Battery Cell Safety Concerns: Thermal Runaway.
Battery Cell in our Lives.
In the past decade, lithium-ion batteries have become pervasive in almost every aspect of our daily lives. From smartphones to headphones, various power tools, and now vehicles, lithium-ion is the most important and widely available battery chemical.
However, lithium-ion batteries are also known to pose a number of significant safety risks if not handled properly. Safety incidents are frequent, threatening personal safety, commercial promotion, and social benefits. The study of the safety of lithium-ion batteries has now become a research hotspot in the battery field.
What is the Battery Cell Thermal Runaway?
The basic characteristics of a lithium-ion battery safety accident are:
1) The accident is initially "thermally triggered" by an internal short circuit that generates;
2) Due to the poor thermal conductivity of the battery, the build-up of heat pushes up the temperature of the battery;
3) When the temperature rises to the point where it causes a chain chemical reaction inside the battery, the temperature rise of the battery will gradually accelerate until the chemical reaction inside the battery releases so much heat that no means of heat dissipation can stop the temperature rise of the battery, i.e. the battery goes into thermal runaway.
There are many reasons for safety accidents in lithium-ion batteries, and it is difficult to restore the cause of an accident when the battery is burnt after an accident, so the only way to find out the possible causes of safety failure in lithium-ion batteries is based on inference. The following 6 main causes have been identified: thermal stability, lithium precipitation in the negative electrode, foreign matter in the positive electrode metal, diaphragm defects, design/manufacturing defects, and deformation of the electrode.
How to Research the Hazards of Thermal Runaway?
Test methods for the safe failure of lithium-ion batteries are still in the early stages of exploration, but due to the frequency of safety accidents, the study of secondary hazards arising from thermal runaway of lithium-ion batteries is a very important topic.
If the lithium battery cell goes into thermal runaway, a large amount of heat and flammable and toxic gases are generated, resulting in the battery blowing up due to the rapid increase in internal temperature and pressure, and the flammable gases then leaking out and causing violent combustion when they meet the outside air at high temperature, forming a jet fire or explosion, thus causing the loss of control of other surrounding cells and causing safety accidents.
At present, the study of secondary hazards arising from thermal runaway of a battery cell generally consists of the following tests:
1) Triggering thermal runaway of the battery cell in a controlled and repeatable manner in a safe pressure vessel.
2) Recording temperature changes on the surface of the battery cell and in the safety valve during the thermal runaway.
3) Extraction of the gas produced after thermal runaway of the battery cell and analysis of its composition.
(4) Analysis of the flammability limit of the gas generated by the thermal runaway.
(5) Analysis of the maximum explosion pressure of the gas generated by the thermal runaway.
(6) Analysis of the burning velocity of the gas generated by the thermal runaway.
Instruments involved in the Battery Cell Thermal Runaway.
Gas Explosion Pressure Test
Gas Chromatography
Gas Flammability
Summary
Lithium-ion batteries bring convenience to our lives, but they also pose challenges in terms of use. Engineers are constantly researching and developing safer batteries and systems.
