Method and apparatus for improving cycle life capacity of a battery pack

• US 9,787,106 B2
• Filed: 09/18/2012
• Issued: 10/10/2017
• Est. Priority Date: 09/18/2012
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Inventors: Maleki, Hossein, Hallmark, Jerald A.
• Primary Examiner(s): Siek, Vuthe
• Assistant Examiner(s): Lin, Aric
• Application Number:
  US13/621,907
• Publication Number:
  US 20140077769A1
• Time in Patent Office: 1,848 Days
• CPC Class Codes: H02J 7/00 Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
• CPC Class Codes: H02J 7/0014 Circuits for equalisation of charge between batteries
• CPC Class Codes: H02J 7/0048 Detection of remaining charge capacity or state of charge [SOC]
• CPC Class Codes: H02J 7/00714 in response to battery charging or discharging current

Abstract

A method (900) of reducing variation of an energy storage capacity of a battery across its cycle life is disclosed. The method can include the step (901) of monitoring one or more voltages of one or more cells of a battery for a predetermined discharge usage time. Where a profile of the one or more voltages during the predetermined discharge usage time meets a predefined usage criterion, the method can include the step (907) of increasing a discharge voltage limit of the one or more cells. An energy management circuit (614) can be configured with a control circuit (702) operable to increase the discharge limit and to limit discharge of the cells when the discharge limit is reached.

Claims

1. A method of managing life cycle capacity of a battery, comprising:

monitoring, with a voltage sensor, one or more voltages of one or more cells of the battery for a plurality of discharge cycles;

determining a plurality of profiles based on the one or more voltages monitored during the plurality of discharge cycles, wherein the plurality of profiles represents a user discharge history of the battery over the plurality of discharge cycles;

determining a minimum unused capacity of the one or more cells by referencing the determined plurality of profiles against a correlation of cell capacity and cell voltage;

determining a characteristic cell voltage exhibited by the one or more cells at the minimum unused capacity of the one or more cells;

in response to determining that the plurality of profiles meets a predefined usage criterion, determining, based on the plurality of profiles, a proposed discharge voltage limit, wherein the proposed discharge voltage limit is above a rated discharge voltage of the one or more cells and below the determined characteristic cell voltage;

determining, based on the plurality of profiles, a predicted amount of daily runtime capacity loss and a predicted amount of life cycle capacity gain for the proposed discharge voltage limit;

indicating, via a user interface, the predicted amount of daily runtime capacity loss and the predicted amount of life cycle capacity gain for the proposed discharge voltage limit;

prompting, via the user interface, for authorization to increase a discharge voltage limit of the one or more cells from the rated discharge voltage limit of the one or more cells of the battery to the proposed discharge voltage limit;

receiving an electronic signal indicating authorization to increase the discharge voltage limit to the proposed discharge voltage limit;

in response to receiving the electronic signal, increasing the discharge voltage limit of the one or more cells to the proposed discharge voltage limit; and

operating the one or more cells in accordance with the increased discharge voltage limit by limiting a discharge current from the one or more cells when the one or more voltages fall to the proposed discharge voltage limit.

2. The method of claim 1, further comprising providing, on the user interface, a low battery indication when the one or more voltages fall to the discharge voltage limit.

3. The method of claim 1, wherein the limiting comprises increasing a series impedance of a discharge control device coupled serially between the battery and a load.

4. The method of claim 1, wherein the increasing comprises increasing the discharge voltage limit by at least 400 mV.

5. The method of claim 1, wherein the increasing comprises increasing the discharge voltage limit from about 2.7 volts to at least 3.1 volts.

6. The method of claim 1, wherein the plurality of discharge cycles comprise five or more charging cycles.

7. The method of claim 1, wherein the anodes of the one or more cells of the battery comprise silicon and a silicon alloying carbon.

8. The method of claim 1, wherein the life cycle capacity gain comprises a reduction of degradation of a charge capacity of the one or more cells of the battery across a cycle life of the one or more cells of the battery.

9. The method of claim 1, further comprising:

determining that the plurality of profiles meets the predefined usage criterion, wherein the predefined usage criterion comprises the one or more voltages remaining above a rated discharge voltage of the one or more cells by a predetermined margin for a predetermined number of discharge cycles.

10. The method of claim 9, wherein the predetermined margin is about twenty-five percent.

11. The method of claim 1, wherein the user interface is a user interface of a portable electronic device operable with the battery.

12. An energy management circuit comprising:

a control circuit, operable with;

a voltage sense node configured to sense a voltage across one or more rechargeable cells; and

a discharge control node configured to control a discharge current limiter coupled serially with the one or more rechargeable cells;

wherein the control circuit is configured to;

determine a plurality of profiles of the voltage at the voltage sense node over a predetermined number of days, wherein the plurality of profiles represents a user discharge history of the one or more rechargeable cells over the predetermined number of days;

determine a minimum unused capacity of the one or more rechargeable cells by referencing the determined plurality of profiles against a correlation of cell capacity and cell voltage;

determine a characteristic cell voltage exhibited by the one or more rechargeable cells at the minimum unused capacity of the one or more rechargeable cells;

in response to determining that the plurality of profiles of the voltage meets a predefined criterion, determine, based on the plurality profiles of the voltage, a proposed discharge voltage limit, wherein the proposed discharge voltage limit is above a rated discharge voltage of the one or more rechargeable cells and below the determined characteristic cell voltage;

determine, based on the plurality of profiles of the voltage, a predicted amount of daily runtime capacity loss and a predicted amount of life cycle capacity gain for the proposed discharge voltage limit;

indicate, with a user interface of an electronic device coupled to the control circuit, the predicted amount of daily runtime capacity loss and the predicted amount of life cycle capacity gain for the proposed discharge voltage limit;

deliver a prompt to the user interface of the electronic device requesting user permission to increase a discharge voltage limit of the one or more rechargeable cells to the proposed discharge voltage limit;

receive a user response from the electronic device in response to the prompt;

when the user response comprises an authorization to increase the discharge voltage limit of the one or more rechargeable cells to the proposed discharge voltage limit, increase the discharge voltage limit for the one or more rechargeable cells to the proposed discharge voltage limit; and

operate the one or more rechargeable cells in accordance with the increased discharge voltage limit by causing the discharge current limiter to limit a discharge current from the one or more rechargeable cells upon the voltage at the voltage sense node falling to the proposed discharge voltage limit.

13. The energy management circuit of claim 12, wherein causing the discharge current limiter to limit the discharge current comprises:

the control circuit applying a control signal to the discharge control node upon the voltage at the voltage sense node falling to the proposed discharge voltage limit, wherein the control signal is configured to increase a serial impedance of the discharge current limiter.

14. The energy management circuit of claim 12, wherein anodes of the one or more rechargeable cells comprise silicon and a silicon alloying carbon.

15. The energy management circuit of claim 12, wherein the one or more rechargeable cells and the control circuit are both disposed within a battery pack.

16. The energy management circuit of claim 12, wherein the control circuit is configured to determine that the plurality of profiles of the voltage meets the predefined criterion, wherein the predefined criterion comprises the plurality of profiles of the voltage remaining above a rated discharge voltage of the one or more rechargeable cells by a predetermined margin for the predetermined number of days.

17. A method of managing life cycle capacity of a battery, comprising:

monitoring, with a control circuit coupled to one or more cells of the battery, a discharge rate of one or more cells of the battery across a plurality of discharge cycles;

determining a plurality of user discharge profiles based on the monitored discharge rate of the one or more cells of the battery, wherein the plurality of user discharge profiles represents a user discharge history of the one or more cells over the plurality of discharge cycles;

determining a characteristic cell voltage exhibited by the one or more cells at a minimum unused capacity of the one or more cells across the plurality of discharge cycles;

when the plurality of user discharge profiles meets a predefined criterion, determining, based on the determined plurality of user discharge profiles, a proposed discharge voltage limit, wherein the proposed discharge voltage limit is above a rated discharge voltage of the one or more cells and below the determined characteristic cell voltage;

determining, based on the plurality of user discharge profiles, a predicted amount of daily runtime capacity loss and a predicted amount of life cycle capacity gain for the proposed discharge voltage limit;

indicating, with a user interface operable with the control circuit, the predicted amount of daily runtime capacity loss and the predicted amount of life cycle capacity gain for the proposed discharge voltage limit;

prompting, with the user interface operable with the control circuit, for authorization to increase a discharge voltage limit from the rated discharge voltage limit of the one or more cells to the proposed discharge voltage limit;

receiving an authorization to increase the discharge voltage limit to the proposed discharge voltage limit;

in response to receiving the authorization, increasing the discharge voltage limit of the one or more cells to the proposed discharge voltage limit; and

operating the one or more cells in accordance with the increased discharge voltage limit by limiting a discharge current from the one or more cells when one or more voltages of the one or more cells fall to the proposed discharge voltage limit.

18. The method of claim 17, further comprising:

monitoring, with the control circuit coupled to the one or more cells of the battery, the one or more voltages of the one or more cells of the battery across the plurality of discharge cycles, wherein the predefined criterion comprises the one or more voltages remaining above the rated discharge voltage of the one or more cells by a predetermined margin for a predetermined number of discharge cycles.

19. The method of claim 17, wherein the anodes of the one or more cells of the battery comprise silicon and a silicon alloying carbon.

20. The method of claim 17, wherein limiting the discharge current from the one or more cells comprises increasing a series impedance of a discharge control device coupled serially between the battery and a load.