Influence of experimental parameter on the Li-content of LiMn2O4 electrodes produced by pulsed laser deposition

Abstract

Thin film deposition by pulsed reactive crossed beam laser ablation has often advantages such as no need for annealing after deposition over conventional pulsed laser deposition. However, when depositing material from a target containing a low atomic mass component such as lithium, the resulting films are frequently sub-stoichiometric in the light elements. This is most probably due to scattering of the plasma plume in the crossed gas pulse, which creates a high local pressure. The light species are scattered more than the heavier elements, which leads to Li-deficiencies in the resulting film. Depositing lithium-spinels without the use of a crossed gas pulse is still strongly dependent on the applied background pressure. A background pressure below 10 Pa results also in lithium-deficient films. However, this is not due to scattering effects but very probably to the evaporation of lithium oxide from the growing film. These boundary conditions allow only a window of conditions for the growth of stoichiometric LiMn2O4 films that is useful as test electrodes for Li-batteries research. A strong influence of the experimental parameters was observed. The films deposited at different background pressures and different substrate/target distances showed very different behaviors in the electrochemical measurements. Extraction and insertion of lithium was only detected for films deposited at a distance between 3 and 4 cm and at a background pressure of 20 Pa, whereas films deposited at other conditions did not show this electrochemical activity.