Synchrotron X-ray diffraction studies of LiMn2O4 and Li4Mn5O12 structures at high pressure (original) (raw)
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Journal of Physics and Chemistry of Solids, 2005
A series of LiMn 2 O 4 spinels, obtained by the sol-gel method maintaining constant Li:Mn ratio, were calcined at different temperatures (300-900 8C) to create crystal lattice defects. The structure and electronic properties of the samples were studied by complementary experimental techniques (XRD with Rietveld analysis, BET-N 2 , DSC, MS-TG/SDTA, electrical conductivity, laser Raman and IR spectroscopy with 2D correlation analysis). The oxygen-spinel equilibrium shifts caused by various calcination in the air and in oxygen free atmosphere modulate the type and concentration of the anionic or cationic defects. The relationship between the local symmetry of MnO 6 octahedrons, manifested in symmetric and asymmetric vibrations, seemed to determine the phase transition at around the room temperature. Removing of the degeneration of t 2g and e g orbitals, due to Jahn-Teller effect, evolves stabilization energy causing increase of activation energy of electron migration. Distortion of the local symmetry makes impossible the Jahn-Teller effect and in consequence stops the phase transition around room temperature. q
Structural transition in Mg-doped LiMn2O4: a comparison with other M-doped Li–Mn spinels
Solid State Communications, 2003
The charge distribution in the Mg-doped lithium manganese spinel Li 1.02 Mg x Mn 1.982x O 4 with 0.00 , x # 0.20 is discussed and compared to those pertinent to other M-doped samples (M ¼ Ni 2þ , Co 3þ , Cr 3þ , Al 3þ and Ga 3þ ). EPR spectra, low temperature X-ray diffraction and conductivity data are related to the cooperative Jahn -Teller (J -T) transition occurring at about 280 K in the undoped sample.
Lithium insertion into manganese spinels
Materials Research Bulletin, 1983
Lithium has been inserted chemically and electrochemically into Mn30 ~ and Li[Mn2]O 4 at room temperature. From X-ray diffraction, it is shown that the [Mn2]O 4 subarray of the A[B2]X 4 splnels remains unperturbed and that the electrons compensating for the Li+-ion charge reduce Mn 3+ to Mn 2+ in Mn304 and Mn 4+ to Mn 3+ in Li[Mn2]O ~.
Journal of Power Sources, 1997
Powders of lithium manganese oxide phases are synthesised and characterised for possible application in a Li-ion battery. A modified phase diagram on the basis of the manganese oxidation state and content is used to interpret the results. X-ray diffraction, flame atomic absorptton spectroscopy, and Jaeger and Vetter titration are performed in order to classify the syntbesised powders. The experiments reveal powders of Li~+ flVln2 ~O4 (0 < 6 < 0.2, i.e. 0 < Lt/Mn < 0.65 l, with a spinel structure. At higher Li/Mn ratios mixtures of Li~ _~Mn~ 804 and Li2MnO~ are formed. Splnels with small &values are favoured since they are more stable than the pure LiMn204, but they have still acceptable capacity. Also, aluminium-doped spinel materials with the composition Li~ + ~A1,Mnz a ,,04 (0 < n < 0.3, 6= 0.0645 ) are synthesised and characterised. However, no improvement in terms of capacity is found. © 1997 Elsevier Science S.A.
Coexistence of two phases having space groups of Fd3m and P4332 in the Mg-doped LiMn2O4 spinel is being reported for the first time in this article. Mg-doped LiMn2O4 powders have been synthesized by sol–gel method using citric acid as a chelating agent. X-ray powder diffraction (XRD) studies show that the crystal structure of LiMgxMn2−xO4 for x<0.25 is a single-phase cubic spinel, which has space group of Fd3m. The cubic spinel structures having space group of Fd3m and P4332 are found to coexist in the compound for x=0.25. The structure becomes single-phase cubic spinel with space group P4332 for x>0.25. Field emission scanning electron microscopy (FESEM) shows that particle size of various synthesized powders ranges from 100 to 350 nm. Particle size decreases with increase in Mg content. Differential thermal analysis (DTA) and thermogravimetry (TG) studies show an exponential decay relationship between Mg-doping content and the decomposition temperature to form nonstoichiomet...
Evidence of a Cationic Substitution Domain in Lithium-Manganese Spinels
Zeitschrift für Naturforschung A, 1998
Magnetic susceptibility measurements and electron paramagnetic resonance spectra of samples prepared from the reactive system MnO/Li2CO3 with different starting Li cationic fraction x are analyzed, taking into account the structural and compositional information provided by x-ray diffraction. Parent phases, as Mn2O3 , Mn3O4 and Li2 MnO3 , arise together with the lithium-manganese spinel as a result of Li-deficiency or Li-excess with respect to the x = 0.33 composition pertinent to the stoichiometric LiMn2O4 spinel. The data show that the spinel phase can sustain a partial Li-Mn substitution in the cation sites, according to compositional models described, for x > 0.33, by Li1+y Mn3+1-3y Mn4+1+2y O4 (Li-rich spinel) and, for x< 0.33, by Li1-|y| Mn2+|y| Mn3+1+|y| Mn4+1-|y| O4 (Li-poor spinel). Paramagnetic resonance data of the Li-poor spinel phase are analyzed to discuss the possible oxidation state of Mn in the tetrahedral site.
Charge ordering at low temperature in lithium manganese oxide spinel
Journal of Physics: Conference Series, 2020
Spinels lithium manganese oxide LiMn2O4-δ synthesized from mixtures of different raw materials were used to study the relationship between the synthesis method and properties of the spinel. The investigation was emphasized on phase transition in lithium manganese oxide spinel compound at low temperature studied by means of neutron powder diffraction. It is found that the cubic structure of LiMn2O4-δ, synthesized from Li2CO3, with space group Fd-3m at room temperature was distorted to orthorhombic symmetry with space group Fddd at 290K and become more obvious down to 10K, where the splitting indicates the structural transition close to tetragonal. The equal proportion of coexisted Mn 3+ (Jahn-Teller) and Mn 4+ ions is associated with partial charge ordering. It is also found that the sample synthesized from LiOH.H2O and MnOx does not show phase transition at low temperatures. The extent of orthorhombic distortion is related to oxygen vacancy, , which is affected by the synthesis method such as the choice of starting materials, mixing method and annealing temperature.
Journal of Power Sources, 1997
The effects of both the initial Li:Mn ratio and the Mn valency on the electrochemical and the magnetic properties and on the structural changes were investigated using stoichiometric and nonstoichiometric LiMnzO4 samples prepared by a solid-state reaction between 673 and 1173 K. A small but known additional plateau near 3.0-3.2 V was observed on discharging the Li/LiMn204 cell using samples wath an Mn valency < 3.60 +. However, no plateau at ~ 3.2 V was observed for the cell using samples with an Mn valency of 3.61 +. Below 280 K the structure of the former samples changed from a cubic spinel structure into two phases with a cubic and a tetragonal structure, whereas the structure of the latter, i.e. an Mn 4 ÷-rich sample, remained cubic down to 20 K. Therefore, the additional plateau could be correlated with the instability of the cubic spinel structure of the sample.
Synthesis and Properties of Lithium Manganese Spinels
2001
Li 1x Mn 2y Co y O 4 (x = 0-0.06, y = 0-0.15) spinels were prepared by solid-state reactions and solgel processing and were characterized by x-ray diffraction and scanning electron microscopy. The spinels offer satisfactory electrochemical performance and are potentially attractive as cathode materials for rechargeable lithium batteries.
Molecular dynamics simulations of spinels: LiMn2O4 and Li4Mn5O12 at high temperatures
IOP Conference Series: Materials Science and Engineering, 2015
Energy storage technologies are critical in addressing the global challenge of clean sustainable energy. Spinel lithium manganates have attracted attention due to their electrochemical properties and also as promising cathode materials for lithium-ion batteries. The current study focused on the effects of high temperatures on the materials, in order to understand the sustainability in cases where the battery heats up to high temperature and analysis of lithium diffusion aids in terms of intercalation host compatibility. It is also essential to understand the high temperature behaviour and lithium ion host capability of these materials in order to perform the armorphization and recrystalization of spinel nano-architectures. Molecular dynamics simulations carried out to predict high temperature behaviour of the spinel systems. The NVE ensemble was employed, in the range 300-3000K. The melting temperature, lithium-ion diffusion and structural behaviour were monitored in both supercell systems. LiMn 2 O 4 indicated a diffusion rate that increased rapidly above 1500K, just before melting (~1700K) and reached its maximum diffusion at 2.756 10-7 cm 2 s-1 before it decreased. Li 4 Mn 5 O 12 indicated an exponential increase above 700K reaching 8.303 10-7 cm 2 s-1 at 2000K and allowing lithium intercalation even above its melting point of around 1300K. This indicated better structural stability of Li 4 Mn 5 O 12 and capability to host lithium ions at very high temperatures (up to 3000 K) compared to LiMn 2 O 4 .