SYSTEMS, METHODS AND COMPUTER READABLE MEDIA FOR ESTIMATING CAPACITY LOSS IN RECHARGEABLE ELECTROCHEMICAL CELL

• US 20110077880A1
• Filed: 09/30/2009
• Published: 03/31/2011
• Est. Priority Date: 09/30/2009
• Status: Active Grant

• Current Assignee: Battelle Energy Alliance LLC (Battelle Memorial Institute)
• Original Assignee: Battelle Energy Alliance LLC (Battelle Memorial Institute)
• Inventors: Gering, Kevin L.
• Granted Patent: US 8,467,984 B2
• Time in Patent Office: Days
• US Class Current: 702/63
• CPC Class Codes: G01R 31/392 Determining battery ageing or deterioration, e.g. state of health
• CPC Class Codes: H01M 10/052 Li-accumulators
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

A system includes an electrochemical cell, monitoring hardware, and a computing system. The monitoring hardware periodically samples charge characteristics of the electrochemical cell. The computing system periodically determines cell information from the charge characteristics of the electrochemical cell. The computing system also periodically adds a first degradation characteristic from the cell information to a first sigmoid expression, periodically adds a second degradation characteristic from the cell information to a second sigmoid expression and combines the first sigmoid expression and the second sigmoid expression to develop or augment a multiple sigmoid model (MSM) of the electrochemical cell. The MSM may be used to estimate a capacity loss of the electrochemical cell at a desired point in time and analyze other characteristics of the electrochemical cell. The first and second degradation characteristics may be loss of active host sites and loss of free lithium for Li-ion cells.

Claims

1. A method wherein at least one act of the method is performed by a processor, the method comprising:

analyzing a first degradation characteristic of an electrochemical cell modeled with a first sigmoid expression;

analyzing a second degradation characteristic of the electrochemical cell modeled with a second sigmoid expression;

combining the first sigmoid expression and the second sigmoid expression to develop a multiple sigmoid model; and

estimating a capacity loss of the electrochemical cell at a desired point in time using the multiple sigmoid model.

2. The method of claim 1, further comprising selecting the first degradation characteristic to comprise a loss of active host sites.

3. The method of claim 1, further comprising selecting the second degradation characteristic to comprise a loss of free lithium.

4. The method of claim 1, further comprising estimating reversible loss elements for one or more of the first degradation characteristic and the second degradation characteristic and augmenting the multiple sigmoid model with the reversible loss elements.

5. The method of claim 1, further comprising estimating irreversible loss elements for one or more of the first degradation characteristic and the second degradation characteristic and augmenting the multiple sigmoid model with the irreversible loss elements.

6. The method of claim 1, further comprising defining a baseline capacity for the electrochemical cell at a substantially low cycling rate.

7. The method of claim 6, wherein the low cycling rate is substantially C/25.

8. The method of claim 1, further comprising defining an offset for the multiple sigmoid model at a beginning-of-life condition using a relatively low cycling rate to model polarization effects at higher cycling rates.

9. The method of claim 1, further comprising predicting a maximum capacity fade from a plateau of the multiple sigmoid model as the electrochemical cell approaches and end-of-life condition.

10. The method of claim 1, further comprising interpolating, extrapolating, or a combination thereof, to estimate capacity loss at various cycle rates.

11. The method of claim 1, further comprising:

analyzing a third characteristic of the electrochemical cell modeled with a third sigmoid expression; and

including the third sigmoid expression in the multiple sigmoid model;

wherein the third characteristic comprises an addition of free lithium from a lithium source or a lithium reserve.

12. The method of claim 1, further comprising:

estimating conductance loss for the electrochemical cell;

determining a fraction of power loss due to conductance loss relative to a power goal; and

determining a fraction of power loss due to capacity fade as a portion of overall power loss not related to the fraction of power loss due to conductance loss.

13. The method of claim 1, wherein each of the first degradation characteristic and the second degradation characteristic are derived from chemical kinetics reaction rates.

14. The method of claim 1, wherein the first degradation characteristic and the second degradation characteristic are determined from cell characteristics sampled from the electrochemical cell.

15. A model development method wherein at least one act of the method is performed by a processor, the method, comprising:

periodically sampling cell characteristics of an electrochemical cell;

determining a first degradation characteristic and a second degradation characteristic from the cell characteristics;

periodically adding the first degradation characteristic to a first sigmoid expression;

periodically adding the second degradation characteristic to a second sigmoid expression; and

combining the first sigmoid expression and the second sigmoid expression to develop or augment a multiple sigmoid model of the electrochemical cell.

16. The model development method of claim 15, further comprising selecting the cell characteristics to include one or more of a cycling rate, a voltage, a current, and a temperature.

17. The model development method of claim 15, further comprising estimating a capacity loss of the electrochemical cell at a desired point in time using the multiple sigmoid model.

18. The model development method of claim 15, further comprising selecting the first degradation characteristic to comprise a loss of active host sites.

19. The model development method of claim 15, further comprising selecting the second degradation characteristic to comprise a loss of free lithium.

20. The model development method of claim 15, further comprising estimating reversible loss elements for one or more of the first degradation characteristic and the second degradation characteristic and augmenting the multiple sigmoid model with the reversible loss elements.

21. The model development method of claim 15, further comprising estimating irreversible loss elements for one or more of the first degradation characteristic and the second degradation characteristic and augmenting the multiple sigmoid model with the irreversible loss elements.

22. A method, comprising:

analyzing a first degradation characteristic of an electrochemical cell modeled with a first sigmoid expression;

analyzing a second degradation characteristic of the electrochemical cell modeled with a second sigmoid expression;

combining the first sigmoid expression and the second sigmoid expression to develop a multiple sigmoid model;

estimating a capacity loss of the electrochemical cell at a desired point in time using the multiple sigmoid model; and

modifying at least one of a discharge process for, a charge process for, and composition of, the electrochemical cell responsive to the estimating the capacity loss.

23. The method claim 22, wherein modifying the composition of the electrochemical cell comprises at least one of modifying a composition of an anode, modifying a composition of a cathode, modifying a composition of an electrolyte, and modifying a relative arrangement of the anode, the cathode, and the electrolyte.

24. A system, comprising:

at least one electrochemical cell;

monitoring hardware operably coupled to the at least one electrochemical cell and configured for periodically sampling cell characteristics of the at least one electrochemical cell;

a computing system operably coupled to the monitoring hardware and configured for periodically;

determining electrochemical cell information from to the cell characteristics of the electrochemical cell;

adding a first degradation characteristic from the electrochemical cell information to a first sigmoid expression;

adding a second degradation characteristic from the electrochemical cell information to a second sigmoid expression; and

combining the first sigmoid expression and the second sigmoid expression to develop or augment a multiple sigmoid model of the at least one electrochemical cell.

25. The system of claim 24, wherein the computing system comprises a memory for storing computing instructions and a processor operably coupled to the memory and configured for executing the computing instructions to carry out the acts of determining the electrochemical cell information, adding the first degradation characteristic, adding the second degradation characteristic, and combining the first sigmoid expression and the second sigmoid expression.

26. The system of claim 24, wherein the computing system is further configured for estimating a capacity loss of the electrochemical cell at a desired point in time using the multiple sigmoid model.

27. The system of claim 24, wherein the first degradation characteristic comprises a loss of active host sites.

28. The system of claim 24, wherein the second degradation characteristic comprises a loss of free lithium.

29. A computer-readable medium including computer-executable instructions, which when executed on one or more processors, perform the acts comprising:

periodically sampling cell characteristics of an electrochemical cell;

determining a first degradation characteristic and a second degradation characteristic from the cell characteristics;

periodically adding the first degradation characteristic to a first sigmoid expression;

periodically adding the second degradation characteristic to a second sigmoid expression; and

combining the first sigmoid expression and the second sigmoid expression to develop or augment a multiple sigmoid model of the electrochemical cell.

30. The computer-readable medium of claim 29, wherein the cell characteristics include one or more of a cycling rate, a voltage, a current, and a temperature.

31. The computer-readable medium of claim 29, wherein the first degradation characteristic comprises a loss of active host sites.

32. The computer-readable medium of claim 29, wherein the second degradation characteristic comprises a loss of free lithium.