(Invited) Interfacial Engineering of Energy Conversion and Storage Materials Using Atomic Layer Deposition
Authors: Dasgupta Neil P. 
Published: February 2020

Nanoscale materials offer several unique opportunities for applications in energy conversion and storage, due to their high surface-to-volume ratios, short transport distances, mechanical strain relaxation, and the ability to tune their material properties. However, despite these potential advantages, increasing surface and interfacial area dramatically can also present challenges. For example, in semiconductor devices such as photovoltaics and photoelectrochemical cells, an increase in surface recombination of excited charge carriers can offset the benefits of nanostructuring. Similarly, in batteries, undesirable side reactions at electrode-electrolyte interfaces, such as electrolyte decomposition and surface passivation, can lead to degradation of performance and limit lifetime. Therefore, in electrochemical engineering of nanostructured electrode materials, we desire the ability to “turn on” the desirable properties, and “turn off” the deleterious effects of moving to the nanoscale.
To improve our ability to precisely control surface and interfacial phenomena in nanoscale materials, we require new methods to control surface chemistry and structure with atomic precision, without introducing inhomogeneities that may arise from diffusion limits during surface modification. One technique that simultaneously accomplishes both of these traits is Atomic Layer Deposition (ALD). In the past two decades, there has been an explosion of research in ALD for interfacial modification of nanostructured materials for energy conversion and storage. However, much of this work has been empirical in nature, and there is often a fundamental lack of understanding of the coupled surface chemistry, structure, and performance relationships at the atomic scale. To overcome this limitation, we must complement ALD interfacial modification with atomically-precise characterization methods. We must also pay attention to not only the initial and final surface properties, but develop novel in situ/operando methods to quantitatively evaluate the evolution of surface properties during dynamic device operation.
To bridge this gap, our research group focuses on using ALD not only as a tool for surface coating, but as a platform for fundamental research on the coupled surface chemical, electrochemical, structural, and mechanical evolution that occurs during operation. In this talk, I will present examples in our work on atomically-precise control of electrode-electrolyte interfaces in rechargeable batteries and photoelectrochemical cells. Examples will include development of superionic lithium solid electrolytes by ALD that enable conformal coating of 3-D battery architectures and interfacial modification of all-solid-state batteries1, control of lithium metal anode electrodeposition and dissolution2, and fabrication of 3-D hierarchical photoelectrodes for artificial photosynthesis and water purification3,4. Common to each of these examples is the ability to decouple beneficial and detrimental processes that occur at the interface, and perform materials design optimization at the atomic scale. Beyond purely performance metrics, and emphasis will be placed on gaining new fundamental mechanistic insight into the origins of improved surface behavior, which provides a perspective on the opportunities that surface and interfacial engineering at the atomic scale provides.

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