Multi-level optimization of low-temperature heating methods for large-capacity lithium-ion batteries based on temperature uniformity

Large-capacity lithium-ion batteries (LIBs) heating technology is a key factor for electric vehicles to cope with low-temperature conditions. However, at the individual cell level, due to the large size and uneven heat generation, large-capacity LIBs exhibit significant temperature non-uniformity. At the module level, temperature non-uniformity can also arise because of different heat transfer conditions and variations in heating power. Temperature non-uniformity can manifest during the operation of the battery, especially during low-temperature warm-up, which adversely affects the battery's lifespan and reliability. Currently, mainstream heating methods face significant challenges in balancing temperature uniformity and heating rate at both the cell and module levels. Internal heating techniques, such as pulsed internal resistance self-heating, and external heating methods, like liquid heating, inherently struggle to optimize temperature uniformity across multiple levels due to their fundamental principles. To address this issue, this study proposed a low-temperature warm-up multi-level optimization method based on temperature uniformity and conducted an optimized design for large-capacity LIBs and a sandwich self-heating structure. An uneven heat generation model is established and validated through a low-temperature heating experiment to analyze the uneven heat generation of LIBs under low temperatures. Building on this, the heating non-uniformity at both the cell level and module level is analyzed. Due to the sandwich structure of the battery and heating sheets, optimization can be simultaneously achieved at both the cell and module levels by modifying the topology and heating power of the heating sheets The results indicate that when heating a cell with a heating speed (5.39 °C/min for cell and 5.04 °C/min for module) in a −30 °C environment, the temperature difference at the cell level can be constrained to within 1.31 °C for cell level and 4.96 °C for module level which are significant improvements of temperature uniformity (29.2 % and 32.7 %). Furthermore, the multi-level optimization methods can be applied to other low-temperature warm-up methods and other levels of batteries. It provides guidance for addressing the temperature non-uniformity optimization issues in batteries and holds the potential for widespread application in different usage scenarios.