Late last week, Samsung released an expanded recall notice for its infamous exploding Galaxy Note 7 phones, asking users to “power down immediately” and send in their phones for a refund. Within a month of the Note 7 release, there had been upwards of 100 reports of the phone exploding or catching on fire, a big enough problem that even the FAA was forced to take notice by banning the phones on all US flights.
The reason the Note 7 phone is so prone to exploding is due to a design issue that places too much pressure on the lithium ion batteries inside the phone. This pressure can create a hole in the barrier separating the north and south poles of the battery which short circuits the battery and leads to the explosion.
This problem is by no means limited to the lithium ion batteries in the Note 7: these batteries power most of our phones, laptops, tablets, hoverboards and electric vehicles, which is why a team of researchers from the University of Michigan is watching lithium batteries grow to keep them from exploding.
Technically speaking, the team is watching the formation of lithium dendrites, small spindles of conductive filaments that form inside of the batteries while they are charging and decharging. The formation of these dendrites poses a significant problem, insofar as they significantly reduce the efficiency of the battery by consuming the liquid electrolyte in its core, in addition to causing fires or explosions by creating filaments inside the battery that can lead to a short circuit.
Prior to the Michigan team’s research, the formation of these dendrites was poorly understood, but they are crucial to getting better batteries into our consumer electronics and electric vehicles. The idea is to one day move beyond lithium ion batteries to lithium metal batteries, which are far more efficient. But in order to do this, the problem of dendrite formation must be addressed.
“Lithium ion, which has really accelerated our use of personal devices over the last two decades is reaching its fundamental limit,” said Neil Dasgupta, an assistant professor of mechanical engineering at Michigan. “However if we move to lithium metal electrodes, we’re able to increase this capacity by a factor of ten.”
When researchers test batteries using different metals, they usually use something called a coin cell, which is a small circular battery encased in metal. They hook these up to a cycler which charges and decharges the coin cell to see how much energy can be moved through the cell before problems start to emerge. The issue, however, is that this process doesn’t really provide much insight into what is happening while the battery is charging or decharging. It’s a black box in that sense and only provides researchers with a glimpse into the result of this process.
In order to get a better handle on what is actually going on inside the battery during charging and recharging, the Michigan team created a see-through battery which allows them to use a high resolution microscope to watch dendrite formation in real time.
“We literally created a window to look inside,” Dasgupta explains in the video. “We’re now able to detect the origins of where and why dendrites form.”
The Michigan team’s see through battery. Image: Michigan Engineering/YouTube
Now that the team has gotten a handle on dendrite formation, the trick will be figuring out how to limit this phenomenon over a battery’s lifetime.
Dasgupta’s colleague Kevin Wood, a postdoctoral fellow at Michigan, imagines a future in which their research leads to electric cars with lithium metal batteries that are so efficient that it is possible to drive from Denver to New York without refueling. In the short term, however, Wood has a far less ambitious goal: “We just don’t want [the battery] to blow up.”