Stanford Energy Student Lectures: Jiayi Li and Yuelang Chen
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Title: Organochalcogenide-halide perovskites
Abstract: Halide perovskites have risen as contenders for low-cost and efficient solar-cell absorbers. However, the composition that can deliver the desired efficiency and stability remains to be found. The moisture/thermal instability and light-induced halide segregation impede long-term stable optoelectronic properties. Therefore, we sought a different type of anion mixing, chalcogenide, to expand the accessible bandgaps of lead-halide perovskites. This talk presents a strategy to design and synthesize a novel family of 3D organochalcogenide-halide perovskites by using zwitterionic ligand. We systematically studied structural and electronic effects of chalcogenide. The highly desirable bandgaps, band dispersion, and improved stability of organochalcogenide-halide perovskites motivate the continued expansion and exploration of this new family of materials.
Bio: Jiayi Li received his B.S. in materials chemistry from Peking University in 2019. He is a fourth-year Chemistry Ph.D. candidate supported by the Stanford Interdisciplinary Graduate Fellowship (SIGF). His research in the Karunadasa Lab focuses on the fundamental properties and structural diversity of halide perovskites.
Title: Fast-charging limitations of advanced electrolytes for lithium metal batteries
Abstract: Lithium metal batteries (LMBs) are being actively developed to meet the high-energy-density demand for electric vehicles (EVs). Fast charging is an important requirement for EV applications. While improving lithium metal Coulombic efficiency (CE) has been a focus for LMB electrolyte design, their performance under high current densities is less explored. Here, we evaluate the moderate-to-high-rate cycling stability of three recently developed advanced electrolytes, all of which are weakly solvating electrolytes with anion-derived solid electrolyte interfaces. All three electrolytes showed soft shorting behavior above various threshold current densities. Based on extensive characterizations, we propose a mechanism by which slow ion transport was the main factor that led to poor cycling stability due to concentration polarization, poor Li morphology, and closely packed residual solid electrolyte interphase (rSEI) structure. This work confirms the importance of fast ion transport for LMBs under moderate to fast charging conditions. Therefore, for electrolyte designs, improving CE must be accompanied by efficient ion transport in order to provide a viable solution to practical LMBs.
Bio: Yuelang Chen received his H.B.Sc. in Chemistry from the University of Toronto in 2019. He is currently a Ph.D. student working with Professor Zhenan Bao and Professor Yi Cui. His research focuses on the impact of electrolyte properties on the stability of lithium metal batteries.