Spinel–rock salt transformation in LiCoMnO _{4− δ}

Abstract

The transformation on heating LiCoMnO4, with a spinel structure, to LiCoMnO3, with a cation-disordered rock salt structure, accompanied by loss of 25% of the oxygen, has been followed using a combination of diffraction, microscopy and spectroscopy techniques. The transformation does not proceed by a topotactic mechanism, even though the spinel and rock salt phases have a similar, cubic close-packed oxygen sublattice. Instead, the transformation passes through two stages involving, first, precipitation of Li2MnO3, leaving behind a Li-deficient, Co-rich non-stoichiometric spinel and, second, rehomogenization of the two-phase assemblage, accompanied by additional oxygen loss, to give the homogeneous rock salt final product; a combination of electron energy loss spectroscopy and X-ray absorption near edge structure analyses showed oxidation states of Co2+ and Mn3+ in LiCoMnO3. Subsolidus phase diagram determination of the Li2O-CoOx-MnOy system has established the compositional extent of spinel solid solutions at approximately 500°C.

Feasibility and Limitations of High-Voltage Lithium-Iron-Manganese Spinels

“…The possibility of Mn 3+ overstoichiometry because of oxygen vacancies (Li + Fe 3+ 0.5 Mn 3+ 0.5+2δ Mn 4+ 1-2δ O 4-δ ) was suggested already in the structural section above. The small shoulder at the high voltage side of the first Mn 4+/3+ redox peak for the LiFe 0.5 Mn 1.5 O 4 sample qualitatively matches with the expected level of oxygen defects (<2%) [54][55][56] and the expected induced Mn 3+ overstoichiometry. CV has been proven to be a sensitive method for recognizing the presence of Mn 3+ for different high voltage spinels [56][57][58] and is here again shown to be a helpful tool to gain insight into the crystal chemistry of the studied spinels.…”

Atomic layer deposition of nickel–cobalt spinel thin films

“…The 220, 311, 511 and 440 peaks of the spinel phase are clearly present showing that it is still the dominant phase at this high x value. The disappearance of the 111 peak is most likely due to the extreme sensitivity of the 111 diffraction to the exact ion distribution within a spinel 34 and a very low intensity of this diffraction peak is also observed for the x = 0.04 film. The relative height of the peak at 44.6 • is much larger than for the film with lower x indicating that some rock-salt phase might already be present.…”

Fast and Scalable Synthesis of LiNi0.5Mn1.5O4 Cathode by Sol–Gel‐Assisted Microwave Sintering

“…A fully reversible spinel to rock salt transformation is driven by a change in oxygen content. [55,56] However, these traces of the rock salt phase can be eliminated by annealing the sample at 700 C. [48,49] The d-spacing values for P-750 were calculated from the XRD data using Scherrer's equation, and the corresponding data are listed as Table S1, Supporting Information. The d-spacing calculated using XRD match well with high-resolution TEM (HR-TEM) shown in Figure 5.…”