The electrochemical behavior of Li1-x(NiyCo1-y)(1+x)O-2 (y = 0.88 and 0.13) solid solutions obtained in the 450-800 degrees C temperature range was studied by step potential electrochemical spectroscopy. The intensity vs voltage curves for cobalt-rich compositions displayed two well-defined signals during Cell charge, which were located at ca. 3.6 and 3.9 V. The low-voltage signal was due to nickel oxidation. For samples prepared below 750 degrees C, the first step of the deintercalation from the pseudospinel phase contributed to this effect, whereas the second was responsible for the 3.9 V peak. For samples prepared above 650 degrees C, the single-phase extraction preserved the trigonal lattice up to 4.2 V with a marked increase in the cia ratio. For Ni-rich compositions, cell performance was poor for samples prepared below 750 degrees C. However, a sample prepared at 750 degrees C showed reversible extraction by a single-phase mechanism and a simple voltammogram, which differed markedly from LiNiO2, electrodes. Ex situ electron paramagnetic resonance studies of Ni3+; ions in the electrodes after the first cycle revealed a better recovery of the oxidation state of metal ions for the nickel-rich composition at 750 degrees C.