Cycling performance of novel lithium insertion electrode materials based on the Li-Ni-Mn-O system

The electrochemical behavior of lithium—nickel—manganese mixed oxides LiNi1 − yMnyO2 + δ with the layered-type, rhombohedral α-NaFeO2 structure (R3m) prepared by means of a new solution technique has been correlated to their manganese content. Test electrodes were developed and their porosity was tuned by using either graphite or carbon black as an electronically conductive additive. The amount of carbon was optimized to achieve the maximum specific charge referred to the oxide fraction of the electrode mass. Porosities of <20% were measured for graphite-based electrodes, with median pore diameters between 0.1 and 0.01 μm. In the case of the carbon black-based electrodes, larger pore sizes and porosities of >40% were obtained for relatively small preparation pressures, leading to better wetting properties of the electrode and maximum specific charges of about 170 mAh g−1 (referred to the oxide) for materials with the best insertion performances, in contrast to about 150 mAh g−1 for oxide/graphite electrodes. A slightly better stability during cycling was observed for graphite-based electrodes which were therefore used for comparative studies. The specific charge and cycling stability of the solution-prepared pure lithium nickel oxide LiNiO2 was low but was significantly enhanced by replacing some nickel with manganese. With increasing manganese content, the specific charge increased to about 160 mAh g−1 for materials with an Ni:Mn ratio of about 1:1. It decreased gradually during cycling to about 80 mAh g−1 after 50 cycles.