The invention concerns a folding roof for vehicle, comprising a rigid front roof element, a rigid intermediate roof element and a rigid rear roof element. The device further has an adaptor that supports the processing unit and the storage unit, when the adaptor is attached to the support stand. By forming the primary particles for composing particles of the iron compound as a pore-free matter, being controlled in a range of 1 to 300 nm, nano effects are brought about, and it is also effective to suppress excessive increase of surface area which may lead to promotion of decomposition of electrolyte, and an excellent discharge capacity is realized stably for a long period.