A Discrete Element Analysis of the Mechanical Behaviour of an Electrode Active Layer

Abstract

One of the main challenges in the development of lithium-ion batteries is mitigating the decrease in charge capacity over time. The loss of charge capacity in lithium-ion batteries stem from different phenomena, one of which is mechanical degradation. This study uses the discrete element method (DEM) to investigate the mechanical properties of a positive electrode layer. The goal is to link the local mechanical behaviour, on the particle scale, to the global behaviour of the electrode layer. Understanding the coupling between length scales is crucial for understanding and reducing the mechanical degradation and as the active particles, and the binder connecting it, form a granular structure in the electrode layer, DEM is a well-suited method to apply. The DEM model developed considered both interaction between active particles, as well as interaction between particles separated by binder. This study targeted to replicate the in-plane unloading stiffness of the electrode layer, which had been measured experimentally by Gupta et al. [1] through a U-shape bending test. The experiments measured the stiffness both in compression and in tension at various strain levels and load rates. The developed model was able to capture the constant stiffness in tension at different strain levels and the stiffness increase at higher compression levels markedly. The viscoelastic behaviour of the layer, with an increased stiffness at increased load rates, could be captured quantitatively by increasing the binder stiffness. This work lays an excellent foundation for further investigations of the mechanical properties of the active layer and its mechanical degradation mechanisms, such as viscoelasticity in the binder and swelling and fracture of the active particles.