During Li+ transport, in Li-ion batteries, a solid electrolyte inter-phase (SEI) composed of breakdown products from the electrode, the solvent, and the electrolyte, forms on both cathode and anode electrode surfaces. Solvents, electrolytes, and electrode materials determine the thickness, morphology, and chemical composition of the SEI layer. Nature of the SEI on different systems determines important properties of the battery. We report on matrix assisted laser desorption time of flight mass spectrometry analysis (MALDI-TOF MS) of the SEI on model and practical anode materials. MALDI-MS analysis of anode materials showed that system specific long chain oligomers are formed during charge/discharge cycles. We will also present electrochemical surface stress measurements of anode materials using the bending cantilever method. Changes in mechanical properties of electrodes during SEI formation, and charge/discharge cycles have great practical consequences for the longevity of a Li-ion battery, since volume changes and stress variations can shorten the lifetime of the electrode materials. On Au surfaces when cycling between 2V to 0.3V (vs. Li/Li+), surface stress is compressive during cathodic scan. During the anodic scan, the compressive stress is removed, and surface stress returns to its original state. Further analysis of this region showed that an initial lithiation before full lithiation occurs at this potential range. First principles density functional theory (DFT) calculations for the Li on Au(111) overlayer models showed a compressive stress during the cathodic scan between 1.1 and 0.3 V. Bulk lithiation and Au-Li alloying happens at a lower potential, ca. 0.2 V. A residual tensile stress is observed on Au surfaces cycled to 0.15 V. This residual stress corresponds to the formation of oligomerized species in the SEI as shown in the MALDI analysis of Au surfaces emersed at different potentials.
Hadi is currently working on his graduate studies at UIUC. He is a member of Professor Andrew A. Gewirth research group. He received hia B.S. from Sharif University of Technology in Applied Chemistry. Hadi's undergraduate research was on electrochemical sensing of DNA molecules. After moving to the U.S., he got his M.Sc. in Analytical Chemistry from Northern Illinois University in 2009, working on electrochemistry of liquid-liquid interfaces with Professor Petr Vanysek.
I spend my time working in the Lab, and designing new experiments and characterization methods to improve Li-ion batteries performance.
Hadi Tavassol, Maria Chan, Maria Catarello, Jeffrey Greeley, David G. Cahill, Andrew A. Gewirth
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University of Illinois Urbana-Champaign, Urbana, IL