POSITIVE ELECTRODE ACTIVE MATERIAL FOR LITHIUM-ION BATTERIES, POSITIVE ELECTRODE FOR LITHION-ION BATTERIES, LITHIUM-ION BATTERY

The present invention provides a positive electrode active material for lithium ion battery which attains a lithium ion battery having high safety. The positive electrode active material for lithium ion battery which has a layer structure represented by the compositional formula: Li x (Ni y M 1-y )O z (wherein M represents Mn and Co, x denotes a number of 0.9 to 1.2, y denotes a number of 0.8 ± 0.025, and z denotes a number of 1.8 to 2.4). After a lithium ion battery using a positive electrode mix produced by the positive electrode active material, a binder, and a conductive material in a ratio by weight of 91%, 4.2%, and 4.8%, respectively, is charged to 4.3 V, an accumulated calorific value in a temperature range from 170 to 300 °C, which is obtained by differential scanning calorimetry (DSC) performed at a temperature rise rate of 5°C/min using an electrolytic solution prepared by dissolving 1 M-LiPF 6 in a mixture solvent of ethylene carbonate (EC)-dimethyl carbonate (DMC) (volume ratio 1 : 1) based on 1.0 mg of the positive electrode mix, is 1.4 kJ/g or less.