Synthesis and anode properties of co-oligomers containing 3,4-diphenyl-1,1-disubstituted-2,5-silolene and ethynylene for lithium-ion secondary batteries

The Stille coupling of co-oligomerizations of 2,5-dibromo-3,4-diphenyl-1,1-disubstituted-siloles (R = i-Pr, n-Hex, Ph; Ia–c) with bis(tributylstannyl)acetylene (II) in the presence of PdCl₂(PPh₃)₂ as catalyst and toluene as solvent yielded oligo[(3,4-diphenyl-1,1-disubstitued-2,5-silolene)-alt-(ethynylene)]s (R = i-Pr, n-Hex, Ph; IIIa–c) as black solids. Co-oligomeric materials IIIa–c were characterized with several spectroscopic methods: nuclear magnetic resonance, Fourier-transform infrared, and ultraviolet–visible spectroscopies. Moreover, the thermal stability and anode properties of the fabricated lithium-ion secondary battery were analyzed. Compounds IIIa–c were stable up to 180 °C without weight loss under nitrogen. The coin cells fabricated using IIIa–c as active anode materials exhibited a reversible process after the 2nd cycle in their cyclic voltammograms. The co-oligomer IIIa showed good anodic properties for lithium-ion secondary battery. With an increase in the current density from 0.1 to 0.2, 0.5, 1, 2, 5, and 10 C, the capacity decreased from 2264 to 451, 361, 318, 292, 248, and 214 mAh g⁻¹, respectively. With a decrease in the current density to 1 C, the capacity returned to 287 mAh g⁻¹ at the 33rd cycle and 309 mAh g⁻¹ at the 38th cycle, indicating a lower reduction rate and superior capacity recovery rate of 97% with respect to the initial value of 318 mAh g⁻¹. The long-cycle performance of IIIa exhibited good anodic property of charge capacities at 1 C; 1602, 494, 391, 346, 364, 435, 528, 625, and 725 mAh g⁻¹ at the 1st, 2nd, 3rd, 50th, 100th, 200th, 300th, 400th, and 500th cycles, respectively. The anodic property of the cell fabricated using the co-oligomer IIIa-Li was generally superior to those of IIIb and IIIc. Therefore, IIIa-Li has the feasibility to be used in lithium-ion secondary batteries.

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