A physics-based aging model for lithium-ion battery with coupled chemical/mechanical degradation mechanisms

Accurately describing the degradation behaviors of lithium-ion batteries is critical for future improved battery management systems in electric vehicles. However, diverse aging mechanisms, dynamic operating conditions, and the complex correlations between them remain major challenges. In this work, a physics-based aging model is developed to describe battery degradation dynamics. This model captures the formation and growth of the solid-electrolyte-interphase (SEI) layer as the dominated degradation mechanism that occurs in the graphite anode. First, the SEI layer is assumed to consist of one compact inner and one porous outer layer. The electron tunneling through the inner SEI layer is considered as the rate-determining step of the growth of SEI during storage conditions. Second, the crack propagation due to the stress generated by the volume expansion of electrode particles during cycling conditions is modeled based on the Paris’ Law formulation of mechanical fatigue. The proposed model is calibrated and validated using cycling data collected from commercial graphite/LiNi_0.8Co_0.15Al_0.05O₂ (NCA) cells under different conditions. The results show that this model can accurately simulate capacity fade as a function of aging stress factors, which are essential for battery health prognosis and the development of control algorithms for batteries.