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nanotimes

Research

10-03 :: March 2010

Batteries //

Self-Assembled Nanocomposites for Battery Anodes

R

esearchers from the Georgia Institute of Technology in Atlanta, USA, developed a new

high-performance anode structure based on silicon- carbon nanocomposite materials that could signi-

ficantly improve the performance of lithium-ion

batteries used in a wide range of applications from hybrid vehicles to portable electronics. The simple, low-cost fabrication technique was designed to be easily scaled up and compatible with existing battery manufacturing.

“Development of a novel approach to producing hierarchical anode or cathode particles with con- trolled properties opens the door to many new directions for lithium-ion battery technology,” said Gleb Yushin, an assistant professor in the School

of Materials Science and Engineering at the Georgia Institute of Technology. “This is a significant step to- ward commercial production of silicon-based anode materials for lithium-ion batteries.”

The popular and lightweight batteries work by transferring lithium ions between two electrodes – a cathode and an anode – through a liquid electrolyte. The more efficiently the lithium ions can enter the two electrodes during charge and discharge cycles, the larger the battery‘s capacity will be.

Silicon-based anodes theoretically offer as much as a ten-fold capacity improvement over graphite, but silicon-based anodes have so far not been stable

enough for practical use. The new nanocomposite

material solves that degradation problem, potenti-

ally allowing battery designers to tap the capacity ad- vantages of silicon. That could facilitate higher power output from a given battery size – or allow a smaller battery to produce a required amount of power.

“At the nanoscale, we can tune materials properties with much better precision than we can at traditio- nal size scales,” said Yushin. “This is an example of where having nanoscale fabrication techniques leads to better materials.”

Electrical measurements of the new composite an- odes in small coin cells showed they had a capacity more than five times greater than the theoretical capacity of graphite.

Fabrication of the composite anode begins with formation of highly conductive branching structures – similar to the branches of a tree – made from carbon black nanoparticles annealed in a high-temperature tube furnace. Silicon nanospheres with diameters of less than 30nm are then formed within the carbon structures using a chemical vapor deposition process. The silicon-carbon composite structures resemble “apples hanging on a tree.”

Using graphitic carbon as an electrically-conductive binder, the silicon-carbon composites are then self-assembled into rigid spheres that have open,