NMR studies of ion mobility and association in polyether‐based polymer electrolytes

Abstract

The results of several investigations of polyether‐based polymer electrolytes by nuclear magnetic resonance (NMR) spectroscopy conducted in the author's laboratory and by other groups are reviewed. For both 7Li and 23Na NMR, the onset of motional line‐narrowing occurs at about the glass transition temperature, illustrating the importance of polymer segmental motion to ion transport. Examples of the ability of NMR to probe cationanion interactions are discussed. These include chemical shift variations corresponding to different Li+ environments and nuclear quadrupole coupling and relaxation behavior as a probe of Na+ environment.

Dynamics of Li ions in an intercalated polymer electrolyte: A 7Li nuclear magnetic resonance study

“…[1][2][3][4][5][6] Nuclear magnetic resonance ͑NMR͒ studies have figured prominently in investigations of both the molecular structure and dynamics of the alkali ion in solid polymer electrolytes ͑SPEs͒, especially since ion mobilities are significant only in the amorphous phase above the glass transition temperature. It was early NMR studies on the onset of 7 Li and 23 Na NMR motional narrowing above the glass transition that highlighted the importance of polymer segmental motion to ion transport. 7 The relative contribution of cations and anions to the measured conductivity, too, was established by NMR measurements.…”

“…It was early NMR studies on the onset of 7 Li and 23 Na NMR motional narrowing above the glass transition that highlighted the importance of polymer segmental motion to ion transport. 7 The relative contribution of cations and anions to the measured conductivity, too, was established by NMR measurements. 8 These measurements indicated that anions were mobile, in some cases more than the cation.…”

“…Pulse field gradient measurements of diffusion of ions in the LiCF 3 SO 3 /PEO SPE, too, arrived at a similar conclusion. 9 Dynamical information from the temperature variation of 7 Li and 23 Na linewidths have been reported. [10][11][12] in SPEs.…”

“…For LiCF 3 SO 3 /polypropylene glycol ͑PPG͒ complexes the results indicate liquidlike behavior of the Li ions with the motion describable by a single-exponential correlation function. The spin-lattice relaxation mechanism was shown to be dominated by quadrupolar interactions between 7 Li nuclear moments and the electric field gradient ͑efg͒ due to the polymer lattice. Line shapes, however, were dominated by both dipolar and quadrupolar interactions.…”

“…The observation was interpreted as indicating a crossover between two distinct dynamical regimes: a regime above T c where there is a coupling of ionic motion to the polymer segmental motion and a regime below T c where decoupling occurs. The dynamics in the composite polymer electrolytes, PEO intercalated in montmorillonite and Li-fluorohectorite, has been probed by 7 Li and 2 H NMR. [13][14][15] Spin-lattice relaxation rate studies indicated that the fluctuating fields responsible for relaxation were the same for both the cation and polymer since the motional parameters, activation energies, and residence times were very similar.…”