Batteries fall into the when-your-well-runs-dry category of technology: We only miss them when they lose their charge or catch fire on the freeway, taking the stuff we really care about down with them. The best battery is basically the one we have to think about the least. Recently, a group of scientists at the University of California, Irvine, stumbled across an innovation that they think could lead to lithium-ion batteries even less demanding of our attention.
So far the new battery component has made it through three months of continuous charging and discharging without losing its ability to hold a charge, says Mya Le Thai, the doctoral candidate behind the innovation — that's 200,000 cycles. (By comparison, iPhone batteries fade to about 80 percent of their original capacity after just 500 cycles, making hers at least 400 times better.) Thai says she's getting impatient, but that the head of her lab won't let her stop the experiment. "I keep asking my primary investigator, 'Can I take it apart?' He says, 'Did it fall apart? No? Well, then, let it keep on going.'"
Lithium-ion batteries, which became commercially available in the early 1990s, have three basic parts: The positive electrode (the cathode); the negative electrode (the anode); and the electrolyte, a conductive material — typically a liquid — that sits between the cathode and anode. When the battery is charging, lithium ions flow from the cathode into the anode across the electrolyte, storing energy. When the battery is being used, the ions flow back. Electrons, which can't pass through the electrolyte, take the long way around, flowing out through the negative terminal, through the light bulb or iPhone or whatever it is you're trying to power, and back into the positive terminal.
Since the cathode is where the battery gets its power, improving its architecture is one of the most promising avenues to better battery storage and lifetime. Thai's lab had been studying how to replace the standard solid cathode with an array of nanowires, each less than a thousandth the thickness of a human hair. "With a lot more surface area, you can store more charge," Thai says. Since nanowires are so thin, though, they quickly corrode and snap, limiting the lifetime of the battery. The manganese-coated gold nanowires the team originally had been using delaminated and fizzled out after just 2,000 to 8,000 cycles.
Thai had been playing around with how to replace the usual liquid electrolyte with a solid. She decided one day to coat an array with PMMA gel (that's polymethyl methacrylate, better known to us laypeople as Plexiglas). Then she plugged that sucker in; the battery kept going, and going, and going. The gel not only kept the nanowires from pulling away from their manganese coating, but even improved the cathode's function. Thai says she's not actually sure how it's doing that, but that she's working now to figure out the chemistry behind it.
So is that it? Batteries we can finally forget about? Someday, but that's probably not a someday soon. New technologies take years to make it from lab to market, and "the overwhelming majority of innovations don't survive the process," as Christopher Mims writes in The Wall Street Journal.
Thai agrees. "There's probably a long way to go," she says. She's working on building a similar array with nickel nanowires, which should work just as well but would be somewhat cheaper (gold nanowire is "just something we have in the lab," she says). Her main focus, though, is not getting the cathode to market, but rather just understanding how the PMMA gel works. (And also, you know, earning her doctorate.)
For now, better keep that power cord handy.