Lithium doping of cobalt-nickel spinel oxides at low temperatures

Article abstract of DOI:10.1016/0025-5408(96)00046-3

Cobalt-nickel spinel oxides containing lithium (Li_y(Ni_xCo_1-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, Ni_xCo_1-x(OH)(NO₃)·H₂O in a lithium nitrate medium. XRD analysis, DTA and magnetic susceptibility measurements show that double-chain Ni_xCo_1-x(OH)(NO₃)·H₂O 0 < x < 0.4 decomposes to nickel-cobalt spinels via layered hydroxide-nitrates Ni_xCo_1-x(OH)_1.5(NO₃)_0.5, but in a LiNO₃ medium, lithium containing nickel-cobalt spinels Li_y(Ni_xCo_1-x)_3-yO₄ are obtained, preceded by a complete oxidative hydrolysis of double-chain Ni_xCo_1-x(OH)(NO₃)·H₂O to layered oxide-hydroxides Ni_xCo_1-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 Ni_xCo_1-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(Ni_xCo_1-x)_3-yO₄ (y ≈ 0.13, x ≈ 0.4) spinels and a rock-salt Ni_1-bCo_bO (b ≤ 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.