BATTERIESIlluminating the Barrier to Next-Generation Battery That Charges Very Quickly
In the race for fast-charging, energy-dense lithium metal batteries, researchers discovered why the promising solid electrolyte version has not performed as hoped. This could help new designs – and eventually battery production – avoid the problem.
New lithium metal batteries with solid electrolytes are lightweight, inflammable, pack a lot of energy, and can be recharged very quickly, but they have been slow to develop due to mysterious short circuiting and failure. Now, researchers at Stanford University and SLAC National Accelerator Laboratory say they have solved the mystery.
It comes down to stress – mechanical stress to be more precise – especially during potent recharging.
“Just 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,” explained senior author William Chueh, an associate professor of materials science and engineering in the School of Engineering, and of energy sciences and engineering in the new Stanford Doerr School of Sustainability.
“Even dust or other impurities introduced in manufacturing can generate enough stress to cause failure,” said Chueh, who directed the research with Wendy Gu, an assistant professor of mechanical engineering.
The problem of failing solid electrolytes is not new and many have studied the phenomenon. Theories abound as to what exactly is the cause. Some say the unintended flow of electrons is to blame, while others point to chemistry. Yet others theorize different forces are at play.
In a study to be published Jan. 30 in the journal Nature Energy, co-lead authors Geoff McConohy, Xin Xu, and Teng Cui explain in rigorous, statistically significant experiments how nanoscale defects and mechanical stress cause solid electrolytes to fail. Scientists around the world trying to develop new, solid electrolyte rechargeable batteries can design around the problem or even turn the discovery to their advantage, as much of this Stanford team is now researching. 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.
Statistical Significance
Many of today’s leading solid electrolytes are ceramic. They enable fast transport of lithium ions and physically separate the two electrodes that store energy. Most importantly, they are fireproof. But, like ceramics in our homes, they can develop tiny cracks on their surface.
The researchers demonstrated through more than 60 experiments that ceramics are often imbued with nanoscopic cracks, dents, and fissures, many less than 20 nanometers wide. (A sheet of paper is about 100,000 nanometers thick.) During fast charging, Chueh and team say, these inherent fractures open, allowing lithium to intrude.
