Nav: Home

Stabilizing molecule could pave way for lithium-air fuel cell

April 26, 2017

ITHACA, N.Y. - Lithium-oxygen fuel cells boast energy density levels comparable to fossil fuels and are thus seen as a promising candidate for future transportation-related energy needs.

Several roadblocks stand in the way of realizing that vision, however. They include poor rechargeability, reduced efficiency due to high overpotentials (more charge energy than discharge energy) and low specific energy.

Two instabilities contribute to these roadblocks. Much of the previous work done 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, has centered on one: the nucleation and growth of dendrites from one electrode to the other, which causes short-circuiting, a source of premature cell failure that invariably ends in fires.

It's the other instability - the loss of battery power, also known as capacity fade - that is the focus of the lab's most recent work. Snehashis Choudhury, a doctoral student in the Archer Research Group, has come up with what Archer terms an "ingenious" answer to the problem of capacity fade.

Their work is detailed in "Designer interphases for the lithium-oxygen electrochemical cell," published this month in Science Advances. Choudhury is co-first author along with Charles Wan, a chemical engineering major.

Capacity fade occurs when the electrolyte, which transports charged ions from the negative electrode (anode) to the positive (cathode), reacts with the electrodes. "It starts to consume the electrodes," Choudhury said. "It forms many insulating products that impede ion transport. Over time, these build up to produce such prohibitive internal cell resistance that finally the battery fades."

The problem: How do you stop one electrolyte-electrode reaction, when it's another necessary reaction between the two - the transfer of ions - that produces power? Choudhury's solution is called an artificial solid-electrolyte interphase (SEI), a material that protects the electrodes while promoting the flow of electrons from one end of the cell to the other.

"Such interphases form naturally in all electrochemical cells ... and their chemo-mechanical stability is critical to the success of the graphite anode in lithium-ion batteries," Archer said. "

Choudhury's approach for creating a functional designer interphase is based on bromide-containing ionic polymers (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.

One challenge still exists: All research-grade lithium-oxygen electrochemical cells are evaluated using pure oxygen as the active cathode material. For a commercially viable lithium-oxygen (or lithium-air, as it's also known) cell, it would need to pull oxygen out of the air, and that oxygen also contains other reactive components, such as moisture and carbon dioxide.

If the inefficiencies that limit performance of lithium-oxygen fuel cells can be resolved, the exceptional energy storage options offered by the cell chemistry would be a giant step forward for electrified transportation and a revolutionary advance for autonomous robotics, Archer said.

"It is telling from observations of the most advanced humanoid robots that they are always either tethered to an ultra-long electrical cable or are using something like a loud lawnmower engine to generate energy," Archer said. "Either energy source compares poorly to those found in nature. Energy storage technologies such as Li-air cells, which harness materials from the surroundings, promise to close this gap."
-end-
Other contributors were Lena Kourkoutis, assistant professor and the Rebecca Q. and James C. Morgan Sesquicentennial Faculty Fellow in applied and engineering physics; CBE doctoral student Wajdi Al Sadat; Sampson Lau, Ph.D. '16; Zhengyuan Tu, doctoral student in materials science and engineering; and Michael Zachman, doctoral student in applied and engineering physics.

Support for this work came from the Advanced Research Projects Agency-Energy. In addition, electron microscopy was done at the Cornell Center for Materials Research, a National Science Foundation-supported Materials Research Science and Engineering Center.

Cornell University

Related Engineering Articles:

Engineering a new cancer detection tool
E. coli may have potentially harmful effects but scientists in Australia have discovered this bacterium produces a toxin which binds to an unusual sugar that is part of carbohydrate structures present on cells not usually produced by healthy cells.
Engineering heart valves for the many
The Wyss Institute for Biologically Inspired Engineering and the University of Zurich announced today a cross-institutional team effort to generate a functional heart valve replacement with the capacity for repair, regeneration, and growth.
Geosciences-inspired engineering
The Mackenzie Dike Swarm and the roughly 120 other known giant dike swarms located across the planet may also provide useful information about efficient extraction of oil and natural gas in today's modern world.
Engineering success
Academically strong, low-income would-be engineers get the boost they need to complete their undergraduate degrees.
HKU Engineering Professor Ron Hui named a Fellow by the UK Royal Academy of Engineering
Professor Ron Hui, Chair Professor of Power Electronics and Philip Wong Wilson Wong Professor of Electrical Engineering at the University of Hong Kong, has been named a Fellow by the Royal Academy of Engineering, UK, one of the most prestigious national academies.
More Engineering News and Engineering Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Anthropomorphic
Do animals grieve? Do they have language or consciousness? For a long time, scientists resisted the urge to look for human qualities in animals. This hour, TED speakers explore how that is changing. Guests include biological anthropologist Barbara King, dolphin researcher Denise Herzing, primatologist Frans de Waal, and ecologist Carl Safina.
Now Playing: Science for the People

#534 Bacteria are Coming for Your OJ
What makes breakfast, breakfast? Well, according to every movie and TV show we've ever seen, a big glass of orange juice is basically required. But our morning grapefruit might be in danger. Why? Citrus greening, a bacteria carried by a bug, has infected 90% of the citrus groves in Florida. It's coming for your OJ. We'll talk with University of Maryland plant virologist Anne Simon about ways to stop the citrus killer, and with science writer and journalist Maryn McKenna about why throwing antibiotics at the problem is probably not the solution. Related links: A Review of the Citrus Greening...