Conductor–Insulator Interfaces in Solid Electrolytes: A Design Strategy to Enhance Li-Ion Dynamics in Nanoconfined LiBH₄/Al₂O₃

Synthesizing Li-ion-conducting solid electrolytes with application-relevant properties for new energy storage devices is a challenging task that relies on few design principles to tune ionic conductivity. When starting originally poor compounds, in many cases, combination of several strategies, such as doping or substitution, needed achieve sufficiently high conductivities. For nanostructured materials, the introduction conductor–insulator interfacial regions represents another important strategy. Unfortunately, most two-phase ceramics studied so far, lower limiting conductivity values applications could not be reached. Here, we show nanoconfined LiBH4/Al2O3 prepared by melt infiltration, percolating network fast Li+ diffusion pathways realized. These heterocontacts provide extremely rapid 7Li NMR spin fluctuations giving direct evidence very jump processes both and LiBH4-LiI/Al2O3. Compared nanocrystalline, Al2O3-free reference system LiBH4-LiI, nanoconfinement leads strongly enhanced recovery longitudinal magnetization. The fact almost no difference seen between LiBH4-LiI/Al2O3 unequivocally reveals overall spin-lattice relaxation rates are solely controlled near regions. Thus, nanoeffect, which ideal case percolation space charge regions, independent choice bulk crystal structure LiBH4, either being orthorhombic (LiBH4/Al2O3) hexagonal (LiBH4-LiI/Al2O3). (and 1H) shows local Li-ion dynamics corroborated rather small activation energies order only 0.1 eV. In addition, LiI-stabilized layer-structured form LiBH4 guarantees two-dimensional (2D) ion contributes facilitating long-range transport.