Chemical lithiation/delithiation of k+-β-ferrite (k-1+xfe11o17)

Article abstract of DOI:10.1246/bcsj.74.317

The chemical lithiation/delithiation of K⁺-β-ferrite has been performed using butyllithium, lithium naphthalide (for lithiation), and iodine (for delithiation). In lithiation using butyllithium, the lithium content (y) in K_1+xLi_yFe₁₁O_I7 was dependent on the average grain size of K⁺-β-ferrite single crystals; small grains (5 μm) largely reacted with lithium to form K₀.99Li_1.65Fe₁₁O₁₇. Lithiation was performed by the reduction of Fe³⁺ to Fe²⁺. Since the same X-ray diffraction (XRD) patterns were obtained before and after lithiation, the reaction seemed to be restricted to only near the grain surfaces. In lithiation using lithium naphthalide, the lithium content (y), which attained to be 36, was independent of the average grain size of K⁺-β-ferrite single crystals. This lithium content was remarkably large, compared to y = ca. 1.6 in lithiation using butyllithium. A large amount of Fe° (metal) was detected in the samples. According to scanning electron microscope (SEM) and XRD studies, not only pulverization of grains, but also destruction of the β-structure, occurred upon lithiation. On the other hand, delithiation of deeply lithiated samples was achieved by using iodine as an oxidant.

Full text of DOI:10.1246/bcsj.74.317

317
© 2001 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 74, 317–321 (2001)
Chemical Lithiation/Delithiation of K+- -Ferrite (K Fe O )
β
1+x
11 17
Shigeru Ito,* Yoshitomo Omomo, and Takashi Fujii
Department of Industrial Chemistry, Faculty of Science and Technology, Science University of Tokyo,
Noda Chiba 278-8510
(Received August 10, 2000)
The chemical lithiation/delithiation of K+-β-ferrite has been performed using butyllithium, lithium naphthalide (for
lithiation), and iodine (for delithiation). In lithiation using butyllithium, the lithium content (y) in K1+xLiyFe11O17 was de-
pendent on the average grain size of K+-β-ferrite single crystals; small grains (5 µm) largely reacted with lithium to form
K0.99Li1.65Fe11O17. Lithiation was performed by the reduction of Fe3+ to Fe2+. Since the same X-ray diffraction (XRD)
patterns were obtained before and after lithiation, the reaction seemed to be restricted to only near the grain surfaces. In
lithiation using lithium naphthalide, the lithium content (y), which attained to be 36, was independent of the average grain
size of K+-β-ferrite single crystals. This lithium content was remarkably large, compared to y = ca.1.6 in lithiation using
butyllithium. A large amount of Fe0 (metal) was detected in the samples. According to scanning electron microscope
(SEM) and XRD studies, not only pulverization of grains, but also destruction of the β-structure, occurred upon lithia-
tion. On the other hand, delithiation of deeply lithiated samples was achieved by using iodine as an oxidant.
K+-β-ferrite was found in 1938 to be a magnetoplumbite-
like compound by V. Adelsköld,1 and was then clarified to have
the same structure as β-alumina, known to be a superionic con-
ductor.2–4 K+-β-ferrite, as well as β-alumina, has a layer struc-
ture alternating an alkali layer with potassium and oxygen and
a spinel block with γ-Fe2O3. The composition of K+-β-ferrite is
expressed as K1+xFe11O17 (0 < x < 0.5), where x is the excess
amount of potassium. This excess amount is compensated by
the reduction of Fe3+ to Fe2+,5–6 although in β-alumina the oxy-
gen atoms are in the alkali layer to compensate for any excess
amount of alkali ions.
Considering the reduction of Fe3+ to Fe2+, the authors con-
structed a lithium secondary battery using K+-β-ferrite as a
cathode active material (Li|1M LiClO4 PC|K1.3Fe11O17).7–9 This
battery revealed OCV, 3.2 V; discharge potential, 1.5 V vs. Li/
Li+; and capacity, 200 Ah kg–1 at room temperature. This ca-
pacity was larger than those of the conventional cathode active
materials. After discharging, a large amount of lithium was
contained in the cathode active material (K1.3Li6.8Fe11O17). Af-
ter ten cycles of discharge/charge, no degradation was ob-
served in this battery. However, the redox reaction in the cath-
ode material was still unclear. M. Pernet et al. reported that in
the lithiation of γ-Fe2O3 powder using butyllithium, Li+ ions
were inserted into octahedral vacancies in the defect spinel,
and that a large amount of lithium was inserted with the first-
order transition of spinel-rocksalt type to produce Li0.86Fe2O3.10
Therefore, the lithiation was chemically examined by the reac-
tion of butyllithium and K+-β-ferrite powder. The composition
K1.2Li2.2Fe11O17 was obtained and Fe3+ in K+-β-ferrite was re-
duced to Fe2+ by the lithiation, according to a chemical analy-
sis.11 However, lithium hardly reacted with single crystals of
K+-β-ferrite that were 1−2 mm in size. It appears that chemical
lithiation using butyllithium occurs near to the surface of K+-β-
ferrite grains. On the other hand, K. M. Abraham et al. exam-
ined the chemical lithium insertion into α- and γ-Fe2O3 pow-
der, using lithium naphthalide as a strong reductant, and ob-
tained an amorphous phase containing lithium (LixFe2O3, x %
6).12 This amorphous phase contained a large amount of lithi-
um, compared to the product obtained by butyllithium. There-
fore, further research may be required for K+-β-ferrite to clari-
fy the redox reaction in the lithium secondary battery.
In this work, the lithiation of K+-β-ferrite single crystals was
investigated by using butyllithium and lithium naphthalide.
The relation between the amount of lithium and the structure of
the product has been considered. In addition, the reversibility
of the lithiation/delithiation was also examined using iodine as
an oxidant.
Experimental
1. Preparation of K+- -Ferrite Single Crystals. K+-β-fer-
β
rite single crystals, K1.2Fe11O17, were obtained by a flux method
using B2O3−K2O−KF.13–14 A mixed powder of B2O3, K2CO3, KF,
and α-Fe2O3 (1:1:2:1 in molar ratio, 15 g in net weight) in a plati-
num crucible was heated at 1200 °C for 6 h, and then cooled to 700
°C at a cooling rate of 25 °C h–1. The flux was removed by im-
mersing the contents in 2 M HNO3 for 3 days at 50 °C (1 M = 1
mol dm–3). The obtained single crystals were sieved with average
grain sizes of 40, 300, 700, and 1500 µm, respectively. The ground
particles of single crystals were also used as samples with an aver-
age grain size of 5 µm.
2. Lithiation of K+- -Ferrite Single Crystals Using Butyl-
β
lithium. K+-β-ferrite single crystals (0.4 g, 5−1500 µm) were
immersed in 20 ml of 1.6 M butyllithium hexane solution for 5 or
10 days at room temperature under an inert nitrogen atmosphere.
After the reaction with butyllithium, the sample was washed with
hexane and distilled water, and then dried for 1 h at 120 °C in air.

318 Bull. Chem. Soc. Jpn., 74, No. 2 (2001)
Chemical Lithiation/Delithiation of β-Ferrite
3. Lithiation of K+- -Ferrite Single Crystals Using Lithium
On the other hand, small grains (5 µm) largely reacted with
lithium to form K0.99Li1.65Fe11O17. The lithium contents corre-
lated with the amount of Fe2+, as shown in Fig. 1. The grains
with 5 µm contained 7.4 wt% of Fe2+. Assuming that the lithia-
tion is described by the following equation, 7.4 wt% corre-
sponds to y = 1.3, in accordance with the result of a chemical
analysis (y = 1.65):
β
Naphthalide. To prepare lithium naphthalide, first 0.04−10 g of
naphthalene was dissolved in 20 ml of tetrahydrofuran, and then
an excess amount of lithium (0.2−2 g) was added to the solution.
K+-β-ferrite single crystals (0.4 g, 40 or 1500 µm) were immersed
in the solution for 5 days at room temperature. The product was
washed with tetrahydrofuran and tetrahydrofuran containing
naphthalene, and then dried for 1 h at room temperature in vacu-
um. To remove oxygen and moisture from the reaction system,
these experiments were carried out in a vacuum dry box filled with
argon. Tetrahydrofuran was previously dried with molecularsieves
3 A.
K1+xFe2+xFe3+11−xO17 +yLi+ +ye−
→ K1+xLiyFe2+x+yFe3+11−(x+y)O17
(1)
4. Delithiation of Lithiated Samples Using Iodine. Lithiat-
ed samples (0.2 g) obtained in section 2 or 3 were immersed in 20
or 100 ml of 0.1 M iodine acetonitrile solution for 5 days at 60 °C.
After the reaction, the sample was washed with acetonitrile, and
then dried by the same procedure as described in section 2 or 3.
For the samples lithiated using lithium naphthalide, delithiation
was carried out in a vacuum dry box filled with argon. Acetonitrile
was previously dried with molecularsieves, 3 A, to remove any
moisture in the reaction system.
Figure 2 shows the XRD patterns and the lattice constants of
samples lithiated for 10 days. The XRD patterns of lithiated
samples were the same as that of the original K+-β-ferrite. No
relation was recognized between the lattice constants and the
lithium content (y). However, M. Pernet et. al. reported that Li+
ions were inserted into the vacancies of γ-Fe2O3 to increase the
lattice constants.10 If Li+ ions are inserted into the γ-Fe2O3 lay-
ers in K+-β-ferrite, the lattice constants should be increased.
On the other hand, the interlayer distance of K+-β-ferrite was
decreased by inserting alkali ions in the alkali layers, because
of the electrostatic attractive force.15 If Li+ ions are inserted
into the alkali layers of K+-β-ferrite, the electrostatic force
must decrease the interlayer distance. Therefore, the intercala-
tion of Li+ ions does not occur in the reaction of butyllithium
and K+-β-ferrite. Considering that the lithium content (y) de-
5. Characterization. The chemical compositions of K+-β-
ferrite single crystals and lithiated/delithiated samples were deter-
mined by atomic absorption spectroscopy (Shimadzu, AA-630-
12). The contents of metal iron and Fe2+ ions were determined by
following JIS M 8213-1995. The crystalline phase of samples was
identified by X-ray diffraction with Fe Kα radiation (Rigaku CN
2013). In this measurement, a sample obtained using lithium naph-
thalide was ground in a vacuum dry box filled with argon, and the
sample holder was wrapped with polyethylene film. The lithiated
samples were observed by scanning electron microscope (Akashi,
ALPHA-9).
Results and Discussion
1. Lithiation and Delithiation Using Butyllithium and Io-
dine. 1.1. Lithiation Using Butyllithium. Figure 1 shows
the lithium content (y) in K1+xLiyFe11O17 after lithiation for 10
days as a function of the average grain size of K+-β-ferrite sin-
gle crystals. Only a small amount of lithium reacted with sin-
gle-crystal grains having an average grain size > 700 µm, e.g.,
K1.19Li0.12Fe11O17 was obtained by using grains with 1500 µm.
Fig. 1. Lithium content y in K1+xLiyFe11O17 and Fe2+
content after lithiation for 10 days using butyllithium as
a function of average grain size of K+-β-ferrite single
crystals.
Fig. 2. XRD patterns of the samples lithiated for 10 days
using butyllithium.

S. Ito et al.
Bull. Chem. Soc. Jpn., 74, No. 2 (2001) 319
pends on the average size of single crystal grains of K+-β-fer-
rite, the reaction may be restricted to only near the surfaces of
the grains.
1.2. Delithiation Using Iodine. Delithiation was per-
formed for a sample lithiated for 10 days. Table 1 gives the
compositions and Fe2+ contents of the delithiated samples. K+
and Li+ ions were decreased by delithiation using iodine.
K0.81Li1.39Fe11O17 was obtained using a sample with 5 µm in av-
erage grain size. The Fe2+ content decreased corresponding to
the decrease in the K+ and Li+ ions. It seems that K+ and Li+
ions are removed by the oxidation of Fe2+ to Fe3+ according to
the following equations:
1
2
K1+xLiyFe2+x+yFe3+11−(x+y)O17
+
zI2
→ K1+xLiy−zFe2+x+y−zFe3+11−(x+y)+zO17 + zLiI,
(2)
1
2
K1+xLiyFe2+x+yFe3+11−(x+y)O17
+
zI2
→ K1+x−zLiyFe2+x+y−zFe3+11−(x+y)+zO17 + zKI.
(3)
However, the delithiated sample still contained lithium, which
seemed to be in a relatively stable state.
The XRD pattern of the delithiated sample was the same as
those of the original K+-β-ferrite and the lithiated sample. The
lattice constants of the delithiated sample with the composition
of K0.81Li1.39Fe11O17 were a = 0.5931(3) nm and c = 2.379(1)
nm, which were similar to those of the lithiated sample. This
was because the lithiation and delithiation occured near the
surface of the grains.
2. Lithiation and Delithiation Using Lithium Naphtha-
lide and Iodine. 2.1. Lithiation Using Lithium Naphtha-
lide. Figure 3 shows the lithium content (y) in K1+xLiyFe11O17
after lithiation for 5 days as a function of the weight of naph-
thalene in 20 ml of tetrahydrofuran. In lithiation using lithium
naphthalide, naphthalene radical anions, which are formed by
the reaction of lithium and naphthalene, attack K+-β-ferrite to
reduce Fe3+ ions. As shown in Figs. 3(a) and 3(b), the lithium
content (y), which attained to 36 for 1.5−10 g of naphthalene,
was independent of the average grain size of K+-β-ferrite. This
lithium content, which is remarkably large compared to y = ca.
1.6 obtained by butyllithium, resulted from the potential differ-
ence in butyllithium and lithium naphthalide (1 and 0.5 V vs.
Li/Li+, respectively).16 Assuming the reduction of Fe3+ to Fe2+
in the lithiation shown in Eq. 1, the maximum content of lithi-
um (y) is 11. For y = 36, Fe3+ in K+-β-ferrite must be complete-
Fig. 3. Lithium content y in K1+xLiyFe11O17 and metal
iron content after lithiation for 5 days using lithium
naphthalide as a function of weight of naphthalene in
20 ml of THF. K1+xFe11O17 used; Average grain size:
(a) 1500 µ m, (b) 40 µ m, Net weight: 0.4 g.
ly reduced to Fe0 (metal). Figure 3 also shows the metal iron
content. In this lithiation, a large amount of Fe0 was detected
as 45 wt%. However, the Fe2+ content was 2−6 wt%, corre-
sponding to y = 0.3−1.3. Lithiation using lithium naphthalide
seems to proceed as follows:
K1+xFe2+xFe3+11−xO17 + yLi+ + ye−
→ K1+xLiyFe0
1
3
yFe2+xFe3+
1
11−(x+ y)O17
(4)
3
According to Eq. 4, the reaction is completed with y = 33. An
excess amount of lithium in the experimental data of y = 36
may be ascribed to LiOH produced by residual H2O in the reac-
tion system.
Figure 4 shows SEM photographs of samples lithiated for 5
days. Single crystal grains pulverized from the surface, even
for y = 0.48. As the lithiation proceeded, fine grains were ob-
served in the sample. Figure 5 shows XRD patterns of samples
lithiated for 5 days. The intensities of the peaks decreased in a
sample containing a large amount of lithium. The diffraction
peaks completely disappeared in a sample with y = 36.7. It was
concluded that not only the pulverization of grains, but also the
destruction of the β-structure, occurred in lithiation using lithi-
um naphthalide.
Table 1. Compositions and Fe2+ Contents of the Sam-
ples Delithiated for 5 Days Using Iodine
Average grain size
Composition (Fe2+ content/wt%)
After lithiationa)
After delithiation
µm
1500
700
300
40
K1.19Li0.12Fe11O17 (1.1) K1.03Li0.11Fe11O17 (0.8)
K1.15Li0.11Fe11O17 (0.9) K1.04Li0.11Fe11O17 (0.7)
K1.16Li0.17Fe11O17 (1.2) K1.05Li0.14Fe11O17 (0.8)
2.2. Delithiation Using Iodine. The amorphous phase
containing a large amount of lithium was delithiated. Table 2
gives the compositions, Fe2+ contents and metal-iron contents
of the delithiated samples. The delithiation of a sample with y =
K
1.02Li0.69Fe11O17 (3.9) K0.78Li0.48Fe11O17 (1.2)
5
K0.99Li1.65Fe11O17 (7.4) K0.81Li1.39Fe11O17 (5.4)
a) Lithiated for 10 days using butyllithium.

320 Bull. Chem. Soc. Jpn., 74, No. 2 (2001)
Chemical Lithiation/Delithiation of β-Ferrite
Fig. 4. SEM photographs of a K+-β-ferrite single crystal and the samples lithiated using lithium naphthalide.
36.7 proceeded to decrease the lithium content to y = 2.78. The
Fe2+ content was 16 wt% in a sample with y = 2.78, whereas no
metal iron was detected. A large amount of lithium was re-
moved by the oxidation of metal iron using iodine.
Figure 6 shows the XRD patterns of the delithiated samples.
The patterns in Figs. 6(b), 6(c), 6(d), and 6(e) were similar to
those of the lithiated samples in Figs. 5(b), 5(c), 5(d), and 5(e),
respectively. The destroyed structure after the lithiation was
not recovered by delithiation.
2.3. Structure of the Lithiated Sample. From the result
of an X-ray analysis, the lithiated sample was found to be
amorphous. On the other hand, the material contained a large
amount of Fe0. However, Fe atoms could not exist in the amor-
phous phase with the zero valency. Therefore, we deduce that
the lithiated material consisted of nano-sized mixture of Li2O
and Fe (metal). Further work will be required to clarify the
structure of the amorphous phase of the lithiated sample.
In lithiation using butyllithium, the lithium content (y) was
dependent on the average grain size of K+-β-ferrite single crys-
tals. The maximum content of lithium was y = 1.65 in
K1+xLiyFe11O17, when the average grain size was 5 µm. Lithia-
tion was performed by the reduction of Fe3+ to Fe2+. The same
XRD patterns were obtained before and after lithiation. Lithia-
tion using butyllithium may be restricted to only near the sur-
faces of the grains.
In lithiation using lithium naphthalide, the lithium content
(y), which attained to 36, was independent of the average grain
size of K+-β-ferrite single crystals. A large amount of Fe0 (met-
al) was detected. The single-crystal grains pulverized from the
surface. Furthermore, destruction of the β-structure occurred
to form an amorphous phase.
Delithiation using iodine occurred for a sample lithiated us-
ing lithium naphthalide. It is expected that a lithium secondary
battery using K+-β-ferrite as a cathode active material would
have a large capacity.
Conclusions
In this work, the chemical lithiation/delithiation of K+-β-fer-
rite was performed using butyllithium, lithium naphthalide (for
lithiation), and iodine (for delithiation).
This study was performed through Special Coordination
Funds for Promoting Science and Technology from the Science
and Technology Agency.

S. Ito et al.
Bull. Chem. Soc. Jpn., 74, No. 2 (2001) 321
Fig. 6. XRD patterns of the samples delithiated for 5
days using iodine. Patterns (b), (c), (d), and (e) were ob-
tained by the delithiation of the lithiated samples shown
in Figs. 5(b), 5(c), 5(d), and 5(e), respectively. a) X-ray
samples were covered with polyethylene film to prevent
the exposure to air.
Fig. 5. XRD patterns of the samples lithiated for 5 days
using lithium naphthalide. a) X-ray samples were cov-
ered with polyethylene film to prevent the exposure to
air.
ceedings of ICF 6), 101 (1992).
Table 2. Compositions of the Samples Delithiated for 5
Days Using Iodine
6
S. Nariki, S. Ito, T. Uchida, and N. Yoneda, Ferrites (Pro-
ceedings of ICF 6), 644 (1992).
S. Ito, K. Ui, N. Koura, and K.Akashi, to be presented at IS-
SI, Honoruru, Hawaii, Nov, 16 (1997).
S. Ito, K. Ui, M. Ito, N. Koura, and K. Akashi, J. Magnetics
Soc. of Japan, 22, Supplement, 449 (1998).
S. Ito, K. Ui, N. Koura, and K. Akashi, Solid State Ionics,
Composition (Metal iron content/wt%, Fe2+ content/wt%)
7
After lithiationa)
After delithiation
K1.14Li0.48Fe11O17 (–b), 2.0) K1.05Li0.31Fe11O17 (–b), 1.4)
K1.13Li4.76Fe11O17 (10.7, 2.3) K1.02Li0.37Fe11O17 (–b), 2.2)
K1.07Li25.9Fe11O17 (28.2, 3.6) K0.69Li2.00Fe11O17 (–b), 6.6)
K0.85Li36.7Fe11O17 (44.7, 3.3) K0.35Li2.78Fe11O17 (–b), 16.0)
8
9
113, 17 (1998).
10 M. Pernet, P. Strobel, B. Bonnet, and P. Bordet, Solid State
Ionics, 1993, 66, 259.
11 S. Ito, T.Aoyama, and K.Akashi, Solid State Ionics, 113, 23
(1998).
a) Lithiated for 5 days using lithium naphthalide.
b) –; No detection.
12 K. M. Abraham, D. M. Pasquariello, and E. B. Willstaedt, J.
Electrochem. Soc., 137, 743 (1990).
References
1
2
V. Adelsköld, Ark. Kemi, Mineral. Geol., 12A, 1 (1938).
W. L. Roth and R. J. Romanczuk, J. Electrochem. Soc., 116,
13 S. Ito, N. Kubo, and N. Yoneda, J. Cryst. Growth, 71, 253
(1985).
975 (1969).
14 S. Nariki, S. Ito, and N.Yoneda, Ferrite (Proceedings of ICF
6), 101 (1992).
3
T. Takahashi, K. Kuwabara, and Y. Kase, Nippon Kagaku
Kaishi, 1975, 1305.
15 S. Ito, H. Kurosawa, K. Akashi, Y. Michiue, and M.
Watanabe, Solid State Ionics, 86, 745 (1996).
16 J. H. Golden, F. J. DiSalvo, and J. M. J. Frechet, Mater. Sci.
Forum, 152, 209 (1994).
4
G. J. Dudley, B. C. H. Steele, and A. T. Howe, J. Solid State
Chem., 18, 141 (1976).
5
S. Nariki, S. Ito, T. Uchida, and N. Yoneda, Ferrites (Pro-