Army Scientists Publish New Findings on Efficient Batteries

In a peer-reviewed publication from the American Chemical Society, a team of army scientists working on extremely efficient batteries recently published new findings.

In an invited paper featured in the special issue of the Accounts of Chemical Research, Dr. Oleg Borodin, together with collaborators Drs. Arthur von Wald Cresce, Jaroslaw Knap, Xiaoming Ren and Kang Xu from the U.S. Army Research Laboratory, explained modeling insights into battery electrolyte stability and structure.

The "investigation of electrical energy storage over multiple length scales" is showcased by the theme of the publication's exclusive issue.

Lithium-ion batteries dominate energy storage for portable electronics and are penetrating automotive and grid-storage applications, 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.

Dr Oleg Borodin, senior computational chemist, ARL Electrochemistry Branch.

"He is well recognized in the field for his trailblazing work of molecular dynamics simulation," Xu said. "His predictive calculation significantly helped his experimental colleagues in developing new electrolyte and interface chemistries."

Electrolytes

For batteries to operate, it is necessary for electrolytes to conduct electric current in ionic form while insulating any electron current. Electrolytes refer to a substance that is sandwiched between negative and positive electrodes. The properties of the electrolyte are capable of pre-determining how long the battery can last (electrochemical stability), and how fast the battery can supply power or absorb charge (power density).

The team concluded that one of the key factors must be met in order to attain stability.

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", Borodin said.

Thermodynamic stability takes place when a system is found to be in its lowest energy state, or chemical equilibrium, with its environment. While thermodynamic stability is greatly preferred and most perfect, it can rarely be attained in reality, and passivation is frequently the approach to stability, which develops a kinetic barrier and places the system in a meta-stable equilibrium with its environment.

Xu, an ARL fellow, specializes as a scientist of electrolytes.

"The Li-ion battery operates under the principle of this meta-stability", he said.

In recent years, the team headed by Xu and Borodin has developed a number of battery and electrolyte innovations, comprising of a new class of high-voltage aqueous electrolytes, in association with Prof. Chunsheng Wang, professor of Chemical and Biomolecular Engineering at the University of Maryland's A. James Clark School of Engineering.

The laboratory, earlier this year, honored Borodin, Cresce and Xu with the ARL Award of Science for their work on 4-volt aqueous Li-ion Batteries.

"The highly complementary collaboration between Borodin and myself is an excellent example for the collaboration between computation and experimental scientists," Xu said.

Conclusion

"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."