The batteries in Illinois professor Paul Braun’s lab look like any others, but because they can be charged so quickly, they could make electric vehicles much more attractive. They’re also important for medical devices, lasers and military applications.
Researchers are developing batteries that have capacitor-like power with battery-like energy – they can be charged very quickly without sacrificing energy storage capacity.
Most capacitors can be charged quickly, but store very little energy. Most batteries store a lot of energy, but it takes a long time to charge them.
Braun’s technology could bring cell phones that charge in seconds or laptops that charge in minutes. High power lasers and defibrillators wouldn’t need time to power up before or between pulses.
And electric vehicles could potentiall charge up in the same time it takes to fill up a conventional vehicle at the gas station.
The researchers have developed a novel 3-D structure that self-assembles. By putting a thin film nano structure as a coating, they’re able to pack tiny spheres together, forming a lattice. The inexpensive spheres settle into place automatically.
They then fill the space between and around the spheres with metal. The spheres are melted or dissolved, leaving a porous 3-D metal scaffolding, like a sponge. Then a process called electropolishing uniformly etches away the surface of the scaffold to enlarge the pores and make an open framework. Finally, the researchers coat the frame with a thin film of the active material.
The result is a bicontinuous electrode structure with small interconnects, so the lithium ions can move rapidly; a thin-film active material, so the diffusion kinetics are rapid; and a metal framework with good electrical conductivity.
The group demonstrated both NiMH and Li-ion batteries, but the structure is general, so any battery material that can be deposited on the metal frame could be used.
"We like that it’s very universal, so if someone comes up with a better battery chemistry, this concept applies," says Braun. "This is not linked to any specific kind of battery, but rather it’s a new paradigm in thinking about a battery in three dimensions for enhancing properties."
The U.S. Army Research Laboratory and the Department of Energy supported this work.
The paper will be published in Nature Nanotechnology. Braun is a professor in the Department of Materials Science and Engineering at the University of Illinois/ Urbana, Champaign.
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