High densification and Li-ion conductivity of Al-free Li7-La3Zr2-Ta O12 garnet solid electrolyte prepared by using ultrafine powders

Pyrochlore nanocrystals as versatile quasi-single-source precursors to lithium conducting garnets

“…Nyquist plots of symmetric cells using 20 wt% (1.5 mol%) Sn-Li alloy 27 electrodes are shown in Fig. 3c for both conventionally and reactively sintered garnets (1200 C for 2 h, relative densities of 88.0% and 94.1% respectively) possessing room temperature ($21 C) total ionic conductivities of 0.42 and 0.53 mS cm À1 respectively, comparable to those obtained from LLZTO prepared using standard SSR and other methods 7,10,[28][29][30][31][32][33][34][35][36][37][38][39][40][41] (see Table S3 † for detailed comparisons). No obvious grain boundary impedance is noticeable in the Nyquist plots in Fig.…”

Observation of Elemental Inhomogeneity and Its Impact on Ionic Conductivity in Li‐Conducting Garnets Prepared with Different Synthesis Methods

“…We suspect, however, that the situation shown in Figure 10c is quite common. For one thing, most SSRs are performed at as low of a temperature as possible while still forming the garnet phase, generally around 900 C. [20,21,23,27,28] Some methods from the literature use multiple calcination steps with grinding between reactions, [15,21,[24][25][26]64] but this is not always the case. Based on our observation of elemental inhomogeneity in the various materials presented here, we believe that variation in composition most likely also occurs in LLZTO prepared in other examples in the literature but has gone unnoticed.…”

“…[ 10,36,37 ] After the synthesis, further high‐energy ball milling is often required to reduce the particle size of the resultant coarse powder to confer greater sinterability. [ 20 ] In many cases, multiple milling and calcination steps are used to ensure full intermixing of atomic species. [ 10 ] Each of these steps has a large time cost in addition to requiring substantial thermal and mechanical energy input.…”

“…[ 21 ] Similarly, Yi et al obtained a high conductivity of ≈1 mS cm −1 for x = 0.3. [ 20 ] On the other hand, the results of Li et al showed a poor ionic conductivity of 0.28 mS cm −1 for x = 0.2, and a high conductivity up to 1 mS cm −1 for x = 0.6. [ 23 ] Finally, single crystals of LLZTO showed ionic conductivities of 1.1 and 1.3 mS cm −1 for x = 0.4 [ 35 ] and 0.5, [ 34 ] respectively.…”

“…[1,5,6] For this reason, an aliovalent dopant is needed to introduce Li vacancies to stabilize the highly conducting cubic phase. [1,3,[7][8][9][10] Many doping schemes have been explored, including Al 3þ [6,7,11] and Ga 3þ [7,12] to dope the Li sublattice, Nb 5þ [13,14] and Ta 5þ [7][8][9][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] to dope the Zr sublattice, Ca 2þ [22,29] and other alkaline earths such as Ba 2þ [30] to dope the La sublattice (often used in conjunction with another site dopant), and even recently F À[31-33] to dope the oxygen sublattice. Of the many possible compositions of LLZO, Ta-doped LLZO (LLZTO) with formula Li 7Àx La 3 Zr 2Àx Ta x O 12 (0.2 < x < 1) combines good electrochemical stability with lithium metal [14] and high ionic conductivity (>1 mS cm À1 ) [23,34,35] and, by virtue of doping the Zr sites in the garnet structure, does not block sites on the Li sublattice [7] unlike other dopants such as Al or Ga.Li-conducting garnets are generally synthesized via conventional solid-state reaction (SSR) methods that r...…”