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Anionic redox chemistry has emerged as a new paradigm to design higher-energy lithium ion-battery cathode materials such as Li-rich layered oxides. However, they suffer from voltage fade, large hysteresis and sluggish kinetics, which originate intriguingly from the anionic redox activity itself. To fundamentally understand these issues, we decided to act on the ligand by designing new Li-rich layered sulfides Li1.33 – 2y/3Ti0.67 – y/3FeyS2, among which the y = 0.3 member shows sustained reversible capacities of ~245 mAh g−1 due to cumulated cationic (Fe2+/3+) and anionic (S2−/Sn−, n < 2) redox processes. Moreover, its negligible initial cycle irreversibility, mitigated voltage fade upon long cycling, low voltage hysteresis and fast kinetics compare positively with its Li-rich oxide analogues. Moving from the oxygen ligand to the sulfur ligand thus partially alleviates the practical bottlenecks affecting anionic redox, although it penalizes the redox potential and energy density. Overall, these sulfides provide chemical clues to improve the holistic performance of anionic redox electrodes, which may guide us to ultimately exploit the energy benefits of oxygen redox.

An innovative software with a user-friendly interface for calculation of differential phase contrast (DPC) scanning transmission electron microscopy images (integrated iDPC- and differentiated dDPC-STEM) is presented. The underlying algorithm is described and the program functionalities are demonstrated on the examples of Li 5 OsO 6 , α-Ga 2 O 3 , and LiCoO 2 . The software supports interpretation of DPC-STEM images, which is crucial for qualitative and quantitative analysis of crystal structures and defects., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Advanced ionic conductors are crucial for a large variety of contemporary technologies spanning solid state ion batteries, fuel cells, gas sensors, water desalination, etc . In this work, we report on a new member of KTiOPO 4 -structured materials, NaGaPO 4 F, with sodium-ion conductivity. NaGaPO 4 F has been obtained for the first time via a facile two-step synthesis consisting of a hydrothermal preparation of an ammonia-based precursor, NH 4 GaPO 4 F, followed by an ion exchange reaction with NaNO 3 . Its crystal structure was precisely refined using a combination of synchrotron X-ray powder diffraction and electron diffraction tomography. The material is thermally stable upon 450 °C showing no significant structural transformations or degradation but only a ∼1% cell volume expansion. Na-ion mobility in NaGaPO 4 F was investigated by a joint experimental and computational approach comprising solid-state nuclear magnetic resonance (NMR) and density functional theory (DFT). DFT and bond-valence site energy (BVSE) calculations reveal 3D diffusion of sodium in the [GaPO 4 F] framework with migration barriers amounting to 0.22 and 0.44 eV, respectively, while NMR yields 0.3-0.5 eV that, being coupled with a calculated bandgap of ∼4.25 eV, makes NaGaPO 4 F a promising fast Na-ion conductor.

Li[Li x Ni y Mn z Co 1-x-y-z ]O 2 (lithium-rich NMCs) are benchmark cathode materials receiving considerable attention due to the abnormally high capacities resulting from their anionic redox chemistry. Although their anionic redox mechanisms have been much investigated, the roles of cationic redox processes remain underexplored, hindering further performance improvement. Here we decoupled the effects of nickel and cobalt in lithium-rich NMCs via a comprehensive study of two typical compounds, Li 1.2 Ni 0.2 Mn 0.6 O 2 and Li 1.2 Co 0.4 Mn 0.4 O 2 . We discovered that both Ni 3+/4+ and Co 4+ , generated during cationic redox processes, are actually intermediate species for triggering oxygen redox through a ligand-to-metal charge-transfer process. However, cobalt is better than nickel in mediating the kinetics of ligand-to-metal charge transfer by favouring more transition metal migration, leading to less cationic redox but more oxygen redox, more O 2 release, poorer cycling performance and more severe voltage decay. Our work highlights a compositional optimization pathway for lithium-rich NMCs by deviating from using cobalt to using nickel, providing valuable guidelines for future high-capacity cathode design., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

The layered oxide LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811, NCM811) is of utmost technological importance as a positive electrode (cathode) material for the forthcoming generation of Li-ion batteries. In this contribution, we have collected 548 research articles comprising >950 records on the electrochemical properties of NMC811 as a cathode material in half-cells with metallic Li counter electrode. The analysis of distribution histograms provided statistically-relevant values of such key characteristics of NMC811 as the first cycle discharge capacity and Coulombic efficiency, discharge capacities at different upper cut-off voltages, capacity fade and capacity retention at the 0.1C-5C current densities. We derived equations describing the relationships between discharge capacity and upper cut-off voltage, Ni content in the LiNi x Mn y Co z O 2 compositions in vicinity of NMC811, antisite disorder, and the C-rate. Additionally, the distribution histograms were used for a qualitative comparison between various groups of NMC811 materials, such as benchmarks in various optimizations vs obtained in course of synthesis development, lab-made vs commercial, polycrystalline vs single-crystal. The results of this analysis provide justified values to be used as benchmarks in further works related to optimizing and improving NMC811 and related materials, eliminating random picking up from a huge pool of published data., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2023 The Authors.)

We introduce a new synthetic concept that can be broadly adopted for the low-temperature preparation of mixed-metal energy storage materials, such as phosphates, silicates, fluorides, fluorophosphates, and fluorosulfates that exhibit intrinsic low electronic conductivity and thus require a carbon modulation. The development of novel low-temperature approaches for assembling energy-related materials with a complex core-shell microstructure is of great importance for expanding their application scope. The traditional definition of single-source precursors refers to their ability to yield a phase-pure material upon thermal decomposition. We have developed a new way for the utilization of heterometallic molecular precursors in synthesis that goes beyond its common delineation as a single-phase maker. The utility of this approach has been demonstrated upon the low-temperature synthesis of lithium-iron phosphate@C, which represents a celebrated cathode material for Li-ion batteries. The first atomically precise carbonaceous molecular precursors featuring a desired Li:Fe:P ratio of 1:1:1, divalent iron, and sufficient oxygen content for the target LiFe II PO4 phosphate were shown to enable a spontaneous formation of both the olivine core and conductive carbon shell, yielding a carbon-coated mixed-metal phosphate.

Nickel-rich layered oxides are adopted as electrode materials for EV's. They suffer from a capacity loss when the cells are charged above 4.15 V versus Li/Li + . Doping and coating can lead to significant improvement in cycling. However, the mechanisms involved at high voltage are not clear. This work is focused on LiNiO 2 to overcome the effect of M cations. Galvanostatic intermittent titration technique (GITT) and in situ X-ray diffraction (XRD) experiments are performed at very low rates in various voltage ranges (3.8-4.3 V,). On the "4.2-4.3 V" plateau the R2 phase is transformed simultaneously in R3, R3 with H4 stacking faults and H4. As the charge proceeds above 4.17 V cell polarization increases, hindering Li deintercalation. In discharge, such polarization decreases immediately. Upon cycling, the polarization increases at each charge above 4.17 V. In discharge, the capacity and dQ/dV features below 4.1 V remain constant and unaffected, suggesting that the bulk of the material do not undergo significant structural defect. This study shows that the change in polarization results from the electrochemical behavior of the grain surface having very low conductivity above 4.17 V and high conductivity below this threshold. This new approach can explain the behavior observed with dopants like tungsten., (© 2023 The Authors. Small published by Wiley-VCH GmbH.)

The search for efficient anodic electrochromic materials is essential to the development of electrochromic devices, such as smart windows. Magnetron-sputtered lithium-nickel-tungsten mixed oxides are good candidates to tackle this issue; however, they display a complicated microstructure, making it difficult to pinpoint the origin of their electro-optical properties. Herein, by exploring the Li 2 O-NiO-WO 3 phase diagram, we obtained a new phase, Li 2 Ni 2 W 2 O 9 , that crystallizes in the orthorhombic Pbcn space group. This material can reversibly uptake/release 0.75 Li + (31 mA h·g -1 ) when cycled between 2.5 and 5.0 V versus Li + /Li. Moreover, through operando optical microscopy, we show that this new phase is electrochromic, and crucial information can be accessed about the diffusion-limited insertion of lithium at the single-particle scale. This study sets the ground for future syntheses of electrochemically active materials crystallizing in the ramsayite structure and details how the electrochromic properties of battery materials can be used to shed some light on their electrochemical mechanisms.

Magnetic topological insulators (MTIs) have recently become a subject of poignant interest; among them, Z 2 topological insulators with magnetic moment ordering caused by embedded magnetic atoms attract special attention. In such systems, the case of magnetic anisotropy perpendicular to the surface that holds a topologically nontrivial surface state is the most intriguing one. Such materials demonstrate the quantum anomalous Hall effect, which manifests itself as chiral edge conduction channels that can be manipulated by switching the polarization of magnetic domains. In the present paper, we uncover the atomic structure of the bulk and the surface of Mn 0.06 Sb 1.22 Bi 0.78 Te 3.06 in conjunction with its electronic and magnetic properties; this material is characterized by naturally formed ferromagnetic layers inside the insulating matrix, where the Fermi level is tuned to the bulk band gap. We found that in such mixed crystals septuple layers (SLs) of Mn(Bi,Sb) 2 Te 4 form structures that feature three SLs, each of which is separated by two or three (Bi,Sb) 2 Te 3 quintuple layers (QLs); such a structure possesses ferromagnetic properties. The surface obtained by cleavage includes terraces with different terminations. Manganese atoms preferentially occupy the central positions in the SLs and in a very small proportion can appear in the QLs, as indirectly indicated by a reshaped Dirac cone.

Reversible anionic redox reactions represent a transformational change for creating advanced high-energy-density positive-electrode materials for lithium-ion batteries. The activation mechanism of these reactions is frequently linked to ligand-to-metal charge transfer (LMCT) processes, which have not been fully validated experimentally due to the lack of suitable model materials. Here we show that the activation of anionic redox in cation-disordered rock-salt Li 1.17 Ti 0.58 Ni 0.25 O 2 involves a long-lived intermediate Ni 3+/4+ species, which can fully evolve to Ni 2+ during relaxation. Combining electrochemical analysis and spectroscopic techniques, we quantitatively identified that the reduction of this Ni 3+/4+ species goes through a dynamic LMCT process (Ni 3+/4+ -O 2-  → Ni 2+ -O n- ). Our findings provide experimental validation of previous theoretical hypotheses and help to rationalize several peculiarities associated with anionic redox, such as cationic-anionic redox inversion and voltage hysteresis. This work also provides additional guidance for designing high-capacity electrodes by screening appropriate cationic species for mediating LMCT., (© 2022. The Author(s), under exclusive licence to Springer Nature Limited.)

A major feature of the electrolyte/electrode interface (EEI) that affects charge storage in lithium-ion batteries is the electrical double layer (EDL), but most of the available experimental approaches for probing its structuration have limitations due to electrical field and redox reaction disturbances, hence explaining why it is frequently overlooked. Herein we show that this is no longer true by using an advanced electrochemical quartz crystal microbalance (EQCM)-based method in the form of ac -electrogravimetry. For proof of concept, we studied the effect of various solvent/salt combinations, differing in their dipole moment and size/weight, respectively, on the structure of the EDL forming at the EEI of Li x MoO 3 . We show that a significant amount of solvated lithium ions and anions contribute to charge compensation at the interface, and by varying the nature of the solvents (cyclic vs noncyclic), we provide a solid experimental proof of the direct relationship between the ions' solvation and solvent polarity. Moreover, we demonstrated a disappearance of the anionic motion in the less polar solvent (DMC) most likely due to plausible formation of contact ion pairs and agglomerates at the EDL level. Altogether, ac -electrogravimetry, when combined with classical EQCM, stands as an elegant and powerful method to experimentally assess the chemical structure and dynamics of the electrical double layer. We hope that the community will start to adopt it to better engineer interfaces of electrochemical energy storage devices.

Topochemical reactions have led to great progress in the discovery of new metastable compounds with novel chemical and physical properties. With these reactions, the overall crystal structure of the host material is generally maintained. Here we report a topochemical synthesis of a hexagonal nitride hydride, h-Ca 3 CrN 3 H, by heating an orthorhombic nitride, o-Ca 3 CrN 3 , under hydrogen at 673 K, accompanied by a rotational structural transformation. The hydrogen intercalation modifies the Ca-N rock-salt-like atomic packing in o-Ca 3 CrN 3 to a face-sharing octahedral chain in h-Ca 3 CrN 3 H, mimicking a "hinged tessellation" movement. In addition, the h-Ca 3 CrN 3 H exhibited stable ammonia synthesis activity when used as a catalyst., (© 2022 Wiley-VCH GmbH.)

All-solid-state batteries primarily focus on macrocrystalline solid electrolyte/cathode interfaces, and little is explored on the growth and stability of nanograined Li-garnet and cathode ones. In this work, a thin (∼500 nm) film of LiCoO 2 (LCO) has been grown on top of the polycrystalline layer of Ta-doped Li 7 La 3 Zr 2 O 12 (Ta-LLZO) solid electrolyte using the pulsed laser deposition (PLD) technique. Scanning transmission electron microscopy, electron diffraction, and electron tomography demonstrated that the LCO film is formed by columnar elements with the shape of inverted cones. The film appears to be highly textured, with the (003) LCO crystal planes parallel to the LCO/Ta-LLZO interface and with internal pores shaped by the {104} and {102} planes. According to density functional theory (DFT) calculations, this specific microstructure is governed by a competition between free energies of the corresponding crystal planes, which in turn depends on the oxygen and lithium chemical potentials during the deposition, indicating that thermodynamics plays an important role in the resulting LCO microstructure even under nonequilibrium PLD conditions. Based on the thermodynamic estimates, the experimental conditions within the LCO stability domain are proposed for the preferential {104} LCO orientation, which is considered favorable for enhanced Li diffusion in the positive electrode layers of all-solid-state batteries.

Polyanion compounds offer a playground for designing prospective electrode active materials for sodium-ion storage due to their structural diversity and chemical variety. Here, by combining a NaVPO 4 F composition and KTiOPO 4 -type framework via a low-temperature (e.g., 190 °C) ion-exchange synthesis approach, we develop a high-capacity and high-voltage positive electrode active material. When tested in a coin cell configuration in combination with a Na metal negative electrode and a NaPF 6 -based non-aqueous electrolyte solution, this cathode active material enables a discharge capacity of 136 mAh g -1 at 14.3 mA g -1 with an average cell discharge voltage of about 4.0 V. Furthermore, a specific discharge capacity of 123 mAh g -1 at 5.7 A g -1 is also reported for the same cell configuration. Through ex situ and operando structural characterizations, we also demonstrate that the reversible Na-ion storage at the positive electrode occurs mostly via a solid-solution de/insertion mechanism., (© 2022. The Author(s).)

Electrochemical energy storage plays a vital role in combating global climate change. Nowadays lithium-ion battery technology remains the most prominent technology for rechargeable batteries. A key performance-limiting factor of lithium-ion batteries is the active material of the positive electrode (cathode). Lithium- and manganese-rich nickel manganese cobalt oxide (LMR-NMC) cathode materials for Li-ion batteries are extensively investigated due to their high specific discharge capacities (>280 mAh/g). However, these materials are prone to severe capacity and voltage fade, which deteriorates the electrochemical performance. Capacity and voltage fade are strongly correlated with the particle morphology and nano- and microstructure of LMR-NMCs. By selecting an adequate synthesis strategy, the particle morphology and structure can be controlled, as such steering the electrochemical properties. In this manuscript we comparatively assessed the morphology and nanostructure of LMR-NMC (Li1.2Ni0.13Mn0.54Co0.13O2) prepared via an environmentally friendly aqueous solution-gel and co-precipitation route, respectively. The solution-gel (SG) synthesized material shows a Ni-enriched spinel-type surface layer at the {200} facets, which, based on our post-mortem high-angle annual dark-field scanning transmission electron microscopy and selected-area electron diffraction analysis, could partly explain the retarded voltage fade compared to the co-precipitation (CP) synthesized material. In addition, deviations in voltage fade and capacity fade (the latter being larger for the SG material) could also be correlated with the different particle morphology obtained for both materials.

The success and continued expansion of research on metal-oxo clusters owe largely to their structural richness and wide range of functions. However, while most of them known to date are negatively charged polyoxometalates, there is only a handful of cationic ones, much less functional ones. Here, we show an all-inorganic hydroxyiodide [H 10.7 Sb 32.1 O 44 ][H 2.1 Sb 2.1 I 8 O 6 ][Sb 0.76 I 6 ] 2 ·25H 2 O ( HSbOI ), forming a face-centered cubic structure with cationic Sb 32 O 44 clusters and two types of anionic clusters in its interstitial spaces. Although it is submicrometer in size, electron diffraction tomography of HSbOI allowed the construction of the initial structural model, followed by powder Rietveld refinement to reach the final structure. The cationic cluster is characterized by the presence of acidic protons on its surface due to substantial Sb 3+ deficiencies, which enables HSbOI to serve as an excellent solid acid catalyst. These results open up a frontier for the exploration and functionalization of cationic metal-oxo clusters containing heavy main group elements.

A broad range of cationic nonstoichiometry has been demonstrated for the Li-rich layered rock-salt-type oxide Li 2 MoO 3 , which has generally been considered as a phase with a well-defined chemical composition. Li 2+ x Mo 1- x O 3 (-0.037 ≤ x ≤ 0.124) solid solutions were synthesized via hydrogen reduction of Li 2 MoO 4 in the temperature range of 650-1100 °C, with x decreasing with the increase of the reduction temperature. The solid solutions adopt a monoclinically distorted O3-type layered average structure and demonstrate a robust local ordering of the Li cations and Mo 3 triangular clusters within the mixed Li/Mo cationic layers. The local structure was scrutinized in detail by electron diffraction and aberration-corrected scanning transmission electron microcopy (STEM), resulting in an ordering model comprising a uniform distribution of the Mo 3 clusters compatible with local electroneutrality and chemical composition. The geometry of the triangular clusters with their oxygen environment (Mo 3 O 13 groups) has been directly visualized using differential phase contrast STEM imaging. The established local structure was used as input for density functional theory (DFT)-based calculations; they support the proposed atomic arrangement and provide a plausible explanation for the staircase galvanostatic charge profiles upon electrochemical Li + extraction from Li 2+ x Mo 1- x O 3 in Li cells. According to DFT, all electrochemical capacity in Li 2+ x Mo 1- x O 3 solely originates from the cationic Mo redox process, which proceeds via oxidation of the Mo 3 triangular clusters into bent Mo 3 chains where the electronic capacity of the clusters depends on the initial chemical composition and Mo oxidation state defining the width of the first charge low-voltage plateau. Further oxidation at the high-voltage plateau proceeds through decomposition of the Mo 3 chains into Mo 2 dimers and further into individual Mo 6+ cations.

Na 9 V 14 O 35 (η-Na x V 2 O 5 ) has been synthesized via solid-state reaction in an evacuated sealed silica ampoule and tested as electroactive material for Na-ion batteries. According to powder X-ray diffraction, electron diffraction and atomic resolution scanning transmission electron microscopy, Na 9 V 14 O 35 adopts a monoclinic structure consisting of layers of corner- and edge-sharing VO 5 tetragonal pyramids and VO 4 tetrahedra with Na cations positioned between the layers, and can be considered as sodium vanadium(IV,V) oxovanadate Na 9 V 10 4.1+ O 19 (V 5+ O 4 ) 4 . Behavior of Na 9 V 14 O 35 as a positive and negative electrode in Na half-cells was investigated by galvanostatic cycling against metallic Na, synchrotron powder X-ray diffraction and electron energy loss spectroscopy. Being charged to 4.6 V vs. Na + /Na, almost 3 Na can be extracted per Na 9 V 14 O 35 formula, resulting in electrochemical capacity of ~60 mAh g -1 . Upon discharge below 1 V, Na 9 V 14 O 35 uptakes sodium up to Na:V = 1:1 ratio that is accompanied by drastic elongation of the separation between the layers of the VO 4 tetrahedra and VO 5 tetragonal pyramids and volume increase of about 31%. Below 0.25 V, the ordered layered Na 9 V 14 O 35 structure transforms into a rock-salt type disordered structure and ultimately into amorphous products of a conversion reaction at 0.1 V. The discharge capacity of 490 mAh g -1 delivered at first cycle due to the conversion reaction fades with the number of charge-discharge cycles.

Ti 2 Nb 2 O 9 with a tunnel-type structure is considered as a perspective negative electrode material for Li-ion batteries (LIBs) with theoretical capacity of 252 mAh g -1 corresponding to one-electron reduction/oxidation of Ti and Nb, but only ≈160 mAh g -1 has been observed practically. In this work, highly reversible capacity of 200 mAh g -1 with the average (de)lithiation potential of 1.5 V vs Li/Li + is achieved for Ti 2 Nb 2 O 9 with pseudo-2D layered morphology obtained via thermal decomposition of the NH 4 TiNbO 5 intermediate prepared by K + → H + → NH 4 + cation exchange from KTiNbO 5 . Using operando synchrotron powder X-ray diffraction (SXPD), single-phase (de)lithiation mechanism with 4.8% unit cell volume change is observed. Operando X-ray absorption near-edge structure (XANES) experiment revealed simultaneous Ti 4+ /Ti 3+ and Nb 5+ /Nb 4+ reduction/oxidation within the whole voltage range. Li + migration barriers for Ti 2 Nb 2 O 9 along [010] direction derived from density functional theory (DFT) calculations are within the 0.15-0.4 eV range depending on the Li content that is reflected in excellent C-rate capacity retention. Ti 2 Nb 2 O 9 synthesized via the ion-exchange route appears as a strong contender to widely commercialized Ti-based negative electrode material Li 4 Ti 5 O 12 in the next generation of high-performance LIBs.

Anionic redox is a double-edged sword for Li-ion cathodes because it offers a transformational increase in energy density that is also negated by several detrimental drawbacks to its practical implementation. Among them, voltage hysteresis is the most troublesome because its origin is still unclear and under debate. Herein, we tackle this issue by designing a prototypical Li-rich cation-disordered rock-salt compound Li 1.17 Ti 0.33 Fe 0.5 O 2 that shows anionic redox activity and exceptionally large voltage hysteresis while exhibiting a partially reversible Fe migration between octahedral and tetrahedral sites. Through combined in situ and ex situ spectroscopic techniques, we demonstrate the existence of a non-equilibrium (adiabatic) redox pathway enlisting Fe 3+ /Fe 4+ and O redox as opposed to the equilibrium (non-adiabatic) redox pathway involving sole O redox. We further show that the charge transfer from O(2p) lone pair states to Fe(3d) states involving sluggish structural distortion is responsible for voltage hysteresis. This study provides a general understanding of various voltage hysteresis signatures in the large family of Li-rich rock-salt compounds., (© 2021. The Author(s), under exclusive licence to Springer Nature Limited.)

The catalytic activity and stability of an iron-nickel based oxygen-deficient perovskite for the oxygen evolution reaction (OER) are drastically improved with the ppm additive of Fe ions to the alkaline electrolyte. The enhancement is attributed to a 1-2 nm restructured Ni 0.5 Fe 0.5 O x (OH) 2-x (oxy)hydroxide layer, as demonstrated with scanning transmission electron microscopy. La 0.6 Ca 0.4 Fe 0.7 Ni 0.3 O 2.9 shows almost a four-fold increase in OER activity after Fe addition relative to the as-prepared pristine electrolyte, which demonstrates the low Tafel slope of 44 ± 2.4 mV dec -1 and the superior intrinsic activity of 706 ± 71 A g -1 oxide at 1.61 V vs. RHE.

Expanding the chemical space for designing novel anionic redox materials from oxides to sulfides has enabled to better apprehend fundamental aspects dealing with cationic-anionic relative band positioning. Pursuing with chalcogenides, but deviating from cationic substitution, we here present another twist to our band positioning strategy that relies on mixed ligands with the synthesis of the Li 2 TiS 3-x Se x solid solution series. Through the series the electrochemical activity displays a bell shape variation that peaks at 260 mAh/g for the composition x = 0.6 with barely no capacity for the x = 0 and x = 3 end members. We show that this capacity results from cumulated anionic (Se 2- /Se n- ) and (S 2- /S n- ) and cationic Ti 3+ /Ti 4+ redox processes and provide evidence for a metal-ligand charge transfer by temperature-driven electron localization. Moreover, DFT calculations reveal that an anionic redox process cannot take place without the dynamic involvement of the transition metal electronic states. These insights can guide the rational synthesis of other Li-rich chalcogenides that are of interest for the development of solid-state batteries., (© 2021. The Author(s).)

The Li-based layered nickel-tin oxide Li 0.35 Na 0.07 Ni 0.5 Sn 0.5 O 2 has been synthesized via electrochemically-driven Li + for Na + exchange in O3-NaNi 0.5 Sn 0.5 O 2 . The crystal structure of Li 0.35 Na 0.07 Ni 0.5 Sn 0.5 O 2 was Rietveld-refined from powder X-ray diffraction data ( a = 3.03431(7) Å, c = 14.7491(8) Å, S. G. R 3̄ m ). It preserves the O3 stacking sequence of the parent compound, but with ∼13% lower unit cell volume. Electron diffraction and atomic-resolution scanning transmission electron microscopy imaging revealed short-range Ni/Sn ordering in both the pristine and Li-exchanged materials that is similar to the "honeycomb" Li/M ordering in Li 2 MO 3 oxides. As supported by bond-valence sum and density functional theory calculations, this ordering is driven by charge difference between Ni 2+ and Sn 4+ and the necessity to maintain balanced bonding for the oxygen anions. Li 0.35 Na 0.07 Ni 0.5 Sn 0.5 O 2 demonstrates reversible electrochemical (de)intercalation of ∼0.21 Li + in the 2.8-4.3 V vs. Li/Li + potential range. Limited electrochemical activity is attributed to a formation of the surface Li/Ni disordered rock-salt barrier layer as the Li + for Na + exchange drastically reduces the energy barrier for the Li/Ni antisite disorder., Competing Interests: The authors declare no conflict of interest., (This journal is © The Royal Society of Chemistry.)

To realize high-power performance, lithium-ion batteries require stable, environmentally benign, and economically viable noncarbonaceous anode materials capable of operating at high rates with low strain during charge-discharge. In this paper, we report the synthesis, crystal structure, and electrochemical properties of a new titanium-based member of the MPO 4 phosphate series adopting the α-CrPO 4 structure type. α-TiPO 4 has been obtained by thermal decomposition of a novel hydrothermally prepared fluoride phosphate, NH 4 TiPO 4 F, at 600 °C under a hydrogen atmosphere. The crystal structure of α-TiPO 4 is refined from powder X-ray diffraction data using a Rietveld method and verified by electron diffraction and high-resolution scanning transmission electron microscopy, whereas the chemical composition is confirmed by IR, energy-dispersive X-ray, electron paramagnetic resonance, and electron energy loss spectroscopies. Carbon-coated α-TiPO 4 /C demonstrates reversible electrochemical activity ascribed to the Ti 3+ /Ti 2+ redox transition delivering 125 mAh g -1 specific capacity at C/10 in the 1.0-3.1 V versus Li + /Li potential range with an average potential of ∼1.5 V, exhibiting good rate capability and stable cycling with volume variation not exceeding 0.5%. Below 0.8 V, the material undergoes a conversion reaction, further revealing capacitive reversible electrochemical behavior with an average specific capacity of 270 mAh g -1 at 1C in the 0.7-2.9 V versus Li + /Li potential range. This work suggests a new synthesis route to metastable titanium-containing phosphates holding prospective to be used as negative electrode materials for metal-ion batteries.

"Spinel-layered" Li 1+ x Ni 0.5 Mn 1.5 O 4 ( x = 0, 0.5, 1) materials are considered as a cobalt-free alternative to currently used positive electrode (cathode) materials for Li-ion batteries. In this work, their electrochemical properties and corresponding phase transitions were studied by means of synchrotron X-ray powder diffraction (SXPD) in operando regime. Within the potential limit of 2.2-4.9 V vs. Li/Li + LiNi 0.5 Mn 1.5 O 4 with cubic spinel type structure demonstrates the capacity of 230 mAh·g -1 associated with three first-order phase transitions with significant total volume change of 8.1%. The Li 2 Ni 0.5 Mn 1.5 O 4 material exhibits similar capacity value and subsequence of the phase transitions of the spinel phase, although the fraction of the spinel-type phase in this material does not exceed 30 wt.%. The main component of Li 2 Ni 0.5 Mn 1.5 O 4 is Li-rich layered oxide Li(Li 0.28 Mn 0.64 Ni 0.08 )O 2 , which provides nearly half of the capacity with very small unit cell volume change of 0.7%. Lower mechanical stress associated with Li (de)intercalation provides better cycling stability of the spinel-layered complex materials and makes them more perspective for practical applications compared to the single-phase LiNi 0.5 Mn 1.5 O 4 high-voltage cathode material.

Lithium iron phosphate, LiFePO 4 , a widely used cathode material in commercial Li-ion batteries, unveils a complex defect structure, which is still being deciphered. Using a combined computational and experimental approach comprising density functional theory (DFT)+ U and molecular dynamics calculations and X-ray and neutron diffraction, we provide a comprehensive characterization of various OH point defects in LiFePO 4 , including their formation, dynamics, and localization in the interstitial space and at Li, Fe, and P sites. It is demonstrated that one, two, and four (five) OH groups can effectively stabilize Li, Fe, and P vacancies, respectively. The presence of D (H) at both Li and P sites for hydrothermally synthesized deuterium-enriched LiFePO 4 is confirmed by joint X-ray and neutron powder diffraction structure refinement at 5 K that also reveals a strong deficiency of P of 6%. The P occupancy decrease is explained by the formation of hydrogarnet-like P/4H and P/5H defects, which have the lowest formation energies among all considered OH defects. Molecular dynamics simulation shows a rich structural diversity of these defects, with OH groups pointing both inside and outside vacant P tetrahedra creating numerous energetically close conformers, which hinders their explicit localization with diffraction-based methods solely. The discovered conformers include structural water molecules, which are only by 0.04 eV/atom H higher in energy than separate OH defects.

Sodium ion batteries, because of their sustainability attributes, could be an attractive alternative to Li-ion technology for specific applications. However, it remains challenging to design high energy density and moisture stable Na-based positive electrodes. Here, we report an O3-type NaLi 1/3 Mn 2/3 O 2 phase showing anionic redox activity, obtained through a ceramic process by carefully adjusting synthesis conditions and stoichiometry. This phase shows a sustained reversible capacity of 190 mAh g -1 that is rooted in cumulative oxygen and manganese redox processes as deduced by combined spectroscopy techniques. Unlike many other anionic redox layered oxides so far reported, O3-NaLi 1/3 Mn 2/3 O 2 electrodes do not show discernible voltage fade on cycling. This finding, rationalized by density functional theory, sheds light on the role of inter- versus intralayer 3d cationic migration in ruling voltage fade in anionic redox electrodes. Another practical asset of this material stems from its moisture stability, hence facilitating its handling and electrode processing. Overall, this work offers future directions towards designing highly performing sodium electrodes for advanced Na-ion batteries.

Composite positive electrode materials (1- x ) LiNi 0.8 Mn 0.1 Co 0.1 O 2 ∙ x Li 2 SO 4 ( x = 0.002-0.005) for Li-ion batteries have been synthesized via conventional hydroxide or carbonate coprecipitation routes with subsequent high-temperature lithiation in either air or oxygen atmosphere. A comparative study of the materials prepared from transition metal sulfates (i.e., containing sulfur) and acetates (i.e., sulfur-free) with powder X-ray diffraction, electron diffraction, high angle annular dark field transmission electron microscopy, energy-dispersive X-ray spectroscopy, and electron energy loss spectroscopy revealed that the sulfur-containing species occur as amorphous Li 2 SO 4 at the grain boundaries and intergranular contacts of the primary NMC811 crystallites. This results in a noticeable enhancement of rate capability and capacity retention over prolonged charge/discharge cycling compared to their sulfur-free analogs. The improvement is attributed to suppressing the high voltage phase transition and the associated accumulation of anti-site disorder upon cycling and improving the secondary agglomerates' mechanical integrity by increasing interfacial fracture toughness through linking primary NMC811 particles with soft Li 2 SO 4 binder, as demonstrated with nanoindentation experiments. As the synthesis of the (1- x ) LiNi 0.8 Mn 0.1 Co 0.1 O 2 ∙ x Li 2 SO 4 composites do not require additional operational steps to introduce sulfur, these electrode materials might demonstrate high potential for commercialization.

A new monoclinic α-polymorph of the Na 2 FePO 4 F fluoride-phosphate has been directly synthesized via a hydrothermal method for application in metal-ion batteries. The crystal structure of the as-prepared α-Na 2 FePO 4 F studied with powder X-ray and neutron diffraction ( P 2 1 / c , a = 13.6753(10) Å, b = 5.2503(2) Å, c = 13.7202(8) Å, β = 120.230(4)°) demonstrates strong antisite disorder between the Na and Fe atoms. As revealed with DFT-based calculations, α-Na 2 FePO 4 F has low migration barriers for Na + along the main pathway parallel to the b axis, and an additional diffusion bypass allowing the Na + cations to go around the Na/Fe antisite defects. These results corroborate with the extremely high experimental Na-ion diffusion coefficient of (1-5)·10 -11 cm 2 ·s -1 , which is 2 orders of magnitude higher than that for the orthorhombic β-polymorph ((5-10)·10 -13 cm 2 ·s -1 ). Being tested as a cathode material in Na- and Li-ion battery cells, monoclinic α-Na 2 FePO 4 F exhibits a reversible specific capacity of 90 and 80 mAh g -1 , respectively.

Metal-ion batteries are key enablers in today's transition from fossil fuels to renewable energy for a better planet with ingeniously designed materials being the technology driver. A central question remains how to wisely manipulate atoms to build attractive structural frameworks of better electrodes and electrolytes for the next generation of batteries. This review explains the underlying chemical principles and discusses progresses made in the rational design of electrodes/solid electrolytes by thoroughly exploiting the interplay between composition, crystal structure and electrochemical properties. We highlight the crucial role of advanced diffraction, imaging and spectroscopic characterization techniques coupled with solid state chemistry approaches for improving functionality of battery materials opening emergent directions for further studies.

The Li 1.17 Ni 0.17 Mn 0.50 Co 0.17 O 2 Li-rich NMC positive electrode (cathode) for lithium-ion batteries has been coated with nanocrystals of the LiMn 1.5 Co 0.5 O 4 high-voltage spinel cathode material. The coating was applied through a single-source precursor approach by a deposition of the molecular precursor LiMn 1.5 Co 0.5 (thd) 5 (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) dissolved in diethyl ether, followed by thermal decomposition at 400 °C inair resulting in a chemically homogeneous cubic spinel. The structure and chemical composition of the coatings, deposited on the model SiO 2 spheres and Li-rich NMC crystallites, were analyzed using powder X-ray diffraction, electron diffraction, high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and energy-dispersive X-ray (EDX) mapping. The coated material containing 12 wt.% of spinel demonstrates a significantly improved first cycle Coulombic efficiency of 92% with a high first cycle discharge capacity of 290 mAhg -1 . The coating also improves the capacity and voltage retention monitored over 25 galvanostatic charge-discharge cycles, although a complete suppression of the capacity and voltage fade is not achieved.

Layered Li-rich/Mn-rich NMC (LMR-NMC) is characterized by high initial specific capacities of more than 250 mA h g -1 , lower cost due to a lower Co content and higher thermal stability than LiCoO 2 . However, its commercialisation is currently still hampered by significant voltage fade, which is caused by irreversible transition metal ion migration to emptied Li positions via tetrahedral interstices upon electrochemical cycling. This structural change is strongly correlated with anionic redox chemistry of the oxygen sublattice and has a detrimental effect on electrochemical performance. In a fully charged state, up to 4.8 V vs. Li/Li + , Mn 4+ is prone to migrate to the Li layer. The replacement of Mn 4+ for an isovalent cation such as Sn 4+ which does not tend to adopt tetrahedral coordination and shows a higher metal-oxygen bond strength is considered to be a viable strategy to stabilize the layered structure upon extended electrochemical cycling, hereby decreasing voltage fade. The influence of Sn 4+ on the voltage fade in partially charged LMR-NMC is not yet reported in the literature, and therefore, we have investigated the structure and the corresponding electrochemical properties of LMR-NMC with different Sn concentrations. We determined the substitution limit of Sn 4+ in Li 1.2 Ni 0.13 Co 0.13 Mn 0.54-x Sn x O 2 by powder X-ray diffraction and transmission electron microscopy to be x≈ 0.045. The limited solubility of Sn is subsequently confirmed by density functional theory calculations. Voltage fade for x = 0 and x = 0.027 has been comparatively assessed within the 3.00 V-4.55 V (vs. Li/Li + ) potential window, from which it is concluded that replacing Mn 4+ by Sn 4+ cannot be considered as a viable strategy to inhibit voltage fade within this window, at least with the given restricted doping level.

This work represents an important step in the quest to make hetero multi metallic molecules featuring specific metal types and complicated metal ratios. The rational design, synthesis, and characterization of a complex hetero tri metallic single-source molecular precursor for the next generation sodium-ion battery cathode material, Na 2 Mn 2 FeO 6 , is described. A unique pentametallic platform [Mn II (ptac) 3 -Na-Mn III (acac) 3 -Na-Mn II (ptac) 3 ] ( 1 ) was derived from the known polymeric structure of [NaMn II (acac) 3 ] ∞ , through a series of elaborate design procedures, such as mixed-ligand, unsymmetric ligand, and mixed-valent approaches. Importantly, the application of those techniques results in a molecule with distinctively different transition metal positions in terms of ligand environment and oxidation states. An isovalent substitution of Fe III for the central Mn III ion forms the target hetero tri metallic precursor [Mn II (ptac) 3 -Na-Fe III (acac) 3 -Na-Mn II (ptac) 3 ] ( 3 ) with an appropriate metal ratio of Na:Mn:Fe = 2:2:1. The arrangement of metal ions and ligands in this pentametallic assembly was confirmed by single crystal X-ray investigation. The unambiguous assignment of the positions and oxidation states of the Periodic Table neighbors Fe and Mn in 3 has been achieved by a combination of investigative techniques that include synchrotron resonant diffraction, X-ray multiwavelength anomalous diffraction, X-ray fluorescence spectroscopy, Mössbauer spectroscopy, and gas-phase DART mass spectrometry. The hetero tri metallic single-source precursor 3 was shown to exhibit a clean decomposition pattern yielding the phase-pure P2-Na 2 Mn 2 FeO 6 quaternary oxide with high uniformity of metal ion distribution as confirmed by electron microscopy.

Li-ion battery performance and life cycle strongly depend on a passivation layer called solid-electrolyte interphase (SEI). Its structure and composition are studied in great details, while its formation process remains elusive due to difficulty of in situ measurements of battery electrodes. Here we provide a facile methodology for in situ atomic force microscopy (AFM) measurements of SEI formation on cross-sectioned composite battery electrodes allowing for direct observations of SEI formation on various types of carbonaceous negative electrode materials for Li-ion batteries. Using this approach, we observed SEI nucleation and growth on highly oriented pyrolytic graphite (HOPG), MesoCarbon MicroBeads (MCMB) graphite, and non-graphitizable amorphous carbon (hard carbon). Besides the details of the formation mechanism, the electrical and mechanical properties of the SEI layers were assessed. The comparative observations revealed that the electrode potentials for SEI formation differ depending on the nature of the electrode material, whereas the adhesion of SEI to the electrode surface clearly correlates with the surface roughness of the electrode. Finally, the same approach applied to a positive LiNi 1/3 Mn 1/3 Co 1/3 O 2 electrode did not reveal any signature of cathodic SEI thus demonstrating fundamental differences in the stabilization mechanisms of the negative and positive electrodes in Li-ion batteries.

Hard carbon (HC) is considered as a negative electrode material for potassium-ion batteries, but it suffers from significant irreversible capacity loss at the first discharge cycle. Here, we investigated the possible reasons of this capacity loss with a combination of in situ AFM and various ex situ TEM techniques (high resolution TEM and high angle annular dark field scanning TEM imaging, and STEM-EELS and STEM-EDX spectroscopic mapping) targeting the electrode/electrolyte interphase formation process in the carbonate-based electrolyte with and without vinylene carbonate (VC) as an additive. The studied HC consists of curved graphitic layers arranged into short packets and round cages, the latter acting as traps for K + ions causing low Coulombic efficiency between cycling. Our comparative study of solid electrolyte interphase (SEI) formation in the carbonate-based electrolyte with and without the VC additive revealed that in the pristine electrolyte, the SEI consists mostly of inorganic components, whereas adding VC introduces a polymeric organic component to the SEI, increasing its elasticity and stability against fracturing upon HC expansion/contraction during electrochemical cycling. Additionally, significant K + loss occurs due to Na + for K + exchange in Na-carboxymethyl cellulose used as a binder. These findings reflect the cumulative impact of the internal HC structure, SEI properties, and binder nature into the electrochemical functional properties of the HC-based anodes for K-ion batteries.

Solid electrolytes have regained tremendous interest recently in light of the exposed vulnerability of current rechargeable battery technologies. While designing solid electrolytes, most efforts concentrated on creating structural disorder (vacancies, interstitials, etc.) in a cationic Li/Na sublattice to increase ionic conductivity. In phosphates, the ionic conductivity can also be increased by rotational disorder in the anionic sublattice, via a paddle-wheel mechanism. Herein, we report on Na 4 Zn(PO 4 ) 2 which is designed from Na 3 PO 4 , replacing Na + with Zn 2+ and introducing a vacancy for charge balance. We show that Na 4 Zn(PO 4 ) 2 undergoes a series of structural transitions under temperature, which are associated with an increase in ionic conductivity by several orders of magnitude. Our detailed crystallographic study, combining electron, neutron, and X-ray powder diffraction, reveals that the room-temperature form, α-Na 4 Zn(PO 4 ) 2 , contains orientationally ordered PO 4 groups, which undergo partial and full rotational disorder in the high-temperature β- and γ-polymorphs, respectively. We furthermore showed that the highly conducting γ-polymorph could be stabilized at room temperature by ball-milling, whereas the β-polymorph can be stabilized by partial substitution of Zn 2+ with Ga 3+ and Al 3+ . These findings emphasize the role of rotational disorder as an extra parameter to design new solid electrolytes.

The rapid progress in mass-market applications of metal-ion batteries intensifies the development of economically feasible electrode materials based on earth-abundant elements. Here, we report on a record-breaking titanium-based positive electrode material, KTiPO 4 F, exhibiting a superior electrode potential of 3.6 V in a potassium-ion cell, which is extraordinarily high for titanium redox transitions. We hypothesize that such an unexpectedly major boost of the electrode potential benefits from the synergy of the cumulative inductive effect of two anions and charge/vacancy ordering. Carbon-coated electrode materials display no capacity fading when cycled at 5C rate for 100 cycles, which coupled with extremely low energy barriers for potassium-ion migration of 0.2 eV anticipates high-power applications. Our contribution shows that the titanium redox activity traditionally considered as "reducing" can be upshifted to near-4V electrode potentials thus providing a playground to design sustainable and cost-effective titanium-containing positive electrode materials with promising electrochemical characteristics.

The production of hydrogen at a large scale by the environmentally-friendly electrolysis process is currently hampered by the slow kinetics of the oxygen evolution reaction (OER). We report a solid electrocatalyst α-Li 2 IrO 3 which upon oxidation/delithiation chemically reacts with water to form a hydrated birnessite phase, the OER activity of which is five times greater than its non-reacted counterpart. This reaction enlists a bulk redox process during which hydrated potassium ions from the alkaline electrolyte are inserted into the structure while water is oxidized and oxygen evolved. This singular charge balance process for which the electrocatalyst is solid but the reaction is homogeneous in nature allows stabilizing the surface of the catalyst while ensuring stable OER performances, thus breaking the activity/stability tradeoff normally encountered for OER catalysts.

High-energy-density lithium-rich materials are of significant interest for advanced lithium-ion batteries, provided that several roadblocks, such as voltage fade and poor energy efficiency are removed. However, this remains challenging as their functioning mechanisms during first cycle are not fully understood. Here we enlarge the cycling potential window for Li 1.2 Ni 0.13 Mn 0.54 Co 0.13 O 2 electrode, identifying novel structural evolution mechanism involving a structurally-densified single-phase A' formed under harsh oxidizing conditions throughout the crystallites and not only at the surface, in contrast to previous beliefs. We also recover a majority of first-cycle capacity loss by applying a constant-voltage step on discharge. Using highly reducing conditions we obtain additional capacity via a new low-potential P" phase, which is involved into triggering oxygen redox on charge. Altogether, these results provide deeper insights into the structural-composition evolution of Li 1.2 Ni 0.13 Mn 0.54 Co 0.13 O 2 and will help to find measures to cure voltage fade and improve energy efficiency in this class of material.

Rational design of technologically important exotic perovskites is hampered by the insufficient geometrical descriptors and costly and extremely high-pressure synthesis, while the big-data driven compositional identification and precise prediction entangles full understanding of the possible polymorphs and complicated multidimensional calculations of the chemical and thermodynamic parameter space. Here we present a rapid systematic data-mining-driven approach to design exotic perovskites in a high-throughput and discovery speed of the A 2 BB 'O 6 family as exemplified in A 3 TeO 6 . The magnetoelectric polar magnet Co 3 TeO 6 , which is theoretically recognized and experimentally realized at 5 GPa from the six possible polymorphs, undergoes two magnetic transitions at 24 and 58 K and exhibits helical spin structure accompanied by magnetoelastic and magnetoelectric coupling. We expect the applied approach will accelerate the systematic and rapid discovery of new exotic perovskites in a high-throughput manner and can be extended to arbitrary applications in other families.

The applicability of electron diffraction tomography to the structure solution and refinement of charged, discharged or cycled metal-ion battery positive electrode (cathode) materials is discussed in detail. As these materials are often only available in very small amounts as powders, the possibility of obtaining single-crystal data using electron diffraction tomography (EDT) provides unique access to crucial information complementary to X-ray diffraction, neutron diffraction and high-resolution transmission electron microscopy techniques. Using several examples, the ability of EDT to be used to detect lithium and refine its atomic position and occupancy, to solve the structure of materials ex situ at different states of charge and to obtain in situ data on structural changes occurring upon electrochemical cycling in liquid electrolyte is discussed.

NASICON-structured Na 3 V 2 O 2 x (PO 4 ) 2 F 3-2 x (0 < x ≤ 1) solid solutions have been prepared using a microwave-assisted hydrothermal (MW-HT) technique. Well-crystallized phases were obtained for x = 1 and 0.4 by reacting V 2 O 5 , NH 4 H 2 PO 4 , and NaF precursors at temperatures as low as 180-200 °C for less than 15 min. Various available and inexpensive reducing agents were used to control the vanadium oxidation state and final product morphology. The vanadium oxidation state and O/F ratios were assessed using electron energy loss spectroscopy and infrared spectroscopy. According to electron diffraction and powder X-ray diffraction, the Na 3 V 2 O 2 x (PO 4 ) 2 F 3-2 x solid solutions crystallized in a metastable disordered I 4/ mmm structure ( a = 6.38643(4) Å, c = 10.62375(8) Å for Na 3 V 2 O 2 (PO 4 ) 2 F and a = 6.39455(5) Å, c = 10.6988(2) Å for Na 3 V 2 O 0.8 (PO 4 ) 2 F 2.2 ). With respect to electrochemical Na + (de)insertion as positive electrodes (cathodes) for Na-ion batteries, the as-synthesized materials displayed two sloping plateaus upon charge and discharge, centered near 3.5-3.6 V and 4.0-4.1 V vs. Na + /Na, respectively, with a reversible capacity of ∼110 mA h g -1 . The application of a conducting carbon coating through the surface polymerization of dopamine with subsequent annealing at 500 °C improved both the rate capability (∼55 mA h g -1 at a discharge rate of 10C) and capacity retention (∼93% after 50 cycles at a discharge rate of C/2)., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

In this paper, we report on a novel α-VPO 4 phosphate adopting the α-CrPO 4 type structure as a promising anode material for rechargeable metal-ion batteries. Obtained by heat treatment of a structurally related hydrothermally prepared KTiOPO 4 -type NH 4 VOPO 4 precursor under reducing conditions, the α-VPO 4 material appears stable in a wide temperature range and possesses an interesting "sponged" needle-like particle morphology. The electrochemical performance of α-VPO 4 as the anode material was examined in Li-, Na-, and K-based cells. The carbon-coated α-VPO 4 /C composite exhibits 185, 110, and 37 mA h/g specific capacities respectively at the first discharge and around 120, 80, and 30 mA h/g at consecutive cycles at a C/10 rate. The considerable capacity drop after the first cycle in Li and Na cells is presumably due to irreversible alkali ion consumption taking place upon alkali-ion de/insertion. The EDX analysis of the recovered electrodes revealed an uptake of ∼23% of Na after the first discharge with significant cell parameter alteration validated by operando XRD measurements. In contrast to the known β-VPO 4 anode materials, both Li and Na de/insertion into the new α-VPO 4 proceed via an intercalation mechanism with the parent structural framework preserved but not via a conversion mechanism. The dimensionality of alkali-ion migration pathways and diffusion energy barriers was analyzed by the BVEL approach. Na-ion diffusion coefficients measured by the potentiostatic intermittent titration technique are in the range of (0.3-1.0)·10 -10 cm 2 /s, anticipating α-VPO 4 as a prospective high-power anode material for Na-ion batteries.

Hypothesis: Hydrophobic bacteriochlorin based photosensitizer (PS) can be effectively immobilized on MNP covered by human serum albumin (HSA). PS loading into MNP protein shell allows solubilizing PS in water solution without altering its photodynamic activity. MNP@PS can serve as diagnostic tool for tracking PS delivery to tumor tissues by MRI., Experiments: Immobilization on MNP-HSA-PEG was performed by adding PS solution in organic solvents with further purification. MNP@PS were characterized by DLS, HAADF STEM and AFM. Absorbance and fluorescence measurements were used to assess PS photophysical properties before and after immobilization. MNP@PS internalization into CT26 cells was investigated by confocal microscopy in vitro and MRI/IVIS were used for tracking MNP@PS delivery to tumors in vivo., Findings: MNP@PS complexes were stable in water solution and retained PS photophysical activity. The length of side chain affected MNP@PS size, loading capacity and cell internalization. In vitro testing demonstrated MNP@PS delivery to cancer cells followed by photoinduced toxicity. In vivo studies confirmed that as-synthetized complexes can be used for MRI tracking over drug accumulation in tumors., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Perovskite oxides are active room-temperature bifunctional oxygen electrocatalysts in alkaline media, capable of performing the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) with lower combined overpotentials relative to their precious metal counterparts. However, their semiconducting nature necessitates the use of activated carbons as conductive supports to generate applicably relevant current densities. In efforts to advance the performance and theory of oxide electrocatalysts, the chemical and physical properties of the oxide material often take precedence over contributions from the conductive additive. In this work, we find that carbon plays an important synergistic role in improving the performance of La1-xSrxCoO3-δ (0 ≤ x ≤ 1) electrocatalysts through the activation of O2 and spillover of radical oxygen intermediates, HO2- and O2-, which is further reduced through chemical decomposition of HO2- on the perovskite surface. Through a combination of thin-film rotating disk electrochemical characterization of the hydrogen peroxide intermediate reactions (hydrogen peroxide reduction reaction (HPRR), hydrogen peroxide oxidation reaction (HPOR)) and oxygen reduction reaction (ORR), surface chemical analysis, HR-TEM, and microkinetic modeling on La1-xSrxCoO3-δ (0 ≤ x ≤ 1)/carbon (with nitrogen and non-nitrogen doped carbons) composite electrocatalysts, we deconvolute the mechanistic aspects and contributions to reactivity of the oxide and carbon support.

Two new sodium nickel phosphates, Na 5 Ni 2 (PO 4 ) 3 ·H 2 O (I) and Na 6 Ni 2 (PO 4 ) 3 OH (II), have been synthesized hydrothermally and characterized by synchrotron X-ray diffraction, electron diffraction, low-temperature thermodynamic and magnetic measurements, and ab initio calculations. Unlike the majority of Ni 2+ compounds, I and II show predominant ferromagnetic exchange couplings. I crystallizes in the monoclinic space group P2 1 / n ( a = 14.0395(4) Å, b = 5.1847(14) Å, c = 16.4739(4) Å, β = 110.4186(14)°) and features chains of ferromagnetically coupled Ni 2+ ions. In II with the orthorhombic space group Pcmb ( a = 7.5007(15) Å, b = 21.4661(4) Å, c = 7.1732(15) Å), the ferromagnetically coupled Ni 2+ ions form dimers arranged on a spin ladder. Both compounds represent rare examples of quasi-one-dimensional ferromagnets. Structural features behind this unusual magnetic behavior are discussed.

Design of hetero tri metallic molecules, especially those containing at least two different metals with close atomic numbers, radii, and the same coordination number/environment is a challenging task. This quest is greatly facilitated by having a heterobimetallic parent molecule that features multiple metal sites with only some of those displaying substitutional flexibility. Recently, a unique heterobimetallic complex LiMn 2 (thd) 5 (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) has been introduced as a single-source precursor for the preparation of a popular spinel cathode material, LiMn 2 O 4 . Theoretical calculations convincingly predict that in the above trinuclear molecule only one of the Mn sites is sufficiently flexible to be substituted with another 3d transition metal. Following those predictions, two hetero tri metallic complexes, LiMn 2- x Co x (thd) 5 ( x = 1 ( 1a ) and 0.5 ( 1b )), that represent full and partial substitution, respectively, of Co for Mn in the parent molecule, have been synthesized. X-ray structural elucidation clearly showed that only one transition metal position in the trinuclear molecule contains Co, while the other site remains fully occupied by Mn. A number of techniques have been employed for deciphering the structure and composition of hetero tri metallic compounds. Synchrotron resonant diffraction experiments unambiguously assigned 3d transition metal positions as well as provided a precise "site-specific Mn/Co elemental analysis" in a single crystal, even in an extremely difficult case of severely disordered structure formed by the superposition of two enantiomers. DART mass spectrometry and magnetic measurements clearly confirmed the presence of hetero tri metallic species LiMnCo(thd) 5 rather than a statistical mixture of two hetero bi metallic LiMn 2 (thd) 5 and LiCo 2 (thd) 5 molecules. Heterometallic precursors 1a and 1b were found to exhibit a clean decomposition yielding phase-pure LiMnCoO 4 and LiMn 1.5 Co 0.5 O 4 spinels, respectively, at the relatively low temperature of 400 °C. The latter oxide represents an important "5 V spinel" cathode material for the lithium ion batteries. Transmission electron microscopy confirmed a homogeneous distribution of transition metals in quaternary oxides obtained by pyrolysis of single-source precursors.

We demonstrate that changes in the unit cell structure of lithium battery cathode materials during electrochemical cycling in liquid electrolyte can be determined for particles of just a few hundred nanometers in size using in situ transmission electron microscopy (TEM). The atomic coordinates, site occupancies (including lithium occupancy), and cell parameters of the materials can all be reliably quantified. This was achieved using electron diffraction tomography (EDT) in a sealed electrochemical cell with conventional liquid electrolyte (LP30) and LiFePO 4 crystals, which have a well-documented charged structure to use as reference. In situ EDT in a liquid environment cell provides a viable alternative to in situ X-ray and neutron diffraction experiments due to the more local character of TEM, allowing for single crystal diffraction data to be obtained from multiphased powder samples and from submicrometer- to nanometer-sized particles. EDT is the first in situ TEM technique to provide information at the unit cell level in the liquid environment of a commercial TEM electrochemical cell. Its application to a wide range of electrochemical experiments in liquid environment cells and diverse types of crystalline materials can be envisaged.

The electrolysis of water is of global importance to store renewable energy and the methodical design of next-generation oxygen evolution catalysts requires a greater understanding of the structural and electronic contributions that give rise to increased activities. Herein, we report a series of Ruddlesden-Popper La 0.5 Sr 1.5 Ni 1-x Fe x O 4±δ oxides that promote charge transfer via cross-gap hybridization to enhance electrocatalytic water splitting. Using selective substitution of lanthanum with strontium and nickel with iron to tune the extent to which transition metal and oxygen valence bands hybridize, we demonstrate remarkable catalytic activity of 10 mA cm -2 at a 360 mV overpotential and mass activity of 1930 mA mg -1 ox at 1.63 V via a mechanism that utilizes lattice oxygen. This work demonstrates that Ruddlesden-Popper materials can be utilized as active catalysts for oxygen evolution through rational design of structural and electronic configurations that are unattainable in many other crystalline metal oxide phases.

The ABO 3 perovskite oxides exhibit a wide range of interesting physical phenomena remaining in the focus of extensive scientific investigations and various industrial applications. In order to form a perovskite structure, the cations occupying the A and B positions in the lattice, as a rule, should be different. Nevertheless, the unique binary perovskite manganite Mn 2 O 3 containing the same element in both A and B positions can be synthesized under high-pressure high-temperature conditions. Here, we show that this material exhibits magnetically driven ferroelectricity and a pronounced magnetoelectric effect at low temperatures. Neutron powder diffraction revealed two intricate antiferromagnetic structures below 100 K, driven by a strong interplay between spin, charge, and orbital degrees of freedom. The peculiar multiferroicity in the Mn 2 O 3 perovskite is ascribed to a combined effect involving several mechanisms. Our work demonstrates the potential of binary perovskite oxides for creating materials with highly promising electric and magnetic properties.