Lithium batteries are getting unsafe?

Apple has begun investigating the cause of the incident, which is not the first time an iPhone has been in a safety accident. In late January, Samsung also announced the results of the Note7 battery explosion investigation. The problem is still on the battery, and the reasons for the spontaneous combustion caused by the batteries provided by SDI and ATL are different. This will result in Samsung's recall of mobile phones and replacement of batteries to re-market, still unable to solve the explosion problem. Earlier, Tesla's car frequently spontaneously ignited after the collision, and many lithium batteries caught fire in the early days of the Boeing 787. Byd's electric taxi was rear-end and burned.

All of this seems to link cell phone batteries to insecurity, but people's lives can not leave it. Lithium battery is a widely used energy storage tool at this stage. Why will there be frequent safety accidents in the near future, and what will be the future direction of battery development?

Lithium battery working environment

Growing "bad"

Large screens, large memory, and high-speed processors have become the standard for smartphones today. But the bigger screens and the more frequent multicore processors are the biggest consumers. Take Samsung Note7 as an example. Its four-core processor has a main frequency of up to 2.15 GHz and a running memory of 4GB. It is basically the same as the mainstream notebook computer on the market. It is also necessary to handle information communications while maintaining standby. How much pressure is the battery.

How to improve standby time? Under the premise that the power consumption of the system is constant, increasing the battery capacity seems to be the only way. Unlike the 1,8650 batteries used by Tesla, lithium polymer batteries are widely used in electronic products, that is, thin, thin, flexible, massive batteries. Lithium-polymer batteries are "fragile" because they are not protected by hard shells. Excessive extrusion, overheating, and internal or external puncture can make it dangerous to burst into flames.

Samsung announced the official investigation results of the Note7 explosion on January 23, saying that the first batch of batteries had suffered crush damage in the upper right corner, which is consistent with the conclusion that the size of the battery announced by the third party did not match the battery warehouse.; The reason for the second batch of battery problems is that "positive electrode welding has burrs, piercing the battery leads to short-circuit fire." These two points are exactly the "fate" of lithium polymer batteries.

Not only that, but more and more "fast charging" technologies that appear on electronic devices also add a lot of burden to batteries. Since the fast charging current and voltage are much higher than the normal charging state, it is not ruled out that there is a certain chance that some dangerous accidents will occur when the power management module is in trouble. At the same time, frequent use of fast charging will also shorten the battery life.

New approaches are expected to improve

Lithium battery safety

The four main parts of the lithium battery are positive electrode materials, negative electrode materials, isolation membranes, and electrolytes. When dendritic or hand-shaped lithium ions grow inside, it is very easy to short-circuit or randomly explode to form open fire. Once a dendritic process is formed inside the battery, the risk rapidly increases and may eventually pierce the positive and negative insulation membrane.

In order to avoid spontaneous combustion of the next generation of batteries, researchers are trying to find new ways to prevent fire hazards. They added two chemicals to the electrolyte inside the battery, one of which is lithium nitrate, which can improve the endurance performance, and the other is lithium polysulfur, which can decompose electrodes. During the test, it was possible to control the appearance of harmless pancake products rather than dendrites inside the battery. In addition, these two chemical materials also improve the durability of the battery. After 300 battery cycles, the battery capacity remains at more than 99 %.

In terms of reducing the operating temperature of the battery, LG's G6 released at the MWC2017 conference uses the common copper thermal catheter design in the computer and is reported to reduce the thermal energy generated by the battery by about 10 %. At the same time, a more well-designed battery management system can also help electronic equipment in the case of overheated batteries in time to reduce frequency, "cooling" the battery. Despite all the safety problems, lithium-ion batteries were still good partners in our lives until there was a major breakthrough in battery technology. The key point is that national product safety regulatory agencies should introduce a more complete battery detection mechanism. At the same time, consumers should also use lithium batteries correctly. Do not step on batteries and heat them.

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