Thickness effect on the mechanical performance of cathodes in lithium-ion batteries

Abstract

As battery capacity and energy density increase, the safety of batteries deteriorates with a more severe capacity fade. Increasing the electrode thickness is an effective approach to enhance battery capacity and energy density. Currently, research on the influence of electrode thickness on batteries has primarily focused on electrochemical aspects, while there is limited study on the impact of thickness on the mechanical properties of electrodes. In this work, we thoroughly investigated the mechanical behavior of NCA (LiNiaCobAlcO2, a + b + c = 1) cathodes with varying thicknesses through uniaxial tensile tests. Experimental measurements show that as the cathode thickness increases, tensile strength and elastic modulus of the cathode decrease. Cathodes with thin coating exhibit brittle fracture, while cathodes with thick coating display relatively higher toughness prior to fracture. The distribution of cracks and the structure of cathodes varying with thicknesses were studied by scanning electron microscopy. Results show that cathodes with thick coating have wider and deeper cracks. Thinner cathode coatings can withstand larger tensile and shear stresses compared to thicker cathode coatings, thus thicker cathode coatings experience more severe damage. By combining microstructural observation and stress analysis, the mechanism for the degradation of mechanical properties and rapid capacity fade in thick electrodes were revealed. This study provides a reference for the optimal design and safe operation of lithium-ion batteries.