Electrochemical intercalation of lithium in ternary metal molybdates M MoO 4 ( M =Cu,Zn)
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Electrochemical intercalation of lithium in ternary metal molybdates MMoO4 (M = Cu, Zn) Th. Buhrmester, N. N. Leyzerovich, K. G. Bramnik, H. Ehrenberg, H. Fuess
University of Technology Darmstadt, Department of Materials Science, Structure Research, Petersenstrasse 23, D-64287 Darmstadt, Germany Fax: +49 6151 16-60 23; E-mail: [email protected] ABSTRACT Ternary oxides with general formula MMoO4 (where M is a 3d-transitional metal) were characterized as cathode materials for lithium rechargeable batteries by galvanostatic charge-discharge technique and cyclic voltammetry. The significant capacity fading after the first cycle of lithium insertion/removal takes place for different copper molybdates (standard α-CuMoO4 and high-pressure modification CuMoO4 –III) corresponding to the irreversible copper reduction and formation of Li2MoO4 during the first discharge. X-ray powder diffraction data reveal the decomposition of pristine ZnMoO4 by electrochemical reaction, lithium zink oxide with the NaCl-type structure and Li2MoO3 seem to be formed. INTRODUCTION Among the systems which are intriguing in the rechargeable lithium ion technology molybdenum (VI) compounds remain of significant potential. The idea to take an advantage of the charge couple Mo+6/Mo+4 where the metal-redox oxidation state can change by two units is very attractive for the development of batteries with high capacity and consequently, with high energy density. Since more than 20 years the various molybdenum oxides have been tested as cathode materials in lithium rechargeable batteries [1-5]. However, the significant capacity fading after several cycles accompanied with irreversible structure transformations during the first discharge (lithium intercalation) has been reported. Mixed-molybdenum oxides are interesting as matrices for lithium intercalation while the combination of two metals in oxide-matrices produces the materials with new structure and chemical properties compared to that of binary oxides. Additionally, because in many cases the bimetallic oxides can form different crystal structures or phases depending on the synthetic conditions and compositions, a large variety of systems could be modelled and tested. Vanadium-based compounds like MeVO4 (Me = In, Cr, Fe, Al, Y, Ni) were shown to be good candidates for anode materials in lithium batteries [6,7]. However, up to now there are very few investigations concerning lithium intercalation into the same type of molybdenum compounds. Quite early the copper molybdate was probed as cathode for primary lithium batteries, but the reversibility of intercalation was not discussed [8,9]. Recently, the low potential lithium insertion in manganese-molybdenum oxide and its potential application as anode material in lithium batteries has been described [10]. In this work, we report our results of electrochemical insertion of lithium into ternary molybdates α-MeMoO4 (Me = Cu, Zn). α-CuMoO4 is known to crystallize in the triclinic system (space group P¯1), where three molybdenum atoms on diff
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