Wenhao Xia,Biyi Xu,Huanan Duan,Yiping Guo,Hongmei Kang,Hua Li,Hezhou Liu
Li7La3Zr2O12 (LLZO) is a promising electrolyte material for all-solid-state battery due to its high ionic conductivity and good stability with metallic lithium. In this article, we studied the effect of crucibles on the ionic conductivity and air stability by synthesizing 0.25Al doped LLZO pellets in Pt crucibles and alumina crucibles, respectively. The results show that the composition and microstructure of the pellets play important roles influencing the ionic conductivity, relative density, and air stability. Specifically, the 0.25Al-LLZO pellets sintered in Pt crucibles exhibit a high relative density (∼96%) and high ionic conductivity (4.48 × 10–4 S cm–1). The ionic conductivity maintains 3.6 × 10–4 S cm–1 after 3-month air exposure. In contrast, the ionic conductivity of the pellets from alumina crucibles is about 1.81 × 10–4 S cm–1 and drops to 2.39 × 10–5 S cm–1 3 months later. The large grains and the reduced grain boundaries in the pellets sintered in Pt crucibles are favorable to obtain high ionic conductivity and good air stability. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy results suggest that the formation of Li2CO3 on the pellet surface is probably another main reason, which is also closely related to the relative density and the amount of grain boundary within the pellets. This work stresses the importance of synthesis parameters, crucibles included, to obtain the LLZO electrolyte with high ionic conductivity and good air stability.
Crucible is a key vessel in superalloy smelting, and high-performance crucible is quite important to the development of superalloy. Pointed at the easy cracking and poor thermal-shock stability of Al 2 O 3 crucibles for superalloy smelting, particle gradation was managed in slip casting of Al 2 O 3 crucibles. The ceramic slurry in good dispersion was prepared by optimizing particle gradation, with solid content of 86 wt% and viscosity of lower than 0.5 Pa s. For the crucible with optimized particle gradation, the density was 2.37 g/cm 3 , the linear shrinkage was less than 2%, the porosity was 18.72%, the bending strength was close to 22 MPa and the thermal expansivity was 2.77 × 10 −6 /°C. Strength retention rate was raised to evaluate the thermal shock stability of crucibles, which was up to 73.5% after five-time thermal shock, well meeting the requirements of crucibles for superalloy smelting, and the superior thermal-shock stability was attributed to the uniform network microstructure and low thermal expansivity. The optimal particle gradation in experiments was explained in terms of Dinger-Funk model. This work provides a reference for preparing high-performance Al 2 O 3 crucibles for superalloy smelting with low thermal expansivity as well as excellent thermal-shock stability.
Lithium lanthanum zirconate (Li 7 La 3 Zr 2 O 12 , LLZ) solid electrolytes were usually prepared by using Al 2 O 3 crucibles and/or Al 3+ dopants in order to stablize the formation of cubic garnet phase. In this work, we argue that Al-free MgO crucible could be better for the preparation of LLZ-based solid electrolytes through a detailed comparison of LLZ-Ga 0.2 samples prepared respectively by using MgO and Al 2 O 3 crucibles. The solid-state reaction method was firstly used to prepare Li 7-3 x Ga x La 3 Zr 2 O 12 ( x = 0–0.4) pellets by using Al-free MgO crucibles, which were sintered at 1100 °C for 12 h. The highly conductive cubic phase was obtained at Ga 3+ doping content as low as x = 0.05 and the highest room-temperature conductivity was obtained at x = 0.2. Al 2 O 3 crucible was then used to prepare the LLZ-Ga 0.2 pellet for comparing the influence of these two different crucibles. The results show that a higher lattice parameter ( a = 12.9762 (8) Å), a higher relative density (95.5%) and a higher room-temperature ionic conductivity (1.352 (3) mS/cm) were achieved by using the MgO crucible.
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