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Assessing structure and stability of polymer/lithium-metal interfaces from first-principles calculations
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.ORCID-id: 0000-0003-0377-3669
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.ORCID-id: 0000-0002-9862-7375
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.ORCID-id: 0000-0002-8019-2801
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2019 (Engelska)Ingår i: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 7, nr 14, s. 8394-8404Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

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.

Ort, förlag, år, upplaga, sidor
ROYAL SOC CHEMISTRY , 2019. Vol. 7, nr 14, s. 8394-8404
Nationell ämneskategori
Materialkemi
Identifikatorer
URN: urn:nbn:se:uu:diva-382550DOI: 10.1039/c8ta12147hISI: 000464414200040OAI: oai:DiVA.org:uu-382550DiVA, id: diva2:1314902
Forskningsfinansiär
Energimyndigheten, 39036-1Vetenskapsrådet, 621-2014-5984EU, Europeiska forskningsrådet, 771777Carl Tryggers stiftelse för vetenskaplig forskning Tillgänglig från: 2019-05-10 Skapad: 2019-05-10 Senast uppdaterad: 2019-08-05Bibliografiskt granskad
Ingår i avhandling
1. Modelling the Molecular World of Electrolytes and Interfaces: Delving into Li-Metal Batteries
Öppna denna publikation i ny flik eller fönster >>Modelling the Molecular World of Electrolytes and Interfaces: Delving into Li-Metal Batteries
2019 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

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.

Ort, förlag, år, upplaga, sidor
Uppsala: Acta Universitatis Upsaliensis, 2019. s. 81
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1830
Nyckelord
Li-metal battery, solid polymer electrolyte, density functional theory, molecular dynamics simulation, solid electrolyte interphase
Nationell ämneskategori
Naturvetenskap
Identifikatorer
urn:nbn:se:uu:diva-390066 (URN)978-91-513-0703-9 (ISBN)
Disputation
2019-09-20, Polhemsalen, 10134, Ångstrom Laboratory, Lägerhyddsvägen 1, Uppsala, 09:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2019-08-30 Skapad: 2019-08-05 Senast uppdaterad: 2019-09-17

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