| 61. |
- Karlsson, Maths, 1978, et al.
(författare)
-
Structure of Proton-Conducting Alkali Thio-Hydroxogermanates
- 2008
-
Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 20:19, s. 6014-6021
-
Tidskriftsartikel (refereegranskat)abstract
- Using a combination of neutron diffraction, infrared spectroscopy, and first-principles calculations, we have investigated the structure of hydrated and dehydrated proton conducting alkali thio-hydroxogermanates of general formula M2GeS2(OH)2·yH2O (M = K, Rb, and Cs). The results show that the structure of hydrated and dry materials are basically the same, which confirms previous indications that the main effect of heating these materials is just a loss of water. We suggest that in the hydrated state the structure of these materials is built of dimers of thio-hydroxogermanate anions, with the water molecules acting as bridges between such dimers. In the dehydrated structure, the thio-hydroxogermanate anions instead form an extended network through the formation of interdimer hydrogen bonds through the −OH groups in the structure. The alkali ions are suggested to act as “space-fillers” in voids formed by the thio-hydroxogermanate anion dimers, in both the hydrated and the dehydrated state.
|
|
| 62. |
- Karlsson, Maths, et al.
(författare)
-
Temperature-Dependent Infrared Spectroscopy of Proton-Conducting Hydrated Perovskite BaInxZr1-xO3-x/2 (x=0.10-0.75)
- 2010
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114:13, s. 6177-6181
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the temperature dependence of the O-H stretch band in the infrared absorbance spectra of the proton-conducting hydrated perovskites BaInxZr1-xO3-x/2 (x = 0.10-0.75) over the temperature range -160 to 350 degrees C. Upon increasing temperature from -160 to 30 degrees C, we show that there is a redistribution of protons from nonsymmetrical structural configurations, such as Zr-OH-In and Zr-OH-Zr-vacancy, where the degree of hydrogen bonding between the protons and neighboring oxygens is strong, to symmetrical configurations, such as Zr-OH-Zr and In-OH-In, where hydrogen bonding is weaker. Spectra measured at elevated temperatures, 30-350 degrees C, indicate preferential desorption of protons in sites where the degree of hydrogen bonding is strong, and show that the materials gradually dehydrate with increasing temperature. The dehydration rate is found to be highest in the temperature range 275-325 degrees C. Furthermore, the spectroscopic results indicate that strong hydrogen bonding, caused by dopant-induced short-range structural distortions, is favorable for high proton mobility and that the rate-limiting step in the conduction mechanism is the proton transfer between neighboring oxygens.
|
|
| 63. |
|
|
| 64. |
- Karlsson, Maths, 1978, et al.
(författare)
-
Using Neutron Spin-Echo To Investigate Proton Dynamics in Proton-Conducting Perovskites
- 2010
-
Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 22:3, s. 740-742
-
Tidskriftsartikel (refereegranskat)abstract
- The applicability and potential of neutron spin-echo (NSE) to study proton dynamics in proton-conducting ceramics was studied. The experiment was performed on hydrated BaZr 0,90 Y 0.10 O 2.95 (10Y:BZO), a cubic perovskite with a relatively high proton conductivity. The NSE experiment was performed at the IN15 spectrometer at Institut Laue-Langevin (ILL) in Grenoble, France. The relaxation rate for two Q-values for the temperature 563 K was determined. The first-principles calculations were carried out within the framework of density functional theory (DFT). The calculated diffusion harriers far from Y-dopants are found to he 0.20 and 0.18 eV for the proton transfer and hydroxyl rotation motion, respectively. The binding energy to a Y-dopant is 0.16 eV, and the influence of the Y-dopant on the energetics for the proton is quite extended in space, including both the first and the second coordination shells.
|
|
| 65. |
|
|
| 66. |
- Karlsson, Maths, 1978, et al.
(författare)
-
Vibrational Properties of Protons in Hydrated BaInxZr1-xO3-x/2
- 2005
-
Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 72, s. 1-7
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the local proton dynamics in the proton conducting hydrated perovskite system BaInxZr1-xO3-x/2 (x=0.25-0.75) using infrared spectroscopy and first-principles calculations. We show that oxygen vacancies and dopant atoms in the vicinity of the proton tilt the proton toward a neighboring oxygen creating strongly hydrogen-bonded configurations. This is manifested as a strong redshift of the O-H stretch band in the infrared absorption spectrum. We also find considerable fluctuations of the nearest and next-nearest oxygen-proton distances with time, resulting in additional spectral broadening. By comparing the frequencies of computed O-H stretch modes we can relate specific local configurations to different parts of the broad O-H stretch band. Even though hydrogen-bonded configurations favor proton transfer they hinder the long-range migration by decreasing the reorientational rate. Thus, in order to optimize the proton mobility it is important to avoid extreme configurations caused by either oxygen vacancies or dopant atoms in the perovskite structure.
|
|
| 67. |
- Kim, Jae-Kwang, 1978, et al.
(författare)
-
2,3,6,7,10,11-Hexamethoxytriphenylene (HMTP): A new organic cathode material for lithium batteries
- 2012
-
Ingår i: Electrochemistry Communications. - : Elsevier BV. - 1388-2481. ; 21:1, s. 50-53
-
Tidskriftsartikel (refereegranskat)abstract
- We propose a new organic cathode material for rechargeable lithium battery applications: 2,3,6,7,10,11-hexamethoxytriphenylene (HMTP). HMTP is composed of six methoxy functional groups substituted onto a central triphenylene moiety. The cell, incorporating 40 wt.% of organic cathode material, exhibits full specific capacity at current densities up to 3 C. The main advantage of HMTP as organic cathode material lies in a stable cell performance and negligible self discharge, even though the capacity is lower, similar to 66 mAh/g, compared to other organic cathode materials. Cells with the HMTP cathode showed >95% retention of the initial discharge capacity after 50 cycles at 1 C and self-discharge was not observed during a full month of open circuit voltage measurements. The latter is due to the fact that the nature of the HMTP radical is fundamentally different from other organic cathode materials' radicals.
|
|
| 68. |
- Kim, Jae-Kwang, 1978, et al.
(författare)
-
An Imidazolium based ionic liquid electrolyte for lithium batteries
- 2010
-
Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 195:22, s. 7639-7643
-
Tidskriftsartikel (refereegranskat)abstract
- An electrolyte for lithium batteries based on the ionic liquid 3-methy-1-propylimidazolium bis(trifluoromethysulfony)imide (PMIMTFSI) complexed with lithium bis(trifluoromethysulfony)imide (LiTFSI) at a molar ratio of 1:1 has been investigated. The electrolyte shows a high ionic conductivity (1.2 × 10−3 S cm−1) at room temperature. Over the whole investigated temperature range the ionic conductivity is more than one order of magnitude higher than for an analogue electrolyte based on N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide (Py14TFSI) complexed with LiTFSI and used here as a benchmark. Raman results indicate furthermore that the degree of lithium coordinated TFSI is slightly lower in the electrolyte based on PMIMTFSI and thus that the Li+ charge carriers should be higher than in electrolytes based on Py14TFSI. An ionic liquid gel electrolyte membrane was obtained by soaking a fibrous fully interconnected membrane, made of electrospun P(VdF-HFP), in the electrolyte. The gel electrolyte was cycled in Li/ionic liquid polymer electrolyte/Li cells over 15 days and in Li/LiFePO4 cells demonstrating good interfacial stability and highly stable discharge capacities with a retention of >96% after 50 cycles (146 mAh g−1).
|
|
| 69. |
- Kim, Jae-Kwang, 1978, et al.
(författare)
-
Characterization of N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide-based polymer electrolytes for high safety lithium batteries
- 2013
-
Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 224:15 Feb. 2013, s. 93-98
-
Tidskriftsartikel (refereegranskat)abstract
- Poly(vinylidene difluoride-co-hexafluoropropylene) (PVdF-HFP) membrane was prepared by electrospinning. The membranes served as host matrices for the preparation of ionic liquid-based polymer electrolytes (ILPEs) by activation with non-volatile, highly thermally stable, and safe room temperature ionic liquid (RTIL) electrolytes; N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide (Py14TFSI) complexed with 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). In this work, the first combination of electrospun PVdF-HFP fiber polymer host and pyrrolidinium-based ionic electrolyte was employed for highly stable lithium batteries. The ILPE exhibited low Li+-TFSI coordination, low crystallinity, high thermal stability, high electrochemical stability, and high ionic conductivity with a maximum of 1.1 x 10(-4) S cm(-1) at 0 degrees C. The ILPE exhibited good compatibility with a LiFePO4 electrode on storage and good charge-discharge performance in Li/ILPE/LiFePO4!
|
|
| 70. |
- Kim, Jae-Kwang, 1978, et al.
(författare)
-
Effect of carbon coating methods on structural characteristics and electrochemical properties of carbon-coated lithium iron phosphate
- 2014
-
Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738. ; 262, s. 25-29
-
Tidskriftsartikel (refereegranskat)abstract
- The potential of LiFePO4 as cathode material has not been fully exploited due to its intrinsic poor electronic and ionic conductivities. Attempts have been made to improve these properties of which coating of the active carbon on the particle surface is the most viable method so far. Phase-pure LiFePO4 and two LiFePO4/C composites were synthesized by mechanical activation process employing two different methods: (i) direct addition of acetylene black carbon and (ii) addition of sucrose as carbon precursor. The samples were well characterized by various techniques like elemental analysis, Brunauer-Emmett-Teller (BET) method, scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and Raman spectroscopy to establish their composition, morphology, particle size and surface area. The structure of these samples is investigated as olivine structure space group Prima by X-ray powder diffraction. Transmission electron microscopy (TEM) confirms that the carbon nanocoating on the LiFePO4 particles has no visible dislocations and fractures. The electrochemical performance of LiFePO4/C is significantly affected by the nature of the carbon nanocoating, which in turn is affected by the choice of synthesis method.
|
|
