NMR and X-ray Absorption Study of Lithium Intercalation in Micro- and Nanocrystalline Anatase

Abstract

The intercalation of Li into micro-and nanocrystalline anatase xerogel powders using n-butyllithium and various preparation conditions has been studied by 6 Li and 7 Li solidstate NMR and X-ray absorption spectroscopy. The orthorhombic lithium titanate phase which forms for Li/Ti < 0.56 undergoes further structural modification as the Li/Ti ratio increases to 0.70. NMR shows the existence of one type of lithium environment in microcrystalline samples when Li/Ti e 0.30 and two lithium environments when Li/Ti > 0.30. These two lithium environments are assigned to Li + ions in similar structural sites that are uncoupled (species A) and weakly coupled (species B) to conduction band electrons. Nanocrystalline anatase samples produced by sol-gel methods differ from microcrystalline anatase in that the proportion of species A is greater. NMR further suggests that the coordination number of species A cannot be greater than five while no definite conclusions could be reached from NMR concerning species B. Titanium K-edge X-ray absorption near edge structure (XANES) provides a method of monitoring changes in electronic structure as Li is intercalated. Extended X-ray absorption fine structure (EXAFS) analysis provides information on the Ti local environment which changes considerably with the degree of intercalation in microcrystalline samples. For nanocrystalline anatase samples greater amounts of intercalation can be achieved which dramatically affects both the XANES and the EXAFS.

Preparation and characterization of nanotube Li-Ti-O by molten salt method

“…5(B)), 55.7 eV and 55.4 eV denote two chemical shift states of Li + ion, which are attributed to Li + ions in spinel and in anatase, respectively. This is consistent with the result of Wagemaker and Luca et al [23,24]. They identified that two typical Li + ion chemical shift states exist in Li x TiO 2 by MAS NMR method.…”

The Influence of Size on Phase Morphology and Li‐Ion Mobility in Nanosized Lithiated Anatase TiO2

“…This leads to the conclusion that the shape of the anatase signal is less visible because of broadening, which is also suggested by the lower T 2 value (for micron-sized anatase, T 2 reaches values of several ms, [24] while it stays below 0.5 ms for nanoanatase). For Li 0.55 TiO 2 in both nano-and microcrystals next to resonance A, a broad resonance occurs, B (see Figure 3), which was assigned by Luca et al [28] as Li in the Li-titanate phase. The negative chemical shift of species B was explained by a weak coupling of Li to conduction electron density.…”

“…A number of publications have illustrated that the Li-ion chemical shift in anatase Li x TiO 2 , and also in spinel Li 1 + x Ti 2Àx O 4 , appears to be a probe of the conduction electron density at the 7 Li nuclear site, which induces a small Knight shift. [24,28,30] In principle, the applied static field induces a polarization that enhances the field locally at the Liion nucleus. In these materials the polarization lowers the chemical shift, which is explained by polarization of the Li2s electrons by the Ti-3d and O-2p electron density.…”

High specific capacity of TiO2-graphene nanocomposite as an anode material for lithium-ion batteries in an enlarged potential window

“…TiO 2 has been regarded as a promising anode material for lithium-ion batteries due to its structural characteristics, low cost, safety and environmental benignity [1][2][3]. However, its practical capacity and high-rate capability are limited due to the low Li-ion diffusivity and electronic conductivity during reversible Li-ion insertion/extraction process [4][5][6]. In order to improve the electrochemical performance of TiO 2 materials, nanotechnology has been explored to provide increased reaction active sites and short diffusion lengths for electron and Li-ion transport [7][8][9][10][11][12][13].…”