Revealing the Impact of Dual Site Modification on the Phase Transformation and Ion Transport Mechanism of Ni-Rich...

Ni-rich cathode materials have garnered significant attention attributable to the high reversible capacity and superior rate performance, particularly in the electric vehicle industry. However, the structural degradation experienced during cycling results in rapid capacity decay and deterioration of the rate performance, thereby impeding the widespread application of Ni-rich cathodes. Herein, a Mg/Ti co-doping strategy was developed to boost the structure stability and Li-ion transport kinetics of the Ni-rich cathode material LiNi_0.90Co_0.05Mn_0.05O₂ (NCM9055) under long cycle. It is demonstrated that the Mg²⁺ ions inserted into the lithium layer could serve as pillars, enhancing the stability of the delithiated layer structure. The introduction of robust Ti-O bonding mitigated the detrimental H2-H3 phase transition (∼4.2 V) during cycling. In addition, despite the fact that Mg/Ti co-doping slightly reduces Li⁺ diffusion coefficient in the modified cathode material (NCM9055-MT), it effectively stabilized the robustness of the layered structure and maintained the Li⁺ diffusion channel while charging and discharging, thereby improving the Li⁺ diffusion coefficient after a long cycle. Therefore, the Mg/Ti co-doped cathode materials exhibited an exceptional capacity retention rate of 99.9% (100 cycles, 1 C). Additionally, the Li⁺ diffusion coefficient of the co-doped NCM9055-MT (2.924 × 10^-10 cm² s^-1) after 100 cycles was effectively enhanced compared with the case of undoped NCM9055 (4.806 × 10^-11 cm² s^-1). This work demonstrates that the Mg/Ti co-doping approach effectively enhanced the stability of layered Ni-rich cathode materials.