Lithium metal batteries with solid electrolytes are considered the next generation of lithium batteries. These batteries are lightweight, flammable, contain a lot of energy and can be charged very quickly. However, solid electrolytes are susceptible to short-circuiting and interference from lithium metal, and the cause is under debate.
Now researchers from Stanford University and SLAC National Accelerator Laboratory say they’ve finally solved the mystery. The discovery could lead to new battery designs and production methods that help avoid the problem.
In their rigorous, statistically significant experiments, researchers found that mechanical stress during charging causes solid electrolytes to fail.
“Just a slight nick, bending or twisting of the batteries can cause nanoscopic cracks in the materials to open and allow lithium to enter the solid electrolyte, causing it to short circuit.” explained senior author William Chueh. “Even dust or other impurities introduced during production can create enough stress to cause failure.”
The problem of failing solid electrolytes has puzzled researchers for years. Some theories say it was due to the accidental flow of electrons, while others point to chemistry.
Now, through more than 60 experiments, the Stanford researchers have shown that the problems were actually caused by nanoscopic cracks, dents and splits in ceramic electrolytes. Many of these fractures were less than 20 nanometers wide.
During fast charging, the team says, these inherent fractures open allowing the lithium to enter, causing the battery to short or fail.
The researchers applied an electrical probe to a solid electrolyte in each experiment, creating a miniature battery. They used an electron microscope to observe fast charging in real time.
They then used an ion beam as a scalpel to understand why the lithium collects on the surface of the ceramic in some places, while in others it begins to dig deeper and deeper – until the lithium forms a bridge over the solid electrolyte , causing a short circuit. circuit.
After all the experiments, researchers concluded that the difference is pressure. When the electric probe only touches the surface of the electrolyte, lithium collects beautifully on top of the electrolyte, even if the battery is charged in less than a minute.
However, when the probe presses into the ceramic electrolyte – mimicking the mechanical stresses of compression, bending and twisting – the battery is more likely to short out.
“Given the opportunity to burrow into the electrolyte, the lithium will eventually work its way through connecting the cathode and anode,” said McConohy, who completed his doctorate last year in Chueh’s lab and now works in the industry. “When that happens, the battery dies.”
Using these new findings, the team is now looking for ways to intentionally use the same mechanical forces to make the material harder during production. They are also looking at ways to coat the electrolyte surface to prevent or repair cracks if they do form.
As a result of this discovery, energy-dense, fast-charging, non-flammable, long-lasting lithium-metal batteries, among a host of other benefits, could overcome the major barriers to the widespread use of electric vehicles.
Magazine reference:
- Geoff McConohy, Xin Xu, Teng Cui, Edward Barks, Sunny Wang, Emma Kaeli, Celeste Melamed, X. Wendy Gu, and William C. Chueh. Mechanical control of the probability of lithium intrusion into garnet solid electrolytes. Natural energy, 2023; DOI: 10.1038/s41560-022-01186-4
