EV battery capacity decay reduced by almost 50% while using improved cathode material

Researchers in Russia have improved the cathode material, which helped them improve battery lifespan.

Skoltech researchers 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.

The work paves the way for creating more durable, safe, and powerful lithium-ion batteries for electric vehicles, electronic devices, and energy storage systems.

Doping the material

The research team revealed that 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, according to a press release.

“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,” said co-author and Skoltech Materials Science PhD student Lyutsia Sitnikova.

“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.”

The research team also pointed out that 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.

Improved cathode 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,” said Senior Research Scientist Alexandra Savina from Skoltech Energy.

“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.”

Published in Advanced Functional Materials, the work presents a comprehensive investigation into the synthesis of Ni-rich layered oxide cathodes (LiNixMnyCozO2, x+y+z = 1, x = 0.9, NMC9) with concentration-gradient (CG) structures. A modified co-precipitation method is employed to systematically investigate key synthesis parameters, supported by a mathematical model predicting transition metal (TM) distribution within agglomerates.

The preservation of the CG structures during high-temperature lithiation is addressed through Ta2O5 modification, which effectively inhibited both the TM interdiffusion and particle coarsening. The combination of powder X-ray diffraction (PXRD) and advanced transmission electron microscopy (TEM) techniques revealed that the Ta-rich phase epitaxially extends the crystal structure of the primary particles, forming a thick (≈5 nm) Ta-rich surface layer, according to the study.