Mixtures of ionic liquid e Alkylcarbonates as electrolytes for safe lithium-ion batteries Lucia Lombardo a, * , Sergio Brutti b , Maria Assunta Navarra a , Stefania Panero a , Priscilla Reale a a Dipartimento di Chimica, Università di Roma “La Sapienza”, Piazzale Aldo Moro 5, 00185 Roma, Italy b Dipartimento di Chimica, Università della Basilicata, Viale dell’Ateneo Lucano 10, 85100, Potenza, Italy highlights < Mixture electrolytes composed by alkyl-carbonates and ionic liquid (IL). < New electrolytes for lithium-ion cells with enhanced safety profile. < IL-based lithium-ion cell adopting LiFePO 4 and Li 4 Ti 5 O 12 electrodes. article info Article history: Received 23 May 2012 Received in revised form 29 October 2012 Accepted 5 November 2012 Available online 17 November 2012 Keywords: Ionic liquid Alkylcarbonate Electrolyte Lithium Battery Safety abstract Mixtures of alkylcarbonate electrolytes with an ionic liquid (IL) and a lithium salt have been studied in order to develop new electrolytes for lithium-ion cells with enhanced safety profiles. In this work the influence of the addition of N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Py 14 TFSI) on the electrochemical properties of commercial carbonate-based electrolytes, i.e. 1 M LiPF 6 in EC:DMC (LP30) and in EC:DMC:DEC (LP71) is reported. Four new electrolyte compositions have been prepared and characterized. The addition of the ionic liquid in the electrolyte carbonate-based solution results in (i) an ionic conductivity comparable with that of the pristine IL-free carbonate-based electrolyte, (ii) the enlarge- ment of the electrochemical stability window, and (iii) a large reduction of the self-extinguish time (SET) of the electrolyte mixture when exposed to a free flame. All the newly developed electrolytes have been tested in lithium cells versus LiFePO 4 and Li 4 Ti 5 O 12 electrodes: the cells show good performances in galvanostatic cycling. The best performing electrolyte i.e. LP30/Py 14 TFSI 70/30 wt/wt has been also successfully tested in a full Li-ion cell realized by coupling LiFePO 4 and Li 4 Ti 5 O 12 electrodes. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Lithium ion batteries are used today in all the popular portable electronic devices, e.g. mobile phones, laptops, and others, thanks to the high energy content compared to any other electrochemical energy storage device. Commonly a lithium ion cell is constituted by a graphite anode, a lithium metal oxide cathode and a separator soaked with a liquid solution of a lithium salt (e.g., lithium- hexafluorophosphate, LiPF 6 ) in an organic solvent mixture (e.g., ECeDMC mixture). This kind of batteries is light, compact and has an operational voltage averaging on 3.6 V, with an energy density that, according to the structure, ranges from 150 Wh kg 1 up to 250 Wh kg 1 [1,2]. A serious issue in lithium ion cell technology is safety. Electrodes and electrolytes are both hazard factors in Li-ion cells. In particular the use of graphite-based electrodes easily leads to the release upon cycling of gaseous products or even more dangerously to lithium plating on the electrode surface at high current regimes. Substitutes to graphite have been proposed (e.g. titanium oxide, TiO 2 ) [3] and incorporated in advanced Li-ion cells [4]. However electrolytes are the most critical component for the control of safety of lithium batteries because of the high vapor pressure and the flammability of the LiPF 6 -organic carbonate solution electrolytes. One of the best ways to improve safety and reliability of the Li- ion battery electrolytes is the use of an emerging class of electro- lytes based on ionic liquids ILs, namely, low temperature molten salts. Typically, ILs are formed by the combination of a weakly interacting, large cation and a flexible anion. ILs are non-volatile, * Corresponding author. Tel./fax: þ39 (0)649913658. E-mail address: lucia.lombardo@uniroma1.it (L. Lombardo). Contents lists available at SciVerse ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour 0378-7753/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jpowsour.2012.11.017 Journal of Power Sources 227 (2013) 8e14