Patent ID: 6919144

Claim:
A nonaqueous electrolyte secondary cell comprising: a positive electrode comprising mainly of a positive electrode active material; a negative electrode; and a nonaqueous electrolyte, wherein the positive electrode active material is a lithium-containing transition metal composite oxide of a hexagonal crystal system, the composite oxide comprising: a compound represented by a general formula LiCo 1-x M x O 2 , where M is at least one species selected from the group consisting of V, Cr, Fe, Mn, Ni, Al, and Ti, and x is a decimal number in a range 0<x<1; magnesium; and halogen; wherein a halogen content in a total amount of the positive electrode active material is in a range of 0.0007 to 5 mass %; and wherein the magnesium is in an amount necessary to lower the pH of filtrate to below 9.8, the filtrate collected after dispersing the positive electrode active material in water.