a Chemistry Department Thesis Defense ft. David Hoang (Ji Group)

Abstract:

The current power production system heavily depends on fossil fuels to power large turbines generating electricity for local grids. This, however, is not a sustainable source of energy due to diminishing reserves of fossil fuels and the disastrous impacts fossil fuels have on the environment. Thus, we must turn towards more renewable, sustainable, and green energy sources such as solar, hydro, and wind. Unfortunately, these energy sources are intermittent, producing energy only when the sun is shining, or the wind is blowing. Therefore, storing this energy for use during peak times, such as evenings when energy consumption is highest, is crucial for the widespread adoption of these renewable energy sources.

There are many different potential solutions to this issue, with many looking towards the idea of equipping the electrochemical energy storage systems, i.e., batteries, that can efficiently supply or store electricity when there is a mismatch between the time of electricity generation and the time of demand. The current issue with this solution, is that most current battery technologies in use today still face significant challenges related to cost, safety, toxicity, and resource availability, especially when scaling up the size of the battery facilities to one that would be able to provide sufficient electricity to a city. Therefore, to meet the growing demand, it is crucial to continuously develop new battery chemistries that utilize inexpensive, safe, and environmentally abundant materials.

 In this dissertation, the primary objective is to investigate new mechanisms and additives to make aqueous zinc metal batteries more practical and a step towards utilization in grid storage systems. Specifically, we explore the use of vanillin, ethylene carbonate, and vinylene carbonate in water-in-salt electrolytes to suppress dendrites, hydrogen evolution reaction, and improve the Coulombic efficiency of the zinc metal anode.

In the first study we are adding a small concentration of vanillin, 5 mg/mLwater, to 30 m ZnCl2 which significantly improves the reversibility of the Zn metal anode. This improvement is achieved by eliminating dendrites, reducing Hammett acidity, and forming an effective solid electrolyte interphase (SEI).

The second study focuses on optimizing the concentration of ethylene carbonate (EC) and vinylene carbonate (VC) in 30 m ZnCl2 to improve the reversibility of the Zn metal anode. This is done by a cathodic reduction of VC and EC onto the surface of the Zn metal anode which eliminates dendrites, suppresses the hydrogen evolution reaction, and lowers the resistance between the Zn metal surface and the SEI.