Is The Self-Healing Battery That Repairs Itself After Each Charge The Future Of Mobile Electronics?
Every time you recharge a lithium-polymer battery, like the ones in iPhones, tiny molecules inside it swell up. Then they shrink back down when you put them back to use. Do that enough times, and the molecules weaken and crack, reducing the battery's capacity to recharge.
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To solve the problem, scientists at Stanford University have borrowed an idea from nature. By coating the electrodes with self-healing chemicals, the batteries repair themselves in the same way DNA molecules assemble and a scraped knee heals. When they applied the self-healing materials, which are made from silicon microparticles, battery lifespan was 10 times longer, the researchers said in a news release.
"Self-healing is very important for the survival and long lifetimes of animals and plants," said Chao Wang, a Stanford post-doctoral researcher who co-authored a paper on their findings, published this month in the journal Nature Chemistry. "We want to incorporate this feature into lithium-ion batteries so they will have a long lifetime as well."
If you've forgot how batteries work, here's a quick primer. Batteries convert the energy of chemical reactions into electricity, and an electrolyte facilitates the current between positive and negative electrodes. In a disposable battery, the electrodes get used up, and that's that.
But in a rechargeable batteries, a lithium ion carries the charge back and forth between the positive and negative electrodes. When the battery is being used, the lithium ions go to the negative side. When it's charged, the power source reverses the chemical reaction, and the lithium ions are forced into the positive side (the anode). That's what forces it to swell and eventualy wear down.
Research into improving battery life (the length of time it holds a charge) and lifespans (the length of time before it needs replaced) has accelerated under the tremendous commercial demand for powerful, lightweight batteries.
That race, scientists say, has led inventors to use "exotic materials" or techniques that can't be scaled to production. Earlier this year, one of the co-authors on this research, Yi Cui, developed a method they compared to an egg yolk inside an egg shell. Sulfur electrodes can absorb more lithium ions, the lifeblood or rechargeable batteries, but the sulfur always cracked when it expanded. Cui's model cased the electrodes in a shell to allow the elastic yolk inside to expand, but contained it before it burst.
The Stanford lab called this new self-healing method a "potentially commercially viable path." A typical lithium-ion battery loses 20 percent of its capacity after about 500 recharges. The self-healing batteries lost virtually no capacity after 100 charge-recharge cycles, but tapered after that.
"Their capacity for storing energy is in the practical range now, but we would certainly like to push that," Cui said in the statement. One hundred charges is "still quite a way from the goal of about 500 cycles for cell phones and 3,000 cycles for an electric vehicle, but the promise is there, and from all our data it looks like it's working."
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