Atomistic insight into the dopant impacts at the garnet Li₇La₃Zr₂O₁₂ solid electrolyte grain boundaries

Abstract

The atomic-scale impact of dopants at the grain boundary (GB) of the Li7La3Zr2O12 solid electrolyte is revealed by the first-principles calculation. The preferential sites of dopants, ion diffusions, Li interstitial stabilities and phase segregations at doped GBs are uncovered.

The effects of aluminum concentration on the microstructural and electrochemical properties of lithium lanthanum zirconium oxide

“…calculated that it was possible for LaAlO 3 to form at the grain boundaries, as well. 42 With this in mind, the increased presence of secondary grain boundary phases appears to be the cause of the increased observation of intergranular fracture at the LLZO–Al0.55 composition as compared to the largely intragranular fracture in the other three compositions (Fig. S2†).…”

“…In LLZO, aluminum preferentially substitutes for lithium at the 24d tetrahedral site, and secondarily in the 96h and 48g sites. 19,23,42,45,54 It is believed that once the energetically favorable sites have been filled to their maximum aluminum capacity and the solubility limit is reached, the excess aluminum forms aluminum-rich secondary phases, such as LaAlO 3 . 21,37 As was mentioned above, it is commonly observed that La 2 Zr 2 O 7 forms due to lithium loss.…”

“…also calculated that aluminum segregation and aluminum-rich secondary phase formation was possible in the grain boundaries. 42 At this point, it is not possible to determine whether this boundary phase enabled the abnormal grain growth as a solid or as a liquid. However, if it is a liquid phase, it could not be a pure La–Al–O phase, since no liquid forms below 1791 °C, which is over 500 °C more than the hot-pressing temperature.…”

“…It has been suggested that lithium aluminates form at the grain boundaries and act as sintering aids and grain growth aids. 19,36,39–42 Work by Jin and McGinn and Wolfenstine, et. al.…”

“…36,38,44 There are a few theoretical studies on the role of aluminum and lithium site occupancy on LLZO conductivity, though results regarding the overall effect of aluminum concentration on bulk lithium-ion conductivity are not conclusive. 42,44,45 Only a few results from experimental studies are available and were mainly obtained by pressure-less sintering, leading to large variation in microstructure and phase content. 36,38,46 Smetaczek, et.…”