Modification Mechanisms and Synergistic Effects of Nb/Al Codoping in High‐Nickel Cathode Materials for Lithium‐Ion Batteries

Advanced medical imaging systems require exceptional reliability and extended service life. While high‐nickel layered cathode materials (Li[Ni x Co y Mn 1− x − y ]O 2 , Ni ≥ 80%) offer high energy density, their structural instability threatens critical medical operations. This study addresses the challenges of electrochemical performance and structural stability in high‐nickel layered cathode materials. A codoping strategy using Nb 5+ and Al 3+ is employed to deeply explore the modification mechanisms and synergistic effects. The results indicate that Nb 5+ doping induces a contraction of the primary particles, which enhances the crystal structure density and facilitates Li + diffusion; however, it also increases Li + /Ni 2+ cation mixing, potentially leading to irreversible capacity loss during the initial cycles. In contrast, the introduction of Al 3+ effectively mitigates the cation mixing aggravated by Nb 5+ , maintaining the Li + /Ni 2+ disorder within an optimal range. This adjustment significantly reduces electrode polarization during long‐term cycling and prevents the formation of microcracks. Consequently, the codoped cathode half‐cells retain 95.93% of their capacity after 200 cycles, while delivering a discharge capacity of 160.1 mAh g −1 at a 5 C rate. Moreover, both high‐temperature and room‐temperature performances are markedly improved. The synergistic effect of Nb 5+ and Al 3+ codoping not only stabilizes the layered structure but also enhances rate performance and cycle life.