Changes in Structure and Cathode Performance with Composition and Preparation Temperature of Lithium Cobalt Nickel Oxide

Abstract

The electrochemical behavior of (y = 0.88 and 0.13) solid solutions obtained in the 450–800 °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 °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 pre‐pared above 650 °C, the single‐phase extraction preserved the trigonal lattice up to 4.2 V with a marked increase in the c/a ratio. For Ni‐rich compositions, cell performance was poor for samples prepared below 750 °C. However, a sample pre‐pared at 750 °C showed reversible extraction by a single‐phase mechanism and a simple voltammogram, which differed markedly from electrodes. Ex situ electron paramagnetic resonance studies of 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 °C.