Simple Estimation of Creep Properties of Negative Electrode for Lithium-Ion Battery at High Temperature

Since the internal temperature of lithium-ion batteries rise to 80°C during charging or discharging, this study investigated the macroscopic creep properties at high temperature of negative electrodes in lithium-ion batteries and their estimation methods based on the microscopic structure of the electrodes. Tensile and creep tests at several temperature levels were conducted on a negative electrode consisting of carbon powder and polyvinylidene fluoride (PVDF) binder. The stress-strain curve, the time history of the tensile strain, and the creep rupture time were measured in these tests and estimated using the simple model proposed in this study. The proposed model approximates the alignment of carbon particles as body-centered cubic (bcc) or face-centered cubic (fcc). The test results showed that the stiffness and the strength of the negative electrode decreased with the increase of the test temperature. The PVDF binder gradually shrank in the creep test at high temperature. This affected the creep properties of the negative electrode. The time history of the tensile strain and the creep rupture time were located between the upper and lower limits of the proposed model taking the thermal shrinkage of the PVDF binder into account.