The development of new lithium metal batteries with solid electrolytes has been slow due to strange short circuits and malfunctions. These batteries are light, flammable, have a large energy capacity and can be charged extremely quickly. This conundrum has reportedly been resolved, according to researchers at Stanford University and the SLAC National Accelerator Laboratory.
William Chueh, senior author of the study and associate professor of materials science and engineering in the School of Engineering and energy sciences and engineering at the new Stanford Doerr School of Sustainability, says that even slight indentation, bending, or buckling of batteries can cause nanoscopic cracks in materials to open and lithium to enter the solid electrolyte to short-circuit. explained that it might cause him to do so.
According to Chueh, who led the study with Wendy Gu, assistant professor of mechanical engineering, “Even dust or other impurities found in production can be stressed enough to cause failure.”
Solid electrolyte failure is an extensively researched problem. There are many theories as to the exact cause. Some attribute the problem to the unintentional transition of electrons, while others blame chemistry. Others argue that many forces are at work.
The study's lead authors, Geoff McConohy, Xin Xu, and Teng Cui, describe in their paper published Jan. 30 in the journal Nature Energy, how mechanical stress and nanoscale defects contribute to the breakdown of solid electrolytes.
This challenge can be studied and even used to their advantage by researchers aiming to create new, solid electrolyte rechargeable batteries, as the Stanford team is currently investigating. Energy-intensive, fast-charging, non-combustible lithium metal batteries can remove major barriers to the proliferation of electric cars, along with many additional benefits.
Most of the best solid electrolytes in use today are ceramics. They physically separate the two electrodes, which act as energy storage devices, and allow rapid passage of lithium ions. The most important feature is that they are fireproof. However, just like the porcelain in our homes, they can also be subject to microscopic surface breaks.
In more than 60 trials, the researchers proved that ceramics often contain nanoscopic cracks, pits and crevices, most of which are smaller than 20 nanometers. According to Chueh and his team, these internal cracks become visible during fast charging and allow lithium to penetrate.
In each experiment, the scientists built a small battery by attaching an electrical probe to a solid electrolyte and used an electron microscope to monitor the fast charge in action. They then used an ion beam as a scalpel to investigate why lithium collects on the surface of the ceramic as desired in some places, while in others it begins to bury itself deeper until it bridges with the solid electrolyte and causes a short circuit.
The difference is in pressure. Even if the battery is charged in less than a minute, the lithium electrolyte builds up wonderfully on its surface just by touching the electrical probe. When the probe presses against the ceramic electrolyte, the battery is more likely to short-circuit, simulating the mechanical forces of indentation, bending, and twisting.
The cathode-electrolyte-anode layers are stacked on top of each other to actually form a solid-state battery. The cathode and anode are physically separated from each other by the electrolyte, but it allows lithium ions to move freely between the two. A short circuit will occur if the cathode and anode come into contact or are electrically connected in any way, such as through a metallic lithium tunnel.
Even the slightest bend, kink, or dust particle at the interface between the electrolyte and the lithium anode will lead to invisible cracks, as demonstrated by Chueh and colleagues.
Lithium will eventually travel through the electrolyte, joining the cathode and anode, according to McConohy, who completed his doctorate in Chueh's lab last year and now works in industry. “The battery fails when this happens.”
The researchers claimed that numerous examples of the new understanding have been provided. Unable to detect cracks developing in the pure, untested electrolyte, scanning electron microscopes were used to film the process.
According to Xu, this is like a pothole on perfect asphalt. When it rains or snows, car tires flood tiny imperfections in the pavement, causing cracks to grow and eventually deepen.
"Lithium is essentially a soft material, but like water in the pit analogy, all it takes is pressure to expand the space and create a failure," said Xu, a postdoctoral researcher in Chueh's group.
In light of their new insights, Chueh's team is exploring ways to deliberately use these same mechanical stresses to harden material during manufacture, similar to how a blacksmith tempers a knife during manufacture. To prevent cracks from forming or to patch them after they do, scientists are also considering coating the electrolyte surface.
“These advances all start with a simple question: Why? “We work in the field of engineering. Finding out why something happens is the most important thing we can do. When we realize this, we can make improvements.
Source: “Mechanical regulation of lithium intrusion probability in garnet solid electrolytes”, 30 January 2023, Nature Energy.
Günceleme: 31/01/2023 12:48
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