There is disclosed a secondary battery wherein either one of positive electrode and negative electrode elements is made of an active material, the color of which is changed according to a voltage between these electrodes and wherein= a window is formed for observing the color change of the electrode. Further, an electrochromic display device is disclosed in which a working electrode is made of a pyrolytic carbonaceous material which is obtained by thermal decomposition of a hydrocarbon compound at a low temperature of about 1,000.degree. C.

This invention is directed to a method for patterning colorable areas of an electrochromic device. The device comprises two substrates and therebetween: one electrode layer; an electrochromic layer; an insulator material which is (i) non-ionically conductive and (ii) electronically insulating; a solid ion conductive material; and another electrode layer, at least one of the one electrode layer and the other electrode layer being transparent and each electrode layer being in contact with a respective one of the substrates. The ion conductive layer is adapted to communicate ions to and from the electrochromic layer upon application of a voltage across the electrode layes. The method comprises providing areas of the surface of the electrochromic layer which are not to be colorable during operation of the device in contact with the insulator material and not in contact with the ion conductive material, and providing the colorable areas of the surface of the electrochromic layer, which are to be colored upon application of a voltage across the electrode layers, in contact with the ion conductive material. Another aspect of this invention is directed to an electrochromic device patterened according to the method described above.