Abstract: Electrochemical insertion of lithium into titanium dioxide initially in its rutile form, the insertion being performed at an elevated temperature (for example 120.degree. C.), produces a material Li.sub.x TiO.sub.2 with x between 0.5 and 1.0. This material is suitable as an active cathode material in a secondary cell as it can be repeatedly recycled. The material has a crystal struture, different from that of the initial rutile titania, which is believed to be hexagonal.

Abstract: A secondary cell includes as its active cathode material a first insertion material, such as V.sub.6 O.sub.13, into which ions are inserted during discharge. To prevent irreversible lattice changes leading to a decline in capacity the discharge should be terminated before a threshold cell voltage is crossed. Such irreversible changes are suppressed by including in a surface coating of the cathode a minor proportion of a second insertion material, such as a titanium oxide, whose discharge commences before the threshold cell voltage is reached.