Insights on the electrode/electrolyte interfaces in LiFePO 4 based cells with LiAl(Al) and Li(Mg) anodes Rafael Trócoli a,1 , Sylvain Franger b , Julián Morales a , Jesús Santos-Peña c,d,⇑ a Departamento de Química Inorgánica e Ingeniería Química, Instituto Universitario de Investigación en Química Fina y Nanoquímica, Campus de Rabanales, Universidad de Córdoba, 14071 Córdoba, Spain b ICMMO-ERIEE (UMR CNRS 8182), Université Paris Sud, 91405 Orsay, France c Laboratoire de Physico-Chimie des Matériaux et Electrolytes pour l’Energie (PCM2E), Campus de Grandmont, Université de Tours, 37200 Tours, France d Laboratoire de Recherche Correspondante PCM2E-CEA Le Ripault, 37260 Monts, France article info Article history: Received 25 June 2014 Received in revised form 9 August 2014 Accepted 18 August 2014 Available online 30 August 2014 Keywords: Lithium ion batteries Anode Surface film Electrochemical impedance spectroscopy Infrared spectroscopy abstract Understanding the electrode/electrolyte interfaces is an essential issue when describing a lithium ion battery. This work reports the application of electrochemical impedance and infrared spectroscopies on the study of interfacial properties of two novel kinds of lithium reservoirs: an electrodeposited Li film onto magnesium foil and an electroformed Li–Al alloy onto aluminium foil. LiFePO 4 -based lithium ion cells with both electrodes showed high values of energy densities. However, LiAl(Al) failed in guarantee- ing capacity retention due to irreversible crumbling. Nevertheless, optimization of its practical cycling life can be envisaged. We observed that the impedance of a LiFePO 4 -battery built with LiAl(Al) in 1 M LiPF 6 (EC/DMC) solution, is quite smaller than for a Li(Mg)-based system by virtue of an attenuated formation of surface films on the former. It was also evidenced that electrolyte degradation products migrate from the negative electrode towards the positive one. This phenomenon proceeds in a major extent for LiAl(Al) but results in the formation of a thinner and more conductive film onto the positive electrode than when Li(Mg) acts as negative electrode. The major interfacial drawback of LiAl(Al) is the lack of its passivation since a corrosion process is still observed after 10 cycles. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction With the advent of lithium ion battery technology in 90s [1,2], big attention has been paid to the development of positive and anodes. Two decades later, available market batteries contain lithium cobaltite and other cobalt-derived layered oxides as cathodes meanwhile graphite represents the material of choice as anode due to its low potential (close to that of the Li + /Li redox couple) and low cost [2]. More recently, Li 4 Ti 5 O 12 has been purposed for power devices since the lithium inserts fastly in this oxide following a topotatic reaction [3,4]. However it drawbacks of a limited capacity, a high operating voltage (1.5 V vs. Li + /Li) and consequently, the lithium titanium oxide-based devices are more suitable for power than for energy requirements. Therefore the use of anodes with potentials close to that of the Li/Li + couple remains very interesting and this is the base of the research on sil- icon and tin-based systems [5–8]. Inherent to the development of the electrode materials, the lithium ion battery studies requires a characterization of the electrode/electrolyte interfaces. The importance of such interfaces was pointed by Aurbach et al. onto lithium [9–12] and graphite [11–13] surfaces leading to pioneer descriptions of the solid electrolyte interface formation and composition depending on the level of discharge in a lithium half-cell or on the cycling stage. Later, the interfacial studies were extended to a number of anodes and cathodes [14,12,15–19], allowing to the scientific community to understand the charge/discharge profiles, prolonged cycling behavior and suitability of electrode and electrolyte configurations in several batteries. Recently we proposed the study of two new anodes for lithium ion cells keeping LiFePO 4 as cathode. These anodes were chosen to guarantee an elevated value of battery operating voltage and high gravimetric capacities. Both electrodes were formed by electrode- position on metallic surfaces. The first film corresponds to the Li film deposited on Mg [20], while the second film corresponds to LiAl alloy prepared on Al [21]. Whereas excellent cycling properties http://dx.doi.org/10.1016/j.jelechem.2014.08.024 1572-6657/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author at: Laboratoire de Physico-Chimie des Matériaux et Electrolytes pour l’Energie (PCM2E), Campus de Grandmont, Université de Tours, 37200 Tours, France. E-mail address: jesus.santos-pena@univ-tours.fr (J. Santos-Peña). 1 Current address: AnalytischeChemie – ZentrumfürElektrochemie, Ruhr-Universi- tät Bochum, Universitätsstr. 150, D-44780 Bochum, Germany. Journal of Electroanalytical Chemistry 732 (2014) 53–60 Contents lists available at ScienceDirect Journal of Electroanalytical Chemistry journal homepage: www.elsevier.com/locate/jelechem