Superior capacity retention spinel oxyfluoride cathodes for lithium-ion batteries

Spinel LiMn2-y-zLiyMzO4-eta F eta (M = Ti, Ni, and Cu) oxyfluoride cathodes have been synthesized by firing the cation-substituted LiMn2-y-zLiyMzO4 oxides with NH4HF2 at a moderate temperature of 450 degrees C. With this low-temperature approach, fluorine contents up to eta = 0.21 could be incorporated into the spinel lattice. The oxyfluoride compositions such as LiMn1.8Li0.1Ni0.1O3.8F0.21 exhibit excellent capacity retention at 60 degrees C with capacities over 100 mAh/g and good rate capability. The superior electrochemical performance is found to be due to a smaller lattice parameter difference between the two cubic phases formed during the charge-discharge process and the consequent suppressed manganese dissolution. (c) 2006 The Electrochemical Society.