Silicon-carbon nanocomposite granule
Anode delivers ten times more capacity than conventional designs

The number of uses for nanocomposite materials is staggering. The material has been the source of some revolutionary breakthroughs in many areas of research. One of the most beneficial places for nanocomposite materials has been in battery research.

Battery research is important for many uses ranging from electronic devices like notebooks with longer run times to electric cars that have greater driving ranges. Two of the key components in the structure of a battery are the anode and cathode. Researchers have developed a new anode structure built using silicon-carbon nanocomposite materials. The new anode promises to allow a massive improvement in the performance of current lithium-ion batteries.

The breakthrough anode uses self-assembling nanocomposite material in a technique that results in a structure with very finely tuned properties. The new breakthrough isn’t the first time researchers have tried to use silicon-based anodes in lithium-ion batteries. Previous attempts to design a silicon-based anode failed because the anodes were not stable enough for practical use.

The reason the silicon-based anodes previously designed weren't practical for normal use was that expansion and contraction of the anode as lithium ions enter and leave the silicon created cracks that cause anode failure rapidly. The new anode breakthrough using the silicon-carbon nanocomposite material uses a "bottom-up" self-assembly technique to tune the structure of the anode to overcome the shortcomings of the previous silicon-based anodes.

Gleb Yushin, an assistant professor in the School of Materials Science and Engineering at the Georgia Institute of Technology said, "Development of a novel approach to producing hierarchical anode or cathode particles with controlled properties opens the door to many new directions for lithium-ion battery technology."

The composite anode is made starting with the formation of a highly conductive branching structure made from carbon black material. The researchers says that the branching structure resembles the branches of a tree. The carbon black used in the structures is then annealed in a high-temperature tube furnace. A chemical vapor is then introduced to create silicon nanosphere with diameters under 30nm and the spheres resemble apples hanging on a tree.

After the nanospheres are formed and the chemical vapor is deposited, graphitic carbon is used as an electrically conductive binder and the silicon-carbon composites self-assemble into ridged spheres with open and interconnected internal pores. The spheres created in the process range from 10 to 30microns in size and are used to form the new anode. The pores and internal channels allow the liquid electrolyte used in a battery to enter the spheres rapidly along with lithium ions for quick battery charging and the spheres can expand without cracking resulting in no breakdown of the anode.

The researchers  say that a battery using the new anode would be able to survive thousands of charge and discharge cycles without degradation while providing a ten times increase in the storage capacity of the battery. The process used for building the anodes is also compatible with current battery construction processes.

Yushin said, "If this technology can offer a lower cost on a capacity basis, or lighter weight compared to current techniques, this will help advance the market for lithium batteries," he said. "If we are able to produce less expensive batteries that last for a long time, this could also facilitate the adoption of many 'green' technologies, such as electric vehicles or solar cells."

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