Electrochemical cells generally have a negative electrode, a positive electrode, and an electrolyte placed between the electrodes. The electrolyte is chosen so that transfer of ions between the two electrodes occurs, thus producing an electrical current. One example of an electrochemical cell is a rechargeable battery. The use of non-layered LiMnO.sub.2 in secondary batteries is proposed in JP 6036799. The use of layered materials such as lithium cobalt oxide, LiCoO.sub.2, as the positive electrode in such a rechargeable battery is well established. The layered material LiCoO.sub.2 consists of sheets of oxygen ions stacked one on top of the other. Between the first and second layers of oxygen are located the cobalt ions, with the lithium ions being located between the second and third oxygen layers. Use of LiCoO.sub.2 in rechargeable batteries allows greater energy storage per unit weight and volume than is possible in conventional rechargeable batteries such as nickel-cadmium. However LiCoO.sub.2 has disadvantages in that it is somewhat toxic, has limited energy storage capacity, and the cobalt containing materials from which it is produced are expensive and scarce.
Attempts have been made to use other compounds with a similar layered structure to that of LiCoO.sub.2, such as LiNiO.sub.2, and LiFeO.sub.2. EP 0 017 400 discloses a range of compounds having layers of the .alpha.-NaCrO.sub.2 structure and GB 2242898 discloses a range of compounds with a layering intermediate that of a ABO.sub.2 structure and a spinel-type structure A(B.sub.2)O.sub.4. However, preparation of the materials according to the present invention is not taught and could not be achieved; see for example E. Rossen, C. D. W. Jones, and J. R. Dahn, "Structure and electrochemistry of Li.sub.x Mn.sub.y Ni.sub.1-y O.sub.2 ", Solid State Ionics, 57 (1992), 311-318.
It is one aim of the present invention to provide a novel layered manganese oxide material which can be used in electrochemical cells.