Abstract: To provide a carbonate compound and a cathode active material, whereby a lithium ion secondary battery having excellent cycle characteristics can be obtained. A process for producing a carbonate compound, which comprises mixing a sulfate (A) comprising a sulfate comprising a sulfate of Mn and a sulfate of Ni, or a sulfate comprising a sulfate of Mn, a sulfate of Ni and a sulfate of Co, and a carbonate (B) which is at least one carbonate selected from the group consisting of sodium carbonate and potassium carbonate, in the form of aqueous solutions and controlling the proportion of Mn to the total of Ni, Co and Mn contained in the sulfate (A) to be higher than 65 mol % at the initiation of the mixing, to precipitate a carbonate compound having a proportion of Mn of from 33.3 to 65 mol %, a proportion of Ni of from 17.5 to 50 mol % and a proportion of Co of from 0 to 33.3 mol % to the total of Ni, Co and Mn in the total average composition.

Abstract: To provide a cathode active material which achieves a high discharge capacity and excellent cycle durability. A cathode active material represented by LiaMOx (wherein M is an element including at least one member selected from Ni element, Co element and Mn element (other than Li element and O element), “a” is from 1.1 to 1.7, and x is the number of moles of O element required to satisfy the valences of Li element and M), wherein in an X-ray diffraction pattern, the ratio (I/r) of the crystallite size (I) of (003) plane to the crystallite size (r) of (110) plane assigned to a crystal structure with space group R-3m is at least 2.6.

Abstract: To provide a cathode active material to be used for a positive electrode of a lithium ion secondary battery having a high discharge capacity and favorable cycle durability. A cathode active material, which comprises a lithium-containing composite oxide containing at least one transition metal element (X) selected from the group consisting of Ni element, Co element and Mn element, and Li element (provided that the molar ratio (Li/X) of the Li element based on the total amount of the transition metal element (X) is from 1.1 to 1.7), wherein the aspect ratio of primary particles is from 2.5 to 10, and in an X-ray diffraction pattern, the ratio (I020/I003) of the integrated intensity (I020) of a peak of (020) plane assigned to a crystal structure with space group C2/m to the integrated intensity (I003) of a peak of (003) plane assigned to a crystal structure with space group R-3m is from 0.02 to 0.3.

Abstract: To provide a carbonate compound and a cathode active material, whereby a lithium ion secondary battery having excellent cycle characteristics can be obtained. A process for producing a carbonate compound, which comprises mixing a sulfate (A) comprising a sulfate comprising a sulfate of Mn and a sulfate of Ni, or a sulfate comprising a sulfate of Mn, a sulfate of Ni and a sulfate of Co, and a carbonate (B) which is at least one carbonate selected from the group consisting of sodium carbonate and potassium carbonate, in the form of aqueous solutions and controlling the proportion of Mn to the total of Ni, Co and Mn contained in the sulfate (A) to be higher than 65 mol % at the initiation of the mixing, to precipitate a carbonate compound having a proportion of Mn of from 33.3 to 65 mol %, a proportion of Ni of from 17.5 to 50 mol % and a proportion of Co of from 0 to 33.3 mol % to the total of Ni, Co and Mn in the total average composition.