| 1. |
- Baur, Christian, et al.
(författare)
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Improved cycling stability in high-capacity Li-rich vanadium containing disordered rock salt oxyfluoride cathodes
- 2019
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 7:37, s. 21244-21253
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Tidskriftsartikel (refereegranskat)abstract
- Lithium-rich transition metal disordered rock salt (DRS) oxyfluorides have the potential to lessen one large bottleneck for lithium ion batteries by improving the cathode capacity. However, irreversible reactions at the electrode/electrolyte interface have so far led to fast capacity fading during electrochemical cycling. Here, we report the synthesis of two new Li-rich transition metal oxyfluorides Li2V0.5Ti0.5O2F and Li2V0.5Fe0.5O2F using the mechanochemical ball milling procedure. Both materials show substantially improved cycling stability compared to Li2VO2F. Rietveld refinements of synchrotron X-ray diffraction patterns reveal the DRS structure of the materials. Based on density functional theory (DFT) calculations, we demonstrate that substitution of V3+ with Ti3+ and Fe3+ favors disordering of the mixed metastable DRS oxyfluoride phase. Hard X-ray photoelectron spectroscopy shows that the substitution stabilizes the active material electrode particle surface and increases the reversibility of the V3+/V5+ redox couple. This work presents a strategy for stabilization of the DRS structure leading to improved electrochemical cyclability of the materials.
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| 2. |
- Etman, Ahmed S., et al.
(författare)
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A one-step water based strategy for synthesizing hydrated vanadium pentoxide nanosheets from VO2(B) as free-standing electrodes for lithium battery applications
- 2016
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 4:46, s. 17988-18001
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis of two dimensional (2D) materials from transition metal oxides, chalcogenides, and carbides mostly involve multiple exfoliation steps in which hazardous solvents and reagents are used. In this study, hydrated vanadium pentoxide (V2O5 center dot nH(2)O) nanosheets with a thickness of a few nanometers were prepared via a facile environmentally friendly water based exfoliation technique. The exfoliation process involved refluxing the precursor, vanadium dioxide (VO2(B)), in water for a few days at 60 degrees C. The proposed exfoliation mechanism is based on the intercalation/insertion of water molecules into the VO2(B) crystals and the subsequent cleavage of the covalent bonds holding the layers of VO2(B) together. The thermal and chemical analyses showed that the approximate chemical composition of the nanosheets is H0.4V2O5 center dot 0.55H(2)O, and the percentage of V-V content to that of V-IV in the nanosheets is about 80(3)% to 20(3)%. The exfoliated aqueous suspension of the V2O5 center dot 0.55H(2)O nanosheets was successfully deposited onto multi-walled carbon nanotube (MW-CNT) paper to form free-standing electrodes with a thickness of the V2O5 center dot 0.55H(2)O layer ranging between 45 and 4 mu m. A series of electrochemical tests were conducted on the electrodes to determine the cyclability and rate capability of lithium insertion into V2O5 center dot 0.55H(2)O nanosheets. The electrodes with the thinnest active material coating (similar to 4 mu m) delivered gravimetric capacities of up to 480 and 280 mA h g(-1) when cycled at current densities of 10 and 200 mA g(-1), respectively.
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| 3. |
- Källquist, Ida, et al.
(författare)
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Advances in studying interfacial reactions in rechargeable batteries by photoelectron spectroscopy
- 2022
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 10:37, s. 19466-19505
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Forskningsöversikt (refereegranskat)abstract
- Many of the challenges faced in the development of lithium-ion batteries (LIBs) and next-generation technologies stem from the (electro)chemical interactions between the electrolyte and electrodes during operation. It is at the electrode-electrolyte interfaces where ageing mechanisms can originate through, for example, the build-up of electrolyte decomposition products or the dissolution of metal ions. In pursuit of understanding these processes, X-ray photoelectron spectroscopy (XPS) has become one of the most important and powerful techniques in a large collection of available tools. As a highly surface-sensitive technique, it is often thought to be the most relevant in characterising the interfacial reactions that occur inside modern rechargeable batteries. This review tells the story of how XPS is employed in day-to-day battery research, as well as highlighting some of the most recent innovative in situ and operando methodologies developed to probe battery materials in ever greater detail. A large focus is placed not only on LIBs, but also on next-generation materials and future technologies, including sodium- and potassium-ion, multivalent, and solid-state batteries. The capabilities, limitations and practical considerations of XPS, particularly in relation to the investigation of battery materials, are discussed, and expectations for its use and development in the future are assessed.
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| 4. |
- Liu, Chenjuan, et al.
(författare)
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3-D binder-free graphene foam as a cathode for high capacity Li-O-2 batteries
- 2016
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 4:25, s. 9767-9773
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Tidskriftsartikel (refereegranskat)abstract
- To provide energy densities higher than those of conventional Li-ion batteries, a Li-O-2 battery requires a cathode with high surface area to host large amounts of discharge product Li2O2. Therefore, reversible formation of discharge products needs to be investigated in Li-O-2 cells containing high surface area cathodes. In this study, a binder-free oxygen electrode consisting of a 3-D graphene structure on aluminum foam, with a high defect level (I-D/I-G = 1.38), was directly used as the oxygen electrode in LiO2 batteries, delivering a high capacity of about 9 x 10(4) mA h g(-1) (based on the weight of graphene) at the first full discharge using a current density of 100 mA g(graphene)(-1). This performance is attributed to the 3-D porous structure of graphene foam providing both an abundance of available space for the deposition of discharge products and a high density of reactive sites for Li-O-2 reactions. Furthermore, the formation of discharge products with different morphologies and their decomposition upon charge were observed by SEM. Some nanoscaled LiOH particles embedded in the toroidal Li2O2 were detected by XRD and visualized by TEM. The amount of Li2O2 formed at the end of discharge was revealed by a titration method combined with UV-Vis spectroscopy analysis.
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| 5. |
- Liu, Chenjuan, 1988-, et al.
(författare)
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A free standing Ru–TiC nanowire array/carbon textile cathode with enhanced stability for Li–O2 batteries
- 2018
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 6, s. 23659-23668
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Tidskriftsartikel (refereegranskat)abstract
- The instability of carbon cathode materials is one of the key problems that hinder the development of lithium–air/lithium–oxygen (Li–O2) batteries. In this contribution, a type of TiC-based cathode is developed as a suitable alternative to carbon based cathodes, and its stability with respect to its surface properties is investigated. Here, a free-standing TiC nanowire array cathode was in situ grown on a carbon textile, covering its exposed surface. The TiC nanowire array, via deposition with Ru nanoparticles, showed enhanced oxygen reduction/evolution activity and cyclability, compared to the one without Ru modification. The battery performance of the Li–O2cells with Ru–TiC was investigated by using in operando synchrotron radiation powder X-ray diffraction (SR-PXD) during a full cycle. With the aid of surface analysis, the role of the cathode substrate and surface modification is demonstrated. The presented results are a further step toward a wise design of stable cathodes for Li–O2 batteries.
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| 6. |
- Sun, Bing, et al.
(författare)
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At the polymer electrolyte interfaces : the role of the polymer host in interphase layer formation in Li-batteries
- 2015
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 3:26, s. 13994-14000
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Tidskriftsartikel (refereegranskat)abstract
- In this study, X-ray photoelectron spectroscopy was applied for compositional analysis of the interphase layers formed in graphite and LiFePO4 Li-battery half cells containing solid polymer electrolytes (SPEs) consisting of poly(trimethylene carbonate) (PTMC) and LiTFSI salt. Decomposition of PTMC was observed at the anode/SPE interface, indicating different reaction products than those associated with the more conventional host material poly(ethylene oxide). Degradation mechanisms of the PTMC host material at low potentials are proposed. Compared to the LiFePO4/PEO interface, the absence of LiOH - a result of water contamination - was generally seen when using hydrophobic PTMC as the polymer host. A clear correlation of moisture content with the constitution of interphase layers in Li polymer batteries could thus be concluded. At the SPE/LiFePO4 interface, good stability was seen regardless of the polymer host materials.
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| 7. |
- Valvo, Mario, et al.
(författare)
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Electrochemical elaboration of electrodes and electrolytes for 3D structured batteries
- 2013
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Ingår i: JOURNAL OF MATERIALS CHEMISTRY A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 1:32, s. 9281-9293
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Tidskriftsartikel (refereegranskat)abstract
- The challenges associated with the fabrication of three-dimensional (3D) electrode and electrolyte materials for Li-ion batteries are discussed. The basic issues for achieving a solid 3D cell foundation, which can simultaneously offer sufficient electronic conductivity to enable stable cycling, as well as enough compatibility with the incorporation of complementary components, have been addressed. Various electrochemical strategies for elaborating such systems are discussed and critically examined. Several current collector systems are presented including electrochemically prepared Cu and Al nanorods and commercial aperiodic carbon structures. Further electrochemical coating approaches then provide a direct method for the deposition of thin layers of active materials successfully demonstrated here as coatings on both 3D metal structures and commercially available 3D-structured carbon substrates. Enhanced capacities per foot print area are demonstrated for a number of 3D electrode materials, namely polyaniline on reticulated vitreous carbon, Cu2O on copper nanorods and TiO2 on Al nanorods. The crucial points for achieving a thin conformal coating of the corresponding 3D electrode structures with solid polymer electrolytes are also carefully analysed and discussed. In this context electro-polymerisation is proposed as a viable route to form thin electrolyte layers with promising characteristics. The high versatility of electro-polymerisation in combination with the various structures and methodologies adopted here represents a further step towards the development of cost-effective 3D microbattery devices.
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| 8. |
- Valvo, Mario, et al.
(författare)
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The impact of size effects on the electrochemical behaviour of Cu2O-coated Cu nanopillars for advanced Li-ion microbatteries
- 2014
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 2:25, s. 9574-9586
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Tidskriftsartikel (refereegranskat)abstract
- The generation of a distribution of nanoparticles upon conversion reaction of thin Cu2O layers is demonstrated to produce a wide electrochemical potential window, as well as a distinctive capacity increase in large area three-dimensional electrodes. Cu nanopillars with a 10-15 nm Cu2O coating containing traces of nanocrystattine Fe2O3 yield capacities up to 0.265 mA h cm(-2) (at 61 mA g(-1)), excellent cycling for more than 300 cycles and an electroactive potential window larger than 2 V. due to the size effects caused by the various Cu/Cu2O nanopartictes formed during conversion/deconversion. These 3D Li-ion battery electrodes based on etectrodeposited Cu nanopillars spontaneously coated with a Cu2O layer are compatible with current densities of 16 A g(-1) (i.e. 61 C rates) after aerosol-assisted infiltration with an iron acetate solution followed by low-temperature pyrolysis. The capacity of the composite material increases by 67% during 390 cycles due to the growth of the electroactive area during the electrochemical milling of Cu2O forced by its repeated conversion/de-conversion. The latter generates a distribution of nanoparticles with different sizes and redox potentials, which explains the broad potential window, as well as the significant capacity contribution from double layer charging. These 3D electrodes should be well-suited for Li-ion microbatteries and Li-ion batteries in general, since they combine high capacities per footprint area with excellent power capabilities. More importantly, such electrodes grant access to fundamental understanding of the electrochemical behaviour of these active materials providing new insights into both conversion mechanisms and nanostructured interfaces more in general.
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| 9. |
- Wang, Zhaohui, et al.
(författare)
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Flexible freestanding Cladophora nanocellulose paper based Si anodes for lithium-ion batteries
- 2015
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 3:27, s. 14109-14115
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Tidskriftsartikel (refereegranskat)abstract
- Freestanding, lightweight and flexible Si paper anodes are prepared via a straightforward paper-making process using Cladophora nano-cellulose, silicon nanoparticles and carbon nanotubes as the building blocks. The uniform Si particle distribution and strong adhesion of the Si nanoparticles to the porous, conductive and flexible nanocellulose/carbon nanotube 3D matrix yield specific capacities of up to 800 mA h g(-1) (based on the weight of whole electrode) and very good cycling performances.
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| 10. |
- Wei, Wei, et al.
(författare)
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High energy and power density TiO2 nanotube electrodes for 3D Li-ion microbatteries
- 2013
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 1:28, s. 8160-8169
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Tidskriftsartikel (refereegranskat)abstract
- Highly ordered anodic TiO2 nanotube arrays with a tube length of 9 mm are shown to provide areal capacities of 0.24 mA h cm(-2) (i.e. 96 mA h g(-1)) at a charge/discharge current density of 2.5 mA cm(-2) (corresponding to a rate of 5 C) and 0.46 mA h cm(-2) (i.e. 184 mA h g(-1)) at 0.05 mA cm(-2), when used as 3D free-standing anodes in Li-ion microbatteries. The present nanotube electrodes, which could be cycled for 500 cycles with only 6% loss of capacity, exhibited significantly higher energy and power densities, as well as an excellent cycling stability compared to previously reported TiO2-based Li-ion microbattery electrodes. The influence of parameters such as ordering, geometry and crystallinity of the nanotubes on the microbattery performance was investigated. A two-step anodization process followed by annealing of the nanotubes was found to yield the best microbattery performance. It is also demonstrated that the rate capability of the electrode depends mainly on the rate of the structural rearrangements associated with the lithiation/delithiation reaction and that the areal capacity at various charge/discharge rates can be increased by increasing the tube wall thickness or the length of the nanotubes, up to 0.6 mA h cm(-2) for 100 cycles.
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