As electric vehicles and energy storage systems continue to expand, lithium-ion batteries are being pushed toward higher energy density, lower cost, and more sustainable material design. One major goal is to reduce or eliminate cobalt from cathode materials, because cobalt increases cost and raises supply-chain concerns. Co-free Ni-rich layered oxides, such as LiNi0.8Mn0.2O2, offer high capacity and a cobalt-free composition, but their performance often deteriorates when operated at high voltage.
A research team led by Chenyu Liu from Guangdong University of Technology and Jiaxiang Cui from the University of Kentucky has proposed a Fe/Zr codoping strategy to address this challenge. The study was published in Energy Materials and Devices.
Under high-voltage cycling, Co-free Ni-rich cathodes can suffer from excessive nickel oxidation, unstable lattice oxygen, irreversible H2→H3 phase transition, and surface reconstruction. These structural changes may lead to voltage decay, capacity fading, and particle degradation. The new strategy introduces iron and zirconium into the layered cathode to build a more stable oxygen–transition metal framework.
"The key point of this work is that Fe and Zr do not simply act as isolated dopants. They play complementary roles in stabilizing the cathode structure," said Chenyu Liu, corresponding author of the study. "Fe helps regulate the local transition-metal–oxygen electronic environment, while Zr provides a strong lattice-anchoring effect through Zr–O bonds."
The researchers synthesized pristine LiNi0.8Mn0.2O2 and Fe/Zr-codoped LiNi0.8Mn0.2O2 cathode materials, then evaluated their crystal structure, morphology, surface chemistry, magnetic interactions, lithium-ion diffusion behavior, and electrochemical performance. X-ray diffraction and electron microscopy confirmed that the codoped material maintained a well-defined layered structure. Elemental mapping showed that Ni, Mn, Fe, and Zr were uniformly distributed without obvious elemental segregation. The codoped cathode delivered a high reversible capacity of 207.06 mAh g-1 at 0.1 C and maintained 141.76 mAh g-1 even at 5 C, indicating strong rate capability. During long-term cycling at 1 C within 2.8-4.4 V, the Fe/Zr-codoped cathode retained 81.55% of its capacity after 200 cycles. It also showed a higher initial coulombic efficiency than the pristine material. Further electrochemical analysis revealed that Fe/Zr codoping reduced charge-transfer resistance and improved lithium-ion diffusion. Microscopy after cycling showed that the codoped cathode experienced much less surface reconstruction and lattice distortion than the pristine material. Ex situ X-ray diffraction also indicated good structural reversibility during charge and discharge.
According to the researchers, this improvement comes from a dual-reinforced mechanism. Fe stabilizes the local oxygen coordination environment through Fe–O interactions and helps tune charge compensation behavior. Meanwhile, Zr4+ strengthens the lattice through robust Zr–O bonding, suppressing oxygen loss and harmful phase transitions during deep delithiation.
"This study provides a practical compositional design strategy for Co-free Ni-rich cathodes," said Jiaxiang Cui, corresponding author of the study. "By stabilizing lattice oxygen and improving lithium-ion transport, Fe/Zr codoping offers a promising route toward high-performance, cobalt-free lithium-ion battery materials."
The authors suggest that this strategy could contribute to the further development of high-energy, lower-cost lithium-ion batteries. Future work may focus on optimizing dopant concentration, scaling up synthesis, and evaluating the material under more practical full-cell conditions.
Other contributors include Zexin Mo, Xiaoyan Xie, Zhiyuan Hua, and Zhan Lin from Guangdong University of Technology, Jilin University.
This work was supported by the National Natural Science Foundation of China(Grant No. 22408053).
DOI Link:
https://doi.org/10.26599/EMD.2026.9370094
