Novel Polyanionic Solid Electrolytes with Weak Coulomb Traps and Controllable Caps and Spacers

New chain polymers that contain weakly coordinating anionic groups at controllable anionic separations in a polyether backbone are described. The anions are mono-diacyl-capped orthoborate moieties. In this paper, the polyanionic electrolytes with mono-oxalato-capped and mono-malonato-capped orthoborate structures (called “polyMOBs” and “polyMMBs”, respectively) are presented. After optimizing the anion separation, the conductivities of these lithium ion conducting polyanionic electrolytes are found to be high relative to those of most “dry” single-ion-conducting polymer electrolytes. A maximum ambient conductivity of almost 10 - 5 S cm - 1 has been obtained for a solid polyMOB with 14 ethyleneoxy repeating units. The electrochemical “window” for these materials is in excess of 4.5 V. As prepared here, the polyMOB materials (but not the polyMMBs) contain some residual lithium bis(oxalato)borate (LiBOB) as a side-product, which can be reduced but so far has not been eliminated. The effect of LiBOB content on conductivity is small, but it may cause the lithium ion transport number to be less than 1.0. These inexpensive, benign materials should be very suitable as electrolytes for electrochemical devices requiring single-ion conduction.