UCr 4 C 4 ‐Type RbLi(Li 3 SiO 4 ) 2 : A New Solid Electrolyte Framework for Fast Li‐Ion Conduction

ABSTRACT Discovery of new structural frameworks based primarily on light elements for solid electrolytes is key to advancing solid‐state batteries with high gravimetric energy density. In this work, a previously overlooked UCr 4 C 4 ‐type framework with one‐dimensional Li channels, RbLi(Li 3 SiO 4 ) 2 , has been confirmed to be an active structural prototype for Li‐ion conduction. Detailed molecular dynamics simulations reveal that the channels are interconnected to form a three‐dimensional pathway. Thus, conduction is not as easily blocked by point defects as it is in purely one‐dimensional conductors. A direction‐averaged activation energy agrees well with the experimental value of the polycrystalline pellet. First‐principles calculations indicate that migration along the Li channels is dominated by interstitial Li. The migration barrier is a markedly low value of 0.30 eV, comparable to those of materials of practical interest, such as Li 7 La 3 Zr 2 O 12 and Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 . The defect formation energy is a relatively high value of 1.26 eV, and exceeds the migration barriers for all crystallographic directions. Therefore, the defect formation is a rate‐limiting factor in stoichiometric RbLi(Li 3 SiO 4 ) 2 . These findings indicate that the UCr 4 C 4 ‐type framework is a promising structure for Li‐ion conduction, and a Li‐rich condition unlocks the full potential of conductivity in this framework.