Method of determining a frequency interval containing a resonance frequency of a rechargeable battery

1. A method of determining a resonance frequency interval containing a resonance frequency of a rechargeable battery, the method comprising:

applying periodic current or voltage signals of different frequencies in succession to at least one battery cell of the battery;

measuring the temperatures of the at least one battery cell occurring for the different frequencies; and

comparing the temperatures, and subsequent selection of a first frequency of the different frequencies as a first interval value of the resonance frequency interval and a second frequency of the different frequencies as a second interval value of the resonance frequency interval based on the comparison of the temperatures.

2. The method of claim 1 comprising the steps of:

a) defining a start frequency interval with a first frequency value and a second frequency value that is larger than the first frequency value;

b) defining a first frequency interval within the start frequency interval with a third frequency value and a fourth frequency value that is larger than the third frequency value;

c) applying a periodic current or voltage signal with a frequency matching the third frequency value to the at least one battery cell and measuring a first temperature value for the battery cell;

d) applying a periodic current or voltage signal with a frequency matching the fourth frequency value to the at least one battery cell and measuring a second temperature value for the at least one battery cell;

e) comparing the first and second temperature values, and selecting the first frequency and fourth frequency values as interval limits of the resonance frequency interval if the second temperature value is larger than the first temperature value, and selecting the third frequency and second frequency values as the interval limits of the resonance frequency interval if the second temperature value is less than the first temperature value.

3. The method of claim 2 wherein the steps a) to e) are repeated at least once, wherein prior to a repetition the start frequency interval is set to the same resonance frequency interval obtained from the previous step e).

4. The method of claim 3 wherein a specified period is waited before repeating the steps a) to e).

5. The method of claim 2 wherein the first frequency interval is selected such that a distance between the fourth frequency value and the first frequency value is r times the interval width of the first start interval, and a distance between the third frequency value and the first frequency value is (1−r) times the interval width of the first start interval, where 0.5<r<1.

6. The method of claim 2 wherein the steps a) to e) are repeated for a fixed specified number.

7. The method of claim 2 wherein the steps a) to e) are repeated in succession until an interval width of the resonance frequency interval determined in step e) is below a specified value.

8. The method of claim 2 wherein the at least one battery cell comprises at least two battery cells and wherein the periodic signal in the process step c) is applied to a first battery cell and the periodic signal in the process step d) to a second battery cell.

9. A method of determining a resonance frequency interval containing a resonance frequency of a rechargeable battery, the method comprising:

a) applying a first signal of a first frequency to at least one battery cell of the battery;

b) applying a second signal of a second frequency to the at least one battery cell of the battery, the second frequency different than the first frequency;

c) measuring a first temperature of the at least one battery cell after the first signal is applied to the at least one battery cell;

d) measuring a second temperature of the at least one battery cell after the second signal is applied to the at least one battery cell;

e) comparing the first temperature and the second temperature; and

f) selecting a resonance frequency interval based on the comparison of the first temperature and the second temperature.

10. The method of claim 9 further comprising the step of defining a start interval with a first start frequency value and a second start frequency value that is larger than the first start frequency value.

11. The method of claim 10 wherein the first frequency and the second frequency define a frequency interval within the start interval.

12. The method of claim 11 wherein the step of selecting a resonance frequency interval comprises selecting the first start frequency value and the second frequency as interval limits of the resonance frequency interval if the second temperature is larger than the first temperature, and selecting the first frequency and the second start frequency value as the interval limits of the resonance frequency interval if the second temperature is less than the first temperature.

13. The method of claim 12 wherein the steps a) to f) are repeated at least once, wherein prior to a repetition the start interval is set to the selected resonance frequency interval.

14. The method of claim 13 wherein a specified period is waited prior to a repetition of steps a) to f).

15. The method of claim 13 wherein the steps a) to f) are repeated for a predetermined number of times.

16. The method of claim 13 wherein the steps a) to f) are repeated in succession until an interval width of the resonance frequency interval is below a specified value.

17. The method of claim 10 wherein the second frequency is equal to r times the difference between the second start frequency value and the first start frequency value, and the first frequency is equal to (1−r) times the difference between the second start frequency value and the first start frequency value, wherein 0.5<r<1.

18. The method of claim 9 wherein the at least one battery cell comprises a first battery cell and a second battery cell and wherein the first signal is applied to the first battery cell and the second signal is applied to the second battery cell.