Carbon-coated Ni_0.5Mg_0.5Fe_1.7Mn_0.3O₄ nanoparticles as a novel anode material for high energy density lithium-ion...

Lithium-ion batteries (LIBs) have gained considerable attention from the scientific community due to their outstanding properties, such as high energy density, low self-discharge, and environmental sustainability. Among the prominent candidates for anode materials in next-generation LIBs are the spinel ferrites, represented by the MFe₂O₄ series, which offer exceptional theoretical capacities, excellent reversibility, cost-effectiveness, and eco-friendliness. In the scope of this study, Ni_0.5Mg_0.5Fe_1.7Mn_0.3O₄ nanoparticles were synthesized using a sol-gel synthesis method and subsequently coated with a carbon layer to further enhance their electrochemical performance. TEM images confirmed the presence of the carbon coating layer on the Ni_0.5Mg_0.5Fe_1.7Mn_0.3O₄/C composite. The analysis of the measured X-ray diffraction (XRD) and Raman spectroscopy results confirmed the formation of nanocrystalline Ni_0.5Mg_0.5Fe_1.7Mn_0.3O₄ before coating and amorphous carbon in the Ni_0.5Mg_0.5Fe_1.7Mn_0.3O₄/C after the coating. The Ni_0.5Mg_0.5Fe_1.7Mn_0.3O₄ anode material exhibited a much higher specific capacity than the traditional graphite material, with initial discharge/charge capacities of 1275 and 874 mA h g^-1, respectively, at a 100 mA g^-1 current density and a first coulombic efficiency of 68.54%. The long-term cycling test showed a slight capacity fading, retaining approximately 85% of its initial capacity after 75 cycles. Notably, the carbon-coating layer greatly enhanced the stability and slightly increased the capacity of the as-prepared Ni_0.5Mg_0.5Fe_1.7Mn_0.3O₄. The first discharge/charge capacities of Ni_0.5Mg_0.5Fe_1.7Mn_0.3O₄/C at 100 mA g^-1 current density reached 1032 and 723 mA h g^-1, respectively, and a first coulombic efficiency of 70.06%, with an increase of discharge/charge capacities to 826.6 and 806.2 mA h g^-1, respectively, after 75 cycles (with a capacity retention of 89.7%), and a high-rate capability of 372 mA h g^-1 at 2C. Additionally, a full cell was designed using a Ni_0.5Mg_0.5Fe_1.7Mn_0.3O₄/C anode and an NMC811 cathode. The output voltage was about 2.8 V, with a high initial specific capacity of 755 mA h g^-1 at 0.125C, a high rate-capability of 448 mA h g^-1 at 2C, and a high-capacity retention of 91% after 30 cycles at 2C. The carbon coating layer on Ni_0.5Mg_0.5Fe_1.7Mn_0.3O₄ nanoparticles played a crucial role in the excellent electrochemical performance, providing conducting, buffering, and protective effects.