Method, apparatus and computer readable recorded medium for secondary battery life evaluation

• US 6,433,513 B1
• Filed: 08/28/2000
• Issued: 08/13/2002
• Est. Priority Date: 08/30/1999
• Status: Expired due to Term

• Current Assignee: NEC Corporation
• Original Assignee: NEC Infrontia Corporation (NEC Corporation)
• Inventors: Hayashi, Katsutoshi
• Primary Examiner(s): TOATLEY, GREGORY J
• Application Number:
  US09/650,159
• Time in Patent Office: 715 Days
• Field of Search: 324/427, 324/426, 324/433, 320/132, 320/134, 320/136
• US Class Current: 320/132
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/3828 using current integration
• CPC Class Codes: H02J 7/0048 Detection of remaining charge capacity or state of charge [SOC]
• CPC Class Codes: H02J 7/005 Detection of state of health [SOH]
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

A method and an apparatus for accurately determining the service life of a secondary battery are provided. If a the battery 14 is re-charged after each discharge, various values of an index related to pre-measured degradation of a fully charged secondary battery 14 are stored in a flash read-only-memory FROM 34 so that they may be compared with discharged amounts of the battery 14. The duration of discharge is obtained by a timing circuit 24, and the discharged amount is computed by the control circuit 26. A value of the index is obtained by referring to FROM 34 using the computed value of discharged power. The service life remaining after the current use is computed by the control circuit 26, according to the maximum service life of the battery 14 and various values of the index obtained after each use of the battery including the current use, and the end of service life of the battery 14 is determined according to whether the computed service life is longer or shorter than a pre-determined threshold value.

Claims

1. A method for determining a service life of a secondary battery subjected to repeated charging/discharging cycles;

comprising the steps of;

storing, in a memory device, pre-measured values of an index related to decrements in service life of the battery, which is fully charged after each discharge event during a charging/discharging cycle, to correspond to discharged amounts produced during charging/discharging cycles experienced by the battery during the respective charging/discharging cycles;

computing a discharged amount after each charging/discharging cycle;

obtaining an index to correspond to the discharged amount from said memory device;

computing a service life remaining after the current cycle of charging/discharging according to a maximum service life of the battery and the values of the index obtained in individual charging/discharging cycles, including the current charging/discharging cycle; and

determining whether or not the remaining service life computed is less than a pre-determined reference value, and deeming that the battery has reached an end of the service life when the computed value is less than the reference value.

13. A computer-readable recorded medium containing a program for determining a service life of a secondary battery according to claim 1.

2. A method for determining a service life of a secondary subjected to repeated charging and discharging processes, comprising the steps of:

storing, in a memory device, pre-measured values of an index related to decrements in service life of the battery and various amounts of charges and discharges produced in charging/discharging cycles corresponding to the charged and discharged amounts experienced by the battery during the respective charging/discharging cycles;

computing a charged amount and a discharged amount after each cycle of charging/discharging;

obtaining an index to correspond to the computed charged amount and the computed discharged amount with reference to said memory device;

computing a service life remaining after the current cycle of charging/discharging according to a maximum service life of the battery and the values of the index obtained in individual charging/discharging cycles, including the current charging/discharging cycle; and

determining whether or not the remaining service life computed is less than a pre-determined reference value, and deeming that the battery has reached an end of the service life when the computed service life is less than the reference value.

14. A computer-readable recorded medium containing a program for determining a service life of a secondary battery according to claim 2.

3. A method for determining a useable time for one additional use, after a current cycle of charging/discharging of a secondary battery subjected to repeated cycles of charging/discharging, comprising the steps of:

computing a service life of the battery remaining after the current cycle of charging/discharging of the battery;

computing an average amount of consumed service life by dividing a cumulative value of consumed service life of individual cycles from a first cycle to the current cycle of charging/discharging by a number of cycles of charging/discharging;

computing an average use time of the battery from the first cycle to the current cycle; and

computing a useable time for one additional use of the battery after the current cycle of charging/discharging, according to the remaining service life computed, the average amount of consumed service life, and the average use time of the battery.

4. A method according to claim 3, wherein said remaining service life of the battery is obtained by subtracting a cumulative consumed service life including the current cycle of charging/discharging from the maximum service life of the battery.

5. A method according to claim 3, wherein said remaining service life of the battery is obtained by:

storing, in a memory device, pre-measured values of an index related to decrements in service life of the battery, which is fully charged after each discharge event during a charging/discharging cycle, to correspond to discharged amounts produced during charging/discharging cycles experienced by the battery during the respective charging/discharging cycles;

computing a first cumulative discharged amount from individual cycles of charging/discharging including a preceding cycle of charging/discharging of the battery;

obtaining a value of the index with reference to said memory device to correspond to the first cumulative discharged amount from individual cycles of charging/discharging including the preceding cycle;

computing a first service life of the battery remaining after the preceding cycle of charging/discharging, according to the maximum service life of the battery and the values of the index obtained from individual cycles of charging/discharging including the preceding cycle of charging/discharging of the battery;

computing a second cumulative discharged amount from individual cycles of charging/discharging including a current cycle of charging/discharging of the battery;

obtaining another value of the index with reference to said memory device to correspond to the second cumulative discharged amount from individual cycles of charging/discharging including the current cycle;

computing a second service life of the battery remaining after the current cycle of charging/discharging, according to the maximum service life of the battery and the values of the index obtained from individual cycles of charging/discharging including the current cycle of charging/discharging of the battery; and

obtaining said remaining service life of the battery by subtracting said first cumulative service life from said second cumulative service life.

6. A method according to claim 3, wherein said remaining service life of the battery is obtained by:

storing, in a memory device, pre-measured values of an index related to decrements in service life of the battery and various amounts of charges and discharges produced in charging/discharging cycles corresponding to the charged and discharged amounts experienced by the battery during the respective charging/discharging cycles;

computing a charged amount and a discharged amount after each cycle of charging/discharging;

computing a first cumulative charged amount and a first cumulative discharged amount from individual cycles of charging/discharging including a preceding cycle of charging/discharging of the battery;

obtaining an index with reference to said memory device to correspond to the first cumulative charged amount and the first cumulative discharged amount from individual cycles of charging/discharging including the preceding cycle;

computing a first service life of the battery remaining after the preceding cycle of charging/discharging, according to the maximum service life of the battery and the values of the index obtained from individual cycles of charging/discharging including the preceding cycle of charging/discharging of the battery;

computing a second cumulative charged amount and the second cumulative discharged amount from individual cycles of charging/discharging including a current cycle of charging/discharging of the battery;

obtaining an index with reference to said memory device to correspond to the second cumulative charged amount and the second cumulative discharged amount from individual cycles of charging/discharging including the current cycle;

computing a second service life of the battery remaining after the current cycle of charging/discharging, according to the maximum service life of the battery and the values of the index obtained for individual cycles of charging/discharging including the current cycle of charging/discharging of the battery; and

obtaining said remaining service life of the battery by subtracting said first service life from said second service life.

15. A computer-readable recorded medium containing a program for determining a service life of a secondary battery according to claim 3.

7. An apparatus for determining a service life of a secondary battery subjected to repeated cycles of charging/discharging of the battery, comprising:

first memory unit which stores values of an index related to decrements in service life of the battery, which is after each discharge event during a charging/discharging cycle, and various discharged amounts produced in charging/discharging cycles so as to correspond to discharged amounts experience by the battery in charging/discharging cycles;

first discharged amount computation unit which computes a discharged amount for each cycle of charging/discharging;

first index obtaining unit which obtains an index to correspond to a discharged amount computed by said first discharged amount computation unit with reference to the first memory unit;

computing a service life remaining after the current cycle of charging/discharging according to a maximum service life of the battery and the values of the index obtained in individual charging/discharging cycles, including the index obtained in the current charging/discharging cycle; and

first determination unit which determines whether or not the remaining service life computed is less than a pre-determined reference value, and deeming that the battery has reached an end of the service life when the computed service life is less than the reference value.

16. A computer-readable recorded medium containing a program for determining a service life of a secondary battery according to claim 7.

8. An apparatus for determining a service life of a secondary battery subjected to repeated cycles of charging/discharging of the battery, comprising:

second memory unit which stores, in a memory device, pre-measured values of an index related to decrements in service life of the battery and various amounts of charges and discharges produced in charging/discharging cycles corresponding to the charged and discharged amounts experienced by the battery during the respective charging/discharging cycles;

computing a charged amount and a discharged amount after each cycle of charging/discharging;

first charged/discharged amount computation unit which computes a charged amount and a discharged amount for each cycle of charging/discharging;

second index obtaining unit which obtains an index to correspond to a charged amount and a discharged amount computed by said first charged/discharged amount computation unit with reference to the second memory unit;

second service life computation unit which computes a remaining service life of the battery after the current cycle of charging/discharging according to the maximum service life of the battery and the index obtained by said second index obtaining unit from individual cycles of charging/discharging including current cycle of charging/discharging; and

second determination unit which determines whether or not the remaining service life computed is less than a pre-determined reference value, and deeming that the battery has reached an end of the service life when the computed service life is less than the reference value.

17. A computer-readable recorded medium containing a program for determining a service life of a secondary battery according to claim 8.

9. An apparatus for determining a useable time for one additional use, after a current cycle of charging/discharging of a secondary battery subjected to repeated cycles of charging/discharging, comprising:

service life computation unit which computes a service life of the battery remaining after the current cycle of charging/discharging of the battery;

average service life computation unit which computes an average amount of consumed service life by dividing a cumulative value of consumed service life of individual cycles from a first cycle to the current cycle of charging/discharging by a number of cycles of charging/discharging;

average use time computing unit which computes an average use time of the battery from the first cycle to the current cycle; and

useable time computation unit which computes a useable time for one additional use of the battery after the current cycle of charging/discharging, according to the remaining service life computed, the average amount of consumed service life, and the average use time of the battery.

10. An apparatus according to claim 9, wherein said remaining service life computed by the remaining service life computation unit is obtained by subtracting from the maximum service life of the battery a cumulative consumed service life in individual cycles of charging/discharging from the first use to the current use.

11. An apparatus according to claim 9, wherein said service life decrement computation unit comprises:

third memory unit which stores, in a memory device, pre-measured values of an index related to decrements in service life of the battery, which is fully charged after each discharge event during a charging/discharging cycle, to correspond to discharged amounts produced during charging/discharging cycles experienced by the battery during the respective charging/discharging cycles;

second discharged amount computation unit which computes a discharged amount for each cycle of charging/discharging;

third index obtaining unit which obtains an index to correspond to a discharged amount computed by said second discharged amount computation unit with reference to the third memory unit; and

first differential outputting unit which outputs a difference between a service life remaining in the battery after the preceding cycle of charging/discharging computed according to the maximum service life of the battery and the values of the index obtained by said third index obtaining unit for individual cycles of charging/discharging including the preceding cycle of discharge, on the one hand, and a service life remaining in the battery after the current cycle of charging/discharging computed according to the maximum service life of the battery and the values of the index obtained by said third index obtaining unit for individual cycles of charging/discharging including the current cycle of discharge, on the other.

12. A useable time computation apparatus according to claim 9, wherein said service life decrement computation unit comprises:

fourth memory unit which stores pre-measured values of an index related to decrements in service life of the battery and various amounts of charges and discharges produced in charging/discharging cycles corresponding to the charged and discharged amounts experienced by the battery during the respective charging/discharging cycles;

computing a charged amount and a discharged amount after each cycle of charging/discharging;

fourth index obtaining unit which obtains an index to correspond to a discharged amount computed by said second discharged amount computation unit with reference to the fourth memory unit; and

second differential outputting unit which outputs a difference between a service life remaining in the battery after the preceding cycle of charging/discharging computed according to the maximum service life of the battery and the values of the index obtained by said fourth index obtaining unit for individual cycles of charging/discharging including the preceding cycle of discharge, on the one hand, and a service life remaining in the battery after the current cycle of charging/discharging computed according to the maximum service life of the battery and the values of the index obtained by said fourth index obtaining unit for individual cycles of charging/discharging including the current cycle of discharge, on the other.

18. A computer-readable recorded medium containing a program for determining a service life of a secondary battery according to claim 9.