Systems and related methods for determining self-discharge currents and internal shorts in energy storage cells

• US 10,036,779 B2
• Filed: 11/30/2015
• Issued: 07/31/2018
• Est. Priority Date: 11/30/2015
• Status: Active Grant

• Current Assignee: Battelle Energy Alliance LLC (Battelle Memorial Institute)
• Original Assignee: Battelle Energy Alliance LLC (Battelle Memorial Institute)
• Inventors: Sazhin, Sergiy V, Dufek, Eric J, Gering, Kevin L
• Primary Examiner(s): PELTON, NATHANIEL R
• Application Number:
  US14/954,446
• Publication Number:
  US 20170153290A1
• Time in Patent Office: 974 Days
• Field of Search: 324434
• CPC Class Codes: G01R 31/003 Environmental or reliability tests of individual semiconductors G01R31/2642; of PCB's G01R31/2817; of IC's G01R31/2855; of other circuits G01R31/2849
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/382 Arrangements for monitoring battery or accumulator variables, e.g. SoC
• CPC Class Codes: G01R 31/396 Acquisition or processing of data for testing or for monitoring individual cells or groups of cells within a battery
• CPC Class Codes: G01R 31/52 Testing for short-circuits, leakage current or ground faults
• CPC Class Codes: H01M 10/42 Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells H01M10/60 takes precedence
• CPC Class Codes: H01M 10/425 Structural combination with electronic components, e.g. electronic circuits integrated to the outside of the casing printed circuits H05K1/00
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

Systems and methods for determining self-discharge currents in an energy storage cell and detecting internal shorts are disclosed. A system includes a DC voltage source configured to provide a constant test voltage selected to be less than an open-circuit voltage of an energy storage cell to the energy storage cell. The system also includes a current measuring device operably coupled between the DC voltage source and the energy storage cell, and control circuitry operably coupled to the current measuring device. A method includes applying the constant test voltage, and measuring the test current flowing between the DC voltage source and the energy storage cell until after the test current switches from a negative current to a positive current. The method also includes determining a self-discharge current of the energy storage cell by analyzing the measured test current with computational models that capture physical processes tied to the test methods.

Claims

1. A method of determining a self-discharge current in an energy storage cell, the method comprising:

applying, with a direct current (DC) voltage source, a constant test voltage to an energy storage cell without an external load connected thereto, the constant test voltage being less than an open-circuit voltage of the energy storage cell at an initial state of charge (SOC) of the energy storage cell;

measuring a test current flowing between the DC voltage source and the energy storage cell until after the test current switches from a negative current to a positive current; and

determining, with control circuitry operably coupled to a current measuring device, a self-discharge current of the energy storage cell by analyzing the measured test current, wherein the self-discharge current is indicative of a rate of internal discharge of charge stored by the energy storage cell.

2. The method of claim 1, wherein determining a self-discharge current of the energy storage cell by analyzing the measured test current comprises determining the self-discharge current to be about an average of the measured test current taken after the measured test current switches from the negative current to the positive current.

3. The method of claim 1, wherein determining a self-discharge current of the energy storage cell by analyzing the measured test comprises computing a slope of a line approximating an accumulated charge of the energy storage cell with respect to time taken after a minimum value of the cumulative charge is reached.

4. The method of claim 1, wherein applying a constant test voltage to an energy storage cell at an initial SOC of the energy storage cell comprises applying the constant test voltage at SOC of fully charged energy storage cell.

5. The method of claim 1, wherein applying a constant test voltage to an energy storage cell at an initial SOC of the energy storage cell comprises applying the constant test voltage to the energy storage cell at a SOC less than SOC for a fully charged cell.

6. The method of claim 1, wherein applying a constant test voltage to an energy storage cell comprises applying the constant test voltage to the energy storage cell, wherein the constant test voltage is about 0.2 to 20 millivolts less than the open-circuit voltage of the energy storage cell.

7. The method of claim 1, further comprising controlling an environmental temperature of the energy storage cell to be similar to an expected operational temperature of the energy storage cell while applying the constant test voltage and measuring the test current.

8. The method of claim 1, further comprising determining that the energy storage cell has developed at least one of an internal soft short circuit or an internal hard short circuit responsive to determining that the determined self-discharge current of the energy storage cell is greater than a previously determined self-discharge current by a predetermined threshold.

9. The method of claim 8, wherein determining that the energy storage cell has developed at least one of an internal soft short circuit or an internal hard short circuit comprises determining that the determined self-discharge current of the energy storage cell is greater than the previously determined self-discharge current by at least about an order of magnitude.

10. The method of claim 8, further comprising indicating, with a user interface operably coupled to the control circuitry, that the energy storage cell has developed at least one of an internal soft short circuit or an internal hard short circuit.

11. A system for determining a self-discharge current of one or more energy storage cells, the system comprising:

a direct current (DC) voltage source configured to provide a constant test voltage to one or more energy storage cells without an external load connected thereto, the constant test voltage selected to be less than an open circuit voltage of the one or more energy storage cells;

a current measuring device operably coupled between the DC voltage source and the one or more energy storage cells and configured to measure a test current flowing between the DC voltage source and the one or more energy storage cells;

control circuitry operably coupled to the current measuring device and configured to determine a self-discharge current of the one or more energy storage cells by analyzing the test current measured by the current measuring device, wherein the self-discharge current is indicative of a rate of internal discharge of charge stored by the energy storage cell; and

a user interface configured to indicate at least one of the determined self-discharge current of the one or more energy storage cells and a health parameter of the one or more energy storage cells generated from the determined self-discharge current determined by the control circuitry.

12. The system of claim 11, further comprising the one or more energy storage cells.

13. The system of claim 12, wherein the one or more energy storage cells include a plurality of energy storage cells, at least one of the plurality of energy storage cells operably coupled in parallel with at least another of the plurality of energy storage cells.

14. The system of claim 12, wherein the one or more energy storage cells include a plurality of energy storage cells, at least one of the plurality of energy storage cells operably coupled in series with at least another of the plurality of energy storage cells.

15. The system of claim 12, wherein the one or more energy storage cells include at least one of a lithium-ion, a lithium metal, a sodium-ion, a lead acid, a nickel-cadmium, and a nickel metal hydride energy storage cell.

16. The system of claim 11, further comprising a battery-powered device including the one or more energy storage cells, the DC voltage source, the current measuring circuitry, the control circuitry, and the user interface.

17. The system of claim 16, wherein the battery-powered device includes a battery-powered device selected from the group consisting of an electric-drive vehicle, an electric grid service, and a consumer electronic device.

18. The system of claim 11, wherein the health parameter of the one or more energy storage cells includes an indication that at least one of the one or more energy storage cells should be replaced responsive to a determination, based at least in part upon the determined self-discharge current, that the at least one of the one or more energy storage cells includes at least one of an internal soft short circuit or an internal hard short circuit.

19. The system of claim 11, wherein the health parameter of the one or more energy storage cells includes an indication that at least one of a short-circuit or a nascent dendrite has formed in the energy storage cell responsive to a change in a determined metric determined by analyzing the test current measured by the current measuring device.

20. The system of claim 19, wherein the determined health metric includes at least one of the determined-self-discharge current, a length of time required for the test current to reach a zero-crossing point, and a determined internal short-circuit resistance.

21. A method of determining a self-discharge current of an energy storage cell, the method comprising:

applying, with a direct current (DC) voltage source, a constant test voltage to an energy storage cell without an external load connected thereto, the constant test voltage selected to be less than an open-circuit voltage of an energy storage cell;

measuring a test current flowing between the DC voltage source and the energy storage cell at least until after the test current switches from a negative current to a positive current flowing from the DC voltage source to the energy storage cell; and

determining, with control circuitry operably coupled to a current measuring device, a self-discharge current of the energy storage cell by analyzing the measured test current wherein the self-discharge current is indicative of a rate of internal discharge of charge stored by the energy storage cell.

22. The method of claim 21, wherein determining a self-discharge current of the energy storage cell by analyzing the measured test current source comprises analyzing the measured test current with a sigmoidal-type model that accounts for multiple physical processes in the cell during test periods.

23. The method of claim 22, wherein determining a self-discharge current of the energy storage cell by analyzing the measured test current comprises using a sigmoidal-type model with which to perform a numeric regression on data points corresponding to the test current measured between a time that the constant test voltage is applied to the energy storage cell and a time that the test current switches from negative current to positive current, thereby shortening the time required to determine the self-discharge current of the energy storage cell.

24. The method of claim 21, wherein analyzing the measured test current is performed with a sigmoidal-type model that covers potentiostatic conditions.

25. The method of claim 21, wherein determining a self-discharge current of the energy storage cell by analyzing the measured test current comprises determining a magnitude of the self-discharge current to be the same as a magnitude that the test current settles to after the test current switches from the negative current to the positive current.

26. The method of claim 21, further comprising determining a change in state of charge (SOC) of the energy storage cell by numerically integrating a mathematical model expression estimating the test current over time to determine a net amount of energy lost by the energy storage cell.

27. The method of claim 21, further comprising the use of a mathematical model and a reference value for self-discharge current for predicting the self-discharge current of the energy storage cell for arbitrarily-chosen conditions of the energy storage cell.

28. The method of claim 27, wherein predicting the self-discharge current of the energy storage cell for arbitrarily-chosen conditions of the energy storage cell comprises predicting the self-discharge current of the energy storage cell for at least one condition of the energy storage cell, wherein the at least one condition is selected from the group consisting of cell chemistry, state of charge, age of cell, and cell temperature.

29. The method of claim 21, wherein determining a self-discharge current of the energy storage cell by analyzing the measured test current source comprises diagnostic analysis of the measured test current with a mathematical model, and identifying parameters of the mathematical model that have at least one of a physical, a chemical, a kinetic, and a material basis that contributes to behavior of the self-discharge current of the energy storage cell.

30. The method of claim 21, wherein determining a self-discharge current is performed for multiple interconnected cells of arbitrarily chosen cell-to-cell configuration.

31. The method of claim 21, further comprising determining key quantities related to self-discharge current for use within battery management and control systems, wherein the monitoring and control of operational conditions and diagnostic determination of the battery state of use and health are continuously performed, such that real-time management actions are facilitated.