Affiliation:
1. Leibniz University of Hanover, Institute of Mineralogy, Callinstr. 3, 30167 Hanover
Abstract
Abstract
Chemical intercalation of lithium in single crystals of TiX2
(X = S, Se, Te) was studied at
pressures of 10–500 MPa and temperatures of
293–363 K. Crystals were synthesized by chemical vapor
synthesis and cut with a LASER into squares (2.2 × 2.2 mm). Samples and 1.6 mol · L
–1
n-butyl lithium solutions in n-hexane (BuLi) were sealed in gold
capsules. Experiments were carried out in cold seal pressure vessels
for 5–20 days using Ar as pressure medium. A large
fraction of samples showed degradation after the experiments, i.e., at
low pressures and at high temperatures. On samples with minor
degradation, lithium profiles were measured parallel to the
crystallographic ab-plane, using femtosecond-LASER
Ablation-Inductively Coupled Plasma-Optical Emission Spectroscopy and
-Mass Spectrometry (fs-LA-ICP-OES and -MS). Most of the profiles could
be well fitted by the specific solution of Fick's second law for the
given boundary conditions. Lithium diffusivities (D
Li) and
lithium contents at the crystal edges (x
Li,S) were
determined from the fits.
At 500 MPa and room temperature lithium diffusivities are
similar in TiS2 ((1.07 to
2.41) × 10
–15 m2 · s
–1) and
TiSe2 ((1.48 to 2.10) × 10
–15 m2 · s
–1) but significantly lower in TiTe2
((0.07 to 0.55) × 10
–15 m2 · s
–1). Moreover, diffusivity of Li in TiTe2 decreases
significantly with increasing pressure whereas for the other
chalcogenides a pressure dependence cannot be evidenced. Lithium
surface contents are lower for TiS2 (x = 0.15 to 0.36)
than for TiSe2 (0.66 to 0.71) and TiTe2
(0.59 to 0.99), slightly elevated compared to ambient pressure
experiments. These findings indicate, that the ionicity of the
Ti–X bonding as well as the size of the interlayer
space (van der Waals gap) play a crucial role for the degree of
lithium insertion and for the pressure dependence of lithium
diffusivity.
Subject
Physical and Theoretical Chemistry
Cited by
5 articles.
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