Ultra-thick porous films of graphene-encapsulated silicon nanoparticles as flexible anodes for lithium ion batteries

Silicon is a highly promising anode material of lithium ion batteries (LIBs) for its low insertion voltage and high reversible capacity. A flexible, honeycomb-like film of reduced graphene (RGO)/Si nanoparticles (NPs) composite with a thickness as thick as 25 μm is synthesized by a facile vacuum filter assembly process. The Si NPs are enwrapped into the RGO sheets with an areal density of 0.65 mg cm−2. The ultra-thick composite film is directly employed as an anode for LIBs without using any binder and conductive additive. The flexible RGO sheet coat enables the electrode to maintain the structural integrity and provide continuous conductive paths for Si NPs. The electrode exhibits a high capacity of 2370 mA h g−1 over 50 cycles at a current of 210 mA g−1 and a capacity higher than 1000 mA h g−1 at a current density of 4200 mA g−1 after 500 cycles. Especially, the electrode exhibits excellent rate capability, indicating that it may be applied to the high-power LIBs as a flexible, high areal capacity, binder-free and free-standing anode.