| 1. |
- Farhat, Douaa, et al.
(author)
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Towards high-voltage Li-ion batteries : Reversible cycling of graphite anodes and Li-ion batteries in adiponitrile-based electrolytes
- 2018
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In: Electrochimica Acta. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0013-4686 .- 1873-3859. ; 281, s. 299-311
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Journal article (peer-reviewed)abstract
- Due to their low vapor pressure and their promising electrochemical and thermal stability, N C- (CH2)n-C N dinitriles are proposed as an electrolyte solvent for Li-ion batteries. Adiponitrile (ADN) has substantial advantages, especially for applications requiring high potential cathodes, because it has high electrochemical/thermal stability (up to 6 V vs. Li/Li+, > 120 degrees C). However, to obtain very high voltage batteries, ADN electrolytes must also passivate the anode of the battery. In this work, reversible cycling of graphite in adiponitrile was successfully achieved by adding a few percent of fluoroethylene carbonate allowing the realization of Graphite/NMC Li-ion battery. The battery of specific capacity of 135 mAhh.g(-1) showed a cycling stability for more than 40 cycles. The composition of the solid electrolyte interphase (SEI) was determined as a function of the FEC concentration as well as the state of charge of the graphite anode using hard X-ray photoelectron spectroscopy (HAXPES) and XPS. With FEC, the SEI layer is thinner and depends on the SOC of the anode, but does not depend on the FEC concentration. SEM characterizations clearly showed that the surface of the anode is completely covered by the SEI layer, regardless of the concentration of FEC. Indeed, 2% of FEC is sufficient to suppress the reduction of adiponitrile which is explained by a specific adsorption of FEC on the graphite anode.
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| 2. |
- Jeschull, Fabian, et al.
(author)
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Solid Electrolyte Interphase (SEI) of Water-Processed Graphite Electrodes Examined in a 65 mAh Full Cell Configuration
- 2018
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In: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 1:10, s. 5176-5188
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Journal article (peer-reviewed)abstract
- Electrode binders, such as sodium carboxymethyl cellulose (CMC-Na), styrene–butadiene rubber (SBR) and poly(sodium acrylate) (PAA-Na) are commonly applied binder materials for the manufacture of electrodes from aqueous slurries. Their processability in water has considerable advantages over slurries based on N-methylpyrrolidone (NMP) considering toxicity, environment and production costs. In this study, water-processed graphite electrodes containing either CMC-Na:SBR, PAA-Na, or CMC-Na:PAA-Na as binders have been prepared on a pilot scale, cycled in graphite||LiFePO4 Li-ion battery cells and analyzed post-mortem with respect to the binder impact on the SEI composition, using in-house (1486.6 eV) and synchrotron-based (2300 eV) photoelectron spectroscopy (PES). The estimated SEI layer thickness was smaller than 11 nm for all samples and decreased in the order: PAA-Na > CMC-Na:SBR > CMC-Na:PAA-Na. The SEI thickness correlates with the surface concentration of CMC-Na, for example, the CMC-Na:PAA-Na mixture showed signs of polymer depletion of the PAA-Na component. The SEI layer components are largely comparable to those formed on a conventional graphite:poly(vinylidene difluoride) (PVdF) electrode. However, the SEI is complemented, by notable amounts of carboxylates and alkoxides, whose formation is favored in water-based negative electrodes. Additionally, more electrolyte salt degradation is observed in formulations comprising PAA-Na. The choice of the binder for the negative electrode had little impact on the surface layer formed on the LiFePO4 positive electrode, except for different contents of sodium salt deposits, as a result of ion migration from the counter electrode.
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| 3. |
- Mogensen, Ronnie, et al.
(author)
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Capacity fading mechanism of tin phosphide anodes in sodium-ion batteries
- 2018
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In: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 47:31, s. 10752-10758
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Journal article (peer-reviewed)abstract
- Tin phosphide (Sn4P3) is here investigated as an anode material in half-cell, symmetrical, and full-cell sodium-ion batteries. Results from the half-cells using two different electrolyte salts of sodium bis(fluorosulfonyl)imide (NaFSI) or sodium hexafluorophosphate (NaPF6) show that NaFSI provides improved capacity retention but results from symmetrical cells disclose no advantage for either salt. The impact of high and low desodiation cut-off potentials is studied and the results show a drastic increase in capacity retention when using the desodiation cut-off potential of 1.2 V as compared to 2.5 V. This effect is clear for both NaFSI and NaPF6 salts in a 1:1 binary mixture of ethylene carbonate and diethylene carbonate with 10 vol% fluoroethylene carbonate. Hard X-ray photoelectron spectroscopy (HAXPES) results revealed that the thickness of the solid electrolyte interphase (SEI) changed during cycling and that SEI was stripped from tin particles when tin phosphide was charged to 2.5 V with NaPF6 based electrolyte.
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| 4. |
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| 5. |
- Rehnlund, David, 1986-, et al.
(author)
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Dendrite-free lithium electrode cycling via controlled nucleation in low LiPF6 concentration electrolytes
- 2018
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In: Materials Today. - : Elsevier BV. - 1369-7021 .- 1873-4103. ; 21:10, s. 1010-1018
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Journal article (peer-reviewed)abstract
- Lithium metal electrodes are not widely used in rechargeable batteries as dendritic lithium growth and electrolyte reactions raise serious stability and safety concerns. In this study, we show that reproducible two-dimensional lithium deposition can be realized using a lithium salt concentration of 0.020 M, an added supporting salt, and a short lithium nucleation pulse. This approach, which is common in electrodeposition of metals, increases the lithium nuclei density on the electrode surface and decreases the extent of Li+ migration favoring dendritic lithium growth. Contrary to common belief, ascribing the dendrite problem to heterogeneous lithium nucleation due to an unstable solid electrolyte interphase layer, we show that the main lithium deposition problem stems from the difficulty to obtain two-dimensional deposition at the low lithium deposition overpotentials encountered in conventional high-lithium concentration electrolytes. The present results hence clearly demonstrate that two-dimensional lithium deposition can be realized in lithium-metal-based batteries.
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