LITHIUM-TRANSITION NITRIDE SYSTMES FOR THE ELECTRODE OF LITHIUM SECONDARY BATTERY

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We have prepared a series of compounds in Li-M-N (M=Co, Ni, Cu) systems and found that they show remarkable electrode properties for a lithium secondary battery, especially as the anode material.Lithium transition metal nitrides, Li_<3-x>M_xN (M=Co, Ni, Cu), were synthesized from Li_3N and metallic powder under a N_2 gas stream. Metal ions are substituted for the Li site in the range of 0*x*0.5,0*x*0.6, and 0*x0.3 for M=Co, Ni, and Cu, respectively.Li/Li_<3-x-z>M_xN cells were sycled in the range of 0*z1.0 and showed a high capacity of 900mAh/g in Li_<2.6-z>Co_<0.4>N,and 750mAh/g in Li_<.6-z>Cu_<0.4>N,but only 200mAh/g in Li_<2.5-z>Ni_<0.5>N.The high capacity in M=Co and Cu was due to the amorphous phase formed during the 1st charge, which shows good reversibility and low potential to Li metal (0.5V in average).The crystalline Li_<3-x-z>M_xN (M=Co and Cu) can deintercalate and intercalate Li ions only in the limited z range. On the contrary, Li ion is deintercalated and intercalated in Li_<3-x-z>Ni_xN more widely (at least z-0.5) showing small change of the cell volume. Li_<3-x>M_xN (M=Co and Cu) is thus suggested to be a good candidate for an anode in a lithium secondary battery because of their good reverisibility and low voltage in Li/Li_<3-x>M_xN cells.