Disclosed is an electrode active material comprising: (a) electrode active material particles capable of lithium intercalation/deintercalation; and (b) a multinary oxide coating layer partially or totally formed on the surface of the electrode active material particles, the multinary oxide coating layer comprising Al, P and a halogen element. A method for preparing the electrode active material, an electrode using the electrode active material, and an electrochemical device comprising the electrode, preferably a lithium secondary battery, are also disclosed. The electrode active material comprising a multinary oxide coating layer has improved structural stability and thermal safety, and thus can provide an electrochemical device having high capacity, long service life and excellent safety.