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_xCo_yMn_1−x−y]O₂, 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 Nb⁵⁺ and Al³⁺ is employed to deeply explore the modification mechanisms and synergistic effects. The results indicate that Nb⁵⁺ doping induces a contraction of the primary particles, which enhances the crystal structure density and facilitates Li⁺ diffusion; however, it also increases Li⁺/Ni²⁺ cation mixing, potentially leading to irreversible capacity loss during the initial cycles. In contrast, the introduction of Al³⁺ effectively mitigates the cation mixing aggravated by Nb⁵⁺, maintaining the Li⁺/Ni²⁺ 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 Nb⁵⁺ and Al³⁺ codoping not only stabilizes the layered structure but also enhances rate performance and cycle life.