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Title:Revealing ion transfer kinetics and charge dynamics at operating battery materials through scanning electrochemical microscopy
Author(s):Gossage, Zachary Tyson
Director of Research:Rodriguez-Lopez, Joaquin
Doctoral Committee Chair(s):Rodriguez-Lopez, Joaquin
Doctoral Committee Member(s):Moore, Jeffrey S; van der Veen, Renske M.; Kenis, Paul J. A.
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Energy storage
, lithium ion
scanning electrochemical microscopy
ion transfer
solid electrolyte interphase
Abstract:Interfacial charge transfer plays a critical role in battery technologies, where it governs the rate of reliable ion or electron movement to and from a battery electrode during charge/discharge. As such, issues with performance are often linked to trouble at the interface across many technologies. Developing higher-performance batteries with improved rates and cycling requires better comprehension of the electrode behavior and evolution during operation. Analytical chemistry is a pivotal field for developing the necessary tools and methods. Specifically, surface-sensitive tools that can access localized or single particle information will help breakdown complexities across the heterogeneous and particulate composition of electrodes applied in real batteries. Among emerging surface tools, scanning electrochemical microscopy (SECM) provides broad opportunity for understanding interphase formation and evolution, measuring single particles, and mapping electrode function. This work presents the development of multiple electroanalytical methods based on SECM to evaluate localized interfacial electrochemistry at various energy storage systems. Within size-exclusion redox flow batteries (RFBs), large, dispersible redox active polymers (RAPs) and colloids (RACs) accept millions of electrons while simultaneously exchanging an equal number of ions with the electrolyte. This charge transfer process occurs at the interface of a current collector involving material adsorption and a reliance on electron transfer kinetics for efficient charge/discharge. Avoiding complications with bulk measurements, I show that single particles can be adhered to a substrate and imaged using feedback at a 300 nm SECM probe. After making contact by slowly approaching the probe, RACs were reliably cycled using cyclic voltammetry and potentiostatic charge/discharge measurements. The results were further verified using Raman spectroscopy and COMSOL modeling. This work shows the power of SECM for understanding charge transfer at an individual particle and helps coordinate back to cycling behavior in bulk. As a perspective, I describe efforts and progress toward single RAC measurements using Raman-SECM. Within intercalation batteries, such as Li+, we find highly complex interphase structures at the electrode-electrolyte interface. These structures stabilize the electrodes and guide ion movement to and from the electrolyte thus playing an essential role in device performance. In spite of its significance, ion transfer at the interphase remains poorly understood with little guidance on manipulating its structure for improved performance. Building on previous work in the Rodríguez-López group with Hg probes, I developed localized, in situ methods for measuring ion flux at operating battery electrodes. Using a Hg disc-well (HgDW), I show the potentials at which graphite edge plane and graphene electrodes consume Li+ to form and stabilize their SEI. Further, the probe revealed transitions between SEI formation and (de)intercalation. I modeled the HgDW response with COMSOL to extract ion intercalation kinetics at each applied potential, thus providing quantification of the localized Li+ transfer rate. In a follow up study, I introduced a pulsed methodology to expand our technique for mapping ionic flux across a functioning electrode and coordinate the response to electron transfer at the same locations. The techniques for understanding charge transfer at Li+ batteries were further used to solve longstanding challenges in more traditional systems, such as Pb-acid batteries. Looking toward future applications, I present efforts to develop a robust HgDW probe based on a 300 nm Pt electrode for evaluating nanoscale battery materials and discuss applications of SECM toward understanding interphase formation in cathode materials. My projects have expanded on others’ efforts to push Hg probes and SECM forward as a powerful analytical platform for evaluating interface chemistry in battery systems. This work seeds opportunity for wide access to key information for improving current and next generation technologies.
Issue Date:2020-07-14
Rights Information:Copyright 2020 Zachary Gossage
Date Available in IDEALS:2021-03-05
Date Deposited:2020-08

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