多孔球形电极颗粒中的扩散-应力耦合分析

具有良好化学稳定性及较高存储容量的多孔材料在锂离子电池及超级电容器中有广泛的应用,但已有的扩散-应力耦合模型大多忽略多孔材料的微观结构.基于此,建立考虑孔隙率和迂曲度的多孔球形电极颗粒中的扩散-应力耦合模型.针对Mn_2O_4电极进行恒压充电下的数值计算,探讨孔隙率和迂曲度系数对锂离子浓度、径向应力、环向应力及体积应变的影响,并将模型结果与他人结果进行对比.数值结果表明:迂曲度系数越大,电极中锂离子的扩散越差、体积应变越小且径向应力和环向应力越大;孔隙率越大,电极中的锂离子浓度和体积应变越大但径向应力和环向应力越小;多孔电极结构更有利于提高嵌锂能力.因此,应选择孔隙率大且迂曲度系数小的材料作为高存储容量的电极材料.

Diffusion-stress coupling analysis of porous spherical electrode particles

Porous materials with good chemical stability and high storage capacity are widely used in lithium ion batteries and super capacitors. However, the influence of the microstructure of porous materials on diffusion and deformation are ignored in the existed most research work on diffusion-induced stress coupling models. Based on these, the diffusion-stress coupling model considering porosity and tortuosity in spherical porous electrode particles is developed by using porous medium theory, mass conservation law and elastic mechanics theory. Then according to the developed model, the numerical calculations of Mn₂O₄ electrode material under potentiostatic charging are carried out. The effects of porosity and tortuosity coefficient on lithium ion concentration distribution, radial stress and hoop stress are discussed, respectively. Finally,StheSsimulationSresultsSin this work areScomparedSwith those in other literature. The simulation results show that the larger the tortuosity coefficient, the worse the diffusion of lithium ions in the electrode and the greater the radial and hoop stress of the electrode particles. The larger the porosity, the larger the concentration of lithium ion in the electrode and the smaller the radial stress and hoop stress in the electrode particles. The porous electrode structure is more favorable to improve the lithium embedding ability. Therefore, a material having a large porosity and a small tortuosity coefficient should be selected as the electrode material with a high storage capacity.