Electrochimica Acta 78 (2012) 177–182 Contents lists available at SciVerse ScienceDirect Electrochimica Acta jou rn al hom epa ge: www.elsevier.com/locate/electacta Diagnostic of the failure mechanism in NiSb 2 electrode for Li battery through analysis of its polarization on galvanostatic cycling Cyril Marino a , Julien Fullenwarth a , Laure Monconduit a,∗ , Bernard Lestriez b a Institut Charles Gerhardt Montpellier – UMR 5253 CNRS-UM2-ENSCM-UM1 Agrégats, Interfaces et Matériaux pour l’Energie, Montpellier, France b Institut des Matériaux Jean Rouxel (IMN), CNRS, Université de Nantes, France a r t i c l e i n f o Article history: Received 23 March 2012 Received in revised form 23 May 2012 Accepted 24 May 2012 Available online 17 June 2012 Keywords: Li ion battery Composite electrode formulation Failure mechanism a b s t r a c t A simple analysis of the polarization resistance of the electrodes as function of the loading mass for various cycling rates allows identifying the fading mechanism on cycling of NiSb 2 , a typical conversion material: pulverization of active mass and further degradation of the electronic wiring at high rate and agglomeration of the active mass at low rate. Such rate-control of the degradation mechanism might reflect a thermodynamic instability of interfaces in the lithiated compound, which would however be in kinetic competition with the Lithium de-insertion. The analysis of the electrode polarization resistance fingerprint to rapidly identify the failure mechanism in a composite electrode can be generalized to other active materials. © 2012 Elsevier Ltd. All rights reserved. 1. Introduction The commercialized lithium ion batteries based on graphite [1] and LiCoO 2 [2] deliver limited capacities (372 mAh g -1 and 145 mAh g -1 respectively) considering the increase of demand in high energy storage. Owing to the development of electrically fueled and hybrid vehicles, new generation of lithium ion accumu- lators with higher energy and long cycling life is strongly required. The recently discovered conversion electrode materials offer numerous opportunities to reach impressive capacity gains. These electrodes can electrochemically react toward Li leading to sustain- able reversible capacities as high as 1500 mAh g -1 , by the following conversion reaction: M x X y + nyLi → xM 0 + yLi n X [3–7]. However their poor cycling life prohibits their use in commercial batteries. NiSb 2 was recently proposed as new conversion electrode mate- rial delivering reversible capacity of 520 mAh g -1 (4150 mAh cm -3 ) [8,9], close to the theoretical capacity of 558 mAh g -1 . It was shown that during first discharge, NiSb 2 undergoes a conversion process leading to (Ni 0 + 2Li 3 Sb) and that during the first charge an orig- inal conversion reaction takes place leading to both NiSb 2-x and Sb, which are back converted during the second (and further) dis- charges into Li 3 Sb and Ni nanoparticles. Volume changes and poor electronic conductivity were suspected to be responsible of the rapid capacity fading after few cycles. Note that from the crys- tallographic values the calculated volume expansion during the conversion NiSb 2 → 2Li 3 Sb/Ni is time 2.7. ∗ Corresponding author. E-mail address: laure.monconduit@univ-montp2.fr (L. Monconduit). It has been demonstrated recently the benefit of the engineering of composite electrode formulations for intermetallic (FeSn 2 , NiSb 2 , TiSnSb) and conversion (Co 3 O 4 ) type materials with different addi- tives and binders with the improvement of the electrochemical cycling behavior [10,11]. The improvement of performance results from the design of an efficiency electronic percolation web around the active material particles. That was achieved for FeSn 2 , NiSb 2 and TiSnSb by using the carboxymethyl cellulose (CMC) binder which allows getting a homogeneous architecture of the composite electrode with good connections between active material and con- ductive additive particles [12]. However, even if a good electronic wiring of the active mass can be established, the NiSb 2 electrode still shows capacity retention of only 70 cycles at 4C rate. In the present paper we show that analyzing the electrode polarization resistance is a convenient and efficient mean of interpreting the failure mechanism for intermetallic and conversion type materials. Let us note that the electrode polarization resistance is different from the cell resistance. The former is defined as the ratio between half of the potential difference between charge and discharge and the current imposed to the cell. 2. Experimental 2.1. Composite electrode formulation The orthorhombic NiSb 2 phase was prepared by high temper- ature route [8,9]. The conductive additive used was carbon black Y50A (BET primary particle size 20–60 nm, primary aggregate size 100 nm, 70 m 2 g -1 , DBP oil absorption 640 ml/100 g, SN2A [13]). Carboxymethyl cellulose (CMC) (DS = 0.7, Mw = 250,000; Aldrich) 0013-4686/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.electacta.2012.05.126