High-efficiency and low-cost preparation of solid electrolytes Li7La3Zr2O12 based on molten salt method

Abstract

Solid electrolyte Li7La3Zr2O12 (LLZO) has received widespread attention due to its excellent comprehensive properties. However, in order to realize its industrial application in all-solid-state lithium batteries, an efficient and low-cost preparation method must be developed. Herein, molten salt method is applied and the effect of sintering temperature, washing solvent and mother powder distribution on the microstructure and properties of LLZO are investigated. Results show that pure cubic LLZO can be obtained at 1250–1300 °C, the lithium loss phase La2Zr2O7 is generated at higher temperature of 1330 °C. The Li+ conductivity of LLZO obtained at 1300 °C with short time of 80 min reach 2.9 × 10−4 S cm−1. Secondly, compared with washing with deionized water, the LiO4 occupation reduced while the LiO6 occupation increased when washing with LiOH aqueous, representing an exchange of Li+/H+. The Li+ conductivity of LLZO washed with LiOH solution (6.53 × 10−5 S cm−1) is 76% lower than that of deionized water washing (2.73 × 10−4 S cm−1) which due to the excessive Li+ concentration. Besides, the Li+ conductivity of LLZO (2.57 × 10−5 S cm−1) obtained with mother powder of 2.5 g: 2.5 g is close to one order of magnitude lower than that with 4 g: 1 g (2.23 × 10−4 S cm−1) which is due to too much lithium loss through the upper surface. Excessive mother powder on the upper surface is beneficial to obtain cubic phase LLZO. The molten salt method greatly reduces the mixing time (less than 30 min) and sintering time (80 min) of materials which is an effective and low-cost method to achieve mass production.