Diagnostic device for secondary battery and recovery method for secondary battery

A diagnostic method for a secondary battery having a structure in which positive electrodes and negative electrodes are alternately arranged, the diagnostic method comprising:

• acquiring a first resistance value indicating a magnitude of electrical resistance of the secondary battery before compression, and then compressing at least a part of the secondary battery;
• acquiring a second resistance value indicating a magnitude of electrical resistance of the secondary battery after the compression;
• determining, using the first resistance value and the second resistance value, whether an amount of decrease in electrical resistance of the secondary battery by the compression is greater than a first predetermined value;
• determining whether an increase in electrical resistance due to distortion of at least one of the positive electrodes and the negative electrodes occurs in the secondary battery using a result of the determination on the amount of decrease in electrical resistance;
• and
• upon determining that the increase in electrical resistance due to the distortion of at least one of the positive electrodes and the negative electrodes occurs in the secondary battery, executing a predetermined recovery process,
• wherein the predetermined recovery process includes charging, while a load that compresses the secondary battery is applied to the secondary battery, the secondary battery in a discharged state in which a state-of-charge (SOC) of the secondary battery has become equal to or less than a predetermined SOC value.