Self-Formed Channel Boosts Ultrafast Lithium Ion Storage in Fe3O4@Nitrogen-Doped Carbon Nanocapsule.

Investigations into conversion-type materials such as transition-metal oxides have dominated in energy-storage systems, especially for lithium ion batteries in recent years. A common understanding of taking account of high energy density and high power density allows us to design reasonable electrodes. In this study, the unique Fe3O4@nitrogen-doped carbon (denoted as Fe3O4@NC) nanocapsule with self-formed channels was synthesized based on a facile hydrothermal-coating-annealing route. With respect to the effect of this rational architecture on lithium-storage performance, excellent behavior (a high reversible capacity of 480 mAh g-1) could be maintained at 20 A g-1 during 1000 cycles, with an average Coulombic efficiency of 99.97%. It also means that such a Fe3O4@NC electrode can meet a fast-charge challenge (end-of-charge within ∼2 min). By a series of investigations, we certainly considered that uniform carbon coating improved electrical conductivity and acted as a buffer layer to accommodate volume variations of Fe3O4 nanoparticles during cycling. It is more interesting that self-formed channels can effectively shorten the ion diffusion path and provide a necessary space to buffer volume expansion as well. Benefiting from these synergetic advantages, this Fe3O4@NC nanocapsule also delivered outstanding electrochemical performances in full cells.

Ultrahigh Rate Performance of Hollow Antimony Nanoparticles Impregnated in Open Carbon Boxes for Sodium-Ion Battery under Elevated Temperature.

Antimony is a competitive and promising anode material for sodium-ion batteries (SIBs) due to its high theoretical capacity. However, the poor rate capability and fast capacity fading greatly restrict its practical application. To address the above issues, a facile and eco-friendly sacrificial template method is developed to synthesize hollow Sb nanoparticles impregnated in open carbon boxes (Sb HPs@OCB). The as-obtained Sb HPs@OCB composite exhibits excellent sodium storage properties even when operated at an elevated temperature of 50 °C, delivering a robust rate capability of 345 mAh g-1 at 16 A g-1 and rendering an outstanding reversible capacity of 187 mAh g-1 at a high rate of 10 A g-1 after 300 cycles. Such superior electrochemical performance of the Sb HPs@OCB can be attributed to the comprehensive characteristics of improved kinetics derived from hollow Sb nanoparticles impregnated into 2D carbon nanowalls, the existence of robust SbOC bond, and enhanced pseudocapacitive behavior. All those factors enable Sb HPs@OCB great potential and distinct merit for large-scale energy storage of SIBs.