Uncovering the Network Modifier for Highly Disordered Amorphous Li‐Garnet Glass‐Ceramics
Abstract
Highly disordered amorphous Li7La3Zr2O12 (aLLZO) is a promising class of electrolyte separators and protective layers for hybrid or all-solid-state batteries due to its grain-boundary-free nature and wide electrochemical stability window. Unlike low-entropy ionic glasses such as LixPOyNz (LiPON), these medium-entropy non-Zachariasen aLLZO phases offer a higher number of stable structure arrangements over a wide range of tunable synthesis temperatures, providing the potential to tune the LBU-Li+ transport relation. It is revealed that lanthanum is the active “network modifier” for this new class of highly disordered Li+ conductors, whereas zirconium and lithium serve as “network formers”. Specifically, within the solubility limit of La in aLLZO, increasing the La concentration can result in longer bond distances between the first nearest neighbors of Zr─O and La─O within the same local building unit (LBU) and the second nearest neighbors of Zr─La across two adjacent network-former and network-modifier LBUs, suggesting a more disordered medium- and long-range order structure in LLZO. These findings open new avenues for future designs of amorphous Li+ electrolytes and the selection of network-modifier dopants. Moreover, the wide yet relatively low synthesis temperatures of these glass-ceramics make them attractive candidates for low-cost and more sustainable hybrid- or all-solid-state batteries for energy storage.
Y.Z. acknowledges financial support from the MIT Energy Initiative fellowship offered by ExxonMobil. J.L.M.R. thanks the Thomas Lord Foundation for financial support. This work made use of the MRSEC Shared Experimental Facilities at MIT, supported by the National Science Foundation under award number DMR‐1419807. This work was performed in part at the Center for Nanoscale Systems (CNS), a member of the National Nanotechnology Coordinated Infrastructure Network (NNCI), supported by the National Science Foundation under NSF award no. 1541959. CNS was part of Harvard University. The transmission electron microscopy analysis was performed at the Molecular Foundry at Lawrence Berkeley National Laboratory. Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE‐AC02‐05CH11231. A portion of the electron microscopy research was conducted as part of a user project at the Center for Nanophase Materials Sciences (CNMS), which is a US Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory.