Discrete element modelling of mechanical degradation mechanisms in lithium-ion battery electrode layers

Mechanical degradation of the positive electrode in lithium-ion batteries is one of the leading causes of charge capacity degradation over charge cycling. This study utilises a discrete element method modelling framework to investigate the mechanical degradation of the positive electrode constituents, the active particles and the conductive binder domain. The mechanical degradation is modelled as the fracture of the layer's two constituents, and simulations are performed to represent calendering, charge cycling, and tensile testing. The modelling results indicate that active particle fracture reduces the load-bearing capacity of the layer in compression. In contrast, the conductive binder domain fracture presents a dominant influence on the mechanical integrity of the full active layer. Charge cycling induces significant mechanical degradation during the first charge cycle, driven by the volumetric expansion of the active particles, for the conductive binder domain. Further charge cycling resulted in minimal additional degradation. Under tensile loading, the conductive binder domain governs the mechanical response as fracture limits the maximum tensile stress. The study concludes that the mechanical properties of the conductive binder domain are critical to the electrode's overall mechanical performance. The discrete element method framework captures multiscale interactions and degradation mechanisms that are challenging to observe experimentally, providing new insight into optimising electrode design for improved mechanical stability. • Fracture of the active layer constituents significantly reduces the mechanical integrity of the electrode layer during both the calendering and charge cycling process. • The modelling framework accurately captured experimentally observed fraction of fractured active particles after calendaring. • A critical loss of mechanical integrity at the electrode scale was predominantly associated with extensive conductive binder domain fracture. • Under tensile loading, the mechanical response of the electrode layer was governed primarily by conductive binder domain fracture.