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This paper compares the applicability of a few theoretical models for determining effective elastic moduli, using published experimental data on ceramic materials in a porosity range of 0 4 0 % and on a cellular material with a porosity of about 90%. As the experimental data for the effective Poisson's ratio involve a large scatter, a set of numerical experiments using the finite element method was carried out to obtain the variation of the effective Poisson's ratio with porosity. These variations show that the effective Poisson's ratio approaches 0.25 with increasing porosity, irrespective of the material Poisson's ratio. The effect of pore shapes on the effective elastic moduli and the Poisson's ratio has also been analyzed using FEM.

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A phenomenological Li-ion cell degradation model, pertaining to charge-discharge cyclic fatigue, is proposed and validated. It is known that Solid Electrolyte Inter-phase (SEI) formation on the particle surfaces consumes active Li leading to capacity loss. The problem is further aggravated by the creation of fresh surfaces by the fracture that develops as a result of intercalation induced stresses. In addition, fracture could result in isolation of chunks of electrode material or SEI could electronically isolate certain electrode material zones, both essentially rendering the active Li or electrode material ineffective. The degradation leads to increase in electronic resistance and decrease of ionic conductivity as well as diffusivity. Central to the model is a parameter expressed as the normalized reaction surface area, diminishing with charge-discharge cycles. Here, we develop phenomenological evolution expressions for the Fracture, SEI formation and Isolation, and incorporate them in Newman's Porous Composite Electrode framework. The model is implemented in the battery module of COMSOL. Notably, the utility of a lumped parameter ‘ΔSOC*SOCmean’, based on the State of Charge (SOC) is brought out.