The influence of discharge current to temperature distribution of lithium ion cells

Abstract

Lithium-ion is used in battery electric vehicles as an effective and efficient energy storage medium. The energy density and life cycle of Lithium-ion battery are better than lead-acid batteries. But for Lithium-ion batteries, like every other battery, when operating in a high discharge current which causes an increase in battery temperature. This increase in temperature causes degradation in the performance of available electrical capacity of the battery. An experimental method was carried out to determine the effect of discharging current of the 18650 Lithium-ion cells to the surface temperature of the battery. The first measurement was carried out on a cell by installing three temperature sensors to measure the surface temperature distribution of the battery. The temperature sensors are each installed at 16mm (point A), 32mm (point B) and 48mm (point C) from the positive end of the battery. The initial treatment before the Lithium-ion cell test is charging up to a voltage of 4,2Vdc, then drained to a voltage of 2,7Vdc. Constant discharging currents are applied to the cells i.e. 3.5A, 7.5A, 11A, and 15A, respectively. The second measurement was carried out on a battery module consisting of 35 cells arranged in 7 cells in series and 5 cells in parallel (7S5P). Each temperature sensor is installed in the center of the cell (point B). The cell with the sensor was put in the middle of the series or parallel of the battery module. Before the discharge current, the battery module is charged to a voltage of 29.4Vdc. Constant discharge current is applied to the battery modules i.e. 15A, 20A, 25A, and 30A, respectively. The result of the temperature measurement of a cell (point B) to time shows that the 15A discharge current produces the highest temperature compared to 3.5A, 7.5A, and 11A. The temperature at point A has a lower tendency compared to points B and C. The temperature of point D in the direction of the series and parallel arrangement shows a tendency for higher temperatures compared to other points. This condition indicates that the highest temperature concentration of the battery module is in the middle of the battery cell arrangement.