Why does cell phone lithium battery become "bomb"?

Samsung's flagship Galaxy Note 7 has been in the headlines for some time, not because of its performance or design(of course, the Note7's performance and design are indeed good), but because it was released shortly after its launch. That is, it was found that the built-in battery has major safety hazards, and the probability of an explosion without reason is far beyond the normal range.

When the incident broke out, Samsung suffered a huge blow and lost countless money. Electronics consumers and even people from all walks of life began to "talk about change". This is from the recent definition of Samsung mobile phones by some airlines as civilspecial dangerous goods. It is evident in the behavior.

But then again, it's not uncommon for electronics to explode in everyday life, so what happens when the devices that are supposed to serve consumers suddenly turn into "bombs"? Let's take a look at the chemical interpretation of this article.

They're all lithium batteries, but why are they so different?

Today, the vast majority of electronic products have entered the "age of lithium batteries." As a battery with more application experience, lithium batteries have long life, large capacity, and low cost, so it is widely welcomed. It is entirely reasonable.

However, although many types of batteries can be called "lithium batteries," do you know that there is a big difference between lithium batteries and lithium batteries?

In fact, lithium batteries can be roughly divided into two categories-traditional lithium ion batteries and lithium ion polymer batteries. They have many properties that differ:

Traditional lithium-ion batteries:

The typical representative of such batteries is the 1,8650 lithium battery that frequently appears in various "charging treasures(mobile power sources)". The battery is named after its appearance characteristics(18mm in diameter, 65mm in height, and cylindrical)., Because of its low cost and durability, it has become a "fighter" in the lithium battery market today.

Traditional lithium-ion batteries, like other traditional batteries, contain electrolytes responsible for the transfer of electrons(because battery charging and discharging is essentially an electronic directional movement process), so a certain packaging volume is required(this sometimes makes it not portable).), And the hard shell that is responsible for protecting the electrolyte.

Lithium-ion polymer battery:

At present, all portable electronic products such as mobile phones, tablets, and most laptops use batteries of this type.

Lithium-ion polymer batteries use polymer series battery structures so that they require only a small amount of liquid electrolytes. Therefore, this type of battery does not require hard shells for protection. There is no limit to its shape, and its packaging volume can be greatly reduced.

Based on these characteristics, lithium-ion polymer batteries are heavily equipped in some electronic products that seek lightness and require equipment thickness, and have a tendency to replace traditional lithium-ion batteries.

Why did lithium batteries become "bombs"?

In the Samsung Galaxy Note7 explosion described at the beginning of the article, Samsung later confirmed that the explosion of mobile phones was closely related to the design flaws of its lithium battery, and the explosion of electronic products in recent years(such as the explosion of Sony laptop computers in 2006). In the end, Sony conducted a global recall of problematic products.) All but the exception was the explosion of lithium batteries.

From a chemical point of view, there are many reasons for the explosion of lithium batteries, and a considerable part of the reasons have a lot to do with the manufacturer's design flaws.

It is well known that an important cause of battery explosion is a short circuit of the battery(that is, the circuit in which the battery is located does not have an electrical appliance, and even the current passing through the battery in a short period of time is too large). Whether the battery is short-circuited or over-charged(another important cause of lithium battery explosion, that is, the battery charging voltage is higher than its set upper limit), it will cause the lithium battery to accumulate a large amount of heat and gas in a short period of time(lithium batteries will work. Generate gas).

In this way, in order to release pressure, the lithium battery either activates the internal pressure release device or directly splits its shell, and both of these conditions cause the internal material of the battery to contact the air directly and cause combustion.

In general, explosion combustion of lithium batteries is rarely due to external circuit failure, which means that the vast majority of lithium battery explosion combustion events are due to design defects inside the battery.

For example, in the explosion of the Sony notebook battery mentioned above, the electrolyte part of the problem battery was detected as a metal impurity. The accident was also caused by an unexpected electrical conductivity caused by metal impurity, resulting in an internal short circuit and causing an explosion.

Coincidentally, the fire of the lithium battery of the Boeing 787 aircraft was also related to the performance of the electrolyte in the special environment of the aircraft battery, which caused an internal short circuit.

Of course, the two lithium battery explosions involved both traditional lithium ion batteries, and the "protagonist" of the Samsung Galaxy Note 7 explosion was a lithium ion polymer battery, so the lithium ion polymer battery was in such an event. What's so special about it?

In fact, in general, lithium-ion polymer batteries do not have a hard shell, and the possibility of violent explosion and combustion has been greatly reduced. When such batteries have an explosion accident, they will explode in advance due to the poor impact resistance of the shell, which is usually shown. Slow combustion after explosion.

However, the high degree of shape variability of lithium-ion polymer cells not only gives equipment manufacturers more free design space, but also often requires additional design of the battery components. In this way, it is inevitable that the battery pack design does not pass, which in turn causes an accident.

In the Samsung Galaxy Note 7 explosion, it has been initially determined that batteries with major defects in the production process are likely to be responsible for the explosion.

How to avoid a repeat of the explosion?

Although Samsung has launched a recall of products with faulty batteries, the impact of the incident, including damage to brand image, value, and company reputation, is bound to be irreversible. The incident can also be included in one of the major safety incidents in the history of the development of lithium batteries.

In that case, where do we need to improve in order to avoid a repeat of the accident?

Today, lithium-ion polymer batteries have been widely promoted. The most important thing that major lithium battery manufacturers must do is undoubtedly to strengthen the control of battery safety. This not only needs to carry on the strict product factory inspection, the new product test and the good rate control, but also can not leave the battery design work and input.

After all, theoretically, a battery that is designed and produced fully qualified has a very low probability of accidents after long-term use. Even if there is an accident, it will not damage the reputation of the manufacturer. However, if the battery has major problems in these links, The manufacturer will pay a heavy price.

For consumers, choosing the right lithium batteries and using them correctly in the right environment are key to preventing accidents.

Some consumers are greedy for a time and choose various types of irregular batteries. In fact, they have laid a hidden danger for future use. Similarly, even if a fully qualified lithium battery is not used by consumers in an appropriate environment(such as using batteries in extreme weather, water, and high temperatures), Or use inappropriate methods to treat batteries(such as smashing or cutting lithium batteries) can lead to accidents.

The page contains the contents of the machine translation.