The Australian
12:00AM March 21, 2017
CHRIS GRIFFITH
Technology reporter
Sydney
Exploding batteries are back in the limelight and with it more concerns
that the lithium-ion cells powering our devices may not be as foolproof
or safe
as they ought to be.
The latest victim was a woman on a flight from Beijing to Melbourne on
February 19, who suffered facial injuries when the batteries in her
headphones exploded.
With her face and lips covered in soot, remnants of plastic in her hair,
and a blister from a burn on her hand, the aftermath of the incident,
especially
when it comes to air travel, is troubling. The battery and cover both
melted and stuck to the floor of the aircraft, according to the
Australian Transport
Safety Bureau, which has refused to release the name of the headset and
battery.
It didn’t reply when we asked whether the exploding headphones had been
subject to any legal settlement which prevented disclosure of its
branding, instead
saying that it only wanted to get its message out about in-flight
battery safety.
It’s a pertinent lesson given the dozens of well publicised cases last
year, In one incident a Samsung Galaxy Note 7 started smoking at the
start of a
Southwest Airlines flight from Louisville to Baltimore. The owner of the
phone had followed the instructions of crew, switched off his phone, and
put in
his pocket, all to no avail.
So what seems to be the problem with lithium-ion batteries?
Small errors, big consequences
Lithium-ion cells are attractive because they are lightweight, small,
and have a high energy density. They store lots of charge. However,
their structure
is delicate and they need to be made precisely. With manufacturers under
pressure to make even thinner batteries, at less cost, things evidently
do slip.
Samsung’s reports into the failure of its Note 7 batteries show that
small machining errors can have huge consequences.
A typical lithium-ion battery comprises cells with positive and negative
electrodes and a thin plastic separator that lets ions in an electrolyte
pass
from one side to the other.
Lithium ions move from the electrolyte to the carbon-based negative
electrode during charging, and back when discharging, generating a
countervailing current.
Heat is the enemy of lithium-ion batteries and if chemicals mix and
generate it, that leads to a more ferocious reaction and more heat. In
milliseconds
you have what’s called “thermal runaway” and fire and possibly an explosion.
This can happen in several ways. The battery is poorly made and the
electrodes touch causing a short circuit.
The battery might get too hot, causing the electrolyte to catch fire.
The separator gets damaged, and a short circuit results. Overcharging or
charging
too quickly can be problematic if the battery isn’t suited to the fast
charging technology that you use.
A battery can also explode as a result of an accident. In August last
year a Sydney cyclist suffered severe burns when he fell off his bike,
causing the
iPhone in his pocket to ignite. You can generate a short circuit if you
puncture or crush a battery.
Cheap and here to stay
In the case of Note 7 batteries, the problem was two separate
manufacturing errors at two factories. Samsung said in its report that
in “company A”, electrodes
in the upper right-hand corner of the battery didn’t correctly fit the
case around them and were bent and damaged. The tip of the negative
electrode was
incorrectly located.
At “Company B”, welding burrs on the battery’s positive electrode caused
the penetration of insulation tape and the separator between the
positive tab
and negative electrode. A number of batteries were missing insulation
tape altogether. All of these had the potential to cause batteries to
short circuit,
but the lack of advancement in battery technology means that lithium-ion
is here to stay. They are low-cost, easy to reproduce and mostly safe.
