Defective lithium manganospinel films with excellent electrochemical characteristics

Major effort in the past two decades has been focused on rechargeable batteries with high capacity, long cycle life, and high discharge rate capabilities. Although several approaches in LiMn2O4-based cathodes have been tried, including composition and doping variation, formation of novel phases, and microstructural tailoring, none of the materials has successfully satisfied all of the above criteria. We show the formation of metastable oxygen-rich lithium manganospinels, using a unique UV assisted deposition process, which results in thin film cathodes that exhibit high capacity (>230 mAh/gm), long cycle life (<0.05% capacity loss per cycle for 700 cycles), and high discharge rates (>25 C for 25% capacity loss). The long cycle life and high capacity was attributed to the ability to cycle the Mn+ valence to less than 3.5 without onset of Jahn-Teller structural transformation, while the high discharge rate was attributed to the extremely high diffusivity of Li+ in the defective Li1-8Mn2-2deltaO4 phase. In addition, these films also exhibit the ability to be cycled at both 3 and 4 V regions. (C) 2002 The Electrochemical Society.