(657a) A Cellular Automata Framework for Porous Electrode Reconstruction and Ion Transport Simulation

Due to its high charge transfer efficiency compared to that of non-porous materials, porous electrode with larger surface area and thinner solid pore wall has been widely applied in lithium battery field. The capacity and charging efficiency of batteries are closely related with the microstructure of porous materials, e.g. porosity, tortuosity, size distribution etc., however, the influence of electrode microstructure on battery performance still requires further study. As exploring a set of electrode with different microstructure by experiments is very expensive in cost and time, model-based simulation has become a significant tool to explore and pre-design the possible microstructure of porous electrode. A comprehensive model is able to generate a wide range of electrode microstructure and evaluate the battery performance via simulating the migration of Li-ions.

Most electrode models are described by partial differential equations (PDEs), which are derived from Fick's second law and Nernst equation, e.g. the widely used pseudo-two-dimensional (P2D) model. However, due to the assumption of uniformly dispersed spherical particles, the effect of electrode microstructure on lithium-ion movement has not been considered. In fact, disordered porous media are difficult to be represented by PDEs, and PDE system is hard to be solved due to the irregular solid-liquid boundary conditions. As a useful framework, cellular automata (CA) models can be focused on the inherent dynamics of systems and provide evolution mechanism for complex process, such as reaction-diffusion, infection transmission, drug release and many others. Compared with PDEs, CA is more convenient to construct the porous structure and simulate the mass transfer under complex boundary conditions. The implement of CA models is fully synchronous and will not suffer from non-convergence phenomena during calculation.

In this work, a two-dimension CA framework for reconstructing the microstructure of porous electrodes is proposed. The CA simulation structure is associated with actual electrodes by four parameters i.e. porosity, particle circumference, size distribution and eccentricity distribution, which are calculated from a set of X-ray tomography images by statistical methods. The CA simulation results effectively represent the geometric property of actual electrode along the thickness direction. On this basis, another CA model is proposed to simulate the transport and electrochemical reaction of lithium-ions. The influence of electrode microstructure on lithium-ion concentration distribution and local electric potential are studied based on the porous media formed in the previous step, which can provide more diverse microstructure of electrode than that of models based on idealized microstructure, such as spherical electrode particles. As application example, the microstructure of LiCoO₂ electrode is simulated, and the parameter deviations between CA image and tomographic image are all less than 5%. The electrochemical characteristic and species transport properties of LiCoO₂ electrode under different porosity are predicted, which is helpful for electrode pre-design and fabrication.

The proposed CA model provides a useful framework to study the effect of electrode microstructure on battery performance and can be used to optimize electrode morphology design.