Author: Donal Finegan
The answer is not as obvious as it might seem.
Work led by Siddhartha Nanda and Hadi Khani published in Royal Society of Chemistry journal of Energy and Environmental Science, dives into the sources of heat generation for Triethyl Phosphate (TEP) with KFSI electrolyte and a potassiated graphite anode:
Potassium (K)-ion batteries are an attractive alternative to lithium-ion batteries due to their resource abundance, graphite-anode compatibility, manufacturability, and reduced reliance on critical metals. However, their thermal safety remains poorly defined. Here, we investigate a widely accepted “safer” anode–electrolyte pair, a graphite anode with a low-flammable electrolyte, 2.5 M potassium bis(fluorosulfonyl)imide (KFSI) in triethyl phosphate (TEP), to clarify decomposition pathways and interfacial reactivity. This work shows that stand-alone TEP primarily volatilizes, whereas in the presence of KFSI it thermally decomposes via FSI-derived intermediates, producing exothermic reactions totalling ∼264 J g−1 above 200 °C and generating organophosphate/fluorophosphate species (e.g., diethyl fluorophosphate) together with SO2, HNO3, and SOF2. This is roughly twice the heat released by a conventional LiPF6-based carbonate electrolyte, underscoring that low flammability does not equate to safety.
Despite TEP being a low-flammability solvent, exothermic reactions occurred at temperatures below 100°C and the heat of thermal runaway in this system was around 2x the heat of an equivalent flammable carbonate electrolyte with LiPF6. This was due to the sources of heat stemming from reactions with electrochemically active interfaces, rather than combustion.
Our findings demonstrate that low flammability alone does not ensure thermal safety; rather, interfacial reactivity governs risk.
This work shows that strategic selection of electrolytes for good thermal stability should go beyond whether the electrolytes are flammable or not, and should account for thermal stability of electrolytes in the electrochemical environments in which they will operate.
References
- Siddhartha Nanda, Andrei Dolocan, Ayrton Yanyachi, Saurabh Sandip Satpute, Doosoo Kim, Kami L. Hull, Donal Finegan, Ofodike Ezekoyeb and Hadi Khani, Thermal decomposition pathways and interfacial reactivity in potassium-ion batteries: focus on the electrolyte and anode, Energy Environ. Sci., 2026, 19, 1215-1236