Floras, Claire2025-04-172025-04-172025-04-15https://hdl.handle.net/10222/85012The work presented in this thesis aims to advance the development of long-lived Li-ion cells for commercial applications by both extending and accurately projecting battery lifetimes. Sets of Li[Ni0.6Mn0.4Co0.0]O2, Li[Ni0.6Mn0.35Co0.05]O2, Li[Ni0.6Mn0.3Co0.1]O2, and LiFePO4 cylindrical 18650 cells were designed and constructed in order to have as few degradation modes as possible. Electrochemical cycling at varied rates, post-cycling analyses of electrolyte and electrode conditions, and the use of Ultra-High Precision Coulometry metrics all contributed to understanding degradation processes. With this insight into degradation, and by conducting cycling over a wide range of temperatures between 20 and 100°C, it was possible to use high temperature cells to make lifetime predictions which are, and will continue to be, verified with low temperature cycling results. Some cells developed completed continuous charge-discharge cycling for more than 16 months (1900 cycles) at 85°C and are still above 80% of their original capacity.enlithium-ion battery