A team of scientists from Stanford University has made a significant discovery in the field of battery technology by identifying a new high-energy state in iron. This groundbreaking research suggests that iron could play a crucial role in the development of powerful and cost-effective batteries, potentially eliminating the need for cobalt and nickel.
Iron, a widely abundant metal, has surprised researchers by demonstrating its ability to release and reabsorb a greater number of electrons than previously believed possible. This advancement could lead to batteries that not only offer enhanced performance but are also more affordable than current models that rely on cobalt or nickel.
The research was conducted by three Stanford PhD students—Hari Ramachandran, Edward Mu, and Eder Lomeli—alongside a collaborative team of 23 researchers from various U.S. universities, national laboratories, and international partners in Japan and South Korea. They successfully manipulated iron into a state previously thought unattainable by fine-tuning the structure of a compound composed of lithium, iron, antimony, and oxygen.
By arranging the material at the nanoscale, the team enabled iron atoms to repeatedly donate and accept five electrons, surpassing the conventional limits of two or three electrons. Initially, Ramachandran and Mu faced challenges as their early samples would collapse during the charging process. The solution came when they reduced the particle size to between 300 and 400 nanometers, significantly smaller than prior attempts.
After successfully growing their crystals from a meticulously mixed liquid solution, the team conducted electrochemical tests. These tests indicated that the material allowed iron to reversibly give up and retrieve five electrons while maintaining a stable crystal structure throughout the charging cycles.
To confirm their findings, Lomeli worked with his advisor, Tom Devereaux, an expert in modeling X-ray spectra. Their analysis revealed that the additional electrons were not solely from the iron atoms, but also involved oxygen. “It is overly simplistic to attribute the success solely to iron or oxygen,” Lomeli stated. “The atoms in this well-ordered material function as a cohesive unit.”
This research represents a pivotal moment in the evolution of battery technology, as iron has previously been dismissed due to its low voltage for advanced energy storage applications. However, iron-based cathodes are now emerging as sustainable alternatives to cobalt, which is often associated with high costs and hazardous mining practices.
“A high-voltage, iron-based cathode could eliminate the tradeoff between higher voltage and the use of expensive metals that have dominated cathode materials in the past,” Mu explained.
The concept of utilizing iron in this manner dates back to 2018, when former Stanford PhD student William Gent proposed that iron could achieve higher oxidation states with precise spacing of neighboring atoms. Although Gent was unable to complete the experiment, the current team successfully realized his vision.
Initial tests at the SLAC-Stanford Battery Center confirmed that the lithium-iron-antimony-oxygen compound remained structurally sound, flexing slightly instead of fracturing during charge cycles. Co-lead author William Chueh remarked, “Reports of high-voltage iron-based materials are rare. Our detailed exploration of the electronic structure of this iron species provides undeniable evidence of oxidation beyond three electrons.”
The full study detailing these findings was published earlier this month in Nature Materials.
