Skoltech researchers have developed a new method to improve the cathode, a key battery component. They proposed doping the cathode material with high-valent tantalum and discovered that adding 0.5 mole percent of tantalum oxide (Ta₂O₅) reduced the rate of battery capacity decay per cycle by nearly half. This research, published in the Nature-indexed journal Advanced Functional Materials and supported by the Russian Science Foundation, paves the way for creating more durable, safe, and powerful lithium-ion batteries for electric vehicles, electronic devices, and energy storage systems.
Modern lithium-ion batteries use layered nickel-rich oxide cathodes to store more energy. However, the higher the nickel content, the faster the battery degrades. Repeated charging and discharging causes cracks to slowly form in the material particles, leading to capacity loss.
One possible solution is to create a concentration gradient structure, in which the nickel content is highest at the center of the cathode particle. It then slowly diminishes toward the surface, while the concentration of manganese and cobalt stabilizers increases. A key initial difficulty has to do with creating this gradient.
“In gradient structures, it is very difficult to create an optimally thick and stable manganese- and cobalt-rich surface and achieve linear variation of transition metal content from the particle’s center toward its edges. To accomplish this, we developed a mathematical model that predicts how the concentration of nickel, manganese, and cobalt in the cathode agglomerate will change as key synthesis parameters vary. Our research differs from other studies in that our model accounts for the spherical shape and radius of the particles. We synthesized three different types of gradient structures using this model and validated the calculations with experimental data,” study co-author and Skoltech Materials Science PhD student Lyutsia Sitnikova commented.
Another challenge is maintaining the gradient during the final manufacturing stage, which involves doping the material with lithium at a high temperature. To address this issue, the team added tantalum oxide to the material.
“We found that this high-valence element doesn’t merely dope the crystal structure of the layered oxide; rather, tantalum segregates onto the surface of the primary crystallites and facilitates cationic disordering in the layered structure. Remarkably, the tantalum-rich regions do not form a separate phase at grain boundaries. Instead, they extend the crystal structure of the primary crystallites in an epitaxial manner, forming a tantalum-rich surface layer several nanometers thick,” the lead author of the study, Senior Research Scientist Alexandra Savina from Skoltech Energy, said.
Distinguished Professor Artem Abakumov of the Energy Center, who supervised this study, commented on the team’s key findings: “Quantum-chemical calculations using density functional theory confirmed that tantalum segregation is thermodynamically favorable and effective at suppressing nickel migration and grain boundary mobility. Tantalum effectively preserves both the gradient structure by blocking the interdiffusion of nickel, manganese, and cobalt, and the elongated shape of the primary crystallites by preventing the growth of the primary particles. This greatly enhances the material’s cycling stability and thermic stability. The findings we published are of both fundamental interest and practical import: They will underlie the pilot production of the first batches of the cathode material NMC90-GTa at Skoltech’s experimental production line with an annual output of up to 100 tons.”
