Modeling Of Porous Electrode Using Stacked-agglomerates

The booming electric vehicles demand lithium-ion batteries to simultaneously increase energy and power performance.The design of the electrode structure is the key to balance the trade-off relationship between energy and power density.In the industry,however,experimental trial-and-error still remains the main method for battery design,which costs much time and money.This thesis adopts a forward design method based on the electrochemical model and focuses on the microstructure of the electrode(regardless of material types).Through the progressively development of electrode models,this study reveals the relationship between the structural parameters and the electrode performance to enhance the energy and power performance of the electrode.The single active material particle is the element for the electrode.In this study,a two-dimensional single agglomerate model with sphere shaped is developed and validated using discharge curves with different rates from a single particle microelectrode experiment.In order to clarify the effect of the agglomerate structure,a solid core particle model is developed and the simulation results from the two models are compared.The influence of the liquid-phase mass transfer and solid-phase mass transfer is analyzed by the sensitivity analysis of material parameters and structural parameters.The electrode structure of lithium-ion batteries can be considered as several or several tens particles stacking.Therefore,the single agglomerate model can be extend to an electrode model with regular arranged agglomerates.The simulation results show that the discharge rate performance of the electrode model is significantly attenuated compared with the single agglomerate model.The great gradient of the liquid phase potential and the liquid lithium ion concentration is found using the electrode model and leads to the inhomogeneous lithium intercalation,which is the main limiting factor of the electrode rate performance.This model can characterize the structure of conductive additive network distributed in the electrode.It is found that the conductive additive network with spatial homogeneous distribution and high dimensional structure can reduce the amount of the conductive additives and provide a better electrode performance.A randomly stacking agglomerate electrode model is developed with consideration of the disorder and complexity of the porous structure of the electrode.The model is validated by the discharging experiments using a lithium-plated reference electrode based three-electrode cell.The influence of the battery design parameters,such as the volume fraction of active material,the average particle size,the dispersity of particle size and the electrode thickness,are investigated by the simulation results.Further,the disorder of the porous electrode is quantitatively characterized by calculating tortuosity.It should be noted that the stacked-agglomerate electrode model can provide both macro-and micro-structure characterizations,which can be the guidance for the porous electrode design with different material system.