The principle of battery operation and "thermal runaway"

To understand battery safety issues, we need to understand how the battery works. The battery has two electrodes, one of which has a positive ion, called the cathode. The cathode is where the "fuel" is stored, filled with lithium. The other electrode has a negative ion called the anode.

Lithium ions move from the cathode to the anode during charging. While the battery is being used, lithium ions move from the anode to the cathode. The chemical between the cathode and the anode is called an electrolyte, which helps the ion to move and conduct current. The current electrolyte is mainly liquid (the solid electrolyte will be mentioned later). Although the ions need to move from one electrode to the other, the two electrodes themselves must not be in contact. So the battery manufacturer inserted a separator between the cathode and the prototype.

“Now the partitions are really thin, so the battery can be slimmer,” says Isidor Buchmann, founder and CEO of battery equipment manufacturer CADEX.

The problem with the Galaxy Note 7 battery is that the separator is defective and the two electrodes are not properly separated. "This is one of the worst situations, because the battery is very likely to catch fire or even explode." Yacher said.

The electrolyte itself is not very stable, and the movement of the ions in it also brings instability. When a large amount of heat is generated – whether through two electrodes touching each other or simply because of external overheating – the electrolyte may react with other chemicals to produce a gas that releases more heat. As the chemical reaction recurs, the gas releases more and more heat at a faster and faster rate. This process will create a "thermal runaway" and may cause a fire to burn.

This is why many mobile phones automatically shut down when they overheat. However, battery explosions may also be caused by other causes. Overcharging or overcharging the battery can cause the battery to catch fire or explode.

Battery overcharging is often the responsibility of the manufacturer

Overcharging is like loading too much water into a bucket. It doesn't matter if you put too much water in the bucket, because the water will overflow. But for the battery, when it is overcharged, too much lithium will enter the anode.

Dan Steingart, a materials scientist at Princeton University, says the battery is like a rubber band. When you charge the battery, it seems to be stretching the rubber band; when you use the battery, it is like releasing the rubber band. If you overstretch the rubber band, it will break, and if the battery is overcharged, it will also break.

However, overcharging is not a user error, as most batteries have an automatic overcharge prevention function. However, if the manufacturer is not strict in the production process, the battery circuit is faulty, and the overcharge cannot be automatically prevented, the problem is big.

In addition, charging too fast is also a problem. Fast charging means charging too much power into the battery in a short period of time, which is the danger of "fast charging technology". If the charger is not compatible with the battery, the battery may also be shorted.

We can think of the battery as two egg crates. Lithium ions need to shuttle between the two egg crates for safe accumulation. If you charge slowly, lithium ions have enough time to find their place in the crate. However, if the charge is too fast or overcharged, lithium ions will build up outside the crate. Then, each time the lithium ions self-deposit, a pin-like structure called a "dendritic" is formed, which can cause a short circuit.

Another common cause of battery accidents is that manufacturers attempt to store more power in the battery by increasing the voltage. The voltage is like the height of a waterfall, and the current is like the amount of water flowing. The higher the waterfall, the more water there is. Similarly, the higher the voltage, the more energy is stored in the battery. Therefore, manufacturers try to increase the voltage by adding a nickel element (or other element) to the battery. However, the higher the voltage, the more easily the electrolyte is produced, resulting in a fire or explosion.

How can users prevent the battery from exploding?

The following 5 suggestions may help you:

1. Don't put your phone under the pillow

Don't put your phone under the pillow, because it will get hot when you charge your phone. If it is still pressed under the pillow at this time, it will generate more heat. The battery needs to cool down. You may find it convenient to put your phone under the pillow, but the most important thing is safety.

2, use an authorized charger

Please use the original charger of the mobile phone, their quality is guaranteed. Lithium-ion batteries can only be charged at 2.5 to 3.65 volts. With the original charger, you can guarantee the right current. If you lose your original charger, you will need to purchase a charger from an authorized retailer. Don't be reluctant to spend money, it will only lose money because of small money.

3, do not put the phone in an overheated environment

Do not use your phone directly in the sun. Avoid the high temperature environment and keep your phone away from everything that generates a lot of heat. Don't lock your phone in the car for a long time in the summer, it will burn the phone. When the ambient temperature exceeds 45 degrees Celsius, try not to charge your phone. Charging in the interval from 5 ° C to 45 ° C is safer. You should avoid charging your phone in an environment where the temperature is too low or too high.

4, do not use too many APP at the same time

Executing multiple tasks at the same time generates a lot of heat, so it is better to use only one app at a time. After you download a movie, download another one, don't download two or three movies at the same time. Play less graphics-intensive games on your phone, which puts a heavy burden on the battery. Close all tasks that you have not used. The more resource-intensive application can't be opened without opening. Although you may feel that playing a mobile phone is not so fun, it is better than a battery explosion.

5, do not use too thick mobile phone sets

The phone case can protect and decorate the phone. Some phone cases are designed to be fun. But be careful not to choose a phone case that is too thick, which is not conducive to heat dissipation. The most important thing is that when wearing a mobile phone case, don't overuse the phone, otherwise the phone will get hotter and hotter. The Pikachu phone case looks really cute. But you also have to pay attention to whether it is too thick.

Can lithium-ion batteries be used with confidence?

Some people think that battery explosion may be the result of manufacturers pushing technology to the limit. The bigger the screen, the more powerful the function, the more power it consumes, and most of us always want the battery life to be as long as possible, and the faster the charging, the better.

According to Lynden Archer, a materials scientist at Cornell University in the United States, the battery life of lithium batteries is now almost 90% of the theoretical limit. Therefore, major mobile phone manufacturers are pushing to the limit and hope to obtain the longest possible battery life.

"Smartphone manufacturers want to get the longest possible battery life, which is a bit like an arms race." Yacher said. “The result is more and more prone to battery accidents.”

Having said that, you don't have to worry too much. Just look at the statistics and you will know that lithium-ion batteries are relatively safe. KM Abraham, a professor of lithium-ion batteries and a professor at Northeastern University in the United States, said, “There are billions of mobile phones and computers in use around the world every day.” Relatively speaking, the proportion of accidents is very small.

“In general, the possibility of a cell phone catching fire is very small,” Abraham said. “The failure rate of lithium-ion batteries is less than one in a million.” Just a comparison is needed. According to the National Oceanic and Atmospheric Administration, the probability of a person being hit by lightning for a lifetime is 13,000. one.

Although the possibility of an explosion is small, do you want to abandon lithium-ion batteries for safety? This is unlikely, Buchman said. Although security is a problem, it is just one of several factors to consider when designing a battery. Most of the other factors are related to energy density, battery life and charging performance.

Lithium-ion battery vs. competitor

"It's very difficult to develop a better battery than a lithium-ion battery," Buchman said. But the lithium-ion battery itself is getting better and better.

“There are many companies that are trying to use better materials to improve safety,” Abraham said. The next generation of lithium-ion batteries will use polymer separators with higher melting points to prevent thermal runaway. “There are still some companies that are developing new electrolytes that won’t catch fire when in contact with air,” he said.

While lithium-ion batteries represent the highest level of design available today, some companies are working hard to develop new battery types that hope to surpass lithium-ion batteries in terms of safety and performance.

The most promising competitor is the "solid state battery." The electrolyte in such batteries is solid rather than liquid. It is much less likely to burn, so it is expected to be an ultra-stable battery with a much better energy density, burning or explosion.

The Michigan-based company Sakti3 is working on solid-state batteries. In 2015, vacuum cleaner giant Dyson spent $90 million to acquire the company.

George Crabtree, director of the Joint Energy Storage Research Center, believes that the company's solid-state battery technology looks promising, but if it is ready to launch a lithium-ion that can be used on smartphones Battery replacement, then an electronics giant such as Apple or Samsung can offer a price 10 times higher.

Solid-state batteries, while having many benefits, have a huge drawback: lithium ions move much faster in solid electrolytes than in liquid electrolytes. For this reason, the speed at which solid-state batteries can be charged can only be described by the speed of the turtle.

The lithium-sulfur battery is a solid-state battery that has the advantage of being lightweight and ideal for use in high-altitude drones. But this battery also has a problem: the number of times of charging is very limited, currently about 20 times. This means that the use of lithium-sulfur batteries will require significant improvements in order to be used in mobile phones, notebook computers and other consumer electronics.

There are more battery technologies under development, each with its own advantages and disadvantages. Although mobile phone lithium-ion batteries are still irreplaceable in the next year or two, there are so many competitors in this field, and some experts believe that it will take less time to produce better and safer batteries.

“I think it’s an important moment now. In the next 5 to 10 years, we will see a huge change in battery technology,” Crabtree said.

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