Variable Duty Cycle Heating Strategy Considering Internal Inconsistency for Fast Self-Heating Lithiumion Batteries

Preheating batteries at low temperatures is an important approach to improve the environment adaptability of lithium-ion batteries, in which compound fast self-heating is an efficient method. However, current compound fast self-heating under a fixed duty cycle also leads to severe internal temperature uniformity problems, while there is still a lack of theoretical basis for temperature difference limitation within a cell during heating. To solve the problems, a layered electro-thermal coupling model is established at first. It is found that temperature uniformity leads to internal current inhomogeneity through internal resistance difference. Further, a dynamic temperature difference limitation is introduced based on the temperature characteristics of internal resistance, and a novel variable duty cycle heating strategy with internal inconsistency improvement is proposed. The results show that the relative internal resistance difference can be reduced from 43% to 30%, improving internal resistance uniformity by 30% with the same heating rate, which indicates better internal inconsistency than the fixed duty cycle strategy.