Characterization of Lithium Storage in TiO₂(B) by⁶Li-NMR and X-Ray Diffraction Analysis

Abstract

Lithium storage in TiO 2 (B) was investigated by 6 Li magic-angle spinning (MAS) nuclear magnetic resonance (NMR) and exsitu X-ray diffraction (XRD) analysis combined with the entropy ( S) and galvanostatic intermittent titration technique (GITT) measurements. Lithium storage sites in TiO 2 (B) were characterized to be separated from four bands assigned to different lithium storage sites. Band A at 0 ppm vs. LiCl in the 6 Li NMR spectra and S measurements indicated that ionic lithium was stored at surface domain of Li x TiO 2 (B) up to x = 0.18. Band B at 2.5 ppm significantly increased with lithium insertion in the region for 0.25 < x < 0.5, which indicated that lithium was mainly inserted into the site lying between bridging oxygens in Li x TiO 2 (B). Additionally, the site on the lithium diffusion path along b-axis was also occupied by a small amount of lithium. The stepwise change of OCV and S at around x = 0.45 indicated that lithium was inserted at the site in TiO 2 layer in Li x TiO 2 (B). In the region for x > 0.75, Band D was observed at more positive chemical shift than Band B. The lithium at the site distorted the local structure of Li x TiO 2 (B), which leads to decrease of the lithium diffusivity in Li x TiO 2 (B).

Strong Li-Content Dependence of Li Diffusivity in TiO2-B

“…Therefore, the low capacity of bulk TiO 2 -B is due to kinetics limitation, which is in line with experimental proposals. 8,14,15,23,24 The values reported in Figure 6a are for structures with fully optimized atomic coordinates and unit cells. To investigate the influence of unit cell optimization on our results, we have recalculated diffusion barriers of the most favorable pathways in Figure 6a by performing only atomic coordinate optimization.…”

“…They proposed that nanowires with shorter diffusion length can compensate the slow Li self-diffusivity so that a larger number of Li atoms per unit volume can be incorporated/​removed in/​from nanowires than the bulk form of TiO 2 -B. Furthermore, a galvanostatic intermittent titration technique (GITT) measurement by Hoshina et al reported a significant lowering of diffusion coefficient in bulk Li x ­TiO 2 -B above a Li content of x = 0.7.…”

Is TiO2(B) the Future of Titanium‐Based Battery Materials?

“…Consequently,t he crystal, local, and electronic structures of TiO 2 (B) and their changes upon lithiation have been subjectt o intense research. [82][83][84][85] An interesting debate concerning the degree and order of filling of the three lithium sites (A1, A2, and C) and, thus, the role of open channels in the TiO 2 (B) structure has been going on among theoreticians. [34,[86][87][88][89] The computational studies indicated low Li migration energies for paths along the b-axisc hannel and the [001] direction, suggesting favorable Li-ion mobility.…”

Optimized Design Principles for Silicon‐Coated Nanostructured Electrode Materials and their Application in High‐Capacity Lithium‐Ion Batteries

“…In general, however, it is difficult to compare the absolute D values of TiO 2− x ‐C NTs and other TiO 2 polymorphs, because D is known to vary depending on the measuring method and the sample morphology. For instance, D values of anatase TiO 2 have been reported from 10 −12 to 10 −18 cm 2 s −1 . This is especially critical for the calculation of D in the low‐potential region in which Si is lithiated as the morphology changes substantially because of the strong expansion in the volume of the Li–Si alloy (Figure f) .…”