Microelectrochemistry study of metal-hydride battery materials Cycling behavior of LaNi 3.55 Mn 0.4 Al 0.3 Co 0.75 compared with LaNi 5 and its mono-substituted derivatives A. Merzouki a , C. Cachet-Vivier b,* , V. Vivier b , J.-Y. Ne ´de ´lec b , L.T. Yu b , N. Haddaoui a , J.-M. Joubert c , A. Percheron-Gue ´gan c a Laboratoire de Physico-Chimie des Hauts Polyme `res, De ´pt. Ge ´nie des Proce ´de ´s, Faculte ´ des Sciences de l’Inge ´nieur, Universite ´ F. Abbas, Se ´tif 19000, Algeria b Laboratoire d’Electrochimie Catalyse et Synthe `se Organique -UMR 7582 CNRS-Universite ´ Paris 12, 2-8 rue H. Dunant, 94320 Thiais, France c Laboratoire de Chimie Me ´tallurgique des Terres Rares, CNRS, 2-8 rue H. Dunant, 94320 Thiais, France Received 9 November 2001; received in revised form 18 January 2002; accepted 22 January 2002 Abstract LaNi 5 intermetallic-hydride forming compound and several metal-substituted derivatives have been compared in terms of cycling behavior observed by means of the cavity microelectrode (CME) at high scan rates (50 mV s 1 ). LaNi 3.55 Mn 0.4 Al 0.3 Co 0.75 was found to have a stable behavior over 1000 cycles, whereas, the capacity of LaNi 5 decreases after only 200 cycles. The performances for the mono-substituted compounds are intermediate. The rechargeability decreases according to the following order: LaNi 4:6 Mn 0:4 > LaNi 4:7 Al 0:3 > LaNi 4:25 Co 0:75 > LaNi 5 . This study demonstrates the capability of the CME to check numerous battery materials in a very short period of time, which allows to bring out the effect due to the corrosion of the material. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Mono-substituted; Intermetallic compounds; Cavity microelectrode 1. Introduction LaNi 5 intermetallic compound and its metal-substituted derivatives are studied by numerous authors, because they are used in nickel–metal-hydride (Ni–MH) batteries as anodic material, replacing the toxic Cd element in alkaline batteries. Binary LaNi 5 suffers from severe corrosion during cycling due to the intermetallic decomposition in the alka- line electrolyte, resulting in a fast decrease of the capacity as a function of cycle number [1]. To overcome this problem, various substituted derivatives have been studied leading to the set-up of a composition [MmNi 3.55 Mn 0.4 Al 0.3 Co 0.75 (Mm: mischmetal)] offering adequate compromise between initial capacity and cycle life [2,3]. These compounds are usually studied with the composite electrode device. How- ever, the size of such an electrode (1 cm in diameter and a fraction of a mm in thickness) induces both high ohmic drop and double layer capacitance, which distort voltammo- grams. For minimizing these side phenomena, low potential scan rates (lower than 1 mV s 1 ) must be used. The cavity microelectrode (CME) [4–9], also called the powder elec- trode, which is recently developed, presents dimensions of 50 mm diameter and 20 mm depth. It allows the study of pure materials using scan rates higher than some tens of mV s 1 . Accordingly, it is possible to achieve several hundred cycles within a short time. In the present work, we compare the cyclability of the three-substituted LaNi 3.55 Mn 0.4 Al 0.3 Co 0.75 compound with one of the binary LaNi 5 and single-sub- stituted LaNi 5x M x (M ¼ Mn, Al, Co) compounds in order to check the possibility of evaluating the cycling behavior of metal-hydride electrodes with the short term cycling pro- cedure given by the CME method. 2. Experimental The materials are synthesized by induction melting of the elements followed by an appropriate annealing treatment. Homogeneity and single phase character is checked by X-ray diffraction and electron probe microanalysis [10]. The materials were manually ground in a mortar and SEM Journal of Power Sources 109 (2002) 281–286 * Corresponding author. Tel.: þ33-149-7811-37; fax: þ33-149-7811-48. E-mail address: cachet@glvt-cnrs.fr (C. Cachet-Vivier). 0378-7753/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0378-7753(02)00074-5