LiCoO2电池正极微结构重构及有效传输系数预测

采用Monte Carlo方法重构了LiCoO2电池正极的三维微结构,重构单元的特征尺寸为几十纳米量级,从而得到了明确区分活性材料、固体添加物以及孔相(电解液)的微结构.通过对重构电极的特征化分析,得到了微结构中特定相的连通性和扭曲率、组分体积分数的空间分布、比表面积、孔径分布等特征信息.采用D3Q15格子Boltzmann模型(LBM)计算了该重构电极的有效热导率、电解液(或固相)的有效传输系数.同时发现,与随机行走方法以及Bruggemann关系式计算获得的扭曲率数值相比,LBM预测值更可靠.

Reconstruction of LiCoO2 Cathode Microstructure and Prediction of Effective Transport Coefficients

Understanding the impact of microstructure of lithium-ion battery electrodes on performance is important for the development of relevant technologies. In the present work, the Monte Carlo Ising model was extended for the reconstruction of three-dimensional (3D) microstructure of a LiCoO₂ lithium-ion battery cathode. The electrode is reconstructed with a resolution on the scale of 50 nanometers, which allows three individual phases to be evidently distinguished: LiCoO₂ particles as the active material, pores or electrolyte and additives (polyvinylidene fluoride (PVDF) + carbon black). Characterization of the reconstructed cathode reveals some important structural and transport properties, including the geometrical connectivity and tortuosity of specific phases, the spatial distribution and volume fractions of specific phases, the specific surface area, and the pore size distribution. A D3Q15 lattice Boltzmann model (LBM) was developed and used to calculate the effective thermal conductivity and the effective transport coefficient of the electrolyte (or solid) phase. It is found that tortuosity values determined by LBMare more reliable than those predicted by the random walk simulation or the Bruggeman equation.