Li‐La‐Zr‐O Garnets with High Li‐Ion Conductivity and Air‐Stability by Microstructure‐Engineering

Abstract

Li7La3Zr2O12 (LLZO) solid electrolyte (SE) is a potential candidate for developing safe and economically all‐solid‐state batteries (ASSBs) owing to its high Li‐ion conductivity and electrochemical stability against lithium anodes. However, poor stability and significant reduction in conductivity when exposed to air, limit its practical use. Herein, a unique two‐step sintering approach is designed to tailor the microstructure of LLZO that can withstand extended air exposure. The record high Li‐ion conductivity (≈1.7 mS cm−1 at 25 °C) is obtained for coarse‐grained Li6.25Ga0.25La3Zr2O12 (GLLZO) samples, whereas fine‐grained samples exhibit a relatively lower yet still substantial conductivity (≈1.3 mS cm−1). However, coarse‐grained samples are vulnerable to atmospheric attacks, forming larger Li2CO3 on the surface, leading to spontaneous cracking and significantly reduced conductivity (≈4 order). Despite these limitations, coarse‐grained samples can still be good SE for ASSBs under certain conditions. Interestingly, fine‐grained samples maintain structural integrity and Li‐ion conductivity even after prolonged exposure to air. The differing transport and stability behaviors are attributed to variations in the bulk compositions originating from distinct sintering mechanisms. These findings represent a significant step toward achieving air‐stable, highly conductive solid electrolytes with normal grain growth that will reduce interfacial resistance and improve the power density and cyclability of next‐generation ASSBs.

Electrical Conductivities and Conduction Mechanism of Lithium-Doped High-Entropy Oxides at Different Temperature and Pressure Conditions

“…In order to determine both the electronic and ionic conductivities in Li x -HEO, EIS measurements are needed. EIS is a modern technique widely used to study the ionic conductance in solid electrolyte and electrode materials. ,,,− …”

“…Figure a,b (inset) shows, respectively, the schematics of the EIS setup and its equivalent circuit used to do the numerical fitting from which both the ionic and electronic conductivities of a mixed electronic/ionic conductor can be deduced. ,, Typically, Ag − or Au electrodes are used as the ion-blocking electrodes in the EIS measurements. To examine the influence of different ion-blocking electrodes, we conducted a comparative study of the EIS (and the linear sweeping voltammetry (LSV)) measurements of Li 0.117 -HEO using either Ag paste or Au thin films as the ion-blocking electrodes.…”

Review on Interface Issues between a Garnet Li7La3Zr2O12 Solid Electrolyte and Li Anode: Advances and Perspectives

“…In the research aimed at optimizing the LLZO structure to enhance its stability, Park et al devised a dense and high-quality crystal structure by altering the sintering process design. Compared to the traditional LLZO with coarse and relatively porous grain structure (Figure a), the density of fine-grained LLZO prepared using a two-step sintering process controlled by sintering temperature (Figure b) reaches up to a maximum of 97%, and its stability in ambient air significantly increases.…”

“…(a) Schematic diagram of LLZO structure prepared using traditional sintering process. (b) Schematic diagram of fine-grained and dense LLZO structure prepared using a two-step sintering process controlled by sintering temperature . Reproduced with permission from ref .…”

Investigating the Effect of Co-doping on Structural and Electrical Properties of Li7La3Zr2O12 Solid Electrolyte

“…(LLZO)는 뛰어난 특성으로 주목받고 있다. 이러한 특성 으로는 높은 이온전도성(∼1 mS/cm), [5,6] 리튬 금속 전극과의 우수한 화학적 안정성, [7] 넓은 전기화학적 창 (∼5V), [8] 낮은 전자전도성 [6,9]이 있다. LLZO는 두 가지 결정 구조, 즉 입방체(공간 군:   ) [10]와 사방체 (공간 군: I4 1 /acd) [11]를 가지고 있다.…”