Low-temperature one-step solid-phase synthesis of carbon-encapsulated TiO2 nanocrystals as anode materials for lithium-ion batteries

A simple and highly efficient method is developed for in situ one-step preparation of carbon co-encapsulated anatase and rutile TiO2 nanocrystals (TiO2@C) with core-shell structure for lithium-ion battery anode. The synthesis is depending on the solid-phase reaction of titanocene dichloride with ammonium persulfate in an autoclave at 200 degrees C for 30 min. The other three titanocene complexes including bis(cyclopentadienyl)dicarbonyl titanium, cyclopentadienyltitanium trichloride, and cyclopentadienyl(cycloheptatrienyl)titanium are used instead to comprehensively investigate the formation mechanism and to improve the microstructure of the product. The huge heat generated during the explosive reaction cleaves the cyclopentadiene ligands into small carbon fragments, which form carbon shell after oxidative dehydrogenation coating on the TiO2 nanocrystals, resulting in the formation of core-shell structure. The TiO2 nanocrystals prepared by titanocene dichloride have an equiaxed morphology with a small diameter of 10-55 nm and the median size is 30.3 nm. Hundreds of TiO2 nanocrystals are encapsulated together by the worm-like carbon shell, which is amorphous and about 20-30 nm in thickness. The content of TiO2 nanocrystals in the nanocomposite is about 31.1 wt.%. This TiO2@C anode shows stable cyclability and retains a good reversible capacity of 400 mAh g(-1) after 100 cycles at a current density of about 100 mA g(-1), owing to the enhanced conductivity and protection of carbon shell.