Methods for Characterization of Heterogeneous Aging in Large Lithium-Ion Batteries

Abstract

Lithium-ion batteries have become the predominant storage solution for electrified vehicles and therefore research is moving forward at high speed. The high demand for improvements in extension of the battery life requires effective methods for the detection and understanding of aging phenomena. Recent high energy lithium-ion batteries teardown analyses, performed at KTH [1], have revealed a considerable extent of heterogeneity in the degradation phenomena on multiple levels. These phenomena are expected to strongly affect the rate of ageing of cells, and in turn contribute to an early end-of-life of the system.This presentation will focus on the description of the characterization methods that will be used for future studies on the uneven distribution of cell ageing. Testing has been performed on multiple configurations of silicon – graphite composite electrodes where, given the large volume expansion of the silicon during operation, has additional variables in the degradation mechanisms.Material characterization has been performed in the form of cross section SEM, and NMR, following a methodology developed at KTH to quantify Li-plating in different areas of the jellyroll [2], but extending it to Si. On the other hand, electrochemical measurements have been performed with small lab cells under controlled conditions. In parallel a physics-based model for describing the behaviour of such cells is being developed. The model is currently able to interpret quasi-OCV experimental data and derive the behaviour of each active material involved during these processes.[1] Smith, Alexander J., et al. "Localized lithium plating under mild cycling conditions in high-energy lithium-ion batteries." Journal of Power Sources 573 (2023): 233118.[2] Fang, Yuan, et al. "Quantifying lithium lost to plating and formation of the solid-electrolyte interphase in graphite and commercial battery components." Applied Materials Today 28 (2022): 101527.