Conduction mechanism in operating a LiMn 2 O 4 cathode J. Marzec a , K. S ´ wierczek a , J. Przewoz ´nik b , J. Molenda a, , D.R. Simon c , E.M. Kelder c , J. Schoonman c a Faculty of Materials Science and Ceramics, Stanisl B aw Staszic University of Mining and Metallurgy, Al. Mickiewicza 30, 30-059 Cracow, Poland b Faculty of Physics and Nuclear Techniques, Stanisl B aw Staszic University of Mining and Metallurgy, Al. Mickiewicza 30, 30-059 Cracow, Poland c Delft Interfaculty Research Center: Sustainable Energy, Delft University of Technology, Julianalaan 136, 2628 DL Delft, The Netherlands Received 25 June 2001; received in revised form 26 September 2001; accepted 7 November 2001 Abstract Two series of the Li x Mn 2 O 4 spinel samples were studied at low temperatures (200 – 300 K) on electrical, thermal (DSC) and structural (X-ray diffraction (XRD)) properties for different lithium contents. Results obtained for deintercalated spinel samples with x f 1 revealed the existence of a broad (100 K) phase transition that can be attributed to the molecular polaron condensation, leading to the orthorhombic distortion of the initial cubic form. The differential scanning calorimetry (DSC) measurement results enable us to regard the phase transition as a form of order – disorder one. Corresponding thermoelectric power (TEP) and electrical conductivity measurements fall within such description, moreover, indicating clear inconsistency between the measured regular DC conductivity of the spinel sample and that observed for the cathode in the working lithium cell. This discrepancy points to an alternative charge transport mechanism existing in the manganese spinel cathode, and it seems to be essential for the lithium cell performance. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Conduction mechanism; LiMn 2 O 4 cathode; Differential scanning calorimetry 1. Introduction The manganospinel LiMn 2 O 4 is widely considered as a favourable material for the cathode in recharge- able lithium batteries due to its high voltage (4 V) and acceptable large reversible capacity ( f 100 mAh/g) [1,2]. Recently, particularly stoichiometric Li 1 Mn 2 O 4 has attracted attention due to the presence of a structural transition at room temperature ( f 290 K), which is attributed to the Jahn–Teller distortion of the environ- ment of the Mn +3 ions. It was found that the Li/Mn ratio and Mn valency influence the structural changes [3]. The nature of this phase transition now seems to be deciphered from the X-ray, neutron and electron dif- fraction patterns, explicitly indicating that the transi- tion from a cubic (Fd3m) to orthorhombic (Fddd) structure is accompanied by simultaneous charge ordering taking place within the manganese sublattice [4]. This so-called ‘‘electronic crystallization’’ is 0167-2738/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII:S0167-2738(01)01022-0 * Corresponding author. Faculty of Material Science and Ceramics, Stanisl B aw Staszic University of Mining and Metallurgy, Al. Mickiewicza 30, 30-059 Cracow, Poland. Fax: +48-12-617- 2522. E-mail address: molenda@uci.agh.edu.pl (J. Molenda). www.elsevier.com/locate/ssi * Solid State Ionics 146 (2002) 225 – 237