LI DEINTERCALATION-INTERCALATION REACTION AND STRUCTURAL-CHANGE IN LITHIUM TRANSITION-METAL NITRIDE, LI7MNN4

Li7MnN4 which has cubic symmetry, P43n, a = 9.5453 is prepared by heating a mixture of Li3N and Mn4N in a 1%H-2-99%N2 gas stream. The Li ion is easily deintercalated in a Li/Li7MnN4 cell forming Li7-xMnN4 over a wide range of 0 less-than-or-equal-to x less-than-or-equal-to 1.25. The specific capacity of the cell is about 210 mAhg-1. With an increase in x, a new phase which also has cubic symmetry but has a smaller lattice parameter appears. The original phase decreases with an increase in x, and disappears at x = 0.625. A two-phase reaction then occurs. In the range of 0.625 less-than-or-equal-to x less-than-or-equal-to 1.25, the lattice parameter of the second phase decreases with an increase in x. The Li/Li7MnN4 cell shows a good reversibility under high current density (1200 muA/cm2). Li7MnN4 is thus suggested to be a good candidate for an electrode for a lithium secondary battery.