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Synchrotron radiation based techniques are powerful tools for battery research and allow probing a wide range of length scales, with different depth sensitivities and spatial/temporal resolutions. Operando experiments enable characterization during functioning of the cell and are thus a precious tool to elucidate the reaction mechanisms taking place. In this perspective, the current state of the art for the most relevant techniques (scattering, spectroscopy, and imaging) is discussed together with the bottlenecks to address, either specific for application in the battery field or more generic. The former includes the improvement of cell designs, multi-modal characterization and development of protocols for automated or at least semi-automated data analysis to quickly process the huge amount of data resulting from operando experiments. Given the recent evolution in these areas, accelerated progress is expected in the years to come, which should in turn foster battery performance improvements., The authors are grateful for funding through PTI+ TRANS-ENER+: “Alta Tecnología clave en la transición en el ciclo energético”, part of the CSIC program for the Spanish Recovery, Transformation and Resilience Plan funded by the Recovery and Resilience Facility of the European Union, established by the Regulation (EU) 2020/2094. ICMAB-CSIC members thank the Spanish Agencia Estatal de Investigación Severo Ochoa Programme for Centres of Excellence in R&D (CEX2019-000917-S)., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).

Rare earth activated nitridosilicates have important applications as phosphor components in white light emitting diodes. (Oxy)nitridosilicates with beta-K2SO4 structure doped with Eu2+ are luminescent materials with emission wavelengths ranging from green to red under excitation with blue-UV light. Here we report the synthesis of isostructural NdEuSiO3N and the new oxynitridosilicate NdEuSiO3N by solid state reaction between Nd2O3, NdN, Eu2O3 or SrO and Si3N4 under N-2/H-2 gas at temperatures of 1300 degrees C and 1500 degrees C respectively. These compounds are the limiting compositions of the solid solution NdSr1-xEuxO3N crystallizing in the space group Pmnb with cell parameters a = 5.62293(1), b = 7.02285(1), c = 9.64784(2) A for NdEuSiO3N, and a = 5.63074(9), b = 7.01658(10), c = 9.65765(15) A for NdSrSiO3N. The Nd(3+)and Eu2+ cations in NdEuSiO3N or Nd3+ and Sr2+ in NdSrSiO3N show partial order in the two available crystallographic sites of coordination numbers 10 (M1) and 9 (M2), with strongly preferred occupancy of the larger divalent cations Eu2+ (77%) and Sr2+ (78%) for the M1 site, whereas the M2 site is preferred by Nd3+. Magnetic susceptibility measurements down to 2 K show that NdEuSiO3N is ferromagnetic with Tc = 3 K, in contrast to NdSrSiO3N that shows antiferromagnetic interactions at low temperatures. The band gaps of NdEuSiO3N and NdSrSiO3N determined from diffuse reflection spectroscopy are 2.37 and 3.72 eV respectively. NdEuSiO3N and the members of the solid solution NdSr0.98Eu0.02SiO3N and NdSr0.5Eu0.5SiO3N are orange-red light emitting luminescent materials, showing a broad emission band centered between 605 and 639 nm under excitation at 405 nm. These compounds are new phosphor materials with emission wavelengths shifted to the red with respect to the isostructural oxysilicates, which is induced by the introduction of nitride., This work was supported by the Ministerio de Ciencia e Innovación, Spain (PID2020-113805 ​GB-I00 and CEX2019-000917-S), and it has been developed under the PhD program in Materials Science of the UAB. We thank Alba for beam time provision and Dr. François Fauth for assistance in data collection at Alba. We acknowledge assistance from ICMAB-CSIC Scientific & Technological Services: X-Ray Diffraction (Mr. Joan Esquius), Thermal Analysis (Ms. Roberta Ceravola), Spectroscopic Techniques (Dr. Vega Lloveras) and Low Temperatures and Magnetometry (Dr. Bernat Bozzo). JRG acknowledges the AEI predoctoral fellowship PRE2018-085204., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S)., SI

Magnesium batteries have attracted great attention as an alternative to Li-ion batteries but still suffer from limited choice of positive electrode materials. V2O5 exhibits high theoretical capacities, but previous studies have been mostly limited to α-V2O5. Herein, we report on the β-V2O5 polymorph as a Mg intercalation electrode. The structural changes associated with the Mg2+ (de-) intercalation were analyzed by a combination of several characterization techniques: in situ high resolution X-ray diffraction, scanning transmission electron microscopy, electron energy-loss spectroscopy, and X-ray absorption spectroscopy. The reversible capacity reached 361 mAh g-1, the highest value found at room temperature for V2O5 polymorphs., The authors are grateful to the ALBA synchrotron for beamtime (proposal 2021024935). The Spanish Agencia Estatal de Investigación Severo Ochoa FUNFUTURE (CEX2019-000917-S) Excellence Centre distinction, the European Union’s Horizon 2020 research and innovation programme under grant agreement 824066 (E-MAGIC), and Junta de Andalucía (EMERGIA programme, grant 00153) are gratefully acknowledged. G.C.B.A., P.P., R.F.K., and J.C. were solely supported by the Joint Center for Energy Storage Research (JCESR) and Energy Innovation Hub funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences. I.R. acknowledges support from the National Science Foundation via grant DMR-2118020. This research used resources of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract DE-SC0012704. The authors acknowledge the free distribution of VESTA software, With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).

Defects in crystalline structures play a vital role in their properties, so their proper characterization is essential to understanding and improving the behaviour of the materials. In this work, their presence in Ca4Fe9O17 has been analysed. Its structure exhibits three different iron coordination topologies and can be described as layers of corner-sharing FeO5 bipyramids stacked along the c axis together with layers of edge-sharing FeO6 octahedra, both being linked by FeO4 tetrahedra. The relative position of the FeO4 tetrahedra generates three possible stacking directions, which results in stacking faults when more than one is combined. Structural refinement using the Rietveld method in X-ray and neutron powder diffraction data was not possible due to significant mismatches between the observed and calculated integrated intensities for several peaks resulting from this atomic disorder. Selected area electron diffraction (SAED) and high-resolution scanning transmission electron microscopy (HR-STEM) images confirm the local defective nature of the material. The FAULTS software enabled a successful refinement of the structure considering a high concentration of planar defects, conferred by the existence of three possible stacking directions in the crystal structure, all of them confined in the basal plane., We acknowledge beamtime at ALBA synchrotron (proposal 2019073634) and ILL (EASY access system) and Dr François Fauth and Dr Clemens Ritter, respectively, for their help during data collection. ICMAB authors acknowledge Spain's Agencia Estatal de Investigación Severo Ochoa Program for Centers of Excellence in R&D (CEX2019-000917-S) and funding through grant PID2020-113805GB-I00. ICTS-CNME at UCM is acknowledged for offering access to STEM microscopy and expertise., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).

Magnesium batteries have attracted great attention as an alternative to Li-ion batteries but still suffer from limited choice of positive electrode materials. V

1D Ca3Co2–zMzO6 (M = Co z = 0, M = Mn z = 1, and M = Fe z = 0.4) were prepared and tested electrochemically. While the iron-containing phase was not found to be active, the iron- and manganese-containing phases were found to be potentially interesting as positive electrode materials for calcium metal-based high-energy battery technologies and were investigated by operando synchrotron X-ray diffraction. Results indicate that electrochemically driven calcium deintercalation from the crystal structure (ca. 0.7 mol per formula unit) takes place upon oxidation in both cases. The oxidized phases have incommensurate modulated crystal structures with the space group R 3m(00γ)0s and a = 9.127(1) Å, c1 = 2.4226(3) Å and c2 = 4.1857(3) Å, and γ = 0.579 (M = Co) and a = 9.217(1) Å, c1 = 4.9076(4) Å and c2 = 4.3387(4) Å, and γ = 1.139 (M = Mn), which exhibit differences due to the presence of manganese and Mn/Co ordering. The degree of calcium re-intercalation within the structure was found to be extremely limited, if any. Complementary experiments carried out in lithium cells did not show any reversibility either, thus pointing at intrinsic structural/migration constraints in the oxidized phase rather than slow kinetics of high desolvation energies associated with divalent ion charge carriers., The authors are grateful to Alexandre Ponrouch and ALISTORE-ERI members for helpful discussions and to ALBA synchrotron for beamtime (proposal 2019073634). ICMAB-CSIC members thank the Spanish Agencia Estatal de Investigación Severo Ochoa Programme for Centres of Excellence in R&D (CEX2019-000917-S). D.M. acknowledges the EC for a H2020 MSCA-IF grant (contract number 743439). R.G.H. acknowledges the EC for a H2020 MSCADOC-FAM grant (contract number 754397).

Sustainability combined with high energy density prospects makes Fe-based oxides attractive as cathodes for calcium rechargeable batteries. This work presents a DFT evaluation of the CaFe2+nO4+n (0n3) family, for which both the average intercalation voltage and the theoretical specific capacity decrease with the increasing n value. The term n = 1/4, Ca4Fe9O17, meets the most appealing characteristics: a calculated average voltage of 4.16 V, a theoretical specific capacity of 230 mA h g-1 and the lowest energy barrier for Ca migration so far predicted for an existing oxide (0.72 eV). To overcome the previously reported synthesis difficulties, we employed a novel synthesis procedure in sealed quartz tubes followed by quenching in water. The XRD and SAED patterns of the prepared Ca4Fe9O17 powder reveal a certain degree of stacking defects along the c axis. Attempts to deinsert Ca ions from Ca4Fe9O17 by chemical means (NO2BF4 in ACN) and in electrochemical Ca cells were unsuccessful, although some hints of oxidation are observed in Li cells with the LP30 electrolyte. The suitability of Ca4Fe9O17 as a Ca cathode is pending further studies utilizing Ca-electrolytes with high anodic stability.

We present herein a systematic study of solvent co-intercalation during electrochemical reduction of titanium disulfide in lithium cells using state of the art in situ cells and synchrotron X-ray diffraction. To understand the role of the electrolyte components, four salts (LiBF4, LiBOB, LiPF6 and LiTFSI) and three solvents (ethylene carbonate, propylene carbonate and dimethyl carbonate) were investigated. Various types of in situ cells were assembled and X-ray diffraction patterns were collected in operando upon cycling. Co-intercalated phase formation was found to be triggered by the presence of propylene carbonate and to be electrochemically driven. This co-intercalated phase is formed in the early stages of reduction, with cell parameters a = 3.514 Å, c = 17.931 Å, corresponding approximately to a tripling of the pristine TiS2 cell along the c-axis. This phase does not seem to evolve upon further oxidation and hence induces an overall loss of capacity. Whereas the nature of the anion does not appear to influence the co-intercalated phase formation, the content of propylene carbonate in the electrolyte is clearly correlated to both its amount and the extent of capacity loss., The authors acknowledge funding from Ministry of Science and Innovation through grant MAT2017–86616-R, from the "Severo Ochoa" Programme for Centres of Excellence in R&D (CEX2019-000917-S). This project has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement N° 754397. The ALBA synchrotron is acknowledged for provision of beamtime within the in-house project program (proposals 2019013225 and 2020014004).

EuTi0.5W0.5O3-xNx oxynitrides with nitrogen contents between 0.87 and 1.63 have been synthesized by ammonolysis of EuTi0.5W0.5O4 scheelite at high temperature. They are B-site disordered perovskites that show two different crystal symmetries as a function of the nitrogen content, changing at x near 1.3 from cubic Pm-3m to orthorhombic Pbnm. The nitriding degree is tuned by the ammonia flow rate and synthesis temperature, and determines the oxidation states of the cations and the equilibrium Eu2+ ​+ ​W6+ ↔ Eu3++W5+ promoting the decrease of the tolerance factor and the structural transition for large x values and electronic reconstructions. Accompanying the symmetry lowering, the nature of the magnetic order of Eu2+ moments changes from ferromagnetic to antiferromagnetic as a result of a complex interplay of antiferromagnetic/ferromagnetic superexchange interactions balanced by structural effects and the carrier-mediated magnetic exchange between Eu2+ ions., This work was supported by the Spanish Ministerio de Ciencia, Universidades e Investigación, Spain (Projects MAT2017-86616-R and MAT2017-85232-R and from Generalitat de Catalunya (2017SGR1377, 2017SGR581). ICMAB acknowledges financial support from MINECO through the Severo Ochoa Program (SEV-2015-0496). We thank Alba synchrotron (Experiment number AV-2017092391) for the provision of beam time; we also thank Dr. François Fauth for assistance during data collection and Dr. Bernat Bozzo (ICMAB-CSIC) for performing the magnetic measurements.

The topotactic nitridation of cation ordered, tetragonal Sr2FeMoO6 in NH3 at moderate temperatures leads to cubic, Fm3[combining macron]m double perovskite oxynitride Sr2FeMoO4.9N1.1 where double-exchange interactions determine ferromagnetic order with TC ≈ 100 K. Substitution of oxide by nitride induces bond asymmetries and local electronically driven structural distortions, which combined with Fermi level lowering restricts charge itinerancy to confined regions and preclude spontaneous long-range magnetic order. Under a magnetic field, ferromagnetic correlations expand, favoring charge delocalization and a negative magnetoresistance is observed.

The topotactic nitridation of cation ordered, tetragonal Sr2FeMoO6 in NH3 at moderate temperatures leads to cubic, Fm[3 with combining macron]m double perovskite oxynitride Sr2FeMoO4.9N1.1 where double-exchange interactions determine ferromagnetic order with TC ≈ 100 K. Substitution of oxide by nitride induces bond asymmetries and local electronically driven structural distortions, which combined with Fermi level lowering restricts charge itinerancy to confined regions and preclude spontaneous long-range magnetic order. Under a magnetic field, ferromagnetic correlations expand, favoring charge delocalization and a negative magnetoresistance is observed., This work was supported by the Spanish Ministerio de Ciencia, Universidades e Investigación, Spain (Projects MAT2017-86616-R, MAT2017-85232-R, MAT2015-71664-R, MAT2015-67593-P and ENE2015-63969) and by Generalitat de Catalunya (2017SGR1377, 2017SGR581). ICMAB acknowledges financial support from MINECO through the Severo Ochoa Program (SEV-2015-0496). We thank the Institut Laue Langevin (ILL) and Alba synchrotron for the provision of beam time., We acknowledge support of the publication fee by the CSIC Open Access Support Initiative through its Unit of Information Resources for Research (URICI)

International audience; Vanadium pentoxide has been investigated for multivalent ion battery technologies but the structural characterization of inserted phases is poor, and conflicting reports exist in the literature. This study presents a critical overview of controversial aspects related to Mg and Ca insertion in α-V2O5 under diverse conditions by combined electrochemical and ex-situ XRD experiments. Galvanostatic tests are carried out in dry and wet alkyl carbonate-based electrolytes at RT and 100 °C. The formation of protonated phases with negligible divalent ion content if any is evidenced by Rietveld refinements of the XRD data, unambiguously dismissing the presence of AV2O5 (A: Mg, Ca) as electrochemical reduction products. Furthermore, thermal instability of V2O5 at 100 °C in alkyl carbonate solvents is demonstrated by XRD and TEM analysis and the formation of an orthorhombic phase with increased a parameter, most likely due to degradation favored by both water and temperature, is observed for both Mg and Ca. In order to assess the feasibility of the reverse reaction, fully intercalated AV2O5 (A = Ca, Mg) phases were also prepared by solid state reaction and oxidation attempted both electrochemically and chemically without evidence of any significant amount of Mg2+ or Ca2+ extraction, further corroborating the sluggish diffusion kinetics of divalent cations in α-V2O5.

RHfO2N perovskites with R = La, Nd and Sm show a GdFeO3-type structure and are semiconductors with band gaps of 3.35, 3.40 and 2.85 eV and relative dielectric constants of 30, 16 and 28 respectively. These compounds have adequate reduction and oxidation potentials to conduct the overall water splitting reaction, and the analogous perovskite LaZrO2N with a band gap of 2.8 eV shows photocatalytic activity under visible light irradiation for O2 evolution.

A simple crossover from two-dimensional to three-dimensional correlated disorder of O and N atoms on a cubic lattice has been discovered within the Ba1xSrxTaO2N series of perovskite oxynitrides. The crossover is driven by lattice expansion as x decreases, and provides a rapid increase in entropy due to a change from subextensive to extensive configurational entropy regimes., We thank STFC, UK for support for H. J. and provision of ISIS beamtime, and EPSRC for additional support. This work was also supported by the Ministerio de Economia y Competitividad (MINECO), Spain through Project MAT2017-86616-R, the Severo Ochoa Program SEV-2015-0496, and Fellowship support to AB (MAT2011-24757). We thank the ALBA synchrotron for the provision of beamtime and Prof. Rosa Palacin, Dr Carlos Frontera (ICMAB-CSIC) and Dr F. Fauth (ALBA) for assistance with data collection.

The new compounds LaSrSiO3N and LaBaSiO3N activated with Eu(2+) are orange-red light-emitting luminescent materials under excitation in the UV-blue range. They represent the first examples of stoichiometric alkaline earth oxynitridosilicates with a β-K2SO4 structure. The isostructural compound LaEuSiO3N is ferromagnetic with a Curie temperature of 3 K and also shows red luminescence (λmax = 705 nm) under excitation at 405 nm.

Layered MgMoN2 was prepared by solid state reaction at high temperature between Mo and Mg3N2 in N2 which represents a simple synthetic pathway compared to the previously reported method that used NaN3 as nitrogen source. The crystal structure of MgMoN2 was studied by synchrotron X-ray and neutron powder diffraction. The feasibility of oxidizing this compound and concomitantly extracting magnesium from the structure was assessed by both chemical and electrochemical approaches, using different protocols. The X-ray diffraction patterns of oxidized samples do not exhibit any relevant difference with respect to that of the as prepared MgMoN2 and no differences in the cell parameters are deduced from Rietveld refinements. No hints pointing at the presence of any amorphous phase are observed either. These results are rationalized through DFT calculated energy barriers for Mg2+ ion migration in MgMoN2, We acknowledge Ministerio de Ciencia e Innovación (Spain) for grants MAT2014-53500-R and MAT2015-67593-P, and for “Severo Ochoa” Programme for Centres of Excellence in R&D (SEV- 2015- 0496) awarded to ICMAB. We thank the Institut Laue Langevin (ILL) and Alba synchrotron for the provision of beamtime; we also thank Dr. Clemens Ritter (ILL) and Dr. F. Fauth (Alba) for assistance during data collection M.E. Arroyo acknowledges access to computational resources from Universidad de Oviedo (MALTA-Consolider cluster) and the Spanish's national high performance computer service (I2 Basque Centre).

This paper is part of the JES Focus Issue on Challenges in Novel Electrolytes, Organic Materials, and Innovative Chemistries for Batteries in Honor of Michel Armand., A comparative study of the reduction of TiS2 in diverse electrolyte formulations involving Ca(BF4)2 and Ca(TFSI)2 salts was carried out at different temperatures (from 25 °C to 100 °C). While for the former salt intercalation of calcium is only observed at high temperatures, calcium intercalated phases are also observed for the latter even at room temperature. The nature of the electrolyte does also have an impact on the relative amounts of the phases formed. Since Ca(TFSI)2 based electrolytes do not enable calcium plating, cycling was attempted using activated carbon as counterelectrode, and the reversibility of the process was ascertained. Even if corrosion of stainless steel current collectors and side reactions do still prevent proper cyclability, the results achieved should contribute to the establishment of reliable and viable cell set-up and methodology for the unambiguous study of the intercalation process in multivalent battery systems., Funding from the European Union's Horizon 2020 research and innovation programme H2020 FETOPEN-1-2016-2017 (CARBAT, grant agreement No. 766617) and ERC-2016-STG, (CAMBAT grant agreement No 715087) is gratefully acknowledged. Authors are grateful to the Spanish Ministry for Economy, Industry and Competitiveness Severo Ochoa Programme for Centres of Excellence in R&D (SEV-2015-0496).

Topochemical nitridation in ammonia at moderate temperatures of cation ordered Sr2FeWO6 produces new antiferromagnetic double perovskite oxynitrides Sr2FeWO6-xNx with 0 < x ≤ 1. Nitrogen introduction induces the oxidation of Fe2+ to Fe3+ and decreases TN from 38 K (x = 0) to 13 K for Sr2FeWO5N which represents the first example of a double perovskite oxynitride with both high cationic order and nitrogen content. This synthetic approach can be extended to other cation combinations expanding the possibility of new materials in the large group of double perovskites., This work was supported by the Spanish Ministerio de Economia y Competitividad (MINECO), Spain (Projects MAT2014-53500-R, MAT2015-71664-R, MAT2015-67593-P and ENE2015-63969) and it has been developed under the Materials Science PhD program of the Universitat Autònoma de Barcelona. Fellowship support to AB from MINECO (FPI, project MAT2011-24757) is gratefully acknowledged. ICMAB acknowledges financial support from MINECO through the Severo Ochoa Program (SEV- 2015-0496).

LnCrO3-xNx perovskites with Ln = La, Pr and Nd and nitrogen contents up to x = 0.59 have been synthesised through ammonolysis of LnCrO4 precursors. These new materials represent one of the few examples of chromium oxynitrides. Hole-doping through O(2-)/N(3-) anion substitution suppresses the magnetic transition far less drastically than Ln(3+)/M(2+) (M = Ca, Sr) cation substitutions because of the greater covalency of metal-nitride bonds. Hence, nitride-doping is a more benign method for doping metal oxides without suppressing electronic transitions.

Ca2MnO3.5 and CaV2O4 were found to be potentially interesting as positive electrode materials for calcium metal-based high-energy density batteries with DFT-predicted average voltages of 3.7 V and 2.5 V and energy barriers for Ca migration of 1.1 eV and 0.6 eV, respectively. Both compounds were prepared by solid state reaction under reducing atmospheres. Optimum conditions to achieve Ca2MnO3.5 comprised the reduction of Ca2MnO4 under NH3 gas at 420⁰C with a flow rate of 1200 ml/min while CaV2O4 was achieved by reduction of CaV2O6 at 700 ⁰C under H2 flow. Electrochemical oxidation of Ca2MnO3.5 in lithium or calcium cells resulted in the formation of an orthorhombic phase with cell parameter (a= 5.2891(1), b= 10.551(2), c= 12.1422(1)). Operando synchrotron radiation diffraction experiments indicate that the charge compensation mechanism is not related to Ca2+ extraction but to intercalation of F− (originated from electrolyte salt decomposition) into the anion vacancy position, as confirmed by EELS and EDS. This process was found to be irreversible. In the case of CaV2O4, oxidation induces the electrochemical extraction of calcium with the formation of an orthorhombic phase (space group Pbnm) with cell parameters a = 10.72008(9) Å, b = 9.20213(2) Å and c = 2.89418(3) Å. The process was also investigated via operando synchrotron radiation diffraction, with the oxidized phase being found to reintercalate Ca2+ ions upon reduction, with the formation of a solid solution. Preliminary cycling tests reveals a decrease in the polarization after the first cycle and call for further investigation of this system., This research was funded by the European Union's Horizon 2020 research and innovation programme H2020 FETOPEN-1- 2016-2017 (CARBAT, grant agreement no. 766617). The authors are grateful for access to the computational facilities from Universidad de Oviedo (MALTA-Consolider cluster) and to ALBA synchrotron for beamtime (proposal 2021024935). ICMAB-CSIC members thank the Spanish Agencia Estatal de Investigación Severo Ochoa Programme for Centres of Excellence in R&D (CEX2019-000917-S)., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).