Researchers from Stanford University and SLAC National Accelerator Laboratory have said that they have solved the mystery behind the persistent problem of short-circuit and failure in new lithium metal batteries.

The team identified that the problem comes down to nanoscale defects and mechanical stress, especially during potent charging.

William Chueh, an associate professor in the new Stanford Doerr School of Sustainability, explained that modest indentation, bending, or twisting of the batteries can cause nanoscopic fissures in the materials to open and lithium to intrude into the solid electrolyte causing it to short circuit.

“Even dust or other impurities introduced in manufacturing can generate enough stress to cause failure,” added Chueh.

New lithium metal batteries with solid electrolytes are lightweight, inflammable, packed with energy, and can be recharged very quickly, but they have been slow to develop.

Energy-dense, fast-charging, non-flammable lithium metal batteries that last a long time could overcome the main barriers to the widespread use of electric vehicles, among numerous other benefits, the study said.

The researchers demonstrated through more than 60 experiments that ceramics are often imbued with nanoscopic cracks, dents, and fissures, many less than 20 nanometres wide.

During fast charging, the team of researchers said, these inherent fractures open, allowing lithium to intrude.

Theory into Practice

A solid-state battery is made of layers of cathode-electrolyte-anode sheets stacked one atop another.

The electrolyte’s role is to physically separate the cathode from the anode while allowing lithium ions to travel freely between the two.

If the cathode and anode touch or are connected electrically in any way, as by a tunnel of metallic lithium, a short circuit occurs.

“Given the opportunity to burrow into the electrolyte, the lithium will eventually snake its way through, connecting the cathode and anode… When that happens, the battery fails,” said a researcher in the study.

The new understanding was demonstrated repeatedly in various experiments, the researchers said.

“Lithium is actually a soft material, but, like the water in the pothole analogy, all it takes is pressure to widen the gap and cause a failure,” said Xu, a postdoctoral scholar in Chueh’s lab.

With their new understanding in hand, the team is looking at ways to use mechanical forces intentionally to toughen the material during manufacturing.

The team is also looking at ways to coat the electrolyte surface to prevent cracks or repair them if they emerge.

Earlier in January, researchers at the Daegu Gyeongbuk Institute of Science & Technology said they have developed a new electrolyte technology through magnetic nanoparticles that can improve both the stability and lifespan of next-generation lithium batteries.

In December last year, researchers at the University of Sydney claimed to have developed a new, low-cost sodium-sulfur battery with four times the energy capacity of lithium-ion batteries.