Nanostructured Metal Foam Electrodes Could Lead to Ultrafast-Charging Batteries

Compact, rechargeable, and capable of incorporating intelligent electronics, lithium-ion (Li-ion) batteries are playing an increasingly important role in portable medical devices. Now, a team of researchers at the University of Illinois at Urbana-Champaign has developed a method of using nanostructured metal foams to create battery electrodes that enable Li-ion batteries to undergo a 90% charge in just two minutes.

The speed at which batteries can charge up and release power is primarily limited by the movement of electrons and ions into and out of the cathode, the electrode that is negative during recharging. As reported in MIT's Technology Review, materials science and engineering professor Paul Braun and his team have overcome this limitation by making highly porous metal foams that allow ions to move about unimpeded. When coated with active battery materials, this technology can provide high electrical conductivity and can also hold enough active material to store a sufficient amount of energy.

The cathodes are created using a slurry of polymer spheres on the surface of a conductive substrate. Because of their shape and surface charge, the spheres self-assemble into a regular pattern. The scientists then electroplate the structure to fill the space between the spheres with nickel. The next step is to dissolve the polymer spheres and most of the metal, leaving a nickel sponge, approximately 90% of which is open space. Finally, the active material is grown on top of the sponge.

In addition to its suitability for fabricating Li-ion batteries, this fabrication method can also be used to make rapid-charging batteries based on a variety of other chemistries, such as nickel-metal-hydride.

While some scientists believe that Braun's process for manufacturing these fast-charging batteries is complicated and potentially too expensive to achieve commercialization, Braun tells Technology Review that his fabrication process combines existing methods that are currently used to make other products, if not batteries. Adapting them should not be too difficult, he says. And although his processing method would involve extra battery-making steps, they are not particularly expensive or complex.

For more information on Li-ion and other battery technologies, see "Leader of the Pack" in the April issue of MPMN.