An electrochemical in-situ cell for diffraction studies of battery materials has been developed. The cell works in transmission geometry with sample rotation, and the performance was characterized by experiments on the cathode material LiMn2O4. Several charge and discharge cycles can be studied over a few days without any misfunction of the cell. The quality of the obtained data allows for full structure refinements by the Rietveld method. The whole set-up is about I turn thin and consists of an aluminum piston as cathode current collector with a thickness below 0.1 mm in direct contact with a pellet of active cathode material, carbon black and binder. The lithium anode is separated from the cathode by a glass-fibre, soaked with electrolyte. The very good time and angular resolution of this set-up reveals three distinct spinel phases for different charging states of LiMn2O4, prepared by subsolidus reaction. (c) 2005 Elsevier B.V. All rights reserved.