Highly efficient solid-state synthesis of carbon-encapsulated ultrafine MoO2 nanocrystals as high rate lithium-ion battery anode

Abstract

A simple and highly efficient method is developed for the one-step in situ preparation of carbonencapsulated MoO 2 nanocrystals (MoO 2 @C) with coreshell structure for high-performance lithium-ion battery anode. The synthesis is depending on the solid-state reaction of cyclopentadienylmolybdenum tricarbonyl dimer with ammonium persulfate in an autoclave at 200°C for 30 min. The large amount of heat generated during the explosive reaction cleaves the cyclopentadiene ligands into small carbon fragments, which form carbon shell after oxidative dehydrogenation coating on the MoO 2 nanocrystals, resulting in the formation of core-shell structure. The MoO 2 nanocrystals have an equiaxial morphology with an ultrafine diameter of 2-8 nm, and the median size is 4.9 nm. Hundreds of MoO 2 nanocrystals are encapsulated together by the worm-like carbon shell, which is amorphous and about 3-5 nm in thickness. The content of MoO 2 nanocrystals in the nanocomposite is about 69.3 wt.%. The MoO 2 @C anode shows stable cyclability and retains a high reversible capacity of 443 mAh g −1 after 50 cycles at a current density of 3 A g −1, owing to the effective protection of carbon shell.

Highly efficient one-step synthesis of carbon encapsulated nanocrystals by the oxidation of metalπ-complexes

“…Moreover, it is worth mentioning that the MoO 2 nanocrystals coexist with a small amount of MoS 2 folded into a few layers (figure 3(f)). The formation mechanism has been discussed elsewhere [18]. ).…”

“…Compared to the conventional preparation techniques, the oxidizing agent is indispensable for the formation of carbon [16], implying that the effect of the presence of oxygen in the reaction apparatus on the product can be negligible, and that only a sealed reactor is sufficient for the synthesis. As no other specific apparatus or operating steps are needed, this method shows distinct advantages such as its simple procedure, low temperature, and high efficiency and yield, which is attractive for lithium-ion batteries [17][18][19]. Until now, most metallocene complexes, typically consisting of cyclopentadienyl ligand with the formula C 5 H 5 bound to central metal atoms, have been proved to be promising precursors for the preparation of carbon encapsulated nanocrystals by this method.…”

Carbon coating on metal oxide materials for electrochemical energy storage

“…This structure not only provides a large number of electrochemically active sites, but also promotes rapid electronic transitions and higher electrolyte permeability. Liu et al split the cyclopentadiene ligand into small carbon fragments to fabricate a core-shell structure [77]. Zhan et al prepared CuO@C core/shell arrays by CVD method [26].…”