Toward Understanding the Lithium Transport Mechanism in Garnet-type Solid Electrolytes: Li+ Ion Exchanges and Their Mobility at Octahedral/Tetrahedral Sites

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• 作者：Dawei Wang ; Guiming Zhong ; Wei Kong Pang ; Zaiping Guo ; Yixiao Li ; Matthew J. McDonald ; Riqiang Fu ; Jin-Xiao Mi ; Yong Yang
• 刊名：Chemistry of Materials
• 出版年：2015
• 出版时间：October 13, 2015
• 年：2015
• 卷：27
• 期：19
• 页码：6650-6659
• 全文大小：681K
• ISSN：1520-5002

文摘

The cubic garnet-type solid electrolyte Li₇La₃Zr₂O₁₂ with aliovalent doping exhibits a high ionic conductivity, reaching up to 鈭?0^鈥? S/cm at room temperature. Fully understanding the Li⁺ transport mechanism including Li⁺ mobility at different sites is a key topic in this field, and Li_7鈥?x鈥?yAl_yLa₃Zr_2鈥?i>xW_xO₁₂ (0 鈮?x 鈮?1) are selected as target electrolytes. X-ray and neutron diffraction as well as ac impedance results show that a low amount of aliovalent substitution of Zr with W does not obviously affect the crystal structure and the activation energy of Li⁺ ion jumping, but it does noticeably vary the distribution of Li⁺ ions, electrostatic attraction/repulsion, and crystal defects, which increase the lithium jump rate and the creation energy of mobile Li⁺ ions. For the first time, high-resolution NMR results show evidence that the 24d, 96h, and 48g sites can be well-resolved. In addition, ionic exchange between the 24d and 96h sites is clearly observed, demonstrating a lithium transport route of 24d鈥?6h鈥?8g鈥?6h鈥?4d. The lithium mobility at the 24d sites is found to dominate the total ionic conductivity of the samples, with diffusion coefficients of 10^鈥? m² s^鈥? and 10^鈥?2 m² s^鈥? at the octahedral and tetrahedral sites, respectively.