Positive electrode active material for nonaqueous electrolyte secondary batteries

A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the positive electrode active material is a composite oxide that has a crystal structure belonging to a space group Fm-3m and is represented by a general formula:

• LixTMtmMyO2-fFf, in the general formula, TM represents a transition metal, M represents a non-transition metal, and when Q=2×tm×{1−(1−f/2)5}, Q<1 is satisfied, and
• when the composite oxide is used for a half-cell manufactured by the following method, one or more peaks in an SOC range of greater than or equal to 10% and less than or equal to 40% appear in a dV/dq-SOC curve showing a relationship between a state of charge SOC of the half-cell and dV/dq, which is a ratio of a change amount dV of a voltage V of the half-cell to a change amount dq of a battery capacity q of the half-cell, the dV/dq-SOC curve being obtained by charging the half-cell with a charging current of 0.1 C at 25° C. to an end voltage in a range of greater than or equal to 4.7 V and less than or equal to 4.95 V,
• (Method:
• a slurry for a positive electrode mixture layer is prepared by mixing the composite oxide, acetylene black, and polyvinylidene fluoride at a mass ratio of 7:2:1, and the mixture is dispersed using N-methyl-2-pyrrolidone;
• the slurry for a positive electrode mixture layer is applied to an aluminum foil, dried, and then rolled so that a film thickness is in a range of greater than or equal to 20 μm and less than or equal to 50 μm;
• thereafter, punching is performed into a size of 20 mm×20 mm to obtain a positive electrode;
• and an electrode assembly in which a separator is interposed between the positive electrode and a metal lithium foil (thickness:
• 0.3 mm) as a negative electrode is housed in an outer body of an aluminum laminate film, and a non-aqueous electrolyte in which LiPF6 is dissolved in a mixed solvent of fluoroethylene carbonate and methyl propionate (volume ratio:
• 1:3) so that a concentration thereof is 1 mol/liter is injected into the outer body and sealed to form a half-cell).