シリコーン含有ポリイミドから調製したSi/C/Oコンポジットのリチウムイオン挿入脱離特性

Abstract

Si/C/O composites were formed by carbonization of Kapton type polyimide films containing 0–10 at% Si. About 24 mass% of Si was present in the composite derived from the polyimide containing 7 at% Si at 1350°C and, by 29Si MAS NMR, they were mainly Si(O)4 type components around −110 ppm with unidentifiable components in a range of −100 to −20 ppm. This composite showed the best performance of Li+ ion insertion/extraction: the coulomb efficiency was nearly 100% except for the 1st cycle and the extraction capacities were 648 mA h g−1 after 10 cycles at 50 mA g−1 and 393 mA h g−1 after 50 cycles at 500 mA g−1, and the latter was increased to ca. 470 mA h g−1 by preliminary cycles at low current densities. After 10 cycles at 50 mA g−1 the components around −110 ppm almost disappeared from the NMR spectrum and a broad and noisy band was observed in a range of −100 to −50 ppm. Since sub-micrometer fused silica particles did not react as the composites performed, the components around −110 ppm are not necessarily silica. The mechanism of reversible insertion/extraction of Li+ ion for the composites was not completely clarified, but the results by cyclic voltammetry and MAS NMR left room for doubt about an alloying/dealloying mechanism between Si and Li.