Layered electro-thermal modeling and self-heating optimization for large-capacity Li-ion batteries

Integrated internal/external heating at low temperatures is an important approach to improving the environmental adaptability of lithium-ion batteries. However, for large-capacity batteries, it faces the problem of temperature non-uniformity caused by inhomogeneous heat production and slow heat diffusion. Due to the lack of effective modeling of internal non-uniformity, the impact of temperature gradients during heating on battery degradation remains unclear, and there is a lack of theoretical constraints on temperature non-uniformity. In this study, a layered one-dimensional electro-thermal coupled model with 6 sections is proposed to analyze electro-thermal non-uniformity during battery heating, followed by experimental validation. Based on the model, a multi-stage variable duty cycle heating strategy is obtained through multi-objective optimization and constraints considering aging. Subsequently, the characteristics of internal non-uniformity are further analyzed to reveal the theoretically based control patterns of temperature non-uniformity. The results show that under various operating conditions, the relative error of the model is less than 5 %, and the calculation time for a single heating is less than 10 s. The proposed strategy can increase the heating rate by up to 12.5 % without increasing degradation. It is found that a control strategy with dynamically increasing heating power can ensure rapid heating while improving electro-thermal uniformity and reducing battery degradation. This work solves a critical challenge for electric vehicles, enabling rapid cold-start without accelerating degradation in large-format power batteries. The proposed model and method have broad applicability in the field of battery thermal management.