Effects of Charge/Discharge of Li_<1-x>Ni_<1-y>Mn_yO_2 on Their Crystal Structures and Electronic States

概要

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The variations of structure and electrochemical properties of Li_<1-x>Ni_<1-y>Mn_yO_2(y=0 and 0.2)were studied as lithium was deintercalated from the materials. The LiNi_<1-y>Mn_yO_2 was prepared by easily available LiOH, Ni(OH)_2 and γ-MnOOH under air flow. Exchange of nickel into the lithium site(3(a)site)made it difficult for the lithium ion to move through the lithium layer, and decreased the electrical capacity for cyclic charge/discharge. Partial substitution of manganese for nickel was effective in preventing abrupt changes of the lattice constant c and Ni-O distances as x increases, resulting in suppressing the phase transitions(hexagonal→monoclinic→hexagonal). XPS, XANES and ESR analyses suggested that the charge compensation in charge/discharge of Li_<1-x>Ni_<0.8>Mn_<0.2>O_2 could be attributed to changing valences of nickel.
2000-09-15