Every now and again we hear unfortunate stories about gadget batteries catching fire and even exploding. Samsung Galaxy Note 7 phones were the latest casualty. But what’s the cause of all this trouble?
Lithium ion in the spotlight
The story starts in the early 1990s with the arrival of lithium-ion batteries as a common feature in phones and other devices. Lithium is a lightweight metallic element which is less toxic than previous battery materials such as cadmium or lead. Unlike earlier “single use” batteries, they can normally be recharged thousands of times.
The other clever innovation in lithium-ions lies in the detailed compact structural design of the layered battery. These optimise the thermal pathways and the accompanying software-driven power system control that (normally) avoids overcharging and over-discharging the cells.
These designs have become more and more refined since the mid 1990s thanks to voracious investment in the technology. The energy density that the cells can achieve has grown from 100 watt hours per kilo to 270 watt hours per kilo, which means you can have far more power in a smaller space. This has of course been crucial for the advance of modern consumer electronics in which the size and weight of devices are critical selling points.
With more energy comes more heat
But with more energy comes more heat, and when things get hot inside a battery the packaging and physical space for expansion become increasingly critical.
The race to produce better and better products and capture market share from rivals has required an enormous amount of manufacturing. In the process, it looks as though insufficient consideration has been given to these heating issues, and that new products are emerging that have not been fully time-tested.
But why use lithium-ion in our gadgets if they can go up in flames?
Simply because they are so much better than anything else out there, in terms of energy density on both a volumetric and gravimetric basis. In other words, you get more charge for the battery's size and weight than competing materials “ and both are key to keeping our smartphones slim and light.
Plus they're "low maintenance." That means they don't need prolonged "priming" before they're used “ you can charge them to full once, and they're good to go “ and they don't have "memory", so you don't need to discharge them now and then to keep them fresh.
If you're using a device with a lithium-ion battery, and it starts to hiss or bulge, unplug it from the mains, remove the battery from the gadget if that's possible, and move it away from anything flammable.
One might ask if there are other dangers lurking in the wings. The answer is yes, unfortunately. The investment appetite for batteries is producing a range of devices for large-scale use, such as battery parks for future residential areas and what are sometimes referred to as smart and resilient cities. These parks would be used to smooth the power supply, offer emergency storage and store power from sources like wind farms that can’t produce all the time.
The concept is excellent. Various systems using redox flow batteries containing either lithium or vanadium are already being used to power residential areas in the US and Europe. For example the small town of Braderup in northern Germany has a system that produces 2MW of power and can store 2MWh “ roughly three hours of output from the average onshore wind turbine, for instance. In Washington state in the US, the system pictured below is used to power laboratories.
China has been a leading player in the sector. Current experimental facilities at Zhangbei, a town near Beijing, are reported to be testing systems at 14MW and recently announced plans to create a single 500MWh storage facility with an intention to deliver 64GW of power across China by 2020 “ enough for perhaps 50m homes.
The problem is that the sheer intensity and scale of energy in such parks poses a potential serious explosion and fire risk. If we are to avoid such consequences, designers will need to learn the lessons from smaller batteries. Close attention to safety and proper testing is thus essential.
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After incidents of overheating smartphones worldwide, Samsung made the unprecedented decision to recall every single one of the Galaxy Note 7 smartphones sold. That's 1 million of the 2.5 million that were manufactured. supposedly safe replacement Note 7 phones caught fire as well resulting in Samsung asking all users to shut down their phones.
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What happens when lithium-ion batteries overheat and explode has been imaged inside and out for the first time by a team led by UCL PhD student Donal Finegan (UCL Chemical Engineering) and Dr Paul Shearing (UCL Chemical Engineering).
Scan the QR code to understanding how Li-ion batteries fail.
