Method Of Diagnosing Degradation Of Electrode Active Material For Lithium Secondary Battery

A method of diagnosing degradation of an electrode active material for a secondary battery including obtaining a first differential curve (dQ/dV) by differentiating an initial charge/discharge curve obtained by performing first charging and first discharging of the lithium secondary battery in a voltage range of 2.5 V to 4.2 V, and obtaining a second differential curve (dQ/dV) by differentiating a charge/discharge curve obtained by performing second charging and second discharging of the lithium secondary battery in a voltage range of 2.5 V to 4.2 V, and diagnosing whether a beta phase of the positive electrode active material has been formed by comparing maximum discharge peak values of the first differential curve and the second differential curve.