Papers by Kristina Edström
Ether Based Electrolyte, LiB(CN)<sub>4</sub> Salt and Binder Degradation in the Li–O<sub>2</sub> Battery Studied by Hard X-ray Photoelectron Spectroscopy (HAXPES)
Journal of Physical Chemistry C, Aug 23, 2012
ABSTRACT Li−O 2 cells composed of a carbon cathode containing an α-MnO 2 nanowire catalyst and a ... more ABSTRACT Li−O 2 cells composed of a carbon cathode containing an α-MnO 2 nanowire catalyst and a Kynar (PVDF-HFP) binder were cycled with different electrolytes containing 0.5 M LiB(CN) 4 salt in polyethylene glycol dimethyl ether (PEGDME) or tetraethylene glycol dimethyl ether (Tetraglyme) solvents. All cells exhibited fast capacity fading. To explain this, the surface chemistry of the carbon electrodes were investigated by synchrotron based hard X-ray photoelectron spectroscopy (HAXPES) using two photon energies of 2300 and 6900 eV. It is shown that the LiB(CN) 4 salt and Kynar binder were degraded during cycling, forming a layer composed of salt and binder residues on the cathode surface. The degradation mechanism of the salt differed in the two tested solvents and, consequently, different types of boron compounds were formed during cycling. Larger amounts of the degraded salt was observed using Tetraglyme as the solvent. With a nonfluorined Li-salt, the observed formation of LiF, which might be a reason for the observed blockage of pores in the cathode and for the observed capacity fading, must be due to Kynar binder decomposition. The amount of LiF formed in the PEGDME cell was larger than that formed in the Tetraglyme cell. The results indicate that not only the electrolyte solvent, but also electrolyte salt as well as the binder used for the porous cathode must be carefully considered when building a successful rechargeable Li−O 2 battery.
Journal of The Electrochemical Society, Nov 14, 2015
Photoelectron spectroscopy (PES) has become an important tool for investigating Li-ion battery ma... more Photoelectron spectroscopy (PES) has become an important tool for investigating Li-ion battery materials, in particular for analyzing interfacial structures and reactions. Since the methodology was introduced in the battery research area, PES has undergone a dramatic development regarding photon sources, sample handling and electron energy analyzers. This includes the possibility to use synchrotron radiation with increased intensity and the possibility to vary the photon energy. The aim of the present paper is to describe how PES can be used to investigate battery interfaces and specifically highlight how synchrotron based PES has been implemented to address different questions useful for the development of the Li-ion batteries. We also present some recent developments of the techniques, which have the potential to further push the limits for the use of photoelectron spectroscopy in battery research.
The Influence of Electrochemical Cycling and Side Reactions on Battery Electrode Materials Analyzed by Photoelectron Spectroscopy
The Influence of Electrochemical Cycling and Side Reactions on Battery Electrode Materials Analyz... more The Influence of Electrochemical Cycling and Side Reactions on Battery Electrode Materials Analyzed by Photoelectron Spectroscopy
Nature Communications, Jul 12, 2019
Operando ambient pressure photoelectron spectroscopy in realistic battery environments is a key d... more 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.
Review of Scientific Instruments, Apr 1, 2015
We have performed the first "high-pressure" XPS study on the palladium, hydrogen and olefin (tran... more We have performed the first "high-pressure" XPS study on the palladium, hydrogen and olefin (trans-2-pentene) system in order to gain a better insight into the hydrogenation reaction. We report here data collected using a Pd(111) single crystal and a polycrystalline foil. Hydrogenation was observed on polycrystalline foil (RT and 373 K), but not on Pd(111) single crystal, revealed by on-line mass-spectrometry. We observed the reaction in the presence of huge amount of carbon (up to 73 %) in the information depth of XPS. On Pd(111) mainly graphite was present while other components C-H and C-Pd were also formed on the foil in much higher extent. C-Pd characterizes a carbon species in the interaction with palladium whereas C-H represents hydrogenated carbon including chemisorbed species. The d-band of the foil showed a remarkable up-shift towards E FERMI as compared to Pd(111). We concluded that both differences found in the valence and in C 1s region are indicators for different electronic structures that contribute to the variation in activity. The palladium foil lost its activity at elevated temperature (523 K), most probably due to desorption of hydrogen. Using additional UPS measurements we concluded that trans-2-pentene is hydrogenated in σ-bonded chemisorption modus, at least in UHV conditions.
Manganese in the SEI Layer of Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub> Studied by Combined NEXAFS and HAXPES Techniques
Journal of Physical Chemistry C, Feb 5, 2016
A combination of hard X-ray photoelectron spectroscopy (HAXPES) and near edge X-ray absorption fi... more A combination of hard X-ray photoelectron spectroscopy (HAXPES) and near edge X-ray absorption fine structure (NEXAFS) are here used to investigate the presence and chemical state of crossover manganese deposited on Li-ion battery anodes. The synchrotron-based experimental techniques—using HAXPES and NEXAFS analysis on the same sample in one analysis chamber—enabled us to acquire complementary sets of information. The Mn crossover and its influence on the anode interfacial chemistry has been a topic of controversy in the literature. Cells comprising lithium manganese oxide (LiMn2O4, LMO) cathodes and lithium titanate (Li4Ti5O12, LTO) anodes were investigated using LP40 (1 M LiPF6, EC:DEC 1:1) electrolyte. LTO electrodes at lithiated, delithiated, and open circuit voltage (OCV-stored) states were analyzed to investigate the potential dependency of the manganese oxidation state. It was primarily found that a solid surface layer was formed on the LTO electrode and that this layer contains deposited Mn from t...
The Influence of PMS-Additive on the Electrode/Electrolyte Interfaces in LiFePO<sub>4</sub>/Graphite Li-Ion Batteries
Journal of Physical Chemistry C, Oct 28, 2013
ABSTRACT The influence of a film-forming additive, propargyl methanesulfonate (PMS), on electroch... more ABSTRACT The influence of a film-forming additive, propargyl methanesulfonate (PMS), on electrochemical performance and electrode/electrolyte interface composition of LiFePO4/graphite Li-ion batteries has been studied. Combined use of in-house X-ray photoelectron spectroscopy (XPS) and soft and hard X-ray photoelectron spectroscopy (PES) enabled nondestructive depth profiling at four different probing depths in the 2-50 nm range. Cells cycled with PMS and LiPF6 in ethylene carbonate/diethyl carbonate (EC/DEC) were compared to a reference sample cycled without PMS. In the first cycle, PMS cells showed a higher irreversible capacity, which is explained by formation of a thicker solid electrolyte interphase (SEI). After three cycles, the SET thicknesses were determined to be 19 and 25 nm for the reference and PMS samples, respectively. After the initial cycling, irreversible losses shown by the PMS cells were lower than those of the reference cell. This could be attributed to a different SET composition and lower differences in the amount of lithium between lithiated and delithiated electrodes for the PMS sample. It was suggested that PMS forms a triple-bonded radical on reduction, which further reacts with the electrolyte. The PMS additive was shown to influence the chemical composition at the positive electrode/electrolyte interface. Thicker interface layers with higher C-O and smaller LiF contributions were formed on LiFePO4 cycled with PMS.
Journal of Power Sources, Mar 1, 2013
h i g h l i g h t s < The presence of O 2 influences the composition of the SEI on Li of the LieO... more h i g h l i g h t s < The presence of O 2 influences the composition of the SEI on Li of the LieO 2 battery. < The SEI on Li anode of the LieO 2 battery is unstable and changes during the cycling. < LiPF 6 and PC decompose on the surface of the Li and contribute in formation of the SEI. < Decomposed Kynar binder (degraded on the cathode) was observed on the surface of Li. < Oxygen increases the resistance of the cells and influences the lithium stripping and plating.
Chemistry of Materials, Jun 3, 2019
The increased energy density in Li-ion batteries is particularly dependent on the cathode materia... more 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 nextgeneration 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 Li 2 VO 2 F is investigated, and it is shown to begin with degradation of the particle surface that spreads inward with continued cycling.
Journal of Physical Chemistry C, Nov 28, 2017
Photoelectron spectroscopy (PES) is an important technique for tracing and understanding the side... more 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
ACS Applied Materials & Interfaces, Feb 5, 2013
The surface compositions of a MnO 2 catalyst containing carbon cathode and a Li anode in a Li−O 2... more The surface compositions of a MnO 2 catalyst containing carbon cathode and a Li anode in a Li−O 2 battery were investigated using synchrotron-based photoelectron spectroscopy (PES). Electrolytes comprising LiClO 4 or LiBOB salts in PC or EC:DEC (1:1) solvents were used for this study. Decomposition products from LiClO 4 or LiBOB were observed on the cathode surface when using PC. However, no degradation of LiClO 4 was detected when using EC/DEC. We have demonstrated that both PC and EC/ DEC solvents decompose during the cell cycling to form carbonate and ether containing compounds on the surface of the carbon cathode. However, EC/DEC decomposed to a lesser degree compared to PC. PES revealed that a surface layer with a thickness of at least 1−2 nm remained on the MnO 2 catalyst at the end of the charged state. It was shown that the detachment of Kynar binder influences the surface composition of both the carbon cathode and the Li anode of Li−O 2 cells. The PES results indicated that in the charged state the SEI on the Li anode is composed of PEO, carboxylates, carbonates, and LiClO 4 salt.
The Cathode Electrolyte Interphase on Graphite Positive Electrode in Dual-ion Batteries Probed Using X-ray Photoelectron Spectroscopy
The Cathode Electrolyte Interphase on Graphite Positive Electrode in Dual-ion Batteries Probed Us... more The Cathode Electrolyte Interphase on Graphite Positive Electrode in Dual-ion Batteries Probed Using X-ray Photoelectron Spectroscopy
Batteries at work: towards operando photoelectron spectroscopy on lithium ion batteries
The influence of counter electrode on the capacity fading in LiNi0.33Mn0.33Co0.33O2based Li-ion b... more The influence of counter electrode on the capacity fading in LiNi0.33Mn0.33Co0.33O2based Li-ion battery cells. In: Nynäshamn N.B. When citing this work, cite the original published paper.
Recent progress in high pressure analyser and experimental method development applied to liquid/solid interface studies
Recent progress in high pressure analyser and experimental method development applied to liquid/s... more Recent progress in high pressure analyser and experimental method development applied to liquid/solid interface studies
The polymer electrolyte SEI-layer: a comparative XPS study of the surface chemistry in solid-state Li-batteries
The polymer electrolyte SEI-layer: a comparative XPS study of the surface chemistry in solid-stat... more The polymer electrolyte SEI-layer: a comparative XPS study of the surface chemistry in solid-state Li-batteries
A novel HPXPS experimental method for characterization of the interface between a solid electrode and electrolyte demonstrated with a Li-ion battery system
With an increasing demand for renewable energy sources, research efforts on different solar cell ... more With an increasing demand for renewable energy sources, research efforts on different solar cell technologies are increasing rapidly. The dye-sensitized solar cell (DSC) is one such technology, taking advantage of light absorption in dye molecules. The liquid based DSC contains several interesting and important interfaces, crucial for the understanding and development of the solar cell performance. Examples of such interfaces include dye-semiconductor, electrode-electrolyte and solute-solvent interfaces. Ultimately, complete interfaces with all these components included are of particular interest. One major challenge is to understand the key functions of these systems at an atomic level and one way to achieve this is to use an element specific and surface sensitive tool, such as photoelectron spectroscopy (PES). This thesis describes the use and development of PES for studying interfaces in the DSC.The materials part of the thesis focuses on interfaces in DSCs studied with PES and the methodology development parts focus on methods to use PES for investigations of solvated heterogeneous interfaces of interest for photoelectrochemical systems such as the DSC. More specifically, beginning with standard vacuum techniques, dye molecules bound to a semiconductor surface have been studied in terms of energy level alignment, surface coverage and binding configuration. To increase the understanding of solvation phenomena present in the liquid DSC, liquid jet experiments have been performed in close combination with theoretical quantum calculations. As a step towards an in-situ method to measure a complete, functioning (in operando) solar cell, methodology development and measurements performed with higher sample pressures are described using new high pressure X-ray photoelectron spectroscopy techniques (HPXPS).
ACS Applied Materials & Interfaces, Jan 12, 2021
Dual-ion batteries (DIBs) generally operate beyond 4.7 V vs Li + /Li 0 and rely on the intercalat... more Dual-ion batteries (DIBs) generally operate beyond 4.7 V vs Li + /Li 0 and rely on the intercalation of both cations and anions in graphite electrodes. Major challenges facing the development of DIBs are linked to electrolyte decomposition at the cathode−electrolyte interface (CEI), graphite exfoliation, and corrosion of Al current collectors. In this work, X-ray photoelectron spectroscopy (XPS) is employed to gain a broad understanding of the nature and dynamics of the CEI built on anionintercalated graphite cycled both in highly concentrated electrolytes (HCEs) of common lithium salts (LiPF 6 , LiFSI, and LiTFSI) in carbonate solvents and in a typical ionic liquid. Though Al metal current collectors were adequately stable in all HCEs, the Coulombic efficiency was substantially higher for HCEs based on LiFSI and LiTFSI salts. Specific capacities ranging from 80 to 100 mAh g −1 were achieved with a Coulombic efficiency above 90% over extended cycling, but cells with LiPF 6-based electrolytes were characterized by <70% Coulombic efficiency and specific capacities of merely ca. 60 mAh g −1. The poor performance in LiPF 6-containing electrolytes is indicative of the continual buildup of decomposition products at the interface due to oxidation, forming a thick interfacial layer rich in Li x PF y , PO x F y , Li x PO y F z , and organic carbonates as evidenced by XPS. In contrast, insights from XPS analyses suggested that anion intercalation and deintercalation processes in the range from 3 to 5.1 V give rise to scant or extremely thin surface layers on graphite electrodes cycled in LiFSI-and LiTFSI-containing HCEs, even allowing for probing anions intercalated in the near-surface bulk. In addition, ex situ Raman, SEM and TEM characterizations revealed the presence of a thick coating on graphite particles cycled in LiPF 6-based electrolytes regardless of salt concentration, while hardly any surface film was observed in the case of concentrated LiFSI and LiTFSI electrolytes.
On the Use of Ti3C2Tx MXene as a Negative Electrode Material for Lithium-Ion Batteries
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Papers by Kristina Edström