28-10-2016 | By Paul Whytock
The recent publicity frenzy focusing on the Samsung 7 phone fires has created more questions over the safety of Lithium batteries than any previous event, including a potentially catastrophic one such as whether or not Lithium battery fires could bring down a Boeing 787 Dreamliner passenger aircraft.
In fact the Samsung Lithium battery phone fires prompted the Federal Aviation Administration (FAA) in the US to ban passengers from taking their Galaxy Note 7 phones onboard flights. To do so risked anything from having your phone confiscated to being criminally prosecuted if you tried to transport your phone by hiding it in checked luggage.
This all added to the blaze of media hype surrounding Lithium and certainly took attention away from a previous FAA decision regarding Lithium batteries bursting into flame on board Boeing 787 Dreamliner aircraft.
Those Dreamliner Lithium batteries were packed in sealed metal boxes with no means of venting excessive heat. So when a single cell became hot enough to ignite its electrolyte the battery burst into flame.
However, The FAA allowed US Dreamliners to return to service after changes were made to their battery systems that would help to contain battery fires. (Note the word contain here rather than resolve.) Boeing redesigned the batteries to beef-up protection around the cells to contain overheating. The batteries are still housed in a steel case but with the vaguely Heath Robinson addition of a tube that vents fumes outside the fuselage. Quaint.
So the Dreamliner continued to fly with FAA approval yet the actual cause of the fires remained unknown, just as it remains unknown in Samsung Note 7 phones.
There can be numerous reasons why a Lithium battery decides to combust and not all of these reasons are anything to do with the manufacturer of the battery or the company using them.
Lets not forget that ten years ago in 2006, product recalls where made by Apple, HP, Toshiba, Lenovo and Dell, after a small number of batteries used in their products overheated. According to the Consumer Product Safety Commission in America.
Apple recalled 1.8 million iBook and PowerBook battery packs because of overheating.
In Samsung’s case there have been 35 incidences of the Galaxy Note 7 catching fire reported worldwide following 2.5 million sales.
The lithium ion batteries used by Samsung are in common use so what’s the problem? The problem is there can be any number of problems than can cause battery ignition.
Lithium batteries contain a cathode, an anode and lithium.
The cathode and anode are separated by an organic liquid called an electrolyte and a porous material called the separator. The lithium travels through the separator within the liquid between the cathode and anode.
The lithium-ion battery's explosive tendencies are the result of a process known as thermal runaway. It's essentially an energetic positive feedback loop whereby increasing temperature causes the system to get hotter, which increases the temperature, which causes the system to get even hotter and meltdown. Thermal runaway is a common phenomenon and can be found in numerous physical and chemical processes.
It occurs for a variety of reasons. Much like bridging a 9V battery's terminals with a metal paper clip, short circuits caused by a tear in the membrane that separates the negative and positive poles of a Li-ion battery will often cause a thermal meltdown. Ambient temperatures exceeding 60degrees C, repeated overcharging, or unauthorised modifications to the case have all been documented as reasons for battery fires.
It can also be caused by faults in the battery manufacturing process whereby short circuits are caused by the inclusion of small fragments of metal during the production process or minute holes in the sealing occur. These product defects often remain dormant until the battery has been charged and discharged several times causing the battery structure to expand and contract.
Large batteries like those used in electric vehicles usually incorporate short circuit protection but smaller batteries generally do not have this feature.
However some battery fires are not the fault of Lithium or the battery manufacturer or the product using the battery. For example if a mobile phone or laptop is dropped onto a hard surface internal damage can occur to the battery which can possibly result in a thermal runaway situation. The answer here is consumers should take their product to a service centre for checking. Also, how often do consumers change the battery in their laptop? The answer for most of us is never but in fact they should be checked and possible replaced every three years.
So given that it is the electrolyte fluid in Lithium batteries that is flammable what is the alternative? Basically dump the fluid and go solid-state. And plenty of work is being done to develop that principle.
One possible design still uses Lithium-ion technology, but instead of employing a liquid electrolyte uses a thin layer of material that’s not flammable.
A solid-state concept is inherently reliable because it can withstand thousands of re-charging sequences and also has the ability to cope with high ambient temperatures.
Although it may be several years before such batteries become available, major car manufacturers already consider solid-state batteries as a key component in future electric vehicles. But there are design challenges related to functionality and also costs. Fundamentally it’s not easy to push Lithium ions through a solid-state electrolyte.
But research by Toyota has shown that some solids are very capable at conducting lithium ions. The trick is that these solids need to have a crystal structure that arranges the lithium ions in a line, essentially creating a channel for them to travel along.
These crystal structures are showing some very positive characteristics when it comes to battery design. Among these are increased conductivity, the ability to operate in very wide temperature ranges and extremely fast charging capability.
So solid-state electrolytes looks like the way forward in the creation of more stable Lithium based battery products.
It certainly seems a more credible strategy than the technology suggested recently involving urine-powered batteries.
The Bill Gates Foundation is funding research by the Bristol Robotic Laboratory into pee-powered phones. Urine would enter fuel cells via connected tubes and micro-organisms would process the urine and create electricity. This would of course have to happen on a scale sufficiently large enough to charge a phone. Just what quantity of urine and how often the process would have to happen is not immediately clear but suppliers of bottled mineral water seem particularly keen on the concept.