Effect of nanostructuring and ex situ amorphous carbon coverage on the lithium storage and insertion kinetics in anatase titania

Abstract

Implications of nanostructuring and conductive carbon interface on lithium insertion/removal capacity and insertion kinetics in nanoparticles of anatase polymorph of titania is discussed here. Sol−gel synthesized nanoparticles of titania (particle size ∼6 nm) were hydrothermally coated ex situ with a thin layer of amorphous carbon (layer thickness: 2−5 nm) and calcined at a temperature much higher than the sol−gel synthesis temperature. The carbon-titania composite particles (resulting size ∼10 nm) displayed immensely superior cyclability and rate capability (higher current rates ∼4 A g⁻¹) compared to unmodified calcined anatase titania. The conductive carbon interface around titania nanocrystal enhances the electronic conductivity and inhibits crystallite growth during electrochemical insertion/removal thus preventing detrimental kinetic effects observed in case of unmodified anatase titania. The carbon coating of the nanoparticles also stabilized the titania crystallographic structure via reduction in the accessibility of lithium ions to the trapping sites. This resulted in a decrease in the irreversible capacity observed in the case of nanoparticles without any carbon coating.