Origin of the enhanced Li⁺ ionic conductivity in Gd⁺³ substituted Li_5+2xLa₃Nb_2−xGd_xO₁₂ lithium conducting garnets

Abstract

In the present study, we report the synthesis and the Li(+)-ion conductivity of new Gd(+3) substituted Li5+2xLa3Nb2-xGdxO12 (x = 0.0, 0.25, 0.4, 0.5, 0.6) garnets. The structural study by XRD showed that pure cubic garnet phases were obtained with upto x = 0.5 composition. With the further increase of the Gd(+3) content to x≥ 0.6, secondary phases are observed. The ionic conductivity was studied by impedance spectroscopy. We found that the Li(+) ionic conductivity increased with increasing Gd(+3) content with a maximum value of 1.12 × 10(-4) S cm(-1) at RT, which was two orders of magnitude larger than the previously reported value of 10(-6) S cm(-1) for pure Li5La3Nb2O12. A slight drop in the conductivity value to 6.25 × 10(-5) S cm(-1) was observed for x = 0.6 composition. By a systematic analysis of the conductivity spectra at different temperatures of the investigated materials, we are able to estimate the true values of the concentration, nc, and mobility, μ, of mobile Li(+) that contribute to the conduction process; nc was found to increase by a factor of only ∼2 with increasing Gd(+3) content from x = 0.0 to x = 0.5, whereas the mobility/diffusivity of Li(+) increased considerably with increasing Gd(+3) content. Therefore, the enhanced conductivity of the current materials is mainly due to the enhanced mobility of Li(+). Surprisingly, the fraction of mobile Li(+) represents only 3.44-6.96% of the total Li(+) density of the materials.

Toward garnet electrolyte–based Li metal batteries: An ultrathin, highly effective, artificial solid-state electrolyte/metallic Li interface

“…The peaks match well with cubic garnet Li 5 La 3 Nb 2 O 12 (PDF 80-0457). Li 5 La 3 M 2 O 5 (M = Nb, Ta) is the first structural example of a rapid, Li-ion conductive garnet and is the conventional structure used to study the garnet-type LLZO materials (26,(46)(47)(48). Electrochemical impedance spectroscopy (EIS) was used to measure the Li-ion conductivity of sintered LLCZN.…”

Materials space of solid-state electrolytes: unraveling chemical composition–structure–ionic conductivity relationships in garnet-type metal oxides using cheminformatics virtual screening approaches

“…97 The disagreement between the experimental and predicted values was acceptable (B0.2 in log s tot ) for Li 102 were systematically underestimated by models that included the difference in the experimental temperatures, the oxygen nonstoichiometry of these compounds or their instability to moisture. 103 In contrast, the total conductivities of Gd 3+ -substituted LLN 79 were overestimated by the models, except those for LLN-Gd60 (impurity phases were observed for this particular compound). The incorrect predictions for these compounds as well as for supervalent (Ce 4+ )-substituted LLZO Li 6.6 La 2.6 Ce 0.4 Zr 2 O 12 104 remain unexplained.…”

Effect of Sm3+ Substitutions on the Lithium Ionic Conduction and Relaxation Dynamics of Li5+2xLa3Nb2−xSmxO12 Ceramics

“…It is suggested that Sm 3+ substitutions in LLN garnets will force Li + ions at 24d sites to leave their positions and move to occupy 48 g/96 h octahedral sites [33][34][35]. This process will allow more vacant 24d sites, which are essential for 3D diffusion process through the 24d-96h-48g-96h-24d chain pathway, as illustrated in Figure 6 [27,[33][34][35][36]. The relaxation dynamics of the LLN-Sm ceramics are studied by the complex electric modulus M * (ω), which can be expressed as follows [37]:…”

“…Although most research work on lithium garnet materials is directed towards Li 7 La 3 Zr 2 O 12 , high ionic conductivity values in the 10 −4 S/cm range could also be obtained in doped Li 5 La 3 Nb 2 O 12 (LLN) and Li 5 La 3 Ta 2 O 12 (LLT) materials [21,[27][28][29][30]. In our recent work on Gd 3+ −substituted Li 5+2x La 3 Nb 2−x Gd x O 12 , the ionic conductivity was found to increase to 1.12 × 10 −4 S/cm for x = 0.5, which is about two orders of magnitude higher than the un-doped LLN material [27]. Similarly, Sc 3+ doping in Li 5+2x La 3 Nb 2−x Sc x O 12 garnets leads to ionic conductivity of 3.7 × 10 −4 S/cm for x = 0.625 [28].…”