Mesoscopic Framework Enables Facile Ionic Transport in Solid Electrolytes for Li Batteries

• Published in: Advanced energy materials Vol. 6; no. 11; pp. np - n/a
• Main Authors: Ma, Cheng, Cheng, Yongqiang, Chen, Kai, Li, Juchuan, Sumpter, Bobby G., Nan, Ce-Wen, More, Karren L., Dudney, Nancy J., Chi, Miaofang
• Format: Journal Article
• Language: English
• Published: Weinheim Blackwell Publishing Ltd 08.06.2016; Wiley Subscription Services, Inc; Wiley
• Subjects: coherence length; Design engineering; Electric batteries; Electrolytes; ENERGY STORAGE; Ionic conductivity; ionic transport; Ions; Li batteries; Order disorder; Scanning transmission electron microscopy; Solid electrolytes; Three dimensional; Transport
• ISSN: 1614-6832; 1614-6840
• DOI: 10.1002/aenm.201600053

Li‐ion‐conducting solid electrolytes can simultaneously overcome two grand challenges for Li‐ion batteries: the severe safety concerns that limit the large‐scale application and the poor electrolyte stability that forbids the use of high‐voltage cathodes. Nevertheless, the ionic conductivity of solid electrolytes is typically low, compromising the battery performances. Precisely determining the ionic transport mechanism(s) is a prerequisite for the rational design of highly conductive solid electrolytes. For decades, the research on this subject has primarily focused on the atomic and microscopic scales, where the main features of interest are unit cells and microstructures, respectively. Here, it is shown that the largely overlooked mesoscopic scale lying between these extremes could be the key to fast ionic conduction. In a prototype system, (Li0.33La0.56)TiO3, a mesoscopic framework is revealed for the first time by state‐of‐the‐art scanning transmission electron microscopy. Corroborated by theoretical calculations and impedance measurements, it is demonstrated that such a unique configuration maximizes the number of percolation directions and thus most effectively improves the ionic conductivity. This discovery reconciles the long‐standing structure–property inconsistency in (Li0.33La0.56)TiO3 and also identifies mesoscopic ordering as a promising general strategy for optimizing Li+ conduction. The importance of the previously overlooked mesoscopic ordering to the design of future superionic conductors for Li batteries is demonstrated through a combination of atomic‐resolution scanning transmission electron microscopy and molecular dynamics simulations. By maximizing the number of Li transport pathways in three dimensions, such a unique atomic framework effectively facilitates the ionic conduction within the material.