Confinement and Self-Supply of Carbon Sources by Micro-Containers Enable Efficient In Situ Growth of Carbon Nanotubes for Li-Ion Storage.

Confinement effects generated by micro/nanoscale physical spaces for chemical reactions may enable to effectively modulate nanostructures or create novel nanostructures by remarkably changing reaction kinetics and behaviors, which needs to be explored. Herein, a productive and up-scalable approach is proposed for in situ growth of nitrogen-doped carbon nanotubes (N/CNTs) by introducing commercial expanded graphites (EGs) as micro-containers for enhancement of reaction rates and reduction of energy costs. With the solid carbonaceous (polyvinylpyrrolidone, PVP) and catalytic (Fe-based or Co-based) precursors incubated in the micro-containers, the local sufficient self-supply of C/N sources ensures the in situ growth of high-quality N/CNTs with a high yield over 14% and a faster formation rate compared to a conventional open configuration. Growth behavior, morphology, and structure of products are conditioned by the dimension and structure of micro-containers, the ratio of source/catalyst precursors, and pyrolyzation temperature. The N/CNTs-based hierarchical architectures are demonstrated to have superior Li-ion storage performance as anode materials, say, a capacity of 1129.5 mAh g-1 at 0.05 A g-1 and a retention of 99.5% (95.0%) for 0.1 A g-1 (10 A g-1) after 100 (10 000) cycles. This strategy can be generalized for the preparation of other nanostructures.