Decoupling the roles of Ni and Co in anionic redox activity of Li-rich NMC cathodes.

Li[LixNiyMnzCo1-x-y-z]O2 (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, Li1.2Ni0.2Mn0.6O2 and Li1.2Co0.4Mn0.4O2. We discovered that both Ni3+/4+ and Co4+, 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 O2 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.

Electrochromic Corundum-like Compound Based on the Reversible (De)insertion of Lithium: Li2Ni2W2O9.

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 Li2O-NiO-WO3 phase diagram, we obtained a new phase, Li2Ni2W2O9, 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.

Understanding the High Voltage Behavior of LiNiO2 Through the Electrochemical Properties of the Surface Layer.

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 LiNiO2 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.

Capturing dynamic ligand-to-metal charge transfer with a long-lived cationic intermediate for anionic redox.

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 Li1.17Ti0.58Ni0.25O2 involves a long-lived intermediate Ni3+/4+ species, which can fully evolve to Ni2+ during relaxation. Combining electrochemical analysis and spectroscopic techniques, we quantitatively identified that the reduction of this Ni3+/4+ species goes through a dynamic LMCT process (Ni3+/4+-O2- → Ni2+-On-). 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.

Multi-functional Single-Source Molecular Precursors for Carbon-Coated Mixed-Metal Phosphates.

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 LiFeIIPO4 phosphate were shown to enable a spontaneous formation of both the olivine core and conductive carbon shell, yielding a carbon-coated mixed-metal phosphate.

Unlocking anionic redox activity in O3-type sodium 3d layered oxides via Li substitution.

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 NaLi1/3Mn2/3O2 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-NaLi1/3Mn2/3O2 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.

Chemistry, Local Molybdenum Clustering, and Electrochemistry in the Li2+xMo1-xO3 Solid Solutions.

A broad range of cationic nonstoichiometry has been demonstrated for the Li-rich layered rock-salt-type oxide Li2MoO3, which has generally been considered as a phase with a well-defined chemical composition. Li2+xMo1-xO3 (-0.037 ≤ x ≤ 0.124) solid solutions were synthesized via hydrogen reduction of Li2MoO4 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 Mo3 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 Mo3 clusters compatible with local electroneutrality and chemical composition. The geometry of the triangular clusters with their oxygen environment (Mo3O13 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 Li2+xMo1-xO3 in Li cells. According to DFT, all electrochemical capacity in Li2+xMo1-xO3 solely originates from the cationic Mo redox process, which proceeds via oxidation of the Mo3 triangular clusters into bent Mo3 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 Mo3 chains into Mo2 dimers and further into individual Mo6+ cations.

Topochemical Synthesis of Ca3 CrN3 H Involving a Rotational Structural Transformation for Catalytic Ammonia Synthesis.

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-Ca3 CrN3 H, by heating an orthorhombic nitride, o-Ca3 CrN3 , 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-Ca3 CrN3 to a face-sharing octahedral chain in h-Ca3 CrN3 H, mimicking a "hinged tessellation" movement. In addition, the h-Ca3 CrN3 H exhibited stable ammonia synthesis activity when used as a catalyst.

Hydroxyl Defects in LiFePO4 Cathode Material: DFT+U and an Experimental Study.

Lithium iron phosphate, LiFePO4, 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 LiFePO4, 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 LiFePO4 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.

α-TiPO4 as a Negative Electrode Material for Lithium-Ion Batteries.

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 MPO4 phosphate series adopting the α-CrPO4 structure type. α-TiPO4 has been obtained by thermal decomposition of a novel hydrothermally prepared fluoride phosphate, NH4TiPO4F, at 600 °C under a hydrogen atmosphere. The crystal structure of α-TiPO4 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-TiPO4/C demonstrates reversible electrochemical activity ascribed to the Ti3+/Ti2+ 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.

Sodium-Vanadium Bronze Na9V14O35: An Electrode Material for Na-Ion Batteries.

Na9V14O35 (η-NaxV2O5) 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, Na9V14O35 adopts a monoclinic structure consisting of layers of corner- and edge-sharing VO5 tetragonal pyramids and VO4 tetrahedra with Na cations positioned between the layers, and can be considered as sodium vanadium(IV,V) oxovanadate Na9V104.1+O19(V5+O4)4. Behavior of Na9V14O35 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 Na9V14O35 formula, resulting in electrochemical capacity of ~60 mAh g-1. Upon discharge below 1 V, Na9V14O35 uptakes sodium up to Na:V = 1:1 ratio that is accompanied by drastic elongation of the separation between the layers of the VO4 tetrahedra and VO5 tetragonal pyramids and volume increase of about 31%. Below 0.25 V, the ordered layered Na9V14O35 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.

Heterotrimetallic Precursor with 2:2:1 Metal Ratio Requiring at Least a Pentanuclear Molecular Assembly.

This work represents an important step in the quest to make heteromultimetallic molecules featuring specific metal types and complicated metal ratios. The rational design, synthesis, and characterization of a complex heterotrimetallic single-source molecular precursor for the next generation sodium-ion battery cathode material, Na2Mn2FeO6, is described. A unique pentametallic platform [MnII(ptac)3-Na-MnIII(acac)3-Na-MnII(ptac)3] (1) was derived from the known polymeric structure of [NaMnII(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 FeIII for the central MnIII ion forms the target heterotrimetallic precursor [MnII(ptac)3-Na-FeIII(acac)3-Na-MnII(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 heterotrimetallic single-source precursor 3 was shown to exhibit a clean decomposition pattern yielding the phase-pure P2-Na2Mn2FeO6 quaternary oxide with high uniformity of metal ion distribution as confirmed by electron microscopy.

Structural Polymorphism in Na4Zn(PO4)2 Driven by Rotational Order-Disorder Transitions and the Impact of Heterovalent Substitutions on Na-Ion Conductivity.

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 Na4Zn(PO4)2 which is designed from Na3PO4, replacing Na+ with Zn2+ and introducing a vacancy for charge balance. We show that Na4Zn(PO4)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-Na4Zn(PO4)2, contains orientationally ordered PO4 groups, which undergo partial and full rotational disorder in the high-temperature ß- and γ-polymorphs, respectively. We furthermore showed that the highly conducting γ-polymorph could be stabilized at room temperature by ball-milling, whereas the ß-polymorph can be stabilized by partial substitution of Zn2+ with Ga3+ and Al3+. These findings emphasize the role of rotational disorder as an extra parameter to design new solid electrolytes.

Monoclinic α-Na2FePO4F with Strong Antisite Disorder and Enhanced Na+ Diffusion.

A new monoclinic α-polymorph of the Na2FePO4F fluoride-phosphate has been directly synthesized via a hydrothermal method for application in metal-ion batteries. The crystal structure of the as-prepared α-Na2FePO4F studied with powder X-ray and neutron diffraction (P21/c, a = 13.6753(10) Å, b = 5.2503(2) Å, c = 13.7202(8) Å, ß = 120.230(4)°) demonstrates strong antisite disorder between the Na and Fe atoms. As revealed with DFT-based calculations, α-Na2FePO4F 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 cm2·s-1, which is 2 orders of magnitude higher than that for the orthorhombic ß-polymorph ((5-10)·10-13 cm2·s-1). Being tested as a cathode material in Na- and Li-ion battery cells, monoclinic α-Na2FePO4F exhibits a reversible specific capacity of 90 and 80 mAh g-1, respectively.

Origins of irreversible capacity loss in hard carbon negative electrodes for potassium-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.

Crystal Structures and Low-Dimensional Ferromagnetism of Sodium Nickel Phosphates Na5Ni2(PO4)3·H2O and Na6Ni2(PO4)3OH.

Two new sodium nickel phosphates, Na5Ni2(PO4)3·H2O (I) and Na6Ni2(PO4)3OH (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 Ni2+ compounds, I and II show predominant ferromagnetic exchange couplings. I crystallizes in the monoclinic space group P21/ n ( a = 14.0395(4) Å, b = 5.1847(14) Å, c = 16.4739(4) Å, ß = 110.4186(14)°) and features chains of ferromagnetically coupled Ni2+ 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 Ni2+ 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.

Decoupling the roles of carbon and metal oxides on the electrocatalytic reduction of oxygen on La1-xSrxCoO3-δ perovskite composite electrodes.

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.

In Situ Electron Diffraction Tomography Using a Liquid-Electrochemical Transmission Electron Microscopy Cell for Crystal Structure Determination of Cathode Materials for Li-Ion batteries.

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 LiFePO4 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 Role of Semilabile Oxygen Atoms for Intercalation Chemistry of the Metal-Ion Battery Polyanion Cathodes.

Using the orthorhombic layered Na2FePO4F cathode material as a model system we identify the bonding of the alkali metal cations to the semilabile oxygen atoms as an important factor affecting electrochemical activity of alkali cations in polyanion structures. The semilabile oxygens, bonded to the P and alkali cations, but not included into the FeO4F2 octahedra, experience severe undercoordination upon alkali cation deintercalation, causing an energy penalty for removing the alkali cations located in the proximity of such semilabile oxygens. Desodiation of Na2FePO4F proceeds through a two-phase mechanism in the Na-ion cell with a formation of an intermediate monoclinic Na1.55FePO4F phase with coupled Na/vacancy and Fe2+/Fe3+ charge ordering at 50% state of charge. In contrast, desodiation of Na2FePO4F in the Li-ion cell demonstrates a sloping charge profile suggesting a solid solution mechanism without formation of a charge-ordered intermediate phase. A combination of a comprehensive crystallographic study and extensive DFT-based calculations demonstrates that the difference in electrochemical behavior of the alkali cation positions is largely related to the different number of the nearest neighbor semilabile oxygen atoms, influencing their desodiation potential and accessibility for the Na/Li chemical exchange, triggering coupled alkali cation-vacancy ordering and Fe2+/Fe3+ charge ordering, as well as switching between the "solid solution" and "two-phase" charging mechanistic regimes.

An electrochemical cell with sapphire windows for operando synchrotron X-ray powder diffraction and spectroscopy studies of high-power and high-voltage electrodes for metal-ion batteries.

A new multi-purpose operando electrochemical cell was designed, constructed and tested on the Swiss-Norwegian Beamlines BM01 and BM31 at the European Synchrotron Radiation Facility. Single-crystal sapphire X-ray windows provide a good signal-to-noise ratio, excellent electrochemical contact because of the constant pressure between the electrodes, and perfect electrochemical stability at high potentials due to the inert and non-conductive nature of sapphire. Examination of the phase transformations in the Li1-xFe0.5Mn0.5PO4 positive electrode (cathode) material at C/2 and 10C charge and discharge rates, and a study of the valence state of the Ni cations in the Li1-xNi0.5Mn1.5O4 cathode material for Li-ion batteries, revealed the applicability of this novel cell design to diffraction and spectroscopic investigations of high-power/high-voltage electrodes for metal-ion batteries.