Commercially available lithium batteries contain inorganic salts dissolved in a polymer matrix.  These polymer electrolyte solutions serve as electronic insulators between the anode and cathode, but must be good ionic conductors. Poly(ethylene oxide) is frequently used as the polymer matrix because it is chemically inert, able to dissolve a number of inorganic salts, and provides moderate ionic conductivity.  To engineer better polymer electrolytes, we have begun fundamental studies of structures, dynamics, and ionic conductivity in models of poly(ethylene oxide) and poly(ethyleneimine).

Jin-Kee Hyun and Haitao Dong studied amorphous tetraglyme (CH₃O(CH₂CH₂O)₄CH₃), a model for amorphous PEO, and tetraglyme:LiCF₃SO₃ (lithium triflate) with an ether oxygen:Li⁺ ratio of 10:1 by molecular dynamics (MD) simulations at 300K and 400K. Conformational and structural analyses of Li⁺ interactions with tetraglyme and triflate ion oxygens are consistent with decreased Li⁺ coordination by tetraglyme and increased ionic aggregation at the higher temperature. Dihedral angle population density distributions for tetraglyme chains show that the trans conformation is favored for C-O bonds while the more compact gauche conformation is favored for C-C bonds and is enforced by coordination of adjacent oxygens to Li⁺. Calculated populations of tetraglyme conformational triads indicate that the most stable conformation around Li⁺-tetraglyme oxygens is tgt.

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CC torsional angles of tetraglyme favor a gauche conformation (near 60 or 300 degrees) for tetraglyme and revert exclusively to the gauche conformation upon coordinating Li cation:
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Mean-square radius of gyration and end-to-end distance of pure tetraglyme chains decrease with increasing temperature and upon Li⁺-tetraglyme oxygen complexation, but increase at 400K vs. 300K for tetraglyme:LiCF₃SO₃. The calculated Li⁺ coordination number remains the same with increasing temperature, but triflate ions contribute more oxygens to Li⁺ coordination at 400K (4.8) than at 300K (4.6).  The increase in populations of [Li₂CF₃SO₃]⁺ and [Li₃CF₃SO₃]²⁺ from both MD simulations and IR data implies that Li⁺- CF₃SO₃^- association is increased at higher temperature. Monodentate and bidentate coordination geometries of Li⁺ by CF₃SO₃^- were found. The increase in monodentate coordination of Li⁺ by CF₃SO₃^- at the higher temperature frees Li⁺ to bridge between different CF₃SO₃^- ions.
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Li cation by triflate ions is monodentate or bidentate.   Monodentate coordination increases at 400K:

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York, Shawna; Boesch, Scott E.; Wheeler, R.A.; Frech, Roger; “Vibrational Assignments of High Molecular Weight Linear Polyethylenimine (LPEI) Based on Monomeric and Tetrameric Model Compounds”; Macromolecules 2003, 36(19), 7348-7351.

Boesch, Scott E.; York, Shawna; Frech, Roger; Wheeler, R.A.; "Effect of Lithium Triflate and Lithium Bromide on the Vibrational Frequencies of Dimethylethylenediamine (DMEDA)"; J. Chem. Soc., Phys. Chem. Commun. 2002; 5, 99-111.

Dong, Haitao; Hyun, Jin-Kee; Rhodes, Christopher P.; Frech, Roger; Wheeler, R.A.; "Molecular Dynamics Simulations and Vibrational Spectroscopic Studies of Local Structure in Tetraglyme:Sodium Triflate (CH₃O(CH₂CH₂O)₄CH₃:NaCF₃SO₃) Solutions"; J. Phys. Chem. B 2002, 106, 4878-4885.

Dong, Haitao; Hyun, Jin-Kee; Durham, Curtis; Wheeler, R.A.; "Molecular Dynamics Simulations and Structural Comparisons of Amorphous Poly(ethylene oxide) and Poly(ethylenimine) Models"; Polymer 2001, 42, 7809-7817.

Hyun, Jin-Kee; Dong, Haitao; Rhodes,Christopher P.; Frech, Roger; Wheeler, R.A.; "Molecular Dynamics Simulations and Spectroscopic Studies of Structure in Amorphous Tetraglyme (CH₃O(CH₂CH₂O)₄CH₃) and Tetraglyme:LiCF₃SO₃"; J. Phys. Chem. A 2001, 105, 3329-3337.

Boesch, Scott E.; York, Shawna; Frech, Roger; Wheeler, R. A.; "Experimental and Computational Investigation of the Structure and Vibrations of Dimethylethylenediamine, a Model for Poly(ethylenimine)"; J. Chem. Soc., Phys. Chem. Commun. 2001, 1 (electronic publication).

Huang, Weiwei; Wheeler, R.A.; Frech, Roger; "Vibrational Spectroscopic and Ab Initio Molecular Orbital Studies of the Normal and ¹³C-Labeled Trifluoromethanesulfonate Anion"; Spectrochimica Acta, Part A 1994, 50, 985-996.

Huang, Weiwei; Frech, Roger; Wheeler, R.A.; "Molecular Structures and Normal Vibrations of CF₃SO₃^- and its Lithium Ion Pairs and Aggregates"; J. Phys. Chem. 1994, 98, 100-110.