FABRICATION OF THIN-FILM LIMN2O4 CATHODES FOR RECHARGEABLE MICROBATTERIES

We have fabricated thin-film cathodes of lithiated manganese oxide (Li(x)Mn2O4, where x less-than-or-equal-to 1), which can reversibly intercalate nearly one Li atom per unit formula, at a steady potential of 4.1 V. This results in a theoretical energy density of about 600 Wh/kg. The polycrystalline films (thickness of 0.5-2-mu-m) show electrochemical performance exceeding that of bulk materials. This is attributed to the small grain size and the porosity within these Li(x)Mn2O4 three-dimensional spinel films, reducing the diffusion path length for Li+ ions. The films are tested as the cathodes in about 70 charging/discharging cycles, in a secondary lithium cell, at current rates of 10-100-mu-A cm-2. No measurable self-discharge over 12 h periods is observed. These thin-film cathodes with above electrochemical properties are very promising for a new generation thin-film secondary batteries.