Diagnostic device, diagnostic method, and non-transitory computer-readable recording medium storing diagnostic instructions

1 . A diagnostic device comprising:

a voltage detector that detects voltage of a battery cell;

a current detector that detects current of the battery cell;

a storage that stores reference data and measurement data including the detected voltage and the detected current; and

calculators that:

acquire:

a measurement Q-V curve indicating a relation between a voltage and an integrated current amount that are obtained from the measurement data, and

a reference Q-V curve obtained from the reference data,

include:

a first calculator that calculates an amount of capacity deterioration caused by a voltage difference between the measurement Q-V curve and the reference Q-V curve by multiplying an inclination of the measurement Q-V curve by the voltage difference;

a second calculator that calculates a temporary maximum capacity after capacity deterioration caused by a change in the inclination of the measurement Q-V curve to an inclination of the reference Q-V curve by multiplying a ratio between the inclination of the measurement Q-V curve and the inclination of the reference Q-V curve by a reference maximum capacity; and

a maximum capacity calculator that calculates a maximum capacity of the battery cell by subtracting the calculated amount of capacity deterioration from the calculated temporary maximum capacity, and

causes a display to display the calculated maximum capacity.

2 . The diagnostic device according to claim 1 , wherein the voltage difference is a voltage difference between a feature point of a differential curve of the measurement Q-V curve and another feature point of another differential curve of the reference Q-V curve.

3 . The diagnostic device according to claim 2 , wherein

the feature point is a local maximum value that first appears in the differential curve,

the another feature point is a local maximum value that first appears in the another differential curve,

the inclination of the measurement Q-V curve is an inclination at a voltage equal to or greater than a voltage of the feature point, and

the inclination of the reference Q-V curve is an inclination at a voltage equal to or greater than a voltage of the another feature point.

4 . The diagnostic device according to claim 1 , wherein

the calculators further:

generate a function model fitted to the reference Q-V curve,

fit the generated function model to the measurement data of the battery cell, and

calculate the maximum capacity of the battery cell based on the function model after the fitting.

5 . The diagnostic device according to claim 4 , wherein the calculators align a position of a feature point in a differential curve of the function model before the fitting with another position of another feature point in another differential curve of the function model after the fitting.

6 . The diagnostic device according to claim 5 , wherein

the feature point is a local maximum value that first appears in the differential curve,

the another feature point is a local maximum value that first appears in the another differential curve,

the function model before fitting is a function model at a voltage equal to or greater than a voltage of the feature point, and

the function model after fitting is a function model at a voltage equal to or greater than a voltage of the another feature point.

7 . A diagnostic method comprising:

detecting, with a voltage detector, voltage of a battery cell;

detecting, with a current detector, current of the battery cell;

storing reference data and measurement data including the detected voltage and the detected current in a storage;

acquiring:

a measurement Q-V curve indicating a relation between a voltage and an integrated current amount that are obtained from the measurement data, and

a reference Q-V curve obtained from the reference data;

calculating, with a first calculator, an amount of capacity deterioration caused by a voltage difference between the measurement Q-V curve and the reference Q-V curve by multiplying an inclination of the measurement Q-V curve by the voltage difference;

calculating, with a second calculator, a temporary maximum capacity after capacity deterioration caused by a change in the inclination of the measurement Q-V curve to an inclination of the reference Q-V curve by multiplying a ratio between the inclination of the measurement Q-V curve and the inclination of the reference Q-V curve by a reference maximum capacity;

calculating, with a maximum capacity calculator, a maximum capacity of the battery cell by subtracting the calculated amount of capacity deterioration from the calculated temporary maximum capacity; and

causing a display to display the calculated maximum capacity.

8 . The diagnostic method according to claim 7 further comprising:

generating a function model fitted to the reference Q-V curve;

fitting the generated function model to the measurement data of the battery cell; and

calculating the maximum capacity of the battery cell based on the function model after the fitting.

9 . A non-transitory computer-readable recording medium having stored therein diagnostic instructions that cause a computer to execute:

detecting, with a voltage detector, voltage of a battery cell;

detecting, with a current detector, current of the battery cell;

storing reference data and measurement data including the detected voltage and the detected current in a storage;

acquiring:

a measurement Q-V curve indicating a relation between a voltage and an integrated current amount that are obtained from the measurement data, and

a reference Q-V curve obtained from the reference data;

calculating, with a first calculator, an amount of capacity deterioration caused by a voltage difference between the measurement Q-V curve and the reference Q-V curve by multiplying an inclination of the measurement Q-V curve by the voltage difference;

calculating, with a second calculator, a temporary maximum capacity after capacity deterioration caused by a change in the inclination of the measurement Q-V curve to an inclination of the reference Q-V curve by multiplying a ratio between the inclination of the measurement Q-V curve and the inclination of the reference Q-V curve by a reference maximum capacity;

calculating, with a maximum capacity calculator, a maximum capacity of the battery cell by subtracting the calculated amount of capacity deterioration from the calculated temporary maximum capacity; and

causing a display to display the calculated maximum capacity.

10 . The non-transitory computer-readable recording medium according to claim 9 , wherein the diagnostic instructions that further cause the computer to execute:

generating a function model fitted to the reference Q-V curve;

fitting the generated function model to the measurement data of the battery cell; and

calculating the maximum capacity of the battery cell based on the function model after the fitting.