Distribution of relaxation times assisted grain and grain boundary structural diagnosis of La2Zr2O7-modified Al-doped Li7La3Zr2O12 solid electrolyte

Abstract

The garnet-type Li₇La₃Zr₂O₁₂ (LLZO) solid electrolyte is regarded as a promising option for all-solid-state batteries owing to its notable features, including high ionic conductivity and wide electrochemical window. Although aluminum-doped LLZO (Al-LLZO) is crucial for achieving LLZO ceramics with high critical current density, the characteristics of its grain and grain boundary structures remain largely elusive. In this work, the electrochemical impedance spectroscopy (EIS) technique, in conjunction with the distribution of relaxation times (DRT) method, was employed to investigate structural alterations in Al-LLZO ceramics modified by La₂Zr₂O₇ (LZO) additives. Additionally, the impact of sintering temperature and electrolyte testing temperature on ceramic structural changes was investigated using the DRT tools. By optimizing experimental conditions such as the concentration of added LZO and the sintering temperature of Al-LLZO, the study was further refined. This enabled us to successfully identify Al-LLZO solid electrolytes exhibiting uniform morphological structures, moderate crystal grain sizes and high density. By adding 6 wt% of LZO to the Al-LLZO solid electrolyte, we achieved the purest cubic phase and optimal lithium-ion conductivity. Under this condition, the sintered Al-LLZO ceramics exhibited exceeding 4.2 × 10⁻⁴ S·cm⁻¹ conductivity at room temperature and a high critical current density of up to 0.6 mA·cm⁻².

Graphical Abstract