Grant to accelerate lithium-oxygen battery research

The US National Science Foundation (NSF) has awarded a US$219,312, two-year grant to push forward research into cutting-edge lithium-oxygen batteries, believed to be the most promising replacement for lithium-ion batteries.

The grant was awarded to Xianglin Li, an assistant professor of mechanical engineering at the University of Kansas (KU), who claims lithium-oxygen batteries represent “the next generation of energy storage”.

“Theoretically, it has about one order of magnitude higher storage capacity than lithium-ion,” Li said. “So if you switch to this in the future, you’ll only need to charge your phone once a week. There are competing technologies like the zinc-air or lithium-sulfur batteries, but lithium-oxygen clearly is the one with the highest capacity, so it has great advantage.”

But while lithium-oxygen batteries promise much greater energy storage capacity, their shortcoming is an inability to discharge energy as fast as lithium-ion batteries. Until this drawback is overcome, Li said lithium-oxygen battery technology will remain in the lab research stage.

“The problem is lithium-oxygen has low current density — it lasts a long time, but you don’t get a lot of power,” he said. “If you use lithium-oxygen batteries for an electric car, you could drive 500 miles, but you can’t accelerate very fast. Driving just a few miles per hour isn’t very fun. As far as I know, almost all lithium-oxygen batteries are still in the research phase and the technology doesn’t have a very large market yet. Performance, stability and lifetime are all issues for lithium-oxygen batteries now. But in the ’70s and ’80s, lithium-ion batteries had similar issues.”

With his new NSF grant, Li hopes to develop technology to boost the current density of lithium-oxygen batteries to make them more practical. He’ll work in the X-ray Computed Tomography Facility at Carnegie Mellon University, collaborating with Shawn Lister.

“Our objective is to increase the power of lithium-oxygen batteries by one order of magnitude while having the state-of-the-art energy density,” Li said.

Li said lithium-oxygen batteries must absorb oxygen from the air through nanoscale pores to facilitate reactions. So, the electrochemical performance of lithium-oxygen batteries depends on the liquid-gas two-phase flow at the pore scale of the electrode. The researchers aim to better understand the pore-scale transport of the battery electrodes as governed by pore size, structure, connectivity and wettability.

“Shawn Lister at Carnegie Mellon has a unique device to measure morphologies at the nanoscale — technology that’s like a CT scan in a hospital but with very high resolution down to the 20–30 nm resolution,” Li said. “We want to measure the lithium-oxygen battery electrodes and understand how we can transfer oxygen better with an improved design. The battery has to absorb oxygen from the air, so if we don’t supply oxygen fast enough, the power will be limited. We’re going to use his facility along with our advanced models and theories to try to design a high-performing battery electrode — and hopefully we’ll have a prototype for lab demonstration.”

The investigation will focus on improving oxygen’s sluggish mass transfer in battery electrodes.

“Batteries are electrochemical devices where you want a high reaction rate — and the only place the reaction can happen is in the electrode and electrolyte interface,” Li said. “We have to create as high a surface area as possible using nanomaterials, but mass transfer will be very slow because nanopores have higher resistance. In a lithium-oxygen battery, the electrolyte is liquid and the mass transfer through liquid is very slow compared with air. One example is you can’t breathe through a piece of paper soaked with water because of the high water resistance to oxygen transfer. It’s the same case for a liquid electrolyte, so we want to create the gas phase in our electrode to facilitate the oxygen transfer.”

Li said the project, which will support the training of two KU graduate students, has the potential to result in a patented technology that could push forward research and adoption of the lithium-oxygen technology in the coming years. The researchers plan to form potential partnerships with the local industry and reach out to the public through the Kansas City STEM Alliance.

Image caption: Nanotomography of a battery electrode collected from Argonne National Lab. Different colours represent different materials. Image credit: Xianglin Li.

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