A study of binary iron/lithium organometallic complexes as single source precursors to solid state cathode materials for potential Li ion battery application

Article abstract of DOI:10.1016/j.ica.2011.01.074

Solid state and solution phase decomposition of organometallic half sandwich and sandwich complexes of type [CpFeCODLi × DME] 1, [CpFeCODLi × TMEDA] 2 and [(Cp)₂FeLi₂ × 2 TMEDA] 3 (Cp = cyclopentadienyl, COD = 1,5-cyclooctadiene, DME = dimethoxyethane, TMEDA = tetramethylethylenediamine) derived from ferrocene, yield different kinds of lithium ferrites under oxidative and inert conditions. Thermogravimetry (TG) and TG coupled mass spectrometry of these compounds indicate that the decomposition begins above 170 °C for 1, 185 °C for 2 and 190 °C for 3 with removal of all the organic ligands. In the absence of oxygen, compounds 1, 2 and 3 decompose to a mixture of Fe, Fe₃C and Li₂O/Li ₂CO₃ at temperatures above 200 °C. Amorphous α-LiFeO₂ is formed in the temperature range of 200-400 °C in the presence of oxygen. Crystalline α-LiFeO₂ is formed only above 400 °C using 1. Elemental analysis of the LiFeO₂ obtained from 1 indicates a drastic decrease in the carbon and hydrogen content with the increase in the oxidation temperature. XRD reveals the presence of Li ₂CO₃ as second phase formed for precursors 1, 2, and 3 under oxidative conditions. Solution phase decomposition of 2 and 3 in the absence of oxygen followed by annealing at 600 °C yields Li ₂Fe₃O₅, Li₅FeO₄ and Fe₃C depending on the solvent to precursor ratio in contrast to the α-LiFeO₂ phase formed under pure solid state decomposition conditions. However, all lithium ferrites (Li₂Fe₃O ₅, Li₅FeO₄) are converted to α-LiFeO ₂ when oxidized above 500 °C. The α-LiFeO₂ products were further characterized by IR, XPS, and TEM. Electrochemical analysis of the α-LiFeO₂ was performed, showing a moderate initial capacity of 13 mAh/g.

Full text of DOI:10.1016/j.ica.2011.01.074

Inorganica Chimica Acta 370 (2011) 254–259
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
A study of binary iron/lithium organometallic complexes as single source
precursors to solid state cathode materials for potential Li ion battery application
⇑
Jayaprakash Khanderi, Jörg J. Schneider
Fachbereich Chemie, Anorganische Chemie, Eduard-Zintl-Institut für Anorganische und Physikalische Chemie, Technische Universität Darmstadt, Petersenstraße 18,
64287 Darmstadt, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 2 August 2010
Received in revised form 10 January 2011
Accepted 21 January 2011
Available online 4 March 2011
Solid state and solution phase decomposition of organometallic half sandwich and sandwich complexes of
type [CpFeCODLi  DME] 1, [CpFeCODLi  TMEDA] 2 and [(Cp)2FeLi2  2 TMEDA] 3 (Cp = cyclopentadienyl,
COD = 1,5-cyclooctadiene, DME = dimethoxyethane, TMEDA = tetramethylethylenediamine) derived from
ferrocene, yield different kinds of lithium ferrites under oxidative and inert conditions. Thermogravimetry
(TG) and TG coupled mass spectrometry of these compounds indicate that the decomposition begins above
170 °C for 1, 185 °C for 2 and 190 °C for 3 with removal of all the organic ligands. In the absence of oxygen,
compounds 1, 2 and 3 decompose to a mixture of Fe, Fe3C and Li2O/Li2CO3 at temperatures above 200 °C.
Keywords:
Electrochemistry
Iron
Lithium
Amorphous
a-LiFeO2 is formed in the temperature range of 200–400 °C in the presence of oxygen. Crystal-
line -LiFeO2 is formed only above 400 °C using 1. Elemental analysis of the LiFeO2 obtained from 1 indicates
a
a drastic decrease in the carbon and hydrogen content with the increase in the oxidation temperature. XRD
reveals the presence of Li2CO3 as second phase formed for precursors 1, 2, and 3 under oxidative conditions.
Solution phase decomposition of 2 and 3 in the absence of oxygen followed by annealing at 600 °C yields
Ferrite
Organometallic single source precursor
decomposition
Li2Fe3O5, Li5FeO4 and Fe3C depending on the solvent to precursor ratio in contrast to the
formed under pure solid state decomposition conditions. However, all lithium ferrites (Li2Fe3O5, Li5FeO4)
are converted to -LiFeO2 when oxidized above 500 °C. The -LiFeO2 products were further characterized
a-LiFeO2 phase
a
a
by IR, XPS, and TEM. Electrochemical analysis of the
a
-LiFeO2 was performed, showing a moderate initial
capacity of 13 mAh/g.
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
makes the reaction control complicated. Synthetic entries which
make use of milder process conditions may have important impact
on the composition of the resulting product [10]. Along this direc-
tion, we have recently shown that single source molecule [(COD)2-
CoLi  (THF)2] can be employed to form electrochemically active
LiCoO2 in the presence of oxygen already at 400 °C [17]. This
implies that molecular based precursors are able to deliver active
solid state materials with desired functional properties.
Herein we reportour studies towards the synthesis, characteriza-
tion and initial electrochemical performance of electrochemically
active LiFeO2 obtained by decomposition of a family of lithium and
iron containing organometallic single source precursors. The
decomposition of the organometallic precursors was carried out by
solid state as well as solution phase decomposition methods and
could circumvent e.g. external mechanical milling to activate pre-
cursor components as found for the Li2CO3–Fe2O3 system [18].
Electrochemically active LiFeO2 finds application in lithium ion
battery as positive and negative electrode material [1–3]. The poly-
morphs, corrugated layer, goethite and tunnel structured LiFeO2
are found to be electrochemically active morphologies [4]. LiFeO2
and other ferrites have been synthesized mainly by ion exchange
[1,2,5], microwave assisted [6], solid state [7–9] hydrothermal
[10–12] and mechanochemical [13,14] methods using different
inorganic Fe and Li salts involving pre-treatments steps of these
precursors. Precursor decomposition of Lithium ferricarboxylate
complexes with different ligands, Li3[Fe(L)6] Â H2O (L = formate,
acetate, propionate, butyrate) derived from sol gel type synthesis
as well as Li and Fe (acetylacetonate) complexes have also been re-
ported for stöchiometric LiFeO2 as well as non-stoichiometric Li
ferrites [15,16]. The reported methods often need additional
annealing at high temperature to form the desired phase and the
exact composition of the pre-mixtures is often not known, which
2. Experimental
2.1. Lithium ferrite synthesis
⇑
Corresponding author. Tel.: +49 6151 163225; fax: +49 6151 163470.
E-mail addresses: joerg64342@web.de, joerg.schneider@ac.chemie.tu-darm-
Compounds 1, 2 and 3 were synthesized as reported [19–22].
stadt.de (J.J. Schneider).
Typical solid state and solution phase decompositions were
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.01.074

J. Khanderi, J.J. Schneider / Inorganica Chimica Acta 370 (2011) 254–259
255
performed by using 80–100 mg of complexes 1, 2 or 3. Solid state
decomposition experiments under inert atmosphere (Ar flow
200 sccm) were carried out by placing the appropriate compound
in an alumina boat and heating to required temperature and hold-
ing it for 3 h followed by slow cooling. The precursor compounds
were heated to required temperature (200–600 °C) under argon
(flow 200 sccm), held for 2 h and then oxidized by passing 10 sccm
of oxygen in addition to argon and held for 1 h. The cooling of the
products was carried out in argon flow. Depending on the process
temperature the final product appeared black to red-brown.
Solution phase decompositions were carried out in trioctyl-
amine (TOA) as solvent (5–10 ml). Compounds 1, 2 or 3 were
mixed with this high boiling solvent and slowly heated to 300–
400 °C until weak boiling appears and was maintained for 3 h
(heating mantle temperature). The TOA is removed by adding large
amount of dry pentane and the suspension is centrifuged repeat-
edly under air. The resulting product is finally annealed at 600 °C
in argon for 3 h (see Scheme 1).
under vacuum for ꢀ5 h. The electrodes contain 3.44 mg of active
compound. Lithium metal was used as anode and the electrolyte
was 1 M LiPF6 in EC:DMC 1:2. A glass fiber separator was used be-
tween anode and cathode. The cathode was galvanostatically
cycled between 2.5 and 4.2 V.
3. Results
The precursors chosen for the present study contain zerovalent
iron (for 1 and 2) as well as divalent iron (3). An important aspect is
the bonding of lithium in 1, 2 and 3. In the case of 1 and 2 lithium is
directly bonded to the central zerovalent iron, whereas in the case
of 3, lithium is coordinated to the cyclopentadienyl ring ligand. In
the case of 1 and 2 the Fe:Li ratio is 1:1 whereas it is 1:2 for 3. This
offers a different, however constant ratio of the constituent metal
ions and allows to tune the phase composition.
3.1. Thermogravimetry of complexes 1, 2 and 3
The thermal characteristics of 1, 2 and 3 (Fig. 1) have been stud-
ied using thermogravimetry (TG) and TG coupled mass spectrom-
etry (TG/MS) in He atmosphere (flow rate 60 ml/min) with a
heating rate of 10 °C/min. It can be seen that temperature at which
the mass loss occurs for 1 is 60 °C and for 2, 3 it is approximately
83 °C. The decomposition for all the compounds take place in a two
step process followed by progressive weight loss. The initial
2.2. Sample characterization
Thermogravimetric coupled mass spectrometric (TG-MS) stud-
ies were performed using a Netzsch TG209F1 instrument. 10–
12 mg of the precursor complex was heated at a heating rate of
10 °C/min. in Helium atmosphere. IR spectroscopic measurements
were carried out using a Nicolet FTIR spectrometer with standard
KBr pellets. X-ray powder diffraction (XRD) of the samples were
performed using StadiP instrument from StadiP, Stoe & Cie GmbH,
Darmstadt in Debye–Scherrer mode (flat specimen, transmission
mode) with Co Ka1 radiation with a Ge(1 1 1) monochromator.
The diffractograms were compared with the reported powder dif-
fraction standards. XPS measurements were performed using ESCA
lab 250 (thermo VG scientific) with monochromated Al K
tion in constant analyzer energy mode (CAE) with a pass energy
of 50 eV for all spectra. SEM investigations were performed with
Philips XL 30 FEG microscope at 20 keV. HRTEM investigations
were carried out using FEI Technai G2 F20 @ 200 kV to determine
the size and morphology of the lithium ferrite particles. Samples
were prepared in high pure ethanol and dripped on lacy-carbon
copper grids.
decomposition step ends at around 160 °C for 1 (
D
m = À57.4%),
187 °C for 2 ( m = À59.1%) and 190 °C for 3 ( m = À65.3%). The
D
D
second decomposition step ends around 400 °C for all the three
compounds. This indicates, that after removal of the individual
organic moieties of 1, 2 and 3, a similar solid state reaction occurs,
irrespective of the starting compounds composition. The final res-
idues remaining for 1, 2 and 3 are 40.9% (39.8%), 47.2% (45.3%) and
48.4% (48.4%), respectively (theoretical masses for Fe and Li2CO3
for 1; Fe, Li2O and Li2CO3 for 2; and Fe3C, Li2O for 3 are given in
the parenthesis).
a radia-
3.2. Thermogravimetry coupled mass spectrometry (TG/MS) of
complexes 1, 2 and 3
Mass spectra of the gaseous products released from 1 (Fig. 2a
and b) and 2 (Fig. 1, ESI) during the thermal cycle indicate frag-
ments due to the decomposition of the organic ligand periphery.
Fragments at m/z values 16 (CH4) might account for elimination
of methyl moieties from the coordinating ligands and at m/z 18
(H2O) to fragmentation of the oxygenated species in the ligand
periphery of 1. Other primary fragments which evolve during the
decomposition of 1 corresponds to DME [m/z = 29 (formyl), 42
2.3. Electrochemical measurements
Electrochemical studies were carried out with a multichannel
potentiostatic–galvanostatic system VMP (Perkin Elmer Instru-
ments, USA). Swagelok-type cells were assembled in an argon-
filled dry box with water and oxygen contents less than 1 ppm.
The LiFeO2 cathodes were prepared by mixing the products of
decomposition with carbon (Super P@ Li from TIMCAL) and the
carbon from the resulting product, determined by CHN analysis
and PVdF (polyvinylidine fluoride) binder in a proportion 70%,
20% and 10%, respectively, and were intimately mixed, ground in
an agate mortar with NMP (N-methyl pyrrolidone) as solvent.
The resulting mixture is pressed onto an Al-mesh (8 mm in diam-
eter, pressure <5 bar). The so prepared cathode is dried at 120 °C
100
CpFeCODLiTMEDA
CpFeCODLiDME
Cp2FeLi2TMEDA
90
80
70
60
50
40
- -
N
O
2 [Li+]
Fe
Li
Fe
Fe
Li
O
N
100
200
300
400
500
600
ο
Temperature [ C]
1
2
3
Fig. 1. TG of CpFeCODLiDME 1 CpFeCODLiTMEDA 2 and (Cp)2FeLi2 2 TMEDA 3 in He
atmosphere (flow rate 60 ml/min) and at a heating rate 10 °C/min.
Scheme 1. Molecular structures of mixed Fe/Li half-sandwich complexes 1, 2 and 3.

256
J. Khanderi, J.J. Schneider / Inorganica Chimica Acta 370 (2011) 254–259
600 oC
e
24
100
80
200
TG
22
m42
220
20
111
m43
311
222
m60
18
m80
b
16
m81
500 o
C
14
12
10
8
m90
m91
d
c
60
6
400 o
C
C
4
2
40
*
0
*
**
0.8
-2
100
300 o
b
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
m16
m18
m39
m45
m54
m67
a
80
60
40
200 oC
a
20
40
60
2 θ [degree]
80
100
100
200
300
400
500
600
Fig. 5. X-ray diffraction pattern (Co Ka1) of the LiFeO2 derived from in the presence
o
Temperature [ C]
of oxygen at (a) 200, (b) 300, (c) 400, (d) 500 and (e) 600 °C (⁄corresponds to Li2CO3).
Fig. 2. TG/MS of [CpFeCODLi  DME] 1 (a) fragments with nA ion current and (b)
fragments with pA ion current.
Fe 2p3/2
Fe 2p1/2
200 deg C
e
140
120
100
80
300 deg C
400 deg C
500 deg C
Precursor
d
Fe2p
c
b
730
725
720
715
710
705
Li 1s
a
60
Li1sFe3p
66 64 62 60 58 56 54 52 50 48 46
Binding energy [eV]
3500 3000 2500 2000 1500 1000 500
-1
Wavenumber [cm
]
Fig. 6. X-ray photoelectron spectra of LiFeO2 (a) Fe 2p region b) Li1s and Fe3p region.
Fig. 3. IR spectra of the product obtained after decomposition of [CpFeCO-
DLi] Â DME 1 (a) at 200 °C (b) 300 °C (c) 400 °C (d) 500 °C in argon followed by
oxygen and (e) that of 1.
C1s
Li2O
Fe
§
Fe3C
#
*
Cp2FeLi22TMEDA
294 292 290 288 286 284 282 280
#
*
O1s
*
#
*
b
CpFeCODLiTMEDA
538 536 534 532 530 528 526 524 522
Binding energy [eV]
§
§
§
§
#
§
*
§
§
a
§
§
§
*
*
80
Fig. 7. X-ray photoelectron spectra (a) C1s (b) O1s of LiFeO2 obtained from 1.
30
40
50
60
2θ [degree]
70
90
100
3.3. Infrared spectroscopy of 1, 2, and 3
Fig. 4. X-ray powder diffraction pattern of (a) [CpFeCODLi] Â TMEDA
[(Cp)2FeLi2] Â 2 TMEDA 3, solid state decomposition condition.
2 (b)
IR spectra of precursor and product obtained after decomposi-
tion of 1 at different temperatures in the presence of argon fol-
lowed by oxygen is shown in Fig. 3. Comparison of the spectrum
of molecular complex of 1 with the decomposition product of 1 ob-
tained at 200 °C reveals that weak absorption bands at 2936 and
2853 cmÀ1 are present. These can be accounted for the C–H
stretching vibrations of methylene and/or carbene groups resulting
(ethenone), 43 (acetyl), 45 (methoxymethyl), 60 (methoxyethyl),
90 (DME)] and TMEDA for 2 m/z 43 (N-methyl methanimine),
44(methylaminomethyl), 58 (dimethylaminomethyl) as well as
for cyclopentadiene (m/z 39 (C3H4), 67 (C5H8) and 1,5-cyclooctadi-
ene (m/z 39 (C3H4), 54 (C4H6), 67 (C5H8), 80 (C6H8)) in the case of
complexes 1 and 2.

J. Khanderi, J.J. Schneider / Inorganica Chimica Acta 370 (2011) 254–259
257
Fig. 8. TEM (left) and HRTEM (right) of the LiFeO2 powder obtained from thermal decomposition of precursor []CpFeCODLi] Â DME 1 at temperature of 200 °C.
Fig. 9. TEM LiFeO2 powder obtained from thermal decomposition of precursor [CpFeCODLi] Â DME 1 at 600 °C (a) particle of in the size range of 40–90 nm and 150–300 nm,
(b) showing irregular shape and flaky morphology (c) image indicating typical dimension of the particle (d) HRTEM of the LiFeO2, where disordered structure with in the
particle can be seen.
from the decomposition of the cycloalkene ligands of 1, indicating
that the majority of the organic ligands have been removed already
at 200 °C. The remaining decomposition product thus obtained in
the temperature range between 200 and 500 °C show absorptions
at 1495–1503 cmÀ1, 1430 cmÀ1 and 870 cmÀ1 corresponding to
Li2CO3 [23] and those at 1600–1630 cmÀ1 account for carbona-
ceous residues. Importantly it can be concluded that all decompo-
sition products obtained in the decomposition temperature range
between 200 and 500 °C contain Li2CO3.
3.4. X-ray diffraction (XRD)
3.4.1. Solid state decomposition of precursors 2 and 3 in the absence of
oxygen
Precursors 2 and 3 were decomposed in the absence of solvent
and oxygen, at a temperature of 600 °C under an argon atmosphere.
Precursor 2 decomposes to Fe, Fe3C and Li2O (Fig. 4a) whereas 3 gives
Fe and Li2O (Fig. 4b). This indicates that during the decomposition
the reactivity of the components and the amount of carbon

258
J. Khanderi, J.J. Schneider / Inorganica Chimica Acta 370 (2011) 254–259
containing species determines the type of solid state product
formed, accounting for different carbon rich and carbon free phases.
at 531.4 eV can be assigned to oxygen associated with the organo-
metallic precursor 1 [27].
These combined findings show that there are different decom-
position reactions occurring during high temperature decomposi-
tion of 1 at 600 °C. No clear decomposition pathway can be
drawn from these findings.
3.4.2. Solution phase decomposition under absence of oxygen
The solution phase decomposition of 2 and 3 results in different
lithium ferrite solid materials. The formation of these ferrites is
dependent upon the solvent to precursor ratio. When the amount
of the precursor in trioctylamine (TOA) is low, both, 2 and 3 yield
Li2Fe3O5 with varying amount of Li2CO3 for 2 (similar results for 3).
When the amount of the precursor is increased in the same solvent
TOA, 3 however, gives Fe3C and Li5FeO4. In all cases the as synthe-
sized product is tempered at 600 °C to give the final crystalline
product. The primary decomposition products obtained before
the tempering step show only the presence of Fe [ESI, Fig. 2], point-
ing towards the fact that during the tempering step the amorphous
lithium compounds react further with iron or oxides of iron formed
in the decomposition process, giving rise to various type of ferrites.
This fact is studied in the upcoming Section 3.4.3.
3.6. Transmission electron microscopy (TEM)
High resolution (HR)TEM micrographs of the LiFeO2 synthesized
under oxidative conditions at 200 °C are depicted in Fig. 8a and b.
2–4 nm sized particles are found to be embedded inside an amor-
phous shell. The particles are of a rounded morphology and show a
uniform size distribution.
TEM micrographs of LiFeO2 synthesized under oxidative condi-
tions at 600 °C are shown in the Fig. 9a–d. It can be observed that
the LiFeO2 material produced at 600 °C is comprised of particle in
size range 40–90 nm as well as bigger ones being 150–300 nm.
Overall size dimensions of a typical LiFeO2 are shown in Fig. 9c.
A HRTEM image reveal the low crystallinity of the product well
3.4.3. Solid state decomposition of 1 under oxygen
in accordance with previous investigations on
a-LiFeO2 [28]. This
The decomposition of 1 in solid state and in solution under oxy-
gen has been carried out. The experiments were performed by
heating 1 in inert atmosphere at 200–600 °C followed by passing
oxygen over the so prepared material at respective temperatures.
The product obtained in the solution state decomposition (Li2Fe3O5
and Li5FeO4) was heated in air. Fig. 6 shows the XRD of products
obtained from decomposition of 1 at 200–600 °C. First, amorphous
finding already indicates that the electrochemical activity of the
so formed lithium ferrite could not be expected to be extraordinary
high (see Section 3.7)
3.7. Electrochemical analysis
Electrochemical analysis of the LiFeO2 obtained from precursor
1 at 600 °C is shown in Fig. 10. The capacity variation with the volt-
age is shown in Fig. 11a. It can be observed that only in the first
cycle lithium can be extracted, but due to the drastic change in
the structure of the delithiated LiFeO2 the further intercalation be-
comes hindered. The discharge capacity decreases rapidly with
cycle number indicating the instability of the thus formed LiFeO2
for electrochemical cycles (Fig. 10b).
a-LiFeO2 is observed at 200 °C. As the temperature is increased, the
initially formed -LiFeO2 converts to a crystalline phase. Li2CO3
a
formation was also observed above 400 °C. The products of the
solution phase decomposition, Li2Fe3O5 or Li5FeO4, obtained after
annealing, as well as the as synthesized product from the solution
phase decomposition were converted to
a-LiFeO2, with varying
amounts of Li2CO3 when heated to 500 °C or above in air/oxygen.
The product obtained at 200 °C was studied by XRD (Fig. 5). Be-
tween 400 and 550 °C a drastic structural change occurred. At
550 °C however, the [2 2 0] diffraction peak splits into two peaks
at 2h 50.2o and 50.6o. The peak at 2h 50.6o, increases in intensity
with temperature, indicating crystallization and a close structural
relationship between the products obtained at low and higher
temperature.
5.0
a
charge
10
5
1
4.5
4.0
3.5
3.0
3.5. X-ray photoelectron spectroscopy (XPS) obtained from 1
XPS spectra of Fe2p and Li1s/Fe3p for LiFeO2 synthesized from 1 at a
temperatureof 600 °C are shownin Fig. 6. The signals for Fe 2p3/2 and
Fe 2p1/2 are observed at 710.3 eV and 723.8 eV, respectively, and a
good indication for the presence of Fe(II) species in addition to Fe(III)
[24]. The BE of Li1s/Fe3p overlap each other and appear at approxi-
mately 55.6 eV with a shoulder at 53.7 eV. The lower BE shoulder
can be assigned to Fe(II)/Fe(III) state, present in the LiFeO2 product.
The higher BE value overlaps both for 3p Fe and 1s Li.
The high resolution XPS spectra of the C1s and O1s excitations of
LiFeO2 obtained from 1 at 600 °C are depicted in Fig. 7. The C1s
spectrum shows low intensity signals at 283.0 eV, 284.3 eV and
288.1 eV, and an additional shoulder at 289.7 eV. The signal at
283.0 eV can be accounted for carbon such as in the carbide Fe3C.
The peak at BE 284.3 eV shows that at 600 °C a small amount of
the graphitic carbon is still left in the material. The higher BE peak
at 288.1 can be accounted for carbon in a polymeric state. The
shoulder at BE 289.7 eV corresponds to carbon resulting from
carbonate ion, due to the minor presence Li2CO3.
1
2.5
5
10
discharge
2.0
0
10
20
capacity
30
40
50
dis
b
14
12
10
8
6
0
5
10
15
20
25
30
The O1s signals appears at 528.4 eV, 529.7 eV and 531.4 eV
(Fig. 7b). The signal at a BE of 528.4 eV can be accounted for Fe(II)
and Fe(III) [25]. The peak component at 529.7 eV corresponds to
O2À ions in the crystal structure of LiFeO2 [26]. The second peak
cyclenumber
Fig. 10. (a) Capacity variation during charge and discharge cycles and (b) variation
of discharge capacity of LiFeO2 synthesized at 600 °C against cycle number.

J. Khanderi, J.J. Schneider / Inorganica Chimica Acta 370 (2011) 254–259
259
T, Oxygen,
solid state
T, Argon,
solid state
O
T
LiFeO2 + CO2
Fe2O3 + Li2CO3
Fe + Fe3C + Li2O/Li2CO3
Fe
Li
O
- C5H5
- DME
- COD
1
O
T, annealing
T, Argon, DMF, solution
[Fe/Li/C/O polymeric]
Li2Fe3O5 + Li5FeO4
Fe
Li
O
1
Fig. 11. Reaction scheme for the decomposition and further reactions leading to the formation LiFeO2 from compound 1.
Cordier (XRD) and Dr. Jörg Engstler (TEM), for technical assistance.
We thank the Ernst-Ruska-Zentrum, Jülich (Prof. H. Meyer, Dr. L.
Houben, Dr. A. Lysberg) for making TEM studies possible (under
Project ERC1-TUD).
4. Discussion
The solid state decomposition of the precursors 1–3 in the ab-
sence of oxygen results in the formation of iron, Fe3C, and Li2O/
Li2CO3, the latter formed reaction of Li with traces of oxygen and
CO2/H2O as indicated by XRD, IR and TG. TG/MS shows that the or-
ganic ligand sphere for 1–3 is eliminated already below 200 °C.
TEM of the product obtained at 200 °C shows particle dimensions
of 2–4 nm are embedded inside an amorphous matrix. Fe(II) and
Fe(III) is formed during the initial decomposition starting from Fe
(0) in the precursors and form the mixed iron oxide, which further
reacts with Li2CO3 resulting in formation of LiFeO2.
In the case of the solution phase decomposition, ferrites such as
Li2Fe3O5 or Li5FeO4 are formed indicating a different decomposi-
tion pathway compared to the solid state. The decomposition reac-
tions based on the spectroscopic and microscopic findings
resulting in the formation of LiFeO2 from 1, are depicted in Fig. 11.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2011.01.074.
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5. Conclusions
Lithium containing ferrocene derivatives of the type
[(Cp)Fe(COD)Li  (L)] (L = DME, TMEDA) and [(Cp)2FeLi2  2 L]
(L = TMEDA) are suitable single source precursors for the prepara-
tion of lithium ferrites of various compositions. These organome-
tallic compounds can be decomposed in the solid state as well as
in solution to give solid state ferrite materials. The decomposition
in inert atmosphere leads to the formation of a mixture Fe, Fe3C
and Li2O/Li2CO3 as precursor material with the complete removal
of all organic ligands. These initially formed components react fur-
ther under oxidative conditions to form LiFeO2 by reaction of iron
oxide and Li2O/Li2CO3. The so formed amorphous LiFeO2 crystal-
lizes as the temperature is further increased. HRTEM of the final
product obtained at 600 °C reveals no crystalline order. In the case
of solution phase decomposition, various fragments containing
lithium and iron might react in a more complicated route leading
to the formation of other ferrites. The electrochemical test of the
a-LiFeO2 formed via the solid state decomposition route shows
an initial capacity of 13 mAh/g with a rapid decrease in capacity.
To conclude, lithium containing ferrocene derivative are promising
precursors for the synthesis of lithium ferrites.
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Our work is supported through the Deutsche Forschungsgeme-
inschaft (DFG). We acknowledge Dr. Rudolf C. Hoffmann (TG/MS),
Dr. Alexsander Issannin (XPS), Dr. Kathrin Hofmann, Dr. Gerhard