Preparation of an Li0.7Ni0.8Co0.2O2 Electrode Material from a New Li—Co—Ni Mixed-Citrate Precursor.

A new chemical route to prepare the mixed oxide Li 0 . 7 Ni 0 . 8 -Co 0 . 2 O 2 , which is a member of the well-known Li-Ni-Co-O family that is of interest as an electrode material for rechargeable lithium batteries, from a mixed citrate is reported. In a first step the new citrate (NH 4 ) 3 LiNi 0 . 8 Co 0 . 2 (C 6 H 5 O 7 ) 2 , is synthesized, which, after thermal decomposition, gives the layered mixed-oxide phase Li 0 . 7 Ni 0 . 8 Co 0 . 2 O 2 . This oxide has been characterized by chemical analysis, XRD, FTIR, SEM, and DTA, revealing an "ideal" trigonal α-NaFeO 2 type structure with a well-ordered distribution of Li and Ni ions in different lattices. Thermoelectric power and four-point electrical conductivity measurements indicate a nonactivated conductivity mechanism of a small polaron. The Li 0 . 7 Ni 0 . 8 Co 0 . 2 O 2 compound prepared by this so-called "citrate route" has a better reversibility of Li-insertion in charge-discharge cycles than related phases reported previously.