Effect of Li(Li1/3Mn2/3O2) content on structural and electrochemical properties in xLi(Li1/3Mn2/3O2)-(1-x)LiNi0.975V0.025O2 cathode materials for lithium-ion batteries

This study investigated the structural and electrochemical properties of a series of manganese- and lithium-rich xLi(Li1/3Mn2/3O2)-(1-x)LiNi0.975V0.025O2 (where x = 0.0, 0.3, 0.4, 0.45, 0.55, and 0.65) cathode materials. These materials were synthesized using a two-step solid-state reaction. The crystalline structure and layered nature of the synthesized materials were confirmed through X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. Scanning electron microscopy (SEM) analysis revealed grain sizes in the range of 0.44 to 0.56 μm. The distribution of elements was examined using energy-dispersive X-ray spectroscopy (EDS) and high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) mapping. These analyses demonstrated a uniform distribution of Ni and V in the LiNi0.975V0.025O2 (LNV) sample, and a uniform distribution of Ni, Mn, and V in the xLi(Li1/3Mn2/3O2)-(1-x)LiNi0.975V0.025O2 (LMNV-x) samples. X-ray photoelectron spectroscopy (XPS) was employed to investigate the oxidation states of the constituent elements in all samples. An analysis of structural parameters revealed a clear dependence on the Li(Li1/3Mn2/3O2) content within the LMNV-x series. The incorporation of Li(Li1/3Mn2/3O2) improved the electrochemical performance of the LMNV materials. The LMNV-0.55 composition exhibited particularly outstanding electrochemical performance, delivering a discharge capacity of 198.8 mAh/g and retaining 90.4 % of its initial capacity after 50 cycles at a current rate of 0.1C within a voltage window of 2.8 to 4.8 V. Furthermore, LMNV-0.55 achieved the highest initial coulombic efficiency (92 %) and demonstrated superior cycling stability. Electrochemical impedance spectroscopy (EIS) corroborated these findings, identifying LMNV-0.55 as the best-performing cathode material among the synthesized samples. The electrochemical investigation demonstrated the potential of the xLi(Li1/3Mn2/3O2)-(1-x)LiNi0.975V0.025O2 materials as a promising approach for developing high-performance lithium-ion batteries.