Ta-Doped Li7La3Zr2O12 Solid-State Electrolytes with Cubic Structure and High Density Synthesized By Self-Consolidated Method

Abstract

Lithium ion battery (LIB) has become the dominant storage device for commercial wireless applications. However, its safety issues still haven’t been resolved due to its liquid organic electrolytes, which are volatile and flammable. All-solid-state LIB is viewed as a thorough solution for the safety issues. Instead of liquid electrolytes, all-solid-state LIB employs stable inorganic solid-state electrolytes with super ionic conductivity as both separators and ion conductors. Among current inorganic solid-state electrolytes, garnet-like oxides such as cubic LLZO (Li7La3Zr2O12) are the only candidates exhibiting the unique combination of high ionic conductivity and excellent stability against Li metal. For inorganic solid-state electrolytes, higher density generally leads to higher ionic conductivity. Therefore, most researchers prefer ultra-high pressure technology such as cold isostatic pressing (CIP) or hot isostatic pressing (HIP) to obtain high-density electrolytes. However, such preparation processes are too complicated and impractical for large-scale production because of the ultra-high pressure and poor productivity. Moreover, for the inhibition of intergranularly propagation of Li along the grain boundaries, LLZO pellets prepared by conventional high-pressure methods have been reported to be invalid due to their morphology of small particles and numerous grain boundaries. In order to overcome the shortages of conventional high-pressure methods, a novel method defined as self-consolidation was developed for the preparation of LLZO electrolytes in our previous work. The surface tension deriving from the interstitial “liquid” phase is utilized as the intrinsic power for the self-consolidation of ceramic LLZO particles. Not any pressing assistance is employed in the entire process. As a result, the preparation process is dramatically simplified. In this paper, self-consolidation method is tried to synthesize Ta-doped LLZO solid-state electrolytes. Dense LLZO with a solitary cubic phase and a high relative density about 96% was prepared successfully. At 30 oC, the maximum total and bulk ionic conductivities are about 2.74×10-4 and 1.17×10-3 S cm-1, respectively. The results show that, even though the preparation process is dramatically simplified, the sample’s relative density and ionic conductivity are comparable to the highest reported values of the samples prepared by traditional pressing methods. Meanwhile, the morphology and ionic conductivity of the sintered samples are promoted. This work verifies that self-consolidation strategy is effective, reliable, and productive for the preparation of cubic LLZO electrolytes, which would significantly facilitate the development of ceramic electrolyte membrane technology. Figure 1