A simple and fast way of making TiO2 nanocrystals could mean long-lasting anodes for a next generation of high-power Li-ion batteries, according to French and Italian researchers.

The outstanding electrochemical performance, cheapness, and low toxicity of TiO2 make it an attractive alternative to graphite as an anode material. But while TiO2 has a storage capacity on a par with graphite and shows very little change in lattice structure during the insertion and extraction of Li ions, making it intrinsically safer than graphite, it does suffer from lower ionic and electronic conductivity. This and other potential performance-limiting factors can be countered by nanostructuring the electrodes to increase the surface area.

Now a team led by Claudio Gerbaldi of the GAME Lab at the Politecnico di Torino in Italy and colleagues from IRCELYON at the CNRS-Université de Lyon in France have come up with a simple and quick hydrolytic process for producing mesoporous TiO2 nanocrystals, which can be used as anode materials without any further processing [Di Lupo, et al., Acta Mater. 69 (2014) 60-67, http://dx.doi.org/10.1016/j.actamat.2014.01.057]. The novel synthesis route relies on the cationic surfactant tetrabutylammonium bromide to produce TiO2 nanocrystals in the anatase phase – pyramidal crystals in the tetragonal system – with a high surface area of 258 m2 g-1. While the as-prepared TiO2 shows good anode performance, the degree of crystallinity can be increased with further calcination or heat treatment at 550°C. However, although calcination increases the crystal size from ~6 nm to ~13 nm, it also causes a coalescence of pores in the inorganic framework that reduces the surface area. Heat-treating TiO2 could hold some advantages though, suggest the researchers, because it strengthens the porous network thus improving the mechanical integrity of the material and boosting the electronic conduction.

Both as-produced and calcined TiO2 produced in this novel manner show outstanding rate capability and stability over prolonged charging-discharging cycles. The heat-treated TiO2 shows slightly better overall performance, say the researchers, but both the calcined and untreated samples demonstrate an impressive retention of their initial reversible capacity (>85%) over 1000 charge-discharge cycles.

The results indicate that TiO2 could have a promising future as high-power Li-ion battery anodes. Particularly interesting, say the researchers, is the fact that the as-prepared TiO2 performs nearly as well the TiO2 calcinated at 550°C.

“The not calcined material is highly attractive for large-scale production where stable electrochemical performance must be associated with a simple, fast, and low-cost material production,” says Gerbaldi. “The material offers a relatively high theoretical capacity, close to graphite, [and] its higher operating potential makes it safer than almost all the low potential anodes materials.”

The researchers are now investigating other synthesis routes that could be implemented at a large scale, Gerbaldi told Materials Today. Efforts are being focused on tailoring material characteristics to deliver improved specific capacity for high power and energy densities.