Laser Pyrolysed N-Doped SnOx Nanoparticles with Enhanced Conductivity and Stability As Anode in Li-Ion Batteries
Résumé
A novel one-step laser induced pyrolysis method was utilized for the synthesis of pristine SnO2 and p-type conduction N-doped SnOx nanoparticles. Most reports on doping of SnO2 focuses on subtition of Sn with other metallic, while replacement of O is uncommon due to difficulty in synthesis. In particular, laser pyrolysis made the synthesis of N-doped SnO2 possible by the high thermal gradient between the reaction zone and chamber wall to limit particle growth, as well as a brief contact of N atoms and SnO2 under extermely high temperature. The presence of N atoms during the rapid synthesis process substitutes the O2- anion and is hypothesized to improve conductivity of the material. The sample with 3% of N-doping exhibited optimum performance, with high initial and reversible capacities of 1899 and 1241 mAh g-1 respectively. Even when tested at a current density of 10 A g-1, SnO2+N3% can deliver a specific capacity as high as 522 mAh g-1. Moreover, a capacity of 1192 mAh g-1 can be retained at end of the 500th cycle. The cyclability and rate performance of the carbon free SnO2 nanoparticles are by far one of the best reported thus far. Interestingly, SnO2+N8% demonstrated the worst rate capability, which indicates that there could be an optimum doping concentration. The superior performance in SnO2+N3% could be credited to the presence of hole donating N atoms directly situated within the structure of SnO2 and the small particle sizes which permits rapid ion diffusion while preventing pulverization and agglomeration. Ex-situ TEM and XAS will be utilized to further understand correlation between structural properties with enhancement in performance.