ELECTROCHEMICAL PROTECTION OF LITHIUM METAL ANODE IN LITHIUM-SULFUR BATTERIES AND BEYOND
Lee, Sang Bok
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With the growing demand of advanced energy storage devices that have high energy density and high power density to power electric vehicles and electrical grid, scientists and engineers are exploring technologies beyond conventional Li-ion batteries which have transformed the industry in the past thirty years. Li-S batteries have much higher energy density than Li-ion batteries and are gaining momentum. However, the intrinsic issues of Li-S batteries require a comprehensive systematic study of the protection of Li metal anodes to put them into practical applications. In the first study of this dissertation, we investigated using conventional electrolyte of Li-S batteries that includes 1,3-dioxolane to electrochemically pretreat Li metal anodes. We concluded that the electrochemical pretreatment of Li metal anodes generated an organic-inorganic artificial solid electrolyte interface (ASEI) layer that greatly enhanced the battery performance of the Li-S batteries. The properties of this ASEI can be tuned by manipulating the current density and cycle number of the electrochemical pretreatment. In the second study, we studied the comprehensive development and surface protection of Li10GeP2S12 (LGPS) material as solid-state electrolyte, which has ionic conductivity comparable to liquid electrolytes, potentially for solid-state Li-S batteries. Lithium phosphorus oxynitride (LiPON) was coated onto LGPS pellets by atomic layer deposition (ALD). It demonstrated great compatibility with LGPS and extends the electrochemical stability window. The third study explored the potential of transferring this electrochemical pretreatment method to the protection of other metal anodes, particularly Mg. The study discovered the surprising catalytic capability of Mg2+ in the polymerization of solvent 1,3-dioxolane (DOL). A layer with poly-DOL component was also found to grow on the surface of Mg metal anodes as a result of the electrochemical pretreatment, and the overpotential of Mg-Mg symmetric cells cycling dropped with the growth of the layer. Future studies are required to test the effectiveness of this method in Mg batteries. Overall, these studies can help to understand the surface chemistry of the electrochemically pretreated Li metal anodes, provide guidelines on the improvement of Li-S batteries and contribute to the development of solid-state Li-S batteries and multivalent metal anode batteries.