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Safety Issues for

Safety Issues for Lithium-Ion Batteries
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 of failures associated with their use is smal , several wel - publicized incidents related to lithium-ion batteries in actual use (including fires and explosions) have raised concerns about their overall safety. Test standards are in place that mandate a number of individual tests designed to assess specific safety risks associated with the use of lithium-ion batteries. However, Underwriters Laboratories and other standards development organizations are continuing to revise and update existing lithium battery standards to reflect new knowledge regarding lithium-ion battery failures in the field. These organizations are contributing to battery safety research with a focus on internal short circuit failures in lithium-ion batteries. The research is directed toward improving safety standards for lithium-ion batteries.
Overview
Over the past 20 years, rechargeable (also known as secondary) lithium-ion battery
technologies have evolved, providing increasingly greater energy density, greater
energy per volume, longer cycle life, and improved reliability. Commercial lithium-ion
batteries now power a wide range of electrical and electronic devices, including the
fol owing categories:
• Consumer Electrical and Electronic Devices — Lithium- ion batteries power
consumer electrical and electronic devices from mobile phones and digital cameras, to laptop computers.
• Medical Devices — Lithium-ion batteries are also used in medical diagnostic
equipment, including patient monitors, handheld surgical tools, and portable diagnostic equipment.
• Industrial Equipment — Industrial equipment offers a wide range of applications
for lithium-ion batteries, including cordless power tools, telecommunications systems, wireless security systems, and outdoor portable electronic equipment.
• Automotive Applications — A new generation of electric 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.
Safety Issues for Lithium-Ion Batteries
The worldwide market for lithium is the key focus of UL battery research UL is involved in standards development batteries is projected to reach nearly activities and is intended to support the worldwide and has technical staff $10 bil ion (USD) in annual sales by 2014, continual safe public usage and handling participating in leadership and expert roles on several national committees and with the market for lithium-ion batteries of lithium-ion batteries.
maintenance teams associated with battery representing almost 86-percent of those and fuel cell technologies.
sales ($8.6 bil ion)1. However, as the use Lithium-Ion Battery Design and
Ms. Laurie Florence is the convener (chair) of
of lithium batteries is growing global y SC21A — Working Group 5. She is a member of the SC21A US TAG & SC21A WGs 2, 3, 4, and with the large number of batteries A lithium-ion battery is an energy storage and 5. Florence isamemberofTC35USTAG powering a wide range of products in device in which lithium-ions move through &TC35MT15andamemberoftheANSI NEMA an electrolyte from the negative electrode C18 committees. She participated in the a variety of usage environments, there IEEE 1625 and is participating in IEEE 1725 have been several reported incidents ("anode") to the positive electrode revisions. Florence is also on the task group raising safety concerns. While the overall ("cathode") during battery discharge, working on revising UN T6 and participated in CTIA battery ad hoc committee.
rate of failures associated with the use and from the positive electrode to the of lithium- ion batteries is very low negative electrode during charging. Mr. Harry P. Jones is the convener (chair)
of IEC TC105 — Working Group 8.
when compared with the total number The electrochemical y active materials in lithium-ion batteries are typical y a Florence and Jones participated in SAE J2464 of batteries in use worldwide, several and SAE J2929 standards development.
publicized examples involving consumer lithium metal oxide for the cathode and Florence and Mr. Alex Liang (UL Taiwan)
electronics like laptop computers and a lithiated carbon for the anode. The and are on ETF 13 for batteries.
electronic toys have led to numerous electrolytes can be liquid, gel, polymer or UL Taiwan was the first CBTL for IEC 62133,
product safety recal s by manufacturers, ceramic. For liquid electrolytes, a thin (on fol owed by UL Suzhou.
the U.S. Consumer Product Safety the order of microns) micro-porous film UL Japan is approved to provide PSE mark
Commission and others. Some of these provides electrical isolation between the in Japan for lithium-ion batteries as part of the DENAN program.
cases have been linked to overheating of cathode and anode, while still al owing for UL is a CTIA CATL for the battery
lithium-ion batteries, leading to possible ionic conductivity. Variations on the basic fire or explosion.
lithium chemistry also exist to address Though global independent standards various performance and safety issues.
organizations, such as the International The widespread commercial use of Electrotechnical Commission and lithium-ion batteries began in the 1990s. Underwriters Laboratories, have Since then, an assortment of lithium-ion developed a number of standards for designs has been developed to meet electrical and safety testing intended the wide array of product demands. to address a range of possible abuses of The choice of battery in an application lithium-ion batteries, knowledge about is usual y driven by a number of potential failure modes is still growing considerations, including the application as this complex technology continues to requirements for power and energy, the evolve to meet marketplace demands. anticipated environment in which the Understanding and translating this battery-powered product wil be used and knowledge into effective safety standards battery cost. Safety Issues for Lithium-Ion Batteries
Other considerations in choosing internal short circuits that may lead a suitable battery may include: to thermal runaway.
• UL 1642: Lithium Batteries • Anticipated work cycle of the As part of the product development • UL 1973: (Proposed) Batteries for Use product (continual or intermittent) process, manufacturers should conduct a in Light Electric Rail (LER) Applications • Battery life required by risk assessment that might involve tools and Stationary Applications such as failure modes and effects analysis and fault tree analysis. UL employs these • UL 2054: Household and • Battery's physical characteristics Commercial Batteries tools to generate root cause analyses that (i.e., size, shape, weight, etc.) lead to the definition of safety tests for • UL Subject 2271: Batteries For Use • Maintenance and product safety standards2.
in Light Electric Vehicle Applications Applicable Product Safety
• UL 2575: Lithium-Ion Battery Systems Lithium-ion batteries are general y Standards and Testing Protocols
for Use in Electric Power Tool and more expensive than alternative battery Motor Operated, Heating and chemistries but they offer significant To address some of the safety risks Lighting Appliances advantages, such as high energy, density associated with the use of lithium-ion • UL Subject 2580: Batteries For Use levels and low weight-to-volume ratios.
batteries, a number of standards and in Electric Vehicles testing protocols have been developed Causes of Safety Risk Associated to provide manufacturers with guidance
Institute of Electrical and
With Lithium-Ion Batteries
on how to more safely construct and use Battery manufacturers and • IEEE 1625: Rechargeable Batteries for manufacturers of battery-powered Product safety standards are typical y Multi-Cell Mobile Computing Devices products design products to deliver developed through a consensus • IEEE 1725: Rechargeable Batteries for specified performance characteristics in process, which relies on participation Cellular Telephones a safe manner under anticipated usage by representatives from regulatory National Electrical
conditions. As such, failure (in either bodies, manufacturers, industry groups, performance or safety) can be caused consumer advocacy organizations, • C18.2M: Part 2, Portable Rechargeable by poor execution of a design, or an insurance companies and other key safety Cel s and Batteries — Safety Standard unanticipated use or abuse of a product.
stakeholders. The technical committees Society of Automotive Engineers
Passive safeguards for single-cell batteries developing requirements for product and active safeguards for multi-cell safety standards rely less on prescriptive • J2464: Electric and Hybrid Electric batteries (such as those used in electric requirements and more on performance Vehicle Rechargeable Energy vehicles) have been designed to mitigate tests simulating reasonable situations that Storage Systems (RESS), Safety or prevent some failures. However, major may cause a defective product to react.
and Abuse Testing chal enges in performance and safety The fol owing standards and testing • J2929: Electric and Hybrid Vehicle still exist, including the thermal stability protocols are currently used to assess Propulsion Battery System Safety of active materials within the battery at some of the safety aspects of primary and Standard — Lithium-based high temperatures and the occurrence of secondary lithium batteries: Rechargeable Cel s

Safety Issues for Lithium-Ion Batteries
• IEC 62133: Secondary Cel s and Batteries Containing Alkaline or Other Non-acid Electrolytes — Safety Requirements for Portable Sealed Secondary Cel s, and for Batteries Made from Them, for Use in Portable Applications • IEC 62281: Safety of Primary and Secondary Lithium Cel s and Batteries During Transportation United Nations (UN)
• Recommendations on the Transport of Dangerous Goods, Manual of Tests and Criteria, Part II , Section 38.3 Japanese Standards Association
• JIS C8714: Safety Tests for Portable Lithium-Ion Secondary Cel s and Batteries For Use In Portable Electronic Applications Battery Safety Organisation
• BATSO 01: (Proposed) Manual for Evaluation of Energy Systems for Light Electric Vehicle (LEV) — Secondary Lithium Batteries Common Product Safety Tests for Lithium-Ion Batteries
The above standards and testing protocols incorporate a number of product safety
tests designed to assess a battery's ability to withstand certain types of abuse. Table
1 provides an overview of the various abuse tests and il ustrates the extent to which
safety standards and testing protocols for lithium-ion batteries have been harmonized.
It is important to note that similarly named test procedures in various documents might
not be executed in a strictly identical manner. For example, there may be variations
between documents regarding the number of samples required for a specific test, or the
state of sample charge prior to testing.
The most common product safety tests for lithium-ion batteries are typical y intended
to assess specific risk from electrical, mechanical and environmental conditions.
With minor exceptions, all of the above mentioned standards and testing protocols
incorporate these common abuse tests. The fol owing sections describe individual
common tests in greater detail.
Safety Issues for Lithium-Ion Batteries
Safety Standards and Testing Protocols for Lithium-Ion Cel s
Test Criteria/ Standard
UL Subject
UL Subject
IEC 62133
IEC 62281
External short circuit Temperature cycling Low pressure (altitude) Continuous low rate charging Molded casing heating test Open circuit voltage Insulation resistance Internal short circuit test Table 1: Summary of abuse tests found in international safety standards and testing protocols for lithium-ion batteries3 Safety Issues for Lithium-Ion Batteries
Safety Standards and Testing Protocols for Lithium-Ion Cel s
Test Criteria/ Standard
C18.2M, Pt2
Pt.I I,S 38.3
IEEE 1625
IEEE 1725
JIS C8714
External short circuit Temperature cycling Low pressure (altitude) Continuous low rate charging Molded casing heating test Open circuit voltage Insulation resistance Internal short circuit test Table 1: Summary of abuse tests found in international safety standards and testing protocols for lithium-ion batteries3 Safety Issues for Lithium-Ion Batteries
or ignite. (This test is not required temperature ranges above and • External Short Circuit Test — The
under IEC 62281 or UN 38.3).
below room temperature for a external short circuit test creates • Impact Test — The impact test
specified number of cycles. To pass a direct connection between the determines a cel 's ability to this test, the cell may not explode, anode and cathode terminals of withstand a specified impact ignite, vent or leak.
a cell to determine its ability to applied to a cylindrical steel rod • Low Pressure (altitude) Test — The
withstand a maximum current placed across the cell under test. To low-pressure test evaluates a cel flow condition without causing pass this test, a cell may not explode sample for its ability to withstand an explosion or fire.
or ignite. (This test is not required exposure to less than standard • Abnormal Charging Test — The
under SAE J2464, JIS C8714, or atmospheric pressure (such that in abnormal charging test applies an aircraft cabin that experiences an over-charging current rate and • Shock Test — The shock test is
sudden loss of pressure). To pass charging time to determine whether conducted by securing a cell under this test, the cell may not explode, a sample cell can withstand the test to a testing machine that has ignite, vent or leak. (This test is not condition without causing an been calibrated to apply a specified required under UL 2054).
explosion or fire.
average and peak acceleration for Additional Specialized Tests
• Forced Discharge Test — The
the specified duration of the test. In addition to the common abuse tests forced discharge test determines To pass this test, a cell may not discussed above, certain product safety a battery's behavior when a explode, ignite, leak or vent.
standards and testing protocols for discharged cell is connected in series • Vibration Test — The vibration test
lithium-ion batteries require additional with a specified number of charged applies a simple harmonic motion at specialized testing. These specialized tests cel s of the same type. The goal specified amplitude, with variable address specific uses and conditions in is to create an imbalanced series frequency and time to each cel which the batteries might be expected connected pack, which is then short- sample. To pass this test, the cell may circuited. To pass this test, no cel not explode, ignite, leak or vent.
may explode or catch fire. (This test • Projectile (fire) Test — The projectile
is not required under BATSO 01).
test is required under UL 1642. UL • Heating Test — The heating
2054, UL Subject 2271, IEEE 1625 test evaluates a cel 's ability to and IEEE 1725. The test subjects a • Crush Test — The crush test
withstand a specified application cell sample to a flame from a test determines a cel 's ability to of an elevated temperature for a burner, while positioned within a withstand a specified crushing force period of time. To pass this test, the specified enclosure composed of (typical y 12 kN) applied by two flat cell may not explode or ignite. (This wire mesh and structural support. plates (typical y although some test is not required under IEC 62281, If the application of the flame crush methods such as SAE J2464 UN 38.3 or BATSO 01).
results in an explosion or ignition of include a steel rod crush for cel s • Temperature Cycling Test — The
the cel , no part of the cell sample and ribbed platen for batteries). To temperature cycling test subjects may penetrate or protrude through pass this test, a cell may not explode each cell sample to specified the wire mesh enclosure.
Safety Issues for Lithium-Ion Batteries
• Drop Test — The drop test is
test, the measured resistance must developing safety tests that assess the required under UL Subject 2271, UL exceed the specified minimum value.
propensity of a battery to experience a Subject 2580, IEC 62133, IEC 62281, • Reverse Charge Test — The reverse
short circuit under certain NEMA C18.2M Part 2, JIS C8714 and charge test is required under IEC abuse conditions.
BATSO 01. The test subjects each 62133, UL Subject 2271 and UL cell or battery sample to a specified Potential Causes Of Internal
Subject 2580. This test determines number of free fal s to a hard a discharged cell sample's response surface. The cell sample is examined to a specified charging current Although an internal short circuit may after a time fol owing each drop. applied in a reverse polarity have many causes, it is basical y a To pass this test, the cell may not condition for a defined period of pathway between the cathode and explode or ignite.
time. To pass this test, the cell may anode that al ows for efficient but • Continuous Low Rate Charging Test
not explode or ignite.
unintended charge flow. This highly — The continuous low rate charging localized charge flow results in joule • Penetration Test — The penetration
test is required under IEC 62133. heating due to internal resistance, test is required under UL Subject This test subjects ful y-charged with subsequent heating of the active 2271, UL Subject 2580 and SAE J2464. cell samples to a long-term, materials within the lithium-ion battery. The test uses a pointed metal rod to uninterrupted charge at a rate The increased heat may destabilize penetrate a cell and simultaneously specified by a manufacturer. To pass the active materials, in turn starting a this test, the cell may not explode, measures rod acceleration, cel self-sustaining exothermic reaction. The ignite, vent or leak.
deformation, cell temperature, cel subsequent heat and pressure build-up terminal voltage and resistance.
• Mold Stress Test — The molded
within the cell may lead to catastrophic casing-heating test is required under Internal Short Circuits: Potential
structural failure of the battery casing NEMA C18.2M Part 2, UL 2054, IEC Causes And Testing Issues
and the risk of additional combustion as 62133 and UL Subject 2271. The test a result of exposure to outside air.
A review of lithium-ion battery safety exposes plastic-encased batteries research shows a strong focus on internal Lithium-ion batteries are designed with to a specified elevated temperature short circuits. Some field failures resulting integrated safety devices that open the and for a specified time. Once in fires or explosions, leading to product external electrical load in the event of an the battery has cooled to room damage or personnel injury, have been over-current condition or relieve excessive temperature the cell is examined. linked to an internal short circuit within pressure build-up in the cel . However, To pass this test, the internal cel s the lithium-ion battery. these safety devices are unable to may not show any evidence of However, as shown in Table 1, most mitigate all internal cell fault situations, mechanical damage.
lithium-ion battery safety standards such as an internal short circuit. For • Insulation Resistance Test — The
and testing protocols do not specifical y products like electric vehicles, the insulation resistance test is required include testing for internal short circuits. presence of hundreds of these batteries under UL Subject 2580, IEC 62133 and In recent years, UL has partnered with key requires more sophisticated safeguards NEMA C18.2M Part 2 (conducted as battery research facilities such as Argonne such as battery management systems. a pretest condition only). The test National Laboratories and the National Clearly, the desired goal is a test portfolio subjects a cell sample to a resistance Aeronautic and Space Administration (simulating a wide variety of abuse measurement between each battery to better understand the root causes conditions) that can assess the likelihood terminal and the accessible metal of internal short circuits. The focus of of a battery to manifest a parts of a battery pack. To pass this our research has been on defining and short circuit.
Safety Issues for Lithium-Ion Batteries
However, in designing a test for a specific C8714.) This test creates an internal short Moving from Battery
failure, the root causes and failure circuit by disassembling a charged cell to System Safety
pathways must be known. These causes sample casing and placing a specified Lithium-ion batteries are typical y may include a large internal defect or a nickel particle under the cell winding marketed and sold directly to original severe external force that deforms the construction. (This is an inherently equipment manufacturers (OEMs) inner layers of the battery sufficiently dangerous process for the test operator.) as components to be integrated into to compromise the separator. In many The cell sample, minus the casing, is then end-use products. Because the OEM's failure incidents, only partial root-cause subjected to a specified crushing action at product actual y controls these functions, and failure information is available. an elevated temperature. However, best product safety issues involving cell Lithium-ion battery designers and practice in safety test design precludes charging rates, discharging rates and researchers are working to create new disassembly of a product. All tests should reverse charging may not be adequately battery designs that mitigate the impact be designed for execution with minimum addressed by battery testing alone.
of these causes.
risk to laboratory personnel4.
In such cases, international standards Internal Short Circuit Tests
To that end, UL researchers have organizations are working to improve developed a test5 that induces internal OEM product compatibility with The variety of root causes for internal short circuits by subjecting lithium-ion integrated lithium-ion batteries by short circuits makes it difficult to design battery cel s to a localized indentation including appropriate performance a single safety test that can assess the under elevated temperature conditions. testing in applicable standards. An robustness of a lithium-ion battery. During this test, the open circuit example of such an approach to To date, only JIS C8714 specifies an voltage, cell surface temperature force performance testing can be found in internal short circuit test, known as and position of the indenter probe IEC 60950-1 (UL 60950-1), Information the forced internal short circuit (FISC) are measured in real time. The test is Technology Equipment — Safety — Part 1.
test. (Note that IEEE 1625, Annex D currently under development for possible references the FISC test found in JIS inclusion in UL 1642 and UL Subject 2580.
Safety Issues for Lithium-Ion Batteries
Looking Ahead
As the development of lithium-ion batteries is an active area in fundamental research
and product development, knowledge regarding the use and abuse of these products
and their possible failure modes is still growing. Therefore, it is important that
safety standards continue to evolve to help drive toward the safe commercial use of
these energy storage devices as they power more and more products. UL will continue
dedicating significant resources to translating battery safety research into safety
standards. This focus will cover the wide range of chemistries and battery designs.
The work includes the multi-scale continuum, from material and component-level
characterization to battery systems and beyond.
For additional information about this white paper, please contact Ms. Laurie Florence,
Primary Designated Engineer — Batteries, Capacitors, Fuel Cel s and H2 Generators,
at [email protected].
1 "Lithium Batteries: Markets and Materials," Report FCB028E, October 2009, www.bccresearch.com.
2 "FTA/FMEA Safety Analysis Model for Lithium-Ion Batteries," UL presentation at 2009 NASA Aerospace Battery Workshop.
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.
4 Yen, K.H., et al., "Estimation of Explosive Pressure for Abused Lithium-Ion Cells," UL presentation at 44th Power Sources Conference, 5 Wu, Alvin, et al., "Blunt Nail Crush Internal Short Circuit Lithium-Ion Cell Test Method," UL presentation at NASA Aerospace Battery Workshop, 2009.
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