Growth of LiMn2O4 thin films by pulsed-laser deposition and their electrochemical properties in lithium microbatteries

Films of LiMn2O4 were grown by pulsed-laser deposition (PLD) onto silicon wafers using sintered targets which consisted in the mixture of LiMn2O4 and Li2O powders. The film formation has been studied as a function of the preparation conditions, i.e. composition of the target, substrate temperature, and oxygen partial pressure in the deposition chamber. Composition, morphology and structural properties of PLD films have been investigated using Rutherford backscattering spectrocopy, scanning electron microscopy, X-ray diffraction and Raman scattering spectroscopy. The films deposited from target LiMn2O4+15% Li2O have an excellent crystallinity when deposited onto silicon substrate maintained at 300°C in an oxygen partial pressure of 100 mTorr. It is found that such a film crystallizes in the spinel structure (Fd3m symmetry) as evidenced by X-ray diffraction. Well-textured polycrystalline films exhibit crystallite size of 300 nm. Pulsed-laser deposited LiMn2O4 thin films obtained with a polycrystalline morphology were successfully used as cathode materials in lithium microbatteries. The Li//LiMn2O4 thin film cells have been tested by cyclic voltammetry and galvanostatic charge-discharge techniques in the potential range 3.0–4.2 V. Specific capacity as high as 120 mC/cm2 μm was measured on polycrystalline films. The chemical diffusion coefficients for the LixMn2O4 thin films appear to be in the range of 10−11–10−12 cm2/s. Electrochemical measurements show a good cycleability of PLD films when cells are charged-discharged at current densities of 5–25 μA/cm2.