| 1. |
- Edström, Kristina, et al.
(författare)
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Electrode/electrolyte interfaces in lithium and sodium batteries
- 2017
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Konferensbidrag (refereegranskat)abstract
- Lithium-ion batteries (LIB) and sodium-ion batteries (SIB) and their materials is today a large research area due to the practical need for efficient energy storage. SIBs show, compared to LIBs, unique electrochemical reactions that mechanistically need to be understood. The kind of materials that can host sodium ions are, for instance, structurally different from the negative and positive electrode materials for LIBs. Also interfacial reactions occurring between the electrode and the electrolyte are different from LIBs. To understand the chemical properties of electrolyte/electrode interfaces in LIBs and SIBs is one of the core research activities at the Ångström Advanced Battery Centre (ÅABC), Uppsala University. It is at these interfaces, the solid-electrolyte interphase (SEI) on the anode and the cathode electrolyte interface (CEI) on the cathode, charge transfer reactions take place, unwanted side reactions might start and the stability of the interface also influence the thermal stability of the battery. Careful characterization is therefore needed as a base for creating new and more stable interfaces for prolonged battery life. In this presentation we will make a review of several studies we have performed combining electrochemical characterization with in-house and synchrotron-based photoelectron spectroscopy (such as hard X-ray Photoelectron Spectroscopy, HAXPES). We will primarily dwell on the difference in chemical composition of the SEI of anodes used in LIBs and SIBs, respectively. We will also give some examples of ways to improve cycle life: the role of the electrolyte salt, electrolyte additives, but also of ways to protect electrode particle surfaces. We have investigated materials from three different categories of anodes: i.e. conversion, alloying, and insertion anodes. Our HAXPES results on Fe2O3 as a conversion anode material indicated that the SEI on Fe2O3 anode is thicker and more homogeneous in a SIB compared to that in an analogue Li-ion battery.1 We will discuss our work of silicon anodes for LIBs and we will discuss the dissolution of the SEI components in a SIB which is larger than for a LIB2. We will discuss the results which show that the SEI on a carbonacous anode in a SIB is inferior to that of the LIB counterpart. The interfaces of positive electrodes are also important. Often corrosion products will form during battery cycling leading to metal dissolution and poisoning of the negative electrode. We will also here compare the interfaces of Ni- and Mn-based oxide cathodes for LIBs and SIBs3.. References: [1] B. Philippe; M. Valvo; F. Lindgren; H. Rensmo; K. Edström, Chem. Mater. 2014, 26, 5028–5041.[2] R. Mogensen, D. Brandell, R. Younesi, ACS Energy Lett., 2016, 1, 1173–1178.[3] S. Doubaji, B. Philippe, I. Saadoune, M. Gorgoi, T. Gustafsson, A. Solhy, Mario Valvo, H. Rensmo, K. Edström. ChemSusChem, 2916, 9, 97-108.
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| 2. |
- Farhat, Douaa, et al.
(författare)
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Adiponitrile-Lithium Bis(trimethylsulfonyl)imide Solutions as Alkyl Carbonate-free Electrolytes for Li4Ti5O12 (LTO)/LiNi1/3Co1/3Mn1/3O2 (NMC) Li-Ion Batteries
- 2017
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Ingår i: ChemPhysChem. - : WILEY-V C H VERLAG GMBH. - 1439-4235 .- 1439-7641. ; 18:10, s. 1333-1344
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Tidskriftsartikel (refereegranskat)abstract
- Recently, dinitriles (NC(CH2)(n)CN) and especially adiponitrile (ADN, n = 4) have attracted attention as safe electrolyte solvents owing to their chemical stability, high boiling points, high flash points, and low vapor pressure. The good solvation properties of ADN toward lithium salts and its high electrochemical stability (approximate to 6 V vs. Li/Li+) make it suitable for safer Li-ions cells without performance loss. In this study, ADN is used as a single electrolyte solvent with lithium bis(trimethylsulfonyl) imide (LiTFSI). This electrolyte allows the use of aluminium collectors as almost no corrosion occurs at voltages up to 4.2 V. The physicochemical properties of the ADN-LiTFSI electrolyte, such as salt dissolution, conductivity, and viscosity, were determined. The cycling performances of batteries using Li4Ti5O12 (LTO) as the anode and LiNi1/3Co1/3Mn1/3O2 (NMC) as the cathode were determined. The results indicate that LTO/NMC batteries exhibit excellent rate capabilities with a columbic efficiency close to 100 %. As an example, cells were able to reach a capacity of 165 mAhg(-1) at 0.1C and a capacity retention of more than 98% after 200 cycles at 0.5 C. In addition, electrodes analyses by SEM, X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy after cycling confirming minimal surface changes of the electrodes in the studied battery system.
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| 3. |
- Jeschull, Fabian, et al.
(författare)
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On the Electrochemical Properties and Interphase Composition of Graphite : PVdF-HFP Electrodes in Dependence of Binder Content
- 2017
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Ingår i: Journal of the Electrochemical Society. - : Electrochemical Society. - 0013-4651 .- 1945-7111. ; 164:7, s. A1765-A1772
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Tidskriftsartikel (refereegranskat)abstract
- Poly(vinylidene-difluoride) (PVdF) based polymers constitute the most commonly used binders for lithium-ion battery electrodes. In scientific studies, the binder content often exceeds commercially meaningful amounts. At the same time, the battery electrode performance can in various ways be coupled to its binder content, partly due to its influence on the surface properties. For example, an optimum binder content of around 5 wt% has been reported. In this study, graphite: PVdF-HFP electrodes containing 2.5, 5 and 10 wt% of PVdF-HFP are investigated, and their electrochemical behavior are put into context of the electrode-electrolyte interphase of the different formulations. Although the electrodes display similar electrochemical behavior, the SEI layer composition and thickness, analyzed by photoelectron spectroscopy, vary notably depending on binder content. It was found that a binder content of 5 wt% maintained the best cycling stability and also exhibited a thinner SEI layer with a larger fraction of inorganic components. In contrast to higher binder contents, where the binder covers most of the surface, larger parts of the active material are exposed directly to the electrolyte with binder contents of 2.5-5 wt%. The formation of a thinner, yet protective, SEI layer is beneficial for cycling performance of the graphite electrode. (C) 2017 The Electrochemical Society. All rights reserved.
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| 4. |
- Lindgren, Fredrik, et al.
(författare)
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Breaking Down a Complex System : Interpreting PES Peak Positions for Cycled Li-ion Battery Electrodes
- 2017
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 121, s. 27303-27312
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Tidskriftsartikel (refereegranskat)abstract
- Photoelectron spectroscopy (PES) is an important technique for tracing and understanding the side reactions responsible for decreasing performance of Li-ion batteries. Interpretation of different spectral components is dependent on correct binding energy referencing and for battery electrodes this is highly complex. In this work, we investigate the effect on binding energy reference points in PES in correlation to solid electrolyte interphase (SEI) formation, changing electrode potentials and state of charge variations in Li-ion battery electrodes. The results show that components in the SEI have a significantly different binding energy reference point relative to the bulk electrode material (i.e. up to 2 eV). It is also shown that electrode components with electronically insulating/semi-conducting nature are shifted as a function of electrode potential relative to highly conducting materials. Further, spectral changes due to lithiation are highly depending on the nature of the active material and its lithiation mechanism. Finally, a strategy for planning and evaluating PES experiments on battery electrodes is proposed where some materials require careful choice of one or more internal reference points while others may be treated essentially without internal calibration.
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| 5. |
- Maibach, Julia, et al.
(författare)
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Surface Layer Evolution on Graphite During Electrochemical Sodium-tetraglyme Co-intercalation
- 2017
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Ingår i: ACS Applied Materials and Interfaces. - : AMER CHEMICAL SOC. - 1944-8244 .- 1944-8252. ; 9:14, s. 12373-12381
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Tidskriftsartikel (refereegranskat)abstract
- One obstacle in sodium ion batteries is the lack of suitable anode materials. As recently shown, the most common anode material of the state of the art lithium ion batteries, graphite, can be used for sodium ion storage as well, if ether based electrolyte solvents are used. These solvents cointercalate with the sodium ions leading to the highly reversible formation of ternary graphite intercalation compounds (t-GIC). In order for the solvent cointercalation to work efficiently, it is expected that only a very thin surface layer forms during electrochemical cycling. In this article, we therefore present the first dedicated study of the surface layer evolution on t-QICs using soft X-ray photoelectron spectroscopy. This technique with its inherent high surface sensitivity and low probing depth is an ideal tool to study the underlying interfacial reactions during the sodiation and desodiation of graphite. In this report, we apply this approach to graphite composite electrodes cycled in Na half cells with a 1 M sodium bis(fluorosulfonyl)imide/tetraethylene glycol dimethyl ether (NaFSI/TEG-DME) electrolyte. We have found a surface layer on the cycled electrodes, mainly composed of salt decomposition products and hydrocarbons, in line with irreversible capacity losses observed in the electrochemical cycling. Although this surface layer does not seem to block cointercalation completely, it seems to affect its efficiency resulting in a low Coulombic efficiency of the studied battery system.
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| 6. |
- Mogensen, Ronnie, et al.
(författare)
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Evolution of the solid electrolyte interphase on tin phosphide anodes in sodium ion batteries probed by hard x-ray photoelectron spectroscopy
- 2017
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Ingår i: Electrochimica Acta. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0013-4686 .- 1873-3859. ; 245, s. 696-704
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Tidskriftsartikel (refereegranskat)abstract
- In this work the high capacity anode material Sn4P3 for sodium ion batteries is investigated by electrochemical cycling and synchrotron-based hard x-ray photoelectron spectroscopy (HAXPES) in order to elucidate the solid electrolyte interphase (SEI) properties during the first 1.5 cycles. The electrochemical properties of tin phosphide (Sn4P3) when used as an anode material are first established in half cells versus metallic sodium in a 1 M NaFSI in EC: DEC electrolyte including 5 vol% FEC as SEI forming additive. The data from these experiments are then used to select the parameters for the samples to be analysed by HAXPES. A concise series of five cycled samples, as well as a soaked and pristine sample, were measured at different states of sodiation after the initial sodiation and after the following full cycle of sodiation and desodiation. Our results indicate that the SEI is not fully stable, as both significant thickness and composition changes are detected during cell cycling. (C) 2017 Elsevier Ltd. All rights reserved.
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| 7. |
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