From DOE’s Sandia National Laboratories (US) : “The hidden culprit killing lithium-metal batteries from the inside”

From DOE’s Sandia National Laboratories (US)

July 14, 2021

Troy Rummler

First-of-their-kind snapshots reveal byproduct crippling powerful, experimental cells.

Sandia National Laboratories scientists Katie Harrison, left, and Katie Jungjohann have pioneered a new way to look inside batteries to learn how and why they fail. Photo by Bret Latter.

For decades scientists have tried to make reliable lithium-metal batteries. These high-performance storage cells hold 50% more energy than their prolific, lithium-ion cousins but higher failure rates and safety problems like fires and explosions have crippled commercialization efforts. Researchers have hypothesized why the devices fail, but direct evidence has been sparse.

Now, the first nanoscale images ever taken inside intact, lithium-metal coin batteries (also called button cells or watch batteries) challenge prevailing theories and could help make future high-performance batteries, such as for electric vehicles, safer, more powerful and longer lasting.

“We’re learning that we should be using separator materials tuned for lithium metal,” said battery scientist Katie Harrison, who leads Sandia National Laboratories’ team for improving the performance of lithium-metal batteries.

Sandia scientists, in collaboration with Thermo Fisher Scientific Inc., the University of Oregon (US) and DOE’s Lawrence Berkeley National Laboratory (US), published the images recently in ACS Energy Letters.


Figure 1. Scanning electron micrographs of intact angled-sections of high-rate cycled Li-metal half cells. (a) Uncycled cell, including: stainless-steel cap, Cu current collector, stack of two Celgard 2325 separators, Li metal, bottom Cu current collector, and lower stainless-steel disc, (b) 1st Li plating, (c) 1st Li stripping, (d) 11th plating, (e) 51st plating, and (f) 101st plating step. White arrows indicate cracks in the SEI matrix and gray regions indicate structures out-of-plane from the cut face.

Figure 2. Electrochemical performance of the 101st Li plating sample. (a) Capacity of the plating and stripping cycles, for Li plating at a high rate of 1.88 mA/cm2 up to the 101st plating step. (b) Coulombic efficiency of each full cycle, exhibiting the battery’s ability to efficiently recapture Li, even after the quantity of plated Li significantly decreases at ∼75 cycles. Capacity (c) and Coulombic efficiency (d) of the plating and stripping cycles at a low rate of 0.47 mA/cm2 to a capacity of 1.88 mAh/cm2. (e) Scanning electron micrograph of an intact angled-section of the 101st Li plating low-rate cycled half-cell. The brown layer at the top of the image is the stainless-steel cap, and the gray contrast indicates structures out-of-plane from the cut face.

Figure 3. Scanning electron micrographs of high-rate cycled angled-sections showing failure within two stacked Celgard 2325 separators. (a) Uncycled cell and (b) higher-magnification image of the separator porosity (with the lighter contrast indicating iron redeposition from laser ablation), (c) 1st Li plating, (d) 1st Li stripping, (e) 11th plating, (f) 51st plating, and (g) 101st plating step.

Figure 4. Schematic short-circuit mechanism for conductive Li pathways through the polymeric separator via SEI formation and subsequent deformation of the separator. SEI formed during the current plating step is colored yellow; SEI that formed in a prior step is colored gray.

Internal byproduct builds up, kills batteries

The team repeatedly charged and discharged lithium coin cells with the same high-intensity electric current that electric vehicles need to charge. Some cells went through a few cycles, while others went through more than a hundred cycles. Then, the cells were shipped to Thermo Fisher Scientific in Hillsboro, Oregon, for analysis.

In this new, false-color image of a lithium-metal test battery produced by Sandia National Laboratories, high-rate charging and recharging red lithium metal greatly distorts the green separator, creating tan reaction byproducts, to the surprise of scientists. Image by Katie Jungjohann.

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 buildup formed as a byproduct of the battery’s internal chemical reactions. Every time the battery recharged the byproduct 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 byproduct were much more destructive than previously believed, acting less like a needle and more like a snowplow.

“The separator is completely shredded,” Harrison said, adding that this mechanism has only been observed under fast charging rates needed for electric vehicle technologies, but not slower charging rates.

As Sandia scientists think about how to modify separator materials, Harrison says that further research also will be needed to reduce the formation of byproducts.

Scientists pair lasers with cryogenics to take ‘cool’ images

Determining cause-of-death for a coin battery is surprisingly difficult. The trouble comes from its stainless-steel casing. The metal 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.

“We have different tools that can study different components of a battery, but really we haven’t had a tool that can resolve everything in one image,” said Katie Jungjohann, a Sandia nanoscale imaging scientist at the Center for Integrated Nanotechnologies. The center is a user facility jointly operated by Sandia and Los Alamos national laboratories.

She 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 minus 148 and minus 184 degrees Fahrenheit (minus 100 and minus 120 degrees Celsius, respectively). 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. The tool will be used broadly across Sandia to help solve many materials and failure-analysis problems.

“This is what battery researchers have always wanted to see,” Jungjohann said.

The research was funded by Sandia’s Laboratory Directed Research and Development program and the Department of Energy.

See the full article here .


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DOE’s Sandia National Laboratories (US) managed and operated by the National Technology and Engineering Solutions of Sandia (a wholly owned subsidiary of Honeywell International), is one of three National Nuclear Security Administration(US) research and development laboratories in the United States. Their primary mission is to develop, engineer, and test the non-nuclear components of nuclear weapons and high technology. Headquartered in Central New Mexico near the Sandia Mountains, on Kirtland Air Force Base in Albuquerque, Sandia also has a campus in Livermore, California, next to DOE’sLawrence Livermore National Laboratory(US), and a test facility in Waimea, Kauai, Hawaii.

It is Sandia’s mission to maintain the reliability and surety of nuclear weapon systems, conduct research and development in arms control and nonproliferation technologies, and investigate methods for the disposal of the United States’ nuclear weapons program’s hazardous waste.

Other missions include research and development in energy and environmental programs, as well as the surety of critical national infrastructures. In addition, Sandia is home to a wide variety of research including computational biology; mathematics (through its Computer Science Research Institute); materials science; alternative energy; psychology; MEMS; and cognitive science initiatives.

Sandia formerly hosted ASCI Red, one of the world’s fastest supercomputers until its recent decommission, and now hosts ASCI Red Storm supercomputer, originally known as Thor’s Hammer.

Sandia is also home to the Z Machine.

The Z Machine is the largest X-ray generator in the world and is designed to test materials in conditions of extreme temperature and pressure. It is operated by Sandia National Laboratories to gather data to aid in computer modeling of nuclear guns. In December 2016, it was announced that National Technology and Engineering Solutions of Sandia, under the direction of Honeywell International, would take over the management of Sandia National Laboratories starting on May 1, 2017.