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Sodium‐ion‐batteries (SIB) are a low‐cost alternative to currently used lithium‐ion batteries (LIB) but suffer from poor cycling stability. Spray drying provides porous, hierarchically structured particles of cathode active material (CAM) in large amounts, suitable for up‐scaling. Changing the chemical composition of the Na0.6Al0.11 − xNi0.22 − yFex + yMn0.66O2 layered oxides under identical synthesis conditions lead to differences in particle morphology, conductivities, sodium vacancy ordering, and phase transition, therefore influencing the electrochemical performance via several mechanisms. Here, a broad overview on these changes for samples with variable nickel and iron content is presented. With increasing iron content, the particle porosity is reduced and lower initial capacity is received for most cycling windows. Substituting half of the original Ni amount with Fe still leads to high capacities and improved cycling stability. The influence of Al as electrochemically inactive element becomes visible in stabilized cycling stability as well. [ABSTRACT FROM AUTHOR]

High‐voltage cathode active materials, such as LiNi0.5Mn1.5O4 (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. [ABSTRACT FROM AUTHOR]

LiNi0.5Mn1.5O4 (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. [ABSTRACT FROM AUTHOR]

Li0.35La0.55TiO3 (LLTO) coated spinel LiNi0.5Mn1.5O4 (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. [ABSTRACT FROM AUTHOR]

In an assisted self‐assembly approach starting from the [Mn6O2(piv)10(4‐Me‐py)2(pivH)2] cluster a family of Mn−Ln compounds (Ln=Pr−Yb) was synthesised. The reaction of [Mn6O2(piv)10(4‐Me‐py)2(pivH)2] (1) with N‐methyldiethanolamine (mdeaH2) and Ln(NO3)3 ⋅ 6H2O in MeCN generally yields two main structure types: for Ln=Tb−Yb a previously reported Mn5Ln4 motif is obtained, whereas for Ln=Pr−Eu a series of Mn7Ln3 clusters is obtained. Within this series the GdIII analogue represents a special case because it shows both structural types as well as a third Mn2Ln2 inverse butterfly motif. Variation in reaction conditions allows access to different structure types across the whole series. This prompts further studies into the reaction mechanism of this cluster assisted self‐assembly approach. For the Mn7Ln3 analogues reported here variable‐temperature magnetic susceptibility measurements suggest that antiferromagnetic interactions between the spin carriers are dominant. Compounds incorporating Ln=NdIII(2), SmIII(3) and GdIII (5) display SMM behaviour. The slow relaxation of the magnetisation for these compounds was confirmed by ac measurements above 1.8 K. [ABSTRACT FROM AUTHOR]

The "butterfly" molecule [Fe3Y(μ3-O)2(CCl3COO)8(H2O)(THF)3] (in brief {Fe3YO2}) includes three Fe3+ ions which build a robust Fe3 cluster with a strong intracluster antiferromagnetic exchange and a total spin S = 5/2. It represents the starting magnetic system to study further interactions with magnetic rare earths when Y is replaced with lanthanides. We present heat capacity and equilibrium susceptibility measurements below 2 K, which show that each cluster has a sizeable magnetic anisotropy pointing to the existence of intercluster interactions. However, no phase transition to a long-range magnetically ordered phase is observed down to 20 mK. The intercluster interaction is analysed in the framework of the one-dimensional Blume–Capel model with an antiferromagnetic chain interaction constant J/kB = −40(2) mK between Fe3 cluster spins, and a uniaxial anisotropy with parameter D/kB = −0.56(3) K. This is associated to single chains of Fe3 clusters oriented along the shortest intercluster distances displayed by the crystal structure of {Fe3YO2}. Ac susceptibility measurements reveal that the magnetic relaxation is dominated by a quantum tunnelling process below 0.2 K, and by thermally activated processes above this temperature. The experimental activation energy of this single chain magnet, Ea/kB = 3.4(6) K, can be accounted for by the combination of contributions arising from single-molecule magnetic anisotropy and spin–spin correlations along the chains. [ABSTRACT FROM AUTHOR]