Simultaneous internal heating for balanced temperature and state-of-charge distribution in lithium-ion battery packs

Lithium-ion battery cells are widely known to work reliably in a certain range of temperatures. While operating in a high-temperature condition might lead to thermal runaway, they also suffer significant performance degradation and power/energy capacity loss in sub-zero temperatures. Consequently, heating the cells before usage plays a critical role in battery-powered applications. Among different heating methods, one promising approach is internal mutual pulse heating which offers many advantages as it utilizes the internal resistance of the battery cell to create heat and increase the cell temperature. However, in the context of a large battery pack, the nonuniform distribution of temperature and State-of-Charge (SOC) between the cells heavily affect the performance of the battery pack and remain to be unsolved. In this study, we present a internal heating technique for simultaneously balancing temperature and SOC of the battery cells considering the geometrical and thermal characteristics of the battery pack without requiring the characterization of the cell impedance. The proposed technique schedules the order and timing of mutual pulse heating for different groups of cells in a battery pack to reduce the variance in temperature and SOC during and after pre-heating. The simulation results showed that the SOC and temperatures among the cells can be kept balanced while the average pack temperature is maintained around a target temperature during a long period in a wide range of temperatures below zero degrees Celsius.