Advancing Lithium-ion Battery Standards
Updates to safety standards covering a variety of applications and uses for small-form and large-form lithium-ion batteries.
WHY ADVANCING LITHIUM-ION BATTERY STANDARDS MATTERS
The use of lithium-ion batteries is on the rise, with the market expected to double globally by 2016.1 With new uses and potential safety hazards, it is therefore important to update existing standards and create new ones as our information and knowledge increase. In this way, we can maximize the safety of lithium-ion batteries as well as safeguard the adoption of new applications and uses of these batteries.
In recent years there have been reports of field failures involving lithium-ion batteries. These range from failures in 2006 of laptops powered by lithium-ion batteries to cargo plane fires involving bulk transport of lithium-ion cells.2 Since March 2012, the Consumer Product Safety Commission documented 467 reported incidents that identified lithium-ion cells as the battery type involved, with 353 of those being incidents involving fire/burn hazards.3 Further, in 2013 there were two reported incidents related to lithium-ion batteries employed in the Boeing 787 aircraft, in which flames were seen coming from an auxiliary power unit (APU) battery and/or odd smells were detected in the cockpit and cabin.4
Dangers related to lithium-ion batteries include fire, explosion, electric shock and hazardous material exposure (vented toxic gases, leaked electrolytes). With the electric vehicle market aggressively growing, the worldwide capacity for lithium-ion batteries for this mode of transportation will multiply tenfold by 2020.5 UL — along with various other industry stakeholders, including manufacturers and industry associations — has been prioritizing the updating of existing standards and advancing the creation of new standards.
WHAT DID UL DO?
THE STANDARDS TODAY
UL 1642 covers secondary (rechargeable) lithium-ion cells and primary (non-rechargeable) cells and batteries. Lithium primary cells have metallic lithium or lithium alloy anodes. Lithium-ion cells do not contain metallic lithium and typically have lithiated graphite at the negative electrode and a lithium metal oxide or phosphate at the positive electrode. Batteries may consist of a single cell or two or more cells connected in series or parallel — both with and without protection and control circuitry. UL 1642 includes the following tests: short circuit, abnormal charging, forced discharge, vibration, shock, crush, cell impact, temperature cycling, heating, altitude simulation and projectile/fire exposure.
Battery Safety Standards7
UL 2054 covers secondary (rechargeable) and primary (non-rechargeable) cells (chemistries include nickel [Ni-Cad, Ni-MH], alkaline, carbon zinc and lead acid) for portable applications. It also covers battery packs for portable applications and for all types of cells, including lithium-ion and lithium primary. UL 2054 includes short circuit, abnormal charging, abusive overcharge, forced discharge, limited power source, battery pack component temperature, battery pack surface temperature, 250 N steady force, mold stress relief and drop impact. UL 2054 also requires the lithium-ion cells to comply with UL 1642.6
At the cell level, UL is working on developing a new internal short circuit (ISC) test method for lithium-ion cells for inclusion in the lithium battery safety standard UL 1642. The test, which is referred to as an “indentation induced internal short circuit” (IIISC) test:
- Causes an ISC by creating a small localized defect in the cell separator (limited to only the surface layer of the electrode)
- Induces failure of the cell for cylindrical, prismatic and pouch format cells
- Is sensitive to design changes that affect the cell safety performance
- Is a method suitable for standards testing8
There are also improvements to ongoing product criteria and quality requirements.9 At the cell level, UL 1642 now includes the cell safe operating region parameter requirements for lithium-ion cells, and UL 2054 now includes requirements that the battery pack maintain cells within the cell safe operating region parameters. There is also greater attention to application-specific design challenges, abuse conditions and improvements to the certification process.10
LARGE-FORMAT FOCUSED STANDARDS
In addition to updates to UL 1642/UL 2054, UL is working on large-format focused standards, including UL 2271 and revisions to UL 2580 and UL 1973, given the growing global market needs. When UL 2271 is published, all three will be American National Standards Institute (ANSI) standards. UL 2580 covers safety (electric shock, mechanical hazards, toxic and combustible releases) of electrical energy storage assemblies (EESAs) for on-road vehicles and industrial off-road vehicles. The standard is not chemistry-specific and includes batteries, electrochemical capacitors, and hybrid combinations of batteries and electrochemical capacitors. The standard also includes safety requirements for cells and electrochemical capacitors used in the EESAs.
A safety analysis of electric energy storage assemblies such as a failure mode and effects analysis (FMEA) is required as well as specific construction requirements and tests, including electrical, mechanical, environmental and production tests.11 The UL 2580 test program includes short circuit, overcharge, overdischarge, humidity/isolation resistance, thermal control failure, temperature cycling, drop, vibration endurance, mechanical shock, rotation, crush, immersion, fire exposure, temperature and imbalanced charge tests.12 UL 2271 covers batteries, electrochemical capacitors and hybrid EESAs for use in light electric vehicles (LEVs). Heavy-duty industrial trucks are outside the scope of this standard (their EESAs are covered under UL 2580, above). Construction criteria are similar to UL 2580 with some exceptions, including:
- Enclosure relative thermal index (RTI) minimum of 80°C
- IP3X accessibility (tool as persons may be more exposed to these EESAs compared with UL 2580 types)
- Battery more apt to be user-removable for charging or replacement and may have handles
- Cell criteria same as proposed for UL 2580
The test program for UL 2271 has some differences from UL 2580 due to application and includes the following:13 short circuit, overcharge, overdischarge, humidity/isolation resistance, thermal control failure, temperature cycling, vibration, drop, mechanical shock, rotation, crush, immersion, temperature and imbalanced charge tests.14 UL 1973 covers electric energy storage systems (EESSs) for stationary applications such as photovoltaic (PV), wind turbine storage or uninterruptable power supply (UPS) applications. UL 1973 also covers EESSs for use in light electric rail (LER) applications and stationary rail applications. As with UL 2580 and UL 2271, UL 1973 includes construction criteria and tests.15 UL 1973 includes short circuit, overcharge, overdischarge, imbalance charge, dielectric voltage withstand, continuity, temperature, failure of thermal stability system, temperature cycling, vibration endurance, shock, drop, enclosure, water exposure, and external fire and internal fire tests.16
Updates to lithium-ion battery safety standards
For all the above standards, UL is including cell safety requirements to address specific applications, verify cell operating regions, help ensure that systems maintain cell operation region, require a system FMEA and, if necessary, evaluate functional safety.17
UL is continuing to advance safety by developing updates to existing standards and creating new standards when information, research and consensus are complete. These standards and UL’s leading role comprise the New Science that is spearheading the important role lithium-ion batteries play today and in the future, while helping ensure their safe continued use, adoption and expansion.