New boron compounds as additives for lithium polymer electrolytes

• Published in: Electrochimica acta Vol. 53; no. 4; pp. 1481 - 1489
• Main Authors: Zygadło-Monikowska, E., Florjańczyk, Z., Tomaszewska, A., Pawlicka, M., Langwald, N., Kovarsky, R., Mazor, H., Golodnitsky, D., Peled, E.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Oxford Elsevier Ltd 31-12-2007; Elsevier
• Subjects: Boron derivatives; Chemistry; Electrochemistry; Exact sciences and technology; General and physical chemistry; Ionic conductivity; Lewis acid properties; Lithium polymer electrolytes; Lithium transference number; Properties of electrolytes: conductivity; Lithium transference number; Boron derivatives; Lewis acid properties; Lithium polymer electrolytes; Ionic conductivity; Boron 11; Nyquist diagram; Fluorine 19; Temperature effect; Polymer solid electrolyte; NMR spectrometry; Oligomer; Grain boundary; Ethylene oxide polymer; Hydrogen 1; Transport process; Lewis acid; Differential scanning calorimetry; Electrical properties; Operating conditions; Lithium Compounds; Boron Organic compounds; Thermal analysis; Transport number; Electrochemical impedance spectroscopy
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2007.02.046

A new class of difluoroalkoxyborane compounds ([R
n
OBF
2]
2) containing oligooxyethylene groups of various molecular weight in the form of a methyl monoether (R
n
=
CH
3(OCH
2CH
2)
n
,
n
=
1, 2, 3 and 7) has been obtained in the reaction of BF
3 etherate with appropriate glycols.
1H,
11B and
19F NMR spectral analysis of the derivatives obtained was carried out and the properties as Lewis acids of these derivatives have been compared with that of corresponding trialkoxyboranes and boron trifluoride in reaction with pyridine. The strength of the interaction of [R
2OBF
2]
2 with the differing in “hardness” anions of various lithium salts has been analyzed on the basis of NMR spectra. The [R
n
OBF
2]
2 obtained were used as additives for polymer electrolytes containing PEO as polymer matrix and various lithium salts at an equimolar ratio of the boron compound to salt. The highest ionic conductivities, in the order 10
−5 to 10
−4
S
cm
−1 at 20–70
°C, were achieved for systems containing LiI and LiN(CF
3SO
2)
2. The lithium transference number (
t
+) values, determined by the electrochemical method by steady-state technique for LiF and LiCF
3SO
3 are in the 0.6–0.8 range.