Researchers at Empa, the Swiss Federal Laboratories for Materials Science and Technology, have developed a flexible solid electrolyte for batteries that could overcome key limitations of current solid-state technology and pave the way for safer, more efficient energy storage.
Unlike most batteries which utilize flammable liquid electrolytes, solid-state batteries employ a solid substance to transport ions between electrodes. This approach not only enhances safety but also allows for the use of materials like pure lithium metal for the anode, potentially increasing energy density – a critical factor for applications ranging from electric vehicles to portable electronics.
The primary challenge with existing solid electrolytes lies in their rigidity. Empa’s innovation centers on a polysiloxane-based polymer, commonly known as silicone, modified to conduct ions while retaining its elasticity. “The polymer base for the electrolyte is a polysiloxane, more commonly known as silicone in everyday language,” explained Dorina Opris, a researcher at Empa’s Functional Polymers laboratory. “This elastic plastic has a major disadvantage for battery research: We see apolar. In other words, charged particles, the ions, do not dissolve in it at all.” Opris and her team successfully integrated functional groups into the polymer structure, enabling ion conduction without sacrificing its flexibility.
This elasticity addresses a significant problem encountered when using pure lithium metal anodes. During charging and discharging, lithium ions migrate to and from the anode, but tend to form dendrites – tree-like structures that can cause short circuits. While solid electrolytes generally suppress dendrite growth, the volume changes associated with ion migration can lead to a loss of contact between the anode and electrolyte, reducing battery capacity. The Empa team’s flexible electrolyte conforms to these volume changes, maintaining contact and preventing dendrite formation.
The new electrolyte also holds promise for flexible battery designs. “Current batteries for medical implants, such as pacemakers, are generally hard and uncomfortable for patients,” said Opris. “Our polymer can serve not only as an electrolyte but also as a binding material for the cathode.” Can Zimmerli, also a researcher at Empa, added that the polymer’s compatibility with various cathode materials allows for customization for diverse applications.
Beyond flexibility and safety, the material offers potential cost advantages. According to Opris, the silicone-based electrolyte can be produced as thin films and is potentially less expensive than traditional solid polymer electrolytes. The research team is currently working to further improve the electrolyte’s ionic conductivity and is seeking an industrial partner to begin commercialization. Their findings were recently published in ChemSusChem.
Recent advancements in lithium battery technology have focused on increasing energy density. Researchers at Nankai University and the Shanghai Institute of Space Power Sources in China, for example, have reportedly achieved an energy density of approximately 700 watt-hours per kilogram using a redesigned electrolyte, as reported by Intriguing Engineering. But, this remains a laboratory-scale achievement. All-solid-state batteries, utilizing sulfur-based cathodes, are also being explored as a cost-effective route to high specific energy, according to research published in Nature, though challenges remain with active material utilization and cycle life.
