There remains intense interest in developing solid polymer electrolytes, free from low molecular weight plasticiser and with a sufficiently high ionic conductivity for application in all-solid-state rechargeable lithium batteries. For such applications, conductivities above the present maximum of 10(-4) S cm(-1) are required. Innovative designs of polymers and salts which suppress crystallinity and yield amorphous polymer electrolytes with a low T-g have led to substantial improvements in the level of ionic conductivity compared with early systems, but the above mentioned barrier remains. We promote the view that it is important now to change our thinking concerning how to optimise ionic conductivity. We emphasise the importance of understanding the structure of polymer electrolytes in order to better understand the ion transport mechanism. Such studies indicate the importance of organising polymer chains while preserving chain dynamics. Recent evidence is presented from the work of others, supporting the view that more structured polymer electrolytes can lead to enhanced ionic conductivity. En route to this view, we present the crystal structures of several polymer salt complexes including the first structure of a 6:1 complex PEO6:LiAsF6. (C) 2000 Elsevier Science Ltd. All rights reserved.