Increased performance of lithium sulfur batteries


In Canada, a laboratory of the University of Waterloo has made a prototype of a lithium battery that can store and release more than three times the energy of classic lithium-ion batteries. The results are published in the online edition of Nature Materials, 17 May

Chemists have been working for years on this lithium-sulfur combination because the chemical properties of two elements generate high energy densities.

Moreover, the sulfur is still less expensive than many other materials currently used in lithium batteries. This association should be able to store and transport energy in a reliable rechargeable battery, low cost and long duration.

"The problem has always been the cathode, ie the part of the battery that stores and releases electrons during the charging cycles and recharge," says professor Linda Nazar. "To allow a reversible electrochemical reaction to current high levels, sulfur active electronically must remain in close contact with a driver, like carbon."

The Canadian research team has outstripped the performance of other combinations of carbon and sulfur in solving the problem of contact at the nanometer scale. They chose for their validation study of the principle member and tightly structured porous carbon family known as mesoporous carbon. At this scale, this type of carbon has a pore diameter and uniform volume.

With a gauge casting method, the research team assembled a structure made of carbon rods of 6.5 nanometers thick, separated by empty channels from three to four nanometers in width. Micro fiber spanning keep channels open and prevent the collapse of the architecture.

The filling of empty tiny proved simple. The sulfur is heated and melted. Once in contact with carbon, it is drawn by capillary or soak in the canals, where it solidifies and shrinks to form nanofibers sulfur. Cuts made with a scanning electron microscope showed that all areas were uniformly filled with sulfur, carbon exposing a huge surface area of the active element and causing the outstanding results obtained in testing the new battery.

"This composite can provide nearly 80% of theoretical capacity of sulfur, which corresponds to three times the energy density provided by the oxide cathodes with a transition metal lithium, at reasonable rates and with good cyclic stability "Nazar says.

Moreover, according to the researchers, the large capacity of carbon materials to incorporate the assets opens the door to similar composites "soaked" that could have applications in many fields of materials science.

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