Abstract: A method of recovering valuable materials from lithium batteries wherein a lithium/transition metal composite oxide is used as a positive electrode active material. In this disposal method, a sheeted positive electrode having a positive electrode active material disposed on a positive electrode collector is immersed in an oxalic acid solution. By virtue of this oxalic acid treatment (step 240), any lithium element contained in the positive electrode active material can be leached into the oxalic acid solution. Using oxygen gas produced by a reaction between the positive electrode active material and oxalic acid, attachments, such as the positive electrode active material, can be self-detached from the positive electrode collector. The transition metal element contained in the positive electrode active material is converted by the oxalic acid treatment to insoluble transition metal compounds (oxalate, oxide, etc.).