Tetrabromobisphenol a Bis(dibromopropyl ether) As a Flame Retardant Additive for Lithium-Ion Batteries

Increasing demands for portable electronic appliances have expanded the spectrum of lithium-ion batteries applications to a wider extent. In spite of the widespread use and deserved promise of lithium-ion batteries, battery safety is still a substantial issue of concern. [1]. Besides other aspects, the flammability of carbonates, frequently used as electrolyte components in most batteries, is one of the major challenges in battery safety. There are different approaches to overcome this problem. One approach is to replace the liquid electrolytes with, for example ionic liquids, gel polymer electrolytes or even solid electrolytes. Another approach is to add flame retardants (FRs) to suppress the flammability of the electrolytes. [2].

Among the wide range and variety of flame-retardants available, there is one class that has rarely been studied as an electrolyte additive in Li-ion batteries, that is, the brominated compounds. [3]. The organobromine compounds are known as the most effective as flame retardant additives for polymers. The reasons are explained as the C-Br bond is stable enough for environmental exposure and yet unstable enough that heat can easily break the bond, releasing the bromine under fire conditions to inhibit combustion free radical reactions. Also industrially speaking, producing organobromine compounds as flame retardants turns out to be a very efficient chemistry, making it possible to produce large amounts of organobromine compounds, cost effectively. This again is because of the unique aspects of bromine and carbon chemistry that make these compounds easy to perbrominate, and so one small organic molecule can deliver a high payload of effective bromine to the fire. [4]

In this work, tetrabromobisphenol A bis(dibromopropyl ether)  (TBBA-BDBPE) was analyzed as a potential brominated flame retardant candidate for lithium ion battery field. Electrolyte compositions with different concentrations of (TBBA-BDBPE) were prepared by mixing with reference electrolyte which is 1 M LiPF₆in [EC:EMC (3:7) + 2%VC]. Self extinguishing time measurements were done to compare the flammability of different electrolyte systems.(Table1). Constant current cycling experiments were performed by full cells of MCMB as anode and NMC as cathode. (Figure 1) The electrolyte system with FR was tested on MCMB anode and NMC cathode as half cells with CV method. It was observed that on the cathode side there is no additional reaction occurring but on the anode side the FR decomposes at 1.3 V which only occurs in the first cycle and doesn’t go further. In order to prevent the decomposition of FR in the electrolyte system, different additives such as ES and LiBOB which reduce at potentials higher than 1.3 V were added to the system.

0.5 % LiBOB was enough to suppress the decomposition of FR on the anode side, also the addition of LiBOB to the system resulted an increase in initial cycle efficiency.It was concluded that the tetrabromobisphenol A bis(dibromopropyl ether)  (TBBA-BDBPE) might be an effective candidate for Li-ion battery systems in terms of flame retardancy and cost. The addition of both (TBBA-BDBPE) and LiBOB to the reference electrolyte system, resulted to an enhanced intrinsic safety and stable cyclization performance.

References

[1]G.Dixon,R.S.Morris,.Dallek,Journal of Power Sources, 138, 2004,274-276

[2] J.B. Goodenough, Y. Kim, Chem Mater, 22 (2010) 587-603.

[3] D.Belov, D.T. Shieh, Journal of Power Sources, 247 (2014),865-875

[4] A.Morgan, J.Gilman, Fire and Materials, 37, (2012), 259–279