High-energy density Li-ion battery; semi-empirical model; heat generation rates; inverse calculation method; optimum temperature range
In this paper, the electrical and thermal characteristics of the high-energy density of 100 Ah (over 350 Wh/L) pouch-type lithium-ion battery (LIB) cell are analyzed experimentally. To determine the effects of applying current-rate (crate) on its behavior, the battery is charged and discharged in different c-rate ranging from 0.5C to 1.2C. The changes in discharged capacity and heat generation rates of battery cells are examined and its mechanism is analyzed deeply in the view of variations on internal resistance. The battery heat generation is considered with two heat sources, joule and entropic heat. A newly developed inverse calculation method is adopted to derive the entropic coefficient in the function of the state of charge. The heat capacity of the battery cell is determined from the convective cooling experiment of battery cell with aluminum block and the combined heat transfer coefficient to calculate the cooling rates of battery cells is also determined appropriately from the Nusselt number correlation. It is confirmed that the numerical model based on the above methods is well suited as a whole from the experiments. In addition, the cell is discharged in different ambient temperature ranging from -15℃ to 45℃ to find out the temperature effects on LIBs. The decrease of capacity and more heat generation of LIB is found under both low and high ambient temperature. As a result, the optimum operating temperature range is redefined as 25℃-35℃ through analyzing the change of electrical and thermal performances of the battery cells.