Li Ion Diffusion in Nanocrystalline and Nanoglassy LiAlSi₂O₆ and LiBO₂ - Structure-Dynamics Relations in Two Glass Forming Compounds

Abstract

In the present study the Li diffusivity in nanostructured samples of two glass forming model systems, spodumene (LiAlSi 2 O 6 ) and lithium metaborate (LiBO 2 ), was examined using 7 Li nuclear magnetic resonance (NMR) spin-lattice relaxometry and dc conductivity measurements. The nanostructured samples were prepared by high-energy ball milling of the respective crystalline starting material on the one hand and the corresponding glass on the other hand. The diffusivity of the glass exceeds that of the crystalline sample for both systems. However, when the crystalline samples are mechanically treated by ball milling the diffusivity is enhanced. Nevertheless, the diffusivity of these nanocrystalline samples remains lower than that of the corresponding glass. Surprisingly, when the glassy samples are treated in the same way the diffusivity decreases. After sufficiently long milling times the diffusivity of these nanoglassy samples approaches that of the nanocrystalline samples. This convergence effect seems to be due to structural relaxation processes as is suggested by supplementary infrared spectroscopy and 27 Al, 12B magic angle spinning NMR measurements.

Oxide Electrolytes for Lithium Batteries

“…In nanocrystalline ionic conducting ceramics, the increased concentration of interfacial regions may form percolation pathways for fast ion diffusion, resulting in more obviously enhanced conductivity compared to those with microsize grains . Examples in this concern are mainly the model systems with single phase such as LiBO 2 , LiAlSi 2 O 6 , LiNbO 3 , or LiTaO 3 . The discovery of interfacial fast lithium‐ion diffusion opens up a route for improving the conductivity of oxide electrolytes.…”

Nanostructured Ceramics: Ionic Transport and Electrochemical Activity

“…At first glance one would expect no significant influence when an already disordered material is milled. So far only few reports, however, showed that high-energy ball-milling of glassy materials ( LiAlSi 2 O 6 (β-spodumene, [105]), LiBO 2 [20,106]) results in a decrease of the ionic DC conductivity, see also Ref. [107].…”

The ionic conductivity in lithium-boron oxide materials and its relation to structural, electronic and defect properties: insights from theory

“…Due to the fast ionic conduction property, lithium metaborate has a number of potential applications in advanced materials with controlled chemical and new physical properties such as lithium ion batteries, electrochromic displays, gas sensors, etc [1,72,134]. Recently, experimental studies on ion transport and diffusion in nanocrystalline and glassy ceramics of LiNbO 3 , LiAlSi 2 O 6 and LiBO 2 using the measurement of dc conductivities and 7 Li nuclear magnetic resonance spin-lattice relaxation rates have been performed [72,73]. Their measured activation energy for the Li + ion long-range transport as derived from the dc conductivity in LiBO 2 (with α-LiBO 2 as the majority phase) is 0.80-0.71 eV when going from the microcrystalline via the nanocrystalline to the glassy state, whereas the activation energy for the short-range Li + ion migration obtained from the spin-lattice relaxation rates is 0.23-0.21 eV when going from the nanocrystalline to the glassy state.…”