Tuning the Li Diffusivity of Poor Ionic Conductors by Mechanical Treatment: High Li Conductivity of Strongly Defective LiTaO₃ Nanoparticles

Abstract

Lithium tantalum oxide, LiTaO 3 , with an average particle size in the µm range is known as a very poor Li ion conductor. It is shown here that its Li conductivity can be drastically increased by ball milling. The so-obtained nanostructured powder with an average particle size of about 20 nm shows a dc conductivity, σ dc , of about 3 × 10 -6 S cm -1 at T ) 450 K (σ dc T ) 1.4 × 10 -3 S cm -1 K) which is about 5 orders of magnitude larger than that of the corresponding microcrystalline powder at the same temperature. The activation energy E A is reduced by about one-third, i.e., it decreased from E A ) 0.90(1) eV to about E A ) 0.63(1) eV. The effect of different milling times on the ionic conductivity is studied. Furthermore, the thermal stability of the nanocrystalline materials against grain growth has been examined by in situ impedance spectroscopy. Interestingly, the Li conductivity of a sample milled for 16 h does not change much even when the material is exposed to about 700 K for several hours. Moreover, the Li self-diffusion in the nanostructured as well as the coarse grained materials has been investigated by various solid-state 7 Li NMR techniques.

F anion dynamics in cation-mixed nanocrystalline LaF3: SrF2

“…During ball milling the number density of defect sites usually increases which causes the bulk ionic conductivity also to increase as compared to the more ordered, single crystalline state. This effect has, in particular, been shown for oxides such as LiNbO 3 [16] and LiTaO 3 [17]. Recently, a quite similar enhancement has been reported for LiAlO 2 [18] and Li 2 TiO 3 [19].…”

“…The effect of abraded material from vial sets and milling balls has only a negligible effect if other factors, such as cation mixing, governs ion dynamics [14]. As has been documented for other nanocrystalline systems, the main change in ionic conductivity is caused by structural disorder, lattice strain introduced and the mixed cation effect [15][16][17]. The mismatch in size of the cations sensitively changes the potential landscape the mobile F anions are exposed to.…”

“…Analyzing the reflections of the nanocrystalline materials with the Scherrer equation [27,28] resulted in mean crystallite sizes in the order of 14 to 20 nm, see also Refs. [17,22,23] for similar analyses on nanocrystalline oxides that partly also considered the effect of lattice strain on samples prepared mechanochemically.…”

Synthesis of ternary transition metal fluorides Li3MF6via a sol–gel route as candidates for cathode materials in lithium-ion batteries

“…Generally, nm-sized particles can be easily prepared by high-energy ball milling of the coarse grained materials. [13][14][15] Besides activation, mechanochemistry has also successfully been used for the synthesis of a variety of materials from precursors at room temperature including oxides and fluorides. [16][17][18] However, in contrast to such a top-down approach, the preparation of nanostructured particles by precipitation from aqueous solution is much more beneficial when the shape and surface morphology of the crystallites have also to be controlled.…”

Atomic-scale measurement of ultraslow Li motions in glassyLiAlSi2O6by two-timeL6Wilkening1, Kuhn2, Heitjans3 2008Phys. Rev. BSelf Cite594500View full textAdd to dashboardCite

“…This is due to the often found observation that structurally disordered Li conductors exhibit exceptionally fast ionic diffusivity as compared to their low-defective crystalline counterparts. [9][10][11][12][13][14] Understanding the basics of transport phenomena in such materials in more detail is indispensable in effective battery research. In this context, it will be useful to study Li diffusion over a preferably large dynamic range, i.e., including also extremely slow cation motions.…”