Lithium-ion batteries with silicon anodes thanks to the cages of graphene

A group of scientists at Stanford University and the Department of Energy SLAC National Accelerator Laboratory, US, have developed a method that makes possible the realization of lithium-ion batteries with silicon anodes. This type of anode is able to store an amount of energy per charge 10 times higher than the existing anodes on the market, and consequently allow the realization of smaller high-performance and lighter batteries.

While charging the silicon particles swell three times as much compared to their original size until they crack and shatter. The particles also react with the battery electrolyte and form a film that compromises their performance. To mitigate this kind of problem researchers have wrapped each silicon particle in a sort of "cage" of graphene.

The cage is sufficiently large to allow the silicon particles expand during charging, but small enough to keep all the pieces together when the particles tend to shatter, so that they can continue to operate at peak performance. The cradles can also stop the destructive chemical reactions with the electrolyte.

"This new method that allows the use of much larger silicon particles, from one to three microns in diameter, that are cheap and widely available. In fact the particles we used are very similar to the gap created by the polishing of silicon ingots used for the production of chips. the particles of this size have never shown good behavior in the anodes of the batteries before, so this is a very exciting result, and we think we can offer a practical solution, "said Yi Cui, associate professor at Stanford and who coordinated the research.

To realize the cages graphene the right size, the researchers coated silicon particles with nickel and then grown graphene layers on the nickel acting as a catalyst to promote the growth of graphene. As a final step removed the nickel through an acid bath, leaving enough space in the graphene cage because the silicon particle can expand. The next step in the research is to be able to optimize the process and achieve silicon particles "caged" in sufficient quantities to be able to build batteries of tests to check their possible commercialization.