Electrochemical and Physical Properties of Ti-Substituted Layered Nickel Manganese Cobalt Oxide (NMC) Cathode Materials

The effect of partial substitution of titanium for cobalt on 3b sites in Li 1+z (Ni x Mn x Co 1-2x-y Ti y )O 2 (x = 1/3, 0.4) cathode materials (NMCs) has been investigated for this study. Materials were prepared by glycine-nitrate combustion and co-precipitation methods and solid solutions were observed over a narrow substitution range limited to below about y = 0.07 for both the x = 1/3 and x = 0.4 series, although this depended on the synthesis technique. Increased discharge capacities, lower first cycle inefficiencies and better cycling behavior were observed for several of the Ti-substituted compositions in electrochemical cells. The improved first cycle efficiencies allow higher discharge capacities to be obtained between normal voltage limits, which partly explain the observations. Results from synchrotron X-ray diffraction also indicate that Ti substitution leads to a decreased cell volume change during deintercalation of lithium, which contributes to the improved cycling performance. Magnetic measurements suggest that reduction of some Mn 4+ to Mn 3+ compensates for the aliovalent substitution in as-made lithium-stoichiometric materials.