Lithium batteries are one of the indispensable power sources in today’s aerospace industry, often serving as backup energy for various aircraft equipment startup, communication, and emergency response. They are important components of aerospace vehicles. However, in normal operation, lithium batteries are very sensitive to environmental temperature, and the impact of temperature is crucial during the battery’s cyclic use, but it is easily overlooked.
The battery capacity and charging and discharging characteristics will change with temperature, and high or low temperatures will seriously affect the performance and service life of the battery. Due to the long-term operation of aviation cobalt acid lithium batteries in unfavorable environments such as low voltage and low temperature, this will inevitably lead to a shortened cycle life of lithium batteries, which can seriously lead to battery scrapping or unpredictable losses. Therefore, it is necessary to study the temperature characteristics of aviation lithium cobalt oxide batteries.
This article will delve into the changes in battery capacity and charge discharge characteristics of lithium cobalt oxide batteries under different temperature conditions. Through experiments, the changes in battery capacity and charge discharge characteristics of lithium cobalt oxide batteries at different temperatures will be determined, providing a theoretical basis for estimating the SOC of lithium cobalt oxide batteries at different temperatures.
1.1 Research Object and Test Equipment
The experimental object is lithium cobalt ion batteries. The battery has a Nameplate capacity of 45Ah, a nominal voltage of 3.7V, and can be discharged at ambient temperature of -20~60 ℃. The battery cathode material is lithium cobalate. Battery charging and discharging equipment. DGBELL temperature and humidity test chamber to achieve temperature control.
1.2 Experimental Steps
The capacity testing of aviation lithium cobalt acid batteries adopts the full discharge method. Sufficient cobalt acid lithium batteries are placed in different temperature environments for discharge experiments, and the impact of environmental temperature changes on the battery’s discharge capacity is discussed. The specific steps are as follows:
(1) Activate the battery by repeatedly charging and discharging the battery with a current of 0.5C to activate the internal ions of the battery;
(2) The charging method is to charge the battery at a constant current rate of 0.2C. When the battery voltage reaches 4.15V, the charging method is changed to constant voltage charging until the charging current drops to 03A, and the charging is stopped;
(3) The discharge method is to let the battery sit at ambient temperature for 1b, and then discharge it at a constant current rate of 0.2C until the battery voltage drops to 3V to stop discharging, and calculate the amount of electricity released by the battery;
(4) Change the SOC state of the battery: Conduct charging and discharging experiments, record the voltage changes of the battery during the charging and discharging process;
(5) Place 7 lithium drilling acid batteries of the same model at -20, -10, 0, 10, 20, 30, and 40 ℃ for charging and discharging, with the same steps as above;
(6) Record the experimental results, organize the experimental data, and calculate the battery discharge capacity;
(7) Turn off the charging power supply after charging, turn off the electronic load after discharging, and clean the experimental equipment;
(8) Based on experimental data, plot the variation curve of battery voltage with SOC at different temperatures during the charging and discharging process.
2 Experimental Results and Analysis
The Influence of Environmental Temperature on Charging and Discharging Characteristics
By analyzing the voltage variation curve, it can be seen that the voltage variation in the platform area of rechargeable batteries is significant in low temperature environments. As the ambient temperature increases and the same amount of charge is applied, the trend of voltage change decreases. When the batteries at different temperatures are at the same voltage, the batteries at higher ambient temperatures have more mass than energy. If the Battery management system does not set temperature detection, the batteries may be discharged or overcharged at low temperatures, but not fully charged at high temperatures, thus affecting the service life of the battery
In the initial stage of charging, constant current charging is adopted, and the battery absorbs heat. As the charging process progresses, the temperature rise of the battery intensifies. After reaching the maximum charging voltage, it switches to constant voltage charging, and the battery voltage growth slows down. The lower the temperature, the easier it is for the battery to reach the charging cutoff voltage
By analyzing the curve changes, it can be seen that under constant current discharge conditions, the voltage change of aviation drilling acid lithium batteries can be roughly divided into three stages:
(1) in the early stage of discharge, the battery voltage drops rapidly;
(2) After a certain period of discharge, the battery voltage decreases slowly and enters the platform area;
(3) At the end of discharge (with a state of charge less than 0.2 S0C), the battery voltage shows a linear downward trend.
When a lithium battery discharges from a fully charged voltage of 4.2V to 3.7V, it takes a long time, but once it exceeds 3.7V, the battery voltage drops rapidly. This is because the battery has a discharge platform, and the platform area has the most sufficient battery power. In the middle stage of discharge, the voltage of lithium cobalt oxide batteries decreases slowly. When the SOC value is below 0.2 and the battery continues to discharge, the voltage drops rapidly, and the difference is not significant at different temperatures; When the battery voltage is 38V, the SOC of the battery in a 40 ℃ environment is about 0.6, while the SOC of the battery in a 20 ℃ environment is only about 0.2. This means that the lower the temperature, the easier it is for the battery to reach the discharge cut-off condition.
By drawing voltage curves at temperatures of 40, 20 ℃, and -10 ℃, it can be seen. There is a difference in the voltage curve between charging and discharging processes, and the voltage curve obtained from discharging is always slightly lower than the curve obtained from charging. This is because when the battery is charged to a certain SOC value and begins to stand still, the voltage continues to decrease until it gradually approaches the true voltage value of the battery, while when it is discharged to the same SOC value and begins to stand still, the voltage continues to increase until it gradually approaches the same true voltage value of the battery.
Due to the slow convergence process and the long required time, even if the battery has been stationary for a considerable period of time when measuring the voltage, the voltage obtained on the discharge curve is still lower than the voltage obtained on the charging curve. And as the temperature decreases, the difference between the charging and discharging curves gradually narrows.
This article analyzes the relationship between temperature and the characteristics of aviation cobalt acid lithium batteries by testing the changes in charge capacity and charge discharge voltage curves of aviation cobalt acid potassium batteries at different temperatures. The following conclusions can be drawn:
(1) The capacity change of aviation lithium cobalt oxide battery is particularly obvious at low temperature. When the ambient temperature is -20 ℃, the battery charging capacity can only reach 62% of the Nameplate capacity. With the temperature rising, the battery capacity increases, and the charging capacity can reach 107% SOC at the ambient temperature of 40 ℃. Therefore, the working environment temperature of the battery should be kept within the range of 0~40 ℃ as much as possible;
(2) During the charging and discharging process, the battery voltage changes with the change of environmental temperature. The lower the temperature, the easier it is for the battery to reach the charging and discharging cut-off voltage. When the battery voltage is the same, the lower the temperature, the smaller the SOC value of the battery;
(3) The voltage obtained on the discharge curve is smaller than the voltage obtained on the charging curve, and the pressure difference comes from the internal resistance of the battery