Ultrashort pulsed laser texturing of Li-ion battery current collectors: modeling mechanical stress during cycling

The finite element method (FEM) is employed within COMSOL Multiphysics to simulate mechanical stress during cycling of Li-ion battery electrodes with ultrashort pulsed laser-textured current collectors. Two- and three-dimensional models of electrodes with flat (untextured) current collectors are firstly compared, after which a parametric study is performed with the 2D model to determine the effects of current collector topography and active material porosity on the resulting stress distribution during lithiation of the anode and delithiation of the cathode. The first principal stress (sigma 1) is evaluated within the active materials due to their fragile nature, while the Von Mises stress (sigma v) is evaluated within the current collects due to their ductile nature. Normal (p) and shear (tau) contact pressures are evaluated at the interface between the two layers as indicators of the likelihood of delamination. Stress concentration at and near the interface between laser-textured current collectors and electrode active materials is shown to induce significant increases in peak stresses, with all evaluated parameters exhibiting strong dependence on the aspect ratio of the current collector surface topography. Approximately one-order-of-magnitude increases in sigma 1, p and tau are observed with a texture aspect ratio of 1, while sigma v approximately doubles. Over the same range of parameters, the theoretical increase in interface area between the current collector and active material is approximately +130%, implying that selection of laser parameters to achieve a given surface topography must be a compromise between improving adhesion and limiting stress concentration during electrochemical cycling.