Abstract
Garnet-type Li7La3Zr2O12 (LLZO) is considered as a promising solid electrolyte. Nb-doped LLZO ceramics exhibit significantly improved ion conductivity. However, how to prepare the Nb-doped LLZO ceramics in a simple and economical way, meanwhile to investigate the relationship between process conditions and properties in Li7-xLa3Zr2-xNbxO12 ceramics, is particularly important. In this study, Li7-xLa3Zr2-xNbxO12 (LLZNxO, x = 0, 0.2, 0.4, 0.6) ceramics were prepared by conventional solid-state reaction. The effect of sintering process on the structure, microstructure, and ionic conductivity of LLZNxO (x = 0, 0.2, 0.4, 0.6) ceramics was investigated. Due to the more contractive Nb-O bonds in LLZNxO ceramics, the cubic structures are much easier to form and stabilize, which could induce the decreased preparation time. High-performance garnet LLZNxO ceramics can be obtained by optimizing the sintering process with lower calcining temperature and shorter holding time. The garnet samples with x = 0.4 calcined at 850 °C for 10 h and sintered at 1250 °C for 4 h exhibit the highest ionic conductivity of 3.86 × 10−4 S·cm−1 at room temperature and an activation energy of 0.32 eV, which can be correlated to the highest relative density of 96.1%, and good crystallinity of the grains.
Highlights
As a typical representative in the solid electrolyte family, garnet-typeLi7 La3 Zr2 O12 (LLZO) is considered as a promising material that could solve the safety issues of the leakage of flammable organic liquid electrolytes in traditional Li-ion batteries because of its high Li-ion conductivity, high stability versus metallic Li, wide electrochemical window, and good chemical stability [1,2,3,4]
1250 ◦ C for 4 h exhibit the highest ionic conductivity of 3.86 × 10−4 S·cm−1 at room temperature and an activation energy of 0.32 eV, which can be correlated to the highest relative density of 96.1%, and good crystallinity of the grains
The substitution of Nb on Zr sites can stabilize the cubic structure of LLZO ceramics
Summary
As a typical representative in the solid electrolyte family (including perovskitetype, NASICON-like, LI-SICON-like, sulfide-based series and garnet-type), garnet-typeLi7 La3 Zr2 O12 (LLZO) is considered as a promising material that could solve the safety issues of the leakage of flammable organic liquid electrolytes in traditional Li-ion batteries because of its high Li-ion conductivity, high stability versus metallic Li, wide electrochemical window, and good chemical stability [1,2,3,4]. The cubic LLZO shows higher Li-ion conductivity (10−4 ~10−3 S·cm−1 ) than the tetragonal one, it is unstable at room temperature [5] and its conductivity is still lower than that of commercially used liquid organic electrolytes. Besides the type and content of substitution ions, the structure and conductivity of LLZO-based ceramics are quite sensitive to the preparation process. The conductivity of Ta-doped LLZO ranged from 10−6 to 10−4 S·cm−1 with different sintering processes [16]. These phenomena were observed in Nb-doped LLZO ceramics [17,18,19,20,21]
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