Method for detecting cell state-of-charge and state-of-discharge divergence of a series string of batteries or capacitors

• US 8,581,547 B2
• Filed: 03/31/2009
• Issued: 11/12/2013
• Est. Priority Date: 03/31/2008
• Status: Active Grant

• Current Assignee: LG Energy Solution Vertech Incorporated
• Original Assignee: A123 Systems Incorporated
• Inventors: Hoff, C. Michael
• Primary Examiner(s): Tso, Edward
• Assistant Examiner(s): OMAR, AHMED H
• Application Number:
  US12/416,072
• Publication Number:
  US 20090243548A1
• Time in Patent Office: 1,687 Days
• Field of Search: 320/116
• US Class Current: 320/116
• CPC Class Codes: H02J 2207/40 adapted for charging from various sources, e.g. AC, DC or multivoltage
• CPC Class Codes: H02J 7/0013 acting upon several batteries simultaneously or sequentially H02J7/1423 takes precedence
• CPC Class Codes: H02J 7/00302 Overcharge protection
• CPC Class Codes: H02J 7/00306 Overdischarge protection
• CPC Class Codes: H02J 7/0048 Detection of remaining charge capacity or state of charge [SOC]
• CPC Class Codes: H02J 7/00712 the cycle being controlled or terminated in response to electric parameters
• CPC Class Codes: H02J 7/007184 in response to battery voltage gradient
• CPC Class Codes: H02J 7/007194 of the battery
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

A system for charging a battery includes a battery pack having at least two lithium ion cells. A controller detects a rate of change of voltage with respect to a state of charge (dV/dSOC) of the battery pack based on a calculated dV/dSOC that represents the battery pack as a whole, without calculating dV/dSOC individually on a cell-by-cell basis. Charging is terminated when dV/dSOC reaches a predetermined value.

Claims

1. A system for charging a battery comprising:

a battery pack having at least two lithium ion cells;

a controller that detects a rate of change of voltage with respect to a state of charge (dV/dSOC) of the battery pack based on a calculated dV/dSOC that represents the battery pack as a whole, without calculating dV/dSOC individually on a cell-by-cell basis;

wherein charging is terminated when dV/dSOC reaches a predetermined value.

2. The system of claim 1, wherein the battery pack consists of at least two lithium ion cells connected in series.

3. The system of claim 1, wherein the battery pack may be one from the group comprising a n series (nS), wherein n is at least two and no more than ten.

4. The system of claim 1, wherein the controller comprises a microprocessor that terminates the charging.

5. The system of claim 1, wherein the controller comprises analog circuitry.

6. The system of claim 4, wherein the microprocessor is a battery manager.

7. The system of claim 1, wherein the dV/dSOC is indicative of at least one cell reaching the predetermined value before another of the cells.

8. The system of claim 1, wherein the controller is configured to detect temperature of the internal components of the battery pack and will terminate charging if the temperature exceeds a predetermined threshold value.

9. The system of claim 8, wherein the temperature is detected by a thermistor.

10. The system of claim 1, wherein the at least two lithium ion cells comprises LiFe_1-yMn_yPO₄, wherein y represents various concentrations of Mn.

11. A battery charger, comprising:

a battery pack comprising lithium ion cells;

a circuit which determines a rate of change of voltage of the battery pack with respect to a state of charge (dV/dSOC) of the battery pack based on a calculation of the dV/dSOC that represents the battery pack as a whole, without individually calculating dV/dSOC on a cell by cell basis; and

wherein charging of the battery pack is terminated when a predetermined dV/dSOC has been reached.

12. The battery charger of claim 11, wherein the charger comprises a regulated switching power supply capable of accepting an input voltage from an AC or DC power source.

13. The battery charger of claim 12, wherein the power supply is controlled by a microprocessor.

14. The battery charger of claim 13, wherein the microprocessor terminates charging based on readings of the voltage and current of the battery pack.

15. The battery charger of claim 11, further comprising temperature sensing circuitry to monitor the temperature of at least one of the battery pack and the charger.

16. The battery charger of claim 13, wherein the voltage sensing circuitry comprises at least one of digital or analog converter circuitry.

17. The battery charger of claim 13, wherein the microprocessor is coupled to voltage sensing circuitry to determine a series voltage of the battery back as a whole.

18. The battery charger of claim 17, wherein charging of the battery pack is terminated by the microprocessor upon a condition of dV/dSOC of at least one lithium ion cell exceeding a predetermined rate.

19. The battery charger of claim 17, further comprising temperature sensing circuitry to terminate charging of the battery pack upon determination that the temperature of the battery pack has exceeded a predetermined value.

20. A method of charging a battery pack, comprising:

providing a battery pack of at least two or more lithium ion battery cells;

detecting the rate of change of voltage with respect to the state of charge (dV/dSOC) based on a calculated dV/dSOC that represents the battery pack as a whole, without individually detecting dV/dSOC on a cell by cell basis;

comparing the detected dV/dSOC with a predetermined dV/dSOC associated with the battery pack; and

terminating the charging of the battery pack based on the comparison.

21. The method of claim 20, wherein the terminating of the charging of the battery pack occurs if the detected dV/dSOC is equal to or exceeds the predetermined dV/dSOC.

22. The method of claim 20, further comprising detecting the temperature of the battery pack.

23. The method of claim 22, wherein charging is terminated based on the temperature reading.