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

A simple and highly efficient method is developed for the one-step in situ preparation of carbon-encapsulated MoO₂ nanocrystals (MoO₂@C) with core-shell 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 MoO₂ nanocrystals, resulting in the formation of core-shell structure. The MoO₂ nanocrystals have an equiaxial morphology with an ultrafine diameter of 2–8 nm, and the median size is 4.9 nm. Hundreds of MoO₂ nanocrystals are encapsulated together by the worm-like carbon shell, which is amorphous and about 3–5 nm in thickness. The content of MoO₂ nanocrystals in the nanocomposite is about 69.3 wt.%. The MoO₂@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.