| Li-ion batteries are widely used because of their high energy density,high cycle performance,no memory effect and low self-discharge rate.At present,the energy density of Li-ion batteries can not fully meet the market demand,so it is urgent to develop high-capacity Li-ion batteries.However,the coupled chemomechanical problem of high-capacity batteries is prominent due to the large volume deformation.The electrode of Li-ion battery is a typical heterogeneous composite material,which has obvious cross-scale characteristics in charge or discharge process.Based on the homogenization theory,a two-scale chemomechanical coupling theoretical model of standard inelastic dissipation of heterogeneous composite materials is established.Then,a simplified two-step staggered finite element method(FEM)is used to solving two minimization problems involving the macrostructure and microstructure.Finally,the overall capacity and finite deformation of the electrode,as well as the evolution of micro characteristics during charging are qualitatively discussed by numerical examples.The main contents are as follows.In Chapter 2,based on the variational principle,a variational form for the chemomechanical coupling of homogeneous materials with inelastic dissipation mechanism is established,and then a variational form for the incremental chemomechanical coupling problem is established.The variational scheme established in this chapter provides a theoretical basis for the subsequent cross-scale modeling and numerical solution of heterogeneous composites.In Chapter 3,based on the chemomechanical coupling model of homogeneous materials with standard dissipation characteristics established in Chapter 2,the chemical diffusion and chemomechanical coupling models in heterogeneous composites are developed.Firstly,based on the computational homogenization method,a variational form for the two-scale chemomechanical coupling problem of heterogeneous composites is developed.Then,based on hill Mandel principle,a two-scale incremental variational formula for multi-component non-homogeneous composites with local diffusion characteristics and dissipation mechanism is established.Finally,an iterative cross-scale finite element method is developed,which has important theoretical significance and engineering application value for the study of mass diffusion and chemomechanical coupling characteristics in heterogeneous composites.In Chapter 4,for the common Li-ion electrode,the specific energy function and dissipation relation are given,and the chemomechanical coupling constitutive model and evolution equation of Li-ion electrode are obtained.Combined with the alternative iterative cross-scale solution method developed by us,the state field dependent solution variables(SDVS)are used to transfer the data between the two subroutines,and the chemomechanical coupling effect is realized.In order to solve the two-scale transient mass diffusion problem of heterogeneous composites,we discussed the chemomechanical coupling properties:(1)using a simplified simulation model,we discussed the diffusion characteristics of Li-ion at electrode scale and local active particle scale,and the large deformation caused by the diffusion;(2)the effects of charging mode,microstructure and micro plastic evolution on the charging performance of the electrode were discussed by parameter analysis,which provides a theoretical basis for the material preparation and structure design of Li-ion electrode. |
