Tech Insights

Advancing Battery Safety: Self-Extinguishing Electrolytes for Fire Prevention

February 22, 2024 by Jake Hertz

To enhance battery safety and reduce fire risk, researchers substituted non-flammable self-extinguishing electrolytes for combustible electrolytes.

Lithium-ion batteries (Li-ions) are the foundation for many technologies, including electric vehicles (EVs). The popularity of Li-ions necessitates recognizing their fire safety implications as well. While fires from these batteries are relatively infrequent, their impact can be considerable. 

Researchers from Clemson University and Hunan University have attempted to replace highly combustible electrolytes in Li-ions with fire-extinguishing materials. Their study could produce a battery that can extinguish its own fire.

 

Electric vehicle fire

Electric vehicle fire. Image used courtesy of National Highway Traffic Safety Association

 

Why and How Do Lithium-ion Batteries Catch Fire?

A primary reason for Li-ions catching fire is the highly flammable electrolyte used in their construction. This electrolyte, typically composed of a lithium salt dissolved in an organic solvent, can ignite under certain conditions, leading to thermal runaway (a rapid and uncontrollable increase in temperature within the battery). 

Thermal runaway is triggered by internal short circuits, overcharging, physical damage, exposure to heat, or manufacturing defects. With the high-energy density associated with Li-ions, any of these possibilities could cause them to ignite and potentially lead to a fire or powerful explosion. Moreover, the risk of an intense fire increases proportionally with battery size.

 

Dendrite formation

Dendrite formation. Image used courtesy of Lawrence Berkely National Laboratory

 

Another safety concern arises when Li-ions undergo rapid charging, leading to chemical reactions that generate sharp needle-like lithium formations called dendrites on the battery's negative electrode. By design, a separator inside Li-ion batteries prevents the internal electron flow between the anode and cathode. Over time, however, these dendrites can breach the separator, causing internal short circuits and subsequent overheating.

Given Li-ions' ubiquity, their design and construction must balance safety considerations with energy density and performance requirements. Here, the challenging part is to develop safer electrolyte formulations not prone to thermal runaway. 

 

Self-Extinguishing Electrolyte Formation

In electrolytes, most identified non-flammable organic solvents contain fluorine and phosphorus, both of which increase the electrolyte's cost and potential environmental harm. However, in a recent development, researchers at Clemson University addressed the challenge of reducing Li-on battery fire incidents by developing a self-extinguishing battery. 

The team replaced the combustible electrolyte with materials from a commercial fire extinguisher. Specifically, their design aims to reduce the flammability of the commonly used glyme solvent by introducing a fluorinated liquid and a non-polar solvent, known as Novec 7300 coolant fluid and Daikin-T5216, respectively.

The team tested the efficacy of the electrolyte formulation across a wide temperature range, from approximately -100 to +175F. In rigorous testing, they subjected the batteries to the nail penetration test, a common method for assessing lithium-ion batteries’ safety. This test simulates an internal short circuit by driving a stainless steel nail through a charged battery. Remarkably, the team’s batteries withstood the impact without catching fire.

 

Video used courtesy of Electrical Safety First

 

When the electrolyte was implemented in potassium-metal batteries, the cells retained 93% of their capacity after 2,400 cycles. An 18650 Li-ion cell retained 96.7% of capacity over 200 cycles.

 

Reducing Fire Risk With Better Batteries

The Clemson team’s study on self-extinguishing rechargeable batteries marks a significant advancement in battery safety technology, promising to mitigate fire risks associated with Li-ions across various applications. Through the development of self-extinguishing rechargeable batteries, the team hopes to pave the way for safer batteries for public consumption while also being cheaper and more sustainably sourced.