1、Lessons Learned Entry: 2046Lesson Info:a71 Lesson Number: 2046a71 Lesson Date: 2009-5-11a71 Submitted by: Michael Bella71 POC Name: Judith Jeevarajana71 POC Email: judith.a.jeevarajannasa.gova71 POC Phone: 281-483-4528Subject: Limitations of Internal Protective Devices in High-Voltage/High- Capacity
2、 Batteries Using Lithium-Io Abstract: Most commercial cylindrical 18650 Lithium-Ion (Li-Ion) cells have two internal protective devices: the Positive Temperature Coefficient (PTC) and the Current Interrupt Device (CID). The PTC protects the cells under external short conditions and the CID protects
3、the cells under overcharge conditions. While proven to be effective at the single cell and small-size battery levels, these devices do not always offer protection when used in high voltage and high-capacity battery designs.Description of Driving Event: The internal protective devices (PTC and CID) u
4、sed in the most common commercial-off-the-shelf (COTS) Li-Ion cells (cylindrical 18650s) have been extremely reliable at a single-cell level and have resulted in total prevention of the cell reaching a hazardous condition. However, test programs have indicated that batteries built with cylindrical C
5、OTS cells in multi-cell configurations (series and/or parallel) have experienced thermal runaway under various test conditions.Lesson(s) Learned: Test data analysis indicated that the two major causes for the thermal runaway are over voltage (overcharge) and external short conditions. In these cases
6、, the internal protective devices were either not protecting as expected or were a cause for the hazards encountered. PTC ignition above its withstanding (threshold) voltage has been shown Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-to cause ther
7、mal runaway under external short conditions in high-voltage battery modules. Thermal runaway has also been observed during overcharge conditions in high-voltage and high-capacity modules, indicating that the CIDs did not protect the cells from catastrophic events, as seen in single cells. The NESC s
8、ponsored study was conducted to understand the causes for the thermal runaway in high-voltage and high-capacity battery modules, and to determine the limitations of the cell internal protective devices.Recommendation(s): PTC characteristics and limitations vary with cell manufacturer and are rarely
9、provided. This information should be obtained by testing prior to considering a battery design for a specific application. The cell series voltage should not exceed the PTC withstanding voltage. For high-voltage batteries, diodes added to a series string of cells can improve their safety under exter
10、nal short conditions. The diodes must be carefully matched to battery characteristics. In high-voltage and high-capacity batteries where the CID is used as a level of safety control, overcharge tests need to be performed to confirm its safe operation. The number of cells recommended for use in paral
11、lel depends on the charge current. The total charge current used to charge a bank (cells in parallel) should in no way cause an increase in PTC resistance of any single cell. In other words, in the event that all cell CIDs but one have opened, the current seen by the remaining cell should not cause
12、an increase in PTC resistance. The CID voltage tolerance should also be characterized. The charger voltage limit should be set so that the difference between the voltage limit value and the end-of-charge battery voltage does not cause CID arcing. The main causes of failure that prevent the CID from
13、proper safing are the charge current (causing inadvertent PTC activation), high temperatures (causing PTC activation or uncontrollable thermal runaway), and high voltages (causing PTC ignition).Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: NASA Aerospace Flight Batter
14、y Program Year 1 Report Part 1, Volumes 1 and 2, Generic Safety, Handling and Qualification Guidelines for Lithium-Ion (Li-Ion) Batteries, Li-Ion Batteries, Maintaining Technical Communications Related to Aerospace Batteries (NASA Aerospace Battery Workshop), NESC Document Number RP-08-75. Click her
15、e to download document. Mission Directorate(s): Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-N/AAdditional Key Phrase(s): a71 Additional Categories.EnergyAdditional Info: Approval Info: a71 Approval Date: 2009-05-18a71 Approval Name: mbella71 Approval Organization: HQProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
