Electrochemical stability of ether based salt-in-polymer based electrolytes: Computational investigation of the effect of substitution and the type of salt

• Published in: Journal of power sources Vol. 393; pp. 204 - 210
• Main Authors: Pandian, S., Adiga, S.P., Tagade, P., Hariharan, K.S., Mayya, K.S., Lee, Y.-G.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 31-07-2018
• Subjects: Density functional theory; Electrochemical stability; Poly-(ethylene oxide); Polymer electrolytes; Redox potentials; Density functional theory; Polymer electrolytes; Poly-(ethylene oxide); Electrochemical stability; Redox potentials
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2018.04.079

The electrochemical stability window (EW) of polyether based salt-in-polymer electrolytes was investigated using density functional theory (DFT) calculations. The electrolyte systems investigated consisted of polyethylene oxide (PEO) in either lithium-bis(trifluoromethanesulfonyl)imide (LiTFSI) or lithium-hexafluorophosphate (LiPF6) salt and the EW was determined by performing calculations of reduction and oxidation potentials of isolated ethylene oxide (EO) oligomer and the respective salt species in a continuum solvent. The simulations suggest that the cathodic limit of the polymer-salt system is defined by the reduction potential of the salt anion and that both salt anions considered are unstable against Li anode. The anodic limit is defined by EO and it is stable against most commercial cathodes. Including explicit salt molecules in the calculations shows that the predicted EW is changed by ∼0.4 V. The calculations further reveal that the EW is dependent on the type of the salt molecule. Perfluoropolyether, a perfluorinated analog of PEO that has lower reduction potential and higher oxidation potential in isolation as compared to PEO, improved both oxidation and reduction stability of the polymer-salt system. Substitution of other functional groups to PEO improved the electrochemical stability to potentially accommodate higher voltage window requirements.
•Electrochemical windows of salt-in-polymer electrolytes are investigated.•Explicit inclusion of salt molecules in the electrochemical window calculations is important.•Cathodic limit of the electrolyte is defined by reduction potential of the salt anion.•Perfluoropolyether system shows better electrochemical stability than polyethylene oxide.