Collaborative Research: Elucidating Correlations Between Solvation Structure and Electrochemical Behavior of Water-in-Salt Electrolytes for Highly Reversible Zinc Metal Anode

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Renewable energy from wind energy and solar power offers a solution to reducing greenhouse gas emissions and their impact on climate change. Unfortunately, the power that can be generated from these renewable sources is intermittent and typically asynchronous with electrical energy demand. Thus, large-scale energy storage is indispensable for a sustainable economy with reduced reliance on fossil fuels. Representing a promising solution to this energy storage need, aqueous zinc (Zn) metal batteries can store energy at a low cost, with low environmental footprint and high intrinsic safety. However, Zn metal batteries suffer from short cycle life, primarily due to corrosion of the Zn metal anode by water. This corrosion drastically curtails the cycle life of Zn metal batteries and causes a safety concern due to the generation of explosive hydrogen gas—two challenges that require outside-the-box solutions. The recent emergence of highly concentrated “water-in-salt” electrolytes offers a unique opportunity to re-define the stability between the Zn metal anode and the aqueous electrolyte. This project seeks to transform the cyclic stability and increase safe operation of aqueous Zn metal batteries. If successful, this will mark a significant breakthrough for energy storage technologies in the United States. For educational impacts, the investigators will leverage institutional programs their universities to increase the participation of community college students and high school students in summer research experiences. The training of graduate and undergraduate students will feed the workforce need of the next-generation energy sector. The project will elucidate the water stability properties in extremely concentrated solutions by integrating research activities in materials electrochemistry, femtosecond Raman spectroscopy, and ab initio computation. These complementary methods are highly synergistic, providing insights from different vantage points that when integrated can enable deep understanding. In the concentrated electrolytes of study there are few water molecules per solvated ion; therefore, the solvation sheaths are often thinner or incomplete compared to standard dilute solutions. Such solvation structures significantly alter the properties of the solvated ions and the dynamic water molecules as a solvent. Preliminary results have revealed that water molecules exhibit unusually high electrochemical stability against hydrogen evolution and display an intriguing blueshift of vibrational frequencies in stimulated Raman studies. First-principles calculations indicate that there exist peculiar properties of water molecules to be explored in these concentrated solutions. This project will generate an in-depth understanding of the correlation between solvation structures of the concentrated electrolytes and the corresponding stability in contact with the Zn metal anode. The values of such knowledge will transcend different disciplines of physical sciences and engineering and impact a broad range of STEM learners and practitioners in academic and industrial settings.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.