Cindy Millsaps, President and CEO, Energy Assurance
The International Electrotechnical Commission (IEC) Sub-committee 21A, which is responsible for secondary cell and battery standards, has recently completed work on the Second Edition of IEC 62133, the standard for Secondary cells and batteries containing alkaline or other non-acid electrolytes. This standard covers rechargeable Nickel cells and batteries, as well as lithium ion (Li-Ion) cells and batteries. The new revision of IEC 62133 is expected to be issued in early 2012. The Second Edition will have some very significant changes for Li-Ion cell and battery manufacturers. In this article we will review the significant changes related to Li-Ion cells. Part I of the article will examine the proposed changes for cells and Part II the proposed changes for battery packs related to Li-Ion products. Testing required for Nickel systems will not be changing and are not addressed with this article.
Part I: Cells
The revisions in the proposed Second Edition of IEC 62133 have the most impact on Li-Ion cell manufacturers. The required testing as well as the test conditions have been completely revamped. They include a test that is not currently standard in the industry and has questionable repeatability. On a more positive note, the committee did take into consideration that testing done in accordance with the UN Manual of Tests and Criteria, Section 38.3 (UN38.3 testing), was redundant in the first edition of the standard and has removed some of this testing as a result.
The changes related to Li-Ion cells fall into three categories:
• Removal of testing that is redundant with other standards
• Modifications to existing tests
• Completely new requirements
Removal of Testing that is Redundant with Other Standards
The simplest and most straight forward changes are those that removed testing that was redundant with other standards. The main focus here was the removal of items covered under the UN Manual of Tests and Criteria (UN 38.3). This change makes perfect sense because the UN 38.3 testing is mandatory globally in order to ship Li-Ion product by air or sea, and in most countries by ground as well. The tests planned for removal are:
• Temperature Cycling
• Mechanical Shock
• Low Pressure (Altitude Simulation)
• Cell Protection Against High Rate Charging (not a UN 38.3 test)
With the removal of these tests, the proposal does include a new paragraph that mentions the need to comply with the current appropriate transportation regulations and testing requirements. It allows for the fact that these requirements may change over time and permits for presentation of customer documentation to verify compliance. This maintains the ability of the manufacturers to comply with shipping regulations with a self-declaration and does not unnecessarily create a more stringent certification requirement.
Modifications to Existing Tests
Modifications to existing tests are the second type of changes that are being implemented with the new revision of IEC 62133. These are a little more complicated. The most significant of these changes is related to how the samples are prepared testing. In the First Edition of the standard, samples are simply charged at room temperature (20°C ±5°C) in accordance with the manufacturer’s recommended charge method. The proposed Second Edition includes two charge procedures: one at room temperature, and a new procedure at the high and low end of the stated operating temperature range (10°C and 45°C if not stated). The new charge method also requires the charging to be done at the maximum rated charge current of the product. This procedure is only required for samples that will be used for the short circuit, thermal abuse, crush and forced internal short tests at the cell level.
The Continuous Low Rate Charge test is being revised to become a Constant Charge at Constant Voltage test. This modified test requires cells to be charged for seven days at the manufacturer’s recommended charge current and voltage limit. This will result in a significant improvement in cycle time since the current test is a 28-day test.
The modifications to the Crush test includes a clarification to the test specifying that the crush is only required to be completed along the wide side of the cell. Additionally, a termination criteria of 10 percent deformation of the cell has been added. These are explanations that have been needed for some time and should reduce confusion and variability in testing.
A more significant change is the split of the short circuit into a separate section for cells and batteries. The section for cells in the second edition has been modified to include only one test temperature, and to provide a tighter range for the resistance of the circuit. Cell level testing in the second edition will only be required at 20°C ±5°C. Cell level testing is no longer going to be required at 55°C ±5°C. The revised test also includes a more specific value for the resistance used to induce the short circuit. In the previous edition, the requirement was only to be less than 100 m?. This will now be a tightened requirement within a range of 80 m? ±20 m?. Problems for some cells that previously passed testing with a lower resistance circuit may emerge since this tighter range can cause a softer shorting of the cell and result in a more eventful outcome.
Completely New Requirements
The most significant change in the proposed Second Edition of the standard is the addition of a new test at the cell level. This new test is the Forced Internal Short Circuit test. It is very complicated and has questionable repeatability. As the title of the test implies, the intent is to induce an internal short circuit within the jellyroll of the cell. The test procedure very explicitly describes a method that requires the test facility to fully charge a Li-Ion cell, then open it and remove the jellyroll. Once the cell is removed from the can, a small Nickel particle of a specific shape and size is to be place in a very specific location of the cell jellyroll. Following the placement of the particle, the affected jellyroll is to be crushed. All of this is to be done under very specific environmental and time constraints to avoid drying of the jellyroll. Only prismatic and cylindrical cells require this test, and will only be required as a National Deviation for Japan, Korea and Switzerland. In addition to the safety concerns with opening and handling a fully charged cell, the set-up required for the crush portion of the test is very specific. Because of these associated issues, labs that adhere to the Forced Internal Short Circuit Test will need to plan for added resources to meet customer needs.
Modifications to the Standard
There are some modifications to the general requirements of the standard. Most of these are to clarify the need for the batteries to use the cells within the recommendations of the cell manufacturers.
Part 2: Batteries
The revisions in the proposed second edition of IEC 62133 will be less pronounced for battery manufacturers than those noted for cell suppliers. Testing and requirements will actually be reduced for Li-Ion battery manufacturers. This article focuses on Li- Ion batteries because the requirements for Nickel systems will not be changing with the new edition of the standard. In order to accommodate the split of requirements for Lithium systems versus Nickel systems, the standard will be re-numbered. Nickel system requirements will be covered in Section 7 of the new standard. Li-Ion systems will be covered in Section 8.
Revised Charging Procedure
Similar to the cell level charging procedure change, the battery level will have revised charging procedures, but this will only affect a single test at the battery level. This change is derived from the Japanese Li-Ion cell and battery testing requirements, and states that samples to be used for short circuit testing must be charged in an ambient that is equal to the upper and lower use ambient temperature: assumes 45°C and 10°C if not provided by the manufacturer. All other testing at the battery level is performed on units that are charged at room ambient (20°C).
Reduced Sample Requirement
The sub-committee took a more holistic look at the testing required for Lithium Ion batteries than in the past. As a result, the amount of testing required at the battery level under IEC 62133 has declined significantly. The main consideration in this reduction is the fact that all batteries are required to be tested to the requirements of the UN Manual of Tests and Criteria (UN 38.3 testing). The sub-committee reduced the testing requirements by eliminating some testing from the IEC standard if it was already included in the UN Manual of Tests and Criteria. The testing that has been completely removed as a result of this review is:
• Temperature Cycling
• Mechanical Shock
The result is that the change reduces the required number of samples for testing from 31 for First Edition testing to 21 for Second Edition testing.
Two tests remain unchanged with the Second Edition of
• Moulded Case Stress
• Free Fall
While the Second Edition still contains a short circuit at 55°C, it has been modified slightly and the requirement to additionally perform the test at room temperature (20°C) has been removed. The change to the short circuit test is to include the more stringent charge criteria discussed in Part 1 of the article. What this means is that the batteries used for this testing will need to be charged at the high and low end of the recommended operating range prior to being tested. This is assumed to be 10°C and 45°C, unless otherwise stated.
Additionally, the resistance of the external circuit used to implement the short has been tightened from <100 m? to a range of 80 ±20 m?. This is consistent with changes taking place in other standards and is currently the common practice of most test labs.
A new test has also been added at the battery level intended to simulate charging the battery for a longer period of time than specified by the manufacturer using a high charge rate. This test is performed on a fully discharged set of five batteries and charges the batteries with a current of two times the rated current and an upper voltage limit that is set to the maximum voltage available from the charger to be used with the battery. If the charger maximum voltage is not known, a value of 5 V per cell (or cell string) will be used. The current is to be maintained until the maximum charge voltage is reached and temperature is to be monitored during the testing. The test termination is defined as temperature stabilization, and maximum voltage reached, with acceptance criteria of no fire and no explosion.
Since the new standard removes some of the testing based on the requirement to perform UN 38.3 testing, there is a new requirement to provide evidence that the UN 38.3 testing has been successfully completed. Since the UN testing is self-declared and able to be done by the manufacturer, the sub-committee included this requirement with an allowance for the use of manufacturer generated data.
The schedule for implementation will be determined with the actual release date by the IEC. Since the number of samples and testing required in the second edition for batteries is a reduction from what is currently required, many of the battery suppliers may be eager to move to new edition as quickly as possible. However, the changes being introduced on the cell level, the amount of testing and number of samples will increase, and the new Forced Internal Short Circuit testing will be added, thus potentially causing the cell suppliers to be slower to migrate to the new standard. Any cells that are already compliant with first edition will be required to be tested to second edition prior to being used in a battery that will be evaluated to second edition.
The intent of these pending 2012 standards changes reflects the collaborative work of the IEC Technical Sub-Committee for Batteries. Although not drastic, the changes must be adhered to in order to continue to be in compliance with international product safety requirements. Look for the actual publication link on the Energy Assurance Web site.
IEC Committee Draft for Vote (CDV), 21A/481/CDV, Dated 2010-11-05.
For more information, please visit Energy Assurance at www.energy-assurance.com.
This article was printed in the May/June 2012 issue of Battery Power magazine.