Size Particle Effects on Lithium Insertion into Sn-doped TiO₂ Anatase

Abstract

Lithium insertion into Sn-doped TiO2 anatase was studied in order to clarify the mechanism responsible for the first plateau observed at 1.75 V vs Li. One of the other aims of this study was to get deeper insight into the process responsible for the appearance of a first domain observed at a small amount of lithium (before the plateau) and a third domain between 1.7 and 1.2 V (after the plateau). Pure and Sn-substituted anatase were synthesized by several synthetic methods with different precursors and solvents. These materials are expected to have different electrochemical properties because crystallite size modifies the Li-insertion process. Their electrochemical behavior is discussed in order to establish a relationship between the materials properties and the electrochemical performances. Three processes have been identified from both X-ray diffraction and 119Sn Mössbauer spectroscopy: (i) topotactic insertion into the Li-poor compound Li x TiO2, with the x value depending on the particle size; (ii) a two-phase system mechanism leading to the phase transition Li x TiO2 (Anatase, I41/a md) → Li y TiO2 (orthorhombic distortion, Imma); and (iii) another topotactic insertion into the Li-rich compound Li y TiO2. Crystallite size governs the topotactic mechanism but does not improve the overall electrochemical capacity of the material.

Preparation, characterization, and electrochemical performances of carbon-coated TiO2 anatase

“…The cyclic voltammograms of the commercial TiO 2 samples reveal a cathodic peak at~1.75 V and an anodic peak at 2.0 V vs. Li/Li + , corresponding to the Li insertion and extraction into anatase TiO 2 [25,26] according to the following reaction: Upon Li insertion, the anatase converts to a two-phase system, including the Li-poor Li 0.05 TiO 2 (space group I41/ amd) phase with tetragonal symmetry and the Li-rich Li 0.5 TiO 2 (space group Imma) phase with orthorhombic symmetry. The Li ions are randomly distributed over half of the available interstitial octahedral sites, leading to a Li storage capacity of 0.5 (168 mA h g −1 ) [27][28][29][30]. Additionally, at the first cycle, there are two cathodic peaks at 1.4 and 1.1 V, respectively.…”

Highly Organized Mesoporous TiO2 Films with Controlled Crystallinity: A Li‐Insertion Study

“…For the completely crystalline phase, this process is attributed to the further topotactic Li insertion into the Li-rich orthorhombic Li 0.5 TiO 2 phase. [16] For the samples treated at lower temperatures it is complemented by the contributions from the amorphous or disordered crystalline phases, the fraction of which progressively decreases with increasing crystallinity due to the treatment at higher temperatures. [a] Data in the brackets are converted for the film thickness of 280 nm.…”

“…The maximum insertion capacity x of 0.5 mol of Li per 1 mol of anatase is given by the number of vacant 4b sites for Li ions, corresponding to one-half of interstitial sites of the anatase structure. [15][16][17] These electrochemical features enable the quantification of the fraction of anatase, provided that the equilibrium conditions of the insertion process have been achieved. Rutile has a comparable insertion capacity, but a more negative insertion potential (E f = 1.45 V).…”

Correlation investigation on the visible-light-driven photocatalytic activity and coordination structure of rutile Sn-Fe-TiO2 nanocrystallites for methylene blue degradation

“…Judging from the two Mössbauer parameters, it can be deduced that the Sn 4+ ions are located at octahedral sites [40]. However, the Mössbauer parameters of Sn-containing samples are different from those observed for SnO 2 (IS = −0.02 mm s −1 , QS = 0.58 mm s −1 ), which is the evidence that Sn 4+ ions are located at the titanium crystallographic sites in the rutile structure [41].…”