UC San Diego

In realization of carbon neutral and sustainable society, it is an imperative duty to develop giant energy storage systems for solar/wind power plants and for electrified automotive vehicles. Rechargeable lithium (Li) metal battery, once abandoned three decades ago due to the safety issues, has been gaining increasing attention from the battery scientists again to surpass the energy density of the contemporary Li-ion cells. One approach to stabilize the interface between Li metal and organic liquid electrolytes is to passivate the Li surface by protective coatings, which can reduce permeation rate of the liquid electrolyte and improve the morphology of electroplated Li deposits. In Chapter 1, recent progress of the protective coatings is summarized, and the material properties are categorized according to the proposed protection mechanisms. Ion conduction through the inorganic coatings is determined by the intrinsic ion conductivity of the material itself and independent from the liquid electrolytes. In contrast, the ion conductivity of polymer coatings is dependent on the swelling behavior in the liquid electrolytes. However, there is a dearth of understanding on factors controlling the swelling ratio of polymer coatings and the influence on ion-transport properties. To answer these questions, we carry out quantitative analysis on the effect of solvent polarity and cross-link density to the ion-transport and rheological properties of a polymer coating in Chapter 2. In Chapter 3, we develop a gel polymer electrolyte for Li metal battery, which can stabilize the surface of Li metal by in-situ formation of robust passivation layer. The electrolyte also possesses a safety feature which can shut-down the battery cycling under the condition of abusive thermal runaway. In addition to the energy storage systems, we also study an electrochemical method to recover energy from waste heat resources. In Chapter 4, we report the method of using vaporization of a volatile redox couple to achieve the highest conversion ratio of voltage (Seebeck coefficient) generated from the temperature gradient. This dissertation contributes to the development of high-density energy storage system and waste heat recovery by leveraging the multifunctional electrochemistry and through the molecular designs of electrolyte materials.