NMR and Raman studies of a novel fast-ion-conducting polymer-in-salt electrolyte based on LiCF3SO3 and PAN

• We report spectroscopic results from investigations of a novel solid polymeric fast-ion-conductor based on poly(acrylonitrile), (PAN, of repeat unit [CH2CH(CN)]n), and the salt LiCF3SO3. From NMR studies of the temperature and concentration dependencies of 7Li- and 1H-NMR linewidths, we conclude that significant ionic motion occurs at temperatures close to the glass transition temperature of these polymer-in-salt electrolytes, in accordance with a recent report on the ionic conductivity. In the dilute salt-in-polymer regime, however, ionic motion appears mainly to be confined to local salt-rich domains, as determined from the dramatic composition dependence of the ionic conductivity. FT-Raman spectroscopy is used to directly probe the local chemical anionic environment, as well as the Li+-PAN interaction. The characteristic δs(CF3) mode of the CF3SO3- anion at ∼ 750-780 cm-1 shows that the ionic substructure is highly complex. Notably, no spectroscopic evidence of free anions is found even at relatively salt-depleted compositions (e.g. N:Li ∼ 60-10:1). A strong Li+-PAN interaction is manifested as a pronounced shift of the characteristic polymer C=N stretching mode, found at ∼2244 cm-1 in pure PAN, to ∼ 2275 cm-1 for Li+-coordinated C=N moieties. Our proton-NMR data suggest that upon complexation of PAN with LiCF3SO3, the glass transition occurs at progressively lower temperatures. 

Subject headings

NATURVETENSKAP  -- Fysik -- Den kondenserade materiens fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Condensed Matter Physics (hsv//eng)

Keyword

polymer-in-salt electrolyte

lithium and proton NMR

FT-Raman spectroscopy

poly(acrylonitrile)

LiCF3SO3

TRANSPORT-PROPERTIES

SOLID ELECTROLYTES

POLYACRYLONITRILE

LICLO4

MODEL

Publication and Content Type

ref (subject category)

art (subject category)