Battery diagnosis method, battery diagnosis program, battery management apparatus, and power storage system

A battery diagnosis program causes a computer to perform a process comprising:

• identifying a change point where a rise in voltage given by subtracting open circuit voltage of the battery from measured voltage of the battery is varied from a curved line shape to a straight line shape with respect to transition of an increase of a value in which an elapsed time since start of control, in which constant direct current is discharged from a battery for a predetermined time period or the battery is charged with the constant direct current for the predetermined time period, is defined as a square root of time;
• identifying a rise in voltage from the voltage when charge-discharge is started to the change point as a rise in voltage caused by resistance components of electrolyte, a negative electrode, and a positive electrode of the battery and identifying a rise in voltage after the change point as a rise in voltage caused by a diffusion resistance component of the battery;
• and
• identifying a rise in voltage until a predetermined time set in advance based on frequency response of the resistance component of the negative electrode of the battery elapses since the start of the charge-discharge as a rise in voltage caused by the electrolyte and the negative electrode of the battery.

A battery management apparatus includes

• a current measurement unit that measures current flowing through a battery;
• a voltage measurement unit that measures voltage of the battery;
• and
• a control unit that discharges constant direct current from the battery for a predetermined time period or charges the battery with the constant direct current for the predetermined time period to diagnose a state of the battery,
• wherein the control unit identifies a change point where a rise in voltage given by subtracting open circuit voltage of the battery from the measured voltage of the battery is varied from a curved line shape to a straight line shape with respect to transition of an increase of a value in which an elapsed time since start of charge-discharge is defined as a square root of time,
• wherein the control unit identifies a rise in voltage from the voltage when the charge-discharge is started to the change point as a rise in voltage caused by resistance components of electrolyte, a negative electrode, and a positive electrode of the battery and identifies a rise in voltage after the change point as a rise in voltage caused by a diffusion resistance component of the battery, and
• wherein the control unit identifies a rise in voltage until a predetermined time set in advance based on frequency response of the resistance component of the negative electrode of the battery elapses since the start of the charge-discharge as a rise in voltage caused by the electrolyte and the negative electrode of the battery.