CELL_ACCEPTANCE.pdf

EP-WI-031

Specification for Acceptance Testing of Commercial Lithium Ion Cell Lots

Engineering Directorate

Propulsion & Power Division

Aug 2016

National Aeronautics and Space Administration

Lyndon B. Johnson Space Center Houston, Texas

Propulsion and Power Division Work Instruction

Specification for Acceptance Testing Commercial Lithium-Ion Cells

Doc. No. EP-WI-031 Rev No. A Date: Page 3 of 8

Verify that this is the correct version before using

REVISIONS

VERSION CHANGES DATE

-- Original Release Apr 2013 A Increased ambient temperature range from +/-2 to +/-3C, restructured 3.1 similar to 3.2 with sleeve removal and marking occurring pre-inspection and added a note that measurement tasks can be worked in any order, expanded 1C CCV pulse duration to 60sec maximum in

3.1.6 and 4.3, added note about current taper termination criteria in 4.4 and added test/analysis reporting requirement if the noted method is used. Added reference to JSC PRC 9002 for part marking. Specified that cell OCV measurement be done prior to any other electrical measurements both during pre-acceptance sampling and full electrical acceptance testing. Clarified pre-acceptance sampling method and quantity. Added CT/DPA to pre-acceptance. Clarified the applicability of the 14-day soft short test. Deleted leak testing. Updated acronym list.

Aug 2016

Specification for Acceptance Testing Commercial Lithium-Ion Cells

Date: Page 4 of 8

1.0 PURPOSE AND APPLICABILITY

This document defines how a lot of commercial Li-ion cells are acceptance tested for use in batteries for NASA’s crewed spacecraft in a manner compliant to JSC 20793.

Acceptance tests are defined as non-destructive testing that enables assessment of manufacturing and performance quality. The applicability of this specification is determined by the customer of the flight battery for which these commercial cells are the building block. Deviations from the requirements herein to customize it for a specific application or cell design shall be detailed in the authorization document (SOW, TPS, or Test Request) that references this specification.

2.0 APPLICABLE DOCUMENTS

The work performed and products delivered shall conform to the requirements defined in this specification and in the documents listed below:

AS9003 Inspection And Test Quality System (SAE) ISO 9001-2000 Quality Management Systems Requirements PRC-9002 Process Specification for Part Marking JSC 20793 Crewed Space Vehicle Battery Safety Requirements

3.0 RECEIVING INSPECTION

All the tasks herein shall be performed while in a temperature controlled facility to within ± 3°C. It is assumed that cells will arrive in the packaging and state of charge provided by the manufacturer. This packaging can contain multiple boxes of cells. However, this WI can be performed on cell lots repackaged for shipment and/or cycle tested, but if the date of the last capacity cycle is unknown, then the soft short circuit test (4.4) will be required.

3.1 Pre-Acceptance Testing

A statistically valid random sampling plan, shall be developed for conducting Pre- Acceptance testing. At a minimum, 20 cells shall be randomly selected and undergo the following tests and assessments. Tests 3.1.5-3.1.9 can be worked in any order except that OCV must proceed CCV and Impedance measurements:

3.1.1 Identification –Note the marking that represents the date code. Verify that each sampled cell has identical markings to confirm that they are all from the same date code. Assign identification # to each selected cell.

3.1.2 Remove Insulating Sleeve and Preserve Cell Identification – Remove insulating sleeve and donut from each cell without damaging the cell while preserving cell identification.

3.1.3 Visual Inspection - Perform visual inspection of each cell to look for defects (with no more than 10x magnification) such as corrosion, discoloration, evidence of leakage, anomalous seal ring condition, bulging, and physical surface damage (dings, cuts, dents, previous welds, and scratched).

3.1.4 OCV – Measure and record the Open Circuit Voltage (OCV) of each cell.

3.1.5 CCV – Measure and record the Closed Circuit Voltage (CCV) of each cell with a 5 nominal to 60 second maximum pulse at C-rate.

3.1.6 Impedance – Measure and record the AC impedance of each cell at 1 kHz.

3.1.7 Mass – Measure and record the mass of each bare cell.

Specification for Acceptance Testing Commercial Lithium-Ion Cells

Date: Page 5 of 8

3.1.8 Dimensional – Measure and record each cell diameter with calipers in a way that will capture that measurement at the top and bottom of the cell. Measure the height of the cell without shorting it.

3.1.9 Capacity Cycling – Unless otherwise specified by the SOW that references this specification, perform a charge and discharge cycle at the rates and maximum/minimum voltages recommended by the manufacturer for achieving the capacity (C) rating.

3.1.10 Reporting – Identify the manufacturer, cell model # and translate the date code. Tabulate the results of this sample testing with data columns for OCV, CCV, AC impedance, Mass, Diameter, Height, Charge Capacity, Discharge Capacity, and Visual Inspection Comments, with respect to cell identification #. Provide also a plot of charge and discharge voltage vs capacity for a representative cell. Provide these results along with any photographs of physical anomalies.

3.1.11 CT/DPA – 3 cells shall be sent to NASA or kept by NASA to perform CT/DPA to detect gross cell design or manufacturing defects that would merit rejecting the lot.

3.2 Full Lot Receiving Inspection

Once NASA has reviewed the Pre-Acceptance Test data and authorized continuing with acceptance of the rest of the lot, perform the following inspections:

3.2.1 Identification – Assign unique identification # to each cell within a lot with a method approved for spaceflight (certain permanent ink or bar code labels are acceptable for flight hardware per PRC-9002).

3.2.2 Remove Insulating Sleeve and Preserve Cell Identification – Remove insulating sleeve and donut from each cell without damaging the cell while preserving cell identification.

3.2.3 Visual – Perform visual inspection of each cell with no more than 10x to identify such defects as corrosion, discoloration, evidence of leakage, anomalous seal ring condition, bulging, and physical surface damage (dings, cuts, dents, previous welds, and scratches).

3.2.4 Mass - Measure and record the mass of each cell.

3.2.5 Dimensional – A set of “Go” and “No Go” gauges for the diameter and the height of each cell may be used to expedite this measurement. The dimensions of the gauges shall enable quick identification of cells that are ± 6 standard deviations from the average diameter and height dimensions. Use the results of the pre-acceptance to establish the limits.

3.2.6 Temporary Re-sleeving – Return the insulating sleeve and donut to each cell taking care to insure the correct unique identification number is preserved.

3.2.7 Rejects – Mark each cell rejected during receiving inspection per PRC-9002 paragraph 3.4.6 or similar. If the number of rejects exceeds 15% of the screened cells, NASA shall be notified within 24 hours.

4.0 CELL ELECTRICAL TESTING

The following tests shall be performed while in a room temperature controlled (± 3°C) facility or chamber on the rest of the cell lot not subjected to Pre-Acceptance testing, 3.1, and in the order listed:

Specification for Acceptance Testing Commercial Lithium-Ion Cells

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4.1 Initial Electrical Measurements – First measure and record OCV and then AC impedance at 1 kHz for each cell at the “as received” state of charge.

4.2 Charge – Unless specified otherwise, each cell shall be fully charged at the manufacturer’s recommended protocol for achieving rated capacity.

4.3 Discharge – Unless specified otherwise, after a 10 minute rest, each cell shall be fully discharged at the manufacturer’s recommended protocol for achieving rated capacity.

During the discharge, include a pulse between 1 and 60sec that produces a 10-fold increase from the baseline discharge current. If the baseline current is ≥ C-rate, a 10-fold decrease pulse can be used. This pulse is for the purpose of measuring cell internal DC resistance. Alternatively, this cell internal DC resistance can be obtained by a separate CCV measurement as in 3.1.5 during performance of 4.1. Passing cells are then ready for lot certification sampling per EP-WI-033.

4.4 Soft Short Test – This test requirement is only applicable to cells that will be used to populate flight batteries. Cell lots whose date code is less than 1 year from date of this test shall be individually subjected to this test. Discharge each cell at constant voltage to the minimum allowable voltage specified by the manufacturer’s datasheet and terminate when current tapers below C/100. Note: termination can be based on time to achieve required taper current with supporting analysis/test results. Rest for 14 days while monitoring and recording cell OCVs at minimum on Days 1, 3, 7, 10, and 14. Cells with declining voltages > 2.0 mV shall be rejected, marked, and segregated for shipment to

NASA

4.5 Storage Recharge – After completing test 4.4, each passing cell shall be recharged to 10% SoC capacity input at the same rate as used in 4.2.

4.6 Performance Tabulation – For each cell, provide the following performance results listed by unique identifier: OCV, AC Impedance, CC Charge Capacity, Taper Charge Capacity, Total Charge Capacity, Discharge Capacity, and DC resistance.

5.0 MEASUREMENT ACCURACY AND PRECISION

Unless otherwise specified in the authorizing document for this work instruction, the minimum accuracy and precision required for the measurements and tests are:

a. Mass – Accurate to ± 1 mg and precise to ± 0.1 mg.

b. Cell Voltage – Accurate to ± 2 mV and precise to ± 0.1 mV.

c. Current – Accurate to ± 2 mA and precise to ± 0.1 mA.

d. Time – Accurate to ± 10 sec over 24 hours and precise to ± 1 sec.

e. AC Impedance – Accurate to ± 5 m and precise to ± 1 m .

f. Temperature – Accurate to ± 1 °C and precise to ± 0.1 °C.

6.0 DELETED

7.0 REPORTING

The final report shall provide the following data for each cell lot:

a) Include the data from the pre-acceptance reporting from 3.1.10.

b) Tabulation of receiving inspection data and comments by cell serial number. For the mass provide statistics such as mean, standard deviation, standard deviation as % of the average, min, max, range, range as percentage of the mean, mean +3sigma, mean -3sigma, and 6 sigma range, 6 sigma range as percentage of the mean, # of low outliers, # of high outliers, and total outliers, count and outliers % of count.

Specification for Acceptance Testing Commercial Lithium-Ion Cells

Date: Page 7 of 8

c) Tabulation of the cell acceptance data by cell serial number. For the OCV, CCV (if done), AC impedance, CC charge capacity, CV taper capacity, total charge capacity, discharge capacity, and DC internal resistance provide the same statistics as in (b).

d) Tabulation of outlier cells by serial number with list of tests that each failed. Note that all outlier cell performance shall be assumed to be due to workmanship defects and will not require non-conformance reporting.

e) Test/Analysis results if used to determine termination criteria of 4.4.

f) If 6 sigma outliers exists for any parameter, another round of statistics for all parameters shall be calculated with the outliers removed. This process shall be repeated per the flow chart shown below and with the recommended lot pass/reject criteria specified in JSC 20793, 6.4.3.3f.

Outliers outside of +/- 3 sigma

Cells subjected to statistical analysis based on mass, OCV, capacity, ac/dc impedance- Do statistics on one parameter

NO

YES

Remove outliers and assess if std dev would be improved by another pass

YES Is lot uniformity critera 6 sigma % of mean met?

NO

Reject LotNO

Repeat for next parameter

YES

Total Quantity of Rejects > 15% of

Entire Lot?

ALL PARAMETERS

COMPLETE

YES

Cell Matching and Flight

Build

NO

Specification for Acceptance Testing Commercial Lithium-Ion Cells

Date: Page 8 of 8

8.0 ABBREVIATIONS AND ACRONYMS

CCV Closed Circuit Voltage CT Computed Tomography

DC Direct Current DPA Destructive Physical Analysis

JSC Johnson Space Center Li-ion Lithium Ion

NASA National Aeronautics and Space Administration OCV Open Circuit Voltage SoC State of Charge SOW Statement of Work TPS Test Performance Sheet