Danger! Don't treat lithium batteries with violence or exposure

March 26, 2019

Lithium batteries are the most commonly used power source for smartphones and tablets. However, some time ago, the explosion of lithium batteries in several mobile phones was chilling. On July 21, a truck loaded with nearly 40 tons of used lithium batteries caught fire, causing the Xinkun section of the Shanghai-Kunming Expressway to be interrupted for nearly five hours. In these news reports, lithium batteries seem to be a "dangerous product" that is very fragile and prone to fire and explosion.

Yesterday, the reporter confirmed in the Longtan Lake fire squadron that lithium batteries will swell and smoke once physical damage occurs, especially after the water is absorbed, the lithium battery will release more heat.


Firefighter cuts lithium battery


The cut lithium battery is a layered structure inside.


Lithium battery bursts with smoke

experiment

Lithium battery loves to get angry

In order to ensure the experiment has a higher reference, the reporter deliberately prepared three different types of lithium batteries, which are soft-pack lithium batteries used in tablet computers, cylindrical lithium batteries used in notebook computers, and hard used on mobile phones. Shell lithium battery.

The firefighters participating in the experiment first placed the soft lithium battery on an abandoned bench, and then cut the outer casing of the soft lithium battery with a pliers. As the lithium battery case broke, the soft-packed lithium battery bulged, and the gap began to emit white smoke. The firefighters then poured the water on the lithium battery. The white smoke was even more powerful. It also made a "sting" sound, and the water poured on the lithium battery also appeared bubbling.

Then, the firefighters broke the cylindrical lithium battery and the hard-shell lithium battery. After the two lithium batteries were cut, there was not much white smoke at first, but when the water was poured on it, a lot of small bubbles appeared from the crack. In less than two minutes, the temperature around the lithium battery began to rise, and the water trace was actually baked by the heat radiated from the lithium battery. Firefighters said that this is the characteristic of the lithium battery after physical damage.

In January of this year, a fire broke out in a private house on the Stadium Road in Dongcheng District. When the firefighters buried the smoking electric vehicle battery in the snow, the battery actually showed an open flame. It was only afterwards that the electric vehicle battery was a lithium battery.

Quest

Why are you getting angry?

It is understood that lithium metal is very active in chemical properties and is a dangerous item that is in danger of being exposed to moisture. It will release flammable gas when exposed to water or humid air. In fact, the phenomenon of heating or burning of lithium batteries is mainly caused by short circuit and excessive current. For mobile phones, the charging and discharging currents are too large. There are many factors that cause a short circuit in a lithium battery, including physical damage to the battery, temperature of the environment, and short circuit between the positive and negative electrodes. If the lithium battery case is damaged, it will cause a short circuit inside the battery core, which will generate heat.

Yang Yong, an associate professor at the School of Electrical Engineering, Huazhong University of Science and Technology, told the reporter that under normal circumstances, the electrolyte contained in the lithium battery is in a sealed state and will not react. However, when the outer casing of the lithium battery is broken and the electrolyte inside encounters air or water, a chemical reaction occurs, generating gas and heat. "When the reaction is severe, it will burn or even explode."

remind

Avoid violent bumps

It is precisely because of this characteristic of lithium batteries that lithium batteries are classified as dangerous goods (DGR) in the relevant regulations of the International Air Transport Association (IATA). I believe that many people have such experience. When flying in an airplane, electronic devices containing lithium batteries are not allowed to be checked and can only be carried with them. Moreover, the total energy of the lithium battery carried by the passenger should not exceed 160Wh (Watt hours). When carrying, the lithium battery should also be packed in a separate plastic bag or wrapped with insulation.

Among polymer model players, lithium polymer batteries are commonly used. However, this kind of lithium battery that appears later and has more mature technology still has certain dangers. Some players have placed lithium polymer batteries on the window sill. As a result, the sun's exposure caused the internal pressure of the battery to increase, the battery suddenly ruptured, and smoke was emitted. In addition, when the player is flying the helicopter model, the lithium polymer battery is thrown onto the propeller, and several batteries are smoked in the air instantaneously, and the fuselage is also deformed by the high temperature that is released when the lithium battery is damaged.

In the tablet computer, the lithium polymer battery is used as the same, but since the tablet computer has far less capacity for charging and discharging the battery, when the battery is physically damaged, the energy released instantaneously is not so large, but the high temperature is released. "For example, if the tablet is rolled by the wheel, then first observe whether it is smoke. If not, then touch the outer casing of the battery to see if the temperature is normal. Do not rush to put it in the bag, so as not to Caused a bigger fire accident." Wang Hongyu, the squad leader of the Longtan Lake Squadron, suggested that for electronic devices such as tablet computers that use lithium batteries, care must be taken to avoid exposure and to avoid violent bumps.

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