Search

The response of several ceramic oxide high Tc superconductors to NOx and COx in Taguchi-type sensors has been investigated. YBa2Cu3O7−δ decomposes in the presence of NO.Nd1.85Ce0.15CuO4−x has sensitivity to CO and no sensitivity to NOx.Bi2CuO6+x and Bi2Sr2CaCu2O8+x show high selectivity against CO and CO2. They are promising materials for Taguchi-type NOx sensors, the latter exhibiting the better response properties.

The electrical properties of a new polymer-lithium salt complex, methyl siloxane terminated polyethylene oxide (PMSEO)- polymethyl lithium propionate siloxane (PLPMS) have been studied. The temperature dependence of the ionic conductivity obeys the VTF equation. By combining ac-impedance measurement and dc-polarization experiments, the transference number of Li + is determined to be close to 1. Lithium ionic conduction was also confirmed by cyclic voltammetry.

A method capable of transforming LiMnBO glass (such as 0.5LiMnO2–0.5B2O3) by appropriate heating into an electrochemically active cathode material is presented. The pristine lithium manganese borate glass prepared by quenching of the melt in air has almost no electrochemical activity within the potential range from 2.5 to 4.5 V vs. Li/Li+. The oxidation of Mn2+ to Mn3+ and Mn4+ was found to occur around the glass transition temperature (Tg). Single-phase LiMn2O4 can be formed by prolonged heating of the glass powders in air to temperatures around Tg. A composite cathode material in which the electrochemically active substance is dispersed on the surface of a fast-ion-conducting matrix was prepared and found to exhibit a cathodic capacity remarkably higher than that of the pristine glass. Good cycling performance between potentials of 2.5 and 4.5 V vs. Li/Li+ has also been observed.

Storage and transport behaviors of lithium in LiF/Ti nanocomposites, either formed in situ through a conversion reaction from TiF(3) powder electrode or prepared by the pulse laser deposition method, have been investigated. Reversible lithium storage in the LiF/Ti nanocomposites shows a sloped voltage profile. The lithium storage capacity in the LiF/Ti nanocomposite thin film is much higher than that in single Ti or LiF thin film with the same thickness and is increased with increasing film thickness. Accordingly, lithium should store at the grain boundary regions since either the LiF or the Ti phase is not active for lithium storage. Hence, this type of interfacial storage is intermediate between the insertion and storage in supercapacitors. The transport properties of electrons and lithium ions in initial LiF/Ti nanocomposites are also investigated by IV, IS and blocking electrode techniques.

Sodium-ion batteries are promising for grid-scale storage applications due to the natural abundance and low cost of sodium. However, few electrodes that can meet the requirements for practical applications are available today due to the limited routes to exploring new materials. Here, a new strategy is proposed through partially/fully substituting the redox couple of existing negative electrodes in their reduced forms to design the corresponding new positive electrode materials. The power of this strategy is demonstrated through the successful design of new tunnel-type positive electrode materials of Na0.61[Mn0.61-xFexTi0.39]O2, composed of non-toxic and abundant elements: Na, Mn, Fe, Ti. In particular, the designed air-stable Na0.61[Mn0.27Fe0.34Ti0.39]O2 shows a usable capacity of ≈90 mAh g−1, registering the highest value among the tunnel-type oxides, and a high storage voltage of 3.56 V, corresponding to the Fe3+/Fe4+ redox couple realized for the first time in non-layered oxides, which was confirmed by X-ray absorption spectroscopy and Mossbauer spectroscopy. This new strategy would open an exciting route to explore electrode materials for rechargeable batteries.

LiCoO2 is synthesized by microwave heating. It has high capacity and good cycleability. The advantages of microwave synthesis are: (i) the calcination process is very fast; (ii) the synthesized powders have small and uniform grains; (iv) the synthesis temperature can be lower, and (iv) the lithium oxide loss is smaller. (C) 1997 Elsevier Science S.A.

We present a first-principles investigation of the structural, magnetic, and electronic properties of $\mathrm{Li}\mathrm{Fe}\mathrm{P}{\mathrm{O}}_{4}$ olivine. The ground-state antiferromagnetic spin arrangement consistent with a superexchange mechanism through oxygen orbits is found to be preferred, showing an antiferromagnetic order between corner sharing octahedra along the [010] direction. This is in agreement with an oxygen-mediated superexchange mechanism for the iron-iron magnetic interaction. The theoretical N\'eel temperature estimated by a mean-field approximation is in the range between $33.1\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and $53.5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, in acceptable agreement with the experimental susceptibility measurement, which gives ${T}_{\mathrm{N}}=52\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The calculated magnetic moment of $3.72{\ensuremath{\mu}}_{\mathrm{B}}$ is close to the value of $4{\ensuremath{\mu}}_{\mathrm{B}}$ deduced from the ionic model according to the Hund's rule.

The electronic structures of $2\ifmmode\times\else\texttimes\fi{}2$ polar (003) surfaces of ${\mathrm{LiCoO}}_{2}$ have been studied using the first-principles projector augmented-wave (PAW) method within the generalized gradient approximation (GGA), based on the density functional theory (DFT). Several geometry structure models were considered with different terminations in order to obtain the most stable structure. From cleavage energies of separation it reveals that, for ${\mathrm{LiCoO}}_{2}$ (003), the configuration with O termination on one side and Li termination on the other side was the most stable one. Because the exposed Li-O groups easily react with the electrolytes so that the structure is destroyed, this conclusion can indirectly explain the phenomenon that ${\mathrm{LiCoO}}_{2}$ coated by MgO possesses the more stable structure [J. Electrochem. Soc. 149, A466 (2002)]. It is also found that structure relaxation is considerably large, and the electronic density of states (DOS) shows large difference between (003) surfaces and bulk, with, for example, a decrease of the band gap between the valance band and the empty band in (003) surfaces region compared to the bulk. It is possible to reconstruct for the polar (003) surfaces of ${\mathrm{LiCoO}}_{2}$ crystallite.

Abnormal salt content dependence of conductivity is observed in solid electrolytes exclusively composed of small molecules of 3-hydroxypropionitrile (HPN) and lithium iodide (LiI) induced by reinforced hydrogen bonding and formation of ionic clusters at high salt content.

The diffusion mechanism of Li ions in the olivine ${\mathrm{LiFePO}}_{4}$ is investigated from first-principles calculations. The energy barriers for possible spatial hopping pathways are calculated with the adiabatic trajectory method. The calculations show that the energy barriers running along the $c$ axis are about 0.6, 1.2, and 1.5 eV for ${\mathrm{LiFePO}}_{4},$ ${\mathrm{FePO}}_{4},$ and ${\mathrm{Li}}_{0.5}{\mathrm{FePO}}_{4},$ respectively. However, the other migration pathways have much higher energy barriers resulting in very low probability of Li-ion migration. This means that the diffusion in ${\mathrm{LiFePO}}_{4}$ is one dimensional. The one-dimensional diffusion behavior has also been shown with full ab initio molecular dynamics simulation, through which the diffusion behavior is directly observed.

We present a first-principles electronic band structure for pure ${\mathrm{LiFePO}}_{4},$ delithiated ${\mathrm{FePO}}_{4},$ and Cr-doped ${\mathrm{LiFePO}}_{4}.$ It indicates that not only Fe but also O atoms are oxidized in the delithiation process, while P is little affected. This is in contrast to the usual view of the intercalation reaction that the removal of Li only transforms Fe from ${\mathrm{Fe}}^{2+}$ to ${\mathrm{Fe}}^{3+},$ but in agreement with the present x-ray photoemission spectroscopy experiment. Calculation also assumes a significant enhancement of electronic conductivity when lithium ions are replaced by cations with higher valence, ${\mathrm{Cr}}^{3+}.$ We also confirm experimentally, for ${\mathrm{Li}}_{1\ensuremath{-}3x}{\mathrm{Cr}}_{x}{\mathrm{FePO}}_{4}$ with $x=0.01$ and 0.03, an enhancement of the electronic conductivity up to eight orders of magnitude comparing with pure ${\mathrm{LiFePO}}_{4}.$ Besides the conventional p-type doping conductivity, another mechanism has been suggested, which involves the electron hopping within a cluster surrounding the doping atom and related vacancies, and electron tunneling between these conducting clusters.

The electronic structure of Cr-doped ${\mathrm{LiMn}}_{2}{\mathrm{O}}_{4}$ spinels was investigated from first principles. It was found that the structure of material is more favorable in total energy when the doping chromium atoms are dispersed in ${\mathrm{LiMn}}_{2}{\mathrm{O}}_{4}.$ With increasing Cr dopant, more electrons are transferred to the oxygen while the positive valence states of Mn atoms are less affected. Consequently, the doping Cr ions possess a higher valence than Mn in ${\mathrm{LiMn}}_{2}{\mathrm{O}}_{4},$ agreeing qualitatively with previous experimental results. By combining first-principles methods with basic thermodynamics, average intercalation voltages of this doped system have been calculated. It was found that both the value of the calculated intercalation voltages and their varying trend with increasing Cr dopant are consistent with the experimental facts.

Room-temperature sodium storage technology has attracted more and more interest in the electrical energy storage field, particularly for large-scale applications in renewable solar and wind power as well as smart grid. However, the development of suitable anode materials remains a big challenging issue for long-life sodium-ion batteries. In this presentation, we will introduce a new “zero-strain” anode, Na0.66[Li0.22Ti0.78]O2 with P2-layered structure, as a promising material for room-temperature long-life sodium-ion batteries. There are several significantly important results obtained in this work: the reversible capacity is ca. 110 mAh/g; the average sodium storage voltage is ca. 0.75 V; the volume change during sodium insertion and extraction is only 0.77%, showing the “zero-strain” characteristics; the material exhibits very long cycling performance, over 1200 cycles with a capacity retention of 75%; the measured apparent Na+ ion diffusion coefficient is ca. 1x10-10 cm2/s. It is also very interesting to find that the final discharge product is actually a mixture of several phases which also retain the P2-structure confirmed by in situ and ex situXRD. The difference in these several P2-phases lies in different sodium composition and occupation (2b, 2d) in the alkali layer. This contribution demonstrates that P2-Na0.66[Li0.22Ti0.78]O2is a promising anode material for the development of rechargeable long-life sodium-ion batteries. References: [1] Y. S. Wang, X. Q. Yu, S. Y. Xu, J. M. Bai, R. J. Xiao, Y.-S. Hu, H. Li, X.-Q. Yang, L. Q. Chen, X. J. Huang, Nat. Commun. 2013, 4, 2365. [2] H. L. Pan, Y.-S. Hu, L. Q. Chen, Energy &Environ. Sci. 2013, 6, 2338-2360. Figure 1 a) P2-structure, b) Na+ ion diffusion, c) Volume change, d) Discharge/charge curves, e) Cycling performance, f) XRD refinement of final discharged product

Nanosized silicon has been paid much attention as high capacity anode materials for Li-ion batteries since our first report in 1999. The main challenge for Si anode is the large volume variation during lithium insertion and extraction, which shows a linear dependence on the capacity. Several problems are caused consequently: 1) the total specific capacity of anode has to be limited due to fairly strict restriction on volume variation of batteries during operating, especially for tablet devices. Thus, the advantages of the high theoretical capacity and the volumetric energy density are not as significant as expected. 2) The solid electrolyte interphase (SEI) on the surface of silicon is not as stable as graphite and could be very thick, which consume lithium from cathode and nonaqueous electrolyte irreversibly, leading to low columbic efficiency, capacity fading, increase of internal resistance and gas release. 3) Nanosized silicon particles tend to agglomerate or merge into big pieces and follow further cracking, leading to the formation of the SEI on freshed surface and the loss of electronic contact for active particles. In order to solve above problems, great efforts have been paid and many strategies have been considered. Among them, SiOx, amorphous Si alloy and nano-Si/C composite are more promising for practical application in view of the electrochemical performances and cost. In this report, we will summarize our investigation on the formation of very thick solid electrolyte interphase (SEI) on naked silicon anode at low rate, direct 3Dvisualization of multiple layer structured SEI. The optimization on additive, binder and microstructure for controlling interfacial properties and maintaining the structure stability of nano-Si/C composite anodes will be reported. Acknowledgment: Financial support from CAS project (KJCX2-YW-W26), "Strategic Priority Research Program" of the Chinese Academy of Sciences,Grant No. XDA09010102 and National project 973 (2012CB932900) are appreciated.

Insertion electrode materials are included in the majority of ambient-temperature Li/Na-ion batteries, which attract increasing attention in energy storage. Being a commercialized cathode material of Li ion battery, olivine LiFePO4 has undergone intensive research. Previously, the two-phase separation mechanism upon charging was well accepted, while recent experimental results indicates a more subtle atomic structure, lithium-staging, exists upon charging. We show that, through first-principles calculations, the observed lithium-staging configuration in partially delithiated LiFePO4is a kinetically controlled thermodynamically metastable state. Our results shed light on the interactions between electron and ion and hence may have general implications for investigating the ionic transport in other strongly correlated mixed conductor materials. [1] Spinel Li4Ti5O12 is well-known as a “zero-strain” anode for lithium-ion batteries. We found that it can also accommodate sodium ions, displaying an average storage voltage of 0.91V vs. Na+/Na. Through combined density functional theory calculations and scanning transmission electron microscope imaging techniques, a three-phase separation reaction, which has never been seen in any insertion electrode materials for lithium- or sodium-ion batteries, is confirmed in the sodiation process of Li4Ti5O12. Furthermore, interfacial structure is clearly resolved at an atomic scale in electrochemically sodiated Li4Ti5O12for the first time via the advanced electron microscopy. [2] Acknowledge: This work was supported by funding from the “863” Project (2009AA033101), “973” Projects (2013CB934002,2009CB220104) Reference: [1] Yang Sun, Xia Lu, Ruijuan Xiao, Hong Li, and Xuejie Huang. Chem. Mater. 24 (2012) 4693. [2] Yang Sun, Liang Zhao, Huilin Pan, Xia Lu, Lin Gu, Yong-Sheng Hu, Hong Li, Michel Armand, Yuichi Ikuhara, Liquan Chen and Xuejie Huang. Nat. Commun. 4 (2013) 1870

not Available.

The Raman-active vibron modes of solid nitrogen have been investigated by coherent anti-Stokes Raman scattering (CARS) spectroscopy to 22 GPa at room temperature. Frequencies and linewidths were measured with an accuracy of 0.1 to 0.2 cm(-1). From the pressure dependence of the linewidths a dynamical model for the transitions between the delta, delta (loc), and epsilon phases has been developed. These phase transitions are characterized by different degrees of ordering of the N(2) molecules. The processes can be described by an increase in the orientational order with increasing pressure and a decrease in number in the rotational degrees of freedom at the phase transitions coupled with changes in crystal structure. A structural model for the delta (loc) phase is given, in which the delta-delta (loc)-epsilon transition sequence arises from a group/subgroup relationship and can therefore be considered ferroelastic in nature. Sample annealing was found to have a significant effect on the results. (C) 2001 American Institute of Physics.

The temperature dependence of Gibbs energy change for the O-T phase transition of YBa 2 Cu 3 O 7− x has been determined by the EMF measurement of a galvanic cell. The result shows that the O-T phase transition may occur at 1025 K and P O 2 is 1 atm.

Polycrystalline CeO2 nanowires have been synthesized via a solution-phase route using sodium bis(2-ethylhexyl) sulfosuccinate as a structure-directing agent. The obtained CeO2 nanowires were 30-120 nm in diameters and 0.2-5 mum in lengths. The CeO2 nanowire consists of many tiny interconnected nanocrystallites of about 7 nm in size. The Raman spectrum of CeO2 nanowires shows size-dependent effect.

not Available.

We study the crystal structure of a triplite-structured (Li0.5Fe0.5)SO4F with full Li+/Fe2+ mixing. This promising polyanion cathode material for lithium-ion batteries operates at 3.9 V versus Li+/Li with a theoretical capacity of 151 mAh/g. Its unique cation mixing structure does not block the Li+ diffusion and results in a small lattice volume change during the charge/discharge process. The calculations show that it has a three-dimensional network for Li-ion migration with an activation energy ranging from 0.53 eV to 0.68 eV, which is comparable with that in LiFePO4 with only one-dimensional channels. This work suggests that further exploring cathode materials with full cation mixing for Li-ion batteries will be valuable.

We report a new synchrotron based in situ X-ray diffraction (XRD) technique to study the chemical delithiation of LiFePO(4). This technique provides a new powerful tool to study chemical reactions with excellent time-resolving power for dynamic studies.

A systematic study on a LiFePO4 sample with 600 nm particle size was carried out to investigate the electronic and crystal structure changes during charge and their relationships with the charging curve. In situX-ray diffraction data collected at 0.1C rate during first charge shows that the crystal FePO4 is observed at x = 0.3 in Li1−xFePO4, with significant delay than the beginning of the charge plateau. On the other hand, in situ X-ray absorption spectra for the Fe K-edge collected at 0.1C during first charge show that the average oxidation of Fe2+ to Fe3+ almost synchronized with the charging curve. In addition, the ex-situ soft X-ray absorption data for the Fe LII–III edges using surface sensitive partial electron yield detection mode show that the lithium content changes at the surface of the sample particles synchronized or ahead to the charge curve, while the data collected at the same time using bulk sensitive fluorescence yield detection mode show that the lithium content changes in the bulk of the particles lag behind the charging curve. The contents of FePO4 and LiFePO4 calculated from in situXRD in relating to the charge curve are quite different than those calculated from in situXAS and ex-situ soft X-ray absorption data. This tells us that cautious need to be taken when using XRD data alone to track the state of charge of LiFePO4 samples, significant delay in observing the new crystal phase formation could occur, especially at relatively high charging rate.

Lithium bis(fluorosulfonyl)imide (LiFSI) has been investigated as a conducting salt of liquid electrolytes for lithium-ion batteries. It shows high solubility in most polar solvents, and a concentration of 5 M (mol dm(-3)) is reached in dimethyl carbonate (DMC) despite its low dielectric constant. LiFSI shows a thermal stability up to 180 degrees C on the thermogravimetric test. Compared with the LiPF(6)/carbonate electrolytes, the LiFSI-based ones show higher ionic conductivities over a wide temperature range (-50 to 50 degrees C) and higher lithium-ion transference numbers (t(Li+)) of 0.5-0.6. The conductivities of the LiFSI/DMC electrolyte over the 0.1-5 M concentration range obey a modified Casteel-Amis equation. The temperature dependence of 1 M LiFSI/DMC/EMC (3:7, v/v) is governed by the Vogel-Tammann-Fulcher relationship. The Fourier transform infrared spectra of the LiFSI/DMC electrolytes at different concentrations are systematically investigated. DMC shows significant spectral variations upon adding LiFSI, indicating strong interaction of Li(+) cations with the solvent molecules. We also found that the compatibility with graphite anode and LiFePO(4) cathode in the LiFSI-based electrolyte is as good as that in the LiPF(6)-based one, though aluminum (Al) corrosion occurs above 4 V vs Li(+)/Li. LiFSI is a very good contender to replace the latter, with increased performances and safety. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3514705] All rights reserved.

not Available.

not Available.

not Available.

not Available.

not Available.

not Available.

not Available.

Recently, undoped semiconductors have been pushed to the frontiers of diluted magnetic semiconductors (DMSs) since no spurious ferromagnetism (FM) signal from metal segregation occurs. However, some aspects still remain untouched in undoped semiconductors nanostructures, including: 1) the evolution of spin moments during the fabrication process; 2) possible intrinsic relationship between the magnetic properties and morphological features, the latter being also dependent on formation process. In this article, we synthesized undoped InN nanostructures and observed a gradual magnetic transition from diamagnetic to FM, and an obvious morphology evolution from tube-shape to wire-shape products with the increase of nitridation time. It is speculated that increasing surface defects such as N vacancies in the morphology transition process are the intrinsic causes for the enhanced FM order with increase of nitridation time. The results provide some useful clues in understanding the true magnetic origin in nanostructured DMSs and reported properties inconsistencies in nanostructured materials.

A crystallized transparent Li4Ti5O12 thin film is deposited on a fluorine-doped tin oxide (FTO) transparent conducting glass by a pulsed laser deposition method. The transparent Li4Ti5O12 electrode turns dark blue after the injection of Li ions and electrons in an electrochemical cell using a nonaqueous electrolyte. Coloring and bleaching times (700 nm) are 17 and 14 s, respectively, according to in situ UV-visible measurement. The highest contrast between the bleached and colored states is observed at a wavelength of 705 nm, with a variation in the transmittance of 45.8%. The above results confirmed that Li4Ti5O12 is an electrochromic active material with good stability, high switching speed, and color efficiency. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3430658] All rights reserved.

not Available.