U.S. Army researchers seek better batteries

LOS ANGELES, Nov. 30 (Xinhua) -- A team of U.S. Army scientists working on more efficient batteries recently published new findings in Accounts of Chemical Research, a peer-reviewed publication from the American Chemical Society.

In an invited paper published in the special issue of the publication, which showcases the "investigation of electrical energy storage over multiple length scales", researchers from the U.S. Army Research Laboratory (ARL) discussed modeling insights into battery electrolyte structure and stability.

"Lithium-ion batteries dominate energy storage for portable electronics and are penetrating automotive and grid-storage applications," Dr. Oleg Borodin, a senior computational chemist at the ARL Electrochemistry Branch, was quoted as saying in a news release.

"Further progress depends not only on the development of a new high capacity electrode, but also on tailoring electrolytes in order to support fast and yet reversible lithium transport through the bulk electrolyte and across interfaces," said Borodin.

For batteries to work, electrolytes, a substance that is sandwiched between positive and negative electrodes, must conduct electric current in ionic form while insulating any electron current. The properties of the electrolyte pre-determine how fast the battery can deliver power or absorb charge (power density), and how long the battery can last (electrochemical stability).

One of the two factors must be met to achieve stability, the team concluded. Electrolytes must be either "thermodynamically stable with electrodes, or form a stable passivation layer that should be electronically insulating but ionically conducting while accommodating mechanical stresses due to electrode volume changes during battery cycling", said Borodin, who is well recognized in the field for his trailblazing work of molecular dynamics simulation.

Thermodynamic stability, which is highly desired and most ideal, happens when a system is in its lowest energy state, or chemical equilibrium, with its environment. However, it can rarely be achieved in reality, and passivation is often the approach to stability, which builds up a kinetic barrier and place the system in a meta-stable equilibrium with its environment, according to the researchers.

"We demonstrate that depending on their chemical structures, the anions could be designed to preferentially adsorb or desorb from the positive electrode with increasing electrode potential," Borodin concluded. "This provides additional leverage to dictate the order of anion oxidation and to effectively select a sacrificial anion for decomposition." Enditem