Controllable engineering magnetite nanoparticles dispersed in a hierarchical amylose derived carbon and reduced graphene oxide framework for lithium-ion storage.

A straightforward and eco-friendly method is demonstrated to engineer magnetite (Fe3O4) nanoparticles well dispersed by an amorphous amylose-derived carbon (AMC) and reduced graphene oxide (RGO) framework. Naturally available amylose (AM) serves as both reducing agent for few-layered graphene oxide (GO) in the first mild redox coprecipitation system and precursor for small-sized pyrolytic AMC in the following thermal treatment. In particular, the presence of the AM molecules effectively limits the crystal growth kinetics for the akaganeite (FeOOH) in the intermediate FeOOH@AM/RGO sample, which contributes to the transformation to Fe3O4 nanoparticles with significantly controlled size in the final Fe3O4@AMC/RGO composite. As a result, both Fe3O4 nanoparticles and AMC domains are adjacently anchored on the larger sized RGO sheets, and a unique hierarchical structure has been engineered in the Fe3O4@AMC/RGO sample. Compared with the controlled Fe3O4@RGO sample, the Fe3O4@AMC/RGO composite exhibits remarkably enhanced initial coulombic efficiency, superior cycling stability and rate performance for lithium-ion storage. The mechanisms of the interaction between GO sheets and AM molecules as well as the inspiring electrochemical behaviors of the Fe3O4@AMC/RGO electrode have been revealed. The Fe3O4@AMC/RGO sample possesses good potential for scaling-up and finding applications in wider fields.

Engineering tin dioxide quantum dots in a hierarchical graphite and graphene oxide framework for lithium-ion storage.

The spontaneous aggregation and poor electronic conductivity are widely recognized as the main challenges for practically applied nano-sized tin dioxide-based anode candidates in lithium-ion batteries. This work describes a hierarchical graphite and graphene oxide (GO) framework stabilized tin dioxide quantum dot composite (SnO2@C/GO), which is synthesized by a solid-state ball-milling treatment and a water-phase self-assembly process. Characterization results demonstrate the engineered inside nanostructured graphite and outside GO layers from the SnO2@C/GO composite jointly contribute to a good immobilization effect for the SnO2 quantum dots. The hierarchical carbonaceous matrix supported SnO2 quantum dots could maintain good structure stability over a long cycling life under high current densities. As an anodic electrochemically active material for lithium-ion batteries, the SnO2@C/GO composite shows a high reversible capacity of 1156 mAh·g-1 at the current density of 1000 mA·g-1 for 350 continual cycles as well as good rate performance. The large pseudocapacitive behavior in this electrode is favorable for promoting the lithium-ion storage capability under higher current densities. The whole synthetic route is simple and effective, which probably has good potential for further development to massively fabricate high-performance electrode active materials for energy storage.

Facile synthesis of a rod-like porous carbon framework confined magnetite nanoparticle composite for superior lithium-ion storage.

This work demonstrates a streamlined method to engineer a rod-like porous carbon framework (RPC) confined magnetite nanoparticles composite (Fe3O4/RPC) starting from metallic iron and gallic acid (GA) solution. First, a mild redox reaction was triggered between Fe and GA to prepare a rod-shaped metal-organic framework (MOF) ferric gallate sample (Fe-GA). Then, the Fe-GA sample was calcinated to obtain a prototypic RPC supported metal iron nanoparticle intermediate sample (Fe/RPC). Finally, the Fe3O4/RPC composite was synthesized after a simple hydrothermal reaction. The Fe3O4/RPC composite exhibited competitive electrochemical behaviors, which has a high gravimetric capacity of 1140 mAh·g-1 at a high charge and discharge current of 1000 mA·g-1 after 300 cycles. The engineered RPC supportive matrix not only offers adequate voids to buffer the volume expansion from inside well-dispersed Fe3O4 nanoparticles, but also facilitates both the ionic and electronic transport during the electrochemical reactions. The overall material synthesis involves of no hazardous or expensive chemicals, which can be regarded to be a scalable and green approach. The obtained samples have a good potential to be further developed for wider applications.