Globally-Harmonized Battery Safety Standards

A Review of the Latest Revisions to IEC 62133

Beginning with its initial release in 2002, the IEC 62133 family of standards has enabled international harmonization of safety testing for small-format cells and batteries. Since then, the standard has seen a major revision in 2012 and, most recently, a very significant change in 2017. This article will detail those latest changes and their impact on compliance activities.

A Brief History of the Scope of IEC 62133

The full title of IEC 62133 is Secondary cells and batteries containing alkaline or other non-acid electrolytes ‑ Safety requirements for portable sealed secondary cells, and for batteries made from them, for use in portable applications. The scope of the first and second editions of the standard encompassed both nickel and lithium battery chemistries. Back in 2002 when the standard made its debut, this was certainly appropriate as both nickel and lithium had significant shares of the rechargeable cell and battery market.

As technology moved forward, secondary lithium options in the form of lithium-ion and lithium-polymer overtook both nickel-cadmium and nickel-metal-hydride in most portable applications. Despite lithium’s potential volatility concerns, its benefits of higher voltage, higher energy density, and less self-discharge offered greater value to the market. Additionally, the economics of the situation had changed with the cost of lithium coming down dramatically as volumes increased. The net result was that industry focused on improving lithium’s safety and performance, whereas nickel chemistries were relegated to the role of being yesterday’s technology with no significant changes being pursued.

In recognition of this fact, the latest version of the IEC 62133 standard was split into two distinct parts. Part 1 covers nickel chemistries and Part 2 focuses on lithium. This has resulted in some confusion as the previous version was IEC 62133 2nd Edition, where the new versions are renamed to IEC 62133‑1 and -2 but are reset to 1st Edition. It is expected that IEC 62133-1 will likely see few if any changes going forward. Conversely, with all of the ongoing development efforts surrounding lithium chemistries, the prospects for change over time with the IEC 62133-2 are significant. Note that the split of the standard along chemistry lines is but the first step in a much longer narrative of change.

Changes for Nickel-Based Cell and Battery Requirements

Although the focus of the article is on lithium testing, it is appropriate to note the few changes that have been made to IEC 62133-1 (the standard that addresses nickel-based batteries). In addition to internal renumbering with the removal of lithium testing, the standard reflects the following changes and additions:

• Two tests have been renamed to clarify the intent and scope of the tests. The “moulded case stress test” has been renamed “case stress at high ambient temperature (batteries).” Similarly, “overcharge of nickel systems” has been simplified to just “overcharge.” These changes are consistent with the naming conventions used in the new lithium standard, IEC 62133-2;
• A note was added to the test sample table, noting that cell testing is not applicable to button cells;
• Paragraph 8.2 was added to detail the safety information required for small cells and batteries;
• Ingestion concerns were addressed with the addition of paragraph 9.3 and the prescription of a specific ingestion gage to aid in the assessment of specific small cell and battery designs. Additionally, button cell packaging requirements were updated to ensure that packaging is large enough to help mitigate ingestion concerns;
• The thermal abuse test was modified to extend the soak at high temperature from 10 minutes to 30 minutes. This is in line with the corresponding lithium cell requirements;
• The force tolerance on the crush test was reduced from 13 ± 1 kN to 13 ± 0.78 kN. As with the heating test, this harmonizes with changes made to the corresponding lithium cell requirements.

Changes to Lithium Cell and Battery Requirements

Changes to the lithium cell and battery requirements in IEC 62133-2 are considerably more extensive. As a starting point, many of the definitions have been modified or appended for clarification. Significant examples include:

• The inclusion of single-cell batteries in the definition of “secondary battery;”
• The clarification that “leakage” is the unplanned visible escape of liquid electrolyte;
• The addition of an explicit definition for “reference test current It“ as the charge or discharge current expressed as a multiple of the C5 rated capacity (It A) in amp-hours. This value is used throughout the test definitions included in the standard;
• New definitions for “cylindrical cell,” “prismatic cell,” and “cell block;”
• Acknowledging the increasing complexity of portable energy devices which in some cases may include both hardware and software aspects relating to safety performance, a definition for functional safety was added as “part of the overall safety that depends on functional and physical units operating correctly in response to their inputs.”

Not all the changes to the standard represent a tightening of requirements. This can be seen in section 5.6 which covers the assembly of cells into battery packs. In the previous version, most of the requirements were prescriptive and mandatory (“shall”). Perhaps as an acknowledgement that in the modern paradigm of a risk-based standards approach, the designers should have both the authority and responsibility to determine all aspects of the design, even when it comes to safety, the requirements in this section have been modified to being recommended as a best practice (“should”). The section was expanded and reorganized to include many more specific design aspects for consideration. Section 5.8 and Annex F were also added which detail battery pack component reference standards, thus adding additional value to the users of the standard.

Requirements to the actual testing are best characterized as both substantial and important. They represent lessons learned from both the execution of the testing as well as the associated compliance actions resulting from the testing. Specific new or modified requirements include:

• The previous version of the standard included two charging procedures for both cells and batteries. The first procedure was conducted at room temperature while the second procedure was conducted at or above the specified thermal limits of the device. This was sufficient for cells which generally had no additional circuitry, but was often problematic for battery packs. Attempting to charge a battery pack at or outside of a specified ambient thermal limit was often unsuccessful, requiring an incremental reduction of temperature and additional attempts to fully charge the battery packs under test. This created an inefficiency in the testing that many considered of little value. IEC 62133-2 keeps the non-ambient charge for certain cell tests, but transitions to all ambient charging for battery packs;
• As an equally critical change to the charging requirements, the highly prescriptive charging parameter requirements found in the previous version of the standard have been removed in favor of using the charging parameters specified by the cell or battery manufacturer;
• IEC 62133 2nd Edition included the removal of vibration and shock testing. It was felt that such testing was already done as a part of the required lithium battery transport testing under UN 38.3, and thus repetition was not required. This approach has not been without issues as the testing under UN 38.3 is self-certified and, in some cases, stated compliance has been lacking. As mechanical robustness is a central element of portable battery pack safety performance, IEC 62133-2 reinstates the explicit requirement for both vibration and shock testing following the general test parameters found in the UN requirements. With this addition of testing, the requirement to document compliance to the UN transportation testing requirements has been removed;
• Faulting of battery pack safety circuit components was favored by some contributors to the standard, but was not implemented as a mandatory requirement. Instead, it is noted that a safety analysis “should” be provided identifying critical components and that the components “should” be considered for single faulting during short-circuit testing of the battery pack. Note that it is still a possibility that such faults could become a part of country-specific deviations to the IEC standard;
• The ambient temperature conditions for short-circuit testing have been flipped between the cell and battery pack. The new version of the standard calls for cell testing to be conducted at 55°C, while battery pack testing is to be conducted at room temperature (20°C);
• The soak time at high temperature (130°C) for the thermal abuse test was extended from 10 minutes to 30 minutes. The standard also notes a pre-condition to soak the cells at 20 ± 5°C for one hour before testing;
• The crush test has been simplified to remove the 10% maximum deformation requirement. Additionally, as noted with the new nickel battery testing, the force tolerance has been reduced from 13 ± 1 kN to 13 ± 0.78 kN;
• Parameters for the overcharging of battery test have been made more abusive. Although the requirements for a series-connected battery haven’t changed significantly, the voltage for a single cell or cell block battery has been increased to 1.4 times the upper limit charging voltage (not to exceed 6.0V). In the previous version the multiple was only 1.2 and limited to 5.0V. In all test cases, the voltage should be sufficient to maintain 2.0 It A throughout the test or until the supply voltage is reached. An explicit requirement to monitor the battery case temperature was also added;
• The forced internal short circuit (FISC) test has been modified to allow for a protective device in the battery or system to forego the need for this test. Additional clarifications to this highly-prescriptive test such as explicit definition of the voltage level to be used and actions to be taken based on specific response scenarios were added. All references to multi-cell applications have been removed. Polymer and coin cells are excluded from this test requirement;
• Secondary coin cells are excluded from all requirements if their internal resistance is greater than or equal to 3Ω;
• Required safety information to include ingestion hazard concerns as noted for nickel batteries are also applied to lithium coin cells.

Conclusion

Since its release in February 2017, IEC 62133-2 has been adopted by the IECEE for use in CB reports. Although more extensive in some respects than its predecessor, its requirements provide both clarifications and improvements to the world of internationally-harmonized cell and battery testing. It is expected that associated national deviations to the standard as well as related updates to independent national standards will see releases in the coming year. As always, this situation remains fluid with significant variation amongst countries, so frequent consultation with your test provider is highly recommended to help ensure positive compliance outcomes.

John C. Copeland is co-owner and technical manager for Energy Assurance LLC, an independent, fully-accredited cell and battery test laboratory. His career has included various positions in quality engineering, reliability engineering, failure analysis, project management, supplier assessment, and quality management in the electronics and portable energy sectors. John holds a BSEE from Auburn University, MSQA from Southern Polytechnic State University, and is trained as a Six-Sigma Black Belt. He can be reached at johncopland@energy-assurance.com.