Dissertation Defense – Weiping Diao


Title: DEGRADATION ANALYSIS OF LITHIUM-ION BATTERIES WITH KNEE POINTS

Author: Weiping Diao 

Day/Time: 08/26/2021 10:00 AM – 12:00 PM EST

Examining Committee: 
Dr. Michael Pecht, Chair
Dr. Chunsheng Wang, Dean’s Representative
Dr. Michael Azarian
Dr. Hosam Fathy
Dr. Paul Albertus
Dr. Stanislav I. Stoliarov

Abstract: 

Commercialization of lithium-ion batteries has enabled applications ranging from portable consumer devices to high-power electric vehicles to become commonplace. The capacity, which has been used to determine if lithium-ion batteries have reached the end of life, decreases over usage (cycling) and storage (rest). An increase in the capacity fade rate after some charge-discharge cycles is often observed in lithium-ion batteries. The phenomenon has been described as a knee point and can lead to a shorter life than expected. 

Although the general degradation modes, mechanisms, and effects on lithium-ion batteries are known, the dominant degradation modes and mechanisms for the knee point phenomenon have yet to be determined. Understanding why and when the knee point will appear on the capacity fade curves is valuable to battery manufacturers and device companies to predict or mitigate the knee point. This study presents the degradation behavior with knee point identification algorithms, accelerated testing and capacity modeling methods to assess the degradation and predict the knee point, and experimental analysis which identify the dominant degradation modes and mechanisms.