Over the past 20 years, rechargeable lithium battery technology has developed rapidly. It has become an indispensable part of modern life by virtue of its superior performance. However, with the gradual expansion of its application range and the increasing density of individual single-volume energy, the capacity is getting larger and larger, and more and more explosion accidents occur. Its security performance has attracted more and more attention.
In recent years, the detection methods for lithium battery safety have become more and more mature. A number of safety testing standards have been introduced internationally and domestically. For example, the forced internal short-circuit test of JIS C8714 in Japan and the upper and lower limit temperature test of IEC. China has also customized new mandatory standards for lithium batteries.
What is the safety of lithium batteries?
The safety of lithium batteries not only means that there is no fire or explosion under various test conditions. The most important thing is to ensure that users are not harmed by battery abuse. Lithium battery standards, such as IEC 62133 and GB/T 28164, have clear definitions of various phenomena of lithium battery test results, such as leakage, deflation, rupture, and fire.
During use, lithium batteries continue to pass chemical reactions to produce directional flowing electrons to provide sustained energy. In addition, heat is generated in the chemical reaction. If the heat does not spread in time, it will cause the heat to run out of control. However, thermal runaway can cause damage to the battery, such as violent deflation, rupture and fire.
The reasons for the thermal runaway of lithium batteries are as follows:
- The tearing of the separator separating the negative electrode and the positive electrode of the lithium ion battery may cause a short circuit, and the short circuit often causes thermal collapse;
- The ambient temperature is too high, resulting in chemical instability;
- Other abuse operations, etc.
Rules for the classification of dangerous goods in accordance with the UN Recommendations on the Transport of Dangerous Goods. Battery products containing a strong acid or strong alkaline electrolyte are Class 8 (corrosive) dangerous goods, and lithium batteries are No. 9 (Miscellaneous) dangerous goods.
Battery product safety testing items are divided into:
- Expected environmental conditions or use: high altitude simulation, temperature cycling, vibration, low rate charging, etc.;
- Misuse that can reasonably be foreseen: external short circuit, heavy impact, extrusion, mechanical shock, free fall, forced discharge, abnormal charging, thermal abuse, improper installation, overdischarge, overcharge, high rate charging Wait.
Firstly, to classify various dangerous phenomena. Grading is based primarily on the likelihood of each hazard occurring and the outcome of the hazard.
Danger of Battery
The dangers of batteries are mainly divided into:
- Chemical danger
Chemical hazard means overflowing electrolyte or precipitating chemical gas.
- Electrical hazard;
Electrical hazard refers to the electrical hazard generated during charging and discharging.
- Cumulative chemical and electrical hazards
Electrical hazards are electrical hazards that occur during charging and discharging. Accumulated chemical and electrical hazards mainly refer to the possibility of fire, inert or harmful gas generation, spatter. And the root cause is thermal runaway.
- High voltage danger (>60 V)
- The danger of battery failure
For the detection of lithium battery products, the phenomenon mainly includes the following possibilities:
- whether the quality is lost;
- whether there are leakage;
- short circuit;
- whether there will be an explosion or fire;
Hazard Level of Battery Test Result
Based on the above phenomenon, refer to EUCAR (European Council for Automotive R&D) to define the hazard level in automotive applications, and classify the various hazards of lithium battery test results.
|Levels of Danger||Phenomenon||Grade Standard or Impact|
|0||no effect||No effect, no effect loss|
|1||Self-protection start||No effect, no air leakage, no leakage, no fire or burning, no cracking, no explosion, no chemical reaction or thermal runaway, must to repaire protection device|
|2||Influential/damaged||No air leakage, no leakage, no fire or burning, no cracking, no explosion, no chemical reaction or thermal runaway, overall repairable|
|3||Leakage quality reduced by <50%||No leakage, no fire or burning, no cracking, no explosion, electrolyte weight loss <50%|
|4||Leakage quality reduction ≥50%||No fire or burning, no cracking, no explosion, electrolyte weight loss ≥50%|
|5||Fire or burn||No cracks, no explosions (no spills)|
|6||rupture||No explosion (splash allowed)|
|7||explosion||Explosion, the unit completely collapsed|
Hazard levels 1-4 are generally considered safe.
As can be seen from the above, there are various dangerous phenomena in the detection of lithium batteries. In order to prevent people from being harmed for no reason, it is even more necessary to use a safer and more secure testing device for testing. Only in this way can not only ensure the safety of personnel, but also get more accurate test results.
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