Organic electrodes and solid-state electrolytes for lithium electrochemical energy storage

Abstract

Viable electrical energy storage is essential for the development of sustainable energy technologies, such as renewable power and electric vehicles. Electrochemical energy storage devices are promising candidates for these applications, and lithium-ion batteries are the leading available technology. However, the current cost and performance of these devices limit their widespread adoption. In this thesis, we develop materials and design guidelines for positive electrodes and solid-state electrolytes to address these challenges. The positive electrode is one of the main limitations to improving both the capacity and cost of lithium-ion batteries. Organic molecules represent a class of materials, which if selected correctly, can address these issues. The electrochemical properties of various polycyclic aromatic hydrocarbons (PAHs), which are organic molecules produced in significant quantities as industrial waste products, were investigated for use as positive electrodes. By introducing PAHs within a functionalized few-walled carbon nanotube (FWNT) matrix, we developed high-energy and high-power positive electrodes. The redox potential and capacity of various PAHs were correlated with their chemical and electronic structures, and their interaction with the functionalized FWNT matrix. Another challenge limiting the adoption of lithium-ion batteries is the flammability and instability of the organic liquid electrolyte, which increases the risk of dangerous battery failures and limits the use of higher energy-density electrodes. One promising solution is to replace the organic liquid electrolyte with a solid-state lithium-ion conductor. However, the ionic conductivity of solid-state electrolytes are typically several orders of magnitude lower than organic liquid electrolytes. Using lattice dynamics, we developed a framework to understand the migration of lithium through crystalline solid-state electrolytes. The understanding of the use of organic materials in positive electrodes and solid-state lithium-ion conductors as electrolytes provides insight for the design of next-generation electrochemical energy storage solutions.