Abstract
Lithium-ion batteries are used in a variety of products. However, during long-term use, incidents such as overheating and ignition often occur due to fatigue failure of the electrode materials. In this study, mechanical fatigue tests were conducted on these materials to investigate their fatigue mechanisms and to establish a method for predicting fatigue life. Conducting fatigue tests on the electrode materials alone is challenging because they are brittle thin films. Therefore, this study validated a plane bending fatigue tester equipped with strain sensors to measure the fatigue life of the electrode materials coated on metal foil. The electrode material consists of an active material and a binder, with the binder elongating to failure at a microscopic level. To evaluate the strain amplitude of the specimens, it is essential to consider not only the strain on the substrate from the plane bending fatigue tests but also the permanent strain obtained from the tensile fatigue tests. The specimens used for the tensile fatigue tests were thin films with a binder concentration of 30wt%. The test conditions were set with maximum strains ranging from 0.003 to 0.007 and a minimum load of 0.1 N, based on the results of the plane bending fatigue tests. The number of cycles was limited to 1,000 to investigate the relationship between permanent strain and number of cycles. The results indicated that the data trends closely followed the prediction lines derived from the relationship between total dissipated strain energy to fracture, the number of fracture cycles, and both the dissipated strain energy and strain amplitude, focusing on the dissipated energy observed in the tensile fatigue tests.
