Presenter: Jing Ying Ko
Title: Model and experimental studies: Understanding aging mechanisms under high-voltage operation
Affiliation: KTH Royal Institute of Technology
To fulfill the demand of long driving range for electric vehicles without compromising the weight and cost of battery is to increase its energy density, i.e. by extending its voltage window. In this work, we intend to examine the aging phenomena under high-voltage operation of a NMC/graphite cell.
When cycled up to 4.5 V, a rapid performance degradation is observed. Aging stems from the NMC electrode rather than graphite. The severe NMC impedance rise causes an inaccessibility of utilizing its capacity, thus inducing cell failure. Therefore, an extended physics-based impedance model is developed to fit electrochemical impedance spectroscopy data from NMC symmetric cells.
The model indicates the particle surface layer, an electrode layer near separator and current collector resistance as the main causes of impedance rise. Higher temperature enhances the rate of degradation. Experimental evidences from scanning electron microscopy and Raman spectroscopy support these model findings.