| 1. |
- Ebadi, Mahsa, et al.
(författare)
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Assessing structure and stability of polymer/lithium-metal interfaces from first-principles calculations
- 2019
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 7:14, s. 8394-8404
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Tidskriftsartikel (refereegranskat)abstract
- Solid polymer electrolytes (SPEs) are promising candidates for Li metal battery applications, but the interface between these two categories of materials has so far been studied only to a limited degree. A better understanding of interfacial phenomena, primarily polymer degradation, is essential for improving battery performance. The aim of this study is to get insights into atomistic surface interaction and the early stages of solid electrolyte interphase formation between ionically conductive SPE host polymers and the Li metal electrode. A range of SPE candidates are studied, representative of major host material classes: polyethers, polyalcohols, polyesters, polycarbonates, polyamines and polynitriles. Density functional theory (DFT) calculations are carried out to study the stability and the electronic structure of such polymer/Li interfaces. The adsorption energies indicated a stronger adhesion to Li metal of polymers with ester/carbonate and nitrile functional groups. Together with a higher charge redistribution, a higher reactivity of these polymers is predicted as compared to the other electrolyte hosts. Products such as alkoxides and CO are obtained from the degradation of ester- and carbonate-based polymers by AIMD simulations, in agreement with experimental studies. Analogous to low-molecular-weight organic carbonates, decomposition pathways through C-carbonyl-O-ethereal and C-ethereal-O-ethereal bond cleavage can be assumed, with carbonate-containing fragments being thermodynamically favorable.
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| 2. |
- Ebadi, Mahsa, et al.
(författare)
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Density Functional Theory Modeling the Interfacial Chemistry of the LiNO3 Additive for Lithium-Sulfur Batteries by Means of Simulated Photoelectron Spectroscopy
- 2017
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 121:42, s. 23324-23332
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Tidskriftsartikel (refereegranskat)abstract
- Lithium-sulfur (Li-S) batteries are considered candidates for next-generation energy storage systems due to their high theoretical specific energy. There exist, however, some shortcomings of these batteries, not least the solubility of intermediate polysulfides into the electrolyte generating a so-called "redox shuttle", which gives rise to self-discharge. LiNO3 is therefore frequently used as an electrolyte additive to help suppress this mechanism, but the exact nature of the LiNO3 functionality is still unclear. Here, density functional theory calculations are used to investigate the electronic structure of LiNO3 and a number of likely species (N-2, N2O, LiNO2, Li3N, and Li2N2O2) resulting from the reduction of this additive on the surface of Li metal anode. The N is X-ray photoelectron spectroscopy core level binding energies of these molecules on the surface are calculated in order to compare the results with experimentally reported values. The core level shifts (CLS) of the binding energies are studied to identify possible factors responsible for the position of the peaks. Moreover, solid phases of (cubic) c-Li3N and (hexagonal) alpha-Li3N on the surface of Li metal are considered. The N is binding energies for the bulk phases of Li3N and at the Li3N/Li interfaces display higher values as compared to the Li3N molecule, indicating a clear correlation between the coordination number and the CLS of the solid phases of Li3N.
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| 3. |
- Ebadi, Mahsa, et al.
(författare)
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Electrolyte decomposition on Li-metal surfaces from first-principles theory
- 2016
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 145:20, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- Animportant feature in Li batteries is the formation of a solid electrolyte interphase (SEI) on the surface of the anode. This film can have a profound effect on the stability and the performance of the device. In this work, we have employed density functional theory combined with implicit solvation models to study the inner layer of SEI formation from the reduction of common organic carbonate electrolyte solvents (ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate) on a Li metal anode surface. Their stability and electronic structure on the Li surface have been investigated. It is found that the CO producing route is energetically more favorable for ethylene and propylene carbonate decomposition. For the two linear solvents, dimethyl and diethyl carbonates, no significant differences are observed between the two considered reduction pathways. Bader charge analyses indicate that 2 e(-) reductions take place in the decomposition of all studied solvents. The density of states calculations demonstrate correlations between the degrees of hybridization between the oxygen of adsorbed solvents and the upper Li atoms on the surface with the trend of the solvent adsorption energies.
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| 4. |
- Ebadi, Mahsa, et al.
(författare)
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Insights into the Li-Metal/Organic Carbonate Interfacial Chemistry by Combined First-Principles Theory and X-ray Photoelectron Spectroscopy
- 2019
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 123:1, s. 347-355
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Tidskriftsartikel (refereegranskat)abstract
- X-ray photoelectron spectroscopy (XPS) is a widely used technique to study surfaces and interfaces. In complex chemical systems, however, interpretation of the XPS results and peak assignments is not straightforward. This is not least true for Li-batteries, where XPS yet remains a standard technique for interface characterization. In this work, a combined density functional theory (DFT) and experimental XPS study is carried out to obtain the C 1s and O 1s core-level binding energies of organic carbonate molecules on the surface of Li metal. Decomposition of organic carbonates is frequently encountered in electrochemical cells employing this electrode, contributing to the build up of a complex solid electrolyte interphase (SEI). The goal in this current study is to identify the XPS fingerprints of the formed compounds, degradation pathways, and thereby the early formation stages of the SEI. The contribution of partial atomic charges on the core-ionized atoms and the electrostatic potential due to the surrounding atoms on the core-level binding energies, which is decisive for interpretation of the XPS spectra, are addressed based on the DFT calculations. The results display strong correlations between these two terms and the binding energies, whereas electrostatic potential is found to be the dominating factor. The organic carbonate molecules, decomposed at the surface of the Li metal, are considered based on two different decomposition pathways. The trends of calculated binding energies for products from ethereal carbon-ethereal oxygen bond cleavage in the organic carbonates are better supported when compared to the experimental XPS results.
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| 5. |
- Ebadi, Mahsa
(författare)
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Modelling the Molecular World of Electrolytes and Interfaces : Delving into Li-Metal Batteries
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lithium metal batteries (LMBs) are potential candidates for powering portable electronic devices and for electromobility. However, utilizing the reactive Li metal electrode means tackling serious challenges in terms of safety risks. A better understanding of electrolytes and solid electrolyte interphase (SEI) formation are highly important in order to improve these issues.In this thesis, density functional theory (DFT) and molecular dynamics (MD) are used to explore novel electrolyte systems and the interfacial chemistry of electrolyte/Li metal surfaces. In the first part, the electronic structure and possible decompositions pathways of organic carbonates at the Li metal surface are investigated, which provide information about initial SEI formation. Computed X-ray photoelectron spectroscopy (XPS) for these interfacial compounds is used as a tool to find likely electrolyte decomposition pathways and are supported by direct comparison with the experimental results. The electronic structure and computed XPS spectra of electrolyte solvents and the LiNO3 additive on Li metal by DFT provide atomistic insights into the interphase layer.Solid polymer electrolytes (SPEs) are promising electrolytes to be used with the Li metal electrode. In the second part of the thesis, MD simulations of poly(ethylene oxide) (PEO) doped with LiTFSI salt/Li metal interface demonstrate the impact of the surface on the structure and dynamics of the electrolyte. A new interfacial potential model for MD simulations is also developed for the interactions at the SPE/metal interface, which can better capture this chemical interplay. Moreover, the approach to improve the ionic conductivity of SPEs by adding side-chains to the backbone of polymers is scrutinized through MD simulations of the poly(trimethylene carbonate) (PTMC) system. While providing polymer flexibility, a hindering effects of the side-chains on Li+ ion diffusions through reduced coordination site connectivity is observed.In the final part, different polymer hosts interacting with Li metal are explored, and rapid decomposition of polycarbonates and polyester on the surface is seen. The complexes of these polymers with LiTFSI and LiFSI showed significant changes in the computed electrochemical stability window and salt degradations. Lastly, Li2O was obtained by DFT calculations as a thermodynamically stable layer on the surface of the Li metal oxidized by PEO.The modelling studies performed in this thesis highlight the applicability of these techniques in order to probe the SEI and electrolyte properties in LMBs at the atomistic level.
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| 6. |
- Ebadi, Mahsa, et al.
(författare)
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Modelling the Polymer Electrolyte/Li-Metal Interface by Molecular Dynamics simulations
- 2017
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Ingår i: Electrochimica Acta. - : Pergamon-Elsevier. - 0013-4686 .- 1873-3859. ; 234, s. 43-51
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Tidskriftsartikel (refereegranskat)abstract
- Solid polymer electrolytes are considered promising candidates for application in Li-metal batteries due to their comparatively high mechanical strength, which can prevent dendrite formation. In this study, we have performed Molecular Dynamics simulations to investigate structural and dynamical properties of a common polymer electrolyte, poly(ethylene oxide) (PEO) doped with LiTFSI salt in the presence of a Li metal surface. Both a physical (solid wall) and a chemical (slab) model of the Li (100) surface have been applied, and the results are also compared with a model of the bulk electrolyte. The average coordination numbers for oxygen atoms around the Li ions are ca. 6 for all investigated systems. However, the calculated Radial Distribution Functions (RDFs) for Li+-(OPEO) and Li+-(OTFSI) show sharper peaks for the Li slab model, indicating a more well-defined coordination sphere for Li+ in this system. This is clearly a surface effect, since the RDF for Li+ in the interface region exhibits sharper peaks than in the bulk region of the same system. The simulations also display a high accumulation of TFSI anions and Li+ cations close to interface regions. This also leads to slower dynamics of the ionic transport in the systems, which have a Li-metal surface present, as seen from the calculated mean-square-displacement functions. The accumulation of ions close to the surface is thus likely to induce a polarization close to the electrode.
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| 7. |
- Ebadi, Mahsa, et al.
(författare)
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Restricted Ion Transport by Plasticizing Side Chains in Polycarbonate-Based Solid Electrolytes
- 2020
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 53:3, s. 764-774
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Tidskriftsartikel (refereegranskat)abstract
- Increasing the ionic conductivity has for decades been an overriding goal in the development of solid polymer electrolytes. According to fundamental theories on ion transport mechanisms in polymers, the ionic conductivity is strongly correlated to free volume and segmental mobility of the polymer for the conventional transport processes. Therefore, incorporating plasticizing side chains onto the main chain of the polymer host often appears as a clear-cut strategy to improve the ionic conductivity of the system through lowering of the glass transition temperature (T-g) This intended correlation between Tg and ionic conductivity is, however, not consistently observed in practice. The aim of this study is therefore to elucidate this interplay between segmental mobility and polymer structure in polymer electrolyte systems comprising plasticizing side chains. To this end, we utilize the synthetic versatility of the ion-conductive poly(trimethylene carbonate) (PTMC) platform. Two types of host polymers with side chains added to a PTMC backbone are employed, and the resulting electrolytes are investigated together with the side chain-free analogue both by experiment and with molecular dynamics (MD) simulations. The results show that while added side chains do indeed lead to a lower Tg, the total ionic conductivity is highest in the host matrix without side chains. It was seen in the MD simulations that while side chains promote ionic mobility associated with the polymer chain, the more efficient interchain hopping transport mechanism occurs with a higher probability in the system without side chains. This is connected to a significantly higher solvation site diversity for the Li+ ions in the side-chain-free system, providing better conduction paths. These results strongly indicate that the side chains in fact restrict the mobility of the Li+ ions in the polymer hosts.
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| 8. |
- Lourenco, Tuanan C., et al.
(författare)
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A molecular dynamics study of a fully zwitterionic copolymer/ionic liquid-based electrolyte : Li+ transport mechanisms and ionic interactions
- 2021
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Ingår i: Journal of Computational Chemistry. - : John Wiley & Sons. - 0192-8651 .- 1096-987X. ; 42:23, s. 1689-1703
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Tidskriftsartikel (refereegranskat)abstract
- The development of polymer electrolytes (PEs) is crucial for advancing safe, high-energy density batteries, such as lithium-metal and other beyond lithium-ion chemistries. However, reaching the optimum balance between mechanical stiffness and ionic conductivity is not a straightforward task. Zwitterionic (ZI) gel electrolytes comprising lithium salt and ionic liquid (IL) solutions within a fully ZI polymer network can, in this context, provide useful properties. Although such materials have shown compatibility with lithium metal in batteries, several fundamental structure-dynamic relationships regarding ionic transport and the Li+ coordination environment remain unclear. To better resolve such issues, molecular dynamics simulations were carried out for two IL-based electrolyte systems, N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([BMP][TFSI]) with 1 M LiTFSI salt and a ZI gel electrolyte containing the IL and a ZI copolymer: poly(2-methacryloyloxyethyl phosphorylcholine-co-sulfobetaine vinylimidazole), poly(MPC-co-SBVI). The addition of ZI polymer decreases the [TFSI](-)-[Li](+) interactions and increases the IL ion diffusivities, and consequently, the overall ZI gel ionic conductivity. The structural analyses showed a large preference for lithium-ion interactions with the polymer phosphonate groups, while the [TFSI](-) anions interact directly with the sulfonate group and the [BMP](+) cations only display secondary interactions with the polymer. In contrast to previous experimental data on the same system, the simulated transference numbers showed smaller [Li](+) contributions to the overall ionic conductivities, mainly due to negatively charged lithium aggregates and the strong lithium-ion interactions in the systems.
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| 9. |
- Lourenco, Tuanan C., et al.
(författare)
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Interfacial Structures in Ionic Liquid-Based Ternary Electrolytes for Lithium-Metal Batteries : A Molecular Dynamics Study
- 2020
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Ingår i: Journal of Physical Chemistry B. - : AMER CHEMICAL SOC. - 1520-6106 .- 1520-5207. ; 124:43, s. 9648-9657
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Tidskriftsartikel (refereegranskat)abstract
- Lithium-metal batteries are promising candidates to fulfill the future performance requirements for energy storage applications. However, the tendency to form metallic dendrites and the undesirable side reactions between the electrolyte and the Li electrode lead to poor performance and safety issues in these batteries. Therefore, understanding the interfacial properties and the Li-metal surface/electrolyte interactions is crucial to resolve the remaining obstacles and make these devices feasible. Here, we report a computational study on the interface effects in ternary polymer electrolytes composed by poly(ethylene oxide) (PEO), lithium salts, and different ionic liquids (ILs) confined between two Li-metal slabs. Atomistic simulations are used to characterize the local environment of the Li+ ions and the transport properties in the bulk and at the interface regions. Aggregation of ions at the metal surface is seen in all investigated systems; the structure and composition are directly correlated to the IL components. The strong interactions between the electrolyte species and the Li-metal atoms result in the structuring of the electrolyte at the interface region, in which comparatively small and flat ions result in a well-defined region with extensive Li+ populations and high self-diffusion coefficients. In contrast, large ions such as [P222mom](+) increase the PEO density in the bulk due to large steric effects at the interface. Therefore, the choice of specific ILs in ternary polymer electrolytes can tune the structure-dynamic properties at the Li-metal surface/electrolyte interface, controlling the SEI formation at the electrode surface, and thereby improve battery performance.
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| 10. |
- Marchiori, Cleber, et al.
(författare)
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Understanding the Electrochemical Stability Window of Polymer Electrolytes in Solid-State Batteries from Atomic-Scale Modeling : The Role of Li-Ion Salts
- 2020
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 32:17, s. 7237-7246
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Tidskriftsartikel (refereegranskat)abstract
- After decades of development in Li-ion batteries, solid polymer electrolytes (SPEs) are currently experiencing a renaissance as a promising category of materials to be used in all-solid-state batteries. However, a fundamental understanding of their electrochemical properties in the battery environment is still lacking, which in turn limits the implementation of this prospective solution. With the aim of bridging this knowledge gap, we have assessed, through first-principles thermodynamics calculations based on atomic-scale modeling, the electrochemistry of a range of relevant polymer electrolyte hosts in their pristine form and also when doped with commonly used Li-ion salts. A significant change of the electrochemical stability window upon formation of the polymer/salt complexes was found. The mechanisms of the reduction and oxidation reactions are unveiled and correlated to the electronic structures and molecular structural relaxations. In the reduction process, the salt anions control the potentials due to bond cleavage that stabilize the reduced state. In the oxidation process, the mechanism is different with the charge being stabilized either on the polymer or on the salt anion depending on the complex formed. This assessment of the electrochemical stability of the polymer/salt complexes could serve as a guide for electrolyte design in SPE-based all-solid-state batteries.
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