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+delta with the layered-type, rhombohedral alpha-NaFeO2 st ructure (R (3) over bar m) prepared by means of a new solution techniq ue has been correlated to their manganese content. Test electrodes wer e developed and their porosity was tuned by using either graphite or c arbon black as an electronically conductive additive. The amount of ca rbon was optimized to achieve the maximum specific charge referred to the oxide fraction of the electrode mass. Porosities of <20% were meas ured for graphite-based electrodes, with median pore diameters between 0.1 and 0.01 mu m. In the case of the carbon black-based electrodes, lar pr pore sizes and porosities of >40% were obtained for relatively small preparation pressures, leading to better wetting properties of t he electrode and maximum specific charges of about 170 mAh g(-1) (refe rred to the oxide) for materials with the best insertion performances, in contrast to about 150 mAh g(-1) for oxide/graphite electrodes. A s lightly better stability during cycling was observed for graphite-base d electrodes which were therefore used for comparative studies. The sp ecific charge and cycling stability of the solution-prepared pure lith ium nickel oxide LiNiO2 was low but was significantly enhanced by repl acing some nickel with manganese. With increasing manganese content, t he 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. (C) 1997 Elsevier Science S.A.