The systems Li1-xMn2-xO4-delta acid Li1-xNi1+xO2 were studied as oxidic cathode materials for 4 V rechargeable Li-ion cells. From a comparison of the results it follows that the spinel system can be subdivided into three regions: in region I (0 less than or equal to x < 0.05) the electrochemical performance is unsatisfying due to a large volume reduction of about 7.5%, inducing stress, multiphase materials and capacity fading. Region II (0.05 less than or similar to x less than or similar to 0.2) contains the best cathode material with a composition near x = 0.1. The spinel framework is stable against Li extraction. In region III (0.2 less than or equal to x less than or equal to 1/3) the capacity is too low for an application in the 4 V region. In the system Li1-xNi1+xO2 the highest capacity is observed for LiNiO2 with x = 0. Experimental difficulties during material synthesis were overcome by suppression of the decomposition of LiNiO2 into Li1-xNi1+xO2, Li2O and O-2.