Lithium-ion batteries are rapidly becoming the backbone of modern energy systems, powering electric vehicles, consumer electronics, and grid-scale storage. However, their widespread adoption has brought increasing attention to safety concerns, particularly the risk of thermal runaway—a self-accelerating sequence of exothermic reactions that can lead to fire or explosion. As battery energy densities continue to rise, so does the need for fundamentally safer chemistries.

At Purdue University’s Battery Fire-Safety Lab, we address this challenge by combining material design, diagnostics, and fundamental chemical understanding to improve battery safety without compromising performance. Our research focuses on the role of electrolyte chemistry in governing thermal stability and flammability. Electrolytes play a central role in thermal runaway initiation, as their decomposition reactions interact with electrode materials to generate heat, gases, and reactive species. Suppressing these reactions or delaying their onset is key to mitigating failure.

One promising strategy is the use of flame-retardant electrolyte additives. In our recent work, we investigate ethoxy(pentafluoro)cyclotriphosphazene (PFPN), a phosphorus–nitrogen-based compound that suppresses combustion through radical scavenging mechanisms. Battery electrolyte combustion is driven by radical chain reactions involving highly reactive species such as hydrogen and hydroxyl radicals. PFPN disrupts these reactions by generating phosphorus- and fluorine-based radicals that form stable products, effectively inhibiting flame propagation.

Our experiments demonstrate that PFPN significantly enhances electrolyte safety. Self-extinguishing time measurements show a reduction in flammability of up to 43%, and in many cases, electrolyte samples fail to ignite even under extended exposure. Differential scanning calorimetry further reveals improved thermal stability, with decomposition temperatures delayed by approximately 30 °C. Importantly, these safety benefits are achieved with minimal impact on electrochemical performance. Coin cell and pouch cell testing confirm that batteries with PFPN-containing electrolytes retain comparable capacity, cycling stability, and rate.

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