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Researchers at Tokyo University of Science (TUS) have developed a new electrolyte material that improves the conductivity of magnesium ions at room temperature, paving the way for the next step in the development of magnesium ion (Mg2+) batteries. According to researchers, Mg2+ batteries, considered a cheaper alternative to lithium-ion batteries, have faced major obstacles due to the poor conductivity of magnesium ions in solids at room temperature.<\/p>\n
"The lithium-ion battery has an advantage in gravimetric energy density, so it is suitable for mobile use (such as a phone)," said Masaaki Sadakiyo, Ph.D., junior associate professor, Division I, Faculty of Life Sciences, Department of Applied Chemistry. in TUS But lithium (Li) is a rare element, he said.<\/p>\n
"On the other hand, the Mg2+ battery has an advantage in volumetric energy density and cost (i.e., less use of a rare element), which will be beneficial in stationary applications (eg, energy storage for renewable sources)," he added. "Given that lithium is a limited resource on Earth, large-scale energy storage in the future world must be replaced by other batteries such as Mg2+."<\/p>\n
Magnesium is a promising solid-state battery material due to its abundance, and Mg2+-based power devices have high energy density, high safety and low cost, researchers say. However, the widespread use of Mg2+ has been limited by its poor conductivity in solids at room temperature, they reported: \u201cMg2+ has poor solid-state conductivity because the divalent positive ions (2+) experience a strong interaction with neighboring negative ions in the solid. crystal, preventing their migration through the material."<\/p>\n
Researchers at TUS believe they have solved the chemical confinement problem with a metal-organic framework (MOF)-based Mg2+ conductor with superionic conductivity at room temperature. They reported that the Mg2+ electrolyte achieved a superconductivity of 1.9 \u00d7 10\u20133 Cm\u20131, which is the threshold for practical application in solid-state batteries.<\/p>\n
The researchers shared their findings in a study published in the Journal of the American Chemical Society. A key result shows that the conductivity is the highest to date for a crystalline Mg2+ solid, breaking a decades-long barrier.<\/p>\n
Sadakiyo, who led the research on "A Novel Lithium-Free Magnesium Superion Conductor to a Solid State." -State Batteries,\u201d described materials used as MOFs that have a highly porous crystalline structure that enables efficient ion migration.<\/p>\n
The researchers introduced a "guest molecule", acetonitrile, into the pores of the MOF, which accelerated the conduction of Mg2+.<\/p>\n
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Conductor Mg2+, consisting of a metal-organic base. Click to enlarge image. (Source: Masaaki Sadakiyo, Tokyo University of Science)<\/p>\n
"Our paper is related to the development of an electrolyte for solid-state batteries (ie, the Mg2+ conductor)," Sadakiyo said. "We prepared a new Mg2+ conductor and clarified its ion-conducting mechanism. We explained that Mg2+ contained in the pores of a certain solid material (i.e. MOF) migrates efficiently under certain organic vapors, and that the resulting conductivity of Mg2+ is high enough to be used for a battery.\u201d<\/p>\n
The team used a MOF called MIL-101 as a scaffold, encapsulating Mg2+ ions in its nanopores. This created a MOF-based electrolyte where Mg2+ was loosely packed, allowing the migration of divalent Mg2+ ions. Then, to improve ionic conductivity, acetonitrile vapor was introduced into the electrolyte. The samples were subjected to an AC impedance test to measure ionic conductivity.<\/p>\n
Other measurements and tests have shown that acetonitrile molecules adsorbed in the framework ensure efficient migration of Mg2+ ions through the solid electrolyte body. This demonstrated that the MOF-based Mg2+ conductor is a suitable material for batteries.<\/p>\n
Sadakiyo believes this breakthrough brings the industry one step closer to a commercial Mg2+ battery, although more work is needed in other areas. "We believe our findings contribute to the realization of a Mg2+ battery from an electrolyte perspective," he said. "However, as you mentioned, there are many other challenges involved in making a practical Mg2+ battery, not just for the electrolyte materials, but for the electrode materials as well."<\/p>\n
The research team plans to apply this material to a "real" battery in collaboration with another lab. Sadakiyo believes that a special license is not needed for commercial use because they have not received a patent and the work has already been published. "However, at this point, we believe there are many challenges that need to be addressed by additional researchers to achieve real-world use of the battery."<\/p>\n
One of the next steps for the team includes creating "other new materials that exhibit higher Mg2+ conductivity with a higher Mg2+ transport number with lower organic vapor pressures," Sadakiyo said. The team is also "interested in covering the fundamental science of the conductivity of multivalent ions (such as Mg2+) in the solid state."<\/p>\n
According to Sadakiyo, we won't see commercial Mg2+ batteries available on the market for at least 10 to 20 years.<\/p>\n
In addition to Sadakiyo, the research team includes Yuto Yoshida, also of TUS; Professor Teppei Yamada from the University of Tokyo; and Associate Professor Takashi Toyao and Professor Ken-ichi Shimizu from Hokkaido University.<\/p>\n