The effects of electric field on physical properties of LLZO made by flash sintering method

Abstract

Li7La3Zr2O12 (LLZO) is one of the promising electrolytes for all-solid-state lithium-ion batteries. Since in conventional sintering, lithium retention is hard to control in LLZO, flash sintering, characterized by shorter sintering time and lower sintering temperature, can be beneficial. In this study, Al-doped LLZO (LALZO)powder was successfully synthesized by the combustion sol-gel method. The product was characterized by thermal analysis (TG/DTA) to evaluate its thermal behavior. Afterward, the effect of an electrical field in an isothermal approach on the relative density and phase composition of LALZO has been investigated. The obtained LALZO powder was uniaxially pressed into a dog-bone shape at 100 MPa. The samples were held in a tube furnace at 850 °C with an applied DC electrical field ranging from 40 V.cm−1 to 100 V.cm-1, while the current density was limited to 200 mA.mm−2. The phase composition was analyzed with X-ray diffraction (XRD), and the ionic conductivity was investigated using an AC impedance spectroscopy. Dense LALZO was flash sintered successfully, and the sample sintered with an electric field of 60 V.cm−1 showed a pure cubic LALZO with 92.4% relative density and a total ionic conductivity of 0.31 mS and activation energy of 0.37 eV. Moreover, it was revealed that the change in the electric field does not significantly affect the relative density. Also, increasing the electric field causes the incubation time to become shorter. This behavior is thought to be due to electric field strength as a driving force for nucleation mechanisms.