Temperature is an important factor affecting the performance of lithium-ion batteries, so it is a key element in the research of battery thermal characteristics and thermal management to clarify the influence of temperature on battery charge and discharge performance.
In this study, lithium-ion battery cells were discharged at constant current at 10 A, 35 A, 70 A and 140 A in the temperature range of 40 –20°C. The relationship between discharging voltage and capacity of the batteries is shown in Figs. 2.10, 2.11, 2.12 and 2.13.
The working voltage of the battery is used as the ordinate, discharge time, or capacity, or state of charge (SOC), or discharge depth (DOD) as the abscissa, and the curve drawn is called the discharge curve. To understand the discharge characteristic curve of a battery, we first need to understand the voltage of the battery in principle.
With the decrease of the capacity, the charge capacity of the battery increases. The charge and discharge experiments of lithium-ion batteries at −40–20 ℃ showed that with the decrease of temperature, the discharge capacity of lithium-ion batteries decreased rapidly, and the discharge voltage decreased greatly.
It can also explain the phenomenon that the charge performance of the battery decays faster than the discharge performance with the decrease of temperature. At a certain temperature, the ohmic resistance of charge and discharge is higher at both ends of SOC and lower in the range 0.2–0.8. 2.
Charging curves of batteries at 70 A constant current—constant voltage at different temperatures It can be seen from Figs. 2.14, 2.15 and 2.16 that the charge performance of the battery decreases significantly at low temperature. Battery charging at low temperature has the following two characteristics: