System and method for battery charge control based on charge capacity headroom

• US 20040222768A1
• Filed: 05/09/2003
• Published: 11/11/2004
• Est. Priority Date: 05/09/2003
• Status: Active Grant

• Current Assignee: EnerDel, Inc. (Ener1, Inc.)
• Original Assignee: EnerDel, Inc. (Ener1, Inc.)
• Inventors: Moore, Stephen W., Hanauer, Brad T., Schneider, Peter J.
• Granted Patent: US 7,245,107 B2
• Time in Patent Office: Days
• US Class Current: 320/128
• CPC Class Codes: H02J 7/0069 Charging or discharging for charge maintenance, battery initiation or rejuvenation

Abstract

A charging and discharging strategy for a rechargeable battery pack is disclosed. The strategy involves monitoring and learning the battery pack'"'"'s condition (a cycle life parameter) in terms of its progression through its life cycle. The life cycle parameter may be determined as a function of both time (i.e., the battery pack'"'"'s age) as well as the number of discharge/recharge cycles. The strategy intentionally under-utilizes the battery during the initial stages of its life, based on the cycle life parameter, by charging it to a first level less then the maximum state of charge. This approach reduces charge voltages, reducing stress on the battery'"'"'s active materials, thereby increasing its life.

Claims

1. A method of charge control of a battery pack comprising the steps of:

reserving a charge headroom to thereby establish a first charge level based on a cycle life parameter of the battery pack; and

charging the battery pack to the first level corresponding to a maximum state of charge less the reserved charge headroom.

2. The method of claim 1 further comprising the step of determining said cycle life parameter as a function of a condition of capacity degradation.

3. The method of claim 2 wherein the capacity degradation is caused by (i) time and (ii) a number of charge cycles of the battery pack.

4. The method of claim 3 further comprising the step of allowing discharge while the state of charge of the battery pack exceeds a second level corresponding to a complete discharge level increased by an amount that is based on the cycle life parameter.

5. The method of claim 4 further including the step of selecting the first level and second level so as to regulate uniform capacity of the battery pack over a cycle life thereof.

6. A method of operating a battery pack comprising the steps of:

determining a maximum state of charge of the battery pack as a function of a cycle life parameter of the battery pack;

calculating a charge headroom as a function of the cycle life parameter of the battery pack;

charging the battery pack to a first level corresponding to the maximum state of charge less the charge headroom.

7. The method of claim 6 further comprising the step of determining the cycle life parameter as a function of a level of capacity degradation.

8. The method of claim 7 further comprising the step of allowing discharge while the state of charge of the battery pack exceeds a second level corresponding to a complete discharge level elevated by an amount that is based on the cycle life parameter.

9. The method of claim 8 further including the step of selecting the first level and second level so as to regulate uniform capacity of the battery pack over a cycle life thereof.

10. The method of claim 8 wherein said charging step includes the substep of:

increasing a charging voltage applied to the battery pack as the cycle life parameter increases.

11. The method of claim 10 further comprising the step of:

forming the battery pack using lithium chemistry cells.

12. The method of claim 11 wherein said lithium chemistry is one selected from the group comprising lithium ion (Li-Ion), lithium polymer (Li-Po) and lithium sulfur.

13. A rechargeable battery pack comprising:

at least one battery cell configured to produce electrical power on a terminal thereof;

means for calculating a first charge level as a function of a cycle life parameter of the at least one battery cell corresponding to a maximum state of charge less a charge headroom; and

means for controlling charging of said battery cell to the first level.

14. The battery pack of claim 13 wherein said calculating means includes a central processing unit (CPU) configured to calculate said charge headroom, said CPU being further configured to calculate a charge termination voltage that corresponds to said first level.

15. The battery pack of claim 14 wherein said controlling means includes said CPU configured as a charge controller that generates a charge termination signal when a voltage level on said terminal reaches said charge termination voltage.