Testing, Characterization, and Thermal Analysis of Lithium-Ion Batteries Toward Battery Pack Design for Ultra-Fast Charging

Abstract

Ultra-fast charging of electric vehicles will soon be available to charge the batteries in less than 15 minutes to 80% state of charge. However, very few studies of batteries under these conditions exist. To design a battery pack with ultra-fast charging in mind, more information about batteries is needed, both electrically and thermally. In this thesis, the performance of three specific commercial lithium-ion batteries during ultra-fast charging is investigated and their thermal behaviour is simulated for use in the battery pack design process. The cells are charged at 1C to 6C current rates, or as high as 10C, and the surface temperature of each cell is measured. The loss calculated from the charging tests are used in a thermal analysis of the three batteries using finite element analysis. The batteries are modeled in a simple cooling apparatus to determine their thermal management requirements in a pack, i.e., how effectively must the heat be removed from the cells to obtain a specific temperature in a pack. Test results show that ultra-fast charging is possible with very little loss; but, it is dependent on the battery. The analysis illustrates important trade-offs between the battery type, charge rate, and the thermal management system. This thesis presents a holistic view to the study of the batteries for eventual use in the design of a battery pack. The thermal performance of the batteries is equally important as their electrical (charge) performance. It also attempts to justify the observed behaviour of the batteries by their underlying chemical behaviour. The work here can be used as a jumping-off point for further work on the ultra-fast charging of batteries or the design of a battery pack.