Path Dependence in Lithium-Ion Batteries Degradation - a Comparison of Cycle and Calendar Aging

Abstract

The Hawai‘i Natural Energy Institute (HNEI) is leading research efforts to understand the degradation of lithium-ion batteries under two distinct projects. The first research project is focused on grid-scale battery energy storage systems (BESS) while the second project is targeting electric vehicles (EVs) and their synergy with the grid. Both applications require a combination of long cycle-life (1000 cycles or more) and long shelf-life (10 to 20 years in operation) to meet the expectations of the customers. To determine whether these durability goals are realistic or not, we performed accelerated testing of different lithium-ion battery technologies in the laboratory. For each technology, we conducted a series of cycle and calendar aging experiments. The results of these studies will be used to develop predictive performance models. The concept of accelerated aging is only valid if the degradation the cell underwent is the same than of the one it experienced in real life. In this presentation, we want to share our preliminary observations regarding the differences between cycle aging and calendar aging across the different chemistries and across the industries (EVs, BESS). Our primary objective is to showcase the different degradation pathways, whether calendar-driven or cycle-driven, which can lead to identical capacity losses. This concept is better known as path dependence and this talk will highlight its implications for the design of long-life battery systems, the laboratory testing it requires and the validity of accelerated testing strategies. [1] M. Dubarry, N. Vuillaume and B. Y. Liaw, J. Power Sources 186(2), (2009) 500-507. [2] M. Dubarry, C. Truchot and B.Y. Liaw, J. Power Sources 219 (2012) 204-216. [3] https://www.soest.hawaii.edu/HNEI/alawa/[4] M. Dubarry, C. Truchot, A. Devie and B. Y. Liaw, J. Electrochem. Soc 162(6), (2015) A877-A884.