Showing papers on "Ionic conductivity published in 2007"

Lithium superionic conduction in lithium borohydride accompanied by structural transition

Abstract: The electrical conductivity of lithium borohydride (LiBH4) measured by the ac complex impedance method jumped by three orders of magnitude due to structural transition from orthorhombic to hexagonal at approximately 390K. The hexagonal phase exhibited a high electrical conductivity of the order of 10−3Scm−1. Furthermore, the conductivity calculated from the Nernst-Einstein equation using the correlation time obtained from Li7 nuclear magnetic resonance was in good agreement with the measured electrical conductivity. It was concluded that the electrical conductivity in the hexagonal phase is due to the Li superionic conduction.

Anisotropy of Electronic and Ionic Transport in LiFePO4 Single Crystals

Abstract: A material of key relevance as a cathode in rechargeable lithium batteries is LiFePO 4 , whose major shortcoming lies in its sluggish mass and charge transport, the overcoming of which requires a precise knowledge of transport properties, as of yet unavoidable. The present work aims at filling this gap. We report here a clear experimental investigation of electronic and ionic conduction as well as chemical diffusion for Li (D δ Li ) in LiFePO 4 single crystals. We show that the electronic conductivity, ionic conductivity, and chemical diffusivity of Li are essentially two-dimensional (b-c plane) in our single crystals. The ionic conductivities along all three axes are found to be much smaller than the electronic conductivities. Present results on LiFePO 4 are crucial for systematic optimization of its performance in Li-batteries in terms of doping or microstructural design.

Ion gels by self-assembly of a triblock copolymer in an ionic liquid.

Abstract: We report a new way of developing ion gels through the self-assembly of a triblock copolymer in a room-temperature ionic liquid. Transparent ion gels were achieved by gelation of a poly(styrene-block-ethylene oxide-block-styrene) (SOS) triblock copolymer in 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) with as low as 5 wt % SOS triblock copolymer. The gelation behavior, ionic conductivity, rheological properties, and microstructure of the ion gels were investigated. The ionic conductivity of the ion gels is only modestly affected by the triblock copolymer network. Its temperature dependence nearly tracks that of the bulk ionic liquid viscosity. The ion gels are thermally stable up to at least 100 °C and possess significant mechanical strength. The results presented here suggest that triblock copolymer gelation is a promising way to develop highly conductive ion gels and provides many advantages in terms of variety and processing.

Succinonitrile as a Versatile Additive for Polymer Electrolytes

Abstract: Solid polymer electrolytes with high ionic conductivities are prepared by using poly(ethylene oxide) (PEO) and poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) as polymer matrixes, succinonitrile (SN) as an additive, and lithium bis-trifluoromethanesulfonimide (LiTFSI) and lithium bisperfluoroethylsulfonylimide (LiBETI) as salts. In these systems, the introduction of succinonitrile into the polymer electrolytes increases the material's ionic conductivity and conveys excellent mechanical properties. The described composites, with their beneficial combination of mechanical and electric properties, are expected to have significant potential for lithium batteries.

Ion-selective electrodes with three-dimensionally ordered macroporous carbon as the solid contact.

Abstract: Electrodes with three-dimensionally ordered macroporous (3DOM) carbon as the intermediate layer between an ionophore-doped solvent polymeric membrane and a metal contact are presented as a novel approach to solid-contact ion-selective electrodes (SC-ISEs). Due to the well-interconnected pore and wall structure of 3DOM carbon, filling of the 3DOM pores with an electrolyte solution results in a nanostructured material that exhibits high ionic and electric conductivity. The long-term drift of freshly prepared SC-ISEs with 3DOM carbon contacts is only 11.7 μV/h, and does not increase when in contact with solution for 1 month, making this the most stable SC-ISE reported so far. The electrodes show good resistance to the interference from oxygen. Moreover, in contrast to previously reported SC-ISEs with conducting polymers as the intermediate layer, 3DOM carbon is an electron conductor rather than a semiconductor, eliminating any light interference.

Ionic/Electronic Conducting Characteristics of LiFePO4 Cathode Materials The Determining Factors for High Rate Performance

Abstract: +ion diffusion coefficient of lithium iron phosphate LiFePO4 cathode materials should not be measured by the standard method because there is no composition variation but the movement of the LiFePO4/FePO4 interface during Li insertion/ extraction. A method to measure the intrinsic electronic and ionic conductivity of mixed conductive LiFePO4 was reported, for the first time, based on the conductivity measurements of mixed conductive solid electrolyte using blocking electrodes. The conductivities of the three LiFePO4 materials mixed electronic/ionic conductor, electronic conductor, and ionic conductor, were measured using the proposed method, and the electronic and ionic conductivities were linked with their electrochemical reaction kinetics and rate capabilities. These LiFePO4 samples have the same X-ray diffraction crystal structure and similar particle size, but different rate performance due to the difference in the ionic/electronic conductivity. The rate performance of the mixed electronic/ionic conductive LiFePO4 is much higher than that of the electronic conductive LiFePO4 and the ionic conductive

Lithium Ion‐Conducting Glass–Ceramics of Li1.5Al0.5Ge1.5(PO4)3–xLi2O (x=0.0–0.20) with Good Electrical and Electrochemical Properties

Abstract: NASICON-type structured Li1.5Al0.5Ge1.5(PO4)3–xLi2O Li-ion-conducting glass–ceramics were successfully prepared from as-prepared glasses. The differential scanning calorimetry, X-ray diffraction, nuclear magnetic resonance, and field emission scanning electron microscope results reveal that the excess Li2O is not only incorporated into the crystal lattice of the NASICON-type structure but also exists as a secondary phase and acts as a nucleating agent to considerably promote the crystallization of the as-prepared glasses during heat treatment, leading to an improvement in the connection between the glass–ceramic grains and hence a dense microstructure with a uniform grain size. These beneficial effects enhance both the bulk and total ionic conductivities at room temperature, which reach 1.18 × 10−3 and 7.25 × 10−4 S/cm, respectively. In addition, the Li1.5Al0.5Ge1.5(PO4)3–0.05Li2O glass–ceramics display favorable electrochemical stability against lithium metal with an electrochemical window of about 6 V. The high ionic conductivity, good electrochemical stability, and wide electrochemical window of LAGP–0.05LO glass–ceramics suggest that they are promising solid-state electrolytes for all solid-state lithium batteries with high power density.

Ionic liquids based on dicyanamide anion : Influence of structural variations in cationic structures on ionic conductivity

Abstract: A series of dicyanamide [N(CN)2]-based ionic liquids were prepared using 1-alkyl-3-methylimidazolium cations with different alkyl chain lengths and ethyl-containing heterocyclic cations with different ring structures, and the influence of such structural variations on their thermal property, density, electrochemical window, viscosity, ionic conductivity, and solvatochromic effects was investigated. We found that the 1,3-dimethylimidazolium salt shows the highest ionic conductivity among ionic liquids free from halogenated anions (3.6 x 10(-2) S cm(-1) at 25 degrees C), and the elongation of the alkyl chain causes the pronounced depression of fluidity and ionic conductivity. Also, such an elongation gives rise to the increase in the degree of ion association in the liquids, mainly caused by the van der Waals interactions between alkyl chains. N(CN)2 salts with 1-ethyl-2-methylpyrazolium (EMP) and N-ethyl-N-methylpyrrolidinium (PY(12)) cations as well as 1-ethyl-3-methylimidazolium (EMI) cation are liquids at room temperature (RT), while the N-ethylthiazolium salt shows a melting event at higher temperature (57 degrees C). Among the three RT ionic liquids with ethyl-containing cations, RT ionic conductivity follows the order EMI > PY(12) > EMP, which does not coincide with the order of fluidity at RT (EMI > EMP > PY(12)). Such a discrepancy is originated from a high degree of ion dissociation in the PY(12) salt, which was manifested in the Walden rule deviation and solvatochromic effects. A series of N(CN)2/C(CN)3 binary mixtures of the EMI salts were also prepared. RT ionic conductivity decreases linearly with increasing the molar fraction of C(CN)3 anion.

Imidazolium-Based Room-Temperature Ionic Liquid for Lithium Secondary Batteries Effects of Lithium Salt Concentration

Abstract: To understand the basic properties of lithium secondary batteries which consist of nonflammable and nonvolatile room-temperature ionic liquid electrolytes, we examined the ionic conductivity, electrolyte/electrode interfacial resistance, and charge-discharge rate characteristics by varying the lithium salt concentration in the room-temperature ionic liquid, lithium salt binary electrolytes. By using a modified imidazolium cation-based room-temperature ionic liquid as an electrolyte, the lithium secondary batteries achieved a stable charge-discharge operation of more than 100 cycles (cathode LiCoO 2 , anode lithium metal, voltage region 3.0-4.2 V, current density 1/8 C). Moreover, we found that an optimal lithium salt concentration exists for obtaining an excellent battery rate performance, which depends on delicate balances in several factors, such as ionic conductivity (viscosity), interfacial resistances at the LiCoO 2 cathode/electrolyte interface, and the lithium metal anode/electrolyte interface.

Li Ion Conducting Polymer Gel Electrolytes Based on Ionic Liquid/PVDF-HFP Blends

Abstract: Ionic liquids thermodynamically compatible with Li metal are very promising for applications to rechargeable lithium batteries. 1-methyl-3-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (P(13)TFSI) is screened out as a particularly promising ionic liquid in this study. Dimensionally stable, elastic, flexible, nonvolatile polymer gel electrolytes (PGEs) with high electrochemical stabilities, high ionic conductivities and other desirable properties have been synthesized by dissolving Li imide salt (LiTFSI) in P(13)TFSI ionic liquid and then mixing the electrolyte solution with poly(vinylidene-co-hexafluoropropylene) (PVDF-HFP) copolymer. Adding small amounts of ethylene carbonate to the polymer gel electrolytes dramatically improves the ionic conductivity, net Li ion transport concentration, and Li ion transport kinetics of these electrolytes. They are thus favorable and offer good prospects in the application to rechargeable Li batteries including open systems like Li/air batteries, as well as more "conventional" rechargeable lithium and lithium ion batteries.

Design of Ion Conductive Polymers Based on Ionic Liquids

Abstract: Some ionic liquids have been polymerized after introducing vinyl groups on the component ions. Thus obtained polymerized ionic liquids showed relatively low glass transition temperature and moderate ionic conductivity attributable to unique characteristics of the ionic liquids. The properties of the polymers such as glass transition temperature, decomposition temperature, ionic conductivity, etc, have been further improved through the design of corresponding monomers. It is important to consider a task-sharing between component monomers, such as providing conductive path and carrier ion source for the design of conductive polymers for specific ions.