Electrochemical lithium intercalation into a hexagonal WO3 framework and its structural change》.pdf

Solid State Ionics 135 (2000) 61–69 /locate/ssi Electrochemical lithium intercalation into a hexagonal WO3 framework and its structural change Mitsuhiro Hibino*, Wonchull Han, Tstsuichi Kudo Institute of Industrial Science, The University of Tokyo, Roppongi, Minato-ku, Tokyo, Japan Abstract Hexagonal tungsten trioxide (h-WO ) (ideally P6/mmm) has three kinds of lithium intercalation sites which are the 3 hexagonal-window (1a), hexagonal-cavity (1b) and trigonal-cavity (2d). Calculation by the DV-X method using a Li W O(60-x ) cluster showed that inserted lithium ions were more stable at the trigonal-cavity site than at the other sites. x 36 138 When lithium intercalation in h-WO3 was performed electrochemically, OCV (open circuit voltage) traces exhibited large hysteresis between insertion and the extraction process. On the basis of DV-X calculation results and changes in lattice parameters, we concluded that lithium ions started occupying hexagonal-window and/or hexagonal-cavity sites before the trigonal-cavity site was completely filled in the insertion process, and that lithium ions at the trigonal-cavity site were extracted after the hexagonal-window and hexagonal-cavity sites were almost empty during the extraction process.  2000 Elsevier Science B.V. All rights reserved. Keywords : Tungsten trioxide; Lithium intercalation; DV-X Materials : WO3 (tungsten trioxide) 1. Introduction