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 w afers using sintered targets which consisted in the mixture of LiMn2O4 and Li2O powders. The film formation has been studied as a function of the prep aration conditions, i.e. composition of the target, substrate temperature, and oxygen partial pressure in the deposition chamber. Composition, morphol ogy and structural properties of PLD films have been investigated using Rut herford backscattering spectrocopy, scanning electron microscopy, X-ray dif fraction and Raman scattering spectroscopy. The films deposited from target LiMn2O4 + 15% Li2O have an excellent crystallinity when deposited onto sil icon substrate maintained at 300 degrees C in an oxygen partial pressure of 100 mTorr. It is found that such a film crystallizes in the spinel structu re (Fd3m symmetry) as evidenced by X-ray diffraction. Well-textured polycry stalline films exhibit crystallite size of 300 nm. Pulsed-laser deposited L iMn2O4 thin films obtained with a polycrystalline morphology were successfu lly used as cathode materials in lithium microbatteries. The Li//LiMn2O4 th in film cells have been tested by cyclic voltammetry and galvanostatic char ge-discharge techniques in the potential range 3.0-4.2 V. Specific capacity as high as 120 mC/cm(2) mu m was measured on polycrystalline Mms. The chem ical diffusion coefficients for the LixMn2O4 thin films appear to be in the range of 10(-11)-10(-12) cm(2)/s. Electrochemical measurements show a good cycleability of PLD films when cells are charged-discharged at current den sities of 5-25 mu A/cm(2). (C) 2000 Elsevier Science S.A. All rights reserv ed.