High Flashpoint and Eco-Friendly Electrolyte Solvent for Lithium-Ion Batteries

• Published in: Batteries (Basel) 2023-07, Vol.9 (7), p.348
• Main Authors: Ströbel, Marco, Kiefer, Larissa, Pross-Brakhage, Julia, Hemmerling, Jessica, Finster, Philipp, Ziebert, Carlos, Birke, Kai Peter
• Format: Article
• Language: English
• Subjects: Batteries; Boiling points; Conductivity; eco-friendly electrolyte for lithium-ion batteries; Electric cells; Electric properties; Electrodes; Electrolytes; Electrolytic cells; enhanced electrolyte safety based on high flashpoint; Flame retardants; glyceryl tributyrate; Graphite; improved thermal stability of electrolytes; Lithium; Lithium-ion batteries; Melting points; Pharmaceutical industry; R&D; Rechargeable batteries; Research & development; Safety; Solvents; Stainless steel; Temperature; Thermal runaway; Thermal stability; tributyrin; Voltammetry
• ISSN: 2313-0105; 2313-0105
• DOI: 10.3390/batteries9070348

Since Sony launched the commercial lithium-ion cell in 1991, the composition of the liquid electrolytes has changed only slightly. The electrolyte consists of highly flammable solvents and thus poses a safety risk. Solid-state ion conductors, classified as non-combustible and safe, are being researched worldwide. However, they still have a long way to go before being available for commercial cells. As an alternative, this study presents glyceryl tributyrate (GTB) as a flame retardant and eco-friendly solvent for liquid electrolytes for lithium-ion cells. The remarkably high flashpoint (TFP=174°C) and the boiling point (TBP=287°C) of GTB are approximately 150 K higher than that of conventional linear carbonate components, such as ethyl methyl carbonate (EMC) or diethyl carbonate (DEC). The melting point (TMP=−75°C) is more than 100 K lower than that of ethylene carbonate (EC). A life cycle test of graphite/NCM with 1 M LiTFSI dissolved in GTB:EC (85:15 wt) achieved a Coulombic efficiency of above 99.6% and the remaining capacity resulted in 97% after 50 cycles (C/4) of testing. The flashpoint of the created electrolyte is TFP=172°C and, therefore, more than 130 K higher than that of state-of-the-art liquid electrolytes. Furthermore, no thermal runaway was observed during thermal abuse tests. Compared to the reference electrolyte LP40, the conductivity of the GTB-based is reduced, but the electrochemical stability is highly improved. GTB-based electrolytes are considered an interesting alternative for improving the thermal stability and safety of lithium-ion cells, especially in low power-density applications.