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| 2. |
- Böhme, Solveig, 1987-, et al.
(författare)
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Elevated Temperature Lithium-Ion Batteries Containing SnO2 Electrodes and LiTFSI-Pip14TFSI Ionic Liquid Electrolyte
- 2017
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 164:4, s. A701-A708
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Tidskriftsartikel (refereegranskat)abstract
- The performance of lithium-ion batteries (LIBs) comprising SnO2 electrodes and an ionic liquid (IL) based electrolyte, i.e., 0.5 MLiTFSI in Pip14TFSI, has been studied at room temperature (i.e., 22◦C) and 80◦C. While the high viscosity and low conductivity ofthe electrolyte resulted in high overpotentials and low capacities at room temperature, the SnO2 performance at 80◦C was found to beanalogous to that seen at room temperature using a standard LP40 electrolyte (i.e., 1MLiPF6 dissolved in 1:1 ethylene carbonate anddiethyl carbonate). Significant reduction of the IL was, however, found at 80◦C, which resulted in low coulombic efficiencies duringthe first 20 cycles, most likely due to a growing SEI layer and the formation of soluble IL reduction products. X-ray photoelectronspectroscopy studies of the cycled SnO2 electrodes indicated the presence of an at least 10 nm thick solid electrolyte interphase (SEI)layer composed of inorganic components such as lithium fluoride, sulfates, and nitrides as well as organic species containing C-H,C-F and C-N bonds.
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| 3. |
- Böhme, Solveig, 1987-
(författare)
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Fundamental Insights into the Electrochemistry of Tin Oxide in Lithium-Ion Batteries
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis aims to provide insight into the fundamental electrochemical processes taking place when cycling SnO2 in lithium-ion batteries (LIBs). Special attention was paid to the partial reversibility of the tin oxide conversion reaction and how to enhance its reversibility. Another main effort was to pinpoint which limitations play a role in tin based electrodes besides the well-known volume change effect in order to develop new strategies for their improvement. In this aspect, Li+ mass transport within the electrode particles and the large first cycle charge transfer resistance were studied. Li+ diffusion was proven to be an important issue regarding the electrochemical cycling of SnO2. It was also shown that it is the Li+ transport inside the SnO2 particles which represents the largest limitation. In addition, the overlap between the potential regions of the tin oxide conversion and the alloying reaction was investigated with photoelectron spectroscopy (PES) to better understand if and how the reactions influence each other`s reversibility.The fundamental insights described above were subsequently used to develop strategies for the improvement of the performance and the cycle life for SnO2 electrodes in LIBs. For instance, elevated temperature cycling at 60 oC was employed to alleviate the Li+ diffusion limitation effects and, thus, significantly improved capacities could be obtained. Furthermore, an ionic liquid electrolyte was tested as an alternative electrolyte to cycle at higher temperatures than 60 oC which is the thermal stability limit for the conventional LP40 electrolyte. In addition, cycled SnO2 nanoparticles were characterized with transmission electron microscopy (TEM) to determine the effects of long term high temperature cycling. Also, the effect of vinylene carbonate (VC) as an electrolyte additive on the cycling behavior of SnO2 nanoparticles was studied in an effort to improve the capacity retention. In this context, a recently introduced intermittent current interruption (ICI) technique was employed to measure and compare the development of internal cell resistances with and without VC additive.
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| 4. |
- Böhme, Solveig, 1987-, et al.
(författare)
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On the electrochemistry of tin oxide coated tin electrodes in lithium-ion batteries
- 2015
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 179, s. 482-494
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Tidskriftsartikel (refereegranskat)abstract
- As tin based electrodes are of significant interest in the development of improved lithium-ion batteries it is important to understand the associated electrochemical reactions. In this work it is shown that the electrochemical behavior of SnO2 coated tin electrodes can be described based on the SnO2 and SnO conversion reactions, the lithium tin alloy formation and the oxidation of tin generating SnF2. The CV, XPS and SEM data, obtained for electrodeposited tin crystals on gold substrates, demonstrates that the capacity loss often observed for SnO2 is caused by the reformed SnO2 layer serving as a passivating layer protecting the remaining tin. Capacities corresponding up to about 80 % of the initial SnO2 capacity could, however, be obtained by cycling to 3.5 V vs. Li+/Li. It is also shown that the oxidation of the lithium tin alloy is hindered by the rate of the diffusion of lithium through a layer of tin with increasing thickness and that the irreversible oxidation of tin to SnF2 at potentials larger than 2.8 V vs. Li+/Li is due to the fact that SnF2 is formed below the SnO2 layer. This improved electrochemical understanding of the SnO2/Sn system should be valuable in the development of tin based electrodes for lithium-ion batteries.
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| 5. |
- Böhme, Solveig, 1987-, et al.
(författare)
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Overlapping and rate controlling electrochemical reactions for tin(IV) oxide electrodes in lithiu-ion batteries
- 2017
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Ingår i: Journal of Electroanalytical Chemistry. - 0022-0728 .- 1873-2569. ; 797, s. 47-60
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Tidskriftsartikel (refereegranskat)abstract
- The results of this extensive electrochemical study of the electrochemical reactions of SnO2 electrodes in lithium-ion batteries demonstrate that the different reduction and oxidation reactions overlap significantly during the cycling and that the rates of the redox reactions are limited by the mass transport through the layers of oxidation or reduction products formed on the electrodes. The experiments, which were carried out in the absence and presence of the lithium alloy reactions, show that the capacity losses seen on the first cycles mainly can be explained by an incomplete oxidation of the lithium tin alloy and an incomplete reformation of SnO2. The latter can be explained by the formation of thin tin oxide layers (i.e., SnO and SnO2), protecting the remaining tin, as the oxidation current then becomes limited by the Li+ diffusion rate though these layers. The results, also show that the first cycle SnO2 reduction was incomplete for the about 20 μm thick electrodes containing 1 to 6 μm large SnO2 particles. This can be ascribed to the formation of a layer of tin and Li2O (protecting the remaining SnO2) during the reduction process. Although the regeneration of the SnO2 always was slower than the reduction of the SnO2, the results clearly show that the SnO2 conversion reaction is far from irreversible, particularly at low scan rates and increased temperatures. Electrochemical cycling at 60 °C hence gave rise to increased capacities, but also a faster capacity loss, compared to at room temperature. These new findings indicate that a full utilization of SnO2 based electrodes at a given cycling rate only can be reached with sufficiently small particles since the allowed particle size is given by the time available for the mass transport through the formed surface layers. The present results consequently provide important insights into the phenomena limiting the use of SnO2 electrodes in lithium-ion batteries.
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| 7. |
- Böhme, Solveig, 1987-, et al.
(författare)
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Photoelectron Spectroscopic Evidence for Overlapping Redox Reactions for SnO2 Electrodes in Lithium-Ion Batteries
- 2017
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 121:9, s. 4924-4936
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Tidskriftsartikel (refereegranskat)abstract
- In-house and synchrotron-based photoelectron spectroscopy (XPSand HAXPES) evidence is presented for an overlap between the conversion andalloying reaction during the cycling of SnO2 electrodes in lithium-ion batteries(LIBs). This overlap resulted in an incomplete initial reduction of the SnO2 as wellas the inability to regenerate the reduced SnO2 on the subsequent oxidative scan.The XPS and HAXPES results clearly show that the SnO2 conversion reactionoverlaps with the formation of the lithium tin alloy and that the conversion reactiongives rise to the formation of a passivating Sn layer on the SnO2 particles. The latterlayer renders the conversion reaction incomplete and enables lithium tin alloy toform on the surface of the particles still containing a core of SnO2. The results alsoshow that the reoxidation of the lithium tin alloy is incomplete when the formationof tin oxide starts. It is proposed that the rates of the electrochemical reactions andhence the capacity of SnO2-based electrodes are limited by the lithium masstransport rate through the formed layers of the reduction and oxidations products.In addition, it is shown that a solid electrolyte interphase (SEI) layer is continuously formed at potentials lower than about 1.2 VLi+/Li during the first scan and that a part of the SEI dissolves on the subsequent oxidative scan. While the SEI was found tocontain both organic and inorganic species, the former were mainly located at the SEI surface while the inorganic species werefound deeper within the SEI. The results also indicate that the SEI dissolution process predominantly involves the organic SEIcomponents.
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| 9. |
- Rehnlund, David, 1986-, et al.
(författare)
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Lithium trapping in alloy forming electrodes and current collectors for lithium based batteries
- 2017
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Ingår i: Energy & Environmental Science. - : Royal Society of Chemistry (RSC). - 1754-5692 .- 1754-5706. ; 10:6, s. 1350-1357
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Tidskriftsartikel (refereegranskat)abstract
- Significant capacity losses are generally seen for batteries containing high-capacity lithium alloy forming anode materials such as silicon, tin and aluminium. These losses are generally ascribed to a combination of volume expansion effects and irreversible electrolyte reduction reactions. Here, it is shown, based on e.g. elemental analyses of cycled electrodes, that the capacity losses for tin nanorod and silicon composite electrodes in fact involve diffusion controlled trapping of lithium in the electrodes. While an analogous effect is also demonstrated for copper, nickel and titanium current collectors, boron-doped diamond is shown to function as an effective lithium diffusion barrier. The present findings indicate that the durability of lithium based batteries can be improved significantly via proper electrode design or regeneration of the used electrodes. © The Royal Society of Chemistry 2017.
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