A positive electrode active material includes a core including a first lithium complex metal oxide, and a shell located surrounding the core and including a second lithium complex metal oxide, and further includes a buffer layer located between the core and the shell. The buffer layer includes a pore, and a three-dimensional network structure of a third lithium complex metal oxide which is connecting the core and the shell. Accordingly, the positive electrode active material is capable of enhancing an output property and a life property by minimizing destruction of the active material caused by a rolling process during the electrode preparation, maximizing reactivity with an electrolyte liquid, and by the particles that form the shell having a crystal structure with orientation facilitating lithium ion intercalation and deintercalation.