Synthesis, Electronic Structure, and Electrochemical Properties of the Cubic Mg2MnO4 Spinel with Porous-Spongy Structure

Abstract

Mg2MnO4 nanoparticles with cubic spinel structure were synthesized by the sol-gel method using polyvinyl alcohol (PVA) as a chelating agent. X-ray powder diffraction, infrared spectrum (IR), scanning electron microscope (SEM), and transmission electron microscope (TEM) were used to characterize the crystalline phase and particle size of as-synthesized nanoparticles. The electronic structure of Mg2MnO4 spinel was studied by X-ray photoelectron spectroscopy (XPS). The results showed that pure cubic Mg2MnO4 spinel nanoparticles were obtained when the annealing temperature was 500–700 °C. The samples had a porous-spongy structure assembled by nanoparticles. XPS studies indicated that Mg2MnO4 nanoparticles were mixed spinel structures and the degree of cation inversion decreased with increasing annealing temperature. Furthermore, the performance of Mg2MnO4 as lithium anode material was studied. The results showed that Mg2MnO4 samples had good cycle stability except for the slight decay in the capacity at 50 cycles. The coulombic efficiency (ratio of discharge and charge capacity) in most cycles was near 100%. The sample annealed at 600 °C exhibited good electrochemical properties, the first discharge capacity was 771.5 mAh/g, and the capacity remained 340 mAh/g after 100 cycles. The effect of calcination temperature on the charge–discharge performance of the samples was studied and discussed.

Inverse Spinel-Structured Mg2MnO4 Coating to Enable Superior Thermal Stability of LiNi0.83Co0.12Mn0.05O2 Cathodes for Lithium-Ion Batteries

“…The XRD patterns of the pristine NCM cathode and MMO-coated Ni-rich cathode material with different coating amounts all show the same diffraction peaks, perfectly matched the diffraction peaks of LiNiO 2 (PDF # 74-0919), which is a typical layered structure with a hexagonal unit cell ( R 3̅ m ). , According to the apparent peak splitting of (006)/(012) and (018)/(110), the as-obtained NCM materials have a typical layered ordering structure. For comparison, pure MMO is also prepared, and its XRD pattern (Figure S4a) matches well with the target material (PDF # 19-0773). , However, no diffraction peaks of MMO are found in the XRD patterns for 0.5, 1.0, and 1.5% MMO-coated samples, which could be attributed to the tiny contents, since they could be clearly observed when the proportion increases up to 15 wt % (Figure S4b). According to Rietveld refinement (Figure a,b, S5 and Table S2), it is obvious that all samples prove the layered structure with a low cation mixing, among which NCM-1.0% MMO displays the least Li + /Ni 2+ mixing.…”

“…For comparison, pure MMO is also prepared, and its XRD pattern (Figure S4a) matches well with the target material (PDF # 19-0773). 22,25 However, no diffraction peaks of MMO are found in the XRD patterns for 0.5, 1.0, and 1.5% MMO-coated samples, which could be attributed to the tiny contents, since they could be clearly observed when the proportion increases up to 15 wt % (Figure S4b). According to Rietveld refinement (Figure 2a,b, S5 and Table S2), it is obvious that all samples prove the layered structure with a low cation mixing, among which NCM-1.0% MMO displays the least Li + /Ni 2+ mixing.…”

“…20 In this study, we demonstrate a simple and effective surface treatment via the wet coating method to form a phasec o m p a t i b l e M g 2 M n O 4 ( M M O ) l a y e r o n L i -Ni 0.83 Co 0.12 Mn 0.05 O 2 cathode material. 21,22 The resulting uniform MMO coating layer is anticipated to enhance the thermal stability of the cathode materials as well as alleviate the corrosion of the cathode materials by the electrolyte, improving the material's structural stability, especially at high temperatures. The stable MMO material alleviates the occurrence of intergranular cracks and inhibits side reactions and the disordered formation of the rock salt phase.…”