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

Abstract

We review recent theoretical studies on ion diffusion in (Li(2)O)(x)(B(2)O(3))(1-x) compounds and at the interfaces of Li(2)O :B(2)O(3) nanocomposite. The investigations were performed theoretically using DFT and HF/DFT hybrid methods with VASP and CRYSTAL codes. For the pure compound B(2)O(3), it was theoretically confirmed that the low-pressure phase B(2)O(3)-I has space group P3(1)21. For the first time, the structure, stability and electronic properties of various low-index surfaces of trigonal B(2)O(3)-I were investigated at the same theoretical level. The (101) surface is the most stable among the considered surfaces. Ionic conductivity was investigated systematically in Li(2)O, LiBO(2), and Li(2)B(4)O(7) solids and in Li(2)O:B(2)O(3) nanocomposites by calculating the activation energy (E(A)) for cation diffusion. The Li(+) ion migrates in an almost straight line in Li(2)O bulk whereas it moves in a zig-zag pathway along a direction parallel to the surface plane in Li(2)O surfaces. For LiBO(2), the migration along the c direction (E(A) = 0.55 eV) is slightly less preferable than that in the xy plane (E(A) = 0.43-0.54 eV). In Li(2)B(4)O(7), the Li(+) ion migrates through the large triangular faces of the two nearest oxygen five-vertex polyhedra facing each other where E(A) is in the range of 0.27-0.37 eV. A two-dimensional model system of the Li(2)O :B(2)O(3) interface region was created by the combination of supercells of the Li(2)O (111) surface and the B(2)O(3) (001) surface. It was found that the interface region of the Li(2)O:B(2)O(3) nanocomposite is more defective than Li(2)O bulk, which facilitates the conductivity in this region. In addition, the activation energy (E(A )) for local hopping processes is smaller in the Li(2)O :B(2)O(3) nanocomposite compared to the Li(2)O bulk. This confirms that the Li(2)O:B(2)O(3) nanocomposite shows enhanced conductivity along the phase boundary compared to that in the nanocrystalline Li(2)O.

Dielectric dispersion and ac conduction phenomena of Li2O−Sb2O3−PbO−GeO2:Cr2O3 glass system

“…Substitution of Li sites by Cr 3 þ ions in these glasses is important for several reasons. Cr 3 þ centers whether they are in either in high-field sites (energy of 4 T 2g 4 2 E g ) or in lowfield sites (energy of 4 T 2g o 2 E g ) occupy Li þ site and pave the way for the easy transport of Li þ ions in the glass network [15][16][17]. This should lead to some unusual surface segregation effects for dopants occupying the Li þ site [18]; such surface segregation, with an associated contribution to the ion conductivity in turn influences the electrical properties of these glasses.…”

Lithium Ion Conduction in Cathode Coating Materials from On-the-Fly Machine Learning

“…Lithium borates have been recognized for their excellent interfacial stability, 35 but ionic conductors in this category have rarely been identified. 80 The activation energy of lithium ion diffusion in Li₂B₆O₉F₂ has been experimentally determined to be 0.92 eV by heating the sample up to 623 K. 81 Using LOTF-MD, we calculated diffusivities from molecular dynamics simulations at temperatures as low as 570 K. The migration energy in Li₂B₆O₉F₂ calculated in the range of 570 K -670 K is 0.79 ± 0.10 eV, which is 0.13 eV lower than the experimental activation energy. To our knowledge, Li₃B₇O₁₂, which is predicted to have excellent interfacial stability, has not been characterized in terms of Li⁺ conduction.…”

Density Functional Theory Evaluated for Structural and Electronic Properties of 1T-Li x TiS2 and Lithium Ion Migration in 1T-Li0.94TiS2

“…This is especially important in the field of ion migration processes in solids. Experimentally activation barriers for ion migration can be obtained with macroscopic and microscopic methods [54,55]. These cover short and long range transport phenomena at different extents.…”