Effect of carbonates fluorination on the properties of LiTFSI-based electrolytes for Li-ion batteries Marco Bolloli a, b , Fannie Alloin a, b, *, Julian Kalhoff c , Dominic Bresser c, d, e , Stefano Passerini c, d, e , Patrick Judeinstein f , Jean-Claude Leprêtre a, b , Jean-Yves Sanchez a, b a Univ Grenoble Alpes, LEPMI, F-38000 Grenoble, France b CNRS, LEPMI, F-38000 Grenoble, France c Institute of Physical Chemistry & MEET, University of Muenster, Corrensstr. 28/30 & 46, 48149 Muenster, Germany d Helmholtz Institute Ulm, Helmholtzstraße 11, 89081 Ulm, Germany e Karlsruher Institute of Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany f Laboratoire Léon Brillouin, UMR 12CNRS-CEA, CEA Saclay, 91191 Gif sur Yvette Cedex, France A R T I C L E I N F O Article history: Received 6 November 2014 Received in revised form 4 February 2015 Accepted 5 February 2015 Available online 7 February 2015 Keywords: fluorinated carbonates electtrolyte lithium-ion battery LiTFSI A B S T R A C T Electrolyte compositions based on LiTFSI dissolved in fluorinated linear and cyclic carbonates were characterized regarding their transport and thermal properties, viscosity, solvation ability, electrochem- ical stability towards oxidation, as well as their ability to inhibit the aluminum current collector corrosion. As a result of the thorough investigation, different binary mixtures were prepared, which offer beneficial properties in terms of aluminum current collector protection and provide optimized transport properties. The use of LiTFSI as electrolyte salt rather than the state-of-the-art lithium salt, LiPF 6 , enables substantial improvements with respect to safety, while maintaining high performance liquid electrolyte. ã 2015 Published by Elsevier Ltd. 1. INTRODUCTION Nowadays, lithium-ion batteries are the most competitive power source for portable energy storage, due to their high energy and power density. Generally, the state-of-the-art in presently commercially available lithium-ion batteries is the use of graphitic carbons as negative electrode material, lithium transition metal oxides as positive electrode material, and lithium hexafluoro- phosphate (LiPF 6 ) dissolved in alkyl carbonate mixtures as electrolyte. As a matter of fact, the electrolyte salt LiPF 6 has been widely adopted for almost two decades. In fact, LiPF 6 -based electrolytes offer a good compromise of salt dissociation and ion mobility, thus, providing high ionic conductivities [1]. Further- more, the presence of LiPF 6 suppresses the oxidation of the aluminum cathode current collector at elevated cell potentials by forming a protective aluminum fluoride film on it [2,3]. Future large-scale applications as, for instance, electric vehicles, however, require further improvements in terms of energy and power density as well as with respect to safety and recycling aspects. In fact, the limited thermal and chemical stability restrict the use of LiPF 6 in such applications: it is widely accepted that LiPF 6 decomposes into LiF and PF 5 , while the latter readily hydrolyzes to form HF and PF 3 O [4]. Hydrofluoric acid is not only highly toxic, but has a detrimental effect on the reactivity of the electrolytes and the electrode active materials [5,6]. Lithium bis(trifluoromethanesul- fonyl) imide (LiTFSI) is certainly one of the most promising candidates to replace LiPF 6 due to is high ionic conductivity [7], high thermal and electrochemical stability, and substantially lower sensitivity towards moisture [8,9]. However, its high stability turns out as its major drawback since it prevents the formation of a protective passivating layer on the aluminum current collector surface. The consequent corrosion of the current collector results in the degradation of the positive electrode and, hence, in a rapid capacity fading [10,11]. Fluorinated solvents were reported to be a good alternative to classical solvents as they present lower flammability, higher flash points, and frequently an enhanced electrochemical stability towards oxidation compared to non-fluorinated solvents [12,13]. Commonly, they are used in combination with non-fluorinated solvents. However, the resulting electrolytes usually present decreased ionic conductivities relatively to state-of-the-art, non-fluorinated electrolytes [13,14]. In the case of fluorinated * Corresponding author. Tel.: +33 4 76 82 65 61. E-mail address: fannie.alloin@grenoble-inp.fr (F. Alloin). http://dx.doi.org/10.1016/j.electacta.2015.02.042 0013-4686/ ã 2015 Published by Elsevier Ltd. Electrochimica Acta 161 (2015) 159–170 Contents lists available at ScienceDirect Electrochimica Acta journa l home page : www.e lsevier.com/loca te/ele cta cta