Unprecedented chemical transformation: crystallographic evidence for 1,1,2,2-tetrahydroxyethane captured within an Fe6Dy3 single molecule magnet

A nonanuclear {Fe6Dy3} coordination cluster displaying SMM behaviour in which an unprecedented chemical transformation provides structural information for the existence of 1,1,2,2-tetrahydroxyethane is reported

Enhancing the Stability of LiNio.5_{o.5}0Mn1.5_{1.5}O4_{4} by Coating with LiNbO3_{3} Solid-State Electrolyte: Novel Chemically Activated Coating Process versus Sol-Gel Method

LiNbO$_{3}$-coated LiNi$_{0.5}$Mn$_{1.5}$O$_{4}$ spinel was fabricated by two methods: using hydrogen-peroxide as activating agent and sol-gel method. The structure of the obtained cathode materials was investigated using a scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and the electrochemical properties of the prepared cathodes were probed by charge-discharge studies. The morphology of the coating material on the surface and the degree of coverage of the coated particles were investigated by SEM, which showed that the surface of LiNi$_{0.5}$Mn$_{1.5}$O$_{4}$ particles is uniformly encapsulated by lithium innovate coating. The influence of the LiNbO3 coating layer on the spinel’s properties was explored, including its effect on the crystal structure and electrochemical performance. XRD studies of the obtained coated active materials revealed very small expansion or contraction of the unit cell. From the capacity retention tests a significant improvement of the electrochemical properties resulted when a novel chemically activated coating process was used. Poorer results, however, were obtained using the sol-gel method. The results also revealed that the coated materials by the new method exhibit enhanced reversibility and stability compared to the pristine and reference ones. It was shown that the morphology of the coating material and possible improvement of communication between the substrates play an important role

On the Composition of LiNi0.5_{0.5}Mn1.5_{1.5}O4_4 Cathode Active Materials

LiNi$_{0.5}$Mn$_{1.5}$O$_4$ (LNMO) cathode active materials for lithium-ion batteries have been investigated for over 20 years. Despite all this effort, it has not been possible to transfer their favorable properties into applicable, stable battery cells. To make further progress, the research perspective on these spinel type materials needs to be updated and a number of persisting misconceptions on LNMO have to be overcome. Therefore, the current knowledge on LNMO is summarized and controversial points are addressed by detailed considerations on the composition and crystallography of LNMO. The findings are supported by an in-situ high temperature X-ray diffraction study and the investigation of four different types of LNMO materials, including Mn(III) rich ordered LNMO, and disordered LNMO with low Mn(III) content. It is shown that the importance of cation order is limited to a small composition range. Furthermore, new evidence contradicting the idea of oxygen defects in LNMO is presented and an enhanced classification of LNMO based on the Ni content of the spinel phase is proposed. Moreover, a balanced chemical equation for the formation of LNMO is presented, allowing for comprehensive calculations of key properties of LNMO materials. Finally, suitable target compositions and calcination programs are suggested to obtain better LNMO materials

Instantaneous Surface Li3_{3}PO4_{4} Coating and Al–Ti Doping and Their Effect on the Performance of LiNi0.5_{0.5}Mn1.5_{1.5}O4_{4} Cathode Materials

Using hydrogen peroxide (H2O2), a novel approach was applied for the synthesis of LiNi0.5Mn1.5O4 (LNMO) coated with Li3PO4 and doped with Al3+ and Ti4+ ions. The reaction between LNMO and H2O2 resulted in particles with a partially damaged surface. If the same reaction is done in the presence of lithium, aluminum, titanium, and phosphate ingredients, then all particle facets are intact and show no sign of destruction. It appears that the H2O2 decomposition activates the LNMO surface, generating perfect conditions for the homogeneous deposition of the Li, Al, Ti, and phosphate ions. Electrochemical investigations show a very slow fading process during the cycling, and even after more than 500 cycles, the obtained cathode material shows a high specific capacity of 127 mAh g–1 (at 1 C) (∼98% capacity retention) and an excellent Coulombic efficiency (99.5%)

Systematic studies of hexanuclear {MIII4LnIII2} complexes (M = Fe, Ga; Ln = Er, Ho): structures, magnetic properties and SMM behavior

Four isostructural MIII4LnIII2 coordination clusters, [M4Ln2(μ3-OH)2(nbdea)4(C6H5COO)8]•MeCN (M = Fe, Ln = Er (1); M = Ga, Ln = Er (2); M = Fe, Ln = Ho (3); M = Ga, Ln = Ho (4)) have been synthesized and characterized. Single-crystal X-ray diffraction and X-ray powder diffraction studies revealed that all four compounds crystallize isomorphously to each other, and to the previously reported MIII4DyIII2 (M = Fe or Ga) and FeIII4YIII2 analogues. DC magnetic susceptibility measurements for compounds 1-4, taken in combination with those for the FeIII4YIII2 analogue, indicated that the interactions between ErIII ions are weakly ferromagnetic and the FeIII-ErIII interactions are very weakly antiferromagnetic, while the HoIII-HoIII and FeIII-HoIII interactions are both negligible. By comparison, for the FeIII4DyIII2 analogue, the DyIII-DyIII interactions are antiferromagnetic while the FeIII-DyIII are ferromagnetic. Both Er analogues 1 and 2 display single-molecule magnet (SMM) behavior with the effective energy barrier Ueff increasing from 12.8 K (for Fe4Er2 1) to 53.5 K (for Ga4Er2 2), indicating that the very weak 3d-4f interaction enhances the QTM effect

Coating versus Doping: Understanding the Enhanced Performance of High‐Voltage Batteries by the Coating of Spinel LiNi0.5_{0.5}Mn1.5_{1.5}O4_4 with Li0.35_{0.35}La0.55_{0.55}TiO3_3

Li$_{0.35}$La$_{0.55}$TiO$_3$ (LLTO) coated spinel LiNi$_{0.5}$Mn$_{1.5}$O$_4$ (LNMO) as cathode material is fabricated by a new method using hydrogen-peroxide as activating agent. The structure of the obtained active materials is investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), and the electrochemical properties of the prepared cathodes are probed by the charge–discharge studies. The morphology of the coating material on the surface and the degree of coverage of the coated particles is investigated by the SEM, which shows a fully dense and homogeneous coating (thickness ≈ 7 nm, determined by TEM) on the surface of active material. XRD studies of the coated active materials treated at different temperatures (between 300 °C and 1000 °C) reveal expansion or contraction of the unit cell in dependence of the coating concentration and degree of Ti diffusion. It is concluded, that for the LNMO particles calcined at low temperatures, the LLTO coating layer is still intact and protects the active material from the interaction with the electrolyte. However, for the coated particles treated at high temperatures, Ti ions migrate into the structure of LNMO during the modification process between 500 °C and 800 °C, resulting in “naked” and unprotected particles

Magnetic anisotropy of a CoII single ion magnet with distorted trigonal prismatic coordination: theory and experiment

The single ion magnetic properties of Co(II) are affected by the details of the coordination geometry of the ion. Here we show that a geometry close to trigonal prismatic which arises when the ligand 6,6′-((1Z)-((piperazine-1,4-diylbis(propane-3,1-diyl))bis(azanylylidene))bis(methanylylidene))bis(2-methoxyphenol) coordinates to Co(II) does indeed lead to enhanced single-ion behaviour as has previously been predicted. Synthesis of the compound, structural information, and static as well as dynamic magnetic data are presented along with an analysis using quantum chemical ab initio calculations. Though the complex shows a slight deviation from an ideal trigonal prismatic coordination, the zero-field splitting as well as the g-tensor are strongly axial with D = −41 cm−1 and E < 0.01 cm−1. For the lowest Kramers doublet (S = 1/2) g∥ = 7.86 and g⊥ < 0.05 were found. In contrast, the second Kramers doublet possesses a rhombic g-tensor with g∥ = 2.75 and g⊥ = 4.35. Due to large spin–orbit coupling resulting in very different g tensors, it is not possible to simulate the temperature dependence of the magnetic susceptibility with a spin Hamiltonian of the form H = D(Sz2 − S(S + 1)/3) + E(Sx2 − Sy2) + μBgS·B using an effective spin S = 3/2. Calculations on model complexes show the influence of the coordinating atoms and the deviation from the ideal trigonal prismatic coordination. As the distortion is reduced towards idealised D3h, the zero field splitting increases and the g-tensor of the second Kramers doublet also becomes axial

Deciphering the Nature of an Overlooked Rate‐Limiting Interphase in High‐Voltage LiNi0.5_{0.5}Mn1.5_{1.5}O4_4 Cathodes: A Combined Electrochemical Impedance, Scanning Electron Microscopy and Secondary Ion Mass Spectrometry Study

High-voltage cathode active materials, such as LiNi$_{0.5}$Mn$_{1.5}$O$_4$ (LNMO), are of major interest for the development of high-energy lithium-ion batteries. However, it has been reported that composite cathodes based on high-voltage active materials suffer from high impedances and low rate capabilities. The origin of the high impedances has not yet been clarified. Here, we use a combination of electrochemical impedance spectroscopy (EIS), focused ion beam/scanning electron microscopy/energy-dispersive X-ray spectroscopy (FIB/SEM/EDX) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) for showing that in the case of LNMO-based cathodes, a major part of the cathode impedance is related to the formation of a passivating interphase on the Al current collector. Remarkably, the impedance of this interphase can be mitigated by the targeted formation of a distinct passivating interphase, namely on the surface of the LNMO particles. The interplay between these interphases is discussed

A single molecule magnet to single molecule magnet transformation via a solvothermal process: Fe₄Dy₂ →Fe₆Dy₃

Two series of heterometallic FeIII-LnIII compounds, [FeIII4LnIII2([small mu ]3-OH)2(mdea)4(m-NO2C6H4COO)8][middle dot]3MeCN where Ln = Y (1) and Dy (2) and [FeIII6LnIII3([small mu ]4-O)3([small mu ]3-O)(mdea)5(m-NO2C6H4COO)9][middle dot]3MeCN where Ln = Y (3) and Dy (4){,} were synthesized. Compounds 1 and 2 were obtained under ambient conditions{,} whereas 3 and 4 were obtained via a solvothermal transformation process by heating 1 or 2 at 120 [degree]C in MeCN. The magnetic properties of all four compounds have been measured and show that compounds 2 and 4 containing DyIII ions exhibit slow relaxation of magnetization characteristic of Single Molecule Magnetic (SMM) behaviour

Multiple superhyperfine fields in a {DyFe2Dy} coordination cluster revealed using bulk susceptibility and Fe-57 Mossbauer studies

A [DyFeIII2Dy(μ3-OH)2(pmide)2(p-Me-PhCO2)6] coordination cluster, where pmideH2 = N-(2-pyridylmethyl)iminodiethanol, has been synthesized and the magnetic properties studied. The dc magnetic measurements reveal dominant antiferromagnetic interactions between the metal centres. The ac measurements reveal zero-field quantum tunnelling of the magnetisation (QTM) which can be understood, but not adequately modelled, in terms of at least three relaxation processes when appropriate static (dc) fields are applied. To investigate this further, 57Fe Mössbauer spectroscopy was used and well-resolved nuclear hyperfine structures could be observed, showing that on the Mössbauer time scale, without applied field or else with very small applied fields, the iron nuclei experience three or more superhyperfine fields arising from the slow magnetisation reversal of the strongly polarized fields of the DyIII ions