Polyanionic electrolytes with high alkali ion conductivity

We describe the synthesis of chain polymers that contain Lewis base or Lewis acid groups in the backbone that can then be reacted with acidic or basic groups to form polyanions with weak binding sites for alkali cations. We review both 'base-in-chain' and 'acid-in-chain' approaches to this type of polyanion. When the anionic groups are optimally separated, the conductivities of the polymers are found to be high relative to those of most single ionic conducting polymers and even most non-imide salt-in-polymer electrolytes. The concentration of ionic groups, can be varied using polyethylene glycol links (spacers) of variable length. The conductivity is found to maximize near the value which maximizes the conductivity in simple salt-in-fully amorphous polyether polymers (the number of the ethyleneoxy repeating unit n = 12). Finally a novel process, which achieves the same objective by a different route, will be described. This class of weakly coordinating polyanionic electrolyte, in which the coulomb traps for Li⁺ are little if at all stronger than the polyether chelation traps, is seen as a promising development in the solid polymer electrolyte field. Except for the case of 'weak trap' acid-in-chain polymers, all these electrolytes are unicationic in their conduction.