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

1. A battery diagnosis method comprising:

performing a charge-discharge control of discharging constant direct current from a battery for a predetermined time period or charging the battery with the constant direct current for the predetermined time period;

measuring voltage of the battery;

identifying 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 the charge-discharge control is defined as a square root of the elapsed time;

identifying a rise in voltage from the voltage when the charge-discharge control 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 control as a rise in voltage caused by the electrolyte and the negative electrode of the battery.

2. A non-transitory computer readable medium storing a battery diagnosis program, which 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 a charge-discharge 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 the elapsed time;

identifying a rise in voltage from the voltage when the charge-discharge control 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 control as a rise in voltage caused by the electrolyte and the negative electrode of the battery.

3. A battery management apparatus comprising:

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 performs a charge-discharge control, in which the control unit 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 the charge-discharge control is defined as a square root of the elapsed time,

wherein the control unit identifies a rise in voltage from the voltage when the control 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 control as a rise in voltage caused by the electrolyte and the negative electrode of the battery.

4. The battery management apparatus according to claim 3 ,

wherein the control unit calculates a combined resistance value of the electrolyte, the negative electrode, and the positive electrode of the battery by dividing the rise in voltage caused by the resistance components of the electrolyte, the negative electrode, and the positive electrode of the battery by the constant direct current,

wherein the control unit derives a diffusion resistance factor of the battery based on a rate of the rise in voltage caused by the diffusion resistance component of the battery,

wherein the control unit calculates a combined resistance value of the electrolyte and the negative electrode of the battery by dividing the rise in voltage caused by the electrolyte and the negative electrode of the battery by the constant direct current, and

wherein the control unit calculates the resistance value of the positive electrode of the battery by subtracting the combined resistance value of the electrolyte and the negative electrode of the battery from the combined resistance value of the electrolyte, the negative electrode, and the positive electrode of the battery.

5. The battery management apparatus according to claim 4 ,

wherein the control unit performs at least one of output of an alert and stop of the charge-discharge control of the battery if the calculated diffusion resistance factor is higher than or equal to a deterioration determination threshold value for the diffusion resistance,

wherein the control unit performs at least one of the output of an alert and the stop of the charge-discharge control of the battery if the calculated resistance value of the positive electrode is higher than or equal to a deterioration determination threshold value for the positive electrode resistance, and

wherein the control unit performs at least one of the output of an alert and the stop of the charge-discharge control of the battery if the calculated combined resistance value of the electrolyte and the negative electrode is higher than or equal to a deterioration determination threshold value for the combined resistance of the electrolyte and the negative electrode.

6. The battery management apparatus according to claim 4 ,

wherein the control unit changes an upper limit of at least one of charge current and discharge current of the battery based on the calculated diffusion resistance factor, the calculated resistance value of the positive electrode, and the calculated combined resistance value of the electrolyte and the negative electrode.

7. The battery management apparatus according to claim 4 ,

wherein the control unit estimates a remaining usage period or a remaining charge-discharge count of the battery based on transition of the calculated diffusion resistance factor, the calculated resistance value of the positive electrode, and the calculated combined resistance value of the electrolyte and the negative electrode.

8. The battery management apparatus according to claim 3 ,

wherein the control unit causes the constant direct current to flow through the battery for 30 seconds or more.

9. A power storage system comprising:

a battery module including a battery; and

the battery management apparatus according to claim 3 , which manages the battery module.

10. A power storage system comprising:

a battery module including a battery; and

the battery management apparatus according to claim 4 , which manages the battery module.

11. A power storage system comprising:

a battery module including a battery; and

the battery management apparatus according to claim 5 , which manages the battery module.

12. A power storage system comprising:

a battery module including a battery; and

the battery management apparatus according to claim 6 , which manages the battery module.

13. A power storage system comprising:

a battery module including a battery; and

the battery management apparatus according to claim 7 , which manages the battery module.

14. A power storage system comprising:

a battery module including a battery; and

the battery management apparatus according to claim 8 , which manages the battery module.