Dreamliner Nightmares a Factor in New UL Standards Activities for Li-ion Batteries

Underwriters Laboratories, Inc. (UL) has announced that it is developing tests and standards for applications involving cell safety through battery system safety. The focus is on refining large-format lithium-ion (Li-ion) battery standards. Safety concerns that UL is considering related to lithium-ion batteries include fire, explosion, electric shock and hazardous material exposure (vented toxic gases, leaked electrolytes).

“In recent years there have been reports of field failures involving Li-ion batteries. These range from failures in 2006 of laptops powered by Li-ion batteries to cargo plane fires involving bulk transport of lithium-ion cells. Since March 2012, the Consumer Product Safety Commission documented 467 reported incidents that identified Li-ion cells as the battery type involved, with 353 of those being incidents involving fire/burn hazards. Further, in 2013 there were two reported incidents related to Li-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,” according to a recent report issued by UL.

At the cell level, UL is working on developing a new internal short circuit (ISC) test method for Li-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 testing; There are also improvements to ongoing product criteria and quality requirements.

Also 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.

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.

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.

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; And 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: short circuit, overcharge, overdischarge, humidity/isolation resistance, thermal control failure, temperature cycling, vibration, drop, mechanical shock, rotation, crush, immersion, temperature and imbalanced charge tests.

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.

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.

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.