Tailoring TiO₂-shell thickness and surface coverage for best performance of multiwalled carbon nanotubes@TiO₂ in Li-ion batteries

Multiwalled carbon nanotubes@TiO₂ composites are promising anode materials in Li-ion batteries. Studies have shown that incorporating multiwalled carbon nanotubes in the core@shell morphology enhances considerably the electrochemical behavior of TiO₂ during Li-ion storage. Still, the optimization of these composites requires a better understanding of the effect of TiO₂-shell thickness and surface coverage on the performance of multiwalled carbon nanotubes@TiO₂. In this work, different ratios of titanium isopropoxide were hydrolyzed over multiwalled carbon nanotubes to control the degree of surface coverage and shell thickness. Structural characterization indicates that TiO₂ crystal size is not altered by the presence of multiwalled carbon nanotubes, but the size of TiO₂ agglomerates is, enlarging the oxide/electrolyte interface. Optimum shell thickness and surface coverage assure facile Li-ion intercalation kinetics and good interparticle connection, and go along with a minimum disorder on the graphene layer at the interfacial contact. The electrochemical behavior of the multiwalled carbon nanotubes@TiO₂ composites was optimum in a core@shell composite with TiO₂-shell thickness of ~100 nm, degree of surface coverage of the conductive nuclei close to 1, and minimum increment on the ratio of the multiwalled carbon nanotube D and G Raman bands.