Compositional Tuning of Structural Stability of Lithiated Cubic Titania via a Vacancy-Filling Mechanism under High Pressure

Experimental and theoretical studies on the compositional dependence of stability and compressibility in lithiated cubic titania are presented. The crystalline-to-amorphous phase transition pressure increases monotonically with Li concentration (from $\sim 17.5\mathrm{GPa}$ for delithiated to no phase transition for fully lithiated cubic titania up to 60 GPa). The associated enhancement in structural stability is postulated to arise from a vacancy filling mechanism in which an applied pressure drives interstitial Li ions to vacancy sites in the oxide interior. The results are of significance for understanding mechanisms of structural response of metal oxide electrode materials at high pressures as well as emerging energy storage technologies utilizing such materials.

Figure 1

Integrated in situ synchrotron XRD patterns during compression and release of (a) delithiated $c\mathrm{\text{−}}{\mathrm{TiO}}_2$ nanotubes (0%), (b) lithiated $c\mathrm{\text{−}}{\mathrm{TiO}}_2$ nanotubes (100%), (c) 50% lithiated $c\mathrm{\text{−}}{\mathrm{TiO}}_2$ nanotubes, and (d) 75% lithiated $c\mathrm{\text{−}}{\mathrm{TiO}}_2$ nanotubes. Note that the intensity refinement is not applicable here because of the preferential orientation of ${\mathrm{TiO}}_2$ nanotubes. (Peaks marked by “hash” represent diffraction peaks from unmasked neon, and peaks marked by “astreisk” represent diffraction peaks from unmasked rhenium gasket.)

Figure 2

(a) Theoretical PRDF of the pairs for the delithiated (0%) cubic ${\mathrm{TiO}}_2$ at 0 and 5 GPa. (b) PRDF of the pairs for the fully lithiated (100%) cubic at 0 and 60 GPa. (c) Volume changes as a function of the pressure for each concentration. (d) Phase transition pressure as a function of Li concentration.

Figure 3

Relative unit cell volume changes with pressure in $c\mathrm{\text{−}}{\mathrm{TiO}}_2$ nanotubes with different Li concentration based on the data presented in Fig. 1. Solid lines are fitted curves by B-M EOS. Symbols: 0% solid triangles; 75% open circles; 100% open squares. Compression is shown in black, release in red. Error bars are within the symbols.

Figure 4

Structural transition under pressure for (a) delithiated, (b) 50% lithiated, (c) 75% lithiated, (d) 85% lithiated, and (e) fully lithiated at different pressures. Red spheres: O; green spheres: Li; and white spheres: Ti.