An analytic model for effective mechanical properties and local contact stresses in lithium-ion porous electrodes

Explicit expressions for stress–strain relationships and swelling strains are derived for porous lithium-ion electrodes. Local contact stresses between neighboring electrode particles are also predicted. The analytical model is based on similar microstructural averaging techniques that previously have been applied to simulations of powder compaction. Both direct particle–particle and particle–binder–particlecontacts are considered. The model gives explicit dependencies of constituent material properties and parameters describing the microstructure geometry. Examples are presented for electrodes that have particle–particle contacts below the percolation limit. The prediction of the E-modulus shows good agreement with experimental results. Constrained swelling resulting from intercalation of lithium-ions has also been simulated. The resulting electrode stress state compares well with numerical predictions by the finite element and the discrete element method. Local particle–particle contact stresses of the order 1–6 GPa have as well been predicted. A simplified model using a model for rigid-plastic deformation of particles have shown that the stress–strain behavior during the first charging cycle may substantially differ from subsequent cycles, a phenomenon that also has been experimentally observed.