doi:10.1016/j.jeurceramsoc.2004.09.006
Copyright © 2004 Elsevier Ltd All rights reserved.
A structural investigation of the influence of dopants on the electronic properties of LiCoVO4
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N. Van Landschoota, 
, 
, C. Kwakernaakb, W.G. Sloofb, E.M. Keldera and J. Schoonmana
aLaboratory for Inorganic Chemistry, Delft Institute for Sustainable Energy, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands
bLaboratory of Material Science, Delft University of Technology, Rotterdamseweg 137, 2628 AL Delft, The Netherlands
Received 26 May 2004;
revised 10 August 2004;
accepted 27 August 2004.
Available online 17 November 2004.
Abstract
The influence of 6% Co substitution in LiCoVO4 for Fe, Cr and Cu was investigated to determine the influence on the structural and electronic properties of the substituted inverse spinel. It was found that the lattice parameter of the inverse spinel structure changed and that no second phases were found. The oxidation state of the different ions were determined by XPS and it was found that for both the Fe3+ and Cr3+ substitution the oxidation state of the Co2+ did not change. The XPS results showed that the oxidation state of vanadium was 5+ and is the only cation that partly changed to an oxidation state of 4+, for charge compensation. This change in the oxidation state led to an increase in the electrical conductivity by a factor of 10. The Cu2+ substitution also led to an increase in the electrical conductivity but smaller. Rietveld refinement analyses of the inverse spinel led to the conclusion that no large reorientation occurred for the different cations at the different sites.
Keywords: Electrical conductivity; Batteries; X-ray methods; Inverse spinel; LiCoVO4
Fig. 1. X-ray diffractograms for: (a) LiCoVO4; (b) LiFe0.06Co0.94VO4; (c) LiCr0.06Co0.94VO4; (d) LiCu0.06Co0.94VO4. The lines in the diffractograms are calculated by the Rietveld analysis. The differences between the calculated and the observed patterns are represented below the corresponding diffractograms. The vertical bars represent the positions of the diffraction peaks.
Fig. 2. The structure of the dopants in the substituted inverse spinels for: (a) Fe2p lines, (b) Cr2p lines, and (c) the Cu2p lines. The chemical shift is the indication that Fe ions are trivalent. The shake-up satellite of the Fe2p3/2 peak belongs to Fe3+ ions. The shake-up satellites are the indicator for Cu2+ ions. The Cu+ is not a component of the original material but is formed during the XPS measurement due to the reduction of Cu2+ to Cu+ under X-ray bombardment.
Fig. 3. The line shapes of the cobalt 2p lines (a) and auger LMM lines (b) indicate that there is no chemical change of cobalt (II) ions due to the presence of dopants.
Fig. 4. The line shapes of the vanadium 2p lines and oxygen O1s line show that there is no chemical change as the dopant elements are incorporated in the original material.
Fig. 5. Impedance spectra of the cells: (a) Au //LiCoVO4// Au, (b) Au //LiCo0.94Cu0.06VO4// Au, (c) Au //LiCo0.94Fe0.06VO4// Au, (d) Au //LiCo0.94Cr0.06VO4// Au, measured at 160 °C between 1 Hz and 10 MHz. The sample geometry and thickness have been taken into account in the analyses of the measurements.
Fig. 6. Electrical conductivities in (S/cm) of the pristine, LiCoVO4, and the substituted inverse spinel, LiCo0.94M0.06VO4 (M = Fe, Cr, Cu), pellets as a function of the reciprocal temperature.
Table 1.
Crystallographic data, including lattice parameters, site occupancy for LiM0.06Co0.94VO4 (M = Fe, Cr, and Cu) determined via the Rietveld analysis
Strains: Co16d = 2 − Li16d − V16d − M16d, V8a = 1 − V16d.
Table 2.
The binding energy (BE), kinetic energy (KE) and modified Auger parameters (AP) for the dopants of the substituted inverse spinel materials
Table 3.
The binding energy (BE), kinetic energy (KE), and modified Auger parameters (AP) for cobalt in the inverse spinel materials
Table 4.
The binding energy (BE), kinetic energy (KE) for oxygen and vanadium in the inverse spinel materials
Table 5.
The values for the binding energy (BE), kinetic energy (KE), and modified Auger parameter (AP) of oxygen and the binding energy of lithium of the compounds LiCo0.94X0.06VO4 (X = Co, Cr and Fe)
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