Fe Dopants Intensify the Electrochemical Performance of LiNi0.60Mn0.40O₂ Cathode Materials

Co-free Ni-rich layered oxide cathodes need urgent development due to the continuously increasing demand for high-performance lithium-ion batteries. Here, the cathode materials of LiNi0.60Mn0.40O2 (NM) and Fe-doped LiNi0.60Mn0.40–xFexO2 (NMFe, x = 0.01–0.05) were prepared via a coprecipitation method associated with a high shear mixer, and the corresponding electrochemical performance was assessed. The optimal Fe-doped sample (NMFe-3) exhibits a discharge capacity of 185.3 mAh·g–1 (0.1C), higher than that of NM (182.5 mAh·g–1) at 2.8–4.5 V and 25 °C. Characterization based on XRD, XPS, HRTEM, EIS, CV, and GITT tests illustrates the presence of LiFeO2 crystal planes inside the NMFe samples, the lower values of the electrode/electrolyte interface impedance of the Fe-doped samples, and the charge-transfer impedance of the electrodes, as well as higher Li+ diffusion rate during charge/discharge processes. In situ XRD tests confirm that NMFe-3 exhibits excellent reversible phase transition during the charge/discharge process. DFT calculations disclose that Fe dopants would make Li layer spacings enlarged and lower the energy barrier of Li+ diffusion. This work provides a facile route to synthesize Fe-substituted Co-free Ni-rich cathode materials with excellent electrochemical performance for lithium-ion batteries.