ATOMISTIC MODELING OF THE STRUCTURE AND CHARGE TRANSPORT CHARACTERISTICS OF ELECTROLYTES AND INTERFACES

Aniruddha Dive

Global warming concerns with burning fossil fuels and rising energy demands have intensified the need for clean energy. The clean energy generated from renewable energy sources is often intermittent and therefore requires load leveling devices for efficient utilization. Batteries, with varied applications from load leveling devices to electric vehicles, are one of the most sought-after technologies for efficient use of clean energy. Developing safe, durable and high energy density batteries is therefore a critically important aspect of addressing the energy challenge. Ultimately, the materials employed in the electrodes and electrolyte and their mutual electrochemical compatibility determines the battery performance. This dissertation focuses on battery electrolytes and electrode-electrolyte interfacial interactions. The design space for sets of potential materials for battery components is extremely large and therefore experimental fabrication and testing of all possible materials, if possible, is an expensive and time-consuming approach. Motivated by this challenge, this dissertation explores atomistic modeling as a tool to design novel electrolyte materials for batteries. Atomistic modeling techniques such as classical molecular dynamics (MD) and ab initio MD were employed to investigate the local structure of various electrolytes, such as ionic liquids and amorphous sulfide glasses, and correlate the structure to the ionic conductivity of these electrolytes. The dissertation reports impact of temperature on diffusivity of ions in mppy+ TFSI- ionic liquid electrolytes. The dissertation further investigates the impact of Na2S content on the local structure and ionic conductivity in sulfide glasses. The results from above studies help develop suitable guidelines for the experimental design of materials for novel electrolytes. The theoretical calculations were further extended to gain significant insights into the electrode-electrolyte interactions that cannot be easily characterized experimentally. The results from modeling of these interfacial interactions provide a fundamental understanding of some of the factors crucial towards ensuring formation of stable interfaces while designing novel electrodes and electrolytes for batteries. With this motivation, the dissertation reports polysulfide physisorption characteristics of different functional groups on graphene oxide (GO). The results provide guidelines for designing GO structures as novel cathode support structures for lithium-sulfur batteries.

ATOMISTIC MODELING OF THE STRUCTURE AND CHARGE TRANSPORT CHARACTERISTICS OF ELECTROLYTES AND INTERFACES

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