Lithium-air (Li-O2) batteries are among the nost energy-dense electrochemical platforms for mobile energy storage, and are thus considered promising for electrified transportation. A number of severe challenges with the system need to be overcome first, however. These practical shortcomings include poor rechargeability, reduced efficiency due to high overpotentials (more charge energy than discharge energy) and specific energies well below theoretical expectations.
Now, researchers in the lab of Lynden Archer, the James A. Friend Family Distinguished Professor of Engineering in the Robert F. Smith School of Chemical and Biomolecular Engineering (CBE) at Cornell University, are proposing a design approach that may provide a promising platform for addressing these three major technical barriers to practical Li-O2 cells. An open-access paper on their work is published in the journal Science Advances.
Several approaches to overcoming each of the challenges with the Li-O2 cell have been proposed, but a frustrating observation is that promising solutions to one problem often come at the expense of others or create new problems in some cases. … An important conclusion is that because Li deposition is fundamentally unstable, fundamentally based approaches that take advantage of multiple physical processes are likely to be the most successful in guaranteeing long-term stability of rechargeable batteries that use metallic lithium as an anode.
Herein, we report on the stability of Li-O2 cells using liquid electrolytes containing an ionomer salt additive that spontaneously forms a multifunctional SEI at the anode. The additive and the in situ–formed SEI that it forms are deliberately designed to take advantage of three fundamentally based mechanisms for stabilizing electrochemical processes at the anode and cathode of the Li-O2 cell.—Choudhury et al.
The researchers created a functional designer interphase based on bromide-containing ionomers that selectively tether to the lithium anode to form a few-nanometers-thick conductive coating that protects the electrode from degradation and fade. The SEI ionomers display three attributes that allow for increased stability during electrodeposition:
protection of the anode against growth of dendrites;
reduction-oxidation (redox) mediation, which reduces charge overpotentials; and
the formation of a stable interphase with lithium, protecting the metal while promoting ion transport.
We conclude that rationally designed SEIs able to regulate transport of matter and ions at the electrolyte/anode interface provide a promising platform for addressing three major technical barriers to practical Li-O2 cells.—Choudhury et al.
Snehashis Choudhury, Charles Tai-Chieh Wan, Wajdi I. Al Sadat, Zhengyuan Tu, Sampson Lau, Michael J. Zachman, Lena F. Kourkoutis and Lynden A. Archer (2017) “Designer interphases for the lithium-oxygen electrochemical cell” Science Advances Vol. 3, no. 4, e1602809 doi: 10.1126/sciadv.1602809