Date of Award
2024
Degree Type
Dissertation
Degree Name
Doctor of Philosophy in Chemistry
Department
Chemistry
First Advisor
Brett L. Lucht
Abstract
Lithium-ion batteries have become essential to modern day life as people are increasingly reliant on mobile technologies. One rapidly developing application is the use of lithium-ion batteries to make electric vehicles (EV) more feasible for consumers. However, in order to compete with the driving range of the commonly used combustible engine, batteries used in EV applications need to be further improved and optimized to give higher energy densities and increased capacity retention.
One way to improve energy density is to switch the anode material from the relatively low energy dense graphite to the much higher capacity silicon; however, the silicon-lithium alloying process involves severe volume expansion resulting in significant particle pulverization, loss of electrical conductivity, and fracturing of the solid-electrolyte interphase (SEI) which all cause significant capacity fade over extended cycling. Therefore, utilizing different additives like lithium difluoro(oxalato)borate (LiDFOB) and lithium nitrate in the electrolyte to preferentially reduce on the surface and form beneficial SEI products can help improve the capacity retention of silicon-containing anodes for longer periods of time and increase the overall energy density of the cell. In this work, galvanostatic cycling was performed to characterize the electrochemical performance of half and full cells consisting of silicon-containing anodes and NCM523 cathodes. The SEIs formed as a result were characterized using X-ray Photoelectron Spectroscopy (XPS), Infrared spectroscopy (IR), and Scanning Electron Microscopy (SEM). Chapters 2 and 3 investigate the use of a novel electrolyte containing LiDFOB as the salt and triethyl phosphate-solubilized LiNO3 to improve capacity retention and performance of silicon-containing anodes in half cells and full cells. This novel electrolyte was then further adapted in Chapter 4 to utilize more common organic solvents like dimethylacetamide, dimethylformamide, and dimethylsulfoxide to dissolve LiNO3 to even higher concentrations with the resulting cell performance and SEI examined in detail.
Energy density can also be improved by increasing the operating voltage of the battery; however, significant capacity loss is typically observed when cycling cathodes in full cells to high potentials and at high temperatures. This occurs due to transition metal dissolution from the cathode, ion migration through the electrolyte, and deposition on the SEI on the anode. While much research has been done to track the oxidation state of the transition metal ion in the cathode or deposited on the anode, there have been mixed reports on the chemical state of the transition metal ions dissolved in the electrolyte. Therefore, in Chapter 5, X-ray absorption spectroscopy (XAS) was performed on electrolytes extracted from full cells built with four different cathode materials and cycled at standard and high voltages to determine the oxidation state of Mn and Ni in solution. The concentration of deposited metal ions on the anode surface was determined using inductively coupled plasma-mass spectrometry (ICP-MS).
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.
Recommended Citation
Rynearson, Leah, "INVESTIGATION OF ELECTROLYTES FOR SILICON-CONTAINING ANODES AND ON HIGH VOLTAGE CATHODES IN LITHIUM-ION BATTERIES" (2024). Open Access Dissertations. Paper 1652.
https://digitalcommons.uri.edu/oa_diss/1652