A method is provided for forming a porous, electrochemically active lithium manganese oxide layer on a substrate, the method comprising: depositing a porous manganese oxide layer on the substrate; providing a Li containing layer on the porous manganese oxide layer; and afterwards performing an annealing step at a temperature in the range between 200° C. and 400° C., thereby inducing a solid-state reaction between the porous manganese oxide layer and the Li containing layer. The method may further comprise, before depositing the porous manganese oxide layer: depositing a seed layer on the substrate. A method of the present disclosure may be used for forming electrode layers of lithium-ion batteries.