Characterization of pulsed laser-deposited LiMn₂O₄ thin films for rechargeable lithium batteries

The structure and characteristics of thin films of Li_xMn₂O₄ spinel prepared by pulsed laser deposition are reported. X-Ray Diffraction (XRD), Rutherford Backscattering Spectroscopy (RBS) and Nuclear Reaction Analysis (NRA) show that the lithium content of the film is very sensitive to the conditions of deposition. A large target–substrate distance (9 cm) and a stoichiometric LiMn₂O₄ target lead to lithium deficient films, whereas lithium excess films are obtained for a shorter target–substrate distance (5 cm) and a target prepared with excess lithium (10% excess). SEM and AFM measurements show that the films are dense and quite rough. The local structure of the films was studied by infrared spectroscopy. The Fourier Transform Infrared Spectroscopy spectrum of LiMn₂O₄ consists of 2 major bands, the positions of which depend on the thickness of the film. The evolution of the FT-IR spectrum of Li_xMn₂O₄ over the temperature range −150°C to 250°C clearly shows the previously reported temperature-induced Jahn–Teller distortion between O and 10°C.