Synthesis, conductivity and structural aspects of Nd3Zr2Li7−3xAlxO12

Abstract

In this paper we report the synthesis, structure and Li ion conductivity of a new tetragonal garnet phase Nd 3 Zr 2 Li 7 O 12. In line with other tetragonal garnet systems, the Li is shown to be ordered in the tetrahedral and distorted octahedral sites, and the Li ion conductivity is consequently low. In an effort to improve the ionic conductivity of the parent material, we have also investigated Al doping to reduce the Li content, Nd 3 Zr 2 Li 5.5 Al 0.5 O 12 , and hence introduce disorder on the Li sublattice. This was found to be successful leading to a change in the unit cell symmetry from tetragonal to cubic, and an enhanced Li ion conductivity. Neutron diffraction studies showed that the Al was introduced onto the ideal tetrahedral garnet site, a site preference also supported by the results of computer modelling studies. The effect of moisture on the conductivity of these systems was also examined, showing significant changes at low temperatures consistent with a protonic contribution in humid atmospheres. In line with these observations, computational modelling suggests favourable exchange energy for the Li + /H + exchange process.

Structure and Lithium-Ion Dynamics in Fluoride-Doped Cubic Li7La3Zr2O12 (LLZO) Garnet for Li Solid-State Battery Applications

“…Atomistic modelling techniques are well suited to the investigation of defect and transport properties and have been applied successfully to a variety of studies on lithium battery materials. 11,[20][21][22][23][24][25][26][27][28][29][30][31][32][33] In the present study, potentials-based energy minimisation and molecular dynamics (MD) were employed. [32][33][34][35][36] The advantage of employing potentials-based methods is that it allows us to study much larger systems (> 5000 species) for nanosecond timescales which would be infeasible for other methods, such as Density Functional Theory (DFT).…”

“…Using these point defect energies, the formation energy for lithium Frenkel defects as shown in Equation 1 were calculated to be 0.51 eV comparable to other lithium conducting solids. 11,[20][21][22][23][24][25][26][27][28][29][30][31][32][33] The lithium Frenkel defect is of primary importance if LLZO is to be considered as a Li-ion solid state electrolyte material.…”

“…230). [8][9][10][11][12] The adoption of the tetragonal cell is a result of the high Li content, which favours Li ordering to limit short Li + -Li + interactions. Indeed the tetragonal symmetry is observed for all garnets reported so far with 7 A schematic of tetragonal LLZO 7 is shown in Figure 1.…”

Oxide Electrolytes for Lithium Batteries

“…For LLZO, however, there generally exist two phases, i.e., cubic phase (space group ) which is necessary for high conductivity, and tetragonal phase (space group I 4 1 a / cd ) which is thermodynamically more stable at RT, while shows 2–3 orders of magnitude lower ionic conductivity. Bernstein et al attributed the cubic–tetragonal phase transition to the high‐Li‐content‐induced ordering of the Li + ions on the Li sublattice, which was also observed in Li 7 La 3 Sn 2 O 12 and Li 7 Nd 3 Zr 2 O 12 . By combining density‐functional theory and molecular dynamics simulations, they predicted a critical Li vacancy concentration in the range of 0.4–0.5 per LLZO formula unit for stabilization of cubic phase, irrespective of how the vacancies are introduced .…”

Enhanced Densification and Conduction Properties of Li5+xLa3Nb2-xZrxO12 Garnet Solid-State Electrolytes Through Zn Doping on the Nb/Zr Site

“…Further work determined that, in addition to lithium content, lithium ion distribution is key in understanding, and optimizing, the Li + ion conductivity of the garnet SSEs 18 . Subsequent work has employed a variety of aliovalent doping strategies to improve the conductiviry to >10 -4 S cm -1 , including substitution at the A site (Ca, Ba), B site (Zr, Hf, Sn) and C site (Al, Ga) [19][20][21][22][23][24][25][26] .…”