New NASA Study Says Possibly No Limit to Solar Storm Effects - The Latest in NASA Science News

For decades, scientists have thought that there is a ceiling to how intensely Earth responds to solar storms. However, a NASA-led paper published Wednesday in Nature suggests this upper limit is an illusion. If so, it means solar storms could have far worse effects on our technology than previously thought.

Observations have suggested that electric currents in Earth’s upper atmosphere — which can affect satellites, communications, and navigation signals — increase as the solar wind strengthens, but only to a point.

However, a team led by space physicist Nithin Sivadas of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, says this apparent limit is merely an effect of uncertainties in solar wind measurements.

The issue is that most solar wind measurements are taken by spacecraft located a million miles closer to the Sun than Earth is. However, statistically, the solar wind that ultimately reaches Earth’s magnetic shield is most likely weaker, said Sivadas. This makes it look like strong solar winds do not produce equally strong currents, because it is actually driven by weaker solar winds.

As solar wind strikes Earth during a solar storm, electric currents intensify in the upper atmosphere. In the chart on the left, a blue line shows how the average strength of electrical currents in Earth’s upper atmosphere increases with solar wind strength but then gradually levels off or “saturates” when measured about a million miles from Earth. (Both values are represented in millivolts per meter.) In the chart on the right, a new analysis based on solar wind measurements taken closer to Earth suggests that the average strength of the electrical currents (pink line) continues to increase as the solar wind strength increases, with no upper limit.

NASA/Nithin Sivadas

The team analyzed evidence from more than a million solar wind measurements taken by NASA spacecraft much closer to Earth, such as MMS and THEMIS. Unlike the measurements captured farther away, these showed a direct relationship between the strength of the solar wind and the currents, suggesting there is no upper limit.

The findings challenge decades of understanding, and more observations of strong solar wind will help determine whether Earth’s response truly has an upper limit.

By Vanessa Thomas
NASA’s Goddard Space Flight Center, Greenbelt, Md. 

Source: New NASA Study Says Possibly No Limit to Solar Storm Effects  

Magnesium oxide emerges as a promising protective coating for sulfide solid electrolytes - Energy & Green Tech

Computation and experiment were combined to find candidate protective coatings for sulfide-based solid electrolytes and uncover what makes those coatings work. Credit: Image by Argonne National Laboratory

The success of a promising class of next-generation batteries may hinge on something almost impossibly thin: a coating just a nanometer thick—roughly 100,000 times thinner than a human hair. In new research, scientists at the U.S. Department of Energy's (DOE) Argonne National Laboratory combined computation and experiment to find candidate protective coatings for sulfide-based solid electrolytes and uncover what makes those coatings work.

The results, published in Advanced Science, point to magnesium oxide as a particularly promising new coating and sets up a faster way to find others.

Solid-state batteries could store more energy and improve safety compared with today's lithium-ion batteries. But some of the most promising solid electrolytes, especially sulfide-based ones, are chemically fragile. They can react at key battery interfaces, especially where the electrolyte touches lithium metal. Those reactions can hurt performance and shorten battery life.

To tackle that problem, the team studied a type of sulfide solid electrolyte called lithium phosphorus sulfur chloride, or LPSCl. They used an approach based on a computational technique called density functional theory to screen a wide range of oxide coatings made by atomic layer deposition (ALD)—a method that deposits ultrathin, uniform layers with near-atomic precision.

They predicted how those coatings would behave at three important battery interfaces: where the coating meets the electrolyte, the lithium metal and the cathode materials.

Reaction products shape performance

"This work focused on using computation to guide that search," said Justin Connell, an Argonne materials scientist and University of Chicago Consortium for Advanced Science and Engineering (CASE) scientist. "We can't experimentally explore the full range of possible materials in any reasonable way. That would take forever, and it's just not possible."

The team found that the best coatings were not always the least reactive. Instead, the most important factor was what compounds formed when the coating reacted at the interface. The best coatings formed reaction products that still let lithium ions move while limiting electron flow.

"It turned out that the reaction products really dominate the behavior," Connell said. "Zirconium oxide was one of the most stable materials by itself, but it was one of the worst-performing coatings we investigated."

Magnesium oxide stands out

The researchers then tested several candidate coatings by applying them to LPSCl powder with ALD. Magnesium oxide in particular stood out. It made the electrolyte more stable when in contact with lithium metal, reduced resistance at the interface and improved performance. It also helped block electron flow while still allowing lithium ions to move efficiently.

"Atomic layer deposition gives us a unique way to apply uniform coatings that are only about a nanometer thick, even on complex powder surfaces," said senior chemist and Argonne Distinguished Fellow Jeffrey Elam. "That level of control lets us test new coating chemistries efficiently and connect computational predictions to real materials."

The team also used scanning transmission electron microscopy and energy dispersive X-ray spectroscopy at the Center for Nanoscale Materials, a DOE Office of Science user facility at Argonne, to confirm the coatings were uniformly distributed on the powder surfaces.

By contrast, zirconium oxide formed less favorable reaction products and performed poorly. Zinc oxide, despite being predicted to be more reactive overall, still yielded beneficial transport behavior because of the reaction products it formed.

A faster route through chemistry

In addition to evaluating candidate protective coatings, this work provides a better way to search a much larger materials design space.

"Our calculations helped identify which interfacial reactions are most likely to occur and which reaction products will support or hinder battery performance," said Argonne physicist Peter Zapol, who led the study's calculations and computational screening. "That gives us a more predictive way to evaluate coating candidates, rather than relying on trial and error."

Connell said the approach should help speed up the search for future coatings beyond the oxide systems studied here.

"This work shows us a better way to ask the design question, and now we can use the same approach to study many other chemistries," he said.

"That could mean sulfides, fluorides, other binary chemistries, ternary coating chemistries or combinations of materials. It lets us explore that large chemical space much faster, without having to test everything experimentally first." 

Provided by Argonne National Laboratory  

by Argonne National Laboratory

edited by Sadie Harley, reviewed by Andrew Zinin 

Source: Magnesium oxide emerges as a promising protective coating for sulfide solid electrolytes