Carbon-rich SiOC anodes for lithium-ion batteries: Part II. Role of thermal cross-linking

This paper presents the study of lithium insertion into carbon-rich polymer-derived silicon oxycarbide (SiOC) ceramics, synthesized by a thermal treatment of commercially available polysiloxane at 400 degrees C, followed by pyrolysis at 1100 and 1300 degrees C. The investigated samples demonstrate a similar chemical composition and provide a high amount of free carbon as separate phase within their microstructure. XRD- and Raman-measurements led us to identify the free carbon phase as a mixture of disordered carbon, nano-crystalline graphite and graphene sheets. This advantageous composition offers a large variety of Li-Ion storage sites, providing high lithiation capacities and reliable cycling behavior. In particular the 1100 degrees C sample demonstrates a stable, reversible capacity of 521 mAhg(-1) at a cycling current of 37 mAg(-1), which is significantly higher than the theoretical capacity of graphite. The inferior performance of the 1300 degrees C sample with 367 mAhg(-1) at 37 mAg(-1) is attributed to a changed microstructure. namely an increased carbon organization within the free carbon phase and SiC crystallization at this temperature. In both cases, the thermal cross-linking leads to much better electrochemical properties than observed for directly pyrolyzed samples. (C) 2012 Elsevier B.V. All rights reserved.