A micromechanical approach to deformation and damage of nickel foam used in conductive layer of lithium-ion battery

Abstract

Porous conductive nickel foam is used as a tortuous interlayer between the sulfur electrode and the separator in lithium-ion batteries (LIB). Such materials should preserve both surface area and strength for possessing an extended efficient performance in hybrid vehicles. In this research, compressive deformation behavior and failure mechanisms of nickel foam fabricated by electrodeposition are studied by mechanical testing and micromechanical simulation. The micromechanical model is developed to predict the Ni foam compressive load-bearing behavior and correlate material microstructural characteristics with compressive strength. Fulfilling this aim, three different foam samples with different conditions are manufactured, and mechanical testing is done on the samples. Field emission scanning electron microscopy (FE-SEM) integrated with image analysis is utilized to prepare the prerequisite actual microstructure-based data for the FEM numerical simulation. The Johnson-Cook damage model is applied to the computational models to simulate the fracture mode of cellular structures under mechanical loading. The micromechanical, including the JCCRT together with strain and stress distribution, can reasonably predict the elastic limit, plateau region, the first peak with less and densification stages. Furthermore, the model is with potential to determine the deformation pattern, which is in good agreement with the results of the Ashby analysis. A layer-by-layer failure is for the stretch-dominated structures, while the bending accompanied by the shearing banding is more dominated in denser foams. By comparing the stress-strain curves of samples with different densities, it can be observed that all samples are with the densification strain onset at about 0.17 (0.167 for 39% - 0.172 for 45% - 0.178 for 58% porosities), while this stage begins sooner for the sample with less density. The shear band formation in the cell bodies at an average strain level of 0.15 for all samples subjected to uniaxial compression. The power exponent of Ashby law was found to be 0.85, 1.16, and 1.35 for the samples with 58%, 45%, and 39% porosity, consistently that is in good agreement with stretch-dominated and bending-dominated deformation. Both transgranular and intergranular were seen in Ni foam as the former is more ductile while the latter is with brittle manner.