UC Riverside

The demand for rechargeable batteries has rapidly grown due to the increasing gap between limit amount of fossil fuel and rapid growth of energy consumption. Rechargeable battery which known as electrochemical energy storage device was a major focus for academic and industrial research. Sulfur (S) has been regarded as one of the most promising candidates for high specific energy cathode materials due to its high abundance, low toxicity, high theoretical specific capacity, and low density. Owing to the high theoretical specific capacity and low redox potential, lithium (Li) is the most promising anode material which raises most research attention. Researcher also interested in magnesium (Mg) metal anode due to its high natural abundance, good safety and high theoretical volumetric energy. The cathode electrolyte interfacial process in Li-S batteries under lean electrolyte condition was studied with the most widely used electrolyte The interfacial processes on the sulfur cathode under the lean electrolyte condition was probed using operando electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT). The operando EIS reveals a significant and rapid increase in charge transfer resistance during the transition from high-order polysulfides to low-order ones under a low E/S ratio, which is induced by a kinetic bottleneck at the interphase due to Li-ion mass transfer limitation. The GITT results confirm the kinetic bottleneck by revealing a large discharge overpotential during the transition phase. The understanding of Li-S reactions under lean electrolyte condition is then applied to a carboranyl ionic liquid electrolyte system. Such novel ionic electrolyte was first synthesized and reported in this paper with good chemically and electrochemically stability with Li anode and S cathode as well as polysulfide. High specific energy Li-S battery can be achieved via sparingly dissolving pathway during discharging in carboranyl ionic liquid electrolyte. Mg-S batteries in magnesium monocarborane (Mg(CB11H12)2) in tetraglyme (G4) electrolyte was first studied by our group. Understanding of cathode electrolyte interface reveal that sulfur is unstable under oxidation in the Mg(CB11H12)2 electrolyte. With the X-ray Photoelectron Spectroscopy (XPS) data of pristine sulfur cathode after charging, we propose a novel explanation of the overcharge behavior for Mg-S