Journal
JOURNAL OF POWER SOURCES
Volume 298, Issue -, Pages 369-378Publisher
ELSEVIER
DOI: 10.1016/j.jpowsour.2015.08.060
Keywords
Density functional theory; Li-ion batteries; Electrolyte additives; Solid-electrolyte interphase
Funding
- NSERC
- 3M Canada
- Canada Foundation for Innovation (CFI)
- Atlantic Canada Opportunities Agency (ACOA)
- Provinces of Newfoundland and Labrador, Nova Scotia
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Density functional theory (DFT) is used in conjunction with experimental results to propose decomposition pathways that describe the role and ultimate fate of the PES additive in Li-ion batteries. Oxidation of PES produces carbonyl sulfide gas and ethene at the positive electrode, both experimentally observed byproducts. However, the calculated standard potential for simple PES oxidation, E-ox(0) similar to 6.7 V vs. Li/Li+, is quite high, suggesting this pathway is unlikely. A reactive electrode model is presented, in which the positive electrode material is a reagent in the pseudo-combustion of PES (and other solvents). This spontaneous process produces carbonyl sulfide, carbon dioxide, and a rock salt surface layer, all of which are experimentally observed. At the negative electrode, the reduction of PES occurs via two one-electron steps, where E-red,1(0) = 0.9 V and E-red,2(0) = 4.3 V. The reduced species, Li2PES, can react with hydrogen and methyl radicals to produce propene, methylpropene, propane and lithium sulfite. Nucleophilic Li2PES can also react with electrophilic PES, ethylene carbonate, or ethyl methyl carbonate. Eighteen possible organic sulphate 'building blocks' for the solid-electrolyte interphase (SEI) are presented. X-ray photoelectron spectroscopy (XPS) measurements demonstrate that PES reduction indeed results in both lithium sulfite and organic sulphate SEI components. (C) 2015 Elsevier B.V. All rights reserved.
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