UC Riverside

Development of next-generation lithium-ion battery (LIB) systems is crucial not only to keep pace with the advancements in portable electronics applications and electric/hybrid vehicles, but also to decrease the consumption of fossil fuel and reduce its adverse effects on the climate towards a more sustainable society. Traditional LIBs with graphite anode and lithium metal oxide cathodes have reached their limits to meet the demands of fast developments in applications that require high storage capacities and energy densities. Herein, this dissertation explored new methods of electrode synthesis by using abundant and environmentally friendly elements such as sulfur and silicon for the development of next-generation LIB electrodes. Modification of traditional electrode materials to increase the capacity and electrochemical performance was also studied. Presented methods include the synthesis of sulfur electrodes using different active material loadings and various carbon types, and the application of thin film coatings and carbonized interlayers for lithium-sulfur cells. TiO2 coated sulfur electrodes prepared by magnetron sputtering technique showed promise by delivering a reversible use of long-chain polysulfides, representing a more efficient active material utilization compared to the reference sulfur electrodes. Consequently, 40% capacity improvement was achieved at 0.1 C rate for the TiO2 coated porous carbon-composite electrode. Detailed capacity fade analysis in lithium-sulfur cells revealed that the electrolyte-to-sulfur ratio has a big influence on the battery performance, and that an optimal amount of electrolyte is needed to achieve good electrochemical performance. Furthermore, the effect of the conditioning method on a sulfur-silicon full cell was studied in order to maximize the battery performance. In addition, surface modification of LiCoO2 cathode was introduced to increase the capacity of the electrode for high-voltage operations. Coating the electrode surface delivered an improved Coulombic efficiency, indicating suppressed parasitic reactions at the electrode-electrolyte interface. Analytical materials and electrochemical characterization of the battery electrodes were performed using a variety of techniques such as TGA, SEM, EDS, TEM, Raman, EIS, CV and GITT. Challenges and possible solutions related with various electrode chemistries were presented.