Date of Award
2024
Document Type
Thesis
Degree Name
Master of Science in Engineering (MSE)
Department
Mechanical and Aerospace Engineering
Committee Chair
Guangsheng Zhang
Committee Member
George Nelson
Committee Member
Phillip Ligrani
Research Advisor
Guangsheng Zhang
Subject(s)
Lithium ion batteries, Thermal analysis, Energy dissipation
Abstract
Degradation is a big challenge for lithium-ion (Li-ion) batteries in various applications, especially at extreme temperatures. Low and high temperature cycling can cause lithium plating and increased solid-electrolyte interphase (SEI) growth, respectively. However, a previous work in our lab showed that pre-cycling Li-ion cells at low temperature reduced degradation during high temperature cycling. The previous work was based on small single-layer cells. This thesis intends to confirm this phenomenon for larger multi-layer cells and to further understanding of the mechanisms behind the reduced degradation for the low-temperature pre-cycled cells. Multi-layer commercial pouch cells were pre-cycled at 1C at low temperature before cycling at high temperature. Improved capacity retention was observed for these pre-cycled cells, confirming the previous observation. However, compression of the cells was necessary for the observation. Without compression, the pre-cycled cells would swell after shifting to high temperature cycling and degraded quicker than baseline cells cycled only at high temperature. Pre-cycling with a lower C-rate (C/5) at low temperature, which has lower risk of lithium plating than the 1C pre-cycled cells, showed similar degradation to the baseline cells. This implied that lithium plating from 1C pre-cycling at low temperature was responsible for the reduced high temperature degradation. Further cycling of baseline cells and 1C pre-cycled cells with a low discharge rate (C/20) showed that the significant capacity loss of the baseline cells was primarily due to power fade. A baseline cell, a 1C pre-cycled cell, and a C/5 pre-cycled cell were disassembled and examined using optical microscopy and SEM (scanning electron microscopy). It was observed that the baseline cell and the C/5 pre-cycled cell had areas of uneven deposition on the anode. The 1C pre-cycled cell, however, had a more even deposition layer across the entire surface of the anode. It is suspected that this layer offers protection against degradation at high temperatures. Additional investigation is needed for further understanding of this deposition layer.
Recommended Citation
Carter, Muriel, "The effects of low-temperature pre-cycling on high-temperature degradation of lithium-ion cells" (2024). Theses. 678.
https://louis.uah.edu/uah-theses/678