Operando X-ray Powder Diffraction Research Articles

Designing a 3D framework NaVOPO4 as a high-power, low-strain and long-life positive electrode material for Na-ion batteries

Advances in sodium-ion batteries hugely rely on perfecting the performance of active electrode materials. In this paper, we offer a new NaVOPO4 polymorph adopting a KTiOPO4-type framework as a promising high-rate, low-strain and long-life positive electrode material for sodium-ion batteries. NaVOPO4 is prepared via a facile hydrothermally-assisted solid-state ion exchange. The crystal structure is refined based on synchrotron X-ray powder diffraction (XRD) and validated by X-ray absorption spectroscopy (XAS), transmission electron microscopy analysis and density functional theory (DFT) calculations. The electrochemical performance of NaVOPO4 is evaluated through galvanostatic charge/discharge tests, cyclic voltammetry, potentiostatic intermittent titration and electrochemical impedance spectroscopy. A carbon-coated NaVOPO4 demonstrates a specific capacity of ∼110 mAh g–1 at a C/10 rate at an average potential of ∼3.93 V vs. Na+/Na. The material exhibits decent capacity retention and rate capability, maintaining over 74 % of the initial capacity after 1000 cycles at a C/2 rate and around 87% at a 2C charge/discharge rate. Diffusion coefficients of 10–11 cm2 s–1 and DFT-calculated energy barriers of ∼0.15–0.35 eV indicate fast Na+ ion diffusion within the NaVOPO4 framework. The vanadium oxidation state and charge compensation mechanism in NaVOPO4 are studied by XAS and DFT. Moreover, the operando XRD analysis coupled with DFT elucidates several phase transitions occurring in NaVOPO4 with an exceptionally low volume variation of 2.4% in total, highlighting the reversibility and structural stability during Na+ de/insertion. Overall, NaVOPO4 exhibits attractive electrochemical performance and stability, making it a potential candidate for sodium-ion battery cathode materials.

Trace doping realizing superior electrochemical performance in P2-type Na0.50Li0.08Mn0.60Co0.16Ni0.16O2 cathode for sodium-ion batteries

P2-type layered oxides are receiving significant interest due to their superior structure and intrinsic performances. There are strenuous attempts to balance the structure stability, phase transition as well as desirable electrochemical performances by inducing anion/cation ions, changing morphology, adjusting valence, etc. In this work, several same-period elements of Sc, Ti, V, Cr, Fe, Cu and Zn are doped into Na0.50Li0.08Mn0.60Co0.16Ni0.16O2 cathodes, which are manipulated by ions radii and valence state, further studied by operando X-ray powder diffraction patterns (XRD). As a result, the Cu2+ doped cathode performed higher rate capacities (as high as 86 mAh/g even at 10 C) and more stable structures (capacity retention of ∼89.4% for 100 cycles), which owing to the synergistic effect among the tightened TMO2 layer, enlarged d-spacing, reduce OO electrostatic repulsion, ameliorate lattice distortion as well as mitigate ordering of Na+/vacancy.

Complete Three-Electron Vanadium Redox in NASICON-Type Na3VSc(PO4)3 Electrode Material for Na-Ion Batteries

Here we introduce a new NASICON-type Na3VSc(PO4)3 positive electrode material for Na-ion batteries demonstrating reversible (de)intercalation of 3 Na cations per formula unit within a wide voltage range with complex voltage-composition dependence. The total electrochemical capacity of the material is 170 mAh g−1 that corresponds to the complete three-electron V2+/V3+/V4+/V5+ process. All the (de)sodiation stages follow a predominantly solid-solution mechanism, as shown by operando X-ray powder diffraction. The oxidation of vanadium up to +5 upon the charge of Na3VSc(PO4)3 to 4.5 V vs Na/Na+ causes the significant transformation of the unit cell. According to ex situ Fourier-transformed infrared spectroscopy it is accompanied by the increasing distortion of the vanadium coordination environment and shortening of the vanadium-oxygen bonds. This leads to the irreversible character of the charge-discharge curve, and the initial structure can be restored after the strong overdischarge to ≈1.5 V vs Na/Na+.

High Temperature Compatible Conflat Cell with Adjustable Stack Pressure for In-Situ and Operando X-Ray Studies of Lithium-Ion Battery Materials

Lithium-ion batteries have emerged as the dominant energy storage technology for electronic devices, vehicles, and grid-scale applications [1,2]. Further improvements of cell design, components, and materials depend heavily on reproducible characterization. The challenge is to replicate real-world battery operation conditions in laboratory measurements, which makes designing robust in-situ / operando cells a challenging task. Cell materials should be as close as possible to those used in production cells (e.g. steel, aluminum, copper, nickel) [3] and lithium should only react with the test electrode, not with the cell components or the test environment. In addition, a controlled but significant mechanical pressure (0.1 - 1 MPa) should be applied to the electrochemically active material, and in some cases, the cell must operate over a wide temperature range. While existing in-situ and operando electrochemical cell designs meet many of these criteria, no design meets all of them.We have developed a Сonflat in-situ cell for X-ray diffraction studies based on Conflat vacuum flanges and electrical feedthroughs. This cell design is based on readily available components and can provide an ultra-high vacuum compatible seal and controllable and commercially relevant stack pressure over a wide temperature range [4]. Cell sealing is accomplished using knife edges impinging on a copper gasket. Conflat cells have a potential to meet all of the criteria for a robust and reproducible in-situ / operando cell. The challenge lies in properly incorporating an X-ray transparent window for X-ray measurements. While Beryllium windows can be attached to the Conflat flange using metal bonding techniques, such bonding can be cost prohibitive for many laboratories (e.g. thousands of dollars per flange). In our design, we used a readily available steel reinforced epoxy to attach the Beryllium window to the Conflat flange, making it an inexpensive and high quality alternative even for long-term in-situ and operando measurements. In-situ and operando X-ray powder diffraction results from Graphite and Aluminum electrodes cycled at 30℃ and 120℃, respectively, are provided in Fig. 1. Diffraction patterns were combined and plotted as a logarithmic-scale colormap together with the measured cell potential in Fig. 1a) for Graphite and Fig.1b) for Aluminum electrodes [5]. For the C-Li system in Fig.1a), only the C-Li peaks of interest are shown in the ranges of 20°-30° and 75°-85° scattering angle. From the voltage profile in Fig.1a), four intercalation stages can be discerned, as has been extensively reported before, and are marked with dashed red lines. Al-Li phases can be well defined both from the voltage profile and the diffraction pattern. In Fig.1b), the solid vertical lines that do not change their intensity with time, at approximately 42°, 52° and 71° are the peaks from the Beryllium window. The rest of the peaks that change their intensity and position with time can be attributed to the various phases of the Al-Li system that have been reported in our previous ex-situ studies [6]. Phase formation is reversible for both Graphite and Aluminum electrodes and a pure Graphite and Aluminum metal could be recovered when the cell was completely charged again. In both in-situ experiments, the cell performed very well and high quality data was obtained. We will present and discuss the X-ray diffraction data and all of the phases of the C-Li and Al-Li systems in more detail as well as results from the rigorous testing of the cell to assess its superior sealing and longevity [5].[1] M. Li et al., Advanced Materials 30 (33) 1800561 (2018).[2] H. C. Hesse et al., Energies, 10 (12) 2107 (2017).[3] M. Zwicker et al., Journal of Advanced Joining Processes 1 100017 (2020).[4] M.D. Fleischauer et al., Journal of The Electrochemical Society, 166 (2) A398-A402 (2019).[5] O. Sendetskyi et al., Journal of Applied Crystallography, In preparation (2021).[6] M. Ghavidel et al., Journal of The Electrochemical Society, 166 (16) A4034-A4040 (2019).Figure 1. Voltage profiles and operando X-ray diffraction patterns plotted as a log-scale intensity colormap for a) Graphite electrode measured at 30℃ and b) freestanding Aluminum foil electrode measured at 120℃ [5]. Figure 1

Structural evolution and electrochemistry of the Mn-Rich P2– Na2/3Mn0.9Ti0.05Fe0.05O2 positive electrode material

Positive electrodes still limit the maximum attainable energy density of Na-ion batteries. Increasing the amount of electrochemically active transition metal is one way of improving energy density. However, this is complicated by the balance between initial capacity and structural stability/capacity retention. Here, the Mn-rich P2– Na2/3Mn0.9Fe0.05Ti0.05O2 is synthesised via the solid-state method and its structural evolution during operation, between 1.9 and 4.2 V, investigated. Through operando X-ray powder diffraction data, no evidence is found for the formation of Z, OP4 or O2 phases and the material primarily displays regions of two-phase coexistence. P2– Na2/3Mn0.9Fe0.05Ti0.05O2 delivers a second charge/discharge capacity of 152/164 mAh.g−1 at C/10, within the voltage range 4.0–2.0 V and retains 75% of the dis-charge capacity at the 50th cycle. A detailed comparison, in terms of both the electrochemical performance and structural evolution, to related Mn-rich phases is provided. The results further demonstrate that structural stability and battery performance can be improved through subtle co-substitutions.

Going Nano with Confined Effects to Construct Pomegranate-like Cathode for High-Energy and High-Power Lithium-Ion Batteries.

Pomegranate-like Li3V2(PO4)3@C (LVP@C) cathode materials are fabricated through confined effect helped by the vacuum-assisted capillary action. The performance of LixV2(PO4)3 (x = 0-5) at an extended working voltage of 1.2-4.8 V has been studied by operando X-ray powder diffraction and hybrid functional density functional theory (DFT) calculation. The DFT calculation results suggest that Li3V2(PO4)3 can be intercalated with another two Li+ with a stable crystalline structure, which improves the specific capacity of LVP significantly. The cathode exhibits a specific capacity of 320 mAh g-1 with an energy density of 736 Wh kg-1, which is one of the best performances for intercalation cathode materials for Li-ion batteries to our knowledge. Besides, the cathode showed excellent rate capability. In the working potential of 3.0-4.8 V, it exhibits a high specific capacity of 195 mAh g-1 at 0.2 C, and even at a high rate of 30 C, it still delivers the specific capacity of 145 mAh g-1 with a power density of 15.93 kW kg-1. The good performance is mainly attributed to the unique pomegranate structure, which can provide continuous three-dimensional conductive networks for fast electron and Li-ion transfer. This paper provides a new strategy for synthesizing other cathode or anode materials with high energy and power density.

Bifunctional core-shell architecture allows stable H2 production utilizing CH4 and CO2 in a catalytic chemical looping process

We report on the development of a bifunctional catalyst (Pt) - oxygen carrier (Fe2O3) that integrates the dry reforming of methane (DRM) into the chemical looping-based production of hydrogen. The material exhibits a high and stable methane conversion (˜ 80%) and hydrogen yield (10.8 mmol/g catalyst-oxygen carrier) with only a small quantity of impurities (CO, CO2 <2 ppm). The structural changes of the material are followed by operando X-ray powder diffraction and X-ray absorption spectroscopy coupled with gas chromatography. Insight into the evolution of the size of the Pt nanoparticles and their interaction with CeO2 are probed by transmission electron microscopy and X-ray absorption fine structure analysis. Under DRM conditions, the Pt nanoparticles grow in size, however, their re-dispersion on the CeO2 support (via PtOx-support interaction) during air oxidation recovers their activity in the consecutive cycle.

Intercalation of lithium into disordered graphite in a working battery

The structural transformations occurring during the intercalation of lithium into disordered graphite in a working battery were studied in detail by operando X-ray powder diffraction (XRPD). By using a capillary-based micro-battery cell, it was possible to study the stacking disorder in the initial graphite as well as in lithiated graphites. The micro-battery cell was assembled in its charged state with graphite as positive electrode and metallic lithium as counter electrode. The battery was discharged until a stage II compound (LiC12) was formed. The operando XRPD data reveal that the graphitic electrode material retains a disordered nature during the intercalation process. A DIFFaX+ refinement based on the initial operando XRPD pattern shows that the initial graphite generally has an intergrown structure with domains of graphite 2H and graphite 3R. However, the average stacking sequence of the initial graphite also contains a significant concentration of AA-type stacking of the graphene sheets. DIFFaX+ was further used to refine structure models of a stage III type compound and the final stage II compound. The refinement of the stage II compound showed that it is dominated by AαAAαA-type stacking, but that it also contains a significant concentration of AαABβB-type slabs in the average stacking sequence.

Transmission in situ and operando high temperature X-ray powder diffraction in variable gaseous environments.

This work describes a device for time-resolved synchrotron-based in situ and operando X-ray powder diffraction measurements at elevated temperatures under controllable gaseous environments. The respective gaseous sample environment is realized via a gas-tight capillary-in-capillary design, where the gas flow is achieved through an open-end 0.5 mm capillary located inside a 0.7 mm capillary filled with a sample powder. Thermal mass flow controllers provide appropriate gas flows and computer-controlled on-the-fly gas mixing capabilities. The capillary system is centered inside an infrared heated, proportional integral differential-controlled capillary furnace allowing access to temperatures up to 1000 °C.

Improved multivariate analysis for fast and selective monitoring of structural dynamics by in situ X-ray powder diffraction.

The development of two solid-state reactions, Xe absorption into MFI and molecular complex formation, where samples are affected by changes of crystal lattice due to temperature or pressure variation was structurally monitored through in situ or in operando X-ray powder diffraction experiments. Consequent variations of the peak positions prevent collective analysis of measured patterns, aiming at investigating structural changes occurring within the crystal cell. Moreover, an intrinsic and variable error in peak position is unavoidable when using the Bragg-Brentano geometry and, in some cases (sticky, bulky, aggregate samples) the sample mounting can increase the error within a dataset. Here we present a general multivariate analysis method to process in a fast and automatic way in situ XRPD data collected on charge transfer complexes and porous materials, with the capacity of disentangling peak shifts from intensity and shape variations in diffraction signals, thus allowing an efficient separation of the contribution of crystal lattice changes from structural changes. The peak shift correction allowed an improved PCA analysis that turned out to be more sensible than the traditional single pattern Rietveld analysis. The developed algorithms allowed, with respect to the traditional approach, the location of two new Xe positions into MFI with a better interpretation of the experimental data, while a much faster and more efficient recovery of the reaction coordinate was achieved in the molecular complex formation reaction.

Understanding Capacity Fading of LiNi0.8Co0.15Al0.05O2 Via Long-Term Operando X-Ray Diffraction Studies

Layered lithium transition metal oxides are promising high-capacity cathode materials for Li-ion batteries. However, capacity fading has restricted the practical capacity to less than 70% of the theoretical capacity. Higher initial capacity can be achieved by charging to a higher voltage, yet this initial gain in capacity is quickly offset by the rapid fade in capacity. Understanding the capacity fading mechanism will help develop strategies to mitigate this problem. We used operando X-ray powder diffraction to follow the reactions of the layered LiNi0.8Co0.15Al0.05O2 over extended charge-discharge cycles at a slow current rate. The operando result shows that the capacity loss can be explained by the heterogeneity developed in the electrode after extended charge-discharge cycles.

MSn2 (M= Mn, Fe, Co) Intermetallics As Anode Materials for Na-Ion Batteries

Tin is a promising anode material for the storage of large amounts of lithium and sodium; it currently boasts one of the highest specific charges: 990 mAh/g and 846 mAh/g in lithium-ion and sodium-ion batteries upon conversion to Li4.4Sn and Na3.75Sn, respectively1. However, storing such large quantities of these ions is typically accompanied by large volume expansions of up to 400%, which leads to particle fracture and thus electrical isolation resulting in rapid capacity fade with cycle number. By alloying an active metal with an inactive metal the reaction mechanism can be modified, allowing substantial specific charge to be achieved while mitigating the detrimental effects of the volume expansion. Here, we alloy Sn with inactive transition metals Mn25, Fe26 and Co27 to form the tetragonal intermetallic MSn2 (I4/mcm). Since none of the three transition metals form alloys with Na on their own, they are expected to be inactive in the storage of Na; however the three MSn2 materials (M = Mn, Fe, Co) do not behave identically during cycling in sodium ion batteries, demonstrating that the transition metal in fact plays an “active role” in such systems. With the three materials being isostructural and the transition metals being adjacent to each other in the periodic table, the precise influence of the electronic structure of the supposedly inactive transition metal on the active system (here Sn) could be identified. Using electrochemical measurements (CV, GITT, galvanostatic cycling and rate capability), ex situ and operando X-ray powder diffraction (XRD) data and X-ray absorption spectroscopy (XAS) we elucidate the reaction mechanism of all three materials and uncover that the reaction between Na and MSn2 (M = Mn, Fe, Co) is facilitated by intermediate state formation, dependent on the transition metal. The results of this study give an insight into designing the most effective combinations of active and inactive metals that may be selected as suitable alloy hosts for the next generation of novel battery materials.