![]() ![]() Subsequently, they used an ion beam as a scalpel to understand why the lithium collects on the surface of the ceramic in some locations, as desired, while in other spots it begins to burrow, deeper and deeper, until the lithium bridges across the solid electrolyte, creating a short circuit. In each experiment, the researchers applied an electrical probe to a solid electrolyte, creating a miniature battery, and used an electron microscope to observe fast charging in real time. (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. 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. (Image credit: Xin Xu, Geoff McConohy, and Wenfang Shi) But, like ceramics in our homes, they can develop tiny cracks on their surface.Ī scanning electron microscopy video that shows lithium plating as it takes place on a solid electrolyte. They enable fast transport of lithium ions and physically separate the two electrodes that store energy. Many of today’s leading solid electrolytes are ceramic. Energy-dense, fast-charging, nonflammable lithium metal batteries that last a long time could overcome the main barriers to the widespread use of electric vehicles, among numerous other benefits. 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. 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. Yet others theorize different forces are at play. Some say the unintended flow of electrons is to blame, while others point to chemistry. Theories abound as to what exactly is the cause. The problem of failing solid electrolytes is not new and many have studied the phenomenon. “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. “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. It comes down to stress – mechanical stress to be more precise – especially during potent recharging. On the right, the probe is not pressing against the electrolyte and the lithium plates on the ceramic surface, as desired. ![]() This artist’s rendition shows one probe bending from applied pressure, causing a fracture in the solid electrolyte, which is filling with lithium. ![]()
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