Guiding Electrolyte Design with Electrochemical Microscopy
Researchers aim to develop batteries with improved safety and performance, but these features are inherently limited by the properties of the electrolyte in the battery. Our group is exploring ionic liquids as safer electrolytes for batteries, but there are many open questions about how the transport of battery-relevant ion chemistries, such as Li+, behaves in materials where every species is an ion. At the heart of this research direction is a simple question: “What can we learn from what we can see?”
To provide insight into existing knowledge gaps, we use a variety of optical microscopy techniques to directly visualize the motion of ions inside of an electrolyte using dyes that respond to local changes in coordination. This new technique provides us with a complete picture of ion mobility at any composition of redox chemistry in an electrolyte. By coupling this method with additional techniques, such as Raman spectroscopy, electrochemical impedance spectroscopy, diffusion ordered spectroscopy (DOSY) nuclear magnetic resonance measurements, and phase characterization, we can directly link changes in ion coordination to ion transport dynamics. This approach provides unique insights into what kinds of electrolyte interactions lead to improved battery performance. Importantly, these techniques also translate beyond Li-ion to multivalent electrolyte chemistries, which are being considered as safe, energy-dense alternatives to Li-ion or Li-metal batteries.
Additionally, we make use of microscopy approaches for measurement of physical properties of electrolytes in inert environments required for battery chemistries. Our lab is also expanding to include operando measurements of electrochemical devices to study the influence of electrolyte properties on the electrode morphology and performance of batteries. Our areas of expertise include: optical microscopy (fluorescence/darkfield/brightfield), electrochemical impedance spectroscopy, computational programming & image analysis, Raman spectroscopy, nanofabrication, microrheology, colloid science, free space optics, and phase characterization,
Elucidating the effect of ionic correlation on electrolyte properties in the bulk and at interfaces
As use of electricity becomes more widespread than ever, there is a critical demand for innovations in energy storage technology. Lithium-ion batteries have been developed as highly efficient solutions to address this problem. However, these batteries typically consist of electrolytes containing dangerous, flammable materials such as organic carbonates. Salts have emerged as promising candidates for developing safe and efficient solid- and liquid-state electrolytes. However, accurate predictions of concentrated salt solutions are near impossible to make. To specifically tune electrolytes for energy storage applications, the structural assembly of ions must be thoroughly investigated. We aim to determine what factors cause deviations from current theory.
We employ a variety of techniques to investigate the behavior of salts. Some tools more unique to our lab are electrochemical impedance spectroscopy (EIS) and surfaces forces apparatus (SFA). EIS analyzes ionic assembly at charged surfaces and the SFA probes intermolecular forces at electrode-electrolyte interface on the nano scale. These tools allow us to measure ion-ion interactions that few others are capable of quantifying.
We are currently analyzing the effect metal ions have on salt structuring. Whether for insight into charge screening and double layer formation at the electrode-electrolyte interface or for ion coordination and mobility in the bulk salt, these studies can guide electrolyte design for energy storage devices. While our work does not focus on building devices or providing new complex theories, we show the world how small changes can make a big difference. Hopefully, some of these small changes can lead to a safer, greener tomorrow.
Developing a fundamental understanding of double layer formation and its effects on electrocatalysis.
Electrocatalysis, when paired with sustainable energy, has the potential to drastically reduce the carbon footprint of many important chemical processes. However, there remains much to be investigated before industrial-scale deployment of electrocatalytic processes, such as electrochemical CO2 reduction, occurs. A key gap in understanding electric double layers and its role in electrochemical reactions remains. Electric double layers form when an applied potential to an electrode drives the migration of ions to the electrode-electrolyte interface in order to screen the potential. This collective assembly concentrates ions at the interface and forms the environment in which these electrocatalytic reactions proceed. However, the formation of double layers and how ions interact with each other in these dynamic and complex double layers remains difficult to accurately model using existing electrolyte theory. We are studying electrochemical double layers for electrocatalysis using a suite of tools and materials to better understand the driving principles behind the effects of double layer formation on key reactions. Using ionic liquids for CO2 electroreduction, we have found that just by changing the concentration of an ionic liquid, we can drastically change the double layer thickness and the resulting reaction rate. This provides intriguing hints at the powerful nature of the double layer in changing how a reaction proceeds. With a combination of traditional electrochemical, product characterization, and spectroscopic techniques, we aim to ultimately unravel how different chemical and physical properties of electrolyte provide multidimensional ways to modulate double layer and to enhance a wide range of catalytic reactions meaningful to our community.
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