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Safety Issues for Lithium-Ion Batteries

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Underwriters Laboratories (UL), a world leader in safety testing and certification released the first in a series of white papers that review evolving battery technology. ...

Underwriters Laboratories (UL), a world leader in safety testing and certification released the first in a series of white papers that review evolving battery technology.

This paper explores many of the issues and opportunities associated with the new technology as well as current and recommended safety standards to address changes in the technology and use.

Lithium-ion battery technologies have evolved over the last two decades, with batteries now offering longer cycle life and improved reliability for products in the areas of consumer electronics, medical devices, industrial equipment and automotive applications. In the white paper, UL explains the need for risk assessment as part of the product design and development process to identify and address root causes of safety issues.

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Safety Issues for Lithium-Ion Batteries Safety Issues for Lithium-Ion Batteries Document Transcript

  • WHITE PAPER ON: Safety Issues for Lithium-Ion Batteries Lithium-ion batteries are widely used as a power source in portable electrical and electronic products. While the rate UL is involved in standards development worldwide and has technical staff of failures associated with their use is small, several well- participating in leadership and expert roles on several national committees publicized incidents related to lithium-ion batteries in actual and maintenance teams associated with battery and fuel cell technologies. use (including fires and explosions) have raised concerns about Ms. Laurie Florence is the convener (chair) of SC21A — Working Group 5. their overall safety. Test standards are in place that mandate a She is a member of the SC21A US TAG & SC21A WGs 2, 3, 4, and 5. Florence number of individual tests designed to assess specific safety is a member of TC 35 US TAG & TC 35 MT 15 and a member of the ANSI risks associated with the use of lithium-ion batteries. However, NEMA C18 committees. She participated in the IEEE 1625 and is participating Underwriters Laboratories and other standards development in IEEE 1725 revisions. Florence is also on the task group working on revising organizations are continuing to revise and update existing lithium UN T6 and participated in CTIA battery ad hoc committee. battery standards to reflect new knowledge regarding lithium ion battery failures in the field. These organizations are contributing Mr. Harry P. Jones is the convener (chair) of IEC TC105 — Working Group 8. to battery safety research with a focus on internal short circuit failures in lithium ion batteries. The research is directed toward Florence and Jones participated in SAE J2464 and SAE J2929 improving safety standards for lithium ion batteries. standards development. Florence and Mr. Alex Liang (UL Taiwan) and are on ETF 13 for batteries. Overview UL Taiwan was the first CBTL for IEC 62133, followed by UL Suzhou. Over the past 20 years, rechargeable (also known as secondary) UL Japan is approved to provide PSE mark in Japan for lithium ion batteries lithium-ion battery technologies have evolved, providing increasingly as part of the DENAN program. greater energy density, greater energy per volume, longer cycle life, and improved reliability. Commercial lithium-ion batteries now UL is a CTIA CATL for the battery certification program. power a wide range of electrical and electronic devices, including the following categories: • Consumer electrical and electronic devices — Lithium- • Industrial equipment — Industrial equipment offers a ion batteries power consumer electrical and electronic devices wide range of applications for lithium-ion batteries, including from mobile phones and digital cameras, to laptop computers. cordless power tools, telecommunications systems, wireless security systems, and outdoor portable electronic equipment. • Medical devices — Lithium-ion batteries are also used in medical diagnostic equipment, including patient monitors, • Automotive applications — A new generation of electric handheld surgical tools, and portable diagnostic equipment. vehicles is being powered by large format lithium-ion battery packs, including battery-electric vehicles, hybrid-electric vehicles, plug-in hybrid-electric vehicles, and light-electric vehicles. 1 “Lithium Batteries: Markets and Materials,” Report FCB028E, October 2009, www.bccresearch.com. 01 For more information E:: ULUniversity@us.ul.com / T:: 888.503.5536
  • Lithium-ion battery design and selection considerations A lithium-ion battery is an energy storage device in which lithium ions move through an electrolyte from the negative electrode (“anode”) to the positive electrode (“cathode”) during battery discharge, and from the positive electrode to the negative electrode during charging. The electrochemically active materials in lithium-ion batteries are typically a lithium metal oxide for the cathode and a lithiated carbon for the anode. The electrolytes can be liquid, gel, polymer or ceramic. For liquid electrolytes, a thin (on the order of microns) micro-porous film provides electrical isolation between the cathode and anode, while still allowing for ionic conductivity. Variations on the basic lithium chemistry also exist to address various performance and safety issues. The widespread commercial use of lithium-ion batteries began in the 1990s. Since then, an assortment of lithium-ion designs has Photo 1: Examples of lithium-ion batteries for PCs and smart phones been developed to meet the wide array of product demands. The The worldwide market for lithium batteries is projected to reach choice of battery in an application is usually driven by a number of nearly $10 billion (USD) in annual sales by 2014, with the market considerations, including the application requirements for power and for lithium-ion batteries representing almost 86-percent of those energy, the anticipated environment in which the battery-powered sales ($8.6 billion)1. However, as the use of lithium batteries is product will be used and battery cost. Other considerations in growing globally and with the large number of batteries powering choosing a suitable battery may include: a wide range of products in a variety of usage environments, there • Anticipated work cycle of the product (continual or intermittent) have been several reported incidents raising safety concerns. While the overall rate of failures associated with the use of lithium- • Battery life required by the application ion batteries is very low when compared with the total number of • Battery’s physical characteristics (i.e., size, shape, weight, etc.) batteries in use worldwide, several publicized examples involving • Maintenance and end-of-life considerations consumer electronics like laptop computers and electronic toys have led to numerous product safety recalls by manufacturers, the Lithium-ion batteries are generally more expensive than alternative U.S. Consumer Product Safety Commission and others. Some of battery chemistries but they offer significant advantages, such as these cases have been linked to overheating of lithium-ion batteries, high energy, density levels and low weight-to-volume ratios. leading to possible fire or explosion. Though global independent standards organizations, such as Causes of safety risk associated with lithium-ion batteries the International Electrotechnical Commission and Underwriters Battery manufacturers and manufacturers of battery-powered products Laboratories, have developed a number of standards for electrical design products to deliver specified performance characteristics in a and safety testing intended to address a range of possible abuses safe manner under anticipated usage conditions. As such, failure (in of lithium-ion batteries, knowledge about potential failure modes either performance or safety) can be caused by poor execution of a is still growing as this complex technology continues to evolve to design, or an unanticipated use or abuse of a product. meet marketplace demands. Understanding and translating this knowledge into effective safety standards is the key focus of UL Passive safeguards for single-cell batteries and active safeguards for multi-cell batteries (such as those used in electric vehicles) battery research activities and is intended to support the continual have been designed to mitigate or prevent some failures. However, safe public usage and handling of lithium-ion batteries. major challenges in performance and safety still exist, including the thermal stability of active materials within the battery at high temperatures and the occurrence of internal short circuits that may lead to thermal runaway. 2 “FTA/FMEA Safety Analysis Model for Lithium-Ion Batteries,” UL presentation at 2009 NASA Aerospace Battery Workshop. 02 For more information E:: ULUniversity@us.ul.com / T:: 888.503.5536
  • As part of the product development process, manufacturers should Society of Automotive Engineers conduct a risk assessment that might involve tools such as failure • J2464: Electric and Hybrid Electric Vehicle Rechargeable modes and effects analysis and fault tree analysis. UL employs these Energy Storage Systems (RESS), Safety and Abuse Testing tools to generate root cause analyses that lead to the definition of • J2929: Electric and Hybrid Vehicle Propulsion Battery System safety tests for product safety standards2. Safety Standard — Lithium-based Rechargeable Cells Applicable product safety standards and testing protocols International Electrotechnical Commission • IEC 62133: Secondary Cells and Batteries Containing Alkaline To address some of the safety risks associated with the use of or Other Non-acid Electrolytes — Safety Requirements for lithium-ion batteries, a number of standards and testing protocols Portable Sealed Secondary Cells, and for Batteries Made from have been developed to provide manufacturers with guidance on Them, for Use in Portable Applications how to more safely construct and use lithium-ion batteries. • IEC 62281: Safety of Primary and Secondary Lithium Cells and Product safety standards are typically developed through a Batteries During Transportation consensus process, which relies on participation by representatives from regulatory bodies, manufacturers, industry groups, consumer United Nations (UN) advocacy organizations, insurance companies and other key safety • Recommendations on the Transport of Dangerous Goods, stakeholders. The technical committees developing requirements Manual of Tests and Criteria, Part III, Section 38.3 for product safety standards rely less on prescriptive requirements and more on performance tests simulating reasonable situations that Japanese Standards Association may cause a defective product to react. • JIS C8714: Safety Tests for Portable Lithium Ion Secondary Cells and Batteries For Use In Portable Electronic Applications The following standards and testing protocols are currently used to assess some of the safety aspects of primary and secondary Battery Safety Organisation lithium batteries: • BATSO 01: (Proposed) Manual for Evaluation of Energy Systems for Light Electric Vehicle (LEV) — Secondary Lithium Batteries Underwriters Laboratories • UL 1642: Lithium Batteries Common product safety tests for lithium-ion batteries • UL 1973: (Proposed) Batteries for Use in Light Electric Rail The above standards and testing protocols incorporate a number of (LER) Applications and Stationary Applications product safety tests designed to assess a battery’s ability to withstand • UL 2054: Household and Commercial Batteries certain types of abuse. Table 1 provides an overview of the various abuse tests and illustrates the extent to which safety standards and • UL Subject 2271: Batteries For Use in Light Electric testing protocols for lithium-ion batteries have been harmonized. Vehicle Applications It is important to note that similarly named test procedures in various • UL 2575: Lithium Ion Battery Systems for Use in Electric Power documents might not be executed in a strictly identical manner. For Tool and Motor Operated, Heating and Lighting Appliances example, there may be variations between documents regarding the • UL Subject 2580: Batteries For Use in Electric Vehicles number of samples required for a specific test, or the state of sample charge prior to testing. Institute of Electrical and Electronics Engineers • IEEE 1625: Rechargeable Batteries for Multi-Cell Mobile The most common product safety tests for lithium-ion batteries are Computing Devices typically intended to assess specific risk from electrical, mechanical and environmental conditions. With minor exceptions, all of the • IEEE 1725: Rechargeable Batteries for Cellular Telephones above mentioned standards and testing protocols incorporate these National Electrical Manufacturers Association common abuse tests. The following sections describe individual • C18.2M: Part 2, Portable Rechargeable Cells and Batteries — common tests in greater detail. Safety Standard 03 For more information E:: ULUniversity@us.ul.com / T:: 888.503.5536
  • Safety standards and testing protocols for lithium-ion cells Table 1: Summary of abuse tests found in international safety standards and testing protocols for lithium-ion batteries 3 UL IEC NEMA SAE UN IEEE JIS BATSO Test Criteria/Standard UL 1642 UL 2054 UL UL UL 2575 IEC IEC C18.2M, J2464 Pt.III,S IEEE IEEE JIS BATSO Subject Subject 62133 62281 Pt2 38.3 1625 1725 C8714 01 2271 2580 External short circuit • • • • • • • • • • • • • • Abnormal charge • • • • • • • • • • • • • • Forced discharge • • • • • • • • • • • • • Crush • • • • • • • • • • • • Impact • • • • • • • • • Shock • • • • • • • • • • • • • • Vibration • • • • • • • • • • • • • • Heating • • • • • • • • • • • Temperature cycling • • • • • • • • • • • • • • Low pressure (altitude) • • • • • • • • • • • • Projectile • • • • • • Drop • • • • • • • Continuous low rate • • charging Molded casing heating test • Open circuit voltage • Insulation resistance • • Reverse charge • • Penetration • • • Internal short circuit test • • • 3 Jones, H., et al., “Critical Review of Commercial Secondary Lithium-Ion Battery Safety Standards,” UL presentation at 4th IAASS Conference, Making Safety Matter, May 2010. 04 For more information E:: ULUniversity@us.ul.com / T:: 888.503.5536
  • Electrical tests Environmental tests • External short circuit test — The external short circuit test • Heating test — The heating test evaluates a cell’s ability to creates a direct connection between the anode and cathode withstand a specified application of an elevated temperature for a terminals of a cell to determine its ability to withstand a period of time. To pass this test, the cell may not explode or ignite. maximum current flow condition without causing an explosion (This test is not required under IEC 62281, UN 38.3 or BATSO 01.) or fire. • Temperature cycling test — The temperature cycling test • Abnormal charging test — The abnormal charging test subjects each cell sample to specified temperature ranges applies an over-charging current rate and charging time to above and below room temperature for a specified number of determine whether a sample cell can withstand the condition cycles. To pass this test, the cell may not explode, ignite, vent without causing an explosion or fire. or leak. • Forced discharge test — The forced discharge test • Low pressure (altitude) test — The low-pressure test determines a battery’s behavior when a discharged cell is evaluates a cell sample for its ability to withstand exposure connected in series with a specified number of charged cells to less than standard atmospheric pressure (such that in an of the same type. The goal is to create an imbalanced series aircraft cabin that experiences sudden loss of pressure). To connected pack, which is then short-circuited. To pass this pass this test, the cell may not explode, ignite, vent or leak. test, no cell may explode or catch fire. (This test is not required (This test is not required under UL 2054.) under BATSO 01.) Mechanical tests • Crush test — The crush test determines a cell’s ability to withstand a specified crushing force (typically 12 kN) applied by two flat plates (typically although some crush methods such as SAE J2464 include a steel rod crush for cells and ribbed platen for batteries). To pass this test, a cell may not explode or ignite. (This test is not required under IEC 62281 or UN 38.3.) • Impact test — The impact test determines a cell’s ability to withstand a specified impact applied to a cylindrical steel rod placed across the cell under test. To pass this test, a cell may not explode or ignite. (This test is not required under SAE J2464, JIS C8714, or BATSO 01.) • Shock test — The shock test is conducted by securing a cell under test to a testing machine that has been calibrated to apply a specified average and peak acceleration for the specified duration of the test. To pass this test, a cell may not Photo 2: Lithium-ion batteries under test explode, ignite, leak or vent. • Vibration test — The vibration test applies a simple harmonic motion at specified amplitude, with variable frequency and time to each cell sample. To pass this test, the cell may not explode, ignite, leak or vent. 05 For more information E:: ULUniversity@us.ul.com / T:: 888.503.5536
  • Additional specialized tests • Reverse charge test — The reverse charge test is required under IEC 62133, UL Subject 2271 and UL Subject 2580. In addition to the common abuse tests discussed above, certain This test determines a discharged cell sample’s response product safety standards and testing protocols for lithium-ion to a specified charging current applied in a reverse polarity batteries require additional specialized testing. These specialized condition for a defined period of time. To pass this test, the cell tests address specific uses and conditions in which the batteries may not explode or ignite. might be expected to operate. • Penetration test — The penetration test is required under • Projectile (fire) test — The projectile test is required under UL UL Subject 2271, UL Subject 2580 and SAE J2464. The test 1642. UL 2054, UL Subject 2271, IEEE 1625 and IEEE 1725. The uses a pointed metal rod to penetrate a cell and simultaneously test subjects a cell sample to a flame from a test burner, while measures rod acceleration, cell deformation, cell temperature, positioned within a specified enclosure composed of wire mesh cell terminal voltage and resistance. and structural support. If the application of the flame results in an explosion or ignition of the cell, no part of the cell sample may Internal short circuits: potential causes and testing issues penetrate or protrude through the wire mesh enclosure. A review of lithium-ion battery safety research shows a strong focus • Drop test — The drop test is required under UL Subject 2271, on internal short circuits. Some field failures resulting in fires or UL Subject 2580, IEC 62133, IEC 62281, NEMA C18.2M Part 2, explosions, leading to product damage or personnel injury, have JIS C8714 and BATSO 01. The test subjects each cell or battery been linked to an internal short circuit within the lithium-ion battery. sample to a specified number of free falls to a hard surface. The However, as shown in Table 1, most lithium-ion battery safety cell sample is examined after a time following each drop. To standards and testing protocols do not specifically include testing pass this test, the cell may not explode or ignite. for internal short circuits. In recent years, UL has partnered with key • Continuous Low Rate Charging Test — The continuous battery research facilities such as Argonne National Laboratories low rate charging test is required under IEC 62133. This and the National Aeronautic and Space Administration to better test subjects fully-charged cell samples to a long-term, understand the root causes of internal short circuits. The focus of uninterrupted charge at a rate specified by a manufacturer. To our research has been on defining and developing safety tests that pass this test, the cell may not explode, ignite, vent or leak. assess the propensity of a battery to experience a short circuit under certain abuse conditions. • Mold stress test — The molded casing-heating test is required under NEMA C18.2M Part 2, UL 2054, IEC 62133 and Potential causes of internal short circuits UL Subject 2271. The test exposes plastic-encased batteries to a specified elevated temperature and for a specified time. Although an internal short circuit may have many causes, it is Once the battery has cooled to room temperature the cell is basically a pathway between the cathode and anode that allows for examined. To pass this test, the internal cells may not show any efficient but unintended charge flow. This highly localized charge flow evidence of mechanical damage. results in joule heating due to internal resistance, with subsequent heating of the active materials within the lithium-ion battery. The • Insulation resistance test — The insulation resistance test is increased heat may destabilize the active materials, in turn starting required under UL Subject 2580, IEC 62133 and NEMA C18.2M a self-sustaining exothermic reaction. The subsequent heat and Part 2 (conducted as a pretest condition only). The test subjects pressure build-up within the cell may lead to catastrophic structural a cell sample to a resistance measurement between each failure of the battery casing and the risk of additional combustion as battery terminal and the accessible metal parts of a battery a result of exposure to outside air. pack. To pass this test, the measured resistance must exceed the specified minimum value. 06 For more information E:: ULUniversity@us.ul.com / T:: 888.503.5536
  • Lithium-ion batteries are designed with integrated safety devices Moving from battery to system safety that open the external electrical load in the event of an over-current Lithium-ion batteries are typically marketed and sold directly to condition or relieve excessive pressure build-up in the cell. However, original equipment manufacturers (OEMs) as components to be these safety devices are unable to mitigate all internal cell fault integrated into end-use products. Because the OEM’s product situations, such as an internal short circuit. For products like electric actually controls these functions, product safety issues involving cell vehicles, the presence of hundreds of these batteries requires more charging rates, discharging rates and reverse charging may not be sophisticated safeguards such as battery management systems. adequately addressed by battery testing alone. Clearly, the desired goal is a test portfolio (simulating a wide variety of abuse conditions) that can assess the likelihood of a battery to In such cases, international standards organizations are working manifest a short circuit. to improve OEM product compatibility with integrated lithium-ion batteries by including appropriate performance testing in applicable However, in designing a test for a specific failure, the root causes and standards. An example of such an approach to performance testing failure pathways must be known. These causes may include a large can be found in IEC 60950-1 (UL 60950-1), Information Technology internal defect or a severe external force that deforms the inner layers Equipment — Safety — Part 1. of the battery sufficiently to compromise the separator. In many failure incidents, only partial root-cause and failure information is available. Lithium-ion battery designers and researchers are working to create Looking ahead new battery designs that mitigate the impact of these causes. As the development of lithium-ion batteries is an active area in fundamental research and product development, knowledge Internal short circuit tests regarding the use and abuse of these products and their possible failure modes is still growing. Therefore, it is important that The variety of root causes for internal short circuits makes it difficult safety standards continue to evolve to help drive toward the safe to design a single safety test that can assess the robustness of a commercial use of these energy storage devices as they power more lithium-ion battery. To date, only JIS C8714 specifies an internal short and more products. UL will continue dedicating significant resources circuit test, known as the forced internal short circuit (FISC) test. to translating battery safety research into safety standards. This (Note that IEEE 1625, Annex D references the FISC test found in JIS focus will cover the wide range of chemistries and battery designs. C8714.) This test creates an internal short circuit by disassembling The work includes the multi-scale continuum, from material and a charged cell sample casing and placing a specified nickel particle component-level characterization to battery systems and beyond. under the cell winding construction. (This is an inherently dangerous process for the test operator.) The cell sample, minus the casing, For additional information about this white paper, please contact is then subjected to a specified crushing action at an elevated Ms. Laurie Florence, Primary Designated Engineer — temperature. However, best practice in safety test design precludes Batteries, Capacitors, Fuel Cells and H2 Generators, at disassembly of a product. All tests should be designed for execution Laurie.B.Florence@us.ul.com. with minimum risk to laboratory personnel4. To that end, UL researchers have developed a test5 that induces internal short circuits by subjecting lithium-ion battery cells to a localized indentation under elevated temperature conditions. During this test, the open circuit voltage, cell surface temperature force and position of the indenter probe are measured in real time. The test is currently under development for possible inclusion in UL 1642 and UL Subject 2580. 4 Yen, K.H., et al., “Estimation of Explosive Pressure for Abused Lithium-Ion Cells,” UL presentation at 44th Power Sources Conference, July 2010. 5 Wu, Alvin, et al., “Blunt Nail Crush Internal Short Circuit Lithium-Ion Cell Test Method,” UL presentation at NASA Aerospace Battery Workshop, 2009. 07 For more information E:: ULUniversity@us.ul.com / T:: 888.503.5536 Copyright © 2010 Underwriters Laboratories Inc. All rights reserved. No part of this document may be copied or distributed without the prior written consent of Underwriters Laboratories Inc.10/09 BDI 100807.4