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Instruments / Technical Area	Publication Details	Published
I09-Surface and Interface Structural Analysis	On the use of Ti3C2Tx MXene as a negative electrode material for lithium-ion batteries Tatiana Koriukina , Antonia Kotronia , Joseph Halim , Maria Hahlin , Johanna Rosen , Kristina Edström , Leif Nyholm Acs Omega DOI: 10.1021/acsomega.2c05785 Diamond Proposal Number(s): [23159, 26551] Open Access Show Abstract ▼ Abstract: The pursuit of new and better battery materials has given rise to numerous studies of the possibilities to use two-dimensional negative electrode materials, such as MXenes, in lithium-ion batteries. Nevertheless, both the origin of the capacity and the reasons for significant variations in the capacity seen for different MXene electrodes still remain unclear, even for the most studied MXene: Ti3C2Tx. Herein, freestanding Ti3C2Tx MXene films, composed only of Ti3C2Tx MXene flakes, are studied as additive-free negative lithium-ion battery electrodes, employing lithium metal half-cells and a combination of chronopotentiometry, cyclic voltammetry, X-ray photoelectron spectroscopy, hard X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy experiments. The aim of this study is to identify the redox reactions responsible for the observed reversible and irreversible capacities of Ti3C2Tx-based lithium-ion batteries as well as the reasons for the significant capacity variation seen in the literature. The results demonstrate that the reversible capacity mainly stems from redox reactions involving the Tx–Ti–C titanium species situated on the surfaces of the MXene flakes, whereas the Ti–C titanium present in the core of the flakes remains electro-inactive. While a relatively low reversible capacity is obtained for electrodes composed of pristine Ti3C2Tx MXene flakes, significantly higher capacities are seen after having exposed the flakes to water and air prior to the manufacturing of the electrodes. This is ascribed to a change in the titanium oxidation state at the surfaces of the MXene flakes, resulting in increased concentrations of Ti(II), Ti(III), and Ti(IV) in the Tx–Ti–C surface species. The significant irreversible capacity seen in the first cycles is mainly attributed to the presence of residual water in the Ti3C2Tx electrodes. As the capacities of Ti3C2Tx MXene negative electrodes depend on the concentration of Ti(II), Ti(III), and Ti(IV) in the Tx–Ti–C surface species and the water content, different capacities can be expected when using different manufacturing, pretreatment, and drying procedures.	Nov 2022
I09-Surface and Interface Structural Analysis	Stabilisation of Li-rich disordered rocksalt oxyfluoride cathodes by particle surface modification Andrew J. Naylor , Ida Kallquist , David Peralta , Jean-Frederic Martin , Adrien Boulineau , Jean-Francois Colin , Christian Baur , Johann Chable , Maximilian Fichtner , Kristina Edstrom , Maria Hahlin , Daniel Brandell Acs Applied Energy Materials DOI: 10.1021/acsaem.0c00839 Diamond Proposal Number(s): [20870] Open Access Show Abstract ▼ Abstract: Promising theoretical capacities and high voltages are offered by Li-rich disordered rocksalt oxyfluoride materials as cathodes in lithium ion batteries. However, as has been discovered for many other Li-rich materials, the oxyfluorides suffer from extensive surface degradation, leading to severe capacity fading. In the case of Li2VO2F, we have previously determined this to be a result of detrimental reactions between an unstable surface layer and the organic electrolyte. Herein, we present the protection of Li2VO2F particles with AlF3 surface modification, resulting in a much enhanced capacity retention over 50 cycles. While the specific capacity for the untreated material drops below 100 mA h g-1 after only 50 cycles, the treated materials retain almost 200 mA h g-1. Photoelectron spectroscopy depth profiling confirms the stabilisation of the active material surface by the surface modification and reveals its suppression of electrolyte decomposition.	May 2020
I09-Surface and Interface Structural Analysis	Improving capacity retention of Li2VO2F Li-rich cathodes with film-forming additives Ida Kallquist , Jean-Frederic Martin , Andrew Naylor , Christian Baur , Maximilian Fichtner , Jean-Francois Colin , Daniel Brandell , Kristina Edstrom , Maria Hahlin The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.0c02840 Diamond Proposal Number(s): [20870] Show Abstract ▼ Abstract: Li-rich disordered rock-salt structures have due to their high theoretical capacity gained large attention as a promising class of cathode materials for battery applications. However, the cycling stability of these materials have so far been less satisfactory. Here, we present three different film forming electrolyte additives; lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiODFB), and glycolide, which all improve the cycling performance of the high capacity Li-rich disordered rock-salt material Li2VO2F. The best performing additive, LiODFB, show a 12.5% increase of capacity retention after 20 cycles. The improved cycling performance is explained by the formation of a more robust cathode interphase on the electrode surface. Photoelectron spectroscopy is used to show that the surface layer is created from oxidation of the electrolyte salt and additive co-salts. This passivating layer can mitigate oxidation and following degradation of the active material, and thus a higher degree of redox active vanadium can be maintained after 20 cycles.	May 2020
I09-Surface and Interface Structural Analysis	Improved cycling stability in high-capacity Li-rich vanadium containing disordered rock salt oxyfluoride cathodes Christian Baur , Ida Kallquist , Johann Chable , Jin Hyun Chang , Rune E. Johnsen , Francisco Ruiz-Zepeda , Jean-Marcel Ateba Mba , Andrew Naylor , Juan Maria Garcia-Lastra , Tejs Vegge , Franziska Klein , Annika R. Schür , Poul Norby , Kristina Edström , Maria Hahlin , Maximilian Fichtner Journal Of Materials Chemistry A 7, 21244 - 21253 DOI: 10.1039/C9TA06291B Diamond Proposal Number(s): [19602] Open Access Show Abstract ▼ 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.	Sep 2019
I09-Surface and Interface Structural Analysis	Degradation mechanisms in Li2VO2F Li-rich disordered rock-salt cathodes Ida Kallquist , Andrew J. Naylor , Christian Baur , Johann Chable , Jolla Kullgren , Maximilian Fichtner , Kristina Edstrom , Daniel Brandell , Maria Hahlin Chemistry Of Materials DOI: 10.1021/acs.chemmater.9b00829 Diamond Proposal Number(s): [19602] Open Access Show Abstract ▼ Abstract: The strive for increased energy density in Li-ion batteries is particularly dependent on the cathode materials, that so far have been limiting for the overall battery performance. A new class of materials, Li-rich disordered rock-salts, has recently been brought forward as promising candidates for next-generation cathodes due to their ability to reversibly cycle more than one Li-ion per transition metal. Several variants of these Li-rich cathode materials have been developed recently and show promising initial capacities, but challenges concerning capacity fade and voltage decay during cycling need yet to be overcome. Mechanisms behind the significant capacity fade of some materials must be understood to allow for the design of new materials in which detrimental reactions can be mitigated. In this study the origin of the capacity fade in the Li-rich material Li2VO2F is investigated and it is shown to begin with a degradation of the particle surface that spreads inwards with continued cycling.	Jun 2019

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