Lithium-ion (Li-ion) batteries, which provide excellent power density and lengthy service lives, have become the dominant rechargeable battery technologies over the last 30 years. However, thermal runaway incidents, where the energy in a cell is uncontrollably (and frequently violently) transformed into heat, plague their safety record.
The risks that thermal runaway in Li-ion batteries pose are examined in this article, along with its causes.
The Case for Li-Ion Technology
In comparison to other commercially available batteries,1 the first lithium-ion batteries, which were introduced to the market for the first time in 1991, were a significant improvement.
Rechargeable Li-ion batteries offered extremely high energy densities and protracted service lives, which differed significantly from other developing rechargeable battery technologies that were widely used at the time that depended on the transport of lithium ions through a non-aqueous electrolyte.
The need for an energy storage solution that could replace fossil fuels in vehicles and provide longer-term energy storage for a distributed renewables-based grid2,3 increased dramatically over the following years as climate change became an increasingly urgent issue.
The obvious choice was lithium-ion batteries, which have undergone extensive research and development over the past 30 years to increase their performance and lower their cost.4
Today, lithium-ion batteries are almost always the preferred form of energy storage for portable electronics and electric vehicles. They are also frequently used in massive stationary energy storage systems.
Safety Concerns and Thermal Runaway
In addition to having great performance qualities, lithium-ion batteries were and still are largely regarded as safe. Although Li-ion batteries have generally been successful, thermal runaways and catastrophic battery failures continue to plague the industry.
A chemist might refer to a thermal runaway as an unchecked exothermic chain reaction. Materials can experience exothermic decomposition in a matter of milliseconds when a cell’s temperature rises. When this occurs, other battery cells become heated and can start to break down.
After a while, the battery begins to heat up faster than it can release heat into the air around it. When stability is lost, and the battery’s temperature rises exponentially, all of the battery’s remaining thermal, chemical, and electrochemical energy is released into the environment.5
According to testing, mechanical failure, overcharging, high temperatures, or internal short-circuits6 are just a few of the mechanisms that can cause thermal runaway.
Mitigating Thermal Runaway Events
The term “abuse” of the battery, including thermal abuse, mechanical abuse, and electrochemical abuse, is frequently used in research to describe thermal runaway events. In fact, a few common techniques are frequently used in lab tests to purposefully cause thermal runaway, such as by puncturing or overheating a cell.
These test procedures are effective at causing thermal runaway, but they do not accurately reflect battery failures that occur in the real world. In fact, outside of the lab, a significant proportion of thermal runaway events appear to be unrelated to any sort of system “abuse” or overt stress factors.7
In Montreal, Canada, one notable example of thermal runaway occurred in the battery packs of an electronic vehicle.8 The car was parked in the owner’s garage at the time of the incident; it was neither charging nor moving.
The garage had a smoke detector, but it did not detect the thermal runaway until the entire thing exploded, destroying the smoke detector and sending the garage door flying into the street.
Unfortunately, there is no shortage of comparable case studies.9,10 It is not just electric cars at risk either – four firefighters were injured in an explosion caused by a Li-ion energy storage system (ESS) in Arizona in April 2019, despite the fact the facility was compliant with all pertinent standards at the time of commissioning.
Despite being rare, thermal runaway events are acknowledged as serious issues due to their severity. The absence of an apparent cause in a large number of thermal runaway incidents highlights the need for more robust monitoring and detection technologies.
References and Further Reading
- Sony Group Portal | The Lithium-Ion Rechargeable Battery. https://www.sony.com/en/SonyInfo/CorporateInfo/History/SonyHistory/2-13.html#block3.
- Roberts, B. & Sandberg, C. The Role of Energy Storage in Development of Smart Grids. Proceedings of the IEEE 99, 1139–1144 (2011).
- Li, M., Lu, J., Chen, Z. & Amine, K. 30 Years of Lithium‐Ion Batteries. Adv. Mater. 30, 1800561 (2018).
- The price of batteries has declined by 97% in the last three decades. Our World in Data https://ourworldindata.org/battery-price-decline.
- Battery Power Online | Thermal Runaway: Understanding the Fundamentals to Ensure Safer Batteries. https://www.batterypoweronline.com/news/thermal-runaway-understanding-the-fundamentals-to-ensure-safer-batteries/ (2019).
- Feng, X., Ren, D., He, X. & Ouyang, M. Mitigating Thermal Runaway of Lithium-Ion Batteries. Joule 4, 743–770 (2020).
- Xiong, R., Ma, S., Li, H., Sun, F. & Li, J. Toward a Safer Battery Management System: A Critical Review on Diagnosis and Prognosis of Battery Short Circuit. iScience 23, 101010 (2020).
- News ·, C. B. C. Despite Île-Bizard explosion, expert says electric cars safer than others | CBC News. CBC https://www.cbc.ca/news/canada/montreal/experts-say-electric-cars-safer-than-others-1. 5230969 (2019).
- O’Kane, S. Porsche Taycan catches fire in Florida. The Verge https://www.theverge.com/2020/2/18/21142123/porsche-taycan-electric-ev-fire-florida (2020).
- Lambert, F. Tesla vehicle caught on fire while plugged in at Supercharger station. Electrek https://electrek.co/2019/06/01/tesla-fire-supercharger/ (2019).
This information has been sourced, reviewed and adapted from materials provided by Amphenol Advanced Sensors.
For more information on this source, please visit Amphenol Advanced Sensors.