Journal of Power Sources 187 (2009) 229–232 Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour Short communication A novel flame retardant and film-forming electrolyte additive for lithium ion batteries Shiyu Chen a,b , Zhaoxiang Wang a,∗ , Hailei Zhao b , Hongwei Qiao c , Helin Luan c , Liquan Chen a a Laboratory for Solid State Ionics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China b School of Materials Science and Engineering, Beijing University of Science and Technology, Beijing 100083, China c Beijing General Research Institute of Mining and Metallurgy, Beijing 100044, China article info Article history: Received 21 September 2008 Received in revised form 16 October 2008 Accepted 17 October 2008 Available online 6 November 2008 Keywords: Allyl tris(2,2,2-trifluoroethyl) carbonate (ATFEC) Flame retardant Film-forming Electrolyte additive Lithium ion battery abstract Allyl tris(2,2,2-trifluoroethyl) carbonate (ATFEC) was synthesized as a bi-functional additive of flame retar- dant and film former in electrolytes for lithium ion batteries (LIBs). The flame retardancy of the additive was characterized with differential scanning calorimetry (DSC) and self-extinguishing time (SET). It is shown that adding 1 vol.% ATFEC in 1 M LiPF 6 /propylene carbonate (PC) can effectively enhance the ther- mal stability of the electrolyte and suppress the co-intercalation of PC into the graphitic anode. Further evaluation indicates that the additive hardly affect the conductivity of electrolyte. These support the feasibility of using ATFEC as an additive on formulating an electrolyte with multiple functions such as film-forming enhancement, high thermal stability and high ionic conductivity. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Safety issue has been harassing the application of lithium ion batteries (LIBs) with high energy density (energy storage batteries) and high power density (e.g. batteries for hybrid electric vehi- cles). Overcharge and over-discharge of a lithium ion battery will result in electrolyte decomposition, producing various flammable gaseous species, increasing the inner pressure and temperature of the battery. Any of these issues will increase the explosion haz- ard of the battery [1]. Clearly an internal-built safety mechanism is more reliable and effective than the external-built safety mecha- nism such as the positive temperature coefficient (PTC) devices and current intermitted devices (CID) when the temperature, internal pressure, voltage and/or the current of the battery increase(s) very quickly. Currently most studies intended to enhance the electrolyte safety are focused on the (fluorinated) phosphates [2–9] as the flame retardant either in the form of an additive or a co-solvent of the electrolyte. However, some additives such as the com- monly studied trimethyl phosphate (TMP) [10–12] and dimethyl methylphosphonate (DMMP) [3–5] characteristic of excellent ∗ Corresponding author. Tel.: +86 10 82649050; fax: +86 10 82649050. E-mail address: zxwang@aphy.iphy.ac.cn (Z. Wang). self-extinguishing properties suffer from severe reductive decom- position on the graphitic anodes. Therefore they can only be applied in LIBs with non-graphitic carbon anode [11] or with the presence of some film-forming additives in the case of graphitic anode mate- rials [4,5,12]. Propylene carbonate (PC) based electrolytes are attractive due to the low cost of the solvent and the wide temperature window of the resultant electrolyte. However, significant co-intercalation will occur when PC-based electrolytes are combined with graphitic anode, resulting in severe exfoliation of the latter. Molecules con- taining vinyl groups are commonly used as the additive for the formation of the solid electrolyte interphase (SEI) layer on the graphite-based anode because they can reductively decompose prior to the co-intercalation of the electrolyte. In addition, electron- drawing groups such as –F make the vinyl group more electrophillic and thus facilitate the reduction, helpful for the formation of the SEI layers on the graphitic anodes [13]. Moreover, introduction of fluorine into organic molecules usually reduces their boiling temperature and viscosity and suppresses the flammability of the molecule [9]. Therefore, allyl tris(2,2,2-trifluoroethyl) carbonate (ATFEC) was synthesized in this work as a flame retardant and film- forming additive in electrolyte for LIBs. It will be seen that ATFEC is a promising bi-functional additive in enhancing the thermal sta- bility of the electrolyte and in preventing the co-intercalation of PC into graphitic anode materials during discharge. 0378-7753/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2008.10.091