Synthesis and structural characterization of two intercalated lithium and sodium copper iron selenides: LiCuFeSe2 and NaCuFeSe2

Synthesis and structural characterization of two intercalated lithium and sodium copper iron selenides: LiCuFeSe2 and NaCuFeSe2

Journal of Alloys and Compounds, 201 (1993) 103-104 JALCOM 725 103 Synthesis and structural characterization of two intercalated lithium and sodium ...

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Journal of Alloys and Compounds, 201 (1993) 103-104 JALCOM 725

103

Synthesis and structural characterization of two intercalated lithium and sodium copper iron selenides: LiCuFeSe2 and NaCuFeSe2 J. Llanos, C. Contreras-Ortega, J. Pfiez, M. G u z m f i n a n d C. M u j i c a Departamento de Quimica, Facultad de Ciencias, Universidad Cat6lica del None, Casilla 1280, Antofagasta (Chile) (Received January 28, 1993; in final form March 10, 1993)

Abstract The not new phases LiCuFeSe2 and NaCuFeSe2 were prepared from the corresponding carbonates and CuFeSe2. They crystallize as the isostructural sulphide phases LiCuFeS2 and NaCuFeS2 in the trigonal space group P 3 m l (No. 164) in a layered Li2FeSz structure type. The Se atoms form an h.c.p, array, the copper and iron atoms are statistically distributed in the tetrahedral sites whereas the alkali metals are placed in the octahedral sites in the van der Waals gap.

1. Introduction The use of transition metal sulphides as cathode materials in lithium high energy batteries has been intensively investigated [1--4]. Special effort has been invested in the identification and characterization of the lithium intercalated phases which are produced in the cathode during the discharge process. Among the transition metal sulphides, chalcopyrite shows very promising properties as cathode material [5, 6]. In order to gain a better understanding of the intercalation of lithium into copper iron chalcogenides, we have prepared LiCuFeSe2 and NaCuFeSe2 which represent the fully discharged cathodes of the system M/M+/CuFeS2 with M---Li or Na. The crystal structure of the new compounds was solved.

ator). Cell parameters were refined from 32 centred reflections. The intensities were measured in the to-20 scan mode and the absorption correction was done empirically by a ~0 scan. The powder X-ray diffraction pattern of NaCuFeSe2 was obtained with a Siemens D-5000 diffractometer fitted with a graphite monochromator and using the Cu Ka radiation (A = 1.540 57 /~) and silicon as internal standard. The evaluation of the powder diagrams showed that the compounds are isostructural. The lattice parameters of NaCuFeSe2 were refined with an iterative least-squares program. In Table 1 the crystallographic data and details of the structure analysis of LiCuFeSe2 and of NaCuFeSe2 are T A B L E 1. Crystallographic data and details of the structure analysis for LiCuFeSe z and NaCuFeSe 2

2. Experimental details Phases of composition LiCuFeSez and NaCuFeSe2 were prepared by heating stoichiometric amounts of Li2CO3 and Na2CO3 with CuFeSe2 at 1173 K. The latter compound was previously prepared by heating the elements at 973 K. The mixtures were contained in tightly sealed graphite crucibles and held at the reaction temperature over a period of 72 h. The Xray diffraction patterns of the products showed that the materials were single phases.

3. Structure analysis Intensity data for LiCuFeSe2 were collected on a Syntex P1 diffractometer (Mo Ka; graphite monochrom0925-8388/93/$6.00

Crystal system Space group a (pm) c (pm) Z Volume ( × 106 pm 3) /z (Mo Kct cm -1) Diffractometer Radiation; monochromator Scan mode 20max Measured intensities Unique reflection Number of refined parameters Final R; Rw

LiCuFeSe~

NaCuFeSe2

Trigonal P3m l 397.1(1) 664.6(4) 1 90.78(7) 289.03 Syntex P1 Mo Ka; graphite to-20 45 172 95 11

Trigonal P~3ml 400.8(3) 714.4(24) 1 99.4(5) Siemens D-5000 Cu Ka; graphite 20 80 12

0.072; 0.061

© 1993-Elsevier Sequoia. All rights reserved

104

J. Llanos et al. / Synthesis and structure of LiCuFeSe2 and NaCuFeSe2

O0 0,e-

0

C~ 0

C C

,I

"E

i

.D

¢q 010

oo *ff

I

0

10

20

30 40 50 2 Theta (degrees)

60

70

80

Fig. 1. Powder diffraction pattern of NaCuFeSe2. T A B L E 2. Atomic coordinates and equivalent isotropic displacement parameters Atom

Position

x

y

z

SOF

the so-called van der Waals gap. The refined occupancy of Fe in LiCuFeSe2 in the 2d position is consistent with an atom relation 1:1 for both copper and iron. In the lithium phase the octahedra are regular with an Li-Se distance of 280.2(2) pm. The sodium-containing compound shows a slight increase in the c axis with respect to isostructural LiCuFeSe2 and NaCuFeS2 [9]. This can be attributed to the larger Na atom (relative to Li) and the larger Se atom (relative to S) respectively. As expected, the chalcogen-chalcogen distances between the layers of the van der Waals gap are longer in the selenium-containing compounds (322.2 pm) than in those containing sulphur. The same relation is observed in the distances between the layers separated by copper and iron atoms. Experiments to evaluate the electrochemical properties of the new phases are in progress. Preliminary results show that LiCuFeSe2 can also be obtained by coulometric titration of CuFeSe2 against LiAI in LiCI-KCI eutectic at 400 °C.

Ui~,,

(As) Acknowledgments Li

la 2d

0 31

0 ~ 3

0 0.6166(9)

1 1.073(20)

0.044(27) 0.0231(2)

Fe a

Se

2d

23

3

1

0.7577(6)

1

0.0200(1)

"This position was calculated using the scattering factor of iron.

summarized. Figure 1 shows the indexed powder diffractogram of NaCuFeSe2. Calculations to solve the structure were made with the program system SnELX [7] using the atomic positions of LiCuFeS2 as starting values. The bond distances and angles were calculated using the program ORFFE [8]. The refined atomic coordinates, displacement parameters and site occupation factors are summarized in Table 2.

4. Discussion Both new compounds crystallize trigonal in the P3rnl (No. 164) space group. The structures can be described as an h.c.p, array of selenium atoms, with copper and iron statistically distributed in tetrahedral sites and lithium as well as sodium placed in octahedral sites in

This research was sponsored by FONDECYT (Contract 92/586). The authors wish to thank Dr. K. Peters for measuring intensities on the Syntex Diffractometer and Professor H. G. von Schnering for useful discussions. References 1 J.P. G a b a n o (ed.), Lithium Batteries, Academic Press, London, 1983. 2 S. P. S. Badwal and R. J. Thorn, Z Solid State Chem., 43 (1982) 163. 3 C. H. W. Jones, P. E. Kovaks, R. D. Sharma and R. S. McMillan, Z Phys. Chem., 94 (1990) 4325. 4 C. H. W. Jones, P. E. Kovaks, R. D. Sharma and R. S. McMillan, J. Phys. Cherry, 94 (1990) 832. 5 R. M. Fong, J. R. Dahn, R. J. Batchelor, F. W. B. Einstein and C. H. W. Jones, Phys. Rev. B, 39 (1989) 4424. 6 J. Llanos, M. Tejeda, C. Contreras-Ortega and C. Mujica, J. Chem. Soc., Chem. Commun., 96 (1991) 1068. 7 G. M. Sheldrick, SHELX-76, Program for Crystal Structure Determination, University of Cambridge, 1976. 8 W. R. Busing, K. O. Martin and H. A. Levy, ORFFE Rep. ORNL-TM-306, 1964 (Oak Ridge National Laboratory, Oak Ridge, TN). 9 J. Llanos, C. Contreras-Ortega, C. Mujica, H. G. von Schnering and K. Peters, Mater. Res. Bull., 28 (1993) 39.