Developing Preparation Craft Platform for Solid Electrolytes Containing Volatile Components: Experimental Study of Competition between Lithium Loss and Densification in Li₇La₃Zr₂O₁₂

Abstract

is one of the most promising candidate solid electrolytes for high-safety solid-state batteries. However, similar to other solid electrolytes containing volatile components during high-temperature sintering, the preparation of densified LLZO with high conductivity is challenging involving the complicated gas−liquid−solid sintering mechanism. Further attention on establishing low-cost laborastory-scale preparation craft platform of LLZO ceramic is also required. This work demonstrates a "pellet on gravel" sintering strategy, which is performed in a MgO crucible and box furnace under ambient air without any special equipment or expensive consumables. In addition, the competition between lithium loss from the sintering system and internal grain densification is critically studied, whereas the influences of particle surface energy, Li-loss amount, and initial excess Li 2 O amount are uncovered. Based on the sintering behavior and mechanism, optimized craft platform for preparing dense LLZO solid electrolytes including mixing, calcination, particle tailoring and sintering is provided. Finally, exemplary Ta-doped LLZO pellets with 2 wt % La 2 Zr 2 O 7 additives sintered at 1260−1320 °C for 20 min deliver Li + conductivities of ∼9 × 10 −4 S cm −1 at 25 °C, relative densities of >96%, and a dense cross-sectional microstructure. As a practical demonstration, LLZO solid electrolyte with optimized performance is applied in both Li−Li symmetric cells and Li−S batteries. This work sheds light on the practical production of high-quality LLZO ceramics and provides inspiration for sintering ceramics containing volatile compounds.

Production of Ta-Doped Li7La3Zr2O12 Solid Electrolyte with High Critical Current Density

“…One was the deeper surficial contamination degree of Ta5Li6 than that of Ta5Li4. The other one was the tightness differences between MgO crucibles, where the crucible used for sintering Ta5Li6 green pellets leaked more Li 2 O/Li gas than the one for Ta5Li4 . Therefore, it was suggested to elevate the ramping rate and shorten the holding duration at the sintering temperature for the production of LLZO ceramics. , …”

“…The other one was the tightness differences between MgO crucibles, where the crucible used for sintering Ta5Li6 green pellets leaked more Li 2 O/Li gas than the one for Ta5Li4. 50 Therefore, it was suggested to elevate the ramping rate and shorten the holding duration at the sintering temperature for the production of LLZO ceramics. 36,51 All Ta5Li4&6-No.1−8 ceramics were pure cubic LLZO phase with strong crystallinity as shown in Figure S14.…”

“…Yang et al obtained Ta-doped LLZO ceramics via a rapid sintering strategy . In 2022, Huang et al further develop a “pellet-on-gravel” sintering craft without using any noble metals . However, the detailed production craft for dense Ta-doped LLZO ceramic pellets with good repeatability, high conductivity, and high critical current density is less studied.…”

Reactive flash sintering in a bilayer of zirconia and lanthana: Measurement of the diffusion coefficient in real time

“…Later, the method was applied to the synthesis of alumina‐doped lithium–lanthanum–zirconate, Li 6.25 Al 0.25 La 3 Zr 2 O 12 (Al–LLZO), from powders of lithia, lanthana, zirconia, and alumina 12 , a leading candidate for the electrolyte in solid‐state lithium–ion batteries. Here, the short time of RFS processing was especially important because the loss of lithium in the conventional sintering poses a very significant technical barrier 13 …”

“…Here, the short time of RFS processing was especially important because the loss of lithium in the conventional sintering poses a very significant technical barrier. 13 The speed of RFS is unusual, because the cations must migrate from the parent powder particle to mix atomistically with cations from other powders to form a single-phase multicomponent ceramic. Apparently, the rate of solid-state interdiffusion in RFS is anomalously rapid.…”