Indentation Induced ISC Test
An innovative testing method that was developed to help understand the potential severity of internal short circuits (ISCs).
WHY THE INDENTATION INDUCED ISC TEST MATTERS
Driven largely by their long cycle lives, low self-discharge rates and high energy/power densities,1 lithium-ion batteries are becoming an important sustainable energy technology. When considering reported incidents involving lithium-ion batteries, many cite internal short circuits (ISCs) as a possible intermediate cause for the overheating of the cell. Though other test methods exist to simulate ISCs in lithium-ion cells, the Indentation Induced ISC test was developed based on best-practice principles to provide a practical and simple method that is very suitable for battery safety standards. This test gives UL the ability to simulate how a lithium-ion cell behaves when subjected to an ISC condition, which will help mitigate the hazards of ISCs and support the safe commercialization of lithium-ion batteries.
The performance characteristics of lithium-ion batteries, coupled with the projected one-third decrease in their costs by 2017,2 make them increasingly popular in a broad range of applications. For example, lithium-ion batteries now comprise in excess of 95 percent of mobile phone batteries worldwide.3 Lithium-ion batteries are also used in a variety of consumer electrical and electronic devices (e.g., laptop computers, tablet computers and digital cameras), medical devices (e.g., patient monitors, handheld surgical tools and portable diagnostic equipment), industrial equipment (e.g., cordless power tools, wireless security systems and outdoor portable electronic equipment), automotive applications (e.g., electric vehicles), aerospace applications (e.g., aircraft and spacecraft), and energy (e.g., grid-connected electricity storage).4
Although lithium-ion batteries are designed with integrated passive safeguards and active safeguards for pack designs, these batteries have been involved in incidents involving overheating and fire that, while very rare, have put these batteries in the public spotlight.5 In many cases, the battery failures were linked to ISCs that led to thermal runaway, resulting in the explosive release of energy along with fire. These incidents have provided an impetus for research aimed at understanding the causes of lithium-ion battery failures and guiding safer battery cell designs. The number of lithium-ion batteries in use, the complexity of the lithium-ion battery cells and the numerous usage conditions make the design of safe cells and the development of tests for battery safety standards extremely challenging.6 These challenges underscore the need for a reliable ISC simulation method that helps improve product safety by ensuring that consensus-based battery safety standards effectively accommodate the rapidly changing state of lithium-ion cell design and applications.
WHAT DID UL DO?
UL invested research resources and collaborated with other organizations with the goal of developing a reliable and repeatable testing methodology that met two key criteria. First, the test needed to be able to generate a localized ISC within a closed cell that would simulate the conditions similar to those found in the field failures of lithium-ion batteries. Second, the new test needed to be acceptable for battery safety standards.
Our research resulted in the development of the innovative Indentation Induced ISC test. After demonstrating the potential of this testing method, we partnered with NASA and Oak Ridge National Laboratories (ORNL) to further develop the test approach. NASA already had its own ISC test method, but seeing the advances made in the UL test method, it adopted and fine-tuned the Indentation Induced ISC approach. This method is now part of NASA’s battery qualification process for space applications. Next, UL collaborated with ORNL to extend the test setup to cover a variety of form factors.
The Indentation Induced ISC test is appropriate for cylindrical cells and other form factors, such as pouc