(6gk) Beyond Lithium Aqueous Electrochemical Energy Storage

Daniel S. Charles

Department of Chemical Engineering, University of New Hampshire, Durham, NH

Research Interests:

Electrochemical energy storage has become prevalent in daily life for their use in mobile electronics, and electric vehicles. More recently, the need for large scale stationary energy storage to allow for the integration of clean and renewable alternative energy sources to the electric grid has arisen. The shift towards clean energy utilizing alternative energy sources, such as wind and solar energy, will reduce CO₂ emissions and the dependence on fossil fuels. A large-scale energy storage solution is required for load shifting and frequency regulation due to the inconsistent nature of the electrical energy generation from renewable sources. In this regard, aqueous electrochemical energy storage is a promising solution to these problems. Aqueous electrochemical energy storage devices using beyond Li-ions as charge carriers (e.g. Na, K, Mg, Zn) offer an attractive solution to this problem because of their superior safety, lower cost and excellent transport properties compared to non-aqueous devices. However, the energy density and cycle life of aqueous electrochemical energy storage devices are currently insufficient. There are two approaches for improving the energy density of aqueous electrochemical energy storage devices: one is to increase the capacity of the electrode material and the other is to increase the operating voltage. The operating voltage of aqueous electrochemical energy storage devices is limited to 1.23 V by the thermodynamically stable potential window of water, beyond which, the gas evolution reactions occur. My research has focused on gaining a fundamental understanding of and making iterative improvements to electrode materials for aqueous electrochemical energy storage to support implementation of this technology as a large-scale energy storage solution.

My research experience in energy storage has covered the entire scope from synthesis of nanomaterials to fabricating prototype pouch cells. My doctoral and postdoctoral work with Professor Xiaowei Teng at the University of Hampshire explored the structure-function relationship of nanoscale and/or disordered metal oxide electrode materials for aqueous electrochemical energy storage. We are particularly interested in the interaction of water at the interphase and within the structure of the electrode materials. My work on these materials included detailed electrochemical and structural characterization including X-ray and Neutron total scattering measurements and analysis of the Atomic Pair Distribution Function (PDF). To study the structure-function relationship, I designed an electrochemical cell for in situ synchrotron X-ray diffraction and total scattering measurements to study the structural evolution of the electrode with potential during cycling.

Two research highlights from my time at the University of New Hampshire were published in Nature Communications. The first, we reported the formation of layered Mn5O8 pseudocapacitor electrode material with a well-ordered hydroxylated interphase. This unique interphase allowed for a 3.0 V kinetically stable potential window in an aqueous sodium sulfate electrolyte by suppressing the gas evolution reactions. Secondly, we reported on the water induced structural rearrangements of the vanadium-oxygen octahedra which enhanced the stability of the layered highly disordered potassium-intercalated vanadium oxide nanosheets. The promotional effects of structural water lead to much-improved K-ion storage capacity (183 mAh g^-1 in half cell at a scan rate of 5 mV s^-1, corresponding to 0.89 charge transfer per vanadium) and stability of (62.5 mAh g-1 in full cells after 5,000 cycles at 10 C) of the electrode material.

Teaching Interests:

Teaching is a part of being a faculty member that I am looking forward too. As a postdoc, I have thoroughly enjoyed mentoring incoming Ph.D. students that have joined the group. Mentorship is something that I view as very valuable, as my mentors throughout my undergraduate and graduate studies have been integral to my success thus far in my career. I would strive to pass that along and cultivate interpersonal relationships with students. During my time at the University of New Hampshire, I was funded by a Research Assistantship and a Dissertation Year Fellowship. Although I was not assigned a teaching assistant position, I did have the pleasure of covering lectures for my advisor (Kinetics, Nuclear Engineering, and Electrochemical Methods), as well as help teach the laboratory section of the Electrochemical Methods course. I was fortunate to get some teaching experience as an undergraduate student at Rochester Institute of Technology. I served as a teaching assistant for the Math Techniques for Chemical Engineers course in the Fall of 2011. The following year I was a teaching assistant for two courses in the Fall of 2012, Math Techniques for Chemical Engineers and Reaction Engineering I. Both my graduate and undergraduate degrees are in chemical engineering, I am confident in teaching any of the core curricula. In addition, I would be able to teach technical electives in the field of material science and electrochemistry.

Highlighted Publications:

Charles, D.S., Feygenson, M., Page, K., Neuefeind, J., Teng, X.W. “Structural Water Engaged Disordered Vanadium Oxide Nanosheets for High Capacity Aqueous K-ion Storage”. Nature Communications, 2017, 7, 15520

Shan, X., Charles, D.S., Lei, Y., Qiao, R., Wang, G., Yang, W., Feygenson, M., Su, D., Xu, W., Teng, X.W. “Bivalence Mn5O8 with hydroxylated interphase for high-voltage aqueous sodium-ion storage”. Nature Communications, 2016, 7, 13370 (equal contribution first author)