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Lecture/Presentation/Talk

Stanford Energy Student Lectures, Week 5

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Please join us for the 14th Annual Stanford Student Energy Lecture Series! During the series, 16 graduate students/postdoctoral scholars, consisting of two speakers per week, will present their energy-related research to an audience of Stanford students, faculty, and staff. 

 

Dongjae Kong

Talk title: Rapid Room-Temperature Sulfidation of Commercial FeNiCo Alloy for Efficient Oxygen Evolution Reaction

Abstract: Although various highly active transition metal-based electrocatalysts have been identified for the anodic oxygen evolution reaction (OER) for alkaline water electrolysis, the necessity of a binder to coat electrocatalysts onto conductive supports affects the overall durability. Thus, developing a highly active, durable, and binder-free anode is beneficial for advancing alkaline water electrolysis for broader applications. This study presents a new yet effective surface sulfidation method for converting commercial FeNiCo alloy, Kovar, into highly active, stable, and binder-free OER electrodes. The surface sulfidized Kovar electrode demonstrated a significant enhancement in OER performance and the improvement is attributed to key factors, such as surface enrichment of Ni and higher oxidation states of Ni and Fe, and sulfur incorporation into lattice oxygen, which enhances the formation of (oxy)hydroxide and modulates the binding energy of *OH intermediate species. The developed surface sulfidation technique also effectively improves the OER activity for other Ni- or Fe-based commercial alloys.

Bio: Dongjae is a PhD candidate in Mechanical Engineering advised by Prof. Xiaolin Zheng. His research focuses on electrocatalysts for low and high-temperature electrolyzers. Before joining Stanford, he was a full-time lecturer in the Department of Aerospace Engineering at the Republic of Korea Air Force Academy. He completed an M.S. and B.S. in Mechanical Engineering from Seoul National University in 2018 and 2016.

 

Elizabeth Zhang 

Talk title: Monofluorinated Ether Electrolyte with Acetal Backbone for High-Performance Lithium Metal Batteries

Abstract: High degree of fluorination for ether electrolytes has resulted in improved cycling stability of lithium metal batteries (LMBs) due to stable SEI formation and good oxidative stability. However, the sluggish ion transport and environmental concerns of high fluorination degree drives the need to develop less fluorinated structures. Here, we introduce bis(2-fluoroethoxy)methane (F2DEM) which features monofluorination of the acetal backbone. High coulombic efficiency (CE) and stable long-term cycling in Li||Cu half cells can be achieved with F2DEM even under fast Li metal plating conditions. The performance of F2DEM is further compared with diethoxymethane (DEM) and 2-[2-(2,2-Difluoroethoxy)ethoxy]-1,1,1-Trifluoroethane (F5DEE). The structural similarity of DEM allows us to better probe the effects of monofluorination, while F5DEE is chosen as the one of the best performing single-salt and single-solvent ether-based LMB electrolytes for reference. The monofluorine substitution provides improved oxidation stability compared to non-fluorinated DEM, as demonstrated in the linear sweep voltammetry (LSV) and voltage holding experiments in Li||Pt and Li||Al cells. Higher ionic conductivity compared to F5DEE is also observed due to the decreased degree of fluorination. Furthermore, 2 M lithium bis(fluorosulfonyl)imide (LiFSI) / F2DEM displays significantly lower overpotential compared with the two reference electrolytes, which improves energy efficiency and enables its application in high-rate conditions. Comparative studies of F2DEM with DEM and F5DEE in anode-free (LiFePO4) LFP pouch cells and high-loading LFP coin cells further show improved capacity retention of F2DEM electrolyte. Further investigations of the SEI by x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), cryogenic electron microscopy (cryo-EM), focused-ion beam (FIB), electrochemical impedance spectroscopy (EIS), and titration gas chromatography (TGC) suggest that F2DEM facilitates improved Li deposition morphology with reduced amount of dead Li. This enables F2DEM to show superior performance especially under higher charging and slower discharging rate conditions.

Bio: Elizabeth Zhang is a second-year PhD student in the Department of Materials Science and Engineering at Stanford University, where she is co-advised by Professor Zhenan Bao and Professor Yi Cui. Her research is centered on the development of novel electrolytes for next-generation high energy-density lithium metal batteries. Elizabeth's work aims to address critical challenges in battery technology, such as improving safety, enhancing cycle life, and increasing energy storage capacity. Her talk will be focused on novel electrolyte design for lithium metal batteries.

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