Investigation of a Novel Ecofriendly Electrolyte-Solvent for Lithium-Ion Batteries with Increased Thermal Stability

Marco Ströbel,Larissa Kiefer,Kai Peter Birke

doi:10.3390/batteries7040072

Abstract

This study presents tributyl acetylcitrate (TBAC) as a novel ecofriendly high flash point and high boiling point solvent for electrolytes in lithium-ion batteries. The flash point (TFP=217∘C) and the boiling point (TBP=331∘C) of TBAC are approximately 200 K greater than that of conventional linear carbonate components, such as ethyl methyl carbonate (EMC) or diethyl carbonate (DEC). The melting point (TMP=−80∘C) is more than 100 K lower than that of ethylene carbonate (EC). Furthermore, TBAC is known as an ecofriendly solvent from other industrial sectors. A life cycle test of a graphite/NCM cell with 1 M lithium hexafluorophosphate (LiPF6) in TBAC:EC:EMC:DEC (60:15:5:20 wt) achieved a coulombic efficiency of above 99% and the remaining capacity resulted in 90 percent after 100 cycles (C/4) of testing. As a result, TBAC is considered a viable option for improving the thermal stability of lithium-ion batteries.

Highlights

Lithium-ion cells are the technological standard for portable devices such as smartphones, notebooks, and electric vehicles, and as a result, they are viewed as a key for the global transition to electro-mobility
This study presents tributyl acetylcitrate (TBAC) as a novel ecofriendly high flash point and high boiling point solvent for electrolytes in lithium-ion batteries
The melting point is more than 100 K lower than that of ethylene carbonate (EC)

Summary

Introduction

Lithium-ion cells are the technological standard for portable devices such as smartphones, notebooks, and electric vehicles, and as a result, they are viewed as a key for the global transition to electro-mobility. An expensive thermal management system and a massive casing for lithium-ion batteries are required This heavy casing for battery packs for electric vehicles lowers the gravimetric density of the pack and increases the weight of the vehicles. Investigations on new electrolyte formulations have been considered before, for example by using flame retardant additives like organic phosphates [13] or phosphonates [14] Using these additives to improve the thermal stability reduces the cell performance [15]. Co-solvents were able to increase the flash point significantly from TFP,EC:DEC ≈ 36 ◦C of the EC:DEC (3:7 wt) mixture to TFP,EC:ADN ≈ 149 ◦C of the EC:ADN (1:1 wt) mixture This indicates that it is possible to formulate electrolytes with higher flash points by replacing volatile carbonates.

Methods

Results

Discussion

Conclusion