Method of estimating deteriorated state of secondary battery and secondary battery system

1. A method of estimating a deteriorated state of a secondary battery performed by a control device mounted on a vehicle, the method comprising:

obtaining a plurality of times, a voltage value and a current value of the secondary battery mounted on the vehicle for a prescribed period during the vehicle driving and storing the voltage value and the current value in a memory;

calculating an amount of change in current of the secondary battery, an amount of change in temperature of the secondary battery, and an amount of change in SOC of the secondary battery during the prescribed period;

obtaining an allowable amount of change in current, an allowable amount of change in temperature, and an allowable amount of change in SOC which are determined for each temperature, each current, or each SOC of the secondary battery during the prescribed period from the temperature, the current, or the SOC of the secondary battery, the allowable amount of change in current representing an allowable upper limit of the amount of change in current, the allowable amount of change in temperature representing an allowable upper limit of the amount of change in temperature, the allowable amount of change in SOC representing an allowable upper limit of the amount of change in SOC;

calculating, by subjecting voltage values and current values of the secondary battery obtained the plurality of times and stored in the memory to frequency conversion, an impedance component for each frequency bandwidth of the secondary battery based on the frequency-converted voltage values and current values when all of a current condition, a temperature condition, and an SOC condition are satisfied, the current condition being a condition that the amount of change in current is smaller than the allowable amount of change in current, the temperature condition being a condition that the amount of change in temperature is smaller than the allowable amount of change in temperature, the SOC condition being a condition that the amount of change in SOC is smaller than the allowable amount of change in SOC; and

estimating a deteriorated state of the secondary battery in a deterioration mode in accordance with each frequency bandwidth by using the impedance component for each frequency bandwidth.

2. The method of estimating a deteriorated state of a secondary battery according to claim 1 , wherein

the obtaining an allowable amount of change includes obtaining the allowable amount of change in current, the allowable amount of change in temperature, and the allowable amount of change in SOC from an average temperature, an average current, or an average SOC of the secondary battery by referring to correspondence between the average temperature, the average current, or the average SOC of the secondary battery during the prescribed period and the allowable amount of change in current, the allowable amount of change in temperature, and the allowable amount of change in SOC.

3. The method of estimating a deteriorated state of a secondary battery according to claim 1 , wherein

among impedance components for each frequency bandwidth, an impedance component in a frequency bandwidth where deterioration of the secondary battery is more likely to proceed is higher in frequency of calculation of the impedance component.

4. The method of estimating a deteriorated state of a secondary battery according to claim 1 , the method further comprising prohibiting calculation of the impedance component for each frequency bandwidth in spite of all of the current condition, the temperature condition, and the SOC condition being satisfied, when a parameter representing at least one of unevenness of a temperature distribution in the secondary battery, unevenness of a salt concentration distribution in an electrolyte of the secondary battery, and unevenness of a concentration distribution of a charge transport material in an active material of the secondary battery is higher than a reference value.

5. The method of estimating a deteriorated state of a secondary battery according to claim 4 , the method further comprising resuming calculation of the impedance component for each frequency bandwidth when all of the current condition, the temperature condition, and the SOC condition are satisfied and when the parameter is lower than another reference value smaller than the reference value.

6. A secondary battery system used as being mounted on a vehicle, the secondary battery system comprising:

a secondary battery; and

an estimator including a memory and configured to estimate a deteriorated state of the secondary battery,

the estimator

obtaining a voltage value and a current value of the secondary battery a plurality of times for a prescribed period while the vehicle is driven and having the memory store the voltage value and the current value,

calculating an amount of change in current of the secondary battery, an amount of change in temperature of the secondary battery, and an amount of change in SOC of the secondary battery during the prescribed period,

obtaining an allowable amount of change in current, an allowable amount of change in temperature and an allowable amount of change in SOC which are determined for each temperature, each current, or each SOC of the secondary battery during the prescribed period from the temperature, the current, or the SOC of the secondary battery, the allowable amount of change in current representing an allowable upper limit of the amount of change in current, the allowable amount of change in temperature representing an allowable upper limit of the amount of change in temperature, the allowable amount of change in SOC representing an allowable upper limit of the amount of change in SOC,

calculating, by subjecting voltage values and current values of the secondary battery obtained the plurality of times and stored in the memory to frequency conversion, an impedance component for each frequency bandwidth of the secondary battery based on the frequency-converted voltage values and current values when all of a current condition, a temperature condition, and an SOC condition are satisfied, the current condition being a condition that the amount of change in current is smaller than the allowable amount of change in current, the temperature condition being a condition that the amount of change in temperature is smaller than the allowable amount of change in temperature, the SOC condition being a condition that the amount of change in SOC is smaller than the allowable amount of change in SOC, and

estimating a deteriorated state of the secondary battery in a deterioration mode in accordance with each frequency bandwidth by using the impedance component for each frequency bandwidth.