Basic contents of protection
Compared with other types of power batteries, electric vehicle power lithium-ion battery is more prone to unsafe conditions such as combustion and explosion due to its electrochemical characteristics, structural characteristics and application environment, such as no special attention in the test process. During the test, especially in the test with high severity. The safety protection of laboratory is an unavoidable reality.
In order to facilitate the description, the protective measures are divided into hardware facility protection of test personnel and equipment (for the protection of unsafe state caused by leakage, rupture, combustion and explosion) and software early warning / control protective measures for the purpose of avoiding state. Basic design of protection. Both aspects shall be considered comprehensively, and both shall be appropriate and effective. In addition, considering the protected objects, they can be roughly divided into the following aspects.
1) Protection of personnel in the process of laboratory test, the test operators should be protected first. The test operator should also be the designer and executor of soft protection, and also the first object of protection. It is inevitable that the test operator will come into close contact with the sample in the disposal of withdrawal from the test state and the transfer of test connection. Hard protective articles include goggles, masks and helmets; Long insulating gloves (flame retardant, easy to take off), suitable tools for touching and handling samples (should be accessible): coats, skirts and suitable shoes and boots (anti combustion jet, high temperature bonding, anti weight falling), etc.: visual shielding screens shall also be set. Through the combination of soft and hard protection and the selection of appropriate protective articles and methods, the test operators can better carry out the test and avoid injury.
2) It should be noted that software protection can reduce the occurrence of danger to a certain extent, but exit the test in advance. Will result in incomplete test. The objective affects the criterion of the test. This problem can be solved by strengthening the protection of equipment. For the more valuable climate environment test box and vibration test bench. In addition to flame-retardant and explosion-proof partition protection facilities, measures against debris and viscous flocs shall also be set. The secondary instrument shall maintain effective connection and appropriate distance from the primary instrument such as temperature sensor and accelerometer.
3) Protection of test samples even damaged samples have preservation value. The single samples of battery cells are closely arranged, and shall be protected from influence and interference during test: on the one hand, the dangerous state of the battery pack / system shall be found and disposed in time due to the shielding of the shell. Prevent the chain reaction of dangerous state; At the same time, if any condition occurs, the sample shall be preserved as far as possible. For analysis.
4) The preservation of test data, such as combustion or explosion, temperature sensor, accelerometer and other primary instruments close to or attached to the sample may be affected or damaged, but the signals transmitted earlier and recorded data shall still be valid. Whether the sample passes the test or not, these data and information are also of great analytical value. On site monitoring images and pictures taken are also important data and information contents, which should be collected and sorted out.
5) Protection of test environment in case of a condition that can be judged in a closed test environment (such as in an environmental test chamber), the test shall be suspended. After obtaining evidence (such as capturing smoke and fire images), the fire shall be extinguished effectively. The exhaust gas is discharged through the special exhaust channel of the box. Test chamber without dedicated exhaust channel. Smoke and gas will inevitably enter the test site. At this time, personnel shall first have respiratory protective articles against smoke: there shall be corresponding independent ventilation and discharge system in the site. The exhaust gas discharged through the special exhaust channel of the box or the gas discharged by site ventilation. It shall comply with the emission standards specified by the place where the laboratory is located, and shall not be discharged directly.
It is worth noting that when the test is stopped. Even if the battery cell sample or the battery cell in the battery pack / system is not in a state, its internal activities and reactions have not actually stopped or subsided. Temperature measurement and appearance observation shall be continued, and the test shall be withdrawn according to the lag reaction conditions required by the standard.
6) Waste disposal: Test waste after obtaining evidence. Harmless treatment shall be carried out according to the tips of the sample supplier and relevant specifications of the laboratory, or submitted to professional institutions for reasonable disposal according to relevant regulations and procedures.
2.Software early warning / control protection
Sampling through on-line measurement and monitoring. Analyze the collected temperature time curve to understand the basic situation of the internal state of the tested sample in the test. Set the parameters and limits according to the characteristics of the sample. Early warning of sample status can be provided to the tester. Provide options for test control and protection. In addition, the image information collected in real time can provide direct help for taking effective protective measures in time after the sample state occurs.
2.1 Temperature
Under general test conditions, the temperature and its variation characteristics of the tested single cell at each stage will be discussed. During the test, the temperature of the single cell in the sample is mainly monitored, including the single cell in the battery pack / system.
The sensor shall be placed at the geometric center of the body or surface of the single battery cell. Considering from the test principle, it should be set at the most temperature sensitive position; Or stick to the “most unfavorable” position, that is, the position where the most unfavorable parameters can be collected.
Generally, thermocouples with small thermal inertia, short response time constant and low manufacturing cost can be used as temperature measurement sensors. UL recommends a wire diameter of 0.05 ~ 0.21mm ² Thermocouple. The thermocouple shall be close to the core surface. Thermocouples can be placed on thin paper sheets or labels. The secondary instrument can be continuously detected and recorded by multi-channel digital temperature inspection equipment, and sorted and analyzed by computer. It can not only detect the real-time state of temperature, but also give the temperature change rate and its change law.
Experienced test engineer. The actual state of the sample can be judged according to the loading condition of the test sample and the change rate of temperature and temperature change rate or the change rate of temperature change rate. On this basis, setting status warning or early warning “closed hole temperature” and “film breaking temperature” is a meaningful reference frame. Generally, the warning or pre setting of sample status should be about 5K in advance. Temperature change rate and change rate can be referred to as status warning or early warning level identification.
2.2 Arrangement of sensors
Temperature measurement shall be carried out on each cell. Including the battery pack / system, the sensor shall be set at the position most sensitive to the temperature of the battery cell. Even if the product integration of the battery pack / system is hindered, try to negotiate with the supplier to adopt appropriate methods to realize the measurement system, which may not require high accuracy, but the response should be fast; The time interval of patrol inspection shall be uniform. Thus, the reliable temperature rise rate parameters can be obtained. The measuring system including temperature sensor shall be calibrated before test.
2.3 Other parameters
During the test, other parameters such as terminal voltage, current and equivalent internal resistance indirectly obtained from the tested single cell sample. The actual working state of the tested sample can be determined more accurately. Even through sampling comparison. The relative status of the sample in the battery cell set of the whole battery pack / system is analyzed. These measurements and calculations are specified in some performance test items. Due to the problems of data collection volume and processing speed, and the large number of instruments occupied, the test preparation workload is also heavy. Whether it is used in laboratory safety protection depends on the actual situation of the laboratory.