Electrolyte for an electrochromic display

摘要

An electrolyte for an electrochromic display of the kind in which a persistent colored species of an electrochromic substance in solution is deposited onto a display electrode upon the passage of current therethrough is disclosed. The electrolyte comprises an aqueous solution of a di-alkyl bipyridinium salt and a non-polymeric aliphatic alcohol in which either: (a) both alkyl groups of the bipyridinium salt have an odd number of carbon atoms and the alcohol has an even number of carbon atoms; or (b) both alkyl groups of the bipyridinium salt have an even number of carbon atoms and the alcohol has an odd number of carbon atoms. The presence of an alcohol in the electrolyte inhibits recrystallization (spotting) and non-erasure of the display electrodes. A particularly effective alcohol for 1,1' di-heptyl 4,4' bipyridinium dibromide, which has a severe lifetime problem, is n-hexanol.