Cobalt-nickel spinel oxides containing lithium (Li-y(NixCo1-x)(3-y)O-4, y approximate to 0.13, 0 less than or equal to x less than or equal to 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 NixCo1-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 nickel-cobalt spinels Li-y(NixCo1-x)(3-y)O-4 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 Li-y(NixCo1-x)(3-y)O-4 (y approximate to 0.13, x approximate to 0.4) spinels and a rock-salt Ni1-bCobO)b less than or equal to 0.1), the relative amount of the latter increasing with the nickel content in the precursor mixture. Low-temperature 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.