Silicon Anode Confined in Carbon Nano-Spaces for Efficient Lithium Storage

Abstract

Commercial Li-ion batteries employ graphite and other carbonaceous materials as anodes, which has excellent stability and low cost, but has a theoretical capacity limit at 372 mAh/g by forming a fully intercalated LiC6 compound. For anode materials, silicon is also known to have the highest theoretical specific capacity (4200 mAh/g), and is considered to be the active materials for the next generation lithium ion batteries. However it has the large volume change (>400%) during lithiation and delithiation causes pulverization, resulting in capacity loss in a high number of cycles. Here, this study reports the use of engineering nanocarbon film with confined silicon nanoparticles as an anode material for lithium-ion batteries. The unique “concave” graphitic nanostructure, prepared in porous templates with morphology of interconnected arrays, makes nanocarbon electrodes a good lithium-ion intercalation medium and, more importantly, robust nanocontainers to effectively confine high-capacity silicon nanoparticles for lithium-ion storage. Our unique anode, which is based the concave graphitic film and silicon particles confined in its nanospace, have three notable features for the use as the effective electrode material in a lithium-ion battery. First, Li ion diffusion into the interior of the nanocarbons through the opened structures can shorten the diffusion length of the redox couple and provide rapid charge transport. Second, the exposed silicon active materials in the direction of Li ion diffusion increase the accessibility of the electrode interior to the electrolyte, which ensures a high charge/discharge capacity. Finally, the nanoconfined silicon system inside the carbon nanospace improves the cycle life by preventing volume expansion during electrochemical Li insertion/extraction. As a result, high performance Li storage with a mass-specific capacity of 2500 mAh/g was obtained at 0.5A/g. The discharge capacity was retained constantly during 200 cycles with coulombic efficiency of above 98%. These results suggest that the novel structure can lead to high storage capacities and rate capability as anode material in future high performance Li-ion batteries.