Stanford researchers say they have cracked a key problem holding back lithium-ion batteries: which might make the next generation of phones, e-cars and other battery powered equipment a whole lot better.
The issue the researchers were facing is that silicon - though an excellent substance from which to make a modern battery electrode, as it has a high capacity for absorbing and then releasing lithium ions during charging and discharging - swells up and contracts massively when so used. In fact a silicon electrode increases in size by no less than three times over and then returns to its original size duing a charge-discharge cycle, and this naturally tends to mean that it comes to bits in fairly short order.
This is a major underlying reason why li-ion batteries often have a fairly poor service life. That's not a crippling problem in a smartphone - even if it's an iPhone or similar, designed in such a way that it's hard to replace the battery, people tend to get a new phone quite often. But it is a big deal in a much more expensive electric car: while a lot of people change cars frequently, they expect them still to be in saleable condition when they've finished with them - without any need to replace the major component of the power train.
The general distrust felt by the motor industry regarding battery service life, based on many years of beta tests with small groups of vehicles, is one major reason why not very many battery cars are being made. Even Tesla Motors, the flagship firm for battery cars, has admitted in SEC filings that battery life may yet become a major problem for it as its cars age.
But now the Stanford boffins say they're on the track of a fix. They have developed an astronishingly strong and stretchy polymer which can be coated onto a silicon electrode in use. As cracks form, the coating "heals" them. Here's a vid of a balloon coated with the stuff being inflated and deflated, indicating just how stretchy it is:
“Self-healing is very important for the survival and long lifetimes of animals and plants,” says Chao Wang, a postdoc researcher at Stanford. “We want to incorporate this feature into lithium ion batteries so they will have a long lifetime as well.”
Thus far, the silicon+gunge electrodes aren't ready for prime time: they can only do 100 charge cycles before starting to lose performance.
“That’s still quite a way from the goal of about 500 cycles for cell phones and 3,000 cycles for an electric vehicle,” admits Wang's colleague professor Yi Cui, “but the promise is there, and from all our data it looks like it’s working.”
So this technology isn't going to manufacturing yet, or perhaps ever if it can't be improved. But it is impressive enough that it has led to an article by the Stanford lab crew getting published in Nature Chemistry. And perhaps the amazing stretchy-stuff might have other uses, as well. ®