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A binary system of Li2TiO3–LiMnO2 is systematically examined by joint experimental and theoretical studies as electrode materials for Li storage applications. Increase in a fraction of Li2TiO3 effectively activates anionic redox, and thus holes are reversibly formed on oxygen by electrochemical oxidation. Such holes are energetically stabilized through π-type interaction with Mn t2g orbital as suggested by theoretical calculation. However, excess enrichment of Li2TiO3 fractions in this binary system results in the oxygen loss as an irreversible process on delithiation because of a non-bonding character for Ti–O bonds coupled with the formation of O–O dimers, which are chemically and electrochemically unstable species. Additionally, detailed electrochemical study clearly shows that Li migration kinetics is relatively slow, presumably coupled with low electronic conductivity. Nevertheless, nanosizing of primary particles is an effective strategy to overcome this limitation. The nanosized sample prepared by mechanical milling delivers a large reversible capacity, ∼300 mA h g−1, even at room temperature and shows much improved capacity retention. Formation and stabilization of holes for the nanosized sample are also directly evidenced by soft X-ray absorption spectroscopy. From these results, factors affecting the reversibility of anionic redox as emerging new chemistry and its possibility for energy storage applications are discussed in more details.

Lithium- and manganese-rich layered oxides (LMRs) are promising positive electrode materials for next-generation rechargeable lithium-ion batteries. Herein, the structural evolution of Li1.2Ni0.2Mn0.6O2 during the initial charge–discharge cycle was examined using synchrotron-radiation X-ray diffraction, X-ray absorption spectroscopy, and nuclear magnetic resonance spectroscopy to elucidate the unique delithiation behavior. The pristine material contained a composite layered structure composed of Ni-free and Ni-doped Li2MnO3 and LiMO2 (M = Ni, Mn) nanoscale domains, and Li ions were sequentially and inhomogeneously extracted from the composite structure. Delithiation from the LiMO2 domain was observed in the potential slope region associated with the Ni2+/Ni4+ redox couple. Li ions were then extracted from the Li2MnO3 domain during the potential plateau and remained mostly in the Ni-doped Li2MnO3 domain at 4.8 V. In addition, structural transformation into a spinel-like phase was partly observed, which is associated with oxygen loss and cation migration within the Li2MnO3 domain. During Li intercalation, cation remigration and mixing resulted in a domainless layered structure with a chemical composition similar to that of LiNi0.25Mn0.75O2. After the structural activation, the Li ions were reversibly extracted from the newly formed domainless structure.

Conversion-type iron trifluoride (FeF3) has attracted considerable attention as a positive electrode material for lithium secondary batteries due to its high energy density and low cost. However, t...

The photodegradation of methylene blue (MB) was investigated by UV–vis spectroscopy and liquid chromatography-mass spectrometry analyses. For this purpose, undoped, nitrogen-doped, and gold nanoparticle (AuNP)-doped TiO2 thin films for photodegradation were prepared, along with cuboid-shaped WO3 powder samples, some loaded with Pt and the others with Cu. X-ray photoelectron spectroscopy and X-ray absorption near-edge structure analyses revealed that nitrogen atoms were incorporated into the TiO2 crystal both interstitially like KNO3 and NaNO2 and substitutionally like TiN. Mass analysis revealed that MB was degraded under visible-light irradiation via N-demethylation, cleavage of C–N and C–S bonds, and addition reactions of −OH and = O. Products with over m/z values greater than 400 were detected in the solutions degraded by the samples not doped with metals, but not in those degraded by metal-doped samples, which may have been due to the large adsorption capability of the metal-doped samples and their rapid degradation of MB.

Although O3-NaFe

A 41.6MgO-27.1B2O3-31.2SiO2 glass was synthesized by container-less levitation method. B K-edge X-ray absorption near edge structure (XANES) spectroscopy was used to quantify the coordination of boron in the as-made glass, resulting in ~72% of boron in 3-fold coordination. Raman spectroscopy indicated that the glass structure includes depolymerized borate units, which are pyroborate (B2O54−) and ring and/or chain-type metaborate (B3O63−, (BO2O−)∞) groups. The structural changes in the glass under hydrostatic condition were investigated by high-pressure Raman spectroscopy within a diamond anvil cell at pressures up to 8.5 GPa. On the borate structure, metaborate groups decreased with pressure. In contrast, triborate groups, which include tetrahedrally coordinated boron and have a fully polymerized borate network, increased; suggesting that the coordination transformation of B and polymerization were induced via compression. However, the modification of the borate structure units seems to be reversible at least up to 8.5 GPa. As for the silicate network, Q0 and Q1 structures were responsible to compression. Specifically, Q0 could be replaced by Q1 with elevating pressure, which means that the silicate network becomes polymerized with pressure. Whereas, structure of glass samples recovered from the pressure higher than 5 GPa displayed depolymerized silicate network, as dissociation of Q2 to Q1. The observed structural changes in the silicate network implied a partial change of the coordination number of Si4+ ions, which can be enhanced by the presence of a modifier cation with high field strength such as Mg2+.

In lithium–oxygen (Li–O2) batteries, nanocatalysts have been widely employed as a means to suppress the large recharge overpotential and to possibly improve cyclability. However, these studies have consistently been mired with ambiguity relating to the possible exacerbation of side reactions, which in turn has brought into question the role of such catalysts in Li–O2 cells. Here, we shed light on the viability of nanocatalysts by examining the use of Ru, Pt, Pd, Co3O4, and Au nanoparticles supported on carbon nanotubes in Li–O2 cells. We show that while there can be noticeable reduction in overpotential with catalysts, the facile decomposition of Li2O2 is not accompanied by a decrease in side reactions, and as a consequence, there is no notable improvement in rechargeability or cyclability. Instead, highly active catalysts can exhibit nonselectivity for all oxidation reactions including Li2O2 and the electrolyte. This work underscores the importance of metrics beyond simple consideration of the recharge o...

The major challenge facing lithium–oxygen batteries is the insulating and bulk lithium peroxide discharge product, which causes sluggish decomposition and increasing overpotential during recharge. Here, we demonstrate an improved round-trip efficiency of ~80% by means of a mesoporous carbon electrode, which directs the growth of one-dimensional and amorphous lithium peroxide. Morphologically, the one-dimensional nanostructures with small volume and high surface show improved charge transport and promote delithiation (lithium ion dissolution) during recharge and thus plays a critical role in the facile decomposition of lithium peroxide. Thermodynamically, density functional calculations reveal that disordered geometric arrangements of the surface atoms in the amorphous structure lead to weaker binding of the key reaction intermediate lithium superoxide, yielding smaller oxygen reduction and evolution overpotentials compared to the crystalline surface. This study suggests a strategy to enhance the decomposition rate of lithium peroxide by exploiting the size and shape of one-dimensional nanostructured lithium peroxide., While lithium-oxygen batteries offer a green method to power vehicles, the sluggish decomposition of lithium peroxide limits device performance. Here, the authors direct lithium peroxide formation into amorphous nanostructures to enable its facile decomposition and improve charging efficiency.

Based on organelle DNA phylogeographic analyses and ecological niche modeling (ENM), we investigated the range-shift history of the Japanese wingnut (Pterocarya rhoifolia) during the Quaternary climatic oscillations with particular emphasis on the Last Glacial Maximum (LGM). Phylogeographic patterns of this species were determined using 376 individuals from 53 populations for chloroplast DNA sequencing of three spacers. Spatial analysis of molecular variance revealed that the current phylogeographic structure would be sculptured by multiple range shifts from each glacial refugium, which would have been repeated several times during the Quaternary climatic oscillations. High haplotype diversity and private haplotypes were detected in southwestern Japan, where wingnut is currently infrequent and found mainly in high mountains, whereas in northernmost Japan, haplotype diversity was low though this plant is quite common at present. According to ENM approach, during the LGM, the climatically suitable d...

Li2MnO3 is an important parent component in lithium- and manganese-rich layered oxides (LMRs), which are one of the promising positive electrode materials for next-generation lithium ion rechargeable batteries. Here, we report the layered-to-spinel phase transformation in Li2MnO3 during the initial charging process to characterise its unique delithiation behaviour, which gives an insight into the relationship between the structure, superior capacities and degradation of LMR electrodes. The atomic-scale observation using scanning transmission electron microscopy (STEM) techniques suggests that the structural transformation occurs in a biphasic manner within a single particle. The formed phase has a Li-defect spinel structure, indicating that the delithiation leads to Mn migration from the transition-metal layer to the Li layer, accompanied by some oxygen release. This layered-to-spinel phase transformation is an essential bulk process in the initial activation of Li2MnO3. During the lithiation in the 1st discharge, the Mn remigration occurs and the layered structure is again formed with significant disordering. During the multiple cycles, the defect spinel structure is stabilised and becomes more oxygen-deficient with a lower Mn valency. As a consequence, the amount of inserted Li decreases, which corresponds to the capacity and voltage fading observed in Li2MnO3 and LMRs.

Unique heterogeneous catalase-like activity was observed for metallosupramolecular ionic crystals [AuI4CoIII2(dppe)2(d-pen)4]X n ([1]X n ; dppe = 1,2-bis(diphenylphosphino)ethane; d-pen = d-penicillaminate; X n = (Cl-)2, (ClO4-)2, (NO3-)2 or SO42-) consisting of AuI4CoIII2 complex cations, [1]2+, and inorganic anions, X- or X2-. Treatment of the ionic crystals with an aqueous H2O2 solution led to considerable O2 evolution with a high turnover frequency of 1.4 × 105 h-1 for the heterogeneous cobalt complexes, which was dependent on their size and shape as well as the arrangement of cationic and anionic species. These dependencies were rationalized by the presence of cobalt(ii) centers on the crystal surface and their efficient exposure on the (111) plane rather than the (100) plane based on morphological and theoretical studies.

Lithium- and manganese-rich layered oxides (LMRs) are promising positive electrode materials for next-generation rechargeable lithium-ion batteries. Herein, the structural evolution of Li1.2Ni0.2Mn0.6O2 during the initial charge–discharge cycle was examined using synchrotron-radiation X-ray diffraction, X-ray absorption spectroscopy, and nuclear magnetic resonance spectroscopy to elucidate the unique delithiation behavior. The pristine material contained a composite layered structure composed of Ni-free and Ni-doped Li2MnO3 and LiMO2 (M = Ni, Mn) nanoscale domains, and Li ions were sequentially and inhomogeneously extracted from the composite structure. Delithiation from the LiMO2 domain was observed in the potential slope region associated with the Ni2+/Ni4+ redox couple. Li ions were then extracted from the Li2MnO3 domain during the potential plateau and remained mostly in the Ni-doped Li2MnO3 domain at 4.8 V. In addition, structural transformation into a spinel-like phase was partly observed, which is associated with oxygen loss and cation migration within the Li2MnO3 domain. During Li intercalation, cation remigration and mixing resulted in a domainless layered structure with a chemical composition similar to that of LiNi0.25Mn0.75O2. After the structural activation, the Li ions were reversibly extracted from the newly formed domainless structure.

To realize the development of rechargeable sodium batteries, new positive electrode materials without less abundant elements are explored. Enrichment of sodium contents in host structures is required to increase the theoretical capacity as electrode materials, and therefore Na-excess compounds are systematically examined in a binary system of Na

In lithium oxygen (Li–O2) batteries, controlling the structure of lithium peroxide (Li2O2) can reduce the large overpotential of the charge process as this affects the ionic and electronic conductivities of Li2O2. We demonstrate, for the first time, the in situ structural tuning of Li2O2 during the discharge process by virtue of the surface properties of carbon nanotube electrodes. We tailored carbon nanotube surfaces to decouple oxygen functional groups, defective edges, and graphitization, which directly influence the surface-binding affinity of O2 and LiO2. Consequently, conformal and completely amorphous Li2O2 films form in the presence of oxygen functional groups, which can facilely decompose in the subsequent charge. In contrast, crystalline Li2O2 particles grow in more ordered carbon electrodes and consequently require higher overpotential for decomposition. Our comprehensive study reveals the possibility of facile decomposition of Li2O2 by the surface engineering of carbon electrode and gives insi...

A binary system of NaCrO2–TiO2, NaxCrxTi1–xO2 (1.0 ≥ x ≥ 0.5), is systematically examined, and the electrodes’ performance is tested in Na cells. Different layered phases, O3, Na-deficient O3, P2, and P3, are found in this system, as confirmed by X-ray and neutron diffraction techniques. Among them, P2-type Na2/3Cr2/3Ti1/3O2 and P3-type Na0.58Cr0.58Ti0.42O2 show excellent electrode performance as positive and negative electrode materials, respectively. P2 Na2/3Cr2/3Ti1/3O2 shows excellent rate capability as a positive electrode, and average voltage based on Cr3+/Cr4+ redox in a Na cell is increased compared with that of O3-type NaCrO2. The operating voltage of Cr3+/Cr4+ is also enhanced because of an inductive effect of Ti4+ substitution for Cr3+. However, the reversible range is limited to x < 1/3 in Na2/3–xCr2/3Ti1/3O2 associated with partial Cr oxidation to Cr6+ and migration into tetrahedral sites upon charging, as found by X-ray diffraction and X-ray absorption spectroscopy. P3 Na0.58Cr0.58Ti0.42O2 d...

In lithium-oxygen (Li-O2) batteries, it is believed that lithium peroxide (Li2O2) electrochemically forms thin films with thicknesses less than 10 nm resulting in capacity restrictions due to limitations in charge transport. Here we show unexpected Li2O2 film growth with thicknesses of ∼60 nm on a three-dimensional carbon nanotube (CNT) electrode incorporated with cerium dioxide (ceria) nanoparticles (CeO2 NPs). The CeO2 NPs favor Li2O2 surface nucleation owing to their strong binding toward reactive oxygen species (e.g., O2 and LiO2). The subsequent film growth results in thicknesses of ∼40 nm (at cutoff potential of 2.2 V vs Li/Li(+)), which further increases up to ∼60 nm with the addition of trace amounts of H2O that enhances the solution free energy. This suggests the involvement of solvated superoxide species (LiO2(sol)) that precipitates on the existing Li2O2 films to form thicker films via disproportionation. By comparing toroidal Li2O2 formed solely from LiO2(sol), the thick Li2O2 films formed from surface-mediated nucleation/thin-film growth following by LiO2(sol) deposition provides the benefits of higher reversibility and rapid surface decomposition during recharge.

Li-rich layered oxides have attracted attention as promising positive electrode materials for next-generation lithium-ion secondary batteries because of their high energy storage capacity. The participation of the oxygen anion has been hypothesized to contribute to these oxides' high capacity. In the present study, we used O K-edge and Mn L-edge X-ray absorption spectroscopy (XAS) to study the reversible redox reactions that occur in single-phase Li-rich layered manganese oxide, Li2MnO3. We semiquantitatively analyzed the oxygen and manganese reactions by dividing the charge/discharge voltage region into two parts. The O K-edge XAS indicated that the electrons at the oxygen site reversibly contributed to the charge compensation throughout the charge/discharge processes at operating voltages between 2.0 and 4.8 V vs. Li+/Li0. The Mn L-edge XAS spectra indicated that the Mn redox reaction occurred only in the lower-voltage region. Thus, at higher potentials, the electrons, mainly at the oxygen site, contributed to the charge compensation. Peaks whose energies were similar to peroxide appeared in and then disappeared from the O K-edge spectra obtained during the reversible redox cycles. These results indicate that the reorganization of the oxygen network in the crystal structure affects the redox components. By using two kinds of detection modes with different probing depths in XAS measurements, it was found that these redox reactions are bulk phenomena in the electrode.

We investigated the oxygen contributions on delithiation process of different types of layered 3d transition metal oxides, Li2TiO3, Li2MnO3, and LiCoO2, using X-ray spectroscopies with the aid of density functional theory calculations. In delithiatied LiCoO2, electrons are extracted from highly hybridized Co 3d and O 2p orbitals without O2 loss. In Li2TiO3, the hybridized Ti 3d and O 2p orbitals at the valence band is mainly contributed by O 2p orbitals, and delithiated Li2TiO3 loses oxygen as the electrons are extracted. Li2MnO3 exhibits some hybridization. In delithiated Li2MnO3, a certain amount of oxygen is lost, but the large amount of oxidized O anions remains as peroxide and superoxide-like states, which would work as the redox active species. Therefore, the degree of hybridization between metal 3d and O 2p orbitals is a key factor to influence the stability of O anion redox during the oxidation process, which determines the electrode performance.

Although O3-NaFe1/2 Mn1/2 O2 delivers a large capacity of over 150 mAh g-1 in an aprotic Na cell, its moist-air stability and cycle stability are unsatisfactory for practical use. Slightly Na-deficient O3-Na5/6 Fe1/2 Mn1/2 O2 (O3-Na5/6 FeMn) and O3-Na5/6 Fe1/3 Mn1/2 Me1/6 O2 (Me = Mg or Cu, O3-FeMnMe) are newly synthesized. The Cu and Mg doping provides higher moist-air stability. O3-Na5/6 FeMn, O3-FeMnCu, and O3-FeMnMg deliver first discharge capacities of 193, 176, and 196 mAh g-1 , respectively. Despite partial replacement of Fe with redox inactive Mg, oxide ions in O3-FeMnMg participate in the redox reaction more apparently than O3-Na5/6 FeMn. X-ray diffraction studies unveil the formation of a P-O intergrowth phase during charging up to >4.0 V.

FCP-COMPLEX is a newly developed solution containing fluoride, calcium, and phosphoric acid that has the potential to reinforce caries-affected dentin. This study evaluated the effect of FCP-COMPLEX on micro-tensile bond strength (µTBS) and acid-challenge at the dentin-adhesive interface. FCP-COMPLEX, 2% NaF, and distilled water were applied to artificial caries-affected dentin (ACAD) and the effect on acid-induced damage after resin composite restoration was observed. Scanning electron microscopy and X-ray absorption fine structure (XAFS) were used to evaluate tooth morphology. The µTBS test revealed no effect of FCP-COMPLEX either immediately or after 3 months' storage. The area of acid damage in caries-affected dentin was reduced by FCP-COMPLEX. XAFS analysis revealed that absorbed fluorine on the surface would form CaF2. In conclusion, FCP-COMPLEX significantly reduced the damage of acidic attack at the ACAD-adhesive interface, while the µTBS value was maintained after storage.

Recently synthesized Rh-Ni trinuclear complexes hexacoordinated with sulfur ions, 3-aminopropanethiolate (apt) metalloligand [Ni{Rh(apt)$_{3}$}$_{2}$](NO$_{3}$)$_{n}$ ($n$ = 2, 3, 4), are found to be chemically interconvertible between the nominal Ni$^{2+}$ and Ni$^{4+}$ states. In order to clarify the origins of their interconvertible nature and the stability of such a high oxidation state as the tetravalency from the physical point of view, we have systematically investigated the local 3$d$ electronic structures of [Ni{Rh(apt)$_{3}$}$_{2}$](NO$_{3}$)$_{n}$ by means of soft X-ray core-level absorption spectroscopy (XAS). The experimental data have been reproduced by the single-site configuration-interaction cluster-model simulations, which indicate that the charge-transferred configurations are more stable than the nominal $d$-electron-number configuration for $n=3,4$ leading to the prominent charge-transfer effects. These are also supported by S $K$-edge XAS of [Ni{Rh(apt)$_{3}$}$_{2}$](NO$_{3}$)$_{n}$. Our results imply that the found charge-transfer effects have a key role to realize the interconvertible nature as well as the stability of the high oxidization state of the Ni ions., Comment: 16 pages, 4 figures

Since the risk of catch fire using non-aqueous electrolyte solution, aqueous solution-based rechargeable lithium batteries (ARLB) have been highlighted. However, the conventional positive electrodes of lithium transition-metal oxide such as LiCoO2 (LCO) and LiNi1/3Mn1/3Co1/3O2 (NMC) have suffered from poor cyclability in aqueous medium. Representatively, the layered two-dimensional structure of LCO shows notably poor stability, possibly due to the surface degradation from water [1] and proton [2]. The understanding of interfacial reaction of LCO in the aqueous electrolyte solution is still superficial however. Here we present degradation phenomena of LCO electrode in aqueous medium using various X-ray measurement techniques, and suggest the solution to avoid such an irreversible electrochemical reaction. The aqueous solution was prepared with 0.5 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and pH was controlled to ~6.8 and 10. In both cases, there was no evidence for the formation of cathode-electrolyte interphase (CEI) on LCO in contrast to the one with non-aqueous electrolyte solution. The direct contact of aqueous electrolyte solution to LCO surface results in the short-range disorder of LCO structure such as the distortion of octahedral CoO6, and irreversible Li+ desertion during 10 cycles. To improve electrochemical reversibility and structural stability of LCO, we prepared the organic protection layer that opened the Li+ mass transport route while inhibiting H2O contact from hydrophobic surface. As a result, the capacity retention was improved to ~85% during 30 cycles at pH ~ 6.8. Furthermore, we developed the way to protect LCO surface by anion engineering and in the absence of protection layer, which give insight into the inner Helmholtz plane (IHP) structure and its effect for LCO degradation in aqueous medium.

Further increase in energy density of lithium batteries is needed for zero emission vehicles. However, energy density is restricted by unavoidable theoretical limits for positive electrodes used in commercial applications. One possibility towards energy densities exceeding these limits is to utilize anion (oxide ion) redox, instead of classical transition metal redox. Nevertheless, origin of activation of the oxide ion and its stabilization mechanism are not fully understood. Here we demonstrate that the suppression of formation of superoxide-like species on lithium extraction results in reversible redox for oxide ions, which is stabilized by the presence of relatively less covalent character of Mn4+ with oxide ions without the sacrifice of electronic conductivity. On the basis of these findings, we report an electrode material, whose metallic constituents consist only of 3d transition metal elements. The material delivers a reversible capacity of 300 mAh g−1 based on solid-state redox reaction of oxide ions., Energy storage by metal redox reactions sets strict limits on capacity in metal oxide cathode materials used in lithium-ion batteries. Here authors study stabilization of redox reactions at oxygen sites and demonstrate a cathode with a high reversible capacity enabled by the process.

We have examined the local 3d electronic structures of Co-Au multinuclear complexes with the medicinal molecules D-penicillaminate (D-pen) [Co{Au(PPh3)(D-pen)}2]ClO4 and [Co3{Au3(tdme)(D-pen)3}2] by Co L_2,3-edge soft X-ray absorption (XAS) spectroscopy, where PPh3 denotes triphenylphosphine and tdme stands for 1,1,1-tris[(diphenylphosphino)methyl]ethane. The Co L_2,3-edge XAS spectra indicate the localized ionic 3d electronic states in both materials. The experimental spectra are well explained by spectral simulation for a localized Co ion under ligand fields with the full multiplet theory, which verifies that the ions are in the low-spin Co3+ state in the former compound and in the high-spin Co2+ state in the latter., Comment: 7 pages, 5 figures. To be published in J. Phys. Soc. Jpn

Introduction Many attempts have been made to increase the energy density of Li-ion batteries using positive electrode materials such as LiMO2 (LiCoO2, LiNiO2, LiNi1/3Mn1/3Co1/3O2, etc.), which have high charging voltages (typically ≥4.4 V). Various studies to understand the associated degradation mechanism and improve the capacity reversibility during high-voltage charge/discharge have been reported. Generally, the inter-terminal voltage of Li-ion batteries can be practically controlled by changing the electric potential of the positive electrode. Thus, the positive electrodes used for high-voltage charge/discharge are exposed to a high electric potential as well as a large change in the electric potential. In this study, we examined the influence of the operating voltage range on the charge/discharge characteristics, and found that the discharge cutoff voltage greatly influences the capacity reversibility during high-voltage charge/discharge. Additionally, we discuss the mechanisms that determine the capacity reversibility based on the results of electrochemical impedance analysis and soft X-ray absorption spectroscopy (soft XAS). Experimental LiNi1/3Co1/3Mn1/3O2 powder, with a secondary particle diameter of 10 μm (Toda Kogyo Corp.), was used as the active material. Positive electrodes were fabricated from a mixture of 90 wt% LiNi1/3Co1/3Mn1/3O2, 5 wt% acetylene black, and 5 wt% polyvinylidene fluoride. The electrochemical characteristics of the samples were examined in coin cells with a Li-metal counter electrode. A 1.0 mol dm-3 solution of LiPF6 in ethylene carbonate + diethyl carbonate was used as the electrolyte. The cells were cycled at discharge-charge cutoff voltages of 2.5–4.6, 3.0–4.6, 3.8–4.6, and 4.2–4.6 V, at a current rate of 1 C. The Li-ion transfer characteristics were measured by alternating current impedance spectroscopy. The electronic structure of the LiNi1/3Co1/3Mn1/3O2was investigated using soft XAS at the beam line BL11 of Ritsumeikan University SR Center (Shiga, JAPAN). Results and Discussion Figures 1a and b show the discharge capacity and discharge capacity retention versus cycle number for LiNi1/3Co1/3Mn1/3O2 cycled with different voltage ranges. As the discharge cutoff voltage was increased, the initial discharge capacity decreased, accompanied by an improvement in the discharge capacity retention. The retentions at the 143rd cycle for LiNi1/3Co1/3Mn1/3O2cycled with 2.5–4.6, 3.0–4.6, 3.8–4.6, and 4.2–4.6 V, were 8, 37, 56, and 81%, respectively. Figure 2a shows the Nyquist plots for LiNi1/3Co1/3Mn1/3O2 cycled with different voltage ranges at an open circuit voltage of ~4.2 V after 3 cycles. The charge transfer resistances (R ct) calculated from the semicircles in the lower frequency region were almost equal (5–8 Ω) regardless of the discharge cutoff voltage. From the Nyquist plots after 143 cycles (Figure 2b), the R ct for LiNi1/3Co1/3Mn1/3O2 cycled with 2.5–4.6, 3.0–4.6, 3.8–4.6, and 4.2–4.6 V, were obtained as 3800, 300, 65, and 17 Ω, respectively. The increase of R ct with the number of cycles was significantly suppressed as the discharge cutoff voltage was increased, resulting in the higher capacity retention observed in Fig. 1b. These results suggest that a stable interface is retained between the electrode and electrolyte when the charge/discharge voltage is limited to the high-voltage region only. The interface structure and the capacity reversibility mechanism will be discussed along with the electronic state of LiNi1/3Co1/3Mn1/3O2analyzed by soft XAS. Acknowledgements This work is financially supported by the RISINGII project of the NEDO and METI, Japan. Figure 1

Li2FeSiO4 is one of interesting cathode material for lithium ion batteries. The two lithium composition per one iron atom and one poly-anion unit, in principle, exhibits a multi-electron charge transfer with Fe2+/Fe4+redox couple, which enables much high theoretical capacity of 331 mAhg–1. This value is approximately twice as high as the commercialized cathode materials, such as LiCoO2 and LiFePO4. However, the accessible charge-discharge capacity of Li2FeSiO4 was limited to one-electron reaction with Fe2+/Fe3+ redox couple in the early research 1 , 2 ). Recently, some research groups have reported more than one-electron reaction by using nanostructured materials3-6 ). Unfortunately, their high capacity is not stable during charge-discharge cycle and there is a large polarization at high voltage reaction. Therefore, the utilization of Fe2+/Fe3+ redox couple in this system is preferred for the stable battery operation. To maximize this Fe2+/Fe3+ redox reaction in lithium iron silicate system, we investigate composition dependency of Li x Fe2+ (4-x)/2SiO4 on charge-discharge capacity. Although the nonstoichiometric lithium iron silicate has been reported in the previous conference by the other group7 ), we cannot access enough data to discuss the possibility of the nonstoichiometric system. We synthesized various Li x Fe2+ (4-x)/2SiO4 samples and the charge-discharge measurements were performed. Their reaction mechanisms are discussed by using X-ray absorption spectroscopic data. Carbon-coated Li x Fe2+ (4-x)/2SiO4 samples were synthesized by the solid-state reaction. A given amounts of SiO2, FeC2O4・2H2O and Li2CO3 powders were weighed and 10 wt% of carbon (acetylene black) was added prior to mixing. These powders were mixed in a planetary ball mill at 400 rpm for 6 hours. The mixture was calcined at 700°C for 6 hours with a fixed Ar flux. The products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). For electrochemical measurements, Li x Fe2+ (4-x)/2SiO4 samples, carbon black, and polyvinylidene fluoride were mixed at a ratio of 80:10:10 with 1-methyl-2-pyrrolidone. The slurry was coated onto an aluminum foil current collector and dried in a vacuum oven at 80°C. For the charge-discharge measurements, the prepared electrode, lithium metal, and electrolyte-soaked separator (Celgard #2500) were constructed into a stainless steel flat cell. The electrolyte was a 1 mol dm–3 solution of LiPF6 in ethylene carbonate/ethyl methyl carbonate (3:7 volume ratio, Kishida). The cell construction process was performed in an Ar-atmosphere glove box. Galvanostatic charge-discharge measurements were performed at 55°C. For the prepared Li x Fe2+ (4-x)/2SiO4 samples, their crystal structures are almost similar from XRD measurements. Considering the Fe2+/Fe3+ redox reaction in Li x Fe2+ (4-x)/2SiO4 system, the maximum charge-discharge capacity is 203 mAh g-1 in Li1.33Fe1.335SiO4. However, the observed discharge capacity was smaller than the stoichiometric system. The diffusion path of lithium ion might be blocked by the occupation of iron ion in the lithium site. We will discuss the charge-discharge mechanism in this system by using X-ray absorption spectroscopy data. 1) A. Nyten, A. Abouimrane, M. Armand, T. Gustafsson, J.O. Thomas, Electrochem. Commun., 7, 156-160 (2005). 2) A. Nyten, S. Kamali, L. Haggstrom, T. Gustafsson, J.O. Thomas, J. Mater. Chem., 16, 2266-2272 (2006). 3) D. Rangappa, K.D. Murukanahally, T. Tomai, A. Unemoto, I. Honma, Nano Lett., 12, 1146-1151 (2012). 4) Z.X. Chen, S. Qiu, Y.L. Cao, J.F. Qian, X.P. Ai, K. Xie, X.B. Hong, H.X. Yang, J. Mater. Chem. A, 1, 4988-4992 (2013). 5) D.P. Lv, J.Y. Bai, P. Zhang, S.Q. Wu, Y.X. Li, W. Wen, Z. Jiang, J.X. Mi, Z.Z. Zhu, Y. Yang, Chem. Mat., 25, 2014-2020 (2013). 6) T. Masese, C. Tassel, Y. Orikasa, Y. Koyama, H. Arai, N. Hayashi, J. Kim, T. Mori, K. Yamamoto, Y. Kobayashi, H. Kageyama, Z. Ogumi, Y. Uchimoto, J. Phys. Chem. C, 119, 10206-10211 (2015). 7) K. Kam, A. Liivat, D. Ensling, T. Gustafsson, J. Thomas, ECS Meeting Abstracts, MA2009-02, 390 (2009).

A perfluorinated alkyl chain grafted to carbon nanotubes is employed in the lithium–oxygen (Li–O2) cell. We demonstrate a highly localized Li–O2 electrochemical reaction in close proximity to the perfluorinated moiety owing to its high O2 affinity. This hydrophobic modification can provide an enhancement in capacity for a very thin microbattery system.

Li2MnO3-based materials have been extensively studied as positive electrode materials in the past decade. The reaction mechanism of this material had been the controversial subject for a long time. Since the oxidation state of manganese ions is tetravalent, further oxidation of manganese ions is difficult in Li cells. Instead of manganese ions, negatively charged anions, oxide ions (O2-), donate electrons on charge. However, oxidation of oxide ions results in partial loss of oxygen as an irreversible process, i.e., decomposition reaction. The use of anion redox, especially oxide ions, is a crucial strategy to design and develop new electrode materials with high gravimetric/volumetric energy density for rechargeable lithium batteries. Reversible capacity of electrode materials is potentially further increased by the enrichment of lithium contents with less transition metals in the close-packed structure of oxide ions. Our group has reported that Li3Nb5+O4[1] and Li4Mo6+O5[2], which have higher lithium contents than those of Li2MnO3, are potentially utilized as host structures for a new series of high-capacity electrode materials. Among them, Mn3+-substituted Li3NbO4, Li1.3Nb0.3Mn0.4O2 (0.43Li3NbO4 – 0.57LiMnO2), delivers large reversible capacity (approximately 300 mAh g-1) with highly reversible solid-state redox reaction of oxide ions.[1] Recently, Li2Ti4+O3 is also proposed as the host structure for high-capacity electrode materials with redox reaction of oxide ions.[3] Mn3+-substituted sample, 0.5Li2TiO3 – 0.5LiMnO2 (Li1.2Ti0.4Mn0.4O2), also delivers large reversible capacity as shown in Figure 1a. A voltage profile of Li1.2-x Ti0.4Mn0.4O2 quite resembles that of Li1.3-x Nb0.3Mn0.4O2. Available energy density of Li1.2-x Ti0.4Mn0.4O2 exceeds 1,000 mWh g-1 as a positive electrode material. Moreover, charge compensation is realized by oxidation of oxide ions as evidenced by O K-edge X-ray absorption spectroscopy (Figure 1b) as a reversible process. In contrast to the Mn system, an iron counterpart, xLi2TiO3 – (1 – x) LiFeO2 binary system, shows large polarization on charge/discharge,[4] which is similar to that of Li3NbO4-LiFeO2 binary system.[1] For these Fe-containing materials, oxidation of oxide ions seems to trigger oxygen loss as an irreversible process. From these results, we will discuss the origin of stabilization and destabilization in solid-state redox reaction of oxide ions, and the possibility of high-capacity positive electrode materials, which effectively use the solid-state redox of oxide ions for the charge compensation, consisting of only 3d-transtion metals. Acknowledgements This research has been partly supported by Advanced Low Carbon Technology Research and Development Program of the Japan Science and Technology Agency (JST) Special Priority Research Area “Next-Generation Rechargeable Battery.” References [1] N. Yabuuchi, M. Takeuchi, M. Nakayama, H. Shiiba, M. Ogawa, K. Yamanaka, T. Ohta, D. Endo, T. Ozaki, T. Inamasu, K. Sato, and S. Komaba, Proceedings of the National Academy of Sciences, 112, 7650 (2015). [2] N. Yabuuchi, Y. Tahara, S. Komaba, S. Kitada, and Y. Kajiya, Chemistry of Materials, 28, 416 (2016). [3] N. Yabuuchi et al., submitted [4] S. L. Glazier, J. Li, J. Zhou, T. Bond, and J. R. Dahn, Chemistry of Materials, 27, 7751 (2015). Figure 1

High capacity cathode materials of lithium ion secondary battery are desirable to apply to the large-scaled energy devices such as electric vehicles or electricity storage systems. Recently, lithium-rich layered materials such as Li2MnO3 and Li2RuO3 are attended as interesting cathode materials because of their a few times larger theoretical capacity than that of LiCoO2 [1].The reaction mechanism of the lithium-rich cathodes has not been fully understood, especially at the high potential. In this study, Li2MnO3 and Li2RuO3 electrodes were prepared, and the electronic structure change of Li2MnO3 and Li2RuO3 were investigated by using operandosoft X-ray absorption spectroscopy under charge-discharge reaction of these electrodes. The cathode materials were synthesized by solid-state reaction method. Li2MnO3 was prepared from a stoichiometric amount of LiOH-H2O and MnO2. They were dispersed in acetone and ground by a ball milling machine for 3 hours at a speed of 400 rpm using 2 mm ZrO2 beads as grinding media. After drying, the mixture powder was pressed into pellets (10 mm diameter.) and heated at 450 °C for 24 hours in air and then calcined at 400 °C for 48 hours. Li2RuO3 was prepared from LiOH-H2O and RuO2in the same way, however, heated at 1000 °C for 15 hours in air and then ground for 3 hours before calcined at 900 °C for an hour. The cathode for operando X-ray absorption measurements was prepared from a paste by mixing 80 wt% of as-prepared cathode active materials, 10 wt% of acetylene black and 10 wt% of polyvinylidene difluoride binder in 1-methyl-2-pyrrolidone solvent. This paste was coated on the platinum-sputtered silicon nitride thin film. Li4Ti5O12 was used as the counter electrode material and 1 mol/L LiPF6 in an acetonitrile solvent was used as an electrolyte. The operando soft X-ray absorption spectroscopy measurement was carried out at BL27SU of SPring-8. The oxygen K-edge XANES spectra for Li2MnO3 and Li2RuO3 during first charge reaction were measured. For the charge reaction of Li2MnO3, the peaks located at 529.5 eV and 532.0 eV were progressively weaken and broadened (Figure 1a). It implies that the main reaction during the charge process is the oxygen evolution because of the small contribution of Mn 3d - O 2p orbital. For Li2RuO3 (Figure 1b), on the other hand, the peaks at 529.5 eV and 532.0 eV were shifted to the lower energy during the delithiated process from x=2.00 to x=1.00 in LixRuO3 and these peaks were sharpen from x=1.00 to x=0.48. In the Ru L3-egde XANES spectra, the peak was shifted to the higher energy from x=2.00 to x=1.00, however not changed from x=1.00 to x=0.48. These results suggest that the Li2RuO3 charge reaction includes two process, (1) the oxidized reaction of Ru4+→Ru5+, (2) O2 charge compensation owing to the hybridization state between Ru 4d and O 2porbital. This work revealed the contribution of the Ru-O hybrid orbital during the charge process directly and was a guide to design the high-capacity cathode materials in the future. Reference [1] M. Sathiya, K. Ramesha, G. Rousse, D. Foix, D. Gonbeau, A. S. Prakash, M. L. Doublet, K. Hemalatha, and J.-M. Tarascon, Chem. Mater. 25(2013), 1121−1131

Rechargeable lithium batteries have rapidly risen to prominence as fundamental devices for green and sustainable energy development. Lithium batteries are now used as power sources for electric vehicles. However, materials innovations are still needed to satisfy the growing demand for increasing energy density of lithium batteries. In the past decade, lithium enriched materials, Li2MeO3-type layered materials (Me = Mn4+, Ru4+ etc.), which are classified as one of cation-ordered rocksalt-type structures, have been extensively studied as potential high-capacity electrode materials, especially for the tetravalent manganese system (Li2MnO3). Li2MnO3 had been originally thought to be electrochemically inactive because oxidation of manganese ions beyond the tetravalent state in Li cells is difficult. However, the fact is that Li2MnO3 is electrochemically active, presumably because of the contribution of oxide ions for redox reaction. Although the oxidation of oxide ions in Li2MnO3 results in the partial oxygen loss with irreversible structural changes, it has been reported that the solid-state redox reaction of oxide ions is effectively stabilized in Li2Ru1-x Sn x O3 system. Nearly 1.6 moles of lithium ions are reversibly extracted/inserted from/into Li2Ru0.75Sn0.25O3 with excellent capacity retention, indicating that unfavorable phase transition is effectively suppressed in this system. The use of oxide ion redox is the important strategy to further increase the reversible capacity of positive electrode materials for LIBs because the lithium content is potentially further enriched with a lower amount of transition metals in the framework structure. Reversible capacity as electrode materials is not limited by the absence of oxidizable transition metals as a redox center. Negatively charged oxide ions can potentially donate electrons instead of transition metals. However, oxidation without transition metals inevitably result in the release of oxygen molecules, for instance, electrochemical decomposition of Li2O2. Based on these considerations, we have decided to investigate the rocksalt phase with pentavalent niobium ions, i.e., Li3NbO4. Increase in oxidation numbers of transition metals from “tetravalent to pentavalent” states (or even higher than pentavalent) allows us to enrich a lithium content in the close-packed framework structure of oxide ions with fewer transition metals. Similar to Li2MeO3, Li3NbO4 with pentavalent niobium ions is also classified as one of the cation-ordered rocksalt structures. Although Li3NbO4 crystallizes into the lithium-enriched rocksalt-type phase, it is electrochemically inactive because of its insulating character without electrons in a conduction band (4d0 configuration for Nb5+). Therefore, to induce electron conductivity in Li3NbO4, transition metals are partly substituted for Nb5+ and Li+. In this study, x Li3NbO4 – (1-x) LiMeO2 (Me = Mn3+, Fe3+, and V3+) system has been studied as a new series of electrode materials. Among these samples, the Mn3+-substituted sample can deliver large reversible capacities of 250 – 300 mAh g-1 at elevated temperatures (50 – 60 oC). Moreover, the large reversible capacity partly originates from the solid-state redox reaction of oxide ions, which has been evidenced by DFT calculation and soft X-ray absorption spectroscopy. Together with these results, electrode performance and reaction mechanisms are also compared with those of Fe3+- and V3+-substituted samples. From these results, we will discuss the possibility of the new series of positive electrode materials for rechargeable batteries, beyond the restriction of the solid-state redox reaction based on the transition metals used for past three decades.

Despite high theoretical capacity, a Li-O2 cell has suffered from huge oxidation potential polarization on carbon-based positive electrode for charge (>4.2 V vs. Li/Li+), due to sluggish decomposition of non-conductive discharge product, lithium peroxide (Li2O2 ↔ 2Li+ + O2 + 2e-) [1]. Such high potential triggers side reactions such as degradation of electrolyte and carbonaceous electrode, which results in poor cycle-ability [1]. To mitigate this problem during oxygen evolution reaction (OER), solid-state metal or metal oxide nanoparticles (indicated as promoters), which have been widely employed as catalysts in aqueous media, were introduced to the electrode [2]. However, the specific role of promoters in the Li-O2 battery is little known due to complication from accompanying parasitic side reactions [3]. In addition, reasonable comparison of promoters’ activities is not feasible under different performance conditions when various reports were referred [2]. Therefore, to gain a reasonable assessment of their activities in the Li-O2 cell and an understanding of the promoters’ role, it is necessary to examine Li-O2 cells with these promoters under the same condition and analyze their reaction processes in detail. Here I present diagnosis of the true role of promoters, representative of platinum (Pt), gold (Au), palladium (Pd) and cobalt oxide (Co3O4), for OER in Li-O2 cells. After preparation of comparable size and mass loading of promoters on carbon nanotube (CNT) electrode, the Li-O2 cells containing these promoter/CNT combinations were examined using galvanostatic mode under the same operating conditions. The promoter/CNT electrodes show reasonably lower charge potentials than the promoter-free electrode for the 1st charge. Through in situ gas analysis of online electrochemical mass spectroscopy (OEMS) and ex situ chemical analysis of X-ray near-edge fine structure (XANES) spectroscopy, the evolved gas amount and remaining product after charge could be correlated, which accounted for the true reaction occurring for each promoter. References [1] (a) G. Girishkumar, B. McCloskey, A. C. Luntz, S. Swanson and W. Wilcke, J. Phys. Chem. Lett., 2010, 1, 2193–2203; (b) P. G. Bruce, S. A. Freunberger, L. J. Hardwick and J.-M. Tarascon, Nature Mater., 2012, 11, 19–29. [2] (a) Y. –C. Lu, H. A. Gasteiger and Y. Shao-Horn, J. Am. Chem. Soc., 2011, 133, 19048-19051; (b) Z. Peng, S. A. Freunberger, Y. Chen and P. G. Bruce, Science, 2012, 337, 563-566; (c) F. Li, D. –M. Tang, Y. Chen, D. Golberg, H. Kitaura, T. Zhang, A. Yamada and H. Zhou, Nano Lett., 2013, 13, 4702-4707; (d) R. Black, J.-H. Lee, B. Adams, C. A. Mims and L. F. Nazar, Angew. Chem. Int. Ed., 2013, 52, 392–396; [3] B. D. McCloskey, R. Scheffler, A. Speidel, D. S. Bethune, R. M. Shelby and A. C. Luntz, J. Am. Chem. Soc., 2011, 133, 18038-18041. Figure 1