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

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 (T-FP = 174 degrees C) and the boiling point (T-BP = 287 degrees 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 (T-MP = -75 degrees 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 T-FP = 172 degrees 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.

Automated summary

This study introduces glyceryl tributyrate (GTB) as a flame retardant and eco-friendly solvent for liquid electrolytes for lithium-ion cells. Compared to conventional linear carbonate components, GTB has higher flashpoint, boiling point, and lower melting point. The GTB-based electrolyte shows excellent performance in terms of coulombic efficiency and capacity retention, as well as improved electrochemical stability. It is considered as an interesting alternative for improving the thermal stability and safety of lithium-ion cells, especially in low power-density applications.