Non-stoichiometry in LiMn2O4 thin films by laser ablation

We have demonstrated that thin films of LiMn2O4 deposited by laser ablation are stoichiometric when deposited in an oxygen pressure of 0.2 mbar on a substrate heated at 500°C. For higher oxygen pressures, the pure spinel structure is still obtained but non-stoichiometric. We show that the use of the unit cell volume determined by X-ray diffraction can be an accurate tool to determine the oxidation state of manganese in thin films. These results are confirmed by nuclear reaction analysis and X-ray absorption spectroscopy. Furthermore, we have tested the electrochemical properties of such films as a cathode in lithium batteries. The mobility of lithium within the structure determined by cyclic voltammetry depends on the quality of the films and is highest for the stoichiometric films.