The combustion behavior of large scale lithium titanate battery - 24 volt lifepo4 battery pack

Safety has always been a major obstacle to the large-scale application of lithium batteries.
However, knowledge about the burning behavior of the battery is limited.
In order to study the combustion behavior of large lithium batteries, 3 50 ah Li (nixcoym) O2/li4ti5. 0 batteries were heated to fire under different charging states (SOC.
In order to analyze the combustion behavior directly, the change of flame size is described.
The combustion behavior under the reaction mode was deeply analyzed by using mass loss rate, temperature and heat release rate.
According to this phenomenon, the combustion process is divided into three basic stages, which are more complicated under the high SOC where smoke is suddenly emitted.
The reason is that the Li (nixcomo2) O2 material has a phase change from the layer structure to the spinel structure.
The critical temperature of the ignition is 112-121 °c on the anode sheet, and the upper surface temperature of all batteries is 139 to 147 °c.
However, with the increase of SOC, the heating time and combustion time become shorter.
The results show that the risk of battery fire increases with the increase of SOC.
According to the analysis, the distribution of internal short and Li is the main cause of the difference.
An experimental system was established to study the fire and explosion behavior of the battery under thermal radiation conditions.
Temperature, mass loss and heat release rate can be measured.
From the front and side of the battery, the camera records the entire experimental process.
The overall schematic diagram of the experimental system is shown.
The battery is secured in a closed cage with a wire to prevent the surrounding equipment from exploding.
In order to avoid short circuit, the positive and negative poles of the battery are insulated with insulating tape.
To simulate the heat dissipation, a circular electric heater is set up at 85mm from the battery.
During the whole test, the electronic balance measured and recorded the change of battery weight, and the accuracy of the balance reached 0. 01u2005g.
Thermocouple (K-
Type) fixed on the surface of the battery to detect the surface temperature.
As shown in the figure, the thermocouple matrix set on the cathode and anode side of the battery is used to detect the flame temperature when the battery burns.
Based on ISO 9705, the combustion gas is collected by the fan at a speed of 35 liters of s to a gas pipeline with a diameter of 400
Pump the sample gas into the gas analyzer to analyze the concentration of oxygen, carbon dioxide and carbon monoxide.
In the process of collecting gas, the filter absorbs water vapor and smoke.
Using the principle of oxygen exhaust, the concentration of oxygen, carbon dioxide and carbon monoxide is used to calculate the heat release rate of battery combustion.
The lithium ion battery consists of cathode, anode, electrolyte, diaphragm film, aluminum shell and safety valve.
NCM and LiTiO are used as cathode and anode materials, respectively.
The battery is cylindrical.
The size of the battery is 66mm in diameter and 260 in length (regardless of the label length ).
The separator is PP/PE/PP material and LiPF is electrolyte lithium salt, which contains EC, December, DMC as organic solvent.
Design safety valve and electrode at two terminals.
The nominal capacity of the lithium ion battery is 50 u2005 ah.
After the cycle, charge the LTO battery to a different state, empty, half, full and then used to test the burning behavior.
SOC is equivalent to a fuel meter for an electric vehicle, a hybrid vehicle, or an energy storage battery pack.
The unit of SOC is percentage point (empty = 0%, half = 50%, full = 100% ).
In the experiment, four K-
Type thermocouple numbered TC1, TC2, TC3, c4 is placed around the surface of the battery to collect the temperature.
They are placed in the middle of the bottom surface, anode electrode (negative electrode), cathode electrode (positive electrode) and the above table, respectively.
In addition, a thermocouple matrix is placed on both sides of the cathode and anode to test the flame temperature.
The thermocouple numbered E1 to E6 is fixed near the two terminals of the battery, and the vertical interval between the two thermocouple on one side is 100mm.
According to the principle of oxygen consumption, the concentration of oxygen, carbon dioxide and carbon monoxide can be used to calculate the heat release rate of battery fire.
In the process of complete combustion, the rate of heat release can be calculated by equation. (4).
Among them, the initial mass concentration of oxygen is the mass concentration of oxygen in the combustion gas, which is the energy release of oxygen per mass unit.
While combustion is incomplete in most cases, this will lead to the actual formation of carbon dioxide and soot.
The heat release rate is then calculated based on the concentration of carbon monoxide and carbon dioxide.
The camera records the burning process, and the video can be used to analyze changes in the width and height of the flame.
First, turn the video into a black and white video.
Then, using Matlab software to cut and save all frames in black and white video.
The frame rate of the video is 50 frames per second.
Each image is ported to a matrix related to the size of the image.
To exclude interference information, these values in the matrix are divided into 0 and 1 by a constant.
The threshold is set to 0.
Clearly the outline of the flame.
Value greater than 0.
8 is expressed as 1, and the smaller is expressed as 0.
After binary, as shown, the matrix can calculate the width and height of the flame through Matlab software.