Stanford University researchers have made a groundbreaking discovery regarding iron, a metal often overlooked in energy technology. A team led by PhD students Hari Ramachandran, Edward Mu, and Eder Lomeli has unlocked an unprecedented high-energy state in iron, which may significantly influence the future of lithium-ion batteries and other energy storage solutions.
This innovative finding suggests that iron is capable of releasing and reabsorbing more electrons than previously believed, indicating the potential for batteries that are not only more efficient but also cost-effective compared to current cobalt- or nickel-based models. The implications of this discovery extend beyond batteries, potentially impacting various technologies that depend on the magnetic and electronic characteristics of materials, including MRI machines, maglev trains, and superconductors.
The research team, which included 23 members from multiple U.S. universities, national laboratories, and international collaborators from Japan and South Korea, achieved this milestone by manipulating the structure of a compound composed of lithium, iron, antimony, and oxygen. The nanoscale arrangement of this material allowed iron atoms to reversibly give up and absorb five electrons, significantly surpassing the normal capacity of two or three electrons.
Initially, Ramachandran and Mu faced challenges with their early samples collapsing during charging cycles. They discovered that reducing the size of the material”s particles to approximately 300 to 400 nanometers—about 40 times smaller than earlier attempts—was crucial. They eventually developed a method to grow these crystals from a precisely mixed liquid solution.
In their electrochemical tests, the team observed that the compound enabled iron to reversibly donate and reclaim five electrons while maintaining the stability of its crystal structure. To further understand the internal processes, Lomeli collaborated with his advisor, Tom Devereaux, an expert in X-ray spectroscopy modeling. Their findings revealed that the additional electrons were not solely derived from iron but were significantly supported by oxygen as well. Lomeli remarked, “It”s too simplistic to say that iron is the hero or oxygen is the hero. The atoms in this well-organized material function as a cohesive unit.”
The resurgence of iron in battery technology represents a pivotal shift. Historically regarded as too low-voltage for sophisticated energy storage, iron-based cathodes are now emerging as viable, sustainable alternatives to cobalt, which is costly and often sourced from hazardous environments. Mu highlighted that a high-voltage, iron-based cathode could eliminate the trade-off historically seen between voltage levels and expensive metals.
This concept traces back to 2018 when former Stanford PhD student William Gent theorized that iron could achieve higher oxidation states if neighboring atoms were strategically spaced. Although Gent did not complete the experiment, this new team successfully realized his vision. Early tests at Stanford”s SLAC-Stanford Battery Center indicated that the lithium-iron-antimony-oxygen compound retained its structural integrity, exhibiting slight bending rather than breaking during charge cycles.
Co-lead author William Chueh noted, “Scientists have rarely reported high-voltage iron-based materials. Our thorough investigation of this iron species provides definitive evidence of oxidation exceeding three electrons.” The comprehensive study detailing these findings was published in Nature Materials earlier this month.
