Characterization and Electrochemical Performance of Substituted LiNi_0.4Co_0.2-yAl_yMn_0.4O₂ (0≤y≤0.2) Cathode Materials

A complete series of LiNi_0.4Co_0.2-yAl_yMn_0.4O₂ (0{less than or equal to}y{less than or equal to}0.2) materials have been synthesized and investigated as cathode materials for lithium ion batteries. When cycled between 2.0 and 4.3 V vs. Li/Li⁺ at a current density of 0.1 mA/cm², stable capacities of ~160 mAh/g for y=0 to ~110 mAh/g for y=0.2 are achieved. Upon increasing the current density, it is found that all materials containing aluminum show reduced polarization and improved rate performance. The optimal performance at all current densities was found for the compound with y=0.05. The effect of aluminum substitution on the crystal structure of the host is discussed.