Improvement of the electrochemical performance of nanosized α-MnO2 used as cathode material for Li-batteries by Sn-doping

Article abstract of DOI:10.1016/j.jallcom.2011.07.075

Sn-doped MnO₂ was prepared by hydrothermal reaction between KMnO₄ as oxidant, fumaric acid C₄H₄O ₄ as reductant and SnCl₂ as doping agent. XRD analysis indicates the cryptomelane α-MnO

Full text of DOI:10.1016/j.jallcom.2011.07.075

Journal of Alloys and Compounds 509 (2011) 9669–9674
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jallcom
Improvement of the electrochemical performance of nanosized ␣-MnO used as
2
cathode material for Li-batteries by Sn-doping
A.M. Hashem , A.M. Abdel-Latif , H.M. Abuzeid , H.M. Abbas , H. Ehrenbergc,d, R.S. Farage,
a,∗
a
a
b
f
g
A. Mauger , C.M. Julien
National Research Centre, Inorganic Chemistry Department, Behoes St., Dokki, Cairo, Egypt
a
b
c
d
e
f
National Research Centre, Physical Chemistry Department, Behoes St., Dokki, Cairo, Egypt
Institute for Complex Materials, IFW Dresden, Helmholtzstr. 20, D-01069 Dresden, Germany
Materials Science, Technische Universität Darmstadt, Petersenstr. 23, D-64287 Darmstadt, Germany
Department of Chemistry, Faculty of Science, Al-Azhar University, Cairo, Egypt
Université Pierre et Marie Curie, Institut de Minéralogie et Physique de la Matière Condensée (IMPMC), 4 Place Jussieu, 75005 Paris, France
Université Pierre et Marie Curie, Physicochimie des Electrolytes, Colloïdes et Sciences Analytiques (PECSA), 4 Place Jussieu, 75005 Paris, France
g
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 16 May 2011
Received in revised form 20 July 2011
Accepted 22 July 2011
Available online 31 July 2011
Sn-doped MnO was prepared by hydrothermal reaction between KMnO as oxidant, fumaric acid C H O
4
2
4
4
4
as reductant and SnCl2 as doping agent. XRD analysis indicates the cryptomelane ␣-MnO2 crystal struc-
ture for pure and doped samples. Thermal stabilization was observed for both oxides as detected from
thermogravimetric analysis. SEM and TEM images show changes in the morphology of the materials from
spherical-like particles for pristine P–MnO2 to rod-like structure for Sn–MnO2. Electrochemical proper-
ties of the electrode materials have been tested in lithium cells. Improvement in capacity retention and
cycling ability is observed for doped oxide at the expense of initial capacity. After 35 cycles, the Li//Sn
doped MnO2 cell display lower capacity loss.
Keywords:
Lithium ion batteries
Manganese dioxide
Tin doping
©
2011 Elsevier B.V. All rights reserved.
Cryptomelane
1
. Introduction
(2 × 2) hollandite, (2 × 3) romanechite and (3 × 3) todorokite that
have potential applications in chemical separation, catalysis, or
electrochemical devices. Due to their low cost, MDOs have been
largely studied for use as positive electrode materials for Li primary
batteries because their environmental merit and easy prepara-
tion [5], and more recently as electrode of hybrid supercapacitors
[6].
Rechargeable lithium batteries are based on the use of inter-
calation compounds as electrodes in which lithium ions shuttle
between the negative electrode (anode) and positive electrode
(
cathode) hosts. As cathode materials for lithium-ion batteries
layered LiCoO , LiNiO2 and LiMn O4 have been extensively inves-
2
2
tigated world-wide [1,2]. Manganese dioxides (MDOs) have been
intensively investigated as electrode for primary and secondary
lithium batteries [3]. They exhibit a wide variety of structures
that have been utilized in many applications. MnO2 exists in sev-
eral polymorphic modifications: ␣-, ␤-, ␥-, ␧-, ␦-, and ␭-MnO2,
in which the MnO6 octahedra can periodically share their edges
and vertices to generate a wide range of structures with dif-
ferent properties [4]. These complex structures depend on the
preparation conditions and the presence of certain cations in the
solution used for synthesis. Among the MDOs with large tunnel
It is commonly accepted that the some MDOs yield stabi-
lization of their structure by large cations which reside in the
tunnel of the framework; so the ␣-MnO2 form refers to the hol-
landite or cryptomelane (2 × 2)-type according the presence of
Ba or K+ cations, respectively. Most of the ␣-MnO2 samples
prepared by hydrothermal or chemical reaction depend on a two-
step sequence of structure formation and ion exchange reaction
[7–9]. Cryptomelane is a brown, greyish-white mineral of formula
2+
K(Mn4+,Mn ) O16, which crystallizes in the monoclinic system
3+
8
[10,11].
(
n × m) structure, compounds with regular lattice exist such as
The primary driving force for implementation of MnO -based
materials for battery applications is the cost. ␣-MnO2 positive
2
electrode material would be projected to cost 1% of LiCoO , the
2
cathode material of choice in rechargeable Li-ion batteries. Essen-
tially, properties such as cycle life and operation voltage and energy
density may be drawback issues for MnO2 materials, when com-
pared to LiCoO2 due to the potential cost difference. Safety margin
∗ Corresponding author at: National Research Centre, Inorganic Chemistry
Department, Behoes St., Dokki, Cairo, Egypt. Tel.: +20 106305012;
fax: +20 233370931.
E-mail address: ahmedh242@yahoo.com (A.M. Hashem).
0
925-8388/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2011.07.075

9
670
A.M. Hashem et al. / Journal of Alloys and Compounds 509 (2011) 9669–9674
1000
to over-charge conditions of Li-MnO2 system, better than for Co
or Ni based Li-ion batteries, is due to the stable nature of Mn(IV),
which is a common oxidation state for Mn and one that retains
oxygen. Manganese is also an abundant transition metal; it is the
twelfth most abundant element in the earth’s crust. Therefore,
MnO2 type materials are attractive for large energy storage appli-
cations, which would require very large quantities of materials to
supply an emerging market [12,13].
P-MnO2
Sn-MnO2
8
6
00
00
Several works were carried out to stabilize and improve the
+
+
2+
structure of MnO2 using counter ions such as Li , Na , Mg [8],
by doping with Al3+, Co or Ag+ metal ions [5,14,15], with Li O
3+
400
2
[
16]. Because the conduction mechanism in MDOs is governed by
4+
3+
mixed valency, the ratio Mn /Mn redox is an important param-
eter. Surface modification with protective coating was also carried
out with aim to enhance the cycle ability of MnO2 as cathode in
lithium batteries [17,18]. A method was proposed by Cai et al.
2
00
0
[
19] to dope transition-metal iron ions into the framework instead
1
0
20
30
40
50
60
70
80
of the tunnels of (2 × 2) tunnel structure manganese octahedral
molecular cryptomelane. Recently, Gulbinska and Suib [20] sub-
Two-theta (degree)
5
+
4+
stituted V for Mn in porous MDOs producing flat discharge
profiles.
Fig. 1. XRD of (a) P–MnO2 and (b) Sn–MnO2. Samples were synthesized through
redox reaction between KMnO4 and fumaric acid C4H4O4. Doped compound was
prepared using SnCl2.
In this work, we have successfully prepared nanosized particles
of pure P–MnO2 and Sn-doped MnO2 materials via a hydrother-
mal redox method between KMnO4 and fumaric acid. The effect
of doping on the structure, morphology and electrochemical
properties has been investigated. Electrochemical tests were per-
formed in lithium cells by cyclic voltammetry and galvanostatic
charge–discharge
broad diffraction peaks. All these peaks are indexed to a pure cryp-
tomelane ␣-MnO2 with the tetragonal phase (I4/m space group)
in agreement with the JCPDS file #44-0141. As shown in the XRD
diagram of the Sn–MnO2 sample, the doping does not have any
significant effect on the crystal structure of manganese dioxide.
All the h k l reflections were labeled along with the Miller indices
of the ␣-MnO2 phase. No extra peaks related to Sn impurities
were observed. The absence of modification in the XRD diagrams
might indicate that: (i) Sn is in low content or has crystalline
domains beyond the detection limit of XRD; (ii) Sn is incorpo-
rated in the cryptomelane structure, with the formation of a
solid solution; and/or (iii) Sn is incorporated into the channels
of cryptomelane structure, replacing K+ ions in the (2 × 2) tun-
nels.
2
.
Experimental
Hydrothermal redox reaction between potassium permanganate (KMnO4) as
the oxidizing agent and fumaric acid (C4H4O4) as reducing agent was used to prepare
nanosized pure MnO2 (P–MnO2) and Sn-doped MnO2 (Sn–MnO2). Molar ratio of 3:1
of KMnO4:C4H4O4 was used to prepare P–MnO2. 3:1:0.07 KMnO4:C4H4O4:SnCl2
molar ratio was used for Sn–MnO2. This molar ratio between oxidizing and reducing
agents allows the effective oxidation state of the Mn in the final product to be around
Mn . After one hour of stirring in slight acidic solution, dark brown precipitate was
formed at room temperature. The formation of MnO2 was the result of the oxidation
of fumaric acid into volatile CO2 and soluble H2C2O4, while [MnO4] ions were
reduced to MnO2 leading to total consumption of the reactants. Complete reduction
of KMnO4 can be observed also from a change in color of the supernatant liquid from
purple to dark brown. The formed precipitate was collected by filtration. To allow the
removal of K from the precipitate we washed it several times with distilled water.
The resulting precipitate was dried at 100 C for 24 h producing a black powder after
4+
−
The lattice parameters a and c of the tetragonal structure for the
MDOs synthesized materials were calculated by the least-squares
refinement method using 12 well-defined XRD lines. Data are listed
in Table 1. Attempt to make Rietveld refinement was unsuccess-
ful because the low X-ray scattering efficiency that makes to poor
+
◦
◦
calcination the dried powder in an ambient atmosphere at 450 C for 6 h.
The crystalline phase was identified by X-ray diffraction (XRD) using Philips
signal recorded. It appeared very often in the case of MnO as men-
2
X’Pert PROMRO (PW3050) apparatus equipped with a CuK␣ X-ray anticathode
tioned by Pannetier and Chabre [4]. It is observed that no significant
change occurs in lattice parameters, thus the cryptomelane struc-
ture is preserved upon tin doping. Notice that the success of tin
doping in MnO6 octahedra is due to the similarity in the ionic radii
(
ꢀ = 1.5406 A˚ ). XRD measurements were collected under Bragg–Brentano geometry
◦
◦
in the 2ꢁ range 10–80 with step of 0.05 . TG measurements were carried out using a
thermal gravimetric analyzer (Perkin Elmer, TGA 7 series) in the temperature range
of 30–1000 C in air at a heating rate of 10 C/min. The particle morphology of the
MnO2 powders was investigated by scanning electron microscope (SEM, JEOL-Japan,
JXA-840A) and by transmission electron microscope (TEM, JEOL-1230).
◦
◦
3+
4+
of octahedral high-spin Mn (0.65 A˚ ) and Sn (0.69 A˚ ) in crystal.
Thus, Sn4+ can substitute for Mn without causing much structural
disorder and serious charge imbalance. Cai et al. have shown that
incorporation of iron in the tunnel structure cryptomelane did not
change the charge of the framework [19]. We have carried out mag-
netic measurements to verify the Sn4+ substitution. Results show a
decrease of the magnetic moment upon Sn doping, from 4.23 to 3.9
ꢂB that indicates the decrease of Mn3+ concentration in the MnO2
lattice.
3+
The electrochemical tests were performed using
a
multichannel
potentiostatic–galvanostatic system VMP (Perkin Elmer Instruments, USA).
The cathode mixture for the fabrication of the positive electrode was prepared by
mixing 80 wt.% of the active material with 10 wt.% of super P Li carbon (TIMCAL)
and 10 wt.% of polyvinylidene fluoride binder (PVDF), dissolved in N-methyl
pyrrolidone (NMP). For the electrochemical studies, about 10 mg of this mixture
was pressed at a pressure of 5 tons on an aluminum mesh and dried at 100 C for
®
◦
1
h in a vacuum oven. Swagelok-type cells were assembled in an argon filled dry
−
1
box with Li-foil as anode and glass–fiber separator soaked with 1 mol L LiPF6 in
EC–DMC (1:2) as organic electrolyte. Galvanostatic charge–discharge cycling was
carried out at C/15 rate in the voltage range 1.5–4.0 V vs. Li/Li .
+
Table 1
Lattice parameters of P–MnO2 and Sn–MnO2 samples.
3
. Results and discussion
Sample
Lattice parameters
3.1. Structure and morphology
a (Å)
c (Å)
V (Å3)
P–MnO2
Sn–MnO2
9.85(6)
9.86(1)
2.86(1)
2.86(1)
277.9
278.239
Fig. 1 shows the XRD patterns of P–MnO2 (a) and Sn–MnO2
b) samples. The diagram of pure ␣-MnO2 is composed of rather
(

A.M. Hashem et al. / Journal of Alloys and Compounds 509 (2011) 9669–9674
9671
Fig. 2. SEM and TEM images of (a and c) P–MnO2 and (b and d) Sn:MnO2 oxides, respectively.
The relatively broad diffraction peaks of the XRD patterns indi-
cate small particle size for MDOs powders. The coherence length,
Lc, has been estimated using Scherrer formula
Sn doped MnO2 powders display a rod-like morphology with par-
ticles 15 nm thick and 200 nm length. Note that the diameters of
these nanorods observed by SEM are very close to the particle size
calculated by Eq. (1). Obviously, these results show that the Sn dop-
ing alters the shape of the particles. This could be attributed to the
Kꢀ
Lc =
(1)
ˇ cos ꢁ
replacement of Sn4+ for Mn and the increasing amount of K ions
in the (2 × 2) tunnels. It has been pointed out by several workers
that the particle morphology is strongly dependent on the synthetic
conditions. For instance, the direct reaction of potassium perman-
ganate with fumaric acid via a mild hydrothermal route favors the
growth of ␣-MnO2 nanowires or nanorods [21–24]. Portehault et al.
have shown that the monocrystalline primary nanorods are well
ordered together at low pH on the mesocrystal [23].
3+
+
where ˇ is the full width at half maximum (FWHM) in radians, the
constant is K = 0.9, ꢀ is the wavelength of the X-ray, ꢁ is the corre-
sponding Bragg angle. We find Lc = 18 ± 0.5 nm that corresponds to
the particle size, L, estimated from the SEM images (see below).
Fig. 2a and b represents the SEM images of P–MnO2 and
Sn–MnO samples. With the magnification used for the SEM inves-
2
tigations, the two samples have similar non-uniform spongy-like
structure showing very small particles, L < 100 nm. It is shown that
particles have the tendency to agglomerates. The TEM images of
the same samples show difference in the morphology (Fig. 4c and
d). A big difference in the shape of particles is observed. Spherical-
3.2. Thermal stability
The thermal behaviors of P–MnO2 and Sn–MnO2 are viewed
in Fig. 3 by the thermogravimetric curves recorded in the tem-
like particles with size ca. 30 nm were observed for P–MnO , while
2

9
672
A.M. Hashem et al. / Journal of Alloys and Compounds 509 (2011) 9669–9674
a
0
0
0
0
0
.8
.6
.4
.2
.0
1
00
9
8
7
6
0
0
0
0
-
0.2
-0.4
0.6
Ta
P-MnO2
-
Sn-MnO2
1
.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
Potential (V vs. Li/Li+)
2
00
400
600
Temperature (°C)
800
1000
b
0.8
0.6
Fig. 3. Curves of the thermogravimetric analysis for P–MnO2 and the Sn–MnO2
oxides.
0
0
0
.4
.2
.0
◦
◦
perature range 30–1000 C in air at 10 C/min heating rate. There
is almost no difference in the thermal behaviors of both oxides
excepted a small change in the vicinity of 900 C. Both oxides
showed thermal stabilization due to high percent of K ions
detected by chemical analysis. A quantity of about 7 wt.% K ions
was evaluated in both samples. Thus the crystal chemistry of
our samples synthesized via hydrothermal route is K .07MnO2.
The conversion of MnO2 to Mn O3 starts at ca. 700 C in both
◦
-
0.2
-0.4
0.6
+
+
-
0
◦
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
2
oxides, while further thermal decomposition of Mn O to Mn O4
expected to occur above 1000 C (out of the range of our measure-
ments).
Potential (V vs. Li/Li )
+
2
3
3
◦
Fig. 4. Cyclic voltamograms of (a) P–MnO2 and (b) Sn–MnO2 using a scan rate
+
0
.05 V/s in the voltage range 1.5–4.0 V vs. Li/Li .
It could be remarked that the thermal decomposition reac-
tions of MnO2 containing very low content of K+ ions occurred in
two steps as reported in [29]. The first decomposition of MnO2 to
In the case of stoichiometric MnO2 all Mn4+ cations can
◦
Mn O occurs at the range of 500–600 C. The second decompo-
2
3
be reduced to Mn3+ giving a theoretical gravimetric capacity
308 mAh/g. The cell with P–MnO2 delivers a discharge capacity of
1
◦
◦
sition of Mn O to Mn O4 occurred in the range of 900–1000 C.
In this study, the decomposition to Mn O3 starts at above 770 C
2
3
3
2
−
1
60 mAh g at the first cycle. It seems that the presence of large
that means a relatively high concentration of potassium ions
which functions as structural stabilization. Finally, as shown in
+
+
bulky cations, e.g. K , impede the easy diffusion of Li ions in the
tunnels of the ␣-MnO2 framework. At the first order, the number of
available sites for foreign ions inserted into the host and the number
of available electronic states are the limiting factors for discharge
capacity. The cell with Sn-doped cryptomelane delivers 120 mAh/g
at the first cycle. The lower capacity could be due to the lower
fraction of non electroactive Sn4+ ions. The lower initial capacity
observed in case of Sn–MnO2 could have several origins: (i) the
presence of K+ cations, which block the ionic motion via the large
2 × 2 channel in the cryptomelane structure, (ii) the replacement of
Sn for Mn ions, which impede the electronic conduction and (iii) the
Fig. 3, the same function occurs with a removal of Mn3+ by Sn
4+
ions.
3.3. Electrochemical tests
Electrochemical properties have been investigated in Li cell with
−
1
1
mol L
LiPF6 in EC–DMC (1:2) as organic electrolyte. Fig. 4a
and b show the cyclic voltammograms of P–MnO2 and Sn–MnO2,
respectively. The reduction peaks (discharge process) are observed
at ca. 2.25 and 2.20 V for P–MnO2 and Sn–MnO , respectively. In
grain morphology of ␣-MnO electrodes, which plays an important
2
2
both samples the reduction peak occurring at the first discharge is
shifted to higher potentials in the second and forthcoming cycles.
The change in peak position upon cycling has been attributed to
a structural evolution in ␥-MnO2 [25]. The marked change of the
reduction voltammogram from first to second reduction is still
observed as in other MDOs. It has been attributed to the reduc-
tion of surface states mainly in view of its high kinetic reversibility
role in the electrochemical behavior of Li//␣-MnO2 rechargeable
cells. Shao-Horn et al. [27] have demonstrated that crystals with
a small aspect ratio have a large electrochemically active surface
because the large exposed (2 × 2) tunnel cross-sectional area per
unit volume available for lithium insertion.
The discharge capacities vs. the cycle number for P–MnO2 and
Sn–MnO2 are displayed in Fig. 6. The capacities at the 40th cycle
are about 65 and 80 mAh/g for the P–MnO2 and Sn–MnO2 sam-
ples, respectively. Sn doped MnO2 oxide retained about 71%, while
P–MnO2 retained only 40.2% from their initial capacities at 40th
cycle. The fading capacity of the Li//P–MnO2 cell is much higher
than that observed in Li//Sn–MnO2 cell. Better capacity retention
and rechargeability was observed for Sn–MnO2 at the expanse of
its initial capacity. So, we can conclude that the doping process has
a good impact on the electrochemical performance.
[
4]. Brown and Altermatt have shown that a monolayer of water
at the surface of ␥-MnO2 is responsible for the peak at ca. 0.1 V vs.
Hg/HgO [26].
The discharge–charge profile of Li//Manganese dioxide cells for
both P–MnO and Sn–MnO are shown in Fig. 5a and b. It is obvious
2
2
that the cell with Sn doped MnO2 displays better rechargeability
than cell built with P–MnO as positive electrode; the latter exhibits
2
higher capacity fading.

A.M. Hashem et al. / Journal of Alloys and Compounds 509 (2011) 9669–9674
9673
of Mn3+ Jahn-Teller ions. Note that the stabilization of the MnO2
a
4.5
(
2 × 2) tunnel framework has been pointed out by the Thackeray’s
4.0
3.5
3.0
2.5
2.0
1.5
1.0
group [27], who observe a structural instability to chemical lithia-
tion of ␣-MnO . Also, the capacity loss in the first cycle is in most
2
cases due to the shaping of the electrode. It seems that it occurred in
our studies. The porosity plays an important role for the ion transfer
at the interface.
The second reason for this degradation in the capacity in
P–MnO upon cycling may be related to significant amount of
2
2+
2+
Mn ions formed at the end of the discharge. The Mn ions
can be dissolved into the electrolyte causes significant increase
in the capacity fading of lithium manganese oxides [15,28]. It
seems that these two drawbacks were alleviated after doping by
Sn. However, we got better capacity retention and better recharge
1
2
ability for Sn–MnO2 in comparison with P–MnO . This remarkable
2
0
40
80
120
160
improvement in electrochemical behavior observed for Sn–MnO2
is attributed to stabilization in the structure and/or enhancement of
electrical conductivity after doping with Sn. In previous work [14],
Capacity (mAh/g)
b
4.5
we reported that doping MnO with Sn improves both the structure
2
stability and electrical conductivity of ␣-MnO . Thermal stabiliza-
2
4.0
3.5
3.0
2.5
2.0
1.5
1.0
tion and good electrical conductivity have positive effects on the
behavior of ␣-MnO2 in alkaline batteries [14]. The same effect was
observed here in this study in the case of lithium battery.
4. Conclusion
In this work, nanosized manganese dioxide and its tin-doped
product have been prepared by wet-chemical method. XRD analysis
confirmed the cryptomelane-like structure of MnO2 and showed
that no extra peaks related to tin metal or impurities were observed
for MnO2 oxides after doping. The net effect of Sn doping observed
from TEM images is a change in the morphology of MnO2 particles
1
2
0
20
40
60
80
100
120
140
that exhibit a nanorod-like shape. Doping MnO by Sn improved the
2
capacity retention and the rechargeability of MnO2 at the expanse
of the initial capacity.
Capacity (mAh/g)
Fig. 5. Galvanostatic discharge/charge of (a) P–MnO2 and (b) Sn–MnO2. Data were
recorded at C/15 rate in the voltage range 1.5–4.0 V vs. Li/Li .
+
Acknowledgments
The capacity loss observed in the first cycles in P–MnO2 is
attributed to the small amount of lithium ions inserted in the MnO2
electrode and cannot be easily removed from the structure. Simi-
Financial support from the Deutsche Forschungsgemeinschaft
(DFG) within the Research Collaborative Centre 595 on “Electrical
Fatigue in Functional Materials” is gratefully acknowledged.
lar effect, but with smaller amplitude, occurs for Li//Sn–MnO . In
2
spite of this drawback, presence of tin results in an enhancement
of the structural stability, which can be attributed to the reduction
References
[
[
1] W. Kim, K. Chung, Y. Choi, Y. Sung, J. Power Sources 115 (2003) 10.
2] W. Dreyer, J. Jamnik, C. Guhlke, R. Huth, J. Mo sˇ kon, M. Gaber sˇ cek, Nat. Mater. 9
(
2010) 448.
1
1
1
1
60
40
20
00
[
3] Y.F. Shen, R.P. Zerger, R.N. Guzman, S.L. Suib, L. McCurdy, L.I. Potter, C.L. O’Young,
Science 260 (1993) 511.
4] Y. Chabre, J. Pannetier, Prog. Solid State Chem. 23 (1995) 1.
5] E. Machefaux, A. Verbaere, D. Guyomard, J. Power Sources 157 (2006) 443.
[6] T. Brousse, P.-L. Taberna, O. Crosnier, R. Dugas, P. Guillemet, Y. Scudeller, Y.
Zhou, F. Favier, D. Belanger, P. Simon, J. Power Sources 173 (2007) 633.
7] G.V. Sokol’skii, S.V. Ivanov, N.D. Ivanova, E.I. Boldirev, J. Electrochem, Powder
Metall. Met. Ceram. 45 (2006) 3.
[
[
[
Sn-MnO2
[8] M.Y. Liao, J.M. Lin, J.H. Wang, C.T. Yang, T.L. Chou, B.H. Mok, N.S. Chong, H.Y.
Tang, Electrochem. Commun. 5 (2003) 312.
9] C.S. Johnson, J. Power Sources 165 (2007) 559.
8
0
0
0
0
[
6
4
2
[10] S.L. Suib, Curr. Opin, Solid State Mater. Sci. 3 (1998) 63.
P-MnO2
[
[
[
[
11] S. Ching, J.L. Roark, N. Duan, S.L. Suib, Chem. Mater. 9 (1997) 750.
12] H. Malankar, S.S. Umare, K. Singh, J. Mater. Lett. 63 (2009) 2016.
13] Y. Lu, L. Yang, M. Wei, Y. Xie, T. Liu, J. Solid State Electrochem. 11 (2007) 11.
14] A.M.A. Hashem, H.A. Mohamed, A. Bahloul, A.E. Eid, C.M. Julien, Ionics 14 (2008)
7
.
[
15] H.M. Abuzeid, A.M. Hashem, N. Narayanan, H. Ehrenberg, C.M. Julien, Solid State
Ionics 182 (2011) 108.
0
0
5
10
15
20
25
30
35
40
45
[16] C.S. Johnson, D.W. Dees, M.F. Mansuetto, M.M. Thackeray, D.R. Vissers, D.
Argyriou, C.-K. Loong, L. Christiensen, J. Power Sources 68 (1997) 570.
Cycle number
[
[
17] R. Liu, S.B. Lee, J. Am. Chem. Soc. 130 (2008) 2942.
18] A. Bahloul, B. Nessark, F. Habelhames, C.M. Julien, Ionics 17 (2011) 239.
Fig. 6. Discharge capacity vs. cycle number of P–MnO2 and Sn–MnO2 at C/15 rate
in the voltage range 1.5–4.0 V vs. Li/Li .
[19] J. Cai, J. Liu, W.S. Willis, S.L. Suib, Chem. Mater. 13 (2001) 2413.
[20] M.K. Gulbinska, S.L. Suib, J. Power Sources 196 (2011) 2149.
+

9
674
A.M. Hashem et al. / Journal of Alloys and Compounds 509 (2011) 9669–9674
[
[
[
21] Y. Liu, M. Zhang, J. Zhang, Y. Qian, J. Solid State Chem. 179 (2006) 1757.
22] L. Li, Y. Pan, L. Chen, G. Li, J. Solid State Chem. 180 (2007) 2896.
23] D. Portehault, S. Cassaignon, E. Baudrin, J.P. Jolivet, Chem. Mater. 19 (2007)
[25] L.I. Hill, A. Verbaere, D. Guyomard, J. Power Sources 119–121 (2003) 226.
[26] I.D. Brown, D. Altermatt, Acta Cryst. B 41 (1985) 244.
[27] Y. Shao-Horn, S.A. Hackney, C.S. Johnson, M.M. Thacheray, J. Electrochem. Soc.
145 (1998) 582.
5
410.
[
24] Y. Khan, S.K. Durrani, M. Mehmood, M.R. Khan, J. Mater. Sci. (2011),
[28] D.H. Jang, Y.J. Shin, S.M. Oh, J. Electrochem. Soc. 143 (1998) 2204.
[29] T. Ohzuku, I. Tari, T. Hirai, J. Electrochim. Acta 27 (1982) 1049.
doi:10.1557/jmr.2011.138.