SiOC nanolayers directly-embedded in graphite as stable anode for high-rate lithium ion batteries

Abstract

Silicon oxycarbide (SiOC) has been an attractive anode material for lithium ion batteries (LIBs) owing to its high capacity and structure durability. However, due to its low electronic conductivity, SiOC usually owns poor rate performance and exhibits rapid capacity fading at high current density. For the first time, by combining commercialized graphite flakes with SiOC nanolayers, the pyrolysis product of thermoplastic polyphenylsesquisiloxane (PPSQ) sub-micron spheres, a stable SiOC-nanolayer-embedded graphite (SG) composite is prepared, delivering remarkable rate performances with long-term cyclability. The graphite substrate enhances the electron conduction, and ensures the structure integrity and the SiOC nanolayer serves as a major lithium storage unit with improved rate capability, benefiting from its decreased lithium diffusion pathways. The SG electrode exhibits a lithium diffusion coefficient of ~2.0 × 10−10 cm2 s−1 at a fully charged state, a record value of SiOC electrode to this date, and delivers a reversible capacity of ~500 mAh g−1 after 1000 cycles without mechanical failure. The work opens up the opportunity for two-dimensional SiOC electrodes to be efficiently-synthesized and utilized in high-rate and high capacity energy storage devices.