Enhanced thermal stability of a lithiated nano-silicon electrode by fluoroethylene carbonate and vinylene carbonate Irina A. Profatilova * , Christoph Stock, André Schmitz, Stefano Passerini, Martin Winter ** MEET Battery Research Center, Institute for Physical Chemistry, University of Muenster, Corrensstrasse 46, 48149 Muenster, Germany highlights graphical abstract < The thermal behavior of a nano-Li x Si anode in electrolytes has been investigated. < The thermal runaway is delayed by w50  C in the presence of FEC and VC additives. < We identified two mechanisms of Li x Si protection by the additives during heating. < FEC and VC electrochemically generate a thermally stable SEI covering the Li x Si. < A robust “secondary SEI” is formed by thermal degradation of FEC and VC. EC, DEC, FEC, VC, LiPF 6 SEI layer by reductive decomposition of FEC or VC and LiPF 6 Δ, 200 o C VC, FEC, little amount of LiPF 6 Polymers EC, DEC, LiPF 6 Li x Si nano-particle Polymers No heat evolution! LiF, Li 2 CO 3 and metastable compounds Li x Si nano-particle 2 t a Li F L i Li F , L i 2 t s Δ , 2 2 0 0 0 0 o o C C EC, DEC, FEC, VC, LiPF 6 SEI layer by reductive decomposition of FEC or VC and LiPF 6 Δ, 200 o C VC, FEC, little amount of LiPF 6 me t as Polymers EC, DEC, LiPF 6 Li x Si nano-particle a a L i x S i nano - pa r t i c l e Polymers No heat evolution! LiF, Li 2 CO 3 and metastable compounds L i x S S S S S S S S S S S S S S S S S S S i i i i i i i nano nano nano nano nan nano na an nano n nano nan nano ano an ano n na na nano ano - - - - - - - pa pa pa pa pa pa p p pa a a p p pa a pa a pa a a r r r r r r r r r r r t t t t i i i i c c c c c c c c c c c c l l l l e e e e e e e e e e e e me me t t Li x Si nano-particle article info Article history: Received 28 June 2012 Received in revised form 10 August 2012 Accepted 22 August 2012 Available online 5 September 2012 Keywords: Lithium-ion battery Electrolyte Thermal stability Silicon Fluoroethylene carbonate Vinylene carbonate abstract The thermal behavior of the fully lithiated nano-silicon electrode in contact with an 1 M LiPF 6 in EC/DEC electrolyte is investigated by differential scanning calorimetry (DSC) in the absence and presence of fluoroethylene carbonate (FEC) and vinylene carbonate (VC) electrolyte additives. In the additive-free electrolyte, intense exothermic reactions commence at approximately 153  C when in contact with Li x Si. At contrast, the onset temperature of the thermal runaway is shifted to 200  C and 214  C when the charged Li x Si is heated in the presence of FEC and VC in the electrolytes, respectively. The mechanism of this thermal stability improvement by FEC and VC is studied using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and by specific measures to design the SEI on the surface of the nano-Si particles. The additives form a robust “primary SEI” on the surface of the Li x Si particles during the first charge that is rich in polycarbonate species and stable at elevated temperatures. In addition, the thermal degradation of FEC and VC in the electrolyte solution yields a highly resistive “secondary SEI” on the electrode surface that covers the lithiated silicon electrode (together with the “primary SEI”) and protects it from thermal runaway up to 200  C. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction The stringent safety requirements for large-scale lithium-ion batteries (LIBs) are some of the main obstacles slowing down their commercialization for electric vehicle and stationary applications. Over the last decades, active development of the LIB technology has markedly enlarged the technology’s specific energy; increased amounts of energy can now be stored per unit of LIB mass [1e4]. * Corresponding author. CEA/LITEN, Commissariat a l’Energie Atomique/Labo- ratoire d’Innovation pour les Technologies des Energies Nouvelles, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France. Tel.: þ33 04387 822 45; fax: þ33 04387 843 83. ** Corresponding author. E-mail addresses: irishkapro@mail.ru, irina.profatilova@cea.fr (I.A. Profatilova), martin.winter@uni-muenster.de (M. Winter). 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.2012.08.066 Journal of Power Sources 222 (2013) 140e149