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Sandia National Laboratories

Lithium-metal failure mechanism identified

Thu, 07/29/2021 - 13:12 -- Vic
Lithium metal failure mechanism identified

Scientists at in the US have found evidence of an internal mechanism that causes lithium-metal battery failure.

Lithium-metal cells hold 50% more energy than lithium-ion cells, but higher failure rates and safety problems have hindered commercialisation efforts— with direct evidence of the reasons for the failure never confirmed.

The team consisted of researchers from Sandia National Laboratories, working with Thermo Fisher Scientific, the University of Oregon and Lawrence Berkeley National Laboratory.

The first nano-scale images ever taken inside intact, lithium-metal coin batteries challenge prevailing theories.

The images were been published in the journal ACS Energy Letters.

When the team reviewed images of the batteries' insides, they expected to find needle-shaped deposits of lithium spanning the battery. 

Most battery researchers think that a lithium spike forms after repetitive cycling and that it punches through a plastic separator between the anode and the cathode, forming a bridge that causes a short. But lithium is a soft metal, so scientists have not understood how it could get through the separator.

Harrison's team found a surprising second culprit: a hard build-up formed as a by-product of the battery's internal chemical reactions.

Every time the battery recharged, the by-product, called solid electrolyte interphase, grew. 

Capping the lithium, it tore holes in the separator, creating openings for metal deposits to spread and form a short.

Together, the lithium deposits and the by-product were much more destructive than previously believed, acting less like a needle and more like a snowplough. 

Determining cause-of-death for a coin battery is surprisingly difficult because of its stainless-steel casing.

The shell limits what diagnostics, like X-rays, can see from the outside, while removing parts of the cell for analysis rips apart the battery's layers and distorts whatever evidence might be inside. 

Katie Jungjohann, a Sandia nano-scale-imaging scientist at the Center for Integrated Nanotechnologies and her collaborators used a microscope that has a laser to mill through a battery's outer casing.

They paired it with a sample holder that keeps the cell's liquid electrolyte frozen at temperatures between -148 and -184°F (-100 and -120°C). 

The laser creates an opening just large enough for a narrow electron beam to enter and bounce back onto a detector, delivering a high-resolution image of the battery's internal cross section with enough detail to distinguish the different materials.

The original demonstration instrument, which was the only such tool in the United States at the time, was built and still resides at a Thermo Fisher Scientific laboratory in Oregon. 

An updated duplicate now resides at Sandia and will be used broadly across Sandia to help solve many materials and failure-analysis problems.

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Low temperature molten sodium battery demonstrated

Wed, 07/28/2021 - 13:00 -- Vic
Low temperature molten sodium battery

Researchers at Sandia National Laboratories have designed a new class of molten sodium batteries, operating at much cooler temperatures, for grid-scale energy storage. 

The battery consisted of a Sn-saturated Na anode, a Sn-coated (170 nm thickness) NaSICON separator, NaI-GaCl3catholyte, and thermally activated carbon felt cathode current collector. 

The latest development, using a revolutionary high-voltage NaI-GaCl(sodium iodide and gallium chloride) molten salt catholyte, enables stable electrochemical cycling in a molten Na-NaI battery. 

The test battery has operated in the laboratory at the dramatically reduced temperature of 110°C for more than eight months and was cycled more than 400 times. 

The new battery design was shared in a paper published in the scientific journal Cell Reports Physical Science.

While traditional molten sodium batteries operate at around 300°C, Sandia's new molten sodium-iodide battery operates at a much cooler 110°C.

Leo Small, the lead researcher on the project, said: "We've been working to bring the operating temperature of molten sodium batteries down as low as physically possible. 

"There's a whole cascading cost savings that comes along with lowering the battery temperature. 

"You can use less expensive materials, the batteries need less insulation and the wiring that connects all the batteries can be a lot thinner."

Throughout cycling, the battery cycling program was periodically stopped for a few hours to accommodate other experiments in the shared oven space. 

This periodic stoppage appears to have had limited effect on the battery performance, as seen by a <0.5% average drop in energy efficiency in the cycle following the stoppage, which would be recovered within a few cycles. 

The batteries were twice cooled to room temperature, first for one month and second for one week. 

The ability to freeze the charged battery and discharge it at a later time is especially advantageous for long-duration grid-scale energy storage, in which a battery may be charged during one month, and then discharged several months later.

Erik Spoerke, a materials scientist who has been working on molten sodium batteries for more than a decade, said: "This is the first demonstration of long-term, stable cycling of a low-temperature molten-sodium battery. 

"The magic of what we've put together is that we've identified salt chemistry and electrochemistry that allow us to operate effectively at 110°C."

Commercial molten sodium batteries have lifetimes of 10-15 years, significantly longer than standard lead-acid batteries or lithium-ion batteries.

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Researchers use radio frequency to detect health of commercial lithium-ion batteries

Thu, 01/30/2020 - 14:38 -- paul Crompton

Researchers from Sandia National Laboratories have developed a radio-frequency detector that monitors a lithium-ion battery’s health while cycling— a first for commercially available batteries.

Placed inside the battery, the paper-thin magnetic resonance detector could help researchers better understand and characterise batteries to improve them for renewable storage and national security applications.

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