3D battery structure could allow devices to charge in seconds

"This system gives you capacitor like power with battery like energy," said Paul Braun (pictured cente), Professor of materials science and engineering at the University of Illinois, who led the team. "Most capacitors store very little energy. They can release it very fast, but they can't hold much. Most batteries store a reasonably large amount of energy, but they can't provide or receive energy rapidly. This does both." Compared to the performance of typical lithium ion or nickel metal hydride rechargeable batteries, which degrade significantly when charged or discharged, Braun's group wrapped a thin film into a 3d structure to achieve both high active volume (high capacity) and large current. They have since demonstrated battery electrodes that can charge or discharge in a few seconds, yet can perform normally in existing devices. "This kind of performance could lead to phones that charge in seconds or laptops that charge in minutes, as well as high power lasers and defibrillators that don't need time to power up before or between pulses," said Braun, who said he is particularly optimistic for the batteries' potential in electric vehicles. "If you had the ability to charge rapidly, instead of taking hours to charge the vehicle, you could potentially have vehicles that would charge in similar times as needed to refuel a car with gasoline," he said. "If you had five minute charge capability, you would think of this in the same way you do an internal combustion engine. You would just pull up to a charging station and fill up." The key to the group's novel 3d structure, according to Braun, was self assembly. They first began by coating a surface with tiny spheres, packing them tightly together to form a lattice. The researchers then filled the space between and around the spheres with metal. The spheres were melted or dissolved, leaving a porous 3d metal scaffolding, like a sponge, before a process called electropolishing uniformly etched away the surface of the scaffold to enlarge the pores and make an open framework. Finally, the researchers coated the frame with a thin film of the active material. "This resulted in a bicontinuous electrode structure with small interconnects, so the lithium ions could move about rapidly," asserted Braun. The team demonstrated both lithium ion and nickel metal hydride batteries, but claims the structure is general, meaning any battery material that can be deposited on the metal frame could be used. "We like that it's very universal," concluded Braun, "so if someone comes up with a better battery chemistry, this concept applies. This is not linked to one very specific kind of battery, but rather it's a new paradigm in thinking about a battery in three dimensions for enhancing properties." The findings have been published in the 20 March online edition of the journal Nature Nanotechnology.