The safety of lithium ion battery

The lithium battery is a kind of lithium metal or lithium material as the cathode material of chemical power source, lithium battery emergence and rapid development is with the 60 s and 70 s of the 20th century is closely related to the oil crisis, in recent years, due to various reasons such as environmental protection, and changes in lifestyle (new energy vehicles and smart phones, etc.), the market once again set off a "lithium electricity craze ".


Lithium is a silvery white metal, as a result of metallic lithium on all the lightest metal (atomic weight of 2.94), the standard electrode potential minimum relative standard hydrogen electrode (3.05 V), the largest mass energy density (3.86 Ah/g), people began to explore the lithium battery as an alternative energy source.


Lithium - silvery white metal

(image source network)

Lithium electric industries to bring many opportunities and profits, but lithium electricity safety problems are also frequent, 25 February this year, China southern airlines to airlines flight from Guangzhou to Shanghai in the process of passenger boarding, the passenger carries baggage in the overhead bin smoke and fire, after China southern official news, the reason is that passengers carry mobile charging treasure smoke and fire.



On February 25, China southern airlines flight passenger luggage on the rack is on fire

(image source network)

, of course, it is not happenstance, incidentally, on November 30, 2017, Wuhan Dongxihu three many street shops, 225 north road, Wufu electronics technology co., LTD., a fire, later after thespecial investigation, because of the rain infiltration internal react with metallic lithium batteries, burst into flames and cause adjacent warehouse item was burned, is a production safety accident.

Last year in Zhuhai for north Xia Wan Dongsheng west street number 43 a unit to fire, fire officers and soldiers to put the fire out quickly. Things happen or and charging treasure is related to the fire.

If China southern airlines charging treasure fire is an accident, so the events of Wuhan and Zhuhai and how do you explain this? Analysis or safety issues are in the final.

Is what reason causes the lithium battery security issues, is a technical problem?

Of course we cannot deny that there may be some company technical problems, but I think, in addition to technical problems there will be some external human factors in affecting the safety of lithium-ion batteries.

Due to the implementation of environmental policy, new energy vehicles has been more and more appear in our field of vision, new energy vehicles will need a lot of hot battery, and lithium batteries due to its high specific energy, long cycle life, and the obvious advantages of environmentally friendly and popular, some companies want to from the current hot cases and make a lot of money, if the company can't catch sight of opportunity, the late market gradually saturated, they will not profit from it, so many companies, of course, to grasp the current appears to change as the company's operations, this will lead to the battery in the process of production to detect on the safety performance of the battery is too careless, and did not appear on the market at present lithium battery safety problem of thinking too much, some companies didn't put it in heart.

In addition to the small make up when it comes to the above factors, the safety of the battery problem, of course, also restricted by other factors. Lithium battery safety problems, we should blame who?

Suspected one: acupuncture, circuit and extrusion (force)

After a number of studies we found that if the surface of the battery by acupuncture or extrusion, can lead to fire and so on, this is because the battery short-circuit or by acupuncture and extrusion, often easy to cause the battery internal diaphragm rupture, causing the battery in a very short time there were a lot of current flow, it is easy to lead to a dramatic increase in the internal temperature of the battery, causing a series of violent reaction, even combustion, explosion and other security issues.

Two suspects: thermal shock (temperature)

Thermal shock effect on the battery safety is also an important factor, when the battery by thermal shock, heat conduction rate is relatively slow due to battery, so it can withstand short time of thermal shock, if the higher temperature, thermal shock will cause the battery cathode surface decomposition of SEI. Highly intercalated-li anode materials are exothermic reaction with the electrolyte. But whether risk depends on the cooling rate, cooling rate is slow, battery internal temperature, melt the diaphragm, and vice versa.

Three suspects: after charging

Overcharge, if the battery has good heat dissipation, or charging flow is small, the temperature of the battery is low, at this time only after filling the electrolyte decomposition, the battery is still safe, if the battery cooling is poorer, or due to high rate charge battery, high temperature caused chemical reactions and transition metal oxide anode material at this time due to the serious lithium, chemical activity increased significantly, often leads to more than a simple thermal shock serious security problems.

Current to the current process is accompanied by joule heat, when the battery heat production rate is greater than the battery cooling rate, will cause the battery thermal runaway. In addition, when the charging current is too large may lead to negative lithium surface coating, the resulting cells exist in risk of short circuit.

Four suspects: the anode materials

Because the battery in the production of the anode material in use different structure, when the battery temperature rise, the positive material performance of the different problems are evident, one of the anode materials for lithium iron phosphate battery safety performance is best, and nickel cobalt manganese acid lithium battery is better than that cobalt acid lithium batteries, due to other parts of the battery are basically the same, therefore, the security of the anode materials determines the safety performance of the battery.

Affected by many factors of lithium battery safety problems, we can't a Bonzi killed a group of people, or to consider from several aspects, try to reduce the external factors of lithium electricity problem, we hope that relevant enterprises to improve technology and detection ability. Users also have to pay attention to in the process of using, ensure that our life is convenient, really don't want a similar accident again.

The page contains the contents of the machine translation.