Simple Estimation of Mechanical Fatigue Life of Negative Electrode for Lithium-Ion Battery

The macroscopic mechanical fatigue properties of negative electrodes in lithium-ion batteries and their estimation methods have been investigated based on a simple mechanical model. Tensile and bending fatigue tests were conducted on a negative electrode made of carbon powder and polyvinylidene fluoride (PVDF) binder. The simple model proposed in this study was used to estimate the stress and strain in the PVDF binder supporting the structure of the negative electrode. This model approximates the orientation of the carbon particles as the body-centered cubic (bcc) or the face-centered cubic (fcc), referring to the crystal lattice of metallic materials. The carbon particles in the model are bonded by the PVDF binder. The tensile fatigue test results showed that the negative electrode dissipated energy under the repeated loading, and the stress–strain curve showed hysteresis loops. The total dissipated energy of the binder obtained from the tensile fatigue test and the proposed simple model were used to estimate the mechanical fatigue life of the negative electrode with different binder ratios. The estimated S–N curve agreed with the mechanical fatigue life of the negative electrode with low binder ratios in the bending fatigue test.