Monday, April 8, 2013
It’s been a rough ride lately for the lithium-ion battery. Though practically all of us carry one around — they power everything from cell phones to iPods — the lightweight cells have sparked some high-profile product failures.
It was bad enough when they caused laptop computers to burst into flames, leading to millions of recalled batteries since 2000. Their reputation took another hit in January, when battery fires in two of Boeing’s new 787 Dreamliner planes caused airlines to ground their entire 787 fleets.
So why are John Goodenough and Arumugam Manthiram smiling? Despite current setbacks, the two professors at the Cockrell School of Engineering see a bright future for the battered battery. It still stores more energy in less space than any other rechargeable technology. And through the associated Texas Materials Institute, both researchers are hard at work on its next generation.
That’s assuming, of course, that the batteries become less prone to ignite.
As the lightest metal, lithium has long held the promise of lightweight but high-powered batteries. When oil prices jumped in the early 1970s, it attracted researchers like Bell Telephone Laboratories and Exxon. The problem was finding the right materials to partner with it — because the wrong combinations of elements could lead to explosions. Bell and Exxon learned this the hard way. “After they exploded a couple of laboratories,” recalls Goodenough, “they got out of the energy business.”It was Goodenough himself who helped solve that problem. In 1979, at Oxford University, he created an electrode that compounded lithium with cobalt and oxygen. His discovery became the basis of the first stable lithium-ion battery, developed by Sony in 1991. “Sony made the first cell telephone,” he says, “and everything was off to the races.”
While modern lithium batteries are considered stable, they come with several risks. Both external heat and internal short-circuits can cause a cell to overheat. Overcharging releases oxygen, a combustion hazard. To protect against these threats, every battery pack includes what’s essentially a miniature computer, packed with tiny temperature sensors and voltage regulators.
When your cell phone tells you its battery is full, notes Manthiram, it’s actually 50 percent charged – the highest level that’s safe with lithium cobalt oxide.
That’s plenty of juice for small gadgets. But green transportation and renewable energy require bigger batteries. Weaning the world off fossil fuels means storing massive amounts of power, coming out of wind turbines and solar cells and going into electric cars.
The trouble with new and larger batteries, says Manthiram, is that manufacturers have less experience with their hazards and how to control them. Those risks were magnified in the Boeing 787 by linking several large cells together.
“If one cell is shorting inside, then it will cause an explosion of everything,” he explains. “That’s the problem when you have multiple cells.”
The other problem, he says, was that Boeing used the oldest and least stable material: lithium cobalt oxide. Since the 1990s, researchers have devised safer lithium compounds. But each one has tradeoffs, he notes. “We use different materials for different applications. It’s hard to get everything with a single material.”
Goodnenough invented one such compound, with iron, phosphorus, and oxygen. It’s promising for storing power on electric grids, and the Canadian utility Hydro-Quebec has licensed the technology from the University of Texas. But it can’t store a lot of energy in a small space, which makes it impractical for cars.
Some electric cars, like the Chevy Volt, use a different lithium compound. Their batteries, incorporating manganese, can put out a lot of power at once. The tradeoff, so far, is that they have shorter lives.
That means the two professors are still on the quest for a breakthrough battery: the perfect combination of power, storage, life, and cost. With grants from the U.S. Department of Energy, they and their colleagues are testing a new generation of materials:
• Alloys for electrodes that are less prone to short-circuits than graphite.
• Sodium, a more abundant and less-expensive element than lithium.
• Dual-electrolyte batteries, which use both water and non-water solutions to conduct ionic currents inside batteries, opening up more choices for materials.
Will any of these materials prove to be a magic battery bullet? Ask Manthiram in 10 to 20 years, he says. For at least that long, the Texas Materials Institute will keep humming along.
“People are working very, very hard, and who knows when somebody’s going to come up with a brand-new idea that surprises us all?” says Goodnenough. “With the present strategies, it’s a hard stretch. I’m trying to find new strategies.”