Lithium halide coating as an effective intergrain engineering for garnet-type solid electrolytes avoiding high temperature sintering

Abstract

Garnet-type Li 7 La 3 Zr 2 O 12 solid electrolytes were commonly prepared by two steps solid-state reaction method, which undergoes high temperature over 1000°C and thus inevitable for lithium volatilization and formation of secondary phases. Here, we propose a new intergrain architecture engineering of a solution method, to avoid high temperature sintering for preparing lithium halide (LiX) coated garnet-type solid electrolytes, which contain Al and Ta co-doped Li 7 La 3 Zr 2 O 12 (Li 6.75 La 3 Zr 1.75 Ta 0.25 O 12 , LLZTO) synthesized at 900°C with cubic structure. Owing to the increased relative density, the improved formability, and the altered ion transport mode from point to face conduction by LiX coating on LLZTO grains, LiX-coated LLZTO samples demonstrate a good Li dendrite suppression ability and a high ionic conductivity that is three orders of magnitude higher than pristine LLZTO. In another way, this result demonstrates the critical role of the grain boundaries on the ion transport for oxide superionic conductors. The present coating method provides a new strategy to prepare brittle solid electrolytes avoiding high temperature sintering.

Mobile Ions in Composite Solids

“…For example, the directly pelletized Ta-doped LLZO obtained from uniaxial cold-press shows an overall conductivity of 10 −4 mS cm −1 at room temperature. 130 High temperature sintering is required to suppress this problem, which significantly improved interparticle contacts. However, the relative density of the materials is still far from unity, suggesting the presence of high pore volume in these materials, despite the high temperature processing.…”

“…List of Some Important Crystal−Glass Composite Systems cold pelletizing of the resulting powder. 130 The composite has a comparative conductivity of 0.42 mS cm −1 with the sintered pellet (Figure 7(d)). Such an approach also allows good contact and less interfacial reaction between SEs and electrodes since the cross diffusion of elements at low temperature is kinetically disfavored.…”

Ultrafast Sintering of Solid-State Electrolytes with Volatile Fillers

“…It has become more and more difficult for conventional Li-ion battery technologies based on a liquid or gel electrolyte to meet the ever-increasing societal demand. , Solid-state electrolytes (SSEs) made by ion-conducting ceramics hold great promise for the next-generation Li battery technologies with better safety and higher energy density. − A range of ceramic SSEs, such as perovskite-type Li 3 x La 2/3– x TiO 3 , NASICON-type Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 , and Li 1+ x Al x Ge 2– x (PO 4 ) 3 , and garnet-type Li 7 La 3 Zr 2 O 12 (LLZO) and its derivatives have been studied owing to their appealing ionic conductivity (up to 10 –3 S cm –1 ), wide electrochemical window (up to 6 V), good chemical stability against Li metal, and excellent mechanical properties (up to 20 GPa). − However, their application in all-solid-state batteries has been hindered by the presence of voids, gaps, and pinholes upon sintering, as these defects are vulnerable spots for the penetration of Li dendrites, leading to thermal runaway, fire, and even explosion. − This problem is particularly acute when operating cells at medium to high current densities and long durations, making the ceramic SSEs incapable of realizing their high promise. , Among intensive efforts to address such an issue, sintering SSEs with inorganic fillers and sintering aids such as Al 2 O 3 , SiO 2 , MgO, CaO, BaO, LiF, LiCl, Li 3 BO 3 , Li 3 PO 4 , and BN has proven a viable solution to increase density and block the dendrite penetration. − However, many promising fillers and sintering aids were previously excluded due to their susceptibility of decomposition and sublimation during the prolonged heating of conventional sintering methods. − …”

Higher Critical Current Density in Lithium Garnets at Room Temperature by Incorporation of an Li4SiO4-Related Glassy Phase and Hot Isostatic Pressing

“…The absence of the Li 4 SiO 4 peaks in LLZA + LS might be due to the very small concentration of the incorporated Li 4 SiO 4 sintering additive at the grain boundaries. 26 The cross-sectional scanning electron microscopy (SEM) images of the conventionally sintered LLZA(C) and LLZA + LS(C) as well as HIP-treated LLZA + LS(H) are shown in Figure 1. The SEM images indicate a highly porous microstructure for LLZA(C) (Figure 1a,b), whereas LLZA + LS(C) shows integrated grains without voids in between them due to the adhesive nature of the sintering additive at the grain boundaries (Figure 1c,d).…”

“…The powder X-ray diffraction (PXRD) pattern (Figure S1) displays that conventionally and HIP-treated pellets LLZA­(C), LLZA + LS­(C), and LLZA + LS­(H) were stabilized in a pure cubic phase ( Ia 3̅ d ). The absence of the Li 4 SiO 4 peaks in LLZA + LS might be due to the very small concentration of the incorporated Li 4 SiO 4 sintering additive at the grain boundaries …”