| 1. |
- Baur, Christian, et al.
(författare)
-
Improved cycling stability in high-capacity Li-rich vanadium containing disordered rock salt oxyfluoride cathodes
- 2019
-
Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 7:37, s. 21244-21253
-
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.
|
|
| 2. |
- Chen, Heyin, et al.
(författare)
-
Investigating Surface Reactivity of a Ni-Rich Cathode Material toward CO2, H2O, and O2 Using Ambient Pressure X-ray Photoelectron Spectroscopy
- 2023
-
Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 6:22, s. 11458-11467
-
Tidskriftsartikel (refereegranskat)abstract
- Layered Ni-rich transition metal oxide materials are considered the most promising cathodes for use in commercial Li-ion batteries. Due to their instability in air, an impurity layer forms during storage under ambient conditions, and this layer increases electrochemical polarization during charging and discharging, which ultimately leads to a lower cycling capacity. In this work, we found that storage of the LiNi0.8Mn0.1Co0.1O2 (NMC 811) material in ultrahigh vacuum (UHV) can restore the surface by reducing the amount of native carbonate species in the impurity layer. In this work, in situ soft X-ray ambient pressure photoelectron spectroscopy is used to directly follow the interaction between common gases found in air and the NMC 811 surface. During gas exposure of the NMC 811 surface to pure CO2, O2, and a mixture of both pure gases, surface-adsorbed CO2 or/and O2 were detected; however, permanent changes could not be identified under UHV after the gas exposure. In contrast, a permanent increase in metal hydroxide species was observed on the sample surface following H2O vapor exposure, and an increased intensity in the carboxylate peak was observed after exposure to a mixture of CO2/O2/H2O. Thus, the irreversible degradation reaction with CO2 is triggered in the presence of H2O (on relevant time scales defined by the experiment). Additional measurements revealed that X-ray irradiation induces the formation of metal carbonate species on the NMC 811 surface under CO2 and H2O vapor pressure.
|
|
| 3. |
- Källquist, Ida, et al.
(författare)
-
Advances in studying interfacial reactions in rechargeable batteries by photoelectron spectroscopy
- 2022
-
Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 10:37, s. 19466-19505
-
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.
|
|
| 4. |
- Källquist, Ida
(författare)
-
Combining Electrochemistry and Photoelectron Spectroscopy for the Study of Li-ion Batteries
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis photoelectron spectroscopy (PES) is combined with electrochemistry to investigate the electrochemical processes that occur at the electrode/electrolyte interfaces in lithium-ion batteries (LIBs). LIB systems are studied by the use of both ex situ PES, where electrodes are electrochemically pre-cycled and subsequently measured by PES, and operando PES, where electrodes are cycled during PES measurements. Ex situ PES is used to determine the main degradation mechanisms of a novel high capacity material, Li2VO2F. The capacity fade seen for Li2VO2F. is found to be related to an irreversible oxidation of the active material at high voltages, and a continuous surface layer formation at low voltages. To decrease the capacity fading three strategies for optimizing the interface are investigated. The results show that a surface coating of AlF3 most efficiently can mitigate electrolyte reduction, while boron containing electrolyte additives and transition metal substitution more successfully limit the oxidation of the active material. A large part of the work performed in this thesis has been devoted towards developing a methodology suitable for conducting operando ambient pressure photoelectron spectroscopy (APPES) measurements on LIB systems. A general connection between the theory of PES and electrochemistry is made, where in particular a model suitable for interpreting operando APPES results on solid/liquid interfaces is suggested. The model is further developed for the specific case of LIB interfaces. The results from the operando studies show that the kinetic energy shifts of the liquid electrolyte measured by APPES can be correlated to the electrochemical reactions occurring at the interface. If no charge transfer occurs, the kinetic energy shift is proportional to the applied voltage. During charge transfer the behavior is more complex, and the kinetic energy shifts are related to the change in chemical potential of the working electrode. In summary, this thesis exemplifies how both ex situ and operando PES are highly useful techniques for the study of LIB battery interfaces. The possibilities of both techniques are highlighted, and important considerations for an accurate interpretation of the PES results are also discussed.
|
|
| 5. |
- Källquist, Ida, et al.
(författare)
-
Degradation Mechanisms in Li2VO2F Li-Rich Disordered Rock-Salt Cathodes
- 2019
-
Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 31:16, s. 6084-6096
-
Tidskriftsartikel (refereegranskat)abstract
- The increased energy density in Li-ion batteries is particularly dependent on the cathode materials that so far have been limiting 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 because of 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 are 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 degradation of the particle surface that spreads inward with continued cycling.
|
|
| 6. |
- Källquist, Ida, et al.
(författare)
-
Influence of Electrolyte Additives on the Degradation of Li2VO2F Li-Rich Cathodes
- 2020
-
Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 124:24, s. 12956-12967
-
Tidskriftsartikel (refereegranskat)abstract
- rich disordered rock-salt structures have, because of their high theoretical capacity, gained a lot of attention as a promising class of cathode materials for battery applications. However, the cycling stability of these materials has 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, shows a 12.5% increase of capacity retention after 20 cycles. The improved cycling performance is explained by the formation of a protective cathode interphase on the electrode surface. Photoelectron spectroscopy is used to show that the surface layer is created from degradation of the electrolyte salt and additive cosalts. The cathode interphase can mitigate oxidation and following degradation of the active material, and thereby a higher degree of redox-active vanadium can be maintained after 20 cycles.
|
|
| 7. |
- Källquist, Ida
(författare)
-
Interfaces in Li-ion batteries seen through photoelectron spectroscopy
- 2019
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- To accommodate the need for greener energy solutions renewable energy sources aswell as reliable energy storage is a prerequisite. For the latter, high energy densitybatteries with long-term cycling stability are necessary. The cycling properties of abattery is to a large extent dependent on the functionality of the battery interfaces. Assuch, there is a need to understand the reactions occurring between the electrode andelectrolyte, and to limit those that are detrimental to the battery performance. Thetopic of this thesis is these interfaces in Li-ion batteries seen through photoelectronspectroscopy (PES).PES is due to its surface and chemical sensitivity one of the most suitable techniquesto study battery interfaces. In this thesis, PES is used to follow the oxidationstate and chemical environment of different atoms to understand the reactions occurringin the battery. This work uses a combination of soft and hard X-ray photoelectronspectroscopy as well X-ray absorption spectroscopy (XAS) to investigate the degradationmechanisms in high energy density cathode materials. The materials investigatedare in the class of Li-rich disordered rock-salts (DRS) and provide very highinitial capacities, but unfortunately lacks in cycling stability. In this thesis it is shownthat the reason for this is an unstable surface, possibly related to the occurrence ofanionic redox in the material, leading to breakdown of both electrolyte and electrodematerial. In addition, it is shown that the interface stability can be improved by choosingtransition metals that promotes the DRS structure and thus increases the chemicalstability of the material and long term cycling of the battery.Even though ex situ measurements provide many insights into the properties ofbattery interphases, there is still a need for operando measurement to completely answerthe puzzling question of their full functionality. In this thesis first steps towardsoperando measurements are taken by identifying the measurements conditions necessaryto probe a battery electrolyte with ambient pressure photoelectron spectroscopy(APPES) and a thorough characterization of a typical battery electrolyte is performed.The results show that the liquid can be stabilized by using the solvent as ambient gas,and also that care should be taken to avoid radiation damage when synchrotron lightis used. For the electrolyte characterization it is shown that a salt enrichment of particularlyLi+ and ionic fluoride is found at the droplet surface. These results are crucialto be able to single out contributions from the interphase in future operando measurements.When the method of operando APPES has matured and can be performed routinely,this could possibly be the key needed to understand how the interfaces in batteriescan be controlled to unlock the potential of stable high capacity materials infuture batteries.
|
|
| 8. |
- Källquist, Ida, et al.
(författare)
-
Operando ambient pressure photoelectron spectroscopy of solid/liquid interfaces in Li-ion batteries
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Ambient pressure photoelectron spectroscopy (APPES) is combined with electrochemistry (EC) to investigate the interface between the liquid electrolyte and the solid electrode in Li-ion battery (LIB) cells. The combination of these techniques is promising for further understanding the functionality of LIB interfaces, but it is also associated with several experimental challenges. In this work a functional EC-cell which allows for probing the solid/liquid interface is achieved by the dip-and-pull method. Two systems consisting of a 1M LiClO4 in propylene carbonate electrolyte and a sputter deposited lithium cobalt oxide (LCO) or lithium nickel manganese cobalt oxide (NMC) thin film electrode are investigated. A methodology for combined EC/APPES measurements is proposed, where continuously changing the measurement spot is necessary to avoid accumulation of surface species during X-ray exposure. The APPES spectra from the LCO and NMC electrodes show binding energy (BE) shifts depending on applied voltage. It is argued that this is related to the lithiation of the material, as the BE shifts are found to coincide with expected phase transitions to more conductive phases. The experimental data is compared to results from supercell DFT calculations modelling the bulk material. The opposite trends observed in the experimental and computational approaches indicate the importance of an accurate treatment of the exchange for a proper description of the oxidation states of the Co atoms and their corresponding core-level shifts.
|
|
| 9. |
- Källquist, Ida, et al.
(författare)
-
Potentials in Li-Ion Batteries Probed by Operando Ambient Pressure Photoelectron Spectroscopy
- 2022
-
Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 14:5, s. 6465-6475
-
Tidskriftsartikel (refereegranskat)abstract
- The important electrochemical processes in a battery happen at the solid/liquid interfaces. Operando ambient pressure photoelectron spectroscopy (APPES) is one tool to study these processes with chemical specificity. However, accessing this crucial interface and identifying the interface signal are not trivial. Therefore, we present a measurement setup, together with a suggested model, exemplifying how APPES can be used to probe potential differences over the electrode/electrolyte interface, even without direct access to the interface. Both the change in electron electrochemical potential over the solid/liquid interface, and the change in Li chemical potential of the working electrode (WE) surface at Li-ion equilibrium can be probed. Using a Li4Ti5O12 composite as a WE, our results show that the shifts in kinetic energy of the electrolyte measured by APPES can be correlated to the electrochemical reactions occurring at the WE/electrolyte interface. Different shifts in kinetic energy are seen depending on if a phase transition reaction occurs or if a single phase is lithiated. The developed methodology can be used to evaluate charge transfer over the WE/electrolyte interface as well as the lithiation/delithiation mechanism of the WE.
|
|
| 10. |
- Källquist, Ida, et al.
(författare)
-
Probing Electrochemical Potential Differences over the Solid/Liquid Interface in Li-Ion Battery Model Systems.
- 2021
-
Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 13:28, s. 32989-32996
-
Tidskriftsartikel (refereegranskat)abstract
- The electrochemical potential difference (Δμ̅) is the driving force for the transfer of a charged species from one phase to another in a redox reaction. In Li-ion batteries (LIBs), Δμ̅ values for both electrons and Li-ions play an important role in the charge-transfer kinetics at the electrode/electrolyte interfaces. Because of the lack of suitable measurement techniques, little is known about how Δμ̅ affects the redox reactions occurring at the solid/liquid interfaces during LIB operation. Herein, we outline the relations between different potentials and show how ambient pressure photoelectron spectroscopy (APPES) can be used to follow changes in Δμ̅e over the solid/liquid interfaces operando by measuring the kinetic energy (KE) shifts of the electrolyte core levels. The KE shift versus applied voltage shows a linear dependence of ∼1 eV/V during charging of the electrical double layer and during solid electrolyte interphase formation. This agrees with the expected results for an ideally polarizable interface. During lithiation, the slope changes drastically. We propose a model to explain this based on charge transfer over the solid/liquid interface.
|
|
| 11. |
- Lindgren, Fredrik, et al.
(författare)
-
Breaking Down a Complex System : Interpreting PES Peak Positions for Cycled Li-ion Battery Electrodes
- 2017
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 121, s. 27303-27312
-
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.
|
|
| 12. |
- Maibach, Julia, et al.
(författare)
-
Probing a battery electrolyte drop with ambient pressure photoelectron spectroscopy
- 2019
-
Ingår i: Nature Communications. - : NATURE PUBLISHING GROUP. - 2041-1723. ; 10
-
Tidskriftsartikel (refereegranskat)abstract
- Operando ambient pressure photoelectron spectroscopy in realistic battery environments is a key development towards probing the functionality of the electrode/electrolyte interface in lithium-ion batteries that is not possible with conventional photoelectron spectroscopy. Here, we present the ambient pressure photoelectron spectroscopy characterization of a model electrolyte based on 1M bis(trifluoromethane)sulfonimide lithium salt in propylene carbonate. For the first time, we show ambient pressure photoelectron spectroscopy data of propylene carbonate in the liquid phase by using solvent vapor as the stabilizing environment. This enables us to separate effects from salt and solvent, and to characterize changes in electrolyte composition as a function of probing depth. While the bulk electrolyte meets the expected composition, clear accumulation of ionic species is found at the electrolyte surface. Our results show that it is possible to measure directly complex liquids such as battery electrolytes, which is an important accomplishment towards true operando studies.
|
|
| 13. |
|
|
| 14. |
- Naylor, Andrew J., et al.
(författare)
-
Stabilization of Li-Rich Disordered Rocksalt Oxyfluoride Cathodes by Particle Surface Modification
- 2020
-
Ingår i: ACS Applied Energy Materials. - : AMER CHEMICAL SOC. - 2574-0962. ; 3:6, s. 5937-5948
-
Tidskriftsartikel (refereegranskat)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 AIF(3) 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 stabilization of the active material surface by the surface modification and reveals its suppression of electrolyte decomposition.
|
|
| 15. |
- Zhu, Suyun, et al.
(författare)
-
HIPPIE : a new platform for ambient-pressure X-ray photoelectron spectroscopy at the MAX IV Laboratory
- 2021
-
Ingår i: Journal of Synchrotron Radiation. - : INT UNION CRYSTALLOGRAPHY. - 1600-5775 .- 0909-0495. ; 28, s. 624-636
-
Tidskriftsartikel (refereegranskat)abstract
- HIPPIE is a soft X-ray beamline on the 3 GeV electron storage ring of the MAX IV Laboratory, equipped with a novel ambient-pressure X-ray photoelectron spectroscopy (APXPS) instrument. The endstation is dedicated to performing in situ and operando X-ray photoelectron spectroscopy experiments in the presence of a controlled gaseous atmosphere at pressures up to 30 mbar [1 mbar = 100 Pa] as well as under ultra-high-vacuum conditions. The photon energy range is 250 to 2200 eV in planar polarization and with photon fluxes >1012 photons s-1 (500 mA ring current) at a resolving power of greater than 10000 and up to a maximum of 32000. The endstation currently provides two sample environments: a catalysis cell and an electrochemical/liquid cell. The former allows APXPS measurements of solid samples in the presence of a gaseous atmosphere (with a mixture of up to eight gases and a vapour of a liquid) and simultaneous analysis of the inlet/outlet gas composition by online mass spectrometry. The latter is a more versatile setup primarily designed for APXPS at the solid-liquid (dip-and-pull setup) or liquid-gas (liquid microjet) interfaces under full electrochemical control, and it can also be used as an open port for ad hoc-designed non-standard APXPS experiments with different sample environments. The catalysis cell can be further equipped with an IR reflection-absorption spectrometer, allowing for simultaneous APXPS and IR spectroscopy of the samples. The endstation is set up to easily accommodate further sample environments.
|
|
