Researchers at Pusan National University in South Korea have introduced a novel mathematical framework for lithium-ion batteries containing high-nickel cathodes that enables flexible full concentration gradient (FCG) or core-shell designs.
In a new study, an international research team led by Associate Professor Hyun Deog Yoo from the Department of Chemistry and the Institute for Future Earth at the university proposes an approach that allows precise and independent control of average composition, slope and curvature of full concentration gradients in high-nickel cathodes.
In FCG or core-shell structures, the nickel concentration gradually decreases from the core to the surface of each cathode particle, where it is replaced by more stable elements such as cobalt and manganese. This gradient enhances surface stability and mechanical strength.
Traditionally, FCG cathodes are synthesized via a coprecipitation method involving two tanks of metal precursor solutions. The first tank, rich in nickel, feeds directly into the reactor. The second tank, containing cobalt and manganese, is mixed into the first to reduce the nickel concentration over time. However, in conventional systems, the second tank’s fixed flow rate limits each setup to just one specific gradient per average consumption.
The researchers overcame this limitation by expressing the flow rate of the second tank as a time-dependent mathematical function. This allows independent tuning of the average composition, slope, and curvature—enabling the generation of a virtually unlimited range of concentration gradients using just two tanks. By integrating this approach with an automated reactor system, the team successfully synthesized five FCG Ni0.8Co0.1Mn0.1(OH)2 precursors with finely tuned gradients, verified through two- and three-dimensional elemental mapping.
The resulting high-nickel cathodes exhibited improved mechanical and structural stability compared to conventional counterparts. They showed enhanced lithium-ion transport for better electrochemical performance and minimal particle cracking for long cycle life. The FCG cathode retained 93.6% of its initial capacity after 300 cycles, the highest cycling stability reported for FCG cathodes of similar composition.
“Unlike conventional methods, where adjusting one parameter affects the others, our approach allows independent and precise control over multiple descriptors, including average composition, slope, and curvature,” explains Dr. Yoo. The team’s findings were published in the journal ACS Energy Letters. “Our approach has the potential to transform the safety and performance of LIB-based energy storage systems.”
Source: Pusan National University