TiO₂ nanocrystals can be used to store lithium ions, which could make them useful for lithium-ion batteries. However, they have a low electric conductivity, which is a problem when they are used as an electrode in a battery. They also tend to aggregate, which negatively affects their properties. Combining TiO₂ nanocrystals with a conductive carbon material could solve these problems. However, existing composite materials are inhomogenous—which reduces their performance—and/or difficult to prepare.

Hai Wang, Guilin University of Technology, China, and colleagues have developed a new TiO_2–x@C nanocomposite electrode material for lithium-ion batteries. The team prepared TiO₂ nanocrystals from tetrabutyl titanate, using formic acid and anhydrous ethanol to limit crystal growth and sodium dodecylbenzenesulfonate (SDBS) as a surfactant. The resulting nanocrystals were mixed with vitamin C as a carbon source and heated to 200 °C.

The molten vitamin C and the nanocrystals form a solid-liquid mixture, which ensures a uniform distribution of the TiO₂ particles in the composite material (schematically pictured). The vitamin C is converted into a porous, three-dimensional carbon matrix, which is closely connected to the nanocrystals by covalent bonds. The process also introduces surface defects in the TiO₂ crystals that improve the material’s performance as an electrode material.

The structure of the nanocomposite combines the good electrical conductivity of the carbon framework with the useful lithium-ion transport and storage properties of TiO₂. The carbon matrix also prevents the aggregation of the nanocrystals. The resulting electrodes have high reversible capacities.

• Unusual Improvement of Pseudocapacitance of Nanocomposite Electrodes: Three-Dimensional Amorphous Carbon Frameworks Triggered by TiO₂ Nanocrystals,
  Huibing Lu, Caihong Yang, Huiming Bao, Linjiang Wang, Cunjun Li, Hai Wang,
  ACS Appl. Mater. Interfaces 2019.
  https://doi.org/10.1021/acsami.9b17595