Suitable thickness of carbon coating layers for silicon anode

Abstract

Silicon (Si) is capable of delivering a high theoretical specific capacity as anode in Li ion batteries (LIBs), but suffers from remarkable volume expansion, poor electrical conductivity and unstable solid electrolyte interface (SEI) film. Carbon coating is a facile and effective method to improve the electrochemical stability of Si anode. However, the electrode behavior performance of Si@C anode will be affected by the different thickness of carbon coating layer. Here, core-shell nanostructured Si@C materials with various thickness of carbon coating (around 2–30 layers) are prepared via the chemical vapor deposition with different deposition times. Especially, the Si@C composite with 2–3 carbon coating layers exhibits an outstanding electrical conductivity and strong mechanical strength, which is in favor of buffering the dramatic volume expansion of Si nanoparticles during the repeated lithiation/delithiation processes. As the anode material, the Si@C electrode exhibits a high capacity (3019 mA h g−1 at 0.2 A g−1), excellent rate capability (1647 mA h g−1 at 5 A g−1) and long-term cycling stability. Moreover, the excellent durability is also delivered by the full pouch-cell fabricated with Si@C anode and Ni0.6Co0.2Mn0.2O2 cathode. The huge volume expansion and unstable SEI film can be effectively alleviated by the suitable carbon coating layers.