Improved electrochemical performances of oxygen plasma treated LiMn2O4 thin films

LiMn2O4 spinel thin films were deposited by radio frequency (rf) magnetron sputtering followed by annealing at 600 degrees C in air. The films were then post-treated with an rf driven oxygen plasma. The crystallization and surface morphology of LiMn2O4 thin films were seen to change with rf power. The treated samples were tested under harsh conditions such as deep discharge to 1.5V and cycling at elevated temperature of 60 degrees C to verify the electrochemical performances of LiMn2O4 cathodes. The oxygen plasma treatments improved the electrochemical properties of LiMn2O4 thin films significantly. As the cells were cycled in the range of 4.5-2.0V at 60 degrees C, the samples treated at a proper rf power of 50W exhibited an initial capacity greater than similar to 400 mAhg(-1) with reasonable cycling stability. The results were attributed to the change of morphology and the formation of a surface layer induced by the oxygen plasma irradiation.