In response to today's incident in Xi 'an where an NIO ES8 vehicle caught fire while being repaired by the authorized service centre, NIO announced that it has opened an investigation into the cause of the fire and will release the investigation results in a timely manner.

NIO shares fell sharply on the news before the market opened today. NIO shares were down 26 cents, or 5.43%, at USD 4.53 in premarket trading as of 16:47 Beijing time, according to SINA financial data. In the previous session, NIO shares were trading at USD 4.79, up 4.36% from the previous session.

EVs Have Had Many Fire Accidents

Coincidentally, on the evening of April 21, one day earlier, a fire broke out in an underground garage of a residential area in Shanghai. The fire was caused by a Tesla Model S parked on the first floor of the underground garage, which spontaneously ignited and quickly ignited the surrounding vehicles.

It took about an hour for 15 fire trucks to extinguish the blaze. However, the incident has caused the first floor of the other cars almost all burned, the second floor of the car underground because of the fire spray were all flooded.

Fires in new energy vehicles have been a regular occurrence in recent years. In the more than one month period from August to September 2018, there have been as many as 12 fires on electric vehicles in public.

On August 25, 2018, a WM EX5 electric vehicle suddenly caught fire and spontaneously ignited at the WM Motor research institute in Chengdu. It is not just new car manufacturers,  BYD, an old EV manufacturer, has also burned cars. In August of that year, a BYD song SUV with a petrol-electric hybrid also burst into flames at Shanghai Hongqiao railway station. In addition, BAIC BJEV, NISSAN, and other brand products have had similar accidents.

Why EV Battery Fires and The Consequences So Serious？

Although the brand is different, the cause of the fire is very similar, the most common of which is a short circuit inside the battery. When the positive and negative terminals of the battery are short connected, the instantaneous current exceeds 5A and generates a lot of heat, which can make the short junction reach a high temperature and cause the battery to catch fire.

External collision and lineaging will lead to no diaphragm on the cell, diaphragm damage, protection plate instability, cell internal diaphragm paper instability, and then lead to short circuit. Traffic accidents are also an important cause of spontaneous combustion of batteries. However, most of the power batteries on the market fail to pass the acupuncture test.

In fact, related experts have been calling for a long time, and the acupuncture test has not become a mandatory standard for the whole industry because it is too difficult and exceeds the level of technological development, which can be said to be one of the biggest safety risks of electric vehicles at present.

Why do new energy cars always burn and burn so hard? For example, the Model S has a battery capacity of 85kWh. The battery pack consists of 16 batteries in series, and each battery pack consists of 444 lithium batteries and 74 batteries in parallel.

As a result, the vehicle's power battery pack consists of 7,104 lithium batteries, with an average capacity of 12Wh per lithium battery. That translates to 43 kilojoules, or about 100 grams of TNT, stored in 16 cubic centimetres of space. If the battery shortens, the resulting energy release can be scary enough to set a car on fire.

As Tesla pursues energy density with ternary lithium battery, its electrolyte will produce carbon monoxide, toluene, hydrogen sulfide and other toxic and combustible gases after combustion.

In addition, oxygen will be generated during the reaction process to fuel the combustion, which makes the fire of electric cars often erupt in a flash and the fire expands rapidly. However, because of the generation of oxygen, it is difficult to use the traditional fire extinguishing methods such as isolating air, spraying carbon dioxide and dry powder, and firefighters can only use a lot of water to cool down the fire. So electric cars often catch fire because the rescue is not timely, causing irreparable damage.