A positive electrode active material precursor for a nonaqueous electrolyte secondary battery is provided that includes a nickel-cobalt-manganese carbonate composite represented by general formula Ni.sub.xCo.sub.yMn.sub.zM.sub.tCO.sub.3 (where x+y+z+t=1, 0.05?x?0.3, 0.1?y?0.4, 0?t?0.1, and M denotes at least one additional element selected from a group consisting of Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, and W) and a hydrogen-containing functional group. The ratio H/Me of the amount of hydrogen H to the amount of metal components Me included in the positive electrode active material precursor is less than 1.60. The positive electrode active material further includes a secondary particle formed by a plurality of primary particles that have been aggregated.

A positive-electrode active material precursor for a nonaqueous electrolyte secondary battery, contains a nickel-cobalt-manganese carbonate composite represented by a general formula of Ni.sub.xCo.sub.yMn.sub.zM.sub.tCO.sub.3 where x+y+z+t=1, 0.0x0.3, 0.1y0.4, 0.55z0.8, and 0t0.1 are satisfied; and M represents one or more additive elements selected from among Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, and W. The positive-electrode active material precursor includes secondary particles having an average particle diameter greater than or equal to 4 m and less than or equal to 9 m. The secondary particle includes a sparse central portion and a dense outer shell portion outside of the central portion, formed of primary particles.

A positive-electrode active material precursor for a nonaqueous electrolyte secondary battery, contains a nickel-cobalt-manganese carbonate composite represented by a general formula of Ni.sub.xCo.sub.yMn.sub.zM.sub.tCO.sub.3 where x+y+z+t=1, 0.0x0.3, 0.1y0.4, 0.55z0.8, and 0t0.1 are satisfied; and M represents one or more additive elements selected from among Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, and W. The positive-electrode active material precursor includes secondary particles having an average particle diameter greater than or equal to 4 m and less than or equal to 9 m. The secondary particle includes a sparse central portion and a dense outer shell portion outside of the central portion, formed of primary particles.

A positive-electrode active material precursor for a nonaqueous electrolyte secondary battery is provided that includes a nickel-cobalt-manganese carbonate composite represented by general formula Ni.sub.xCo.sub.yMn.sub.zM.sub.tCO.sub.3 (where x+y+z+t=1, 0.05x0.3, 0.1y0.4, 0.55z0.8, 0t0.1, and M denotes at least one additional element selected from a group consisting of Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, and W) and a hydrogen-containing functional group, wherein H/Me representing the ratio of the amount of hydrogen to the amount of metal components Me included in the positive-electrode active material precursor is greater than or equal to 1.60.

A positive-electrode active material precursor for a nonaqueous electrolyte secondary battery is provided that includes a nickel-cobalt-manganese carbonate composite represented by general formula Ni.sub.xCo.sub.yMn.sub.zM.sub.tCO.sub.3 (where x+y+z+t=1, 0.05x0.3, 0.1y0.4, 0.55z0.8, 0t0.1, and M denotes at least one additional element selected from a group consisting of Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, and W) and a hydrogen-containing functional group, wherein H/Me representing the ratio of the amount of hydrogen to the amount of metal components Me included in the positive-electrode active material precursor is greater than or equal to 1.60.

A method for manufacturing a positive-electrode active material precursor for a nonaqueous electrolyte secondary battery containing a nickel-cobalt-manganese carbonate compound includes: an initial aqueous solution preparation process of preparing an initial aqueous solution; a nucleation process of forming nuclei; and a nucleus growth process of growing the nuclei. In the nucleation process, a pH value of the mixed aqueous solution is controlled to be greater than or equal to 8.0 at the reference reaction temperature of 25? C. In the nucleus growth process, the pH value of the mixed aqueous solution is controlled to be greater than or equal to 6.0 and less than or equal to 7.5 at the reference reaction temperature of 25? C. The nucleation process takes a time greater than or equal to 1/20 and less than or equal to 3/10 of a combined time of the nucleation process and the nucleus growth process.

A method for manufacturing a positive-electrode active material precursor for a nonaqueous electrolyte secondary battery containing a nickel-cobalt-manganese carbonate compound includes: an initial aqueous solution preparation process of preparing an initial aqueous solution; a nucleation process of forming nuclei; and a nucleus growth process of growing the nuclei. In the nucleation process, a pH value of the mixed aqueous solution is controlled to be greater than or equal to 8.0 at the reference reaction temperature of 25? C. In the nucleus growth process, the pH value of the mixed aqueous solution is controlled to be greater than or equal to 6.0 and less than or equal to 7.5 at the reference reaction temperature of 25? C. The nucleation process takes a time greater than or equal to 1/20 and less than or equal to 3/10 of a combined time of the nucleation process and the nucleus growth process.

Provided are an impurity-element removing method for selectively removing magnesium from a nickel-containing solution, and a method for producing high-purity nickel sulfate using the impurity-element removing method. The production method includes a production process in the production method of producing high-purity nickel sulfate from a nickel-containing solution, and the nickel-containing solution in the production process is subjected to an impurity-element removal treatment that includes: a hydroxylation step of adding an alkali hydroxide to the nickel-containing solution in the production process to form a hydroxylated slurry; a carbonation step of adding an alkali carbonate to the hydroxylated slurry to form a carbonated slurry, and recovering nickel component from the solution; a solid-liquid separation step for the slurry thus obtained; and a neutralization step of subjecting a solution after reaction obtained by solid-liquid separation to a neutralization, and recovering an impurity element included in the nickel-containing solution in the production process.

A manganese-based carbonate precursor of a positive electrode material for a secondary battery has a specific structure and composition and contains a trace amount of uniformly distributed Na element, a content of Na is in a range of 0.5-3 mol %, which range can ensure that the structural integrity and consistency of carbonate crystals are not affected. In addition, the trace amount of Na element is uniformly distributed inside the manganese-based carbonate precursor provided in the present application, and by means of simple mixing with a lithium source and sintering, a lithium-rich manganese-based material uniformly doped with Na element can be directly obtained without the need for introducing other Na source, whereby uneven doping of Na is effectively avoided, the doping effect is improved, and the electrical properties of the material are significantly improved.

A manganese-based carbonate precursor of a positive electrode material for a secondary battery has a specific structure and composition and contains a trace amount of uniformly distributed Na element, a content of Na is in a range of 0.5-3 mol %, which range can ensure that the structural integrity and consistency of carbonate crystals are not affected. In addition, the trace amount of Na element is uniformly distributed inside the manganese-based carbonate precursor provided in the present application, and by means of simple mixing with a lithium source and sintering, a lithium-rich manganese-based material uniformly doped with Na element can be directly obtained without the need for introducing other Na source, whereby uneven doping of Na is effectively avoided, the doping effect is improved, and the electrical properties of the material are significantly improved.