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The structure of Li3+xV6O13 [x = 0.24 (3)] at 95 K has been solved and refined using single-crystal X-ray diffraction. The refined lithium content corresponds to two fully occupied Li sites and one partially occupied Li site. A doubling of the c axis is observed upon cooling from room temperature, and this change is associated with shifts of the V atoms. The resulting space group is C2/c. The Li disorder present in the Li3V6O13 phase at room temperature is also observed in the low-temperature phase reported here.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270104012508/bc1040sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270104012508/bc1040Isup2.hkl
Contains datablock I

Comment top

V6O13 has been investigated thoroughly as a possible cathode material for lithium polymer batteries during the past two decades. The V6O13 structure was first solved by Aebi (1948) and was later refined by Wilhelmi et al. (1971). The crystal system is monoclinic, in space group C2/m, and the structure is built of edge- and corner-sharing VO6 octahedra forming alternating single and double layers joined by corners. Large channels occur between these layers, along the b direction, which allow Li+ ions to diffuse easily through the V6O13 host. Several stoichiometric phases are formed during lithium insertion, with Li6V6O13 as the end phase. So far, the structure of LixV6O13 has been determined for x= 2/3, 1, 2 and 3 (Björk et al., 2001; Bergström et al., 1997, 1998). The formation of superstructures was observed in Li2/3V6O13 and LiV6O13, with tripling and doubling of the unit-cell volume, respectively. The original V6O13 unit-cell is again observed for Li2V6O13 and Li3V6O13, with only small changes in cell parameters. In all LixV6O13 structures determined so far, including those with superstructures, all atoms are situated in the mirror planes of the C2/m space group. In Li3V6O13, one of the Li+ ions is disordered across an inversion centre in the ab plane, i.e. in the single layer of the V6O13 host structure. This disordered Li+ ion was refined as two partially occupied sites, above and below the inversion centre, and showed relatively large displacement parameters.

V6O13 has been reported to undergo a semiconductor–semiconductor phase transition at ca 150 K (Kachi et al., 1963). The low-temperature structure of V6O13 has recently been reinvestigated, and the phase-transition temperature was determined to be 153 K (Höwing et al., 2003). That study showed that, on passing through the phase transition, all atoms move out the mirror plane, thus destroying the C-centering and replacing the mirror plane by a glide plane; the new space group is Pc. The largest displacements [0.21 (1) Å] occur for the V atoms in the single octahedral layer, with possible partially occupied sites on opposite sides of the glide plane. Unfortunately, this disorder was not characterized further.

In the present study, Li3 + xV6O13 [x = 0.24 (3)] has been investigated at 95 K using single-crystal X-ray diffraction. It is found that a superlattice is formed, with a doubling of the c axis compared with that of the room-temperature structure (Höwing et al., 2004). The mirror plane in C2/m is replaced by a glide plane and an I-centred supercell is formed with the space group I2/a. The standard space-group setting, C2/c, is achieved through cell-axis transformation. The refined structure, with C2/c symmetry, is shown in Fig. 1. The 2c double unit-cell is closely related to the supercell of LiV6O13, although the reason for the supercell formation is quite different. In LiV6O13, the superlattice is formed by long-range interactions between lithium ions inserted into adjacent unit cells. In the present structure, the double c axis results from the movement of atom V2 and V3 away from or towards one another in alternate double octahedral layers. The phase composition, Li3.24V6O13, was derived by refining the occupancy of the Li3 site and is in fair agreement with that expected from the sample preparation (see Experimental). In contrast to V6O13, where the largest atom shifts occur in the single layer, it is the V atoms in the double layer that undergo the largest displacements, although the maximum displacement is only 0.04 (1) Å for atom V2, and the shifts are less than 3σ for most atoms. The differences in bond lengths between the room- and low-temperature structures are very small. Only the V2—O and V3—O distances along the b direction show any significant changes. As the V atoms move out of the original mirror planes, one V—O bond becomes longer while the opposite bond becomes correspondingly shorter.

Another interesting feature is that there is no observable change in the Li2 ion distribution in the single layer at low temperature. If this disorder were dynamic at room temperature on a time-scale short compared to that of the diffraction process, it is likely that some ordering would occur upon cooling. Since this is not the case, it is concluded that the Li2 atom is not oscillating between two equivalent sites but, rather, is statically disordered. The movement of atom Li2 out of the square-planar oxygen coordination environment is thought to be a result of the long distance to any neighbouring atoms above or below the square. This hypothesis is consistent with observations for LixV6O13 (x= 2/3, 1 and 2) where lithium is positioned slightly outside a square-planar pyramidal oxygen coordination environment. The phase-transition temperature has not been determined more precisely.

Experimental top

Single crystals of V6O13 were grown using the Chemical Vapour Transport (CVT) technique described by Saeki et al. (1973). V6O13 powder was synthesized using controlled thermal decomposition of NH4VO3, as described by Lampe-Önnerud & Thomas (1995). Powder cathodes were prepared by ball-milling together the as-synthesized V6O13 powder, carbon black and EPDM (ethylene propylene diene copolymer) dissolved in cyclohexene, in a 80:15:5 mass% ratio. The cathode slurry was spread onto aluminium foil using a wire bar, and 2.0 cm-diameter cathodes were punched out. Five V6O13 single crystals were then incorporated into the powder cathode. The cathode was incorporated into a test-cell of 'coffee-bag' type (Gustafsson et al., 1992). The electrolyte used was 1 M LiPF6 in EC/DMC (ethylene carbonate/dimethyl carbonate) in a 2:1 by volume mixture. The cell was discharged potentiostatically to 2.45 V, corresponding to the approximate composition Li3V6O13. The battery was then held at this potential to equilibrate for two months. The battery was then discharged further to 2.30 V (approximate composition for Li3.4V6O13) and left to equilibrate for one more month. The cell was finally disassembled and the crystals were recovered. All crystals shattered during this electrochemical lithiation process. One piece with the approximate dimensions 0.05×0.02×0.01 mm was attached to a glass fibre for the single-crystal data collection.

Refinement top

Data were collected with the detector set first at 2θ=28° and then at 2θ=72°, thus covering reflections up to ca 2θ=100°. To optimize the benefits of the higher intensity of a synchrotron beam, a special data-collection strategy was used. A complete data set was first collected using the maximum beam intensity, where the detector was saturated for a number of the strong reflections; a second data set was collected with the beam attenuated to such an extent that the strongest low-angle reflection did not saturate the detector. A new data collection was then performed with the detector at 2θ=28°. The occupancy of atom Li3 [0.12 (2)] was refined after setting Uiso(Li3) equal to Uiso(Li1). This is a reasonable constraint since the coordination geometries of atoms Li1 and Li3 are very similar. Atom Li2 was first refined as two partially occupied sites, above and below the inversion centre, in accordance with the model used by Bergström et al. (1998). However, as this procedure did not improve the refinement, atom Li2 was finally refined as a single fully occupied site located on the inversion centre. Atoms Li1 and Li3 were both refined with isotropic displacement parameters. After the final refinement cycle, large electron density residuals were found close to the V2 site.

Computing details top

Data collection: SMART (Bruker 2003); cell refinement: SAINT-Plus (Bruker 2003); data reduction: SAINT-Plus; program(s) used to solve structure: program (reference); program(s) used to refine structure: Jana2000 (Petricek and Dusek, 2000); molecular graphics: Diamond (Berghoff, 1996); software used to prepare material for publication: Jana2000.

Figures top
[Figure 1] Fig. 1. The low-temperature structure of Li3.24V6O13. Displacement ellipsoids and spheres are drawn at the 90% probability level. O, V and Li atoms are shown as white, grey and black, respectively. The Li2 displacement ellipsoid describes two equivalent sites, above and below the inversion centre, and their partial overlap.
(I) top
Crystal data top
Li3.24V6O13F(000) = 1007
Mr = 536.3The diffraction experiment was carried out on beamline I711 at MAX-lab in Lund, Sweden (Cerenius et al., 2000). Data were collected using a Bruker Smart 1000 CCD detector set at 512×512 pixel resolution; λ=0.872 Å. Data were collected at 95 K. The cooling equipment used was an Oxford Cryostreams 600 Series Cryostream Cooler using liquid nitrogen.
Monoclinic, C2/cDx = 3.882 (2) Mg m3
Hall symbol: -C 2ycSynchrotron radiation, λ = 0.872 Å
a = 21.487 (5) ÅCell parameters from 1332 reflections
b = 3.920 (1) Åθ = 5.0–100.7°
c = 11.738 (5) ŵ = 10.34 mm1
β = 111.913 (5)°T = 95 K
V = 917.3 (5) Å3Shard, black
Z = 40.05 × 0.02 × 0.01 mm
Data collection top
Bruker SMART APEX
diffractometer
2500 independent reflections
Radiation source: Synchrotron2499 reflections with I > 15σ(I)
Si(111) monochromatorRint = 0.043
Detector resolution: 512*512 pixels mm-1θmax = 50.5°, θmin = 2.5°
ω scansh = 3726
Absorption correction: empirical (using intensity measurements)
(SADABS; Bruker, 2003)
k = 46
Tmin = 1.000, Tmax = 1.000l = 1620
6862 measured reflections
Refinement top
Refinement on F2102 parameters
R[F2 > 2σ(F2)] = 0.076Weighting scheme based on measured s.u.'s w = 1/σ2(I)
wR(F2) = 0.069(Δ/σ)max = 0.009
S = 2.15Δρmax = 3.17 e Å3
2499 reflectionsΔρmin = 3.31 e Å3
Crystal data top
Li3.24V6O13V = 917.3 (5) Å3
Mr = 536.3Z = 4
Monoclinic, C2/cSynchrotron radiation, λ = 0.872 Å
a = 21.487 (5) ŵ = 10.34 mm1
b = 3.920 (1) ÅT = 95 K
c = 11.738 (5) Å0.05 × 0.02 × 0.01 mm
β = 111.913 (5)°
Data collection top
Bruker SMART APEX
diffractometer
2500 independent reflections
Absorption correction: empirical (using intensity measurements)
(SADABS; Bruker, 2003)
2499 reflections with I > 15σ(I)
Tmin = 1.000, Tmax = 1.000Rint = 0.043
6862 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.076102 parameters
wR(F2) = 0.069Δρmax = 3.17 e Å3
S = 2.15Δρmin = 3.31 e Å3
2499 reflections
Special details top

Refinement. Integration of the collected frames, data reduction, merging of high- and low- intensity data sets, space-group determination and preparation of structure-factor files were all performed using the SAINT+ program package (Bruker, 2003). The datasets were corrected for absorption in the crystal and mounting materials using SADABS (Bruker, 2003). Structure refinements were performed using JANA2000 (Petricek & Dusek, 2000).

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
V10.25074 (2)0.2505 (3)0.15895 (4)0.00891 (9)
V20.43362 (2)0.2602 (2)0.28384 (3)0.00776 (10)
V30.06766 (2)0.2437 (3)0.04010 (3)0.00708 (10)
O10.24970 (10)0.2513 (12)0.32840 (15)0.0100 (4)
O20.05420 (10)0.2553 (10)0.19755 (15)0.0083 (4)
O30.45260 (10)0.2484 (10)0.46420 (14)0.0081 (4)
O40.250.2500.0103 (6)
O50.35033 (9)0.2527 (10)0.22231 (14)0.0090 (4)
O60.14983 (9)0.2503 (10)0.08635 (14)0.0090 (4)
O70.45761 (10)0.2556 (9)0.13822 (14)0.0085 (4)
Li10.0450 (3)0.259 (2)0.3629 (4)0.0127 (8)*
Li20.250.250.50.061 (8)
Li30.155 (2)0.26 (2)0.270 (3)0.0127 (8)*0.12 (2)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
V10.00959 (15)0.00865 (15)0.00822 (11)0.0001 (3)0.00301 (10)0.0000 (2)
V20.00858 (16)0.00870 (18)0.00563 (12)0.0002 (3)0.00224 (10)0.0005 (2)
V30.00856 (16)0.00663 (17)0.00592 (12)0.0002 (3)0.00256 (10)0.0000 (2)
O10.0122 (7)0.0066 (6)0.0110 (6)0.0003 (14)0.0043 (5)0.0015 (12)
O20.0115 (6)0.0073 (6)0.0065 (5)0.0007 (15)0.0039 (4)0.0003 (11)
O30.0112 (7)0.0056 (6)0.0073 (5)0.0008 (16)0.0031 (4)0.0006 (11)
O40.0104 (10)0.0063 (9)0.0124 (9)0.000 (2)0.0022 (7)0.0027 (19)
O50.0098 (7)0.0080 (7)0.0087 (5)0.0004 (15)0.0029 (4)0.0020 (11)
O60.0102 (6)0.0076 (6)0.0081 (5)0.0008 (15)0.0022 (4)0.0011 (11)
O70.0110 (7)0.0086 (7)0.0058 (5)0.0000 (15)0.0030 (5)0.0004 (12)
Li20.151 (18)0.021 (4)0.021 (4)0.003 (15)0.045 (7)0.001 (8)
Geometric parameters (Å, º) top
V1—O11.997 (3)V3—O61.642 (2)
V1—O1i1.964 (4)V3—O7v1.956 (1)
V1—O1ii1.968 (4)Li1—O22.024 (6)
V1—O41.8598 (5)Li1—O2vi1.979 (6)
V1—O51.986 (2)Li1—O3vii2.011 (5)
V1—O62.012 (2)Li1—O7i1.974 (9)
V2—O2i1.999 (4)Li1—O7ii1.948 (9)
V2—O2ii1.959 (4)Li2—O12.012 (3)
V2—O32.001 (1)Li2—O1vii2.012 (3)
V2—O51.661 (2)Li2—O4i1.960 (1)
V2—O71.961 (2)Li2—O4ii1.960 (1)
V2—O7iii2.169 (2)Li3—O11.89 (4)
V3—O21.9743 (16)Li3—O22.01 (4)
V3—O3i1.988 (4)Li3—O5i2.00 (8)
V3—O3ii2.021 (4)Li3—O5ii1.94 (8)
V3—O3iv2.294 (2)Li3—O62.12 (4)
O1—V1—O1i85.62 (14)O3i—V3—O6102.79 (16)
O1—V1—O1ii85.51 (14)O3i—V3—O7v90.20 (11)
O1—V1—O4178.95 (6)O3ii—V3—O3i155.86 (9)
O1—V1—O592.18 (7)O3ii—V3—O3iv77.62 (12)
O1—V1—O690.65 (7)O3ii—V3—O6100.87 (16)
O1i—V1—O185.62 (14)O3ii—V3—O7v90.04 (11)
O1i—V1—O1ii171.12 (11)O3iv—V3—O3i79.05 (12)
O1i—V1—O494.38 (8)O3iv—V3—O3ii77.62 (12)
O1i—V1—O590.66 (13)O3iv—V3—O6176.32 (10)
O1i—V1—O689.78 (13)O3iv—V3—O7v75.88 (7)
O1ii—V1—O185.51 (14)O6—V3—O7v100.84 (8)
O1ii—V1—O1i171.12 (11)O2—Li1—O2vi97.70 (19)
O1ii—V1—O494.49 (8)O2—Li1—O3vii173.3 (3)
O1ii—V1—O590.10 (13)O2—Li1—O7i89.9 (3)
O1ii—V1—O689.90 (13)O2—Li1—O7ii90.8 (3)
O4—V1—O588.87 (4)O2vi—Li1—O297.70 (19)
O4—V1—O688.31 (4)O2vi—Li1—O3vii88.9 (3)
O5—V1—O6177.16 (6)O2vi—Li1—O7i88.0 (3)
O2i—V2—O2ii164.23 (7)O2vi—Li1—O7ii88.9 (3)
O2i—V2—O383.90 (12)O3vii—Li1—O7i89.0 (3)
O2i—V2—O596.12 (15)O3vii—Li1—O7ii90.6 (3)
O2i—V2—O791.15 (12)O7i—Li1—O7ii176.9 (4)
O2i—V2—O7iii82.48 (11)O7ii—Li1—O7i176.9 (4)
O2ii—V2—O2i164.23 (7)O1—Li2—O1vii180
O2ii—V2—O386.53 (12)O1—Li2—O4i90.11 (11)
O2ii—V2—O598.21 (15)O1—Li2—O4ii89.89 (11)
O2ii—V2—O792.23 (12)O1vii—Li2—O1180
O2ii—V2—O7iii83.29 (11)O1vii—Li2—O4i89.89 (11)
O3—V2—O5102.75 (8)O1vii—Li2—O4ii90.11 (11)
O3—V2—O7154.92 (8)O4i—Li2—O4ii180
O3—V2—O7iii77.96 (7)O4ii—Li2—O4i180
O5—V2—O7102.22 (7)O1—Li3—O2176 (3)
O5—V2—O7iii178.37 (16)O1—Li3—O5i92 (3)
O7—V2—O7iii77.02 (7)O1—Li3—O5ii94 (3)
O7iii—V2—O777.02 (7)O1—Li3—O690.5 (19)
O2—V3—O3i86.48 (13)O2—Li3—O5i86 (2)
O2—V3—O3ii84.03 (13)O2—Li3—O5ii88 (2)
O2—V3—O3iv81.38 (7)O2—Li3—O686.0 (11)
O2—V3—O6101.86 (7)O5i—Li3—O5ii170 (3)
O2—V3—O7v157.23 (9)O5i—Li3—O693 (2)
O3i—V3—O3ii155.86 (9)O5ii—Li3—O5i170 (3)
O3i—V3—O3iv79.05 (12)O5ii—Li3—O695 (3)
Symmetry codes: (i) x+1/2, y1/2, z+1/2; (ii) x+1/2, y+1/2, z+1/2; (iii) x+1, y, z+1/2; (iv) x1/2, y+1/2, z1/2; (v) x+1/2, y+1/2, z; (vi) x, y, z+1/2; (vii) x+1/2, y+1/2, z+1.

Experimental details

Crystal data
Chemical formulaLi3.24V6O13
Mr536.3
Crystal system, space groupMonoclinic, C2/c
Temperature (K)95
a, b, c (Å)21.487 (5), 3.920 (1), 11.738 (5)
β (°) 111.913 (5)
V3)917.3 (5)
Z4
Radiation typeSynchrotron, λ = 0.872 Å
µ (mm1)10.34
Crystal size (mm)0.05 × 0.02 × 0.01
Data collection
DiffractometerBruker SMART APEX
diffractometer
Absorption correctionEmpirical (using intensity measurements)
(SADABS; Bruker, 2003)
Tmin, Tmax1.000, 1.000
No. of measured, independent and
observed [I > 15σ(I)] reflections
6862, 2500, 2499
Rint0.043
(sin θ/λ)max1)0.885
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.076, 0.069, 2.15
No. of reflections2499
No. of parameters102
No. of restraints?
Δρmax, Δρmin (e Å3)3.17, 3.31

Computer programs: SMART (Bruker 2003), SAINT-Plus (Bruker 2003), SAINT-Plus, program (reference), Jana2000 (Petricek and Dusek, 2000), Diamond (Berghoff, 1996), Jana2000.

Selected bond lengths (Å) top
V1—O1i1.964 (4)V3—O7v1.956 (1)
V1—O1ii1.968 (4)Li1—O22.024 (6)
V1—O41.8598 (5)Li1—O2vi1.979 (6)
V1—O51.986 (2)Li1—O3vii2.011 (5)
V1—O62.012 (2)Li1—O7i1.974 (9)
V2—O2i1.999 (4)Li1—O7ii1.948 (9)
V2—O2ii1.959 (4)Li2—O12.012 (3)
V2—O32.001 (1)Li2—O1vii2.012 (3)
V2—O51.661 (2)Li2—O4i1.960 (1)
V2—O71.961 (2)Li2—O4ii1.960 (1)
V2—O7iii2.169 (2)Li3—O11.89 (4)
V3—O21.9743 (16)Li3—O22.01 (4)
V3—O3i1.988 (4)Li3—O5i2.00 (8)
V3—O3ii2.021 (4)Li3—O5ii1.94 (8)
V3—O3iv2.294 (2)Li3—O62.12 (4)
V3—O61.642 (2)
Symmetry codes: (i) x+1/2, y1/2, z+1/2; (ii) x+1/2, y+1/2, z+1/2; (iii) x+1, y, z+1/2; (iv) x1/2, y+1/2, z1/2; (v) x+1/2, y+1/2, z; (vi) x, y, z+1/2; (vii) x+1/2, y+1/2, z+1.
 

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