Method for rapidly testing quality of incompletely charged electrochemical cells

• US 4,376,485 A
• Filed: 11/12/1980
• Issued: 03/15/1983
• Est. Priority Date: 07/20/1977
• Status: Expired due to Term

• Current Assignee: Congress Financial Corporation (Wells Fargo & Company)
• Original Assignee: General Electric Company
• Inventors: Shah, Rameschandra V.
• Primary Examiner(s): Reeves, Robert B.
• Assistant Examiner(s): WACYRA, EDWARD MICHAEL
• Application Number:
  US06/205,908
• Time in Patent Office: 853 Days
• Field of Search: 209/573, 209/575, 320/21, 320/48, 324/426-430, 324/432-437
• US Class Current: 209/575
• CPC Class Codes: B07C 5/344 according to electric or electromagnetic properties sorting according to size measured electrically or electronically B07C5/08; material testing by magnetic means G01N24/00, G01N27/00, by electrical means G01N27/00; electrical measuring devices in general G01R; coin testing G07D5/00

Abstract

A method for rapidly testing rechargeable electrochemical cells following assembly which enables the testing of cells to be carried out in a substantially uncharged condition. Cells in the assembly line are energized with a constant current pulse applied to their electrodes via the cell terminals, the current being of sufficient magnitude and duration so as to develop an increased charge voltage between the cell terminals. The charge voltage so developed during the application of the current and while the electrodes of the cell are incompletely charged is then measured and compared with a predetermined zone of acceptable values for cell performance. Preferably, the developed charge voltage is permitted to stabilize prior to measurement. In addition, measurements of open circuit voltage are taken immediately before and after application of the current pulse.

Claims

1. A method for rapidly testing rechargeable electrochemical cells for defects following assembly while the cells are in a substantially uncharged condition, comprising:

applying a current to the uncharged electrodes via the positive and negative terminals of the assembled cell under test, said current substantially having a magnitude greater than the one-hour current capacity of the cell and applied for a duration sufficient to develop an increased voltage between the cell terminals but insufficient to sustain the attained voltage upon removal of such current;

measuring the charge voltage so developed during application of said current at said magnitude and while the electrodes of the cell are incompletely charged; and

thereafter terminating said current so that the total charge applied to the cell does not exceed about one percent (1%) of the cell'"'"'s fully charged capacity.

2. The method of claim 1, wherein:

said applied current is substantially constant during the period of current application.

3. The method of claim 1 wherein:

said current is applied for a time sufficient to cause the charge voltage developed between electrodes of a normal cell to attain a substantially constant value.

4. The method of claim 3, wherein:

the current is applied in sufficient magnitude and for sufficient duration so as to cause the magnitude of the voltage developed between the cell terminals to exceed the open circuit voltage for the cell.

5. The method of claim 1 wherein:

the current is applied at a magnitude and for a time such that the total current charge accumulated by the cell is less than about one percent (1%) of the total charge capacity of the cell when fully charged.

6. The method of claim 5, wherein:

the charge voltage of the cell is measured after said current has been applied for a predetermined period of time, the method further comprising;

comparing, at said predetermined time, the measured charge voltage with at least one predetermined zone of values representing a minimum acceptable performance level for the cell, and

providing an indication when said measured charge voltage is outside the predetermined zone.

7. The method of claim 1, further comprising:

comparing the measured charge voltage with a predetermined maximum value representing a condition of insufficient electrolyte within the cell; and

providing an indication when the measured charge voltage exceeds the predetermined maximum value.

8. The method of claim 1, further comprising:

comparing the measured voltage with a predetermined minimum charge voltage value representing a condition of partial interelectrode shorting of the cell; and

providing an indication when the measured cell voltage is less than the predetermined minimum charge voltage value.

9. The method of claim 1, further comprising:

measuring the open circuit voltage between the cell terminals upon removal of said current.

10. The method of claim 9, further comprising:

comparing the measured open circuit voltage with a predetermined minimum open circuit voltage representing a condition of partial interelectrode shorting of the cell; and

providing an indication when the measured open circuit cell voltage is less than the predetermined minimum value for the open circuit voltage.

11. The method of claim 1, further comprising:

measuring the open circuit voltage of the substantially uncharged cell at the terminals prior to application of said current,

comparing the measured open circuit cell voltage with a predetermined minimum value representing a low resistance interelectrode shorting of the cell, and

providing an indication in the event the measured open circuit cell voltage is less than the predetermined minimum value.

12. The method of claim 11, wherein:

the predetermined minimum value for the open circuit cell voltage is less than about five percent (5%) of the value of the open circuit voltage when the cell is fully charged.

13. The method of claim 1, wherein:

the charge voltage is measured so as to provide an indication of the rate of change of voltage upon application of the constant current.

14. The method of claim 1, wherein at least one electrode of the cell at the time of measurement is in an unformed state.

15. A method for rapidly testing rechargeable electrochemical cells for manufacturing defects immediately following assembly while the cells are in a substantially uncharged condition, comprising:

applying a current pulse to the uncharged electrodes via the terminals of the assembled cell under test, said current pulse having a magnitude greater than the one-hour current capacity of the cell and being applied for a time insufficient to impose a substantial charge on the cell electrodes and insufficient to sustain the cell voltage attained during application of said current pulse, and

measuring the open circuit voltage of the cell after termination of the current pulse.

16. The method of claim 15, wherein:

the total charge applied to the cell terminals by the current pulse is less than about 1% of the total charge capacity of the cell when fully charged.

17. The method of claim 16, wherein:

at least one of the cell electrodes is unformed upon application of the current pulse.

18. A method for rapidly testing rechargeable electrochemical cells on an assembly line basis upon completion of cell assembly and prior to formation of the cell electrodes, comprising:

contacting cells on the assembly line seriatim with electrical supply means adapted to apply a current to the terminals of the completed cell to be tested,

energizing said electrical supply means contacting such cell so as to apply a current to the unformed electrodes of the cell via the cell terminals, said current being greater than the one-hour current rating of said cell and for such time period as to develop a charge voltage between the cell terminals, and

measuring the charge voltage developed during application of said current and while the electrodes of the cell are incompletely charged.

19. The method of claim 18, further comprising:

comparing the measured charge voltage with a predetermined zone of values representing satisfactory cell performance and

separating from said assembly line those cells whose measured charge voltage values are outside the predetermined zone.

20. The method of claim 19, wherein:

the total current charge applied to said cell prior to measurement is significantly less than the total charge capacity of the cell when the formed electrodes thereof are completely charged.

21. The method of claim 20, wherein:

the current is applied to the cell under test in such magnitude and for such time as to produce a charge voltage which is substantially constant for a normal cell, and

the measurement of the cell voltage is made after such time.

22. The method of claim 18, further comprising:

providing a first indication of the number of cells tested wherein the value of the measured charge voltage was outside the predetermined zone of values.

providing a second indication of the total number of cells tested, and

comparing said first and second indications to detect a predetermined ratio between the numbers represented thereby, and

stopping the cell assembly line upon detection of such ratio.

23. The method of claim 18, further comprising:

terminating the applied current prior to cell'"'"'s attainment of a substantial charge,

measuring the open circuit voltage at the cell terminals upon termination of the applied current,

comparing the measured open circuit voltage with a predetermined minimum value representing satisfactory cell performance, and

separating from the assembly line those cells whose measured open circuit voltage value is less than said predetermined minimum value.

24. The method of claim 18, wherein the step of contacting the cell with electrical supply means includes:

supplying current to an actuatable probe,

moving said probe in the direction of the axis of the cell to be tested upon actuation so as to contact the terminals of the cell with said probe.

25. A method for rapidly testing rechargeable electrochemical cells for defects following assembly while the cells are in a substantially uncharged condition, comprising:

applying a current to the uncharged electrodes via the positive and negative terminals of the assembled cell under test, such current having a magnitude at least twice the one hour current capacity of the cell and applied for a duration sufficient to develop an increased voltage between the cell terminals but insufficient to sustain the attained voltage upon removal of such current;

electrically sampling the charge voltage so developed during application of said current at said magnitude and while the electrodes of the cell are substantially uncharged;

comparing said sampled charge voltage with a reference voltage representing a desired minimum level of acceptable performance;

thereafter terminating said applied current; and

providing an indication when the sampled charge voltage departs from said reference voltage by a predetermined amount.

26. The method of claim 25, wherein:

the total charge applied to the cell by said current does not exceed about one percent (1%) of the cell'"'"'s fully charged capacity.

27. A method for rapidly testing rechargeable electrochemical cells for defects following assembly while the cells are in a substantially uncharged condition, comprising;

applying a current pulse to the uncharged electrodes via the positive and negative terminals of the assembled cell under test, said current having a magnitude substantially greater than the one-hour current capacity of the cell and applied for a duration sufficient to develop an increased voltage between the cell terminals but insufficient to sustain the attained voltage upon removal of such current, the total charge applied to said cell by said current pulse not exceeding about one percent (1%) of the total charge capacity of said cell;

electrically measuring the current voltage developed during application of said current pulse and while the electrodes of the cell remain substantially uncharged;

storing an indication of said charge voltage measurement; and

thereafter terminating said current pulse.

28. The method of claim 27, wherein said charge voltage is measured at a time during which the developed charge voltage is increasing as a function of time, and said stored indication represents a function of the rate of change of said voltage.