Synthesis of 1,1-Diisopropyl- or -Diphenyl -2,5-dibromo- or -bis(trimethylsilyl)-3,4-diphenyl-siloles and the Electrochemical Properties as Anode Materials for Lithium-Ion Battery

Abstract

Intramolecular cyclization of 1,1-diisopropyl- or diphenyl-bis(phenylethynyl)-silanes (2a and 2b) followed by bromination or trimethylsilylation were carried out to yield 1,1-diisopropyl- or -diphenyl-3,4-diphenyl-2,5-dibromo-siloles (3a and 3b) and 1,1-diisoproyl- or -diphenyl-3,4-diphenyl-2,5-bis(trimethylsilyl)-siloles (4a and 4b), respectively. The structures of 3a,b and 4a,b were confirmed using 1H, 13C, and 29Si NMR as well as FTIR spectroscopy. The absorption bands of the siloles 3a,b and 4a,b in THF were measured at 303–325 nm with the molar absorptivities of 1.85 × 103 ~ 2.18 × 103 cm−1·M−1. The excitation bands were measured at 347–376 nm and the emission peaks were measured at 409–445 nm. Cyclic voltammograms of 3a and 3b indicated oxidation peaks at 0.90 and 0.80 V and reduction peaks at −1.20 and −1.20 V, respectively. The cyclic voltammograms of 4a and 4b indicated two oxidation peaks between −0.05 and −0.95 V and two reduction peaks between −0.10 and −0.93 V, respectively. Compound 4a exhibits a better long cycle performance by almost 1000 cycles as compared that of 3a and 4b. The rate performance test of the anodes Li-3a and Li-4a exhibited better performance properties at various C rate than Li-4b. According to discharge–charge curves, 4a shows one plateau at approximately 0.58 V of the first discharge curve and the initial discharge specific capacity of 972 mAh/g. The electrochemical impedance spectroscopy of 4a indicates low charge transfer resistance, good conductivity of the electrolyte, and fast chemical adsorption/desorption rate of electrolyte ions on electrode surface, due to the electronic structure of 4a. © 2020 Korean Chemical Society, Seoul & Wiley-VCH GmbH