Recent advances in LiNixCo1-xO2 mixed metal oxide based cathode materials for Li-ion batteries have resulted in an improved generation of Li-ion cells for high capacity, long life batteries. Candidate cathode materials have been characterized and evaluated in prototype 3.5 Ah flat plate prismatic Li-ion cells. For comparison, 3.5 Ah prismatic Li-ion cells which used a LiCoO2 based cathode material were also evaluated. All cells in this study utilized a graphitic carbon based anode material. The most energy dense material evaluated, LiNixCo1-xO2 (x = 0.82), offered 206 mAh/g on the first charge and was cycled at the C/2 rate at 157 mAh/g in prototype 3 Ah cells with rate capability comparable to similar cells which used a LiCoO2 material. Prototype cells using this material offer 130 Wh/kg and 340 Wh/1. This cell design has been scaled to 20 Ah.