batteries. ACS Energy Letters.
3. Yang, G., Kim, K., Wang, W., Chen, B., Mattoussi, H., & Hallinan Jr, D. T. (2018). Scaling Laws for Polymer Chains Grafted onto Nanoparticles. Macromolecular Chemistry and Physics, 219(8), 1700417.
4. Yang, G., Nanda, J., Wang, B., Chen, G., & Hallinan Jr, D. T. (2017). Self-assembly of large gold nanoparticles for surface-enhanced Raman spectroscopy. ACS Applied Materials & Interfaces, 9(15), 13457-13470.
5. Yang, G., Hu, L., Keiper, T. D., Xiong, P., & Hallinan Jr, D. T. (2016). Gold nanoparticle monolayers with tunable optical and electrical properties.Langmuir, 32(16), 4022-4033.
6. Yang, G., & Hallinan Jr, D. T. (2016). Self-assembly of large-scale crack-free gold nanoparticle films using a ‘drain-to-deposit’ strategy.Nanotechnology, 27(22), 225604.
7. Yang, G., & Hallinan, D. T. (2016). Gold Nanoparticle Monolayers from Sequential Interfacial Ligand Exchange and Migration in a Three-Phase System. Scientific Reports, 6, 35339.
8. Yang, G., Chang, W. S., & Hallinan Jr, D. T. (2015). A convenient phase transfer protocol to functionalize gold nanoparticles with short alkylamine ligands. Journal of colloid and interface science, 460, 164-172.