Using a solid electrolyte instead of a liquid one inside a battery could enable rechargeable lithium metal batteries that are safer, store much more energy, and recharge far faster than today’s lithium-ion batteries. This idea has attracted scientists and engineers for decades. However, progress has been limited by a critical weakness. Solid electrolytes made from crystalline materials tend to develop microscopic cracks. Over time, these cracks grow during repeated charging and eventually cause the battery to fail.
Researchers at Stanford, building on work they published three years ago that revealed how tiny cracks, dents, and surface defects form and spread, have now identified a potential fix. They found that heat-treating an extremely thin layer of silver on the surface of a solid electrolyte can largely prevent this damage.
As reported in Nature Materials on January 16, the silver-treated surface became five times more resistant to cracking caused by mechanical pressure. The coating also reduced the risk that lithium would push its way into existing surface flaws. This type of intrusion is especially harmful during fast charging, when very small cracks can widen into deeper channels that permanently degrade the battery.
Why Cracks Are So Hard to Eliminate
“The solid electrolytes that we and others are working on is a kind of ceramic that allows the lithium-ions to shuttle back and forth easily, but it’s brittle,” said Wendy Gu, associate professor of mechanical engineering and a senior author of the study. “On an incredibly small scale, it’s not unlike ceramic plates or bowls you have at home that have tiny cracks on their surfaces.”
Gu noted that eliminating every defect during manufacturing is unrealistic. “A real-world solid-state battery is made of layers of stacked cathode-electrolyte-anode sheets. Manufacturing these without even the tiniest imperfections would be nearly impossible and very expensive,” she said. “We decided a protective surface may be more realistic, and just a little bit of silver seems to do a pretty good job.”
Silver-Lithium Switch
Earlier studies by other research teams examined metallic silver coatings applied to the same solid electrolyte material used in the new study. That material is known as “LLZO” for its combination of lithium, lanthanum, zirconium, and oxygen. While those earlier efforts focused on metallic silver, the Stanford team took a different approach by using a dissolved form of silver that has lost an electron (Ag+).
This positively charged silver behaves very differently from solid metallic silver. According to the researchers, the Ag+ ions are directly responsible for strengthening the ceramic and reducing its tendency to crack.
How the Silver Treatment Works
The team applied a silver layer just 3 nanometers thick to the surface of LLZO samples and then heated them to 300 degrees Celsius (572° Fahrenheit). As the samples heated, silver atoms moved into the surface of the electrolyte, replacing smaller lithium atoms within the porous crystal structure. This process extended about 20 to 50 nanometers below the surface.
Importantly, the silver remained in its positively charged ionic form rather than turning into metallic silver. The researchers believe this is critical to preventing cracks. In areas where tiny imperfections already exist, the silver ions also help block lithium from entering and forming damaging internal structures.
“Our study shows that nanoscale silver doping can fundamentally alter how cracks initiate and propagate at the electrolyte surface, producing durable, failure-resistant solid electrolytes for next-generation energy storage technologies,” said Xin Xu, who led the research as a postdoctoral scholar at Stanford and is now an assistant professor of engineering at Arizona State University.
“This method may be extended to a broad class of ceramics, It demonstrates ultrathin surface coatings can make the electrolyte less brittle and more stable under extreme electrochemical and mechanical conditions, like fast charging and pressure,” said Xu, who at Stanford worked in the laboratory of Prof. William Chueh, a senior author of the study and director of the Precourt Institute for Energy, which is part of the Stanford Doerr School of Sustainability.
To measure how much stronger the treated material had become, the researchers used a specialized probe inside a scanning electron microscope to test how much force was needed to fracture the electrolyte surface. The silver-treated material required almost five times more pressure to crack than untreated samples.
What Comes Next for Solid-State Batteries
So far, the experiments focused on small, localized areas rather than full battery cells. It is still unclear whether this silver-based approach can be scaled to larger batteries, integrated with other components, and maintain its performance over thousands of charging cycles.
The team is now working with complete lithium metal solid-state battery cells and exploring how applying mechanical pressure from different angles might extend battery lifespan. They are also studying additional types of solid electrolytes, including sulfur-based materials that could offer better chemical stability when paired with lithium.
The researchers also see potential applications beyond lithium. Sodium-based batteries could benefit from similar strategies and may help reduce supply-chain pressures tied to lithium demand.
Silver may not be the only viable option. The researchers said other metals could work, as long as their ions are larger than the lithium ions they replace in the electrolyte structure. Copper showed some success in early tests, although it was less effective than silver.
The other senior authors of the study with Gu and Chueh is Yue Qi, engineering professor at Brown University. Stanford co-lead authors with Xu are Teng Cui, now an assistant professor at the University of Waterloo; Geoff McConohy, now a research engineer at Orca Sciences; and current PhD student Samuel S. Lee. Brown University alumnus Harsh Jagad, now chief technology officer at Metal Light, Inc., is also a co-lead author of the study.
