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Garnet-type Li

The ionic conductivity of Li6Y(BO3)3 (LYBO) was enhanced by the substitution of tetravalent ions (Zr4+ and Ce4+) for Y3+ sites through the formation of vacancies at the Li sites, an increase in compact densification, and an increase in the Li+-ion conduction pathways in the LYBO phase. As a result, the ionic conductivity of Li5.875Y0.875Zr0.1Ce0.025(BO3)3 (ZC-LYBO) reached 1.7 × 10−5 S cm−1 at 27 °C, which was about 5 orders of magnitude higher than that of undoped Li6Y(BO3)3. ZC-LYBO possessed a large electrochemical window and was thermally stable after cosintering with a LiNi1/3Mn1/3Co1/3O2 (NMC) positive electrode. These characteristics facilitated good reversible capacities in all-solid-state batteries for both NMC positive electrodes and graphite negative electrodes via a simple cosintering process.

An impurity-free interface was achieved in an oxide-based all-solid-state battery (ASSB) after cosintering, which was facilitated by an enhanced thermal stability between the layered rock-salt LiMO...

Designing composite electrodes with optimal microstructure, composition, and choice of active material (AM) as well as solid electrolyte (SE) is critically important for the development of high-per...

The performances of electrochemical systems such as solid-state batteries (SSBs) can be severely hindered by the three-dimensional (3D) and mesoscopically inhomogeneous electrochemical reactions th...

The use of oxide electrolytes promises the safety of Li-ion batteries but complicates the fabrication of electrochemical interfaces. Herein, we report the facile preparation of ionic-transferable i...

In light emitting diodes, Y3Al5O12:Ce (YAG:Ce) is used as a yellow phosphor in combination with blue LEDs but lacks a red component in emission. Therefore, considerable efforts have been directed toward shifting the emission of YAG:Ce to longer wavelengths. In this study, a Y3Al5O12 (YAG) crystal incorporating a high content of Ce, (Y1−xCex)3Al5O12 (0.006 ≦ x ≦ 0.21), was successfully prepared by a polymerized complex method in which low-temperature annealing (650–750 °C) was employed prior to sintering at 1080 °C. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis indicated that the obtained sample was a single phase YAG crystal with x ≤ 0.21. Interestingly, orange-red emission was observed with x ≥ 0.07 with UV-blue light irradiation. With excitation at 450 nm, the emission peak increases from 538 nm (x = 0.006) to 606 nm (x = 0.21). This massive red shift in the high-x region was not observed without the 1st step of low-temperature annealing, which implied that low-temperature annealing was essential for incorporating a high concentration of Ce. The precursor formed by low-temperature annealing was amorphous at x = 0.04, whereas CeO2 nanocrystals were formed in the amorphous material with x ≥ 0.11, based on the XRD and TEM results. CeLIII X-ray absorption edge structure revealed that Ce existed as Ce4+ in the precursor and Ce3+ in the obtained crystal. It was speculated that CeO2 was formed at low temperature, releasing oxygen, with sintering at 1080 °C, leading to the incorporation of Y3+ in the Ce–O framework. The lattice constant increased significantly from 12.024 A to 12.105 A with increasing x, but the crystal field splitting did not increase and was constant from x = 0.06 to x = 0.21. Hence, the massive red shift in emission was not explained by the large crystal field splitting, but instead by the Stokes shift.

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 ionic conductivity of Li

High-rate operation of oxide-based bulk-type all-solid-state batterie (ASSB) is achieved not only by the development of novel oxide electrolyte (OE) with high bulk ionic conductivity but also by the formable processes of ion-transfer-suited interfaces by powder sintering. Unlike for sulfides and hydrides, the ionic conduction of oxides is bottlenecked by that at grain-boundaries (GBs), that are at the electrolyte/electrolyte homo-interfaces. Moreover, desirable electrode/electrolyte heterointerfaces were difficult to be fabricated by powder sintering because most electrode materials easily engage in thermochemical reactions with the electrolyte. This chapter focuses on the interface formation techniques based on the usage of OE powder.

The performances of electrochemical systems such as solid-state batteries (SSBs) can be severely hindered by the three-dimensional (3D) and mesoscopically inhomogeneous electrochemical reactions that take place in the electrodes. However, the majority of existing methods for analyzing such inhomogeneous reactions are restricted to one- or two-dimensional observations. Herein, we performed 3D

In light emitting diodes, Y

Bulk-type solid-state batteries using a LIthium Super Ionic CONductor (LISICON)-based oxide electrolyte, Li4-2xGe1-xSxO4, were assembled by spark plasma sintering (SPS) and electric furnace sintering (FS), and their charge-discharge performances were investigated. Li4-2xGe1-xSxO4, which has a γ-Li3PO4-type structure, was synthesized by conventional solid-state reaction. The total ionic conductivity of the Li3.6Ge0.8S0.2O4 sample sintered at 600 °C by SPS was 2 × 10−5 S cm−1 at room temperature, which is comparable to the bulk conductivity of the material sintered at 800–1100 °C by FS. No impurity peaks were observed in the X-ray diffraction patterns of the LiNi1/3Mn1/3Co1/3O2-Li3.6Ge0.8S0.2O4 mixture even after high-temperature sintering at 900 °C by FS. The solid-state cells of laminated LiNi1/3Mn1/3Co1/3O2 cathode and Li3.6Ge0.8S0.2O4 electrolyte co-sintered by SPS at 600 °C and FS at 900 °C exhibited first discharge capacities of 130 and 92 mAh g−1, respectively, at 60 °C. These experimental results confirm that the LISICON-based material, Li4-2xGe1-xSxO4, exhibits thermal compatibility to the active material and relatively high lithium ion conductivity, which lead to the high charge-discharge performance of the bulk-type all-solid-state cell.

The commercialization of sintered solid-state devices using oxide electrolyte is hindered by their low total conductivity, which largely originates from high ionic resistance at grain boundaries (G...

Rechargeable potassium-ion batteries have been gaining traction as not only promising low-cost alternatives to lithium-ion technology, but also as high-voltage energy storage systems. However, their development and sustainability are plagued by the lack of suitable electrode materials capable of allowing the reversible insertion of the large potassium ions. Here, exploration of the database for potassium-based materials has led us to discover potassium ion conducting layered honeycomb frameworks. They show the capability of reversible insertion of potassium ions at high voltages (~4 V for K2Ni2TeO6) in stable ionic liquids based on potassium bis(trifluorosulfonyl) imide, and exhibit remarkable ionic conductivities e.g. ~0.01 mS cm−1 at 298 K and ~40 mS cm–1 at 573 K for K2Mg2TeO6. In addition to enlisting fast potassium ion conductors that can be utilised as solid electrolytes, these layered honeycomb frameworks deliver the highest voltages amongst layered cathodes, becoming prime candidates for the advancement of high-energy density potassium-ion batteries. The development of potassium-ion batteries requires cathode materials that can maintain the structural stability during cycling. Here the authors have developed honeycomb-layered tellurates K2M2TeO6 that afford high ionic conductivity and reversible intercalation of large K ions at high voltages.

The compound NaFe2(PO4)(SO4)2 is successfully synthesized via a solid state reaction route and its crystal structure is determined using powder X-ray diffraction data. NaFe2(PO4)(SO4)2 phase is also characterized by cyclic voltammetry, galvanostatic cycling and electrochemical impedance spectroscopy. NaFe2(PO4)(SO4)2 crystallizes with the well-known NASICON-type structure. SAED and HRTEM experiments confirm the structural model, and no ordering between the PO4−3 and SO4−2 polyanions is detected. The electrochemical tests indicate that NaFe2(PO4)(SO4)2 is a 3 V sodium intercalating cathode. The electrical conductivity is relatively low (2.2 × 10−6 Scm−1 at 200 °C) and the obtained activation energy is ∼0.60eV. The GITT experiments indicate that the diffusivity values are in the range of 10−11-10−12 cm2/s within the measured sodium concentrations.

We calculate the atomic and electronic structures of trirutile-type ${\mathrm{Li}}_{x}{\mathrm{FeF}}_{3}\phantom{\rule{4pt}{0ex}}(x=0,0.25,0.5,0.75,\phantom{\rule{4pt}{0ex}}\text{and}\phantom{\rule{4pt}{0ex}}1)$ by first-principles calculations and evaluate the relative stability among the optimized structures by energy analysis. ${\mathrm{Li}}_{0.5}{\mathrm{FeF}}_{3}$ is more stable than the three-phase coexistence of ${\mathrm{FeF}}_{3},{\mathrm{FeF}}_{2}$, and LiF, whereas the other compositions are unstable. The analyses of the local electron density, local atomic volume, and local atomic configurations show that the formal valence of Fe atoms decreases from trivalent (3+) to divalent (2+) after Li insertion. In addition, we calculate Fe $K$-edge x-ray absorption near-edge structure (XANES) spectra in ${\mathrm{Li}}_{x}{\mathrm{FeF}}_{3}$ and compare them with observed spectra. The calculated XANES spectra agree well with the corresponding observed spectra in areas such as the spectral shape and relative position of the main peaks associated with ${\mathrm{Fe}}^{3+}$ and ${\mathrm{Fe}}^{2+}$. In particular, partial XANES spectra of ${\mathrm{Fe}}^{3+}$ in ${\mathrm{Li}}_{x}{\mathrm{FeF}}_{3}$, for $x=0.25,0.5$, and 0.75, have a specific peak between the main peaks, associated with ${\mathrm{Fe}}^{3+}$ and ${\mathrm{Fe}}^{2+}$. The detailed study reveals that the energy level and intensity ratio of the ${\mathrm{Fe}}^{3+}$ main peaks depend on the adjacent cation site of Fe.

Oxide-based all-solid-state lithium-ion battery is prepared by a conventional sintering process, thanks to the intrinsic low melting point of Li2.2C0.8B0.2O3. A well-defined interface between LiCoO2 and Li2.2C0.8B0.2O3 was confirmed without any traces of impurities. Li ion reversibly (de-)intercalated from/into LiCoO2 at initial charge–discharge process when the charge capacity was limited to 120 mAh g− 1. The capacity degradation after subsequent cycling was suppressed by further limitation of the charging capacity. However, capacity fade could still be confirmed after 20 cycles albeit the capacity was limited at 60 mAh g− 1. This study suggests large repetitive expansion–contraction of the electrode during cycling as a possible cause of fatigue failure of the electrode/oxide electrolyte interface.

Structure and valence state change of Li 2 RuO 3 and ruthenium-substituted lithium manganese oxide, Li 2 Mn 0.4 Ru 0.6 O 3 (LMR), with layered structure were investigated using Synchrotron X-ray diffraction (SXRD) and X-ray absorption spectroscopy measurements before and after electrochemical cycling. The charge–discharge voltage curves of both LMR and Li 2 RuO 3 significantly vary in the subsequent cycle. The SXRD Rietveld structural refinements demonstrate that the LMR undergoes irreversible structural transition. The Mn K-edge spectra confirm the structural modification in the MnO 6 octahedra with Li de-intercalation. The Ru L-edge spectra for LMR show similar behavior to Li 2 RuO 3 during electrochemical cycling. These spectra appear reductive peak shift on the way to charging to 4.8 V. The phenomena are not attributed to the reduction of hexavalent Ru to pentavalent but a variation of the splitting between bonding and anti-bonding e g orbitals. The charge–discharge reactions mechanism of LMR and Li 2 RuO 3 are discussed.

1. Purpose Solid-state lithium-ion batteries (SSLIBs) have attracted extensive attentions because of their potentials to improve safety and to achieve higher power and energy densities compared with the conventional lithium-ion batteries. In composite electrodes for SSLIBs, particles of active material (AM) and solid electrolyte (SE) are three-dimensionally distributed and form complicated Li-ion and electron pathways. Then, especially during high rate charging/discharging, the inhomogeneous reaction distribution may be formed in the electrode. The reaction distribution can substantially deteriorate the battery performances of SSLIBs such as capacity, power output, rate capability, and cyclability. Therefore, understanding how the reaction distribution affects the battery performances is crucial for the development of high-performance SSLIBs. In this study, we performed operando three-dimensional (3D) observation of reaction distributions in composite electrodes for SSLIBs using CT-XAFS1 to elucidate the influence of reaction distributions on the battery performances of SSLIBs. 2. Experimental An SSLIB cell with a configuration of Li x CoO2 (LCO)-Li2.2C0.8B0.2O3 (LCBO) composite electrode|LCBO electrolyte|poly (ethylene oxide) (PEO)-based polymer electrolyte|Li metal electrode was fabricated based on the literature2. The composite electrode comprised 8 mg of LCO and 2 mg of LCBO. The SSLIB cell was charged to 4.5V and discharged to 2.0 V with a current of 240 μA (0.3 C) for 3 cycles at 100 °C. The reaction distribution in the composite electrode was observed every 40 minutes during charging and discharging using operando CT-XAFS. The CT-XAFS measurements were carried out in the energy range between 7725.5-7730 eV with an energy step of 0.1 eV under an exposure time of 20 ms per energy and projection angle from -65 to 65° with an angle step of 0.1°. The observation area was 517 × 517 × 49 μm. The spatial and time resolutions were 3.1 μm and 40 min., respectively. 3. Results and Discussion Figure 1(a) shows the charge-discharge curves of the SSLIB cell. The SSLIB cell exhibited the initial charge and discharge capacities of 84 and 46 mAh·g−1, respectively. Those degraded to 24 and 13 mAh·g−1 in the 2nd cycle, and 12 and 12 mAh·g−1 in the 3rd cycle, respectively. Figure 1(b) shows the 3D charging state (Li content) maps of the composite electrode and the representative 2D cross-sectional charging state maps in the in-plane direction at the end of 1st, 2nd, and 3rd charge. Colored/uncolored areas stand for the regions where the AMs exist or not, respectively. The red/blue areas stand for the charged (x = 0.6) /discharged (x = 1.0) AMs, respectively. After the 1st charge, the AMs generally showed a high charging state (red). However, the regions with high charging state significantly decreased after the 2nd charge, and most of the AMs showed a charging state corresponding to x = 0.7 ~ 0.8 (green). The regions with high charging state further decreased after the 3rd charge, and AMs with a low charging state were increased (blue). To more precisely investigate where the less-charged AMs existed after the 2nd and 3rd charge, we subtracted the charging state map after the 1st discharge from that after the 2nd charge, and also the charging state map after the 2nd discharge from that after the 3rd charge (Fig. 1(c)). The 2D maps in Fig. 1(c) thus indicate to what extent the charge reaction progressed during the 2nd or 3rd charge compared with the end of the 1st or 2nd discharge, respectively. The red/blue areas in Fig. 1(c) represent the AM regions where the reaction progressed (Δx = 0.4) or not (Δx = 0) from the end of the 1st or 2nd discharge, respectively. As shown in the left map in Fig. 1(c), the inner parts of the aggregated AMs were significantly less charged compared to the regions near AM/SE interfaces during the 2nd charge. Similarly to the 2nd charge, the charge reaction preferentially progressed near the AM/SE interfaces, while the reaction insufficiently progressed at the inner parts of the aggregated AMs during the 3rd charge. Such a variation in the charging state distribution during cycling could be explained by considering the microstructural change due to the expansion/shrinkage of AM particles. The above results suggest that the expansion/shrinkage of AM particles reduced the connections between AM particles but did not reduce the AM/SE interfaces. We further discuss the mechanism of the capacity degradation during cycling in the presentation. References: (1) H. Matsui et al., Angew. Chem. Int. Ed., 56, 9371 (2017). (2) T. Okumura et al., Solid State Ionics, 288, 248 (2016). Acknowledgement: This work was supported by JST ALCA-SPRING (JPMJAL1301). Figure 1

Submicron particles of Na SuperIonic CONductor (NASICON)-type Li2O-Al2O3-TiO2-P2O5 (LATP) are possible to be densified at low temperature of 300 ºC by applying high pressure of 600 MPa during spark-plasma sintering (SPS) process. This process provides a novel route for assembling bulk-type all-solid-state lithium-ion battery (ASS-LIB), which promises high safety and high durability of energy storages since the origins of flammability and undesirable electrochemical events are prevented by using oxide as an electrolyte instead of the non-aqueous liquid. The main challenge for assembling bulk-type ASS-LIB are how to reduce the sintering temperature of the oxide electrolyte since most of the electrode materials decompose readily at high temperatures. Previously, we have attempted to design LiCoO2-electrode/NASICON-type LiTi2(PO4)3-electrolyte interface by conventional SPS process since quick/low-temperature treatment by the SPS has a possibility for reducing the decomposition kinetically.1 However, the several-μm ion-blocking interphase was easily-produced at the interface. Therefore, further low-temperature technique is required for the design of impurity-free electrode/electrolyte heterointerfaces. Commonly, the low-temperature sinterability of ceramic (or metal) particles could be accomplished with the increase of the contact for active surfaces by reducing particle size and/or applying higher pressure under sintering. Kinemuchi et al. has suggested that the low-temperature densification (LTD) of the oxide was performed by combining the use of nano particles and external pressure of over several-hundred MPa during the SPS.2 The LTDs for lithium-ion conductive oxides have possibilities for producing impurity-free electrode/electrolyte interface, and therefore would be one of the promising techniques for assembling oxide-based bulk-type ASS-LIB. In the present study, we used submicron size of NASICON-type Li2O-Al2O3-TiO2-P2O5 (LATP) powder as high bulk lithium-ion conductive oxides, which have been developed as Lithium Ion Conductive Glass Ceramics; LICGCTM, by OHARA INC..3,4 The densification of the LATP powder compact could be certified at low temperature of 200 - 250 °C under applying a pressure of 600 MPa during the SPS. Generally, the LTDs for oxides were achieved using not submicron particles but nano particles. However, the LTDs of the submicron-size particles could be confirmed in a phosphate group, which includes Li3PO4, AlPO4, and also LATP. Therefore, the bulk-type ASS-LIBs with phosphate-based electrodes such as LiFePO4 and Li2CoPO4F were successfully assembled by the LTD processes because the undesirable-thermal impurities at electrode/electrolyte interface were prevented during the low-temperature treatment. The characterization of LiFePO4/LATP interface and the electrochemical performance of ASS-LIB cell (Li/dry polymer/LATP/LiFePO4) will be presented in the conference. References [1] Y. Kobayashi et al., J. Power Sources, 1999, 81-82, 853. [2] Y. Kinemuchi et al., RSC Adv., 2016, 6, 24661. [3] J. Fu, Solid State Ionics, 1997,96, 195. [4] J. Fu, J. Mater. Sci., 1998, 33, 1549.

A unique charge/discharge mechanism of amorphous TiS4 is reported. Amorphous transition metal polysulfide electrodes exhibit anomalous charge/discharge performance and should have a unique charge/discharge mechanism: neither the typical intercalation/deintercalation mechanism nor the conversion-type one, but a mixture of the two. Analyzing the mechanism of such electrodes has been a challenge because fewer tools are available to examine the “amorphous” structure. It is revealed that the electrode undergoes two distinct structural changes: (i) the deformation and formation of S–S disulfide bonds and (ii) changes in the coordination number of titanium. These structural changes proceed continuously and concertedly for Li insertion/extraction. The results of this study provide a novel and unique model of amorphous electrode materials with significantly larger capacities.

To compensate the large irreversible capacity (Qirr), lithium was pre-doped to Si thin flakes (Si Leaf Powder® (Si-LP), thickness: 100 nm) for different times, and its effects on the charge/discharge characteristics such as reversible capacity, cycleability, and rate-capability were investigated in detail. The charge/discharge test results showed that a large initial Qirr of ca. 2300 mAh g− 1 for the Si-LP can be completely compensated by Li pre-doping, and a high capacity (> 2500 mAh g− 1) was obtained for pre-doped Si-LPs. The pre-doping did not cause any harmful effects on cycleability as long as lithium was uniformly pre-doped. The addition of vinylene carbonate to the electrolyte solution in the pre-doping and in the test cell greatly improved the cycleability, and a high discharge capacity of ca. 2300 mAh g− 1 was kept after 40 cycles.

Bulk and surface structural changes induced in a Li5FeO4 positive electrode with a defect anti-fluorite type structure are examined during its initial charge–discharge cycle by various synchrotron-radiation analysis techniques, with a view to determining the contribution of oxygen to its electrochemical properties. Bulk structural analyses including XRD, Fe K-edge XANES and EXAFS reveal that pseudo-cubic lithium iron oxides (PC-LFOs), in the form of LiαFe(4−α)+O2, are formed during the first charging process instead of the decomposition of pristine Li5FeO4. Moreover, the relative volume of this PC-LFO phase varies nonlinearly according to the charging depth. At the same time, the surface lithium compounds such as Li2O cover over the PC-LFO phase, which also contribute to the overall electrochemical reaction, as measured from the O K-edge XANES operating in a surface-sensitive total-electron yield mode. The ratio of these two different reaction mechanisms changes with the depth during the first charging process, with this tendency causing variation in the subsequent discharge capacity retention in relation to the depth of the charging electron and/or temperature of this “Li-rich” positive electrode. Indeed, such behaviour is noted to be very similar to the specific electrochemical properties of Li2MnO3.

X-ray absorption near-edge structure (XANES) spectroscopy, which reveals the features of the electronic and local structure, of lithium manganese oxides LixMn2O4 (x = 0–2) was examined using first-principles calculations. Both the easily observable parts and the tiny peaks of the theoretical Mn K-edge XANES spectra agreed with the experimental spectra. From the theoretical results of two anti-ferromagnetic LiMn2O4 models, the contributions of the Mn3+ ion and Mn4+ ion centers to the XANES spectra differ due to the difference in the overlap between the Mn 4p partial density of state (PDOS) and the O 2p PDOS. Similar results can be also seen by comparing the theoretical XANES spectra and the PDOS between Li(Mn3+Mn4+)O4 and de-intercalated Li0.5(Mn3+0.5Mn4+1.5)O4 and Mn4+2O4 (λ-MnO2). The XANES spectral changes with the lithium ion displacement (six- to four-coordination) due to the phase transition (cubic Fdm LiMn2O4 to tetragonal I41/amd Li2Mn2O4) can be determined by the indirect contribution of the Li 2p PDOS to the Mn 4p PDOS via the O 2p PDOS.

Oxides are generally non-flammable, durable and non-toxic materials; high safety and reliability in a battery system is assured by the use of oxide as an electrolyte instead of the highly-reactive non-aqueous liquid. To develop an oxide-based solid-state all-lithium-ion battery (ASS-LIB) for large-scale applications such as next-generated wireless IoT devices, the thicknesses of stacked electrode and electrolyte layers need to be curtailed to several ten to hundred μm order. Although the powder technology is an easy formula for obtaining such thick electrode layers, some sort of powder interfacial design is required for the fast-ionic transfer at the electrode/electrolyte hetero-interface. Present-progressive oxide-based electrolytes as perovskites or garnets have high conductivities of ≈ 10-3 S cm-1, but were generally difficult to design the ionic-transferable interface since most electrode materials easily engage in thermochemical reactions with the aforementioned electrolytes. In present study, γ-Li3PO4-type Li3.5Ge0.5V0.5O4 (LGVO), which was one of the Lithium Super-Ionic Conductor (LISICON) families, was focused on as electrolyte of the SS-LIB.1 The LGVO was synthesized via a conventional solid-state reaction, in which pre-prepared Li4GeO4 and pre-prepared Li3VO3 were used as the starting materials. The required amount of each material was ground and cold-pressed into a pellet, and then heated at 700 °C for 12 h. A single γ-Li3PO4-type phase was identified by a powder XRD pattern of the mortar-milled pellet. The prepared LGVO powder was put in a 80 mL ZrO2 cap with five of 20 mm ZrO2 disks, and was further-crushed by disk mill for obtaining sub-micron-sized fine powder before sintering processes. Samples for AC impedance measurement were prepared by two sintering process; conventional furnace sintering (CFS) of uniaxial pressing powder and SPS of Au/ LGVO powder/Au. (Both sides were polished and coated with Au after CFS process.) The sintering temperature and time at CFS and SPS were 700 °C, 2 h and 650 °C, 1 min, respectively. Total Li-ion conductivities for LGVO SPS pellet was 9.5 × 10-5 S cm-1 at 25 °C, which was slightly higher than that of CFS pellet: 8.5 × 10-5 S cm-1 because of the minimalizing grain-boundary resistance. The conductivity was enhanced due to reducing the high-resistive layer near the grain boundary by a short period of SPS process, which has been confirmed in case of γ-Li3PO4-type Li3.5Ge0.75S0.25O4.2 No impurity peak was observed in the powder XRD pattern of the LiNi1/3Mn1/3Co1/3O2 (NMC)-LGVO co-sintered composite produced by either CFS or SPS. This result indicates that the LGVO is thermally-stable during fabricating SS-LIB by powder process. Composite electrode powder was prepared from a mixture of 50 wt% NMC and 50 wt% LGVO. A layer-stacking compact (Au | composite electrode powder | LGVO powder as separator) was co-sintered by SPS process at 500 °C for 1 min. A lithium foil was used as a reference/counter electrode. A poly-(ethylene oxide)-based dry polymer electrolyte film was inserted between the lithium foil and the LGVO electrolyte to reduce the interfacial resistance with adhesion. Electrochemical charge-discharge test was performed at a constant current of 50 μA cm-2 at 60 °C. The SS-LIB shows the reversible charge/discharge capacities of over 120 mAh g-1 thanks to using LGVO electrolyte, which possess the relatively high conductivity of ≈ 10-4 S cm-1 and high thermally-stability even under co-sintering with NMC electrode. Acknowledgements This work was financially supported by the Advanced Low Carbon Technology Research and Development Program of the Japan Science and Technology Agency for Specially Promoted Research for Innovative Next Generation Batteries (JST-ALCA SPRING). Reference s : [1] J. Kuwano and A. R. West, Mat. Res. Bull., 15 (1980) 1661. [2] T. Okumura, S. Taminato, T. Takeuchi and H. Kobayashi, ACS Appl. Energy Mater., 1 (2018) 6303.

The electronic structural changes during lithium-ion intercalation/de-intercalation process of nickel substituted lithium manganese spinel oxides have been investigated by using X-ray absorption near-edge structure (XANES) spectra of O K-edges as well as Ni L 3 -edges and Mn L 3 -edges. The results of the XANES spectra indicate that the electronic structure of both manganese and oxygen atoms contribute on the redox reaction at 0.06 ≤ x x ≤ 1.78 in Li x Ni 0.5 Mn 1.5 O 4 . Thus, the electronic structural change of oxygen atom is also crucial for considering redox reaction at intercalation/de-intercalation process, and the contribution of the oxygen atom on redox reaction differs in various redox cation species.

Experimental Mn and Ni K-edge X-ray absorption near-edge structure (XANES) spectra were well reproduced for 5 V-class LixNi0.5Mn1.5O4 spinels as well as 4 V-class LixMn2O4 spinels using density functional theory. Local environmental changes around the Mn or Ni centres due to differences in the locations of Li ions and/or phase transitions in the spinel oxides were found to be very important contributors to the XANES shapes, in addition to the valence states of the metal ions.

Li 1.20 − y Ni 0.17 Co 0.10 Mn 0.53 O 2 ( y = 0.1–0.93) were prepared electrochemically and characterized using synchrotron XRD and XAFS measurements. Structural analysis using XRD data demonstrated that the lattice parameters of Li 1.20 Ni 0.17 Co 0.10 Mn 0.53 O 2 are a = 0.285214(7) nm and c = 1.42173(3) nm and that the chemical composition can be expressed referring to the Wyckoff positions 3 a and 3 b as [Li 0.988 Ni 0.012 ] 3 a [Li 0.212 Ni 0.158 Mn 0.53 Co 0.10 ] 3 b O 2 . The M ( M = Ni, Co, and Mn) K and L-edge XAFS results suggested that the Li de-intercalation from Li 1.20 Ni 0.17 Co 0.10 Mn 0.53 O 2 proceeded mainly by the oxidation of Ni and Co ions up to y = 0.4 and then by the removal from oxygen from the lattice up to y = 0.93. On the other hand, the O K-edge XANES results indicated no increase in Li 2 CO 3 or Li 2 O on the surface of the positive electrode materials with Li de-intercalation. These results demonstrate that the XAFS method using a combination of soft and hard X-ray is effective way of clarifying the Li de-intercalation/intercalation of the positive electrode materials.

TiO2–B nanowires were prepared by hydrothermal reaction, and the nanosized effect on lithium-ion insertion was investigated by using X-ray absorption spectroscopy (XAS). On the basis of the results of O K-edge X-ray absorption near-edge structure (XANES) of TiO2–B with various particle sizes, it was suggested that the surface of TiO2–B has local and electronic structures being different from the bulk, and the band energy of surface of TiO2–B was lower than that of the bulk. The band vended structure, which is called the space charge layer (SCL), makes lithium-ion insertion in TiO2–B smooth because the local structure of the SCL is maintained during the lithium-ion insertion, which is shown by Ti K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. It is suggested that control of the SCL, that is the nanosized effect, is a new design concept for achieving higher rate capability.

Lithium-ion transfer reactions at the interface between insertion electrodes and electrolyte solutions were investigated by using partially fluorinated lithium manganese spinel oxides as model electrodes. LiMn1.8Li0.1Ni0.1O4−ηFη (η = 0, 0.018, 0.036, 0.055, 0.073) were synthesized as model compounds. Electrochemical impedance spectroscopy was carried out to evaluate the influence of surface fluorine on the interfacial lithium-ion transfer process. Taking an adion model into account, it is considered that an adion formation process takes place with partial desolvation, and then a process with surface diffusion of the adion occurs followed by the electrode incorporation of the adion with the loss of the remaining solvent. The adion model was also used to compare the interfacial resistances for the lithium-ion transfer process. It was suggested that the fluorine substitution influences the latter process. The importance of structural characterization at the electrode surface on the lithium-ion transfer behav...

As a low-cost alternative to lithium, potassium-ion battery (PIB) has recently attracted great attention. PIB can be a high-voltage contender considering the significantly negative potential of the K+/K redox couple, which is close to or even lower than Li depending on the solvent [1,2]. Nonetheless, the large ionic radius of potassium coupled with significant strain accompanying potassium (de)insertion, the number of potassium-based compounds (particularly, cathode materials) that can practically be utilized is limited. Exploration of the broad class of orthotellurate frameworks based on K6TeO6 has led us to identify new cathode frameworks that can reversibly (de) insert potassium ions, not only at high voltage but also at decent capacities. Figure 1 shows a layered crystal structure of K2Ni2TeO6, a new cathode material synthesized via the conventional solid state method. The structure entails a honeycomb-like network of NiO6 octahedra (in purple) surrounding each TeO6 octahedon (in blue). Potassium atoms (in brown) occupy trigonal prismatic sites sharing faces with NiO6 or TeO6 octahedra. During the meeting, we will highlight the synthesis, crystal structure and electrochemical performance of K2Ni2TeO6 as a new cathode material for PIB [3]. Reference s : [1] Y. Marcus, Pure Appl. Chem., 57 (1985) 1129-1132. [2] S. Komaba, T. Hasegawa, M. Dahbi and K. Kubota, J . Power Sources, 60 (2015) 172-175. [3] T. Masese, K. Yoshii, T. Okumura, H. Senoh, M. Shikano, manuscript submitted. Figure 1. Schematic presentation of K2Ni2TeO6 viewed along [110] direction. NiO6 tetrahedra (blue), TeO6 octahedra (purple), and K atoms (brown) are illustrated. Figure 1

Two types of oxide nanosheet-based materials, H3O+-form regularly stacked manganese oxide nanosheets (H3O+-RG(Mn)) and H3O+-form randomly restacked manganese oxide nanosheets (H3O+-RE(Mn)) were synthesized by soft chemical methods, and their oxygen reduction reaction (ORR) activities were examined by cyclic voltammetry (CV) and semi-steady-state voltammetry (SSV) with a rotating ring-disc electrode at 70 °C in 0.1 M KOH. Both samples showed high onset potentials (Eon) of the ORR current and high efficiencies (Eff4) of the 4-electron reduction of oxygen, and Eon and Eff4 values were improved by electrochemical oxidation up to 1.2 V (vs. reversible hydrogen electrode) in the CV measurement prior to the SSV measurement. As a result, the nanosheet-based samples exhibited higher ORR activities than the starting materials, K+-form layered manganese oxide K0.5MnO2 (K+-RG(Mn)) and Mn2O3, and a well-known ORR catalyst, MnO2. The H3O+-RE(Mn) sample electrochemically oxidized up to 1.2 V showed the highest ORR activity, Eon = 0.97 V and Eff4 = 99%, which were comparable to those of a conventional 20 mass% Pt/C catalyst. The comparison of their ORR activities, BET surface areas and X-ray photoelectron spectra suggests that the enhancement of the ORR activity is attributed to an increase in the numbers of the ORR active sites and a large amount of H2O in the interlayers and on the surface of the nanosheets because of rapid of H2O-supply enough for ORR in alkaline solution.

Electrocatalytic oxygen reduction reaction (ORR) activities of the pyrochlore oxides Ln2Zr2O7−δ (LnZ) and Ln2Sn2O7−δ (LnS) (Ln = La, Pr, Nd, Sm) were examined in 0.1 M KOH solution at 70 °C. The onset potential (E on) of the oxygen reduction current and the efficiency (Eff 4) of 4-electron reduction of oxygen were evaluated by semi-steady state voltammetry with a rotating ring-disk electrode. In both LnZ and LnS series, the E on values were ~0.85 V versus reversible hydrogen electrode. A relation was found between the E on values and the lattice parameters; i.e. on the whole, the ORR activity became high with an increase in the lattice parameters. When the Ln ion was the same, the LnZ series exhibited higher ORR activities than the LnS series. The pyrochlore LaZ with the highest ORR activity showed a Eff 4 value higher than 85%. Moreover, Mn-incorporation to LaZ led to a mixed-oxide (1–xLaZ−xLaM) of LaZ and the perovskite LaMnO3 (LaM). However, the E on value apparently sifted to a more positive potential probably due to LaMnO3, and the magnitude of the cathodic ORR current increased with an increase in the mixing content up to x = 0.3. The mixed-oxide 0.7LaZ–0.3LaM exhibited the highest ORR activity (E on = ~0.90 V and Eff 4 > 95%), which was comparable to that of a conventional 20 mass% Pt/C catalyst.

In order to enhance the electrochemical properties, the spinel LiMn 2 O 4 electrode surface was modified with amorphous Al 2 O 3 nanoparticle as heterogeneous phase. LiMn 2 O 4 was in preparation based on a conventional solid-state reaction. The LiMn 2 O 4 procedure was soaked in aluminum tri 2-propoxide solution. The LiMn 2 O 4 whose surface was modified by aluminum oxide was obtained through the heat treatment at 400 °C for 4 h. The Al 2 O 3 -modified LiMn 2 O 4 electrode exhibits a capacity higher than that of the unmodified LiMn 2 O 4 electrode. On the other hand, no variation was shown with open circuit potential and apparent chemical diffusion coefficient of Li ion for LiMn 2 O 4 before and after the surface modification. The charge-transfer resistance of Al 2 O 3 -modified LiMn 2 O 4 decreased significantly in comparison with the unmodified LiMn 2 O 4 . The improved charge-transfer kinetics was largely attributed to Al 2 O 3 which plays an important role of increasing the chemical potential at the electrode/electrolyte interface.

In order to reproduce the observed ionic conductivities and activation energies computationally, the potential parameters (PMs) were optimized for classical molecular dynamic simulations on Li ion conduction in the A-site deficient perovskite solid solution La056Li0.33TiO3 with disordered A-site ion arrangement. By the use of the optimized PMs, the conductivities and the activation energies were improved considerably from 4.1×10-3 Scm-1 to 4.4×10-2 Scm-1 at 800 K and 0.02 eV to 0.2 eV, respectively. The pair correlation functions calculated with the optimized PMs reveal that the Li-ions are located somewhat broadly mainly in the vicinity of the midpoint between the center of the A-site and the center of the bottleneck formed by four O2-, and that the simulated Li location is significantly related to the conductivity.

The locations and local environments of the Li ions in La0.56Li0.33TiO3 have been investigated by classical molecular dynamics (MD) simulations and first-principles (FP) calculations. The pair correlation functions of Li-O and Li-Ti indicate that the Li ions are located somewhat broadly mainly in the vicinity of the midpoint between the center of the A-site and the center of the bottleneck formed by four O2-. This is consistent well with that suggested from previous neutron diffraction and 6Li-NMR studies. The FP calculations suggest a different location of the Li ion in the vicinity of the midpoint between the centers of two adjcent bottlenecks; however it coincides with one of the locations shown by the trajectories simulated with the MD calculations.

Silica mesoporous structures incorporated with phosphorus were prepared and their proton conductivity was evaluated at temperatures of up to 150°C under saturated or controlled water vapor pressure. The fixing of phosphoric acid through heat treatment after forming the mesostructure had a limited effect on the improvement in proton conductivity only in a relatively low-temperature region. The incorporation of phosphorus during mesoporous silica formation decreased the surface area but was effective in improving proton conductivity. A sample with a low P/Si atomic ratio of 0.07 showed the highest proton conductivity above 10 -2 Scm -1 at 100 to 120°C under saturated water vapor pressure. A sample with a high P/Si atomic ratio of 0.25 showed relatively high conductivities being maintained even at low relative humidity at 150°C. An adequate phosphorus concentration and a large surface area were found necessary for high and humidity-independent proton conductivity in mesoporous silica.

NASICON compounds have been well investigated for their luminescence and gas sensor-properties, and as potential hosts for radioactive waste family [1-3]. Owing to their high ionic conductivity, these compounds were extensively studied as solid electrolytes since the mid-70s [4]. When incorporated with transition metals such nickel, manganese and iron cations, the materials regained tremendous attention as possible electroactive materials for sodium-, lithium-, and magnesium-ion batteries [5-7]. In this paper, we report on the structural, electrochemical and conductivity properties of the NASICON phase NaFe2(PO4)(SO4)2. The crystal structure was solved by the Rietveld method using powder x-ray diffraction (PXRD) data. SAED and HRTEM experiments confirmed the proposed structural model. The electrochemical performances were examined by galvanometric cycling, cyclic voltammetry, and impedance spectroscopy. The stability of the NASICON structure during cycling was also followed by ex-situ PXRD experiments. NaFe2(PO4)(SO4)2 was synthesized via a solid state synthesis route from stoichiometric mixtures of NaNO3, Fe(NO₃)₃.9H₂O, (NH4)2SO4, and NH4H2PO4. The starting raw materials, dissolved in an aqueous medium, were stirred at 80oC until evaporation of water. The resulting orange powder was calcined at 550oC for 12h under air, then a pure green powder of NaFe2(PO4)(SO4)2 was obtained. TG-DTA-MS experiments resulted in a 30% weight loss which corresponds to the departure of two SO2 molecules above 600oC, and hence confirm the chemical composition of NaFe2(PO4)(SO4)2. The crystal structure of the latter was solved using the structure of the NASICON NaTi2(PO4)3 as a starting structural model. The Rietveld analysis of the x-ray powder diffraction data led to the reliability factors, Rp = 0.5%, wRp = 0.8%, RB = 9.17%, which corroborates the NASICON crystalline structure of NaFe2(PO4)(SO4)2. When compared to Na4Zr2(SiO4)3, the formula can be rewritten as Na1□3Fe2(PO4)(SO4)2 with the 6b and 18e atomic positions occupied by sodium and vacancies, respectively (□ stands for vacancy). Sodium atoms and vacancies are located in two type of interstitial positions within 3D-interconnected channels formed by the covalent skeleton [Fe2P3O12]- built of FeO6 octahedra and XO4 tetrahedra (X= S, P). To further confirm the x-ray structural model, high resolution electron microscopy (HREM) study was performed along the [010] and [2-21] zone axes. In the case of the [010] zone axis, the corresponding HREM micrograph shows an apparently well-ordered NASICON material with d-spacings of 6.2 and 4.3 Å, corresponding to d10-2 and d104, respectively. The cycling performances of NaFe2(PO4)(SO4)2 were studied in cells embedding (NaPF6:EC:FEC) electrolyte and Na-metal. During the first discharge at a rate of C/20, the title compound delivers a capacity of 89 mAh/g indicating that 70% of the theoretical specific capacity (127mAh.g-1) was achieved (Fig. 1). The material was cycled at the C/5 rate and a 96% capacity retention was obtained after 30 cycles. After the first cycle, the powder XRD pattern was very similar to the one of the initial phase indicating a stable Nasicon structure during cycling. Figure 1. Charge/discharge curves of NaFe2(PO4)(SO4)2 at the rate of C/5, C/10, and C/20 vs. Na+/Na (a), capacity retention (b), and cyclic voltammetry curves at the scan rates of 0.1, 0.25, and 0.5mV/s (c). References: [1] Wang, J.; Zhang, Z.-J., J. Alloys Comp. 2016, 685, 841-847. [2] Takeda, H.; Ueda, T.; Kamada, K.; Matsuo, K., Hyodo, T.; Shimizu, Y., Electroch. Acta 2015, 155, 8–15. [3] Bois, L.; Guittet, M. J.; Carrot, F.; Trocellier, P., Gauthier-Soyer, M., J. Nucl. Mater. 2001, 297, 129–137. [4] Goodenough, J. B.; Hong, H. Y.-P.; Kafalas, J. A., Mat. Res. Bull. 1976, 11, 203–220. [5] Makino, K.; Katayama, Y.; Miura, T.; Kishi, T., J. Power Sources 2002, 112, 85−89. [6] Gaubicher, J.; Wurm, C.; Goward, G.; Masquelier, C., Nazar, L., Chem. Mater. 2000, 12, 3240−3242. [7] Jian, Z.; Zhao, L.; Pan, H.; Hu, Y.-S.; Li, H.; Chen, W., Chen, L., Electrochem. Commun. 2012, 14, 86−89. Figure 1