Date of Award
Doctor of Philosophy (PhD)
Mechanical and Aerospace Engineering
Engineering | Materials Science and Engineering
Majority of the energy in current world is produced and consumed by burning non-renewable fossil fuel sources such as coal, oil, and natural gas, etc. It is taking a toll on our planet earth due to high rates of carbon and greenhouse emissions. This calls for an urgent need of energy transition from conventional fossil fuel to renewable and sustainable energy sources such as solar, wind, geothermal, etc. However, harnessing energy from such renewables are constrained by their intermittency and non-dispatchability, requiring some sort of efficient energy storage systems that can provide continuous energy supply. Batteries in general are considered as a reliable and conventional means of energy storage as they are used in all forms of portable devices and smart electronics. However, batteries with higher energy densities that can safely store energy for long duration and provide uninterrupted energy supply enabling high penetration of renewables in energy usage are still being pursued. Currently commercialized lithium-ion batteries (LIBs) which uses graphite anode intercalation chemistry with energy density of 220 Wh kg-1 are approaching their ceiling of energy density defined as 300 Wh kg-1. So, it is imperative to develop new battery chemistries that can provide even higher energy and power densities to fulfill the ever-increasing energy demand. Lithium metal anodes (LMAs) shows ultrahigh specific capacity of 3,860 mAh g-1, low redox potential (-3.040 V v/s standard hydrogen electrode) and are considered an ideal replacement to conventional graphitic anode for realizing batteries with energy density ~500 Wh kg-1 and more. However, the violently reactive nature of lithium (Li) which incurs severe side reactions when they are used as LMAs results in electrolyte decomposition forming thick insulating solid electrolyte interphase (SEI) layer, and growth of fibrous dendritic structure on its surface. Use of electrolyte additives is one of the effective strategies to form in-situ protective SEI layer that can stabilize LMA against severe side reaction and suppress dendrite growth on its surface. In our work, we reported that at very low concentration optimal amount (3 mM) of novel electrolyte additive, gadolinium nitrate (Gd(NO3)3) in LiTFSI- LiNO3 ether solvent based electrolyte promotes plating/stripping of Li in nodular morphology, significantly suppressing dendritic and dead Li growth and enhancing cycle life, and stability of Li metal batteries. The as formed SEI layer composed with additive compounds ensures fast Li ion diffusion and suppression of Li dendrite growth by tuning the SEI composition and facilitating plating/stripping of Li in nodular morphology. Similarly, Solid-state lithium batteries are another battery technology which are generally considered as the next-generation technology benefitting from inherent nonflammable solid electrolytes that promotes safe harnessing of high-capacity Li metal. Among various solid electrolyte ionic conductors, cubic garnet-type Li7La3Zr2O12 (LLZO) ceramics hold superiority due to their high room temperature ionic conductivity (10-3 to 10-4 S cm-1) and good chemical stability against Li metal. However, commercialization of garnet electrolyte based solid-state batteries has been constrained by poor Li wetting behavior of the garnet surface resulting in interfacial mismatch, uneven current distribution, and high interfacial impedance. In our next work, we demonstrate a facile and effective process to significantly reduce the interfacial impedance by modifying the surface of Al-LLZO garnet-type solid electrolyte with a thin layer of silicon nitride (Si3N4). This interfacial layer provides an intimate chemical and physical contact with Li metal as it shows lithiophilic property and forms an intermediate Li metal alloy at the interface. The interface modified Li/garnet cells exhibited low overpotential and long-term stable plating/stripping cycles at room temperature compared to bare garnet. Thus, this dissertation work provides a significant advancement toward additive and surface engineering techniques for enhancing the overall performance of two different state of the art Li metal battery systems.
Baniya, Abiral, "ADVANCED LITHIUM METAL BATTERIES: FUNCTIONAL ELECTROLYTE ADDITIVE AND LITHIUM METAL/SOLID-STATE ELECTROLYTE INTERFACE ENGINEERING" (2022). Dissertations - ALL. 1628.
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