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Li-ion Battery Thermal Runaway Risk

Storage and Transportation Safety of Li-ion Battery

The safety of lithium-ion batteries refers to the absence of leaks, candles, fires, explosions, and other phenomena under various testing conditions, ensuring that scientific research, production, and user personnel are not injured even under abusive conditions. Batteries produced will undergo storage, transportation, and transportation to the terminal. Whether using air freight, sea freight, railway, or highway, there are logistics consolidation and container transportation links.


Taking sea transportation as an example, if an unexpected factor triggers the thermal runaway combustion of batteries in the cabin during transportation, according to research results, the concentration of carbon monoxide (CO) released during the combustion of 10Ah soft packaged lithium batteries in commercial lithium manganese oxide systems and ternary material systems exceeds 12800ppm. CO at this concentration can cause rapid death in adults within 1-3 minutes.


So, even without considering other toxic and harmful substances released during thermal runaway in high-energy and complex mixed systems such as lithium batteries, CO alone has significant harm. For other local spaces, such as cars, ships, submarines, spacecraft, and in space parking lots, there is a similar issue of lithium electric thermal runaway causing disasters. For open spaces, such as lithium-ion energy storage stations, outdoor parking lots, and charging stations, there are potential environmental pollution hazards.


Due to numerous safety accidents during the transportation of lithium batteries, international organizations such as the United Nations, the International Aviation Association, and relevant domestic departments such as the Civil Aviation Administration of China require that lithium battery transportation must undergo UN38.3 and other tests in accordance with IATADGR requirements.


The US Department of Transportation has classified lithium batteries as hazardous materials, which include flammability, leaching toxicity, corrosiveness, reactivity, and other toxic and harmful substances. It is the battery with the most toxic substances among all types of batteries and cannot be transported casually. Special packaging boxes and methods are required, and all labels must be complete before transportation. In addition, there are various restrictions on air transportation, and lithium batteries must pass UN38.3 certification. Underwriters Laboratories (UL), an American safety testing and certification company, plans to introduce a series of new specifications for electric vehicle batteries. UL Laboratories hopes to establish a set of specifications for electric vehicle batteries, and the government will require battery manufacturers to recognize UL Laboratories’ certification.



Lithium Battery Thermal Runaway

In the entire life cycle of lithium batteries, even if the battery structure is well-designed and reliable in storage and transportation, it is still necessary to establish a toxic database for the thermal runaway process of the battery to respond to emergency situations such as fire, explosion, and toxic leakage. Technical guidance, operating standards, technical compilations, manuals, and other documents related to lithium batteries have always been in the process of competitive revision globally, controlling the battery economy worldwide.


It is currently unclear whether the United States, Japan, and South Korea have a detailed database of secondary toxicity caused by thermal runaway of lithium batteries and corresponding regulatory standards, but the Institute of Chemical Protection has gradually improved its database of lithium electric thermal runaway combustion products. In addition to the publicly available CO and hydrofluoric acid (HF), there are also over 100 species with molecular weights above 45 in the database, including substances with toxic or toxic properties.


In the routine safety test, the abuse test under the conditions of simulated machinery (drop, impact, nail penetration, crush, vibration, acceleration), heat (ignition, sand bath, hot plate, thermal shock, oil bath, microwave heating), electricity (overcharge, overdischarge, external short circuit, forced discharge) and environment (decompression, immersion, height, antibacterial) is the key step of the general safety test, These steps and methods can be used as a reference for testing the secondary toxicity of thermal runaway combustion in lithium batteries.


The research results of ignition induced thermal runaway combustion of lithium batteries indicate that the toxic species released during the thermal runaway process of lithium batteries are highly dependent on the battery material system, battery capacity, and charging state; Regarding toxicity, 100% charging state is the most dangerous state, and the smaller the charging state, the safer it is. The severity of thermal runaway combustion tests on batteries made of different material systems varies significantly, with lithium manganese oxide (LMB) system>ternary (NMC) system>lithium cobalt oxide (LCB) system>lithium iron phosphate (LPB) system, indicating that LPB batteries exhibit high safety against ignition induced thermal runaway.


For lithium batteries with four material systems, the number of species that can be determined in the combustion products is strongly related to the charging state of the lithium battery, and follows the following order: the number of species in the thermal runaway combustion products increases with the charging state increasing from 0% to 100%, but decreases with the charging state increasing to 150% (overcharged state). Why does the number of combustion product species decrease for all four types of batteries when overcharged? The reason is that when the battery is overcharged, the lithium ions in the lithium salt will precipitate metal lithium and deposit on the cathode surface. At the same time, the solvated electrolyte will also be gradually reduced, decomposed, and consumed. When overcharging reaches 150%, only a relatively small number of species are left in the battery to participate in the subsequent combustion reaction, so the number of species in organic combustion products actually decreases. The research results also show that some species in the thermal runaway products are newly generated and toxic.


These organic products released during thermal runaway combustion process have strong irritating effects on human skin, eyes, and respiratory tract, and are harmful to the environment. If these toxic substances are released into small enclosed spaces such as cars or airplanes, they will cause serious harm to people in a short period of time. The combustion products of LCB batteries have the most toxic species, while LPB batteries have the least. The charging state of the battery strongly affects the toxicity of the combustion products. So, from the perspective of toxicity, the 100% charging state is the most dangerous state. Simply put, if a newly charged battery is ignited and loses control, it will release more toxic and harmful substances. The above test results also indicate that when the battery undergoes thermal runaway combustion, different chain reactions occur in different systems, which is strongly related to the charging state chemistry of the battery material system.


The above research work has obtained data on toxic products caused by thermal runaway combustion of lithium batteries, which will provide necessary guidance for the design of new materials for lithium batteries, early warning of fires and toxins caused by thermal runaway of lithium batteries, and improvement of safety of lithium batteries.

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