Nitrogen-Doped Graphitic Layers Deposited on Silicon Nanowires for Efficient Lithium-Ion Battery Anodes

Nitrogen (N)-doped graphitic layers were deposited as shells on pregrown silicon nanowires by chemical vapor deposition. Graphite-like and pyridine-like structures were selectively chosen for 3 and 10% N doping, respectively. Increasing the thickness of the undoped graphitic layers from 20 to 50 nm led to an increase in the charge capacity of the lithium ion battery from 800 to 1040 mA h/g after 45 cycles. Graphite-like 3% N-doping in the 50 nm-thick shell increases the charge capacity by 21% (i.e., to 1260 mA big), while pyridine-like 10% N-doping in the 20 nm-thick shell increases it by 36% (i.e., to 1090 rnA h/g). This suggests that both pyridine- and graphite-like structures can be effective for lithium intercalation. First principles calculations of the graphene sheets show that the large storage capacity of both N-doping structures comes from the formation of dangling bonds around the pyridine-like local motives upon lithium intercalation.