Enhanced Cycling Performance of Fe‐doped LiMn₂O₄ Truncated Octahedral Cathodes for Li‐Ion Batteries

Abstract

LiMn 2 O 4 (LMO) with a spinel crystal structure is a promising cathode for next-generation Li-ion batteries (LIBs), owing to its low cost and high operating voltage of ~4.4 V. However, due to the Jahn-Teller distortion effect, LMO typically exhibits deteriorated cycling performance, owing to the dissolution of Mn into a liquid electrolyte. In this study, Fe-doped truncated octahedral LMO cathodes with different concentrations were synthesized to improve LMO stability in LIBs. The Fe-doped truncated octahedral LMO was characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The Li + ion diffusion coefficients of the cathodes were measured using electrochemical impedance spectroscopy and the galvanostatic intermittent titration technique. Compared to the truncated octahedral undoped LMO, the Fe-doped LMO cathode with an appropriate amount of dopant exhibited the best LIB performance, with the highest Li + ion diffusivity resulting from the increased oxygen vacancy as the path of Li + ion.

The role of oxygen vacancies in the performance of LiMn2O4 spinel cathodes for lithium-ion batteries

“…Combining the calculated lattice parameters of the samples (shown in Table 1), the growth pattern of LMO in a high temperature environment is closely related to the concentration of VOs in the lattice, which may lead to increased lattice distortion in severe cases. [35][36][37] The deoxygenated sample recovered the particle morphology after the oxygenation treatment, but the LMO-4 sample had blunt particle edges due to the irreversible loss of lithium by hightemperature annealing. The lattice structure shrinks due to changes in the composition of the material phase and the degree of defects after oxidation treatment, so that the particle morphology and size change significantly.…”

Influence of the Crystal Plane Orientation in Enhancing the Electrochemical Performance of a Trication-Substituted Cathode for Li-Ion Batteries

“…The extent of the surface orientation of the LMNFA cathode materials is determined by calculating the intensity ratio of the planes (111) and (400) (Table ). From the table, it can be observed that the intensity ratio value of the (111)/(400) plane for LMNFA2 material is slightly more than that of LMNFA1 and LMNFA3, which is due to the dominance of the (111) plane in the crystal structure . In addition, it also shows the dominant facets of the (111) plane, which corresponds to the truncated type .…”

“…From the table, it can be observed that the intensity ratio value of the (111)/(400) plane for LMNFA2 material is slightly more than that of LMNFA1 and LMNFA3, which is due to the dominance of the (111) plane in the crystal structure. 24 In addition, it also shows the dominant facets of the (111) plane, which corresponds to the truncated type. 9 The Mn 3+ (0.64 Å) ions in LiMn 2 O 4 are substituted by Fe 3+ (0.65 Å) ions, which results in a low-angle shift according to Bragg's law.…”

“…Variations in the Fe concentration in all of the materials influence (111) plane dominance in the crystal surface, which could affect the growth of the truncated octahedral shape. 24 The {100} and {110} planes whose orientations are associated with Li diffusion channels are most susceptible to Mn dissolution, whereas the {111} facets, on which Mn atoms are utmost compactly packed, have the lowest surface energy and exhibit better stability. 25 The exposure of the dominant (111) plane forms the crystals with the lowest surface energy state than the (100) and (110) planes.…”

Scope and significance of transition metal oxide nanomaterials for next-generation Li-ion batteries

“…74 Several groups have worked on stabilizing this disproportionation redox issue by employing Ni in the structure alongside the minimal doping of other elements. 5,[75][76][77][78] The final material with the formula of Li x-Ni 0.5 Mn 1.5 O 4 (LNMO) improves the operating voltage up to B4.8 V, where some works reported up to B5 V in half-cell testing scenarios. 44,73,79 Single-crystal LNMO spinel materials by Liu et al have shown superior cycling performance, retaining up to B99% of capacity cycling at higher rates for 2000 cycles.…”