ENERGY STORAGE Standford researchers: Oxygen detrimental to battery energy storage capacity

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Lithium-ion battery degradation is a big problem for increasingly complex modern applications that have higher and more complex power demands. Now, a joint American research team reckons that, with further research, it has found a way to create electrodes that can resist oxygen degradation.

Improving the energy storage capacity of batteries is, for obvious reasons, a core focus area for research teams the world over. A key bugbear for battery energy storage is degradation; all batteries degrade, and their capacities reduce over time as this happens. Being able to identify what conditions cause degradation and engineer a solution to them could help researchers design better batteries that are more able to cope with modern applications and the demand that comes with them.

Probing oxygen’s effect on lithium-ion batteries

Now, researchers from the U.S. Department of Energy’s SLAC National Accelerator Laboratory, along with colleagues from Stanford University, have carried out works that look at what happens when oxygen leaks out of lithium-ion (Li-ion) batteries (or ‘LiBs’) during charging and discharging.

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The research team broke down the intricate nature of the charge cycle process and observed how escaping oxygen atoms changed the structure of the electrode, the battery chemistry itself, and the amount of energy it could then store as a result. With additional research, the team is confident that new ways of creating electrodes could be developed to prevent the gradual reduction in energy storage capacity currently experienced with modern LiBs.

Loss of energy storage capacity

In their paper, the SLAC-Stanford joint research team describe LiBs as functioning somewhat like rocking chairs. These rocking chairs constantly move lithium ions between two electrodes that temporarily store charge. While it has long since been known that oxygen atoms leak out of the nanoparticles that constitute the electrode as these lithium ions move, the signals produced have until now been too small to measure.

In a news release in June, however, the researchers commented that the total amount of oxygen leakage was found to be 6 % over 500 charging cycles. “That’s not such a small number, but if you try to measure the amount of oxygen that comes out during each cycle, it’s about one one-hundredth of a percent.”

The researchers cycled LiBs over different lengths of time, took them apart, and then combed through the nanoparticles to try and see what was going on. They did this by using a specialized X-ray microscope at the Lawrence Berkeley National Laboratory to produce high-res images that showed the holes left by escaping oxygen atoms. Armed with this information and the use of ptychography, an advanced computational technique, the researchers uncovered nanoscale details of the oxygen leaking process.

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Identifying the cause

In addition to their experimental results, the researchers used computer modeling to find out how oxygen could be escaping. Where nanoparticles were more tightly packed together in clumps, less oxygen escaped than where nanoparticles were closer to the surface.

The researchers also found that oxygen atoms escape the nanoparticles in a way that they likened to a volcanic eruption. An initial burst of atoms escapes from the surface and then the oxygen atoms trickle out slowly like a lava flow. As this happens, the voltage of the battery fades. While it’s a slow process, the researchers reckon that over time a battery can lose 10 to 15 % of its storage capacity as a result.

From this new research, the team reckons that new methods for tacking battery degradation could be developed to create LiBs that are safer and last longer.

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