Recent advances in mixed metal oxide (LiNi1−xCoxO2) cathode materials for lithium ion (Li-ion) batteries have resulted in a new generation of high capacity cathode materials. High capacity materials are particularly useful for applications where either volume or weight is limited, such as in space applications. These applications also benefit from cell chemistries with high energy efficiency as this permits reduced ancillary energy storage and dissipation apparatus. Mixed metal oxide materials have been evaluated and demonstrated in prismatic Li-ion cells. The capacity of the mixed metal oxide materials is exceptional, reversible capacity of 160mAh/g is demonstrated although the cell voltage is lower than when LiCoO2 materials are used, 3.58V vs. 3.74V, at low (0.5mA/cm2) discharge rates. The high capacity results in a significant improvement in specific energy, further, the sloping discharge curve characteristic of the mixed metal oxide materials facilitates determination of the state of charge based on cell voltage. The design of composite cathode materials using the mixed metal oxide materials has a significant influence on the cell impedance and the rate capability of the material. Results describing the rate capability of these materials is presented.