- Introduction
As a widely used power source for able to move, lithium ion batteries have the advantages of high energy density, no safety effects, long service life, respect for the environment, etc. When small lithium-ion batteries dominate the field of consumer electronics, large-scale lithium-ion batteries are being produced, entering the market quickly and efficiently. The use of lithium-ion batteries causes fire and explosion, many researchers in the field of batteries have studied and analysed the causes of battery failure under different conditions from a chemical point of view.
According to these studies, there are continuous improvements in the battery: Different anode and cathode developed to improve chemical stability; a multilayer separation was made to prevent heat transfer; appropriate additives have been introduced into the electrolyte to prevent chemical reactions or to charge the battery itself to reduce the risk of overcharging without affecting normal charging, etc. Manufacturing processes and better assembly have also been improved to reduce the chance of failure. However, the details of the battery components and the quality of the battery assembly, which affect the battery storage capacity, are still unknown to the electrical engineers who design the battery energy storage system. Therefore, the principles of lithium-ion batteries should be introduced, and get a basic idea about the dangers of lithium-ion batteries and the causes of these dangers. This concept will provide BESS engineers with a suitable approach to well-organized security.
- Lithium-ion battery cell abuse test
In fact, the failure of the lithium-ion cell is a complete process, which can start from any of the exothermic reactions mentioned above and ends in various risks such as the expansion of the battery, leakage electrolyte, gas pump, fire, explosion, etc. In order to measure the safety level of commercial lithium-ion batteries, mechanical, electrical and electrical tests are made according to UL and IEC standards. In this article, two types of lithium-ion battery cells were tested. All the prisons were fully charged before the trial with unfair practices and standards.
2.1 Fire Damage
The target cells are incubated at room temperature. The temperature of the room was set at 130℃ with an increase of 5℃/min. When the temperature in the room reached 130 ℃, it was kept for 10 min, and then the sample was observed. Under the temperature, there can be a risk from the failure of the SEI, the melting of the separator and the increase in the gas concentration of the electrolyte. After the test, the output, air current and voltage of the battery cells were tested.
Therefore, there is no fire escape of this cell tested. It can be seen in the tissue expansion of prismatic cells and sac-like cells appears. The expansion can be caused by the vaporization of the electrolyte. The rate of expansion of the body under test depends on the amount of low-grade solvent from the electrolyte. And the exact amount of money is not clear to the users. However, according to the research, it is concluded that the example of the type of bag has a better performance that showing a higher level of security. The prismatic form in has good performance due to the high temperature resistance caused by the mass.
2.2 Nailing
A ∅5 mm nail was driven into the sample at 20 mm/s. Removed after 1 minute. Under this test condition, a small internal circuit through the direct contact of the positive and negative can occur. The heat generated by the internal short circuit can cause the reaction of the decomposition of the battery part.
During the test, electrolyte dispersion and gassing were observed for all prismatic cells. The voltage and temperature of the cell were measured. The movements indicated the occurrence of an internal short circuit that resulted in the release of stored energy and a drop in cell voltage. Also, the temperature rises to 130 8 ℃ when the energy is released. The temperature at the surface then fell to a relatively good place, which means that no exothermic chain reaction occurred and heat escaped after the test was completed. For the pocket-type cells, no temperature rise, electrolyte sputter or air leakage was observed during the test except for one of the five samples. The measured voltage is plotted at high temperature. Part of the stored energy is released from the internal short circuit. The internal short circuit is stopped by the gas released from the electrolyte, which is expended in the cell and creates a protective layer between the sound and the negative material in the separator and the penetrated area. An incomplete internal short circuit resulted in low cell voltage reduction at a maximum temperature of 90.5℃. When the surface temperature of the cell fell, the hot runner did not complete the test. Prismatic cell ventilation protection is triggered due to high internal pressure. For a cell-like container, the expansion of the tissue can be seen. In general, bag-type cells have a higher level of protection than prismatic types.
2.3 Weight
The sample is transferred at a current of 0.05 C. Once the cell voltage reaches 5V or the charging time reaches 30min, the test is stopped. 1 C is defined as the rate of current in the battery completely in 1 hour, which means that 1 C is equal to 40 A for a battery with a capacity of 40 Ah.
For all samples tested, no electrolyte leakage, gas leakage or other hazards were observed. The expansion of the sample can be seen after analysis. According to the cell voltage, ambient and cell surface temperature, it was concluded that the thermal runaway point did not occur.
2.4 Short Exit
A circuit contact is connected between the electronic sample and the short-circuit resistance is set at 5 mΩ. During the first run of the test, light is seen on the cable or contact. Through it. Cables and contacts with a current of 1500 A are selected after the test to avoid fire in the test circuit.
