Reassembled graphene-platelets encapsulated silicon nanoparticles for Li-ion battery anodes.

Among lithium alloy metals, silicon is an attractive candidate to replace commercial graphite anode because silicon possesses about ten times higher theoretical energy density than graphite. However, electrically nonconducting silicon undergoes a large volume changes during lithiation/delithiation reactions, which causes fast loss of storage capacity upon cycling due to electrode pulverization. To alleviate these problems, electrodes comprising Si nanoparticles (20 nm) and graphene platelets, denoted as SiGP-1 (Si = 35.5 wt%) and SiGP-2 (Si = 57.6 wt%), have been prepared with low cost materials and using easily scalable solution-dispersion methods. X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) analyses indicated that Si nanoparticles were highly dispersed and encapsulated between graphene sheets that stacked into platelets in which portions of graphite phases were reconstituted. From the galvanostatic cycling test, SiGP-1 exhibited a reversible lithiation capacity of approximately 802 mAh/g with excellent capacity retention up to 30 cycles at 100 mA/g. Further cycling with a step-increase of current density (100-1,000 mA/g) up to 120 cycles revealed that it has an appreciable power capability as well, showing 520 mAh/g at 1,000 mA/g with capacity loss of 0.2-0.3% per cycle. The improved electrochemical performance is attributed to the robust electrical integrity provided by flexible graphene sheets that encapsulated dispersed Si nanopraticles and stacked into platelets with portions of reconstituted graphite phases in their structure.