Overdischarge-induced evolution of Cu dendrites and degradation of mechanical properties in lithium-ion batteries

The degradation of mechanical properties of overdischarge battery materials manifests as a significant effect on the energy density, safety, and cycle life of the batteries. However, establishing the correlation between depth of overdischarge and mechanical properties is still a significant challenge. Studying the correlation between depth of overdischarge and mechanical properties is of great significance to improving the energy density and the ability to resist abuse of the batteries. In this paper, the mechanical properties of the battery materials during the whole process of overdischarge from discharge to complete failure were studied. The effects of depth of overdischarge on the elastic modulus and hardness of the cathode of the battery, the tensile strength and the thermal shrinkage rate of the separator, and the performance of binder were investigated. The precipitation of Cu dendrites on the separator and cathode after dissolution of anode copper foil is a key factor affecting the performance of battery materials. The Cu dendrites attached to the cathode penetrate the separator, causing irreversible damage to the coating and base film of the separator, which leads to a sharp decline in the tensile strength, thermal shrinkage rate and other properties of the separator. In addition, the Cu dendrites wrapping the cathode active particles reduce the adhesion of the active particles binder. Meanwhile, the active particles are damaged, resulting in a significant decrease in the elastic modulus and hardness of the cathode.