Secondary battery degradation determination apparatus and secondary battery degradation determination method

1 . A secondary battery degradation determination apparatus configured to perform degradation determination for a secondary battery as a determination target, the secondary battery degradation determination apparatus comprising a processor configured to:

control a switch such that a constant-current power supply is connected to the secondary battery and charges the secondary battery with a constant current;

measure a voltage value of the secondary battery at a first point in time on a charging curve that indicates a charging characteristic of the secondary battery, when a first predetermined time period has passed from a charging start time of the secondary battery on the charging curve;

measure a voltage value of the secondary battery at a second point in time on the charging curve, when a second predetermined time period has passed from the first point in time;

determine a first voltage value slope between the first point in time and the second point in time;

measure a voltage value of the secondary battery at a third point in time and a fourth point in time on the charging curve, the third point in time being later than the second point in time;

determine a second voltage value slope between the third point in time and the fourth point in time;

calculate an estimated electric capacity of the secondary battery, based on at least (i) the first voltage value slope, (ii) the voltage value at the first point in time, (iii) the second voltage value slope, and (iv) the voltage value at the third point in time; and

perform the degradation determination for the secondary battery, based on the estimated electric capacity that is calculated.

2 . The secondary battery degradation determination apparatus according to claim 1 , wherein the processor is configured to calculate the estimated electric capacity of the secondary battery by using a multiple regression model in which the estimated electric capacity is a response variable, and explanatory variables include (i) the first voltage value slope between the first point in time and the second point in time on the charging curve of the secondary battery and (ii) the voltage value at the first point in time on the charging curve.

3 . The secondary battery degradation determination apparatus according to claim 2 , wherein the processor is configured to calculate the estimated electric capacity of the secondary battery by using the multiple regression model in which the explanatory variables include a voltage value at a time of starting charging of the secondary battery and/or a temperature at a time of measuring the charging curve, in addition to the first voltage value slope between the first point in time and the second point in time on the charging curve and the voltage value at the first point in time on the charging curve.

4 . The secondary battery degradation determination apparatus according to claim 3 , wherein the processor is configured to calculate a coefficient of the multiple regression model, based on charging curves and electric capacities of a plurality of secondary batteries, and calculate the estimated electric capacity of the secondary battery by using the multiple regression model to which the calculated coefficient is applied.

5 . The secondary battery degradation determination apparatus according to claim 1 , wherein the processor is configured to determine that the secondary battery is good and reusable when the estimated electric capacity is equal to or more than a predetermined threshold value, and to determine that the secondary battery is defective and unfit for reuse when the estimated electric capacity is less than the predetermined threshold value.

6 . The secondary battery degradation determination apparatus according to claim 1 , wherein a time period from the third point in time to the fourth point in time is equal to the predetermined second time period.

7 . The secondary battery degradation determination apparatus according to claim 1 , wherein:

the first voltage value slope=(V D −V C )/(t D −t C ), where V C is the voltage value at the first point in time, V D is the voltage value at the second point in time, t C is the first point in time, and t D is the second point in time; and

the second voltage value slope=(V F −V E )/(t F −t E ), where V E is the voltage value at the third point in time, V F is the voltage value at the fourth point in time, t E is the third point in time, and tr is the fourth point in time.

8 . The secondary battery degradation determination apparatus according to claim 1 , wherein the processor is further configured to:

measure a voltage value of the secondary battery at a fifth point in time on the charging curve after a predetermined third time has elapsed from the fourth point in time;

measure a voltage value of the secondary battery at a sixth point in time on the charging curve after a predetermined fourth time has elapsed from the fifth point in time;

determine a third voltage value slope between the fifth point in time and the sixth point in time;

measure a voltage value of the secondary battery at a seventh point in time on the charging curve after a predetermined fifth time has elapsed from the fourth point in time;

measure a voltage value of the secondary battery at an eighth point in time on the charging curve after a predetermined sixth time has elapsed from the seventh point in time; and

determine a fourth voltage value slope between the seventh point in time and the eighth point in time;

wherein the calculating the estimated electric capacity of the secondary battery is further based on (v) the third voltage value slope, (vi) the voltage value at the fifth point in time, (vii) the fourth voltage value slope, and (viii) the voltage value at the seventh point in time.

9 . A secondary battery degradation determination method for a secondary battery degradation determination apparatus configured to perform degradation determination for a secondary battery as a determination target, the secondary battery degradation determination method comprising:

controlling a switch such that a constant-current power supply is connected to the secondary battery and charges the secondary battery with a constant current;

measuring a voltage value of the secondary battery at a first point in time on a charging curve that indicates a charging characteristic of the secondary battery, when a first predetermined time period has passed from a charging start time of the secondary battery on the charging curve;

measuring a voltage value of the secondary battery at a second point in time on the charging curve, when a second predetermined time period has passed from the first point in time;

determining a first voltage value slope between the first point in time and the second point in time;

measuring a voltage value of the secondary battery at a third point in time and a fourth point in time on the charging curve, the third point in time being later than the second point in time;

determining a second voltage value slope between the third point in time and the fourth point in time;

calculating an estimated electric capacity of the secondary battery, based on at least (i) the first voltage value slope, (ii) the voltage value at the first point in time, (iii) the second voltage value slope, and (iv) the voltage value at the third point in time; and

performing the degradation determination for the secondary battery, based on the estimated electric capacity that is calculated.

10 . The secondary battery degradation determination method according to claim 9 , wherein a time period from the third point in time to the fourth point in time is equal to the predetermined second time period.

11 . The secondary battery degradation determination method according to claim 9 , wherein:

the first voltage value slope=(V D −V C )/(t D −t C ), where V C is the voltage value at the first point in time, V D is the voltage value at the second point in time, t C is the first point in time, and t D is the second point in time; and

the second voltage value slope=(V F −V E )/(t F −t E ), where V E is the voltage value at the third point in time, V F is the voltage value at the fourth point in time, t E is the third point in time, and tr is the fourth point in time.

12 . The secondary battery degradation determination method according to claim 9 , further comprising:

measuring a voltage value of the secondary battery at a fifth point in time on the charging curve after a predetermined third time has elapsed from the fourth point in time;

measuring a voltage value of the secondary battery at a sixth point in time on the charging curve after a predetermined fourth time has elapsed from the fifth point in time;

determining a third voltage value slope between the fifth point in time and the sixth point in time;

measuring a voltage value of the secondary battery at a seventh point in time on the charging curve after a predetermined fifth time has elapsed from the fourth point in time;

measuring a voltage value of the secondary battery at an eighth point in time on the charging curve after a predetermined sixth time has elapsed from the seventh point in time; and

determining a fourth voltage value slope between the seventh point in time and the eighth point in time;

wherein the calculating the estimated electric capacity of the secondary battery is further based on (v) the third voltage value slope, (vi) the voltage value at the fifth point in time, (vii) the fourth voltage value slope, and (viii) the voltage value at the seventh point in time.