Synergistic effects of fluorine and molybdenum co-doping on NMC811 cathodes synthesized via hybrid self-combustion and solid-state routes

Abstract

A combination of self-combustion synthesis and solid-state reaction methods has been employed to synthesize carbon, fluorine, and molybdenum-modified NMC811 (LiNi0.8Mn0.1Co0.1O₂). Characterization using field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) revealed that the synthesized samples have a size of approximately 100 nanometers. Diffractograms of X-ray diffraction (XRD) revealed a hexagonal system that belongs to the space group Rm. Depending on the modifying atom, there is a shift of the 2θ to a different angle due to the influence of metal oxide formation that affects the lattice parameters of the crystal, except for the one co-doped with molybdenum and fluorine. Electrochemical performance, as evaluated using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV), demonstrated that electrical conductivity improved from 1.08 × 10−5 S/cm for the as-synthesized NMC811 to 2.23 × 10−5 S/cm for the F-doped NMC811, 2.86 × 10−5 S/cm for the Mo-doped NMC811, and 4.67 × 10−5 S/cm for the molybdenum and fluorine dual-doped NMC811. Additionally, for lithium-ion diffusion, although there is an anomaly with single-doped NMC811, the diffusion coefficient increases from 3.19 × 10−14 cm2/s for the as-synthesized NMC811 to 1.86 × 10−13 cm2/s for the dual-doped NMC811. The most effective modification is achieved through the co-doping of molybdenum and fluorine, resulting in maximum conductivity of 4.67 × 10⁻⁵ S/cm and the smallest potential difference of 0.50 V.