Graphite has been widely used as the anode material of commercial Li-ion secondary battery. With the growing demands of high-capacity secondary battery, the low capacity of graphite (theoretical capacity: 372 mA h/g) has been thought to be the limiting factor in wide applications and a new anode material with a high capacity has been sought. Of the many materials, Li 2 . 6 Co 0 . 4 N showed the best anode performance. It showed very high capacity of 1024 mA h/g, good rate capability (1C/0.2C=94.94%) and extraordinary initial coulometric efficiency (96%). In addition to the excellent capacity of this material, its rate capability was much superior to that of graphite (82-88%). However, it cannot be commercialized because its capacity loss after 30 cycles is around 40%. As a result of various analyses, it was confirmed that the formation of passivating surface film caused by the decomposition reaction between electrolyte and Li 2 . 6 Co 0 . 4 N is the main reason of its cyclic degradation. As a method of improving the cyclic degradation, iron doping in Li 2 . 6 Co 0 . 4 N was suggested and we attempted to restrain the formation of passivating film on the surface of Li 2 . 6 Co 0 . 4 N. Li 2 . 6 Co 0 . 3 5 Fe 0 . 0 5 N had a bit lower capacity (about 900 mA h/g) than Li 2 . 6 Co 0 . 4 N (1024 mA h/g) but showed much better cycle life than Li 2 . 6 Co 0 . 4 N (35%->60% after 50 cycles).