Is the battery very dangerous?

Is the battery very dangerous?

Many devices currently use lithium batteries. However, the fire problem of the Samsung Galaxy Note 7 and the terrible accident of Tesla have caused people to ask a question: Is the battery really safe?
The US press absolutely loves Elon Musk, who brings the success stories of Tesla and SpaceX. Even the company's failure can make the media pay attention: Tesla in early November 2016 The "explosion" report once again became the headline of the media, the same as the accident in Florida (see article 10, "Why does autopilot fail?" in 2016). The accident indicates that the party in the accident was caused by the immature technology. Death.
Samsung Galaxy Note 7 is another device that became the headline because of the "explosion". Shortly after the device was released, the product caused repeated explosions all over the world. Samsung finally decided to recycle and stop production globally. Down the shelf, in fact, the product has been abandoned by Samsung, and Samsung's performance has been greatly affected, so that the Korean economy has also seen a domino effect.
However, Dr. Werner Mitz, a professor at the Center for Solar and Hydrogen Research in Ulm, Germany, believes that people should not have a crisis of confidence in lithium-ion batteries because of these two accidents. Samsung's events show that smartphone manufacturers are more demanding in battery development. In order to get the best power and energy density, battery manufacturers are getting thinner and smaller isolation foils installed between battery electrodes. The latest products have only a few microns of barrier foil, however they are required to reliably ensure that the components are insulated from one another. Production problems may lead to problems such as broken foils. Such problems will lead to obvious circuit short circuits, and battery defects should be detected during quality inspection. According to Dr. Werner Mitz, the battery failure should be caused by the “breathing” of the battery unit, which changes its crystal structure during charging and shrinks during discharge. During the operation of the device, this Mechanical stress can cause damage to the separator foil.

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Damage to the isolation foil causes a short circuit in the battery to generate very high currents and cause the battery to overheat. It becomes dangerous when the temperature is about 200 ° C to 220 ° C. At such temperatures, due to internal pressure, the battery bursts out of the electrolyte and a portion of the electrolyte evaporates. At about 220 ° C, the electrode begins to decay, which will result in the appearance of hydrogen, which can be ignited by a spark. Obviously, the defects of this battery are dangerous, but Dr. Werner Metz pointed out that according to statistics, about one in every 4 million of the 2 million Galaxy Note 7 devices has problems.

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Gasoline car catches fire more frequently
Two people in the unfortunate accident in Indianapolis, Serra, died of a car fire Driving too fast, causing a collision with a tree in the center of Indianapolis. Witnesses at the scene claimed that a large-scale explosion occurred and the fire brigade spent 15 minutes to control the fire so that the victims were not treated in time. In this regard, Dr. Werner Metz believes that Tesla's battery is unlikely to cause a big bang. A video recorded by a firefighter showed that Tesla's battery was destroyed due to heat, and the battery unit was thrown into the air after the burst. However, the bursting strength is not like a bomb, but more like a firecracker.
In a tightly packed battery module, the batterys under combustion and heating are likely to be affected one by one. However, according to Dr. Werner Metz, the chain reaction in the battery takes several minutes, so all involved In the case of the fire of the Sela electric car, the driver was able to stop and walk out.
Dr. Werner Metz also pointed out that according to automobile statistics, fires in traditional cars are more frequent due to accidents or defects, and there are thousands of such accidents every year in Germany alone. When asked if they think electric cars are more likely to catch fire than conventional gasoline-powered cars, Dr. Werner Metz’s clear answer is “no”. Considering the amount of energy, the risk of a gasoline car explosion is actually higher: 50L of fuel contains at least 450kWh of energy, while Tesla's battery contains only 100kWh of energy.

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Editor: Jin Yawen jin_yawen@chip.cn

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