Abstract
Thin‐film cathodes of lithium manganese oxide, 0.3–3 μm thick, were deposited by rf magnetron sputtering of a 
ceramic target onto unheated substrates. The resulting films were dense, 
, with a ∼50 Å nanocrystalline spinel structure. The film composition was typically 
and 1.2 < 
< 2.2. When cycled in a thin‐film rechargeable lithium battery, specific cathode capacities of 145 ± 23 and ∼270 mAh/g were realized for discharge from 4.5 V to either 2.5 or 1.5 V, respectively. The discharge and charge current densities were limited by the resistivity of lithium transport into and through the cathode. After thousands of cycles at 25°C, there was a small increase in cell resistance. After several hundred cycles at 100°C, the discharge curves developed a stable knee at ∼4 V characteristic of crystalline 
cathodes. The polarization of the discharge/charge cycles were interpreted in terms of free energy of mixing curves. © 1999 The Electrochemical Society. All rights reserved.