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- Aktekin, Burak, et al.
(författare)
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Concentrated LiFSI-€“Ethylene Carbonate Electrolytes and Their Compatibility with High-Capacity and High-Voltage Electrodes
- 2022
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Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 5:1, s. 585-595
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Tidskriftsartikel (refereegranskat)abstract
- The unusual physical and chemical properties of electrolytes with excessive salt contents have resulted in rising interest in highly concentrated electrolytes, especially for their application in batteries. Here, we report strikingly good electrochemical performance in terms of conductivity and stability for a binary electrolyte system, consisting of lithium bis(fluorosulfonyl)imide (LiFSI) salt and ethylene carbonate (EC) solvent. The electrolyte is explored for different cell configurations spanning both high-capacity and high-voltage electrodes, which are well known for incompatibilities with conventional electrolyte systems: Li metal, Si/graphite composites, LiNi0.33Mn0.33Co0.33O2 (NMC111), and LiNi0.5Mn1.5O4 (LNMO). As compared to a LiTFSI counterpart as well as a common LP40 electrolyte, it is seen that the LiFSI:EC electrolyte system is superior in Li-metal–Si/graphite cells. Moreover, in the absence of Li metal, it is possible to use highly concentrated electrolytes (e.g., 1:2 salt:solvent molar ratio), and a considerable improvement on the electrochemical performance of NMC111-Si/graphite cells was achieved with the LiFSI:EC 1:2 electrolyte both at the room temperature and elevated temperature (55 °C). Surface characterization with scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) showed the presence of thicker surface film formation with the LiFSI-based electrolyte as compared to the reference electrolyte (LP40) for both positive and negative electrodes, indicating better passivation ability of such surface films during extended cycling. Despite displaying good stability with the NMC111 positive electrode, the LiFSI-based electrolyte showed less compatibility with the high-voltage spinel LNMO electrode (4.7 V vs Li+/Li).
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- Aktekin, Burak, et al.
(författare)
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How Mn/Ni Ordering Controls Electrochemical Performance in High-Voltage Spinel LiNi0.44Mn1.56O4 with Fixed Oxygen Content
- 2020
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Ingår i: ACS Applied Energy Materials. - : AMER CHEMICAL SOC. - 2574-0962. ; 3:6, s. 6001-6013
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Tidskriftsartikel (refereegranskat)abstract
- The crystal structure of LiNi0.5O4 (LNMO) can adopt either low-symmetry ordered (Fd (3) over barm) or high-symmetry disordered (P4(3)32) space group depending on the synthesis conditions. A majority of published studies agree on superior electrochemical performance of disordered LNMO, but the underlying reasons for improvement remain unclear due to the fact that different thermal history of the samples affects other material properties such as oxygen content and particle morphology. In this study, ordered and disordered samples were prepared with a new strategy that renders samples with identical properties apart from their cation ordering degree. This was achieved by heat treatment of powders under pure oxygen atmosphere at high temperature with a final annealing step at 710 degrees C for both samples, followed by slow or fast cooling. Electrochemical testing showed that cation disordering improves the stability of material in charged (delithiated) state and mitigates the impedance rise in LNMO parallel to LTO (Li4Ti5O12) and LNMO parallel to Li cells. Through X-ray photoelectron spectroscopy (XPS), thicker surface films were observed on the ordered material, indicating more electrolyte side reactions. The ordered samples also showed significant changes in the Ni 2p XPS spectra, while the generation of ligand (oxygen) holes was observed in the Ni-O environment for both samples using X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS). Moreover, high-resolution transmission electron microscopy (HRTEM) images indicated that the ordered samples show a decrease in ordering near the particle surface after cycling and a tendency toward rock-salt-like phase transformations. These results show that the structural arrangement of Mn/Ni (alone) has an effect on the surface and "nearsurface" properties of LNMO, particularly in delithiated state, which is likely connected to the bulk electronic properties of this electrode material.
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- Aktekin, Burak, et al.
(författare)
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The Effect of the Fluoroethylene Carbonate Additive in LiNi0.5Mn1.5O4 - Li4Ti5O12 Lithium-Ion Cells
- 2017
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Ingår i: Journal of the Electrochemical Society. - : ELECTROCHEMICAL SOC INC. - 0013-4651 .- 1945-7111. ; 164:4, s. A942-A948
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the electrolyte additive fluoroethylene carbonate (FEC) for Li-ion batteries has been widely discussed in literature in recent years. Here, the additive is studied for the high-voltage cathode LiNi0.5Mn1.5O4 (LNMO) coupled to Li4Ti5O12 (LTO) to specifically study its effect on the cathode side. Electrochemical performance of full cells prepared by using a standard electrolyte (LP40) with different concentrations of FEC (0, 1 and 5 wt%) were compared and the surface of cycled positive electrodes were analyzed by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The results show that addition of FEC is generally of limited use for this battery system. Addition of 5 wt% FEC results in relatively poor cycling performance, while the cells with 1 wt% FEC showed similar behavior compared to reference cells prepared without FEC. SEM and XPS analysis did not indicate the formation of thick surface layers on the LNMO cathode, however, an increase in layer thickness with increased FEC content in the electrolyte could be observed. XPS analysis on LTO electrodes showed that the electrode interactions between positive and negative electrodes occurred as Mn and Ni were detected on the surface of LTO already after 1 cycle. (C) The Author(s) 2017. Published by ECS. All rights reserved.
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- Aktekin, Burak, et al.
(författare)
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Understanding the Capacity Loss in LiNi0.5Mn1.5O4-Li4Ti5O12 Lithium-Ion Cells at Ambient and Elevated Temperatures
- 2018
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 122:21, s. 11234-11248
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Tidskriftsartikel (refereegranskat)abstract
- The high-voltage spinel LiNi0.5Mn1.5O4, (LNMO) is an attractive positive electrode because of its operating voltage around 4.7 V (vs Li/Li+) and high power capability. However, problems including electrolyte decomposition at high voltage and transition metal dissolution, especially at elevated temperatures, have limited its potential use in practical full cells. In this paper, a fundamental study for LNMO parallel to Li4Ti5O12 (LTO) full cells has been performed to understand the effect of different capacity fading mechanisms contributing to overall cell failure. Electrochemical characterization of cells in different configurations (regular full cells, back-to-back pseudo-full cells, and 3-electrode full cells) combined with an intermittent current interruption technique have been performed. Capacity fade in the full cell configuration was mainly due to progressively limited lithiation of electrodes caused by a more severe degree of parasitic reactions at the LTO electrode, while the contributions from active mass loss from LNMO or increases in internal cell resistance were minor. A comparison of cell formats constructed with and without the possibility of cross-talk indicates that the parasitic reactions on LTO occur because of the transfer of reaction products from the LNMO side. The efficiency of LTO is more sensitive to temperature, causing a dramatic increase in the fading rate at 55 degrees C. These observations show how important the electrode interactions (cross-talk) can be for the overall cell behavior. Additionally, internal resistance measurements showed that the positive electrode was mainly responsible for the increase of resistance over cycling, especially at 55 degrees C. Surface characterization showed that LNMO surface layers were relatively thin when compared with the solid electrolyte interphase (SEI) on LTO. The SEI on LTO does not contribute significantly to overall internal resistance even though these films are relatively thick. X-ray absorption near-edge spectroscopy measurements showed that the Mn and Ni observed on the anode were not in the metallic state; the presence of elemental metals in the SEI is therefore not implicated in the observed fading mechanism through a simple reduction process of migrated metal cations.
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- Alimadadi, Hossein, 1983, et al.
(författare)
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Corrosion properties of electrodeposited nanocrystalline and amorphous patterned Ni-W alloy
- 2009
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Ingår i: MATERIALS & DESIGN. - : Elsevier BV. - 0261-3069 .- 0264-1275 .- 1873-4197. ; 30:4, s. 1356-1361
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Tidskriftsartikel (refereegranskat)abstract
- Nickel-tungsten with satisfactory corrosion properties is a promising alloy to replace hard chromium. Relatively high adhesion between copper substrate and electrodeposited Ni-W alloy results in patterned morphology due to crack formation. In this work, corrosion resistance of patterned Ni-W alloys comprising 0-26 at.%.W were studied by potentiodynamic polarization and EIS in a medium containing Cl-. It is shown that corrosion resistance of single phase Ni-W is superior to amorphous and dual phase coated layers. It is also found that crack density is the dominant affecting factor on corrosion resistance of amorphous Ni-W alloys.
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- Asfaw, Habtom D., Dr. 1986-, et al.
(författare)
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Bio-derived hard carbon nanosheets with high rate sodium-ion storage characteristics
- 2022
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Ingår i: Sustainable Materials and Technologies. - : Elsevier. - 2214-9937. ; 32
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Tidskriftsartikel (refereegranskat)abstract
- Biomass is a sustainable precursor of hard carbons destined for use in sodium-ion batteries. This study explores the synthesis of hard carbon nanosheets (HCNS) from oxidized cork and impact of synthesis temperature on the hard carbon characteristics. An increase in the carbonization temperature from 1000 to 1500 °C generally leads to lower BET specific surface areas (~55 to 20 m2 g−1) and d002 interlayer spacing (~ 4.0 to 3.7 Å). The effect of synthesis temperature is reflected in the initial coulombic efficiency (iCE) which increases from 72% at 1000 °C to 88% at 1500 °C, as a result of the decrease in surface area, and structural defects in the hard carbon as verified using Raman scattering. The impact of cycling temperature (~25, 30 and 55 °C) on the rate capability and long-term cycling is investigated using high precision coulometry cycler. For a galvanostatic test at 20 mA g−1 and ~ 25 °C, a reversible capacity of 276 mAh g−1 is observed with an iCE of ~88%. Increasing cycling temperature enhances the rate performance, but slightly lowers the iCE (~86% at 30 °C and ~ 81% at 55 °C). At 20 mA g−1, the reversible capacities obtained at 30 °C and 55 °C are on average ~ 260 and ~ 270 mAh g−1, respectively. For constant-current constant-voltage (CCCV) tests conducted at 30 °C, reversible capacities ranging from 252 to 268, 247–252, and 237–242 mAh g−1 can be obtained at 10, 100, and 1000 mA g−1, respectively. The respective capacities obtained at 55 °C are about 272–290, 260–279, and 234–265 mAh g−1 at 10, 100 and 1000 mA g−1. The applicability of the HCNS electrodes is eventually evaluated in full-cells with Prussian white cathodes, for which a discharge capacity of 152 mAh g−1 is obtained with an iCE of ~90%.
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| 10. |
- Asfaw, Habtom D., et al.
(författare)
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Boosting the thermal stability of emulsion–templated polymers via sulfonation : an efficient synthetic route to hierarchically porous carbon foams
- 2016
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Ingår i: ChemistrySelect. - : Wiley. - 2365-6549. ; 1:4, s. 784-792
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Tidskriftsartikel (refereegranskat)abstract
- Hierarchically porous carbon foams with specific surface areas exceeding 600 m2 g−1 can be derived from polystyrene foams that are synthesized via water-in-oil emulsion templating. However, most styrene-based polymers lack strong crosslinks and are degraded to volatile products when heated above 400 oC. A common strategy employed to avert depolymerization is to introduce potential crosslinking sites such as sulfonic acids by sulfonating the polymers. This article unravels the thermal and chemical processes leading up to the conversion of sulfonated high internal phase emulsion polystyrenes (polyHIPEs) to sulfur containing carbon foams. During pyrolysis, the sulfonic acid groups (-SO3H) are transformed to sulfone (-C-SO2-C-) and then to thioether (-C−S-C-) crosslinks. These chemical transformations have been monitored using spectroscopic techniques: in situ IR, Raman, X-ray photoelectron and X-ray absorption near edge structure spectroscopy. Based on thermal analyses, the formation of thioether links is associated with increased thermal stability and thus a substantial decrease in volatilization of the polymers.
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