Date of Award


Document Type


Degree Name

Master of Science in Engineering (MSE)


Mechanical and Aerospace Engineering

Committee Chair

Guangsheng Zhang

Committee Member

George Nelson

Committee Member

D. Keith Hollingsworth


Lithium ion batteries--Technology, Thermal analysis, Energy dissipation


The effects of non-uniform temperature distribution on degradation of Lithium-ion (Li-ion) batteries are investigated in this study. A Li-ion battery stack consisting of five 3 Ampere hour (Ah) pouch cells connected in parallel was tested for 2215 cycles and compared with a single baseline cell. The behaviors of temperature distribution, degradation, and current distribution of the stack were characterized and discussed. Results supported the hypothesis that non-uniform temperature distribution causes non-uniform and accelerated degradation. All cells in the stack experienced higher temperature rise and degraded faster than the baseline cell. In particular, capacity retention of the middle cell in the stack decreased to 50.7% after 2215 cycles while the baseline cell capacity retention was still 87.8%. Resistance of cells in the stack experienced non-uniform but similar pattern of variation with cycling. The resistances remained stable in early cycles, then experienced a rapid increase, and then became stable again. The middle cell resistance increased abruptly in the last 20 cycles before failure. Current distribution behaviors of the stack also changed significantly during cycling, which was consistent with cell resistance behaviors. The middle cell experienced much higher discharge current (C rate) than average, suggesting its accelerated degradation can be attributed to the synergized effects of higher local temperature and higher local current. Differential voltage analysis suggested that growth of solid-electrolyte-interface (SEI) on the anode is the primary mechanism for accelerated degradation of the middle cell in the stack.



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