Stanford researchers have developed a high-voltage iron-based cathode material that could improve lithium-ion batteries for EVs. The breakthrough enables iron to reversibly exchange five electrons while maintaining structural stability, potentially offering better performance without expensive metals like cobalt and nickel.
A team of 23 scientists led by three Stanford PhD graduates has achieved a significant advancement in battery technology that could benefit EV manufacturers seeking alternatives to expensive and ethically problematic materials.
The research, published in Nature Materials, builds on a 2018 doctoral thesis by William Gent, who theorized that iron could be pushed to a higher energy state than previously thought possible. Hari Ramachandran, Edward Mu, and Eder Lomeli led the interdisciplinary effort spanning three US universities, four national laboratories, and institutions in Japan and South Korea.
The breakthrough centers on making iron atoms reversibly exchange five electrons during charging cycles, rather than the typical two or three. The key lies in keeping iron atoms separated within the crystal structure to prevent side reactions that would otherwise limit performance.
Today, 40 percent of lithium-ion batteries use cathodes made from lithium, iron, and phosphorus. This chemistry has become popular for EVs and grid storage because iron costs far less than cobalt and nickel. Additionally, 70 percent of global cobalt comes from the Democratic Republic of the Congo, where mining operations face criticism for child labor, hazardous conditions, deforestation, and environmental contamination.
However, current iron-based cathodes operate at lower voltages, forcing manufacturers to accept performance tradeoffs. “A high-voltage, iron-based cathode could avoid the tradeoff between higher voltage and higher-cost metals that previously dominated cathode materials,” Mu said. “The best of both worlds.”
The team synthesized their material from lithium, iron, antimony, and oxygen, creating particles just 300 to 400 nanometers in diameter. “Making the particles very small – just 300 to 400 nanometers, or billionths of a meter, in diameter, about 40 times smaller than before – turned out to be a challenge,” said Ramachandran.
The nanoparticles bend slightly when lithium ions move during charging, maintaining structural integrity unlike previous versions that collapsed. William Chueh, one of the faculty advisors, noted that the team is now addressing practical engineering challenges, including finding alternatives to antimony, which faces similar supply chain vulnerabilities as cobalt.
