Search

Lithium-excess disordered rock-salt oxides have opened up a new vista in search of high-capacity cathodes, resulting in a variety of new materials with versatile elemental compositions. This work i...

Elemental substitution in lithium nickel oxide (LiNiO2, LNO) is among the most common strategies employed in search of a commercially viable cathode active material (CAM) with the highest possible energy density at reasonable cost (as offered by Ni-rich CAMs). Here, we revisit Ga substitution of Ni in LNO, for which there is a lack of systematic studies, despite promising electrochemical performances reported in the literature. We demonstrate successful synthesis by wet-mixing, pre-annealing and solid-state reaction of the precursors, as shown by electron microscopy and synchrotron-based X-ray diffraction (XRD). The site occupation of Ga ions in the Li interlayer is suggested (corresponding to Li1−yGayNiO2). Electrochemical testing of the as-prepared CAMs reveals a modified voltage-composition curve upon Li (de)intercalation and improved capacity retention, with the largest specific capacity after 110 cycles obtained for 2.2 mol% Ga content. Operando XRD shows significant differences between structural details of the H2–H3 transition during charge and discharge as well as reduced volume contraction. Although the stabilizing effect of Ga on the LNO structure is clearly evident in our study, degradation upon electrochemical cycling still occurs as shown by the formation of surface rock salt-type layers and stacking faults.

Despite the tremendous theoretical capacities of new materials for lithium-ion battery (LIB) anodes (e.g. Si, Sn, etc.), the conventional design of these electrodes with binders, current collectors, and conductivity enhancers inhibit the translation of performance gains during commercialization. Therefore, consideration should be given to monolithic materials systems which can increase performance while simultaneously reducing design complexity. In the present study, aluminum–silicon thin-films were synthesized with compositions ranging from 0 to 45 at% Si, and the structure, morphology, and electrochemical behavior of the material as an electrode for LIBs were investigated. This analysis confirms that the Li9AlSi3 phase is formed during initial lithiation, prior to the formation of the β phase, and is recognized as the dominant phase in the Al–Si–Li alloy system. These findings also show that by preventing the formation of the β phase during lithiation of the electrode results in an excellent cycling life performance of 70 at% Al–30 at% Si electrode over 100 cycles at the rate of C/20 and a specific capacity of 650 mA h g−1. In situ stress measurements and ex situ SEM analysis performed during cycling confirm the reversibility such that no degradation or delamination is observed in the films despite the high capacity and long-term cycling.

Printed thermoelectrics (TE) could significantly reduce the production cost of energy harvesting devices by large-scale manufacturing. However, developing a high performance printable TE material is a substantial challenge. In this work, a new one-pot synthesis and processing of high performance Ag$_{2}$Se based n-type printed TE materials is reported. Structural analyses reveal that orthorhombic β-Ag$_{2}$Se is the dominant phase in the n-type printed material compounds. For a printed material at room temperature, a breakthrough power-factor of ∼17 μW cm$^{-1}$ K$^{-2}$ with a record high figure-of-merit ZT ∼ 1.03 is achieved. A high average ZT, an important parameter for device applications, of ∼0.85–0.60 has been realized in the temperature range of 300 K to 400 K. Using this material for n-type legs in combination with commercially available PEDOT:PSS for p-type legs, a printed TE generator (print-TEG) of two thermocouples has been fabricated. An output voltage of 17.6 mV and a high maximum power output P$_{max}$ of 0.19 μW are achieved using the print-TEG at ΔT = 75 K.

Laboratory X-ray diffractometers are among the most widespread instruments in research laboratories around the world and are commercially available in different configurations and setups from various manufacturers. Advances in detector technology and X-ray sources push the data quality of in-house diffractometers and enable the collection of time-resolved scattering data during

While maintaining a uniform morphology, the crystal chemistry of a Fe–Ti doped LNMO-material (LNMFTO) is varied systematically. Promising electrochemical properties are found and some long established assumptions about LNMO materials are challenged.

Laboratory X-ray diffractometers are among the most widespread instruments in research laboratories around the world and are commercially available in different configurations and setups from various manufacturers. Advances in detector technology and X-ray sources push the data quality of in-house diffractometers and enable the collection of time-resolved scattering data during operando experiments. Here, the design and installation of a custom-built multipurpose laboratory diffractometer for the crystallographic characterization of battery materials are reported. The instrument is based on a Huber six-circle diffractometer equipped with a molybdenum microfocus rotating anode with 2D collimated parallel-beam X-ray optics and an optional two-bounce crystal monochromator. Scattered X-rays are detected with a hybrid single-photon-counting area detector (PILATUS 300K-W). An overview of the different diffraction setups together with the main features of the beam characteristics is given. Example case studies illustrate the flexibility of the research instrument for time-resolved operando powder X-ray diffraction experiments as well as the possibility to collect higher-resolution data suitable for diffraction line-profile analysis.

Materials with strong magneto-structural coupling have complex energy landscapes featuring multiple local ground states, thus making it possible to switch among distinct magnetic-electronic properties. However, these energy minima are rarely accessible by a mere application of an external stimuli to the system in equilibrium state. Here, we report that a ferromagnetic ground state, with Tc above room temperature, can be created in an initially paramagnetic alloy by non-equilibrium nano-structuring. By dealloying process we transformed bulk chemically-disordered FeRh alloys into a nanoporous structure with a topology of a few nanometer-sized ligaments and nodes. Magnetometry and Mossbauer spectroscopy revealed the co-existence of two magnetic ground states - a conventional low-temperature spin glass and a hitherto-unknown robust ferromagnetic phase. The emergence of the ferromagnetic phase is validated by the density functional theory calculations showing that local tetragonal distortion induced by surface stress favors ferromagnetic ordering. Our study provides a means for reaching conventionally inaccessible magnetic states, resulting in a complete on/off ferromagnetic-paramagnetic switching over a broad temperature range. This article is protected by copyright. All rights reserved.

It has been a substantial challenge to develop a printed thermoelectric (TE) material with a figure-of-merit

Materials with strong magnetostructural coupling have complex energy landscapes featuring multiple local ground states, thus making it possible to switch among distinct magnetic-electronic properties. However, these energy minima are rarely accessible by a mere application of an external stimuli to the system in equilibrium state. A ferromagnetic ground state, with T

Lithium ion batteries (LIBs) are currently a major subject of applied electrochemical research as there is a fast growing demand of electrochemical energy storage, driven by the transformation of the automotive sector and the expansion of renewable energies. One of the key strategies to improve LIBs is the optimization of the cathode active materials (CAMs). Therefore, in order to find structure property relations, both crystallographic and electrochemical properties need to be investigated and well understood. However, standard laboratory powder X-ray diffraction (PXRD) possibly comes to its limit when minor structural variations such as atomic defects, cation order, or minor impurity phases are addressed. In order to focus on such minor structural changes and to find decisive differences in crystalline properties of battery materials, a multi-sample capillary setup for a multipurpose in-house PXRD setup was developed. The latter is made up from a six-circle diffractometer, a microfocus molybdenum rotating anode, and a 2D area detector. The capillary spinner itself is made from commercial components and simple custom-made adapters. A goniometer head is installed on a rotary module and sample spinning is enabled by a 12 V gear motor. Mounted on a xyz-stage of the diffractometer, the position of the rotating capillary exposed to the primary beam can be varied while remaining perfectly aligned in the center of the diffractometer. Hence, by packing up to 10 different powder samples separated from each other into a single glass capillary, subsequent measurements of all samples can be carried out without remounting or readjustment. Within a series of samples, the setup is extremely reliable, precise, and accurate, while errors originating from sample displacement, misalignment, or calibration are minimized.

Li-rich disordered rock-salt oxides such as Li1.2Ni1/3Ti1/3Mo2/15O2 are receiving increasing attention as high-capacity cathodes due to their potential as high-energy materials with variable elemen...

Pinning-type magnets with high coercivity at high temperatures are at the core of thriving clean-energy technologies. Among these, Sm2 Co17 -based magnets are excellent candidates owing to their high-temperature stability. However, despite intensive efforts to optimize the intragranular microstructure, the coercivity currently only reaches 20-30% of the theoretical limits. Here, the roles of the grain-interior nanostructure and the grain boundaries in controlling coercivity are disentangled by an emerging magnetoelectric approach. Through hydrogen charging/discharging by applying voltages of only ≈1 V, the coercivity is reversibly tuned by an unprecedented value of ≈1.3 T. In situ magneto-structural characterization and atomic-scale tracking of hydrogen atoms reveal that the segregation of hydrogen atoms at the grain boundaries, rather than the change of the crystal structure, dominates the reversible and substantial change of coercivity. Hydrogen reduces the local magnetocrystalline anisotropy and facilitates the magnetization reversal starting from the grain boundaries. This study opens a way to achieve the giant magnetoelectric effect in permanent magnets by engineering grain boundaries with hydrogen atoms. Furthermore, it reveals the so far neglected critical role of grain boundaries in the conventional magnetization-switching paradigm of pinning-type magnets, suggesting a critical reconsideration of engineering strategies to overcome the coercivity limits.

Nanoporous metals produced by dealloying have aroused enormous interest due to exotic mechanical and physico-chemical properties that are usually inaccessible in their bulk form. Interestingly, when binary solid-solution alloys, such as Ag–Au alloys, are dealloyed, the resulting nanoporous metals usually inherit the crystal structure of their parent alloys. In this Letter, we examined the evolution of the crystal structure during the dealloying of Fe–Rh alloys that show single-phase solubility over a large range of compositions. In situ x-ray diffraction shows that the crystallographic structure of the Fe85Rh15 alloy transforms from the original bcc to fcc structure during the dealloying. Transmission electron microscopy confirms the fcc structure of the nanoporous sample, which exhibits a typical bi-continuous porous structure with ligament sizes of only 2–3 nm and a high Fe concentration. The bcc–fcc transformation is driven by the chemical disordering of Fe and Rh atoms, induced by the highly dynamic dissolution and diffusion process at the alloy/electrolyte interface. Our study highlights the massive diffusion and the consequent disordered arrangement of elemental components during the evolution of the nanoporous structure.

ACS applied energy materials 3(12), 12565 - 12574 (2020). doi:10.1021/acsaem.0c02494, Commercially used LiNi$_{1/3}$Mn$_{1/3}$Co$_{1/3}$O$_2$ (NMC111) in lithium-ion batteries mainly consists of a large-grained nonporous active material powder prepared by coprecipitation. However, nanomaterials are known to have extreme influence on gravimetric energy density and rate performance but are not used at the industrial scale because of their reactivity, low tap density, and diminished volumetric energy density. To overcome these problems, the build-up of hierarchically structured active materials and electrodes consisting of microsized secondary particles with a primary particle scale in the nanometer range is preferable. In this paper, the preparation and detailed characterization of porous hierarchically structured active materials with two different median secondary particle sizes, namely, 9 and 37 μm, and primary particle sizes in the range 300–1200 nm are presented. Electrochemical investigations by means of rate performance tests show that hierarchically structured electrodes provide higher specific capacities than conventional NMC111, and the cell performance can be tuned by adjustment of processing parameters. In particular, electrodes of coarse granules sintered at 850 °C demonstrate more favorable transport parameters because of electrode build-up, that is, the morphology of the system of active material particles in the electrode, and demonstrate superior discharge capacity. Moreover, electrodes of fine granules show an optimal electrochemical performance using NMC powders sintered at 900 °C. For a better understanding of these results, that is, of process-structure–property relationships at both granule and electrode levels, 3D imaging is performed with a subsequent statistical image analysis. Doing so, geometrical microstructure characteristics such as constrictivity quantifying the strength of bottleneck effects and descriptors for the lengths of shortest transportation paths are computed, such as the mean number of particles, which have to be passed, when going from a particle through the active material to the aluminum foil. The latter one is at lowest for coarse-grained electrodes and seems to be a crucial quantity., Published by ACS Publications, Washington, DC

Flexibility in a printed thermoelectric (TE) material is vital for low-cost manufacturing of shape-conformable TE devices. In this work, a one-pot facile method was adapted to prepare a Cu-Se-based printable ink. The ink was printed on flexible substrates followed by sintering to let β-Cu2-δSe phase be formed. The film is found to be exceptionally flexible with a change in film resistance μ W with an open-circuit voltage VOC of 12 mV is demonstrated using a TE-generator (Flex-TEG) with two thermocouples made of the prepared material.

A novel heterostructured multilayer thin-film solid electrolyte consisting of LiON-AlOx was synthesized by atomic layer deposition (ALD). The ALD-derived films were grown about 200 °C on SiO2/Si substrate by an alternating deposition of lithium oxynitride (LiON) and AlOx sublayers with 1–6 nm thickness and then characterized by various methods for roughness, homogeneity, crystallinity, thickness, composition, chemical environment, and ionic conductivity. The desired layer-by-layer structure of the films was confirmed by both high-resolution transmission electron microscopy and time-of-flight secondary ion mass spectrometry. Compared to pure LiON films without insulating AlOx interlayers, the ionic conductivities of multilayer LiON-AlOx films with various nanoscale sublayers are enhanced due to channeling effects between the heterointerfaces of nanoscale sublayers, while the activation energies are increased due to the incorporation of non-conducting AlOx sublayers. Thickness-dependent conductivity of the multilayer LiON-AlOx films indicates that 3.2 nm of LiON sublayer alternatively combined with 1 nm AlOx sublayer has the best conduction performance. The film with 15 bilayers exhibits a conductivity of 6.2 × 10−4 S/cm at 160 °C with an activation energy of 0.57 eV.

Two major strategies are currently pursued to improve the energy density of lithium-ion batteries using LiNixCoyMnzO2 (NCM) cathode materials. One is to increase the fraction of redox active Ni (≥80%), which allows larger amounts of Li to be extracted at a given cutoff voltage (Umax). The other is to increase Umax, in particular for medium-Ni content NCM materials. However, the accompanying lattice changes ultimately lead to capacity fading in both cases. Here the structural changes occurring in Li1.02NixCoyMnzO2 (with x = 1/3, 0.5, 0.6, 0.7, 0.8 and 0.85) during cycling operation in the voltage range between 3.0 and 4.6 V vs Li are quantified by means of operando X-ray diffraction combined with detailed Rietveld analysis. All samples show a large decrease in unit cell volume upon charging, ranging from 2.4% for NCM111 (33% Ni) to 8.0% for NCM851005 (85% Ni). To make a fair comparison of the structural stability of the different NCM materials, energy densities as a function of Umax are estimated and corre...

Cathode materials with improved safety and energy densities are required for developing next-generation Li-ion battery technology. Among different phosphate-based materials, layered Li9V3(P2O7)3(PO4)2 (LVPP) has recently been explored as a high-voltage cathode. We report the feasibility of multi-electron reactions and the influence of crystallite size on the electrode kinetics. The mechanism of Li extraction/insertion during charge and discharge is investigated and the structural transformations at high voltages are studied by means of in situ and ex situ analysis. The changes induced by electrochemical Li extraction are found to be reversible during cycling in the potential window of 2–4.6 V, whilst voltage profile changes and capacity fading is observed by charging up to 4.8 V, owing to irreversible phase transition and reduction of the interlayer distance. The findings can be applied for optimizing material synthesis as well as the working conditions in Li-ion battery applications.

A new zero-strain LiCaFeF6 cathode material for reversible insertion and extraction of lithium ions is presented. LiCaFeF6 is synthesized by a solid-state reaction and processed to a conductive electrode composite via high-energy ball-milling. In the first cycle, a discharge capacity of 112 mAh g−1 is achieved in the voltage range from 2.0 V to 4.5 V. The electrochemically active redox couple is Fe3+/Fe2+ as confirmed by Mossbauer spectroscopy and X-ray absorption spectroscopy. The compound has a trigonal colquiriite-type crystal structure (space group P 3 ¯ 1 c ). By means of in situ and ex situ XRD as well as X-ray absorption fine structure spectroscopy a reversible response to Li uptake/release is found. For an uptake of 0.8 mol Li per formula unit only minimal changes occur in the lattice parameters causing a total change in unit cell volume of less than 0.5%. The spatial distribution of cations in the crystal structure as well as the linkage between their corresponding fluorine octahedra is responsible for this very small structural response. With its zero-strain behaviour this material is expected to exhibit only negligible mechanical degradation. It may be used as a cathode material in future lithium-ion batteries with strongly improved safety and cycle life.

In the near future, the targets for lithium-ion batteries concerning specific energy and cost can advantageously be met by introducing layered LiNixCoyMnzO2 (NCM) cathode materials with a high Ni content (x ≥ 0.6). Increasing the Ni content allows for the utilization of more lithium at a given cell voltage, thereby improving the specific capacity but at the expense of cycle life. Here, the capacity-fading mechanisms of both typical low-Ni NCM (x = 0.33, NCM111) and high-Ni NCM (x = 0.8, NCM811) cathodes are investigated and compared from crystallographic and microstructural viewpoints. In situ X-ray diffraction reveals that the unit cells undergo different volumetric changes of around 1.2 and 5.1% for NCM111 and NCM811, respectively, when cycled between 3.0 and 4.3 V vs Li/Li+. Volume changes for NCM811 are largest for x(Li) < 0.5 because of the severe decrease in interlayer lattice parameter c from 14.467(1) to 14.030(1) A. In agreement, in situ light microscopy reveals that delithiation leads to differe...

The high voltage LiNi0.5Mn1.5O4 spinel suffers from severe capacity fade when cycled against a graphitic anode as well as a relatively low theoretical capacity. Using metallic lithium as counter electrode, the stability is improved and the ability of the spinel structure to host 2 Li eq. can be used to improve the capacity. This leads to a theoretical specific energy of ∼1000 Wh kg−1. Unfortunately, the cycling of 2 Li eq. involves a phase transition from cubic to tetragonal associated with material degradation. In this work doping is used to improve capacity retention when cycling between 2.0 and 5.0 V. Initial capacities and stabilities are directly dependent on synthesis conditions and doping elements. Therefore, Fe- and Ti-doped spinels are compared with Ru- and Ti-doped spinels and tested at different cycling conditions. The cycling stability can be improved significantly by using reannealed material and by changing the discharge cutoff criteria. Thus a capacity of 190 mAh g−1 is achieved at a rate of C/2 with a capacity retention of ∼92% after 100 cycles. Furthermore, differences in the discharge behavior between the differently treated Ru- and Ti- doped materials are discussed based on the electrochemical behavior, the particle morphology and in-situ XRD analysis.

Disordered rock-salt compounds are becoming increasingly important due to their potential as high-capacity positive electrode materials for lithium-ion batteries. Thereby, a significant number of studies have focused on increasing the accessible Li capacity, but studies to manipulate the electrochemical potential are limited. This work explores the effect of transition-metal substitution on the electrochemistry of ternary disordered rock-salt-type compounds with LiM2+0.5V0.54+O2 stoichiometry (M = Mn, Fe, Co) directly synthesized through mechanochemistry. Rietveld refinements of synchrotron X-ray diffraction patterns confirm the disordered rock-salt structures. First-principles density functional theory study is used to predict the impact of the cation substitution on the expected average voltage and the electronic structures of these materials are used to analyze the underlying redox processes. For LiM2+0.5V4+0.5O2 (M = Mn, Fe, Co), discharge voltages increase in the order of Mn < Fe < Co with 2.28, 2.41, and 2.51 V, exhibiting discharge capacities of 219, 207, and 234 mAh g-1, respectively. In comparison, for the disordered rock-salt Li2VO3, an average discharge voltage of ∼2.2 V with V5+/4+ redox couple has been reported. However, detrimental electrode-electrolyte interactions manifested as transition-metal dissolution has been found to result in severe capacity fading. Thereto, the use of a concentrated 5.5 M LiFSI increased the cycling stability significantly, effectively reducing transition-metal dissolution. The underlying reasons for the capacity fading of disordered rock salts are yet unclear. We stress the importance of cathode-electrolyte interactions, thus opening new directions for the improvement of cation-disordered materials.

Doping of cathode materials can considerably improve electrochemical performance and stability. Here, the high-voltage LiNi0.5Mn1.5O4 spinel is used as a candidate material. It is high-voltage cycling at a potential of approximately 4.7 V and the ability to host 2 eq. Li, thus leading to a theoretical capacity of 294 mAh g−1, that makes this material interesting. In order to improve stability and electronic conductivity, the spinel is doped with titanium and iron. Cycling in a voltage range of 2.0–5.0 V leads to a cooperative Jahn-Teller distortion accompanied by a phase transformation from cubic to tetragonal symmetry. This causes a severe capacity fade. To improve capacity retention, the as-prepared spinel is post-doped with fluorine. Influence of different fluorine amounts in LiNi0.5Mn1.4Fe0.1Ti0.027O4−xFx (x = 0–0.3) on the capacity and stability is analyzed. The initial capacities decrease with increasing fluorine content but the low voltage capacity is stabilized. Best electrochemical results are obtained with a fluorine content of x = 0.15. Furthermore, an additional redox couple is found. The intensity of this depends on the fluorine content. It is assumed that manganese, either in the tetrahedral sites or in octahedral sites, bound to fluorine lead to a higher voltage.

Alloy anodes have been extensively studied over past decades to replace the graphite of lithium-ion batteries (LIBs). Most efforts are made towards those anode materials with high specific capacities such as silicon and germanium. To minimize the negative impacts of the volume expansions during Li incorporation, protective coatings or specific micro- and nanostructures have been suggested, but a commercialization on a larger scale was impeded by such preparation costly procedures. Therefore, the optimal alloy anode candidate should balance the cost, capacity and manufacturing complexity rather than solely maximize the specific capacity. Aluminum, an underappreciated anode material, possesses intrinsic properties that fulfill the criteria mentioned above. The origin of the main capacity of aluminum anode is upon the formation of the β phase (LiAl; ca. 1Ah/g). However, the (de-)alloying processes of Al remain poorly understood, especially at room temperature under which LIBs usually operate. In this study, we investigate the (de-)lithiation that occurs within the solubility range of the β phase Although this Li solubility is highlighted by multiple versions of the Li-Al phase diagrams, the solubility range at low temperatures was not specified yet due to the experimental conditions of previous phase diagram studies (> 400 °C). Various electrochemical analytic tools and methods are used to shed light on the Li solubility within the β phase. The Li solubility range of the β phase is determined to be roughly 5 at% by a potentiostatic charge counting experiment at room temperature. Moreover, the cyclic voltammetry of partially lithiated Al foils shows that the β phase can be (de-)saturated without propagating the phase front towards the α phase. If galvanostatic charge and discharge is smartly controlled by taking into consideration of the solubility range, the cycling life of β-LiAl anode can be significantly improved. Not only does this piece of work provide fundamental data for the β-LiAl phase at room temperature that complements the existing phase diagrams, but also implies that aluminum foil holds great potential as an anode material for the next generation of lithium-based batteries.

The paper focuses on the performance and aging behavior of lithium nickel cobalt manganese oxide commercial standard material (NCM-111) which is improved with a post synthesis process in order to enhance the cathode active material of lithium-ion pouch cells regarding their capacity and cyclic stability. The aging behavior of the cells is analyzed with electrochemical impedance spectroscopy (EIS) during long-term electrochemical load cycling tests based on the Common Artemis Driving Cycle (CADC). Additionally, post-mortem investigations using scanning electron microscopy (SEM) and X-ray diffraction (XRD) were performed. The results demonstrate that post-processing of electrode active material is an effective tool to improve the properties of lithium-ion electrode materials, especially regarding high energy applications and lifetime optimization. The paper bridges the gap between lithium-ion battery electrode material development and the necessary cell testing under automotive relevant conditions which is important for the evaluation of new lithium-ion battery materials for automotive applications.

Lithium transition metal fluorides (Li3MF6; M = Fe, V) with cryolite structure are investigated as positive electrode materials for lithium-ion batteries. A novel sol–gel process with trifluoroacetic acid as fluorine source was used to synthesize monoclinic and orthorhombic Li3CrF6. A ball milling process with Li3CrF6, binder, and conductive agent was applied to form a Li3CrF6 composite, which was electrochemically characterized against lithium metal for the first time. The electrochemical properties of two different modifications are quite similar, with a reversible specific capacity of 111 mAhg−1 for monoclinic Li3CrF6 and 106 mAhg−1 for orthorhombic Li3CrF6 (1 eq. Li ≙ 143 mAhg−1). The electrochemically active redox couple CrIII/CrII was confirmed by X-ray photoelectron spectroscopy.

The energy density of lithium-ion batteries can be raised by increasing the redox potential of the positive electrode. This can be done in principle by substituting oxygen in commonly used lithium transition metal oxides with the more electronegative fluorine. To synthesize the quaternary lithium transition metal fluoride LiMgFeF 6 with triturile structure a sol–gel process without toxic chemicals was used. The as-synthesized LiMgFeF 6 was ball milled with carbon and binder to characterize the electrochemical properties of the LiMgFeF 6 /carbon/binder nanocomposite against lithium metal. After 20 cycles of galvanostatic cycling a reversible specific capacity of 107 mAh g −1 , which is 80% of the theoretical capacity (1 eq. Li = 133 mAh g −1 ), was retained. In a rate performance test up to a discharge rate of 1C the LiMgFeF 6 /carbon/binder nanocomposite provided a specific capacity of 64 mAh g −1 . Moessbauer spectroscopy and cyclic voltammetry confirmed the electrochemically active redox couple Fe 3+ /Fe 2+ during cycling against lithium metal. Structural changes of the trirutile structure after lithium insertion have been investigated by X-ray powder diffraction.

LiNiFeF6 was used as cathode material in lithium-ion cells and studied by in situ X-ray diffraction (XRD), in operando X-ray absorption spectroscopy (XAS) and 7Li MAS NMR spectroscopy. An optimised electrochemical in situ cell was employed for the structural and electrochemical characterisation of LiNiFeF6 upon galvanostatic cycling. The results for the first time reveal the lithium insertion process into a quaternary lithium transition metal fluoride with a trirutil-type host structure (space group P42/mnm). The in situ diffraction experiments indicate a preservation of the structure type after repeated lithium insertion and extraction. The lithium insertion reaction can be attributed to a phase separation mechanism between Li-poor Li1+x1NiFeF6 and Li-rich Li1+x2NiFeF6 (x1 ≲ 0.16 ≲ x2), where not only the weight fractions, but also the lattice parameters of the reacting phases change. The insertion of Li ions into [001]-channels of the trirutile structure causes an anisotropic lattice expansion along the tetragonal a-axes. An overall increase in the unit cell volume of ~6% and a reduction in the c/a ratio of ~4% are detected during discharge. Changes of atomic coordinates and distances suggest the accommodation of intercalated lithium in the empty six-fold coordinated 4c site. This is confirmed by 7Li MAS NMR spectroscopy showing two Li environments with similar intensities after discharging to 2.0 V. Furthermore, in operando XAS investigations revealed that only Fe3+ cations participate in the electrochemical process via an Fe3+/Fe2+ redox reaction, while Ni2+ cations remain electrochemically inactive.

Ni-rich LiNixCoyMnzO2 (NCM) cathode materials have great potential for application in next-generation lithium-ion batteries owing to their high specific capacity. However, they are subjected to severe structural changes upon (de)lithiation, which adversely affects the cycling stability. Herein, we investigate changes in crystal and electronic structure of NCM811 (80% Ni) at high states of charge by a combination of operando X-ray diffraction (XRD), operando hard X-ray absorption spectroscopy (hXAS), ex situ soft X-ray absorption spectroscopy (sXAS), and density functional theory (DFT) calculations, and correlate the results with data from galvanostatic cycling in coin cells. XRD reveals a large decrease in unit cell volume from 101.38(1) Å3 to 94.26(2) Å3 due to collapse of the interlayer spacing when x(Li) < 0.5 (decrease in c-axis from 14.469(1) Å at x(Li) = 0.6 to 13.732(2) Å at x(Li) = 0.25). hXAS shows that the shrinkage of the transition metal-oxygen layer mainly originates from nickel oxidation. sXAS, together with DFT-based Bader charge analysis, indicates that the shrinkage of the interlayer, which is occupied by lithium, is induced by charge transfer between O 2p and partially filled Ni eg orbitals (resulting in decrease of oxygen-oxygen repulsion). Overall, the results demonstrate that high-voltage operation of NCM811 cathodes is inevitably accompanied by charge transfer-induced lattice collapse.

The increase in batteries energy is one of the main issues in current battery research and mandatory for the development of electric vehicles with long ranges. The energy of a battery is determined by the capacity and the potential difference of the active materials. Thus, both parameters offer the ability for an increase in energy. In many studies high capacity cathode materials are analyzed. One of the most promising materials is a Li-rich layered oxide. Other studies use high voltage cathode materials (e.g. LiMxMn2-xO4, with M = e.g. Ni, Co) in order to increase the operational voltage of the cell. Cells with high voltage cathodes suffer from unwanted side reactions with the electrolyte. This is because the operational voltage is higher than the stability window (ca. 1.0 – 4.3 V vs. Li+/Li0 in the presence of transition metal ions like Ni4+ and Mn4+) of current organic electrolytes. The reactions consume active lithium and a severe capacity fade occurs. On the other side, the increase of energy of high capacity cathode materials is limited due to the relatively low voltages of ca. 3.5 V vs. Li+/Li0 of these materials and the need for balancing of anode capacity. In principle the high voltage spinel (LiNi0.5Mn1.5O4) offers the ability to increase the voltage and the capacity compared with other cathode materials. This can be reached when a metallic lithium anode is used. The spinel lattice can host a second lithium and therefore the theoretical capacity is increased from 147 to 294 mAh g-1. The increase in capacity during cycling between 2.0 and 5.0 V and the high operational voltage lead to a theoretical specific energy of more than 1000 Wh kg-1 based on the active materials. During intercalation of the second lithium, the spinel undergoes a phase transition from cubic to tetragonal because of a cooperative Jahn-Teller-distortion of Mn3+in the low voltage area. This is associated with material degradation and capacity loss. Here we use different LiNi0.5Mn1.5O4-spinels doped with transition metals and treated with different temperature programs in order to increase the cycling stability. It is found that the stability and the initial capacities are directly dependent on the treatment and doping elements. At a rate of C/2 a capacity of 190 mAh g-1 is achieved with 92 % of the initial capacity retained after 100 cycles. The difference in the discharge behavior of the materials is analyzed based on electrochemical data, particle morphology and in-situ XRD analysis. A model, which can explain the different behaviors is introduced and will be discussed.

To find new cathode materials for future applications in lithium-ion batteries, lithium transition metal fluorides represent an interesting class of materials. In principle the Li intercalation voltage can be increased by replacing oxygen in the cathode host structure with the more electronegative fluorine. A facile pyrolytic sol–gel process with trifluoroacetic acid as fluorine source was established to synthesize monoclinic Li3FeF6 using nontoxic chemicals. The acicular Li3FeF6 powder was characterized with X-ray diffraction and a detailed structure model was calculated by Rietveld analysis. For the preparation of cathode films to cycle versus lithium monoclinic Li3FeF6 was ball milled with carbon and binder down to nanoscale. After 100 cycles galvanostatic cycling (C/20) 47 % fully reversible capacity of the initial capacity (129 mAh/g) could be retained. To the best of our knowledge the results presented in this work include the first rate performance test for monoclinic Li3FeF6 up to 1 C maintaining a capacity of 71 mAh/g. The redox reaction involving Fe3+/Fe2+ during Li insertion/extraction was confirmed by post-mortem XPS and cyclic voltammetry.

The effects of fluorine co-doping by means of a post-thermal annealing process of iron-doped BST thin films in a fluorine-containing atmosphere have been investigated. XPS and ToF-SIMS sputter depth profiling verified a homogeneous fluorine distribution in the thin films. By employing EPR, it was shown that singly charged ( $$ {\text{Fe}}_{\text{Ti}}^{\prime } $$ – $$ {\text{V}}_{\text{O}}^{ \cdot \cdot } $$ )· defect complexes, as well as ‘isolated’ $$ {\text{Fe}}_{\text{Ti}}^{\prime } $$ centres with a distribution of $$ {\text{F}}_{\text{O}}^{ \cdot } $$ sites in remote coordination spheres exist in the fluorinated films. Tunability enhancement due to fluorine co-doping as well as a Q-factor enhancement due to iron doping is demonstrated.

Powder granulation, Ti-doping and thermal post-treatment have beneficial effects on the electrochemical performance of 5 V LiNi0.5Mn1.5O4 (LNMO) spinel materials. It is shown that spray-drying combined with a post-doping process step is suitable to prepare Ti-doped 5 V materials with a defined and highly reproducible microstructure and chemical composition. Powder granulation via spray-drying and thermal post-treatment provides spherical LNMO granules with nano-crystalline primary particles and a 10 % higher specific discharge capacity compared to pristine LNMO materials due to the presence of the partially ordered P4 3 32 spinel phase and the reduced Mn3+ content. Powder granulation combined with a post-doping process step which utilizes titanium containing sol leads to spherical LiNi0.5Mn1.47Ti0.03O4 granules with uniform nano-crystalline primary particles and a homogenous Ti distribution. The second calcination process after spray-drying as well as the Ti-doping cause a reduced content of the Li x Ni1−x O impurity phase. This facile sol–gel processing leads to doped LiNi0.5Mn1.47Ti0.03O4 with an increased discharge capacity of 18 % compared to the original material. All the granulated materials show a good rate performance up to 10 C due to their particular microstructure.

Normally, the weldability of aluminum alloys is ruled by the temperature range of solidification of an alloy according to its composition by the formation of hot cracks due to thermal shrinkage. However, for materials at nonequilibrium conditions, advantage can be taken by multiple phase formation, leading to an annihilation of temperature stress at the microscopic scale, preventing hot cracks even for alloys with extreme melting range. In this paper, several spray-compacted hypereutectic aluminum alloys were laser welded. Besides different silicon contents, additional alloying elements like copper, iron and nickel were present in some alloys, affecting the microstructure. The microstructure was investigated at the delivery state of spray-compacted material as well as for a wide range of welding speeds ranging from 0.5 to 10 m/min, respectively. The impact of speed on phase composition and morphology was studied at different disequilibrium solidification conditions. At high welding velocity, a close-meshed network of eutectic Al-Si-composition was observed, whereas the matrix is filled with nearly pure aluminum, helping to diminish the thermal stress during accelerated solidification. Primary solidified silicon was found, however, containing considerable amounts of aluminum, which was not expected from phase diagrams obtained at the thermodynamic equilibrium.

The effects of the thermal processing and iron doping on RF magnetron co-sputtered barium strontium titanate thin film properties have been investigated. X-ray diffraction and Raman spectroscopy have been used to determine the structural evolution of the films as a function of the annealing temperature and the amount of iron dopant. X-ray photoelectron spectroscopy and electron paramagnetic resonance spectroscopy were employed to gain information about the chemical binding states and the defect structure. The enhancement of the quality factor Q, as well as the decreasing permittivity and tunability due to iron acceptor doping are demonstrated.

The fabrication of novel iron-doped barium strontium titanate thin films by means of radio frequency (RF) magnetron co-sputtering is shown. Investigations of the elemental composition and the dopant distribution in the thin films obtained by X-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, and time-of-flight secondary ion mass spectroscopy reveal a homogeneous dopant concentration throughout the thin film. The incorporation of the iron dopant and the temperature-dependent evolution of the crystal structure and morphology are analyzed by electron paramagnetic resonance spectroscopy, X-ray diffraction, Raman spectroscopy, atomic force microscopy, and scanning electron microscopy. In summary, these results emphasize the RF magnetron co-sputter process as a versatile way to fabricate doped thin films.

A series of commercially available nanosized barium titanates has been investigated with respect to their use as high-k-ceramic filler in polymer based composites with improved dielectric properties. The thermal treatment of the barium titanate powders at 1,000°C causes a significant increase of the composite’s permittivity. X-ray diffraction experiments prior and after heat treatment revealed that the barium titanate with smallest particle size and the largest specific surface area possesses the thermodynamically unstable cubic phase. In case of the other investigated barium titanates the crystal lattice is distorted. Thermal treatment induces the phase change into the tetragonal one and crystal lattice relaxation enabling higher permittivity values. Composites with a solid load around 78 wt% with a bimodal particle size distribution show high permittivities around 50 and a low loss factor around 5‰ suitable for the realization of embedded capacitors via screen printing or tape casting.

The influence of codoping of Fe, Co, Ni, Cu as acceptors and F as donor on the dielectric properties of screen-printed Ba0.6Sr0.4TiO3 ceramic thick-films has been investigated. The undoped and codoped Ba0.6Sr0.4TiO3 powders were synthesized through a sol-gel route. The thermal gravimetric analysis revealed the difference of the thermal decomposition behaviour between the undoped and codoped precursors. The ceramic powders were characterized with x-ray diffraction, scanning electron microscopy and BET measurements. Larger crystallite sizes of the codoped powders were observed. The densification behaviour of the powders was recorded by dilatometry and indicated that codoping influences the sintering mechanism. The permittivity, dielectric loss and tunability of the undoped and codoped thick-films were characterized with coplanar waveguide structures up to 30 GHz.

LiNi0.5Mn1.5O4 spinel cathode was studied during the first discharge cycle using combined full field Transmission X-ray Microscopy (TXM) and X-ray Absorption Near Edge Structure Spectroscopy (XANES) techniques to follow the chemical phase transformation as well as the microstructural evolution of cathode materials upon operation within an electrochemical cell. The spatial distribution and electrochemical process of the spinel material with spherical granules of 30 μm and 3 μm crystallite size was investigated. The spectroscopic imaging of the cathode within field of view of 40 × 32 μm(2) and spatial resolution of 40 nm has revealed an increase of the LiNi0.5Mn1.5O4 granule size during lithiation providing an insight into the effect of the particle size and morphology on the electrochemical process. The chemical elemental distribution and the content of the different oxidation states of the two absorbing elements (Ni and Mn) have been determined in operando from the XANES imaging. A gradual increase in the content of the oxidation state Mn(3+) from 8% up to 64% has been recorded during the discharge from 5 V to 2.7 V. The study of the local oxidation reduction behavior of Mn(3+) reveals a reversibility aspect in the local electrochemical reaction of Mn(4+) toward Mn(3+) in areas located in the center of the aggregate as well as in areas closed to the electrolyte. During the discharge process, a mixture of Mn(3+) and Mn(4+) has been detected while only single electron valence states have been found in the case of Ni. Probing the chemical changes during the discharge using two-dimensional XANES reveals spatial differences in the electrochemical activities of the two absorbing elements Ni and Mn.

Higher capacities and energies are needed in order to achieve widespread acceptance of Li-ion batteries as power sources in electric vehicles. In principle, Li-ion batteries offer two possibilities to achieve higher specific energies. Since the batteries’ energy is determined by the operational voltage and the active materials capacity, one could improve either the capacity of the active materials or the operating voltage of the cell. Both approaches are pursued by many research groups. Higher capacities can for example be achieved with Li-rich layered oxides, where the use of more than 1 Li in the active material can considerably improve the capacity. The operational voltage is mainly determined by the potential of the cathode material vs. Li-metal. Therefore high voltage cathode materials (e.g. LiMxMn2-xO4, with M = e.g. Ni, Co) are used. However both approaches suffer from different limitations and problems. The need for balancing and the commonly relatively low mean voltages of ca. 3.5 V vs. Li+/Li0 reduce the gain in specific energy for materials with high capacities. On the other hand, the use of high voltage materials leads to unwanted site reactions and severe capacity fade when applied with a graphitic Anode. This is because the cells are operated above the stability window (ca. 1.0 – 4.3 V vs. Li+/Li0 in the presence of transition metal ions like Ni4+ and Mn4+) of current organic electrolytes. Furthermore the theoretical capacity of 147 mAh g-1 for the LiNi0.5Mn1.5O4 high voltage spinel is relatively low. The shortcomings of the high voltage spinel can be overcome, when metallic lithium is used as the anode material. Not only the cycling stability is significantly improved but also the use of metallic lithium leads to the ability of cycling of 2 Li eq. per cycle, since the spinel lattice is able to host 2 Li eq. This is leading to a theoretical capacity of 294 mAh g-1 and therefore a theoretical specific energy of ~1030 Wh kg-1 can be reached when the cell is cycled between 2.0 and 5.0 V vs. Li+/Li0. Unfortunately, the cycling of 2 Li eq. is leading to a severe capacity fade due to a phase transition from cubic to tetragonal in the low voltage region associated with material degradation. In this work doping with transition metal ions is used to improve capacity retention when cycling between 2.0 and 5.0 V vs Li+/Li0. Initial capacities and stabilities are directly dependent on synthesis conditions and doping elements. The goal is to achieve a high stability of the material at a low tradeoff of capacity. Therefore different combinations of doping elements are used and tested at different cycling conditions. In addition to the transition metal ions, fluorine doping is also used to increase cycling stability. The influence of different synthesis, doping and cycling conditions on cycling stability and capacity retention are discussed.