Power unit analysis

Abstract

A method of isolating and quantifying contributions to the impedance of a power unit comprises: obtaining an impedance spectrum from the power unit; fitting a pure capacitance term to remove capacitiv

Claims

1. A method of isolating and quantifying individual contributions to diffusion impedance in a power unit, comprising:obtaining an impedance spectrum from the power unit;fitting a pure capacitance term to remove capacitance effects from the impedance spectrum;fitting at least one of a finite length Warburg term and / or a finite space Warburg term to quantify the diffusion impedance contributions from the impedance spectrum; and outputting the quantified diffusion impedance contributions as diffusion impedance parameters.

2. A method according to claim 1, wherein the impedance spectrum is obtained from the power unit by electrochemical impedance spectroscopy and / or by conversion of pulse relaxation data, obtained following application of a current to the power unit, into an impedance spectrum.

3. A method according to claim 2, wherein the pulse relaxation data is converted into an impedance spectrum by fitting frequency domain elements to the pulse relaxation data using Laplace inversion, and constructing an impedance spectrum from the frequency domain elements.

4. A method according to claim 2 or 3, wherein the pulse relaxation data is obtained by a galvanostatic intermittent titration technique.

5. A method according to claim 2 or 3, wherein the pulse relaxation data is obtained by hybrid pulse power characterisation.

6. A method according to claim 2, wherein the impedance spectrum is obtained from the power unit by electrochemical impedance spectroscopy, wherein the pure capacitance term is created using state of charge-open circuit voltage maps by applying coulomb counting to the electrochemical impedance spectroscopy profile.

7. A method according to any preceding claim, wherein the impedance spectrum is converted into a distribution of relaxation times and the diffusion impedance parameters obtained from fitting to the impedance spectrum are refined by fitting to the distribution of relaxation times.

8. A method according to claim 7, wherein the diffusion impedance parameters are fitted to a predetermined range of the distribution of relaxation times where diffusion effects are known to be found based on the Nyquist plot profile of the impedance spectrum.

9. A computer-readable medium storing instructions which, when executed by a processor, cause the performance of the method of any of claims 1-8.

10. A system comprising:an electrochemical impedance spectroscopy (EIS) instrument for obtaining EIS data from a power unit, and / or a galvanostatic intermittent titration technique (GITT) instrument for obtaining GITT data from a power unit and / or a hybrid pulse power characterisation (HPPC) instrument for obtaining HPPC data from a power unit; anda processor programmed to perform the method of any of claims 1 -8.

11. The system of claim 10, further comprising a display for displaying the diffusion impedance parameters.

12. An electric vehicle comprising a system according to claim 10 or 11, wherein the diffusion impedance parameters are input as battery health data to a battery management system which manages a battery according to the battery health data.

13. An electric vehicle according to claim 12, wherein the battery management system is configured to output a notification to a user when the battery health data indicates the battery health has degraded below a predetermined threshold.

14. A computer-implemented method of comparing power units comprising:obtaining diffusion impedance parameters for a plurality of power units according to any of claims 1-8;inputting the diffusion impedance parameters into a power unit degradation model;outputting the results of the degradation model;displaying the results of the degradation model; andranking the power units by their expected degradation characteristics.

15. A method according to claim 14 further comprising the step of selecting the highest-ranked power unit for use in a vehicle.s

Images