Active Cell Balancing for Life Cycle Extension of Lithium-Ion Batteries under Thermal Gradient

Abstract

Lithium-ion (Li-ion) batteries are currently the preferred choice among energy storage systems for a wide range of applications due to their high energy density, long life span and cost effectiveness. However, in several high-power applications such as electric vehicles, the heat generation of Li-ion battery cells can cause several problems such as accelerated aging and thermal runaway. Although cooling systems are typically utilized to overcome these issues, they suffer from drawbacks such as uneven cooling of the battery cells as well as cumbersome architectures and high energy consumption. In this paper, we propose an active cell balancing (ACB) strategy to mitigate the impact of the temperature gradient on divergent aging of the cells with the goal of increasing the life span of a battery module. We explore balancing architectures dedicated to this goal and study their effectiveness via a simulation framework based on an electrochemical cell model, a computational fluid dynamics (CFD) cooling model and a battery aging model. The experiments show that the life extension of the module is proportional to the amount of ACB circuit, which points toward cost-effective solutions for battery manufacturers. In addition, the results indicate further cost reduction from relaxed cooling system requirements. Our investigation on a 40-cell battery module with standard thermal gradient shows that the life span can be prolonged by about 2.8%. Finally, our extended analysis shows that a life cycle extension of 19.8% is possible with ACB if a relaxed thermal gradient constraint of 12.4°C is assumed.