Abstract: An energy storage device with improved capacity contains an anode from the Group Ia elements, an electrolyte capable of ion transport of anode species and a cathode comprising a layered crystalline material of the formula G.sub.x Me.sub.y Ch.sub.z, where G is at least one guest element selected from the Group Ia elements and 0.0.ltoreq.x.ltoreq.10; Me is selected from the group containing Bi and Sb and y=1, 2; and Ch is a chalcogenide element selected from the group containing S, Se and Te, and z=1, 2, 3. The layered crystalline material is characterized in that is has a sufficiently low defect density and appropriate impurity distribution, together sufficient to permit intercalation of at least 3 moles of lithium within van der Waals channels per one mole of said material without significant distortion of the lattice, said material further characterized in that the change in Gibbs free energy is substantially independent of the lithium intercalant concentration.

Abstract: A double layer electrolytic capacitor of two electrodes each in contact with a common electrolyte. At least one of the electrodes is comprised of a crystalline material characterized by the presence of van der Waals channels in the material. These van der Waals channels are adapted to accommodate the electrolyte within the channels, such that a double layer of charge is formed at interfaces of the van der Waals channels and the electrolyte when a voltage is applied between the two electrodes.