Lithium doping of cobalt-nickel spinel oxides at low temperatures

Cobalt-nickel spinel oxides containing lithium (Liy(NixCo1 − x)3 − yO4, y ≈ 0.13, 0 ≤ x ≤ 0.4) are prepared by thermal decomposition of mixed cobalt-nickel hydroxide-nitrates with a double-chain structure, NixCo1 − x(OH)(NO3) · H2O in a lithium nitrate medium. XRD analysis, DTA and magnetic susceptibility measurements show that double-chain NixCo − x(OH)(NO3)-H2O 0 < x < 0.4 decomposes to nickel-cobalt spinels via layered hydroxide-nitrates NixCo1 − x(OH)1.5(NO3)0.5, but in a LiNO3 medium, lithium containing nickelcobalt spinels Liy(NixCo1 − x)3 − yO4 are obtained, preceded by a complete oxidative hydrolysis of double-chain NixCo1 − x(OH)(NO3) · H2O to layered oxide-hydroxides NixCo1−xOOH. The lithium doping of nickel-cobalt spinels at low-temperature is explained in terms of the ion-exchange properties of the layered oxide-hydroxides NixCo1 − xOOH in a LiNO3 melt. With increasing nickel content (0.4 < x < 1), the thermal decomposition of the coprecipitated cobalt-nickel hydroxide-nitrates in a lithium nitrate medium leads to the formation of two phases consisting of Liy(NixCo1 − x)3 − yO4 (y ≈ 0.13, x ≈ 0.4) spinels and a rock-salt Ni1−bCobO (b ≤ 0.1), the relative amount of the latter increasing with the nickel content in the precursor mixture. Lowtemperature lithium doping of NiO can not be achieved with this preparation procedure since Ni(OH)(NO3) · H2O hydrolyses only to a layered nickel hydroxide-nitrate Ni(OH)1.5(NO3)0.5 in a lithium nitrate medium.