(3) Thermal abuse
Thermal abuse refers to the simulation of improper battery use under high temperature, such as placing mobile phones in sun exposed cars, or placing mobile phones or electronic products in microwave ovens. The external heat source directly acts on the lithium battery, causing complex internal chemical reactions, such as the decomposition of SEI film, the redox reaction between electrolyte and positive and negative electrode materials, which further evolves into heat runaway. In addition, the diaphragm melts and shrinks at high temperature, leading to short circuit of positive and negative poles, which is very likely to cause fire or explosion. In the IEC62133: 2012 standard, only minor changes have been made to the heat abuse test, that is, small electric cores are kept at 130 ℃ for 10 min, and large electric cores are kept at 130 ℃ for 30 min. This is due to the increasing volume energy density and high capacity of single lithium ion battery.
(4) Crush
Crush test content in IEC62133:2012 standard: select the method that causes the most unfavorable result to apply a force of (13 ± 1) k N. Once the maximum pressure is reached, or the voltage suddenly decreases by 1/3 of the initial voltage, or 10% deformation occurs, the pressure shall be released. For square battery, only the wide side test is carried out, instead of the narrow side test. Compared with the 2002 standard, there are only minor changes, that is, the battery cell uses a new charging procedure. The squeeze test simulates a local internal short circuit. The new charging method may reduce the qualification rate of lithium battery cell safety test.
2.2 Add test items
(1) Forced internal short circuit
The forced internal short circuit test attempts to simulate the internal short circuit caused by such metal particles penetrating the diaphragm. The tests in IEC62133:2012 standard investigate internal short circuit from two positions: positive active substance. Between negative active substances; Positive aluminum foil – negative active material. In the test, the fully charged battery cell is first decomposed in an environment where the dew point is lower than – 25 ℃, then small nickel sheets are placed at the upper two positions respectively, rolled back into the battery, and placed in a sealed polyethylene bag.
The battery is placed at the upper (lower) test temperature plus (minus) 5 ℃ for (45 ± 15) min, and then under the upper and lower test temperatures respectively, a standard pressure tool is used to apply pressure at a speed of 0.1mm/s to the nickel sheet position, Until it is observed that the internal short circuit causes a voltage drop of 50 mV or the pressure meets the requirements (800 N for circular batteries and 400 N for square batteries), the pressure will be released after 30 seconds. It is required that the battery will not fire or explode in case of internal short circuit. The content of this test is the same as that in JIS 8714 standard.
In addition, the standard stipulates that this test is only applicable to France, Japan, Korea and Switzerland. Although the forced internal short circuit test can greatly reduce the unsafe factors caused by the defects in the production process, it is still controversial whether it can truly and effectively simulate the internal short circuit of normal batteries. At the same time, the strict operation required for battery disassembly and reassembly is also a challenge.
(2) Transportation test
The transportation test in IEC62281 standard includes: low air pressure, temperature cycle, vibration, impact, external short circuit, impact or extrusion. It is aimed at the cell and battery pack. However, the IEC62133:2012 standard only requires the test of the battery cell, reducing the safety requirements of the battery pack. Compared with IEC62133:2002 standard, the 2012 standard deleted several test items such as low air pressure, temperature cycle, vibration and impact, but added transportation test.
It can be found from the difference comparison analysis that except T6, which is for a single sample, T1-T5 is for the same sample to be tested in turn. The previous test may have a negative impact on the next test, resulting in failure to pass the test. In addition, there are also differences in their testing methods. Temperature cycling and vibration conditions are more stringent in terms of temperature, time and acceleration, which is easy to lead to liquid leakage, internal fracture and other phenomena of lithium battery. In a word, IEC62133:2012 standard greatly enhances the safety test requirements of lithium battery.
3.Conclusion
The preparation and revision of lithium ion battery standards are very active all over the world. Through the comparative analysis between the 2002 edition and 2012 edition of the international standard IEC62133 for lithium-ion batteries for portable equipment, it is found that the 2012 edition is more specific and detailed in the safety assessment of lithium-ion batteries. It also stipulates the safety test methods of lithium ion batteries used in portable electronic equipment under normal use conditions, foreseeable misuse conditions and foreseeable fault conditions, ensuring the safety of lithium batteries during storage, use, transportation, etc.
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