The nickel-containing composite hydroxide disclosed herein contain secondary particles, which are formed from an aggregation of numerous primary particles, which have an average particle size of the primary particles is 0.01 μm to 0.40 μm. These secondary particles have a spherical or ellipsoidal shape, an average particle size of 20 μm to 50 μm, and a BET value of 12 m2/g to 50 m2/g after being roasted in air for 2 hours at 800° C.