Soft X-ray Absorption Spectroscopy Study Research Articles

Ni-rich LiNi0.905Co0.043Al0.052O2 cathode material for high-energy density Li-ion cells: Tuning lithium content, structural evolution, and full-cell performance

Ni-rich LiNi0.905Co0.043Al0.052O2 oxides with the Li excess (x) up to 7 mol.% used in the synthesis are prepared by a facile dry-mixing method. It is shown that the Li/Ni mixing level and crystallite size are dependent on the Li amount, while Al from the precursor acts as a scavenger of the excessive Li. Operando X-ray diffraction (XRD) studies enable explaining differences in the structural evolution of materials exhibiting high and low Li/Ni mixing, especially in the H2↔H3 transition region. Soft X-ray absorption spectroscopy (XAS) studies show differences in the charge state evolution of the surface and bulk Ni. The optimized oxide with the Li excess x = 2 mol.% delivers excellent electrochemical performance, with an initial discharge capacity of 205.5 mAh g−1 at 0.1C, and 91.4 % capacity retention after 100 cycles at 1C. The unmodified in any other way cathode material allows achieving the discharge capacity of 178.5 mAh g−1 at the high rate of 5C, and works well in the full-cells.

Modulating Lattice Oxygen Activity of Iron-Based Triple-Conducting Nanoheterostructure Air Electrode via Sc-Substitution Strategy for Protonic Ceramic Cells.

Iron-based perovskite air electrodes for protonic ceramic cells (PCCs) offer broad application prospects owing to their reasonable thermomechanical compatibility and steam tolerance. However, their insufficient electrocatalytic activity has considerably limited further development. Herein, oxygen-vacancy-rich BaFe0.6Ce0.2Sc0.2O3-δ (BFCS) perovskite is rationally designed by a facile Sc-substitution strategy for BaFe0.6Ce0.4O3-δ (BFC) as efficient and stable air electrode for PCCs. The BFCS electrode with an optimized Fe 3d-eg orbital occupancy and more oxygen vacancies exhibits a polarization resistance of ≈ 0.175Ωcm2 at 600°C, ≈ 1/3 of the BFC electrode (≈0.64Ωcm2). Simultaneously, BFCS shows favorable proton uptake with a low proton defect formation enthalpy (- 81kJmol-1). By combining soft X-ray absorption spectroscopy and electrical conductivity relaxation studies, it is revealed that the enhancement of Fe4+-O2- interactions in BFCS promotes the activation and mobility of lattice oxygen, triggering the activity of BFCS in both oxygen reduction and evolution reactions (ORR/OER). The single cell achieves encouraging output performance in both fuel cell (1.55 Wcm-2) and electrolysis cell (-2.96Acm-2 at 1.3V) modes at 700°C. These results highlight the importance of activating lattice oxygen in air electrodes of PCCs.

Understanding the Anion Effect of Basic Cobalt Salts for the Electrocatalytic Oxygen Evolution Reaction

Basic cobalt salts with distinct acidic anion Co(OH)x(A)y are efficient electrocatalysts toward the oxygen evolution reaction (OER). However, plenty of present studies are still in the try-and-wrong stage, while the underlying anion effect remains unclear. Herein, a series of Co(OH)x(A)y (A = F–, Cl–, and CO32–) are synthesized via a hydrothermal strategy, and the order of the OER activity is determined to be Co(OH)(CO3)0.5 > Co2(OH)3Cl > Co(OH)F > Co(OH)2. X-ray photoelectron spectroscopy and soft X-ray absorption spectroscopy studies reveal that these Co(OH)x(A)y materials undergo surface oxidation during the OER process, and the highly active Co(IV) content is the dominant factor in deciding the OER performance. Furthermore, quantitative analysis of anion concentrations in the electrolyte solution reveals that the anion leaching ability in Co(OH)x(A)y directly relates to the Co(IV) content and finally the OER catalytic activity, which is the essence of the anion effect and can be summarized as an “anion leaching─metal oxidation” model. Our work not only provides deep understanding of the anion effect of metal basic salt-based OER catalysts but also profound insights for the activation process of the OER pre-catalysts.

Structural and Magnetic Properties of Ni Nanoparticles Embedded in Vinyl Polymer Nanocomposite Films

Ni nanoparticles layer of nominal thickness in the range of 5–40[Formula: see text]nm were deposited on polyvinyl alcohol (PVA) film by using the ion beam sputtering (IBS) technique. PVA films were made on a quartz substrate by the solution casting technique. Grazing incidence X-ray diffraction (GIXRD) results reveal Ni is present in a metallic form in the FCC phase. AFM shows that roughness increases with increase in thickness of Ni layer and corresponding MFM images of magnetic domains were recorded. Soft X-ray absorption spectroscopy (SXAS) studies on the PVA/Ni nanocomposites films were recorded using synchrotron radiation. This study is used to study the electronic structure of the as-prepared nanocomposite films and reveals that Ni nanoparticles are present in their metallic form. Magnetic properties were measured using the magneto-optical Kerr effect (MOKE) magnetometer and the films were found to be magnetically soft with higher value of coercivity at lower thickness of Ni nanoparticles layer. The results of magnetic studies are discussed in light of the microstructure and morphological features of PVA/Ni nanocomposite films. The PVA/Ni nanocomposites showed interesting anisotropic magnetic behavior; thus the investigative results may be useful for the development of futuristic flexible functional magnetic material system.

Effect of Cr-substitution on vanadium dioxide thin films studied by soft X-ray magnetic circular dichroism

The tunability of magnetic properties of VO 2 has fascinated substantial attention in the first generation of spintronics-related applications such as read head sensors for hard disk drives and magnetic random-access memory. In this work, we focus on Cr doped VO 2 , V 1− x Cr x O 2 (0 ≤ x ≤ 0 . 3) (VCO) thin films and study the effect of Cr-substitution on the structural, electronic and magnetic properties. The VCO films were deposited on R-sapphire substrates using a pulse laser deposition method. Soft X-ray absorption spectroscopy (XAS) and soft X-ray magnetic circular dichroism (XMCD) studies of VCO thin films were performed to reveal and understand the origin of maTablegnetization and their enhancement with Cr-substitution. The XAS spectra suggest that the valences of V ions are in tetra and pentavalent states and Cr ions in the trivalent state. The XMCD spectra imply that the V and Cr ions are ferromagnetic at room temperature. These results also indicate that the VCO films are in the ferromagnetic insulating state and charge-ordered at the V and Cr sites. These results are consistent with the first principle density functional theory calculations. • XRD results suggest that a gradual structural change from the monoclinic M1 phase (0 ≤ x < 0.05) to triclinic T phase (0.05 ≤ x ≤ 0.20 to monoclinic M2 phase ( x > 0.20). • First Study to understand the origin of magnetization. • The VCO films are in the ferromagnetic insulating state and charge-ordered at the V and Cr sites, consistent with DFT. • The XMCD spectra indicate that the V and Cr ions are ferromagnetic at room temperature.

Detailed study of reactively sputtered ScN thin films at room temperature

To contemplate an alternative approach for the minimization of diffusion at high temperature, present findings impart viability of room-temperature deposited reactively sputtered ScN thin films. The adopted route endows precise control over the RN2 flow for a methodical structural phase evolution from Sc→ScN and probe the correlated physical aspects of the highly textured ScN samples. In the nitrided regime i.e. at RN2 = 2.5–100% flow, incorporation of unintentional oxygen defects was evidenced from surface sensitive soft x-ray absorption spectroscopy study, though less compared to their metal (RN2 = 0%) and interstitial (RN2 = 1.6%) counterparts, due to higher Gibbs free energy for Sc-O-N formation with no trace of ligand field splitting around the O K-edge spectra. To eradicate the skepticism of appearance of N K-edge (401.6 eV) and Sc L-edge (402.2 eV) absorption spectra adjacent to each other, the first-ever Sc K-edge study has been adopted to validate complementary insight on the metrical parameters of the Sc-N system. Optical bandgaps of the polycrystalline ScN thin film samples were found to vary between 2.25 and 2.62 eV as obtained from the UV–vis spectroscopy, whereas, the nano-indentation hardness and modulus of the as-deposited samples lie between 15–34 GPa and 152–476 GPa, respectively following a linearly increasing trend of resistance to plastic deformations with an exception at 34 GPa in case of RN2 = 5% sample. Besides, contrary to other early 3d transition metal nitrides (TiN, VN, CrN), a comprehensive comparison of noticeably large homogeneity range in Sc-N has been outlined to apprehend the minuscule lattice expansion over the large RN2 realm.

One-pot synthesis of multifunctional graphitic carbon-metal oxide nanocomposite for photocatalytic water purification and supercapacitor applications

Multifunctional nanomaterials are emerging as potential materials with a wide variety of applications. Herein, we reported the one-pot facile synthesis of multifunctional graphitic carbon (gC)-CuO-ZnO nanocomposite for various applications of photocatalytic water purification, water disinfection, and supercapacitor electrode. The prepared gC-CuO-ZnO nanocomposite was characterized using microscopic and X-ray analysis techniques. Primarily, the synchrotron soft X-ray absorption spectroscopy studies were performed to investigate the internal environment of the nanocomposite using O K-edge, C K-edge, Zn L-edge, and Cu L-edge. The energy bandgap of the gC-CuO-ZnO nanocomposite was estimated to be 2.97 eV from the Tauc plot using ultraviolet–visible absorption spectra. In this regard, the prepared nanocomposite revealed excellent photocatalytic degradation against pharmaceutical compound amoxicillin and clavulanate potassium tablet, textile industrial effluent, and methylene blue dye under direct sunlight, indicating the efficiencies of 49 %, 89 %, and 97 %, respectively. Anti-microbial studies were performed against multidrug-resistant Escherichia fergusonii (MDR) strain using the gC-CuO-ZnO nanocomposites with different weight% of 1 %, 2 %, and 3 % and the obtained inhibition values were 16, 17.3, and 17.3 mm, respectively. Also, the gC-CuO-ZnO nanocomposite was employed as an electrode material of supercapacitors in energy storage applications. The gC-CuO-ZnO nanocomposite electrode exhibited excellent electrochemical properties, exhibiting the specific capacitance of 1102 F g-1 at 1 A g-1. Consequently, the heterojunction nanocomposite via a facile one-pot synthesis was successfully employed for degradation of industrial effluents, toxicity against MDR bacteria, and an efficient supercapacitor electrode.

Effects of Nonstoichiometry and Plastic Deformation on Charge and Spin States of Cobalt Ions in LnBaCo2BaO5.5 – δ (Ln = Tb, Eu): Soft X-ray Absorption Spectroscopy Studies

We present results of soft X-ray absorption spectroscopy studies of nonstoichiometric Tb1 ‒ yBa1 +yCo2 –xO5.5 – δ cobaltites and EuBaCo2O5.5 cobaltite powders subjected to mechanical impact (milling in a ball mill). It was established that in octahedra of Tb1 – yBa1 + yCo2 – xO5.5 – δ cobaltates Co3+ ions are in the high spin state. In EuBaCo2O5.5 powder after milling in a ball mill, a surface area (5–10 nm) of particles was found to be decomposed into Co3O4, BaCO3, and EuCoO3 phase components. A knowledge of the low-spin state of Co3+ ions in EuCoO3 and Co3O4 and possibilities of surface-sensitive soft X-ray absorption spectroscopy have allowed to determine the composition of the EuBaCo2O5.5 sample (subjected to ball milling) near its surface, which is inaccessible to standard X-ray phase analysis.

Effect of nonstoichiometry on crystal structure, charge and spin states of cobalt ions in Tb1−yBa1+yCo2−xO5.5−δ: Neutron diffraction and soft X-ray absorption spectroscopy studies

Neutron diffraction and soft X-ray absorption spectroscopy have been applied for studying crystal structure, charges, and spin states of cobalt ions in nonstoichiometric Tb1−yBa1+yCo2−xO5.5−δ cobaltites. The following single-phase samples with defects in anion and cation sublattices were synthesized and investigated: TbBaCo2O5.38, TbBaCo1.95O5.31, TbBaCo1.90O5.24, and Tb0.95Ba1.05Co1.90O5.21. Co and Tb charge states have been estimated from soft X-ray absorption spectra. The anisotropic nature of changes of lattice parameters depending on the content of cobalt and oxygen vacancies has been established. A correlation between cobalt and oxygen vacancies in double layered cobaltites and a role of apical and planar oxygen in the formation of the Tb1−yBa1+yCo2−xO5.5−δ structure have been shown. Oxygen vacancies are found to be unevenly distributed across the unit cell. Most vacancies are formed in the O (4u) and O (2s) planar positions. The O (1g) apical positions are also partly vacant. The high spin state of Co3+ ions in octahedra has been found to be realized. This conclusion obtained from neutron diffraction data is consistent with the results of X-ray absorption spectroscopy.

Cr2Te3 Thin Films for Integration in Magnetic Topological Insulator Heterostructures

Chromium telluride compounds are promising ferromagnets for proximity coupling to magnetic topological insulators (MTIs) of the Cr-doped (Bi,Sb)2(Se,Te)3 class of materials as they share the same elements, thus simplifying thin film growth, as well as due to their compatible crystal structure. Recently, it has been demonstrated that high quality (001)-oriented Cr2Te3 thin films with perpendicular magnetic anisotropy can be grown on c-plane sapphire substrate. Here, we present a magnetic and soft x-ray absorption spectroscopy study of the chemical and magnetic properties of Cr2Te3 thin films. X-ray magnetic circular dichroism (XMCD) measured at the Cr L2,3 edges gives information about the local electronic and magnetic structure of the Cr ions. We further demonstrate the overgrowth of Cr2Te3 (001) thin films by high-quality Cr-doped Sb2Te3 films. The magnetic properties of the layers have been characterized and our results provide a starting point for refining the physical models of the complex magnetic ordering in Cr2Te3 thin films, and their integration into advanced MTI heterostructures for quantum device applications.

Milling-induced chemical decomposition of the surface of EuBaCo2O5.5 powders studied by means of soft X-ray absorption spectroscopy

We present results of soft X-ray absorption spectroscopy studies of EuBaCo2O5.5 powders subjected to mechanical impact (milling in a ball mill). We show that in the near-surface region (5–10 nm) of particles of the powder, EuBaCo2O5.5 decomposes into Co3O4, BaCO3, and EuCoO3. A knowledge of the low-spin state of Co3+ ions in EuCoO3 and Co3O4 and possibilities of surface-sensitive soft X-ray absorption spectroscopy have allowed to determine the composition of the EuBaCo2O5.5 sample subjected to mechanical impact near its surface, which is inaccessible to standard X-ray phase analysis.

Photoemission and soft X-ray absorption spectroscopy study of Gd-substituted thermoelectric and topological Bi2Te3

The electronic structures of Gd-substituted Bi2−xGdxTe3 single crystals have been investigated by employing synchrotron-radiation spectroscopies, such as soft X-ray absorption spectroscopy (XAS), soft X-ray magnetic circular dichroism (XMCD), photoemission spectroscopy (PES), and scanning photoelectron microscopy (SPEM). SPEM measurements confirm that Gd ions are substituted homogeneously in Bi2−xGdxTe3 crystals. The measured Gd 3d XAS and XMCD spectra provide evidence that the substituted Gd ions are trivalent and magnetic. The hν-dependence of the valence-band (VB) PES spectra are described well by the hν-dependent contributions of the Te 5p and Bi 6p states. A good agreement is found between the measured VB PES spectra of Bi2−xGdxTe3 and the calculated partial densities of states, revealing that the Te 5p states will play an important role in determining the thermoelectric and topological properties of Bi2−xGdxTe3.

Soft X-ray Absorption Spectroscopy Study of Spin Crossover Fe-Compounds: Persistent High Spin Configurations under Soft X-ray Irradiation

Metal-organic complex exhibiting spin crossover (SCO) behavior has drawn attention for its functionality as a nanoscale spin switch. The spin states in the metal ions can be tuned by external stimuli such as temperature or light. This article demonstrates a soft X-ray–induced excited spin state trapping (SOXEISST) effect in Hofmann-like SCO coordination polymers of FeII(4-methylpyrimidine)2[Au(CN)2]2 and FeII(pyridine)2[Ni(CN)4]. A soft X-ray absorption spectroscopy (XAS) study on these polymers showed that the high spin configuration (HS; S = 2) was prevalent in Fe2+ ions during the measurement even at temperatures much lower than the critical temperatures (&gt;170 K), manifesting HS trapping due to the X-ray irradiation. This is in strong contrast to the normal SCO behavior observed in FeII(1,10-phenanthroline)2(NCS)2, implying that the structure of the ligand chains in the polymers with relatively loose Fe-N coordination might allow a structural adaptation to stabilize the metastable HS state under the soft X-ray irradiation.

Electronic and Magnetic Field Dependent Dielectric Properties of Zn0.95Fe0.05O

We report a magneto-dielectric effect in Zn0.95Fe0.05O, which was synthesized by the microwave-assisted combustion method. The x-ray diffraction (XRD) pattern of Zn0.95Fe0.05O shows the shift in peaks towards lower theta values in comparison to the XRD pattern of ZnO. Rietveld analysis of XRD data shows the presence of 99.29% of Zn0.95Fe0.05O along with 0.71% ZnFe2O4 in Fe doped ZnO. Infrared spectroscopic studies show the shift in absorption peak towards lower wavenumber with Fe doping at Zn sites in ZnO. Soft x-ray absorption spectroscopy studies show the mixed valence states of Fe (Fe+2 and Fe+3). Magnetic properties show paramagnetic behaviour of Zn0.95Fe0.05O at room temperature. The magneto-dielectric effect is originated in Zn0.95Fe0.05O due to the decrease in space polarization effect in the presence of Fe+2 at the Zn site in a magnetic field. The dielectric constant er is found to be 4.09 × 105 in 1 Hz and 11.65 in 1 MHz frequency in the absence of a magnetic field for Zn0.95Fe0.05O. The dielectric constant er is found to be 2.88 × 105 in 1 Hz and 10.37 in 1 MHz frequency in the 500 Gauss magnetic field for Zn0.95Fe0.05O. Magnetic field sensitivity is found as ~ 16% in the 15 kG magnetic field and 30 MHz frequency for Zn0.95Fe0.05O.

Magnetic X-ray spectroscopy of two-dimensional CrI3 layers

The recently confirmed monolayer ferromagnet CrI3 is a frisky example of a two-dimensional ferromagnetic material with great application potential in van der Waals heterostructures. Here we present a soft X-ray absorption spectroscopy study of the magnetic bulk properties of CrI3, giving insight into the magnetic coupling scenario which is relevant for understanding its thickness-dependent magnetic properties. The experimental Cr L2,3 X-ray magnetic circular dichroism spectra show a good agreement with calculated spectra for a hybridized ground state. In this high-spin Cr ground state the Cr–I bonds show a strongly covalent character. This is responsible for the strong superexchange interaction and increased spin-orbit coupling, resulting in the large magnetic anisotropy of the two-dimensionally layered CrI3 crystal.

Soft x-ray absorption spectroscopy study of the electronic structures of the MnFe Prussian blue analogs (RbxBay)Mn[3−(x+2y)]/2[Fe(CN)6]H2O

The electronic structures of Prussian blue analog $({\mathrm{Rb}}_{x}{\mathrm{Ba}}_{y}){\mathrm{Mn}}_{[3\ensuremath{-}(x+2y)]/2}[\mathrm{Fe}{(\mathrm{CN})}_{6}]$ cyanides have been investigated by employing soft x-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD) at the Fe and Mn $L$ $(2p)$ edges. The measured XAS spectra have been analyzed with the configuration-interaction (CI) cluster model calculations. The valence states of the Fe and Mn ions are found to be ${\mathrm{Fe}}^{2+}\text{\ensuremath{-}}{\mathrm{Fe}}^{3+}$ mixed valent, with an average valency of $v(\mathrm{Fe})\ensuremath{\sim}2.8$ and nearly divalent $({\mathrm{Mn}}^{2+})$, respectively. Our Mn/Fe $2p$ XMCD study supports that ${\mathrm{Mn}}^{2+}$ ions are in the high-spin states while ${\mathrm{Fe}}^{2+}\text{\ensuremath{-}}{\mathrm{Fe}}^{3+}$ ions are in the low-spin states. The Fe and Mn $2p$ XAS spectra are found to be essentially the same for $80\ensuremath{\le}T\ensuremath{\le}300$ K, suggesting that a simple charge transfer upon cooling from ${\mathrm{Fe}}^{3+}\text{\ensuremath{-}}\mathrm{CN}\text{\ensuremath{-}}{\mathrm{Mn}}^{2+}$ to ${\mathrm{Fe}}^{2+}\text{\ensuremath{-}}\mathrm{CN}\text{\ensuremath{-}}{\mathrm{Mn}}^{3+}$ does not occur in $({\mathrm{Rb}}_{x}{\mathrm{Ba}}_{y}){\mathrm{Mn}}_{[3\ensuremath{-}(x+2y)]/2}[\mathrm{Fe}{(\mathrm{CN})}_{6}]$. According to the CI cluster model analysis, it is necessary to take into account both the ligand-to-metal charge transfer and the metal-to-ligand charge transfer in describing Fe $2p$ XAS, while the effect of charge transfer is negligible in describing Mn $2p$ XAS. The CI cluster model analysis also shows that the trivalent ${\mathrm{Fe}}^{3+}$ ions have a strong covalent bonding with the $\mathrm{C}\ensuremath{\equiv}\mathrm{N}$ ligands and are under a large crystal-field energy of $10Dq\ensuremath{\sim}3$ eV, in contrast to the weak covalency effect and a small $10Dq\ensuremath{\sim}0.6$ eV for the divalent ${\mathrm{Mn}}^{2+}$ ions.

Soft X-ray absorption spectroscopy study of chemical states, orientation, and oxygen content of ion-irradiated vertically aligned multiwalled carbon nanotubes

Low-energy Ar ions (0.5–2keV) were irradiated onto vertically aligned multiwalled carbon nanotube (VA-MWCNT) films, and the chemical states, orientation, and oxygen content of the irradiated VA-MWCNT films were investigated by soft X-ray absorption spectroscopy (XAS). After irradiation, two additional peaks appeared in the XAS spectra in the C K region, indicating a significant change in the electronic structure. Furthermore, it was found that the VA-MWCNT films were oxidized after irradiation. The results of chemical-state analyses of the XAS spectra in both the C K and O K regions indicated the formation of carboxyl groups (COOH) on the surface of the VA-MWCNT films upon irradiation. The oxygen content of the VA-MWCNT films increased with increasing ion energy and fluence.

Soft X-ray absorption spectroscopy study of multiferroic Bi-substituted Ba1−x Bi x Ti0.9Fe0.1O3

The electronic structures of multiferroic oxides of Ba(1-x)Bi(x)Ti(0.9)Fe(0.1)O(3) (0 < x < 0.12) have been investigated by employing photoemission spectroscopy and soft x-ray absorption spectroscopy (XAS). The measured Fe and Ti 2p XAS spectra show that Ti ions are in the Ti4+ states for all x and that Fe ions are Fe2+-Fe3+ mixed-valent for x > 0. The valence states of Fe ions are found to be nearly trivalent for x=0, and decreases with increasing x from being nearly trivalent (v(Fe)~ 3) for x=0 to v(Fe)~ 2.6 for x=0.12. The valence states of both Ti and Ba ions do not change for all x < 0.12. Based on the obtained valence states of Fe ions, the electronic and magnetic properties of Ba(1-x)Bi(x)Ti(0.9)Fe(0.1)O(3) are explored.

Electronic-Structure Analyses of Li-Ion-Battery Electrodes By Soft X-Ray Absorption/Emission Spectroscopy Including Operando experiments

Improving the energy density and power density of electrode materials for Li-ion batteries (LIBs) is highly important to further develop electric and hybrid-electric vehicles. For the improvements, understanding the charge-discharge mechanisms from a viewpoint of the electronic structure is indispensable. Recently, electronic-structure analyses of the electrode materials using soft x-ray spectroscopy have been of particular importance.In this study we demonstrate operando Mn L 3 soft x-ray emission spectroscopy (XES) for LiMn2O4 [1] which is a typical cathode material of LIB. We developed an operando cell consisting of the LiMn2O4 cathode, a counter electrode and an electrolyte solution [2] by modifying the in situ cell for fuel cell catalysts [3]. The charge-discharge experiments were performed by cyclic voltammetry. The operando XES experiments were carried out using ultrahigh-resolution x-ray emission spectrometer [4] at BL07LSU of SPring-8. The XES spectra were analyzed by theoretical analyses based on the configuration-interaction full-multiplet (CIFM) calculation [5-7].In the operando Mn L 3 XES study for LiMn2O4, we revealed that the open-circuit voltage (OCV) state is almost the same as the initial state consisting of the Mn3+ and Mn4+ states. For the charged state, the Mn L 3 XES spectrum largely changed corresponding to the oxidation of Mn3+ to Mn4+ state at the Mn3+ site for the OCV. The spectrum for the discharged state almost returned to the spectrum for the OCV, while the small difference indicates that the Mn3+ state is slightly enhanced for the discharged state. Thus, the Mn 3d electronic states were reversibly changed for the charge-discharge process [2]. Moreover, charge-transfer (CT) effects between the Mn 3d and O 2p orbitals for each valence state were clarified. For the Mn4+ state, a negative CT energy was determined by the CIFM calculation, suggesting a very strong CT effect from the O 2p to Mn 3d orbitals. In the presentation, XES and soft X-ray absorption spectroscopy studies for other electrode materials will also be reported, and the relationship between the electronic structure and electrochemical performance will be discussed.

High Anodic Performance of Co 1,3,5-Benzenetricarboxylate Coordination Polymers for Li-Ion Battery

We report the designed synthesis of Co 1,3,5-benzenetricarboxylate coordination polymers (CPs) via a straightforward hydrothermal method, in which three kinds of reaction solvents are selected to form CPs with various morphologies and dimensions. When tested as anode materials in Li-ion battery, the cycling stabilities of the three CoBTC CPs at a current density of 100 mA g(-1) have not evident difference; however, the reversible capacities are widely divergent when the current density is increased to 2 A g(-1). The optimized product CoBTC-EtOH maintains a reversible capacity of 473 mAh g(-1) at a rate of 2 A g(-1) after 500 galvanostatic charging/discharging cycles while retaining a nearly 100% Coulombic efficiency. The hollow microspherical morphology, accessible specific area, and the absence of coordination solvent of CoBTC-EtOH might be responsible for such difference. Furthermore, the ex situ soft X-ray absorption spectroscopy studies of CoBTC-EtOH under different states-of-charge suggest that the Co ions remain in the Co(2+) state during the charging/discharging process. Therefore, Li ions are inserted to the organic moiety (including the carboxylate groups and the benzene ring) of CoBTC without the direct engagement of Co ions during electrochemical cycling.