A vapour deposition method for preparing a multi-layered thin film structure comprises providing a vapour source of each component element of a compound intended for a first layer and a compound intended for a second layer, wherein the vapour sources comprise at least a source of lithium, a source of oxygen, a source or sources of one or more glass-forming elements, and a source or sources of one or more transition metals; heating a substrate to a first temperature; co-depositing component elements from at least the vapour sources of lithium, oxygen and the one or more transition metals onto the heated substrate wherein the component elements react on the substrate to form a layer of a crystalline lithium-containing transition metal oxide compound; heating the substrate to a second temperature within a temperature range of substantially 170° C. or less from the first temperature; and co-depositing component elements from at least the vapour sources of lithium, oxygen and the one or more glass-forming elements onto the heated substrate wherein the component elements react on the substrate to form a layer of an amorphous lithium-containing oxide or oxynitride compound.