Uncovering the Network Modifier for Highly Disordered Amorphous Li-Garnet Glass-Ceramics.

Highly disordered amorphous Li 7 La 3 Zr 2 O 12 (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 Li x PO y N z (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. We reveal that lanthanum (La) 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 1 st nearest neighbors of Zr-O and La-O within the same LBU and the 2 nd 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 the future design 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. This article is protected by copyright. All rights reserved.