Facile synthesis of MOF-derived Mn2O3 hollow microspheres as anode materials for lithium-ion batteries

Article abstract of DOI:10.1039/c6ra19334j

In this article, we report a facile and scalable route for the fabrication of Mn₂O₃ hollow microspheres by direct pyrolysis of Mn-based metal-organic frameworks at 450 °C with a heating rate of 10 °C min^-1 in air. The effect of the heating rate on the morphology of the final samples has been also investigated. When evaluated as an anode material for LIBs, these Mn₂O₃ microspheres exhibited a reversible and stable capacity of 582 mA h g^-1 after 60 cycles at a current density of 100 mA g^-1. The improved capacity and excellent cycling stability of the as-prepared Mn₂O₃ microspheres could be attributed to the porous hollow structures, which can reduce diffusion length for lithium ions and electrons, and also can enhance structural integrity for buffering the volume expansion during the discharge/charge processes.

Full text of DOI:10.1039/c6ra19334j

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Facile Synthesis of MOF-derived Mn O Hollow
2
3
Microspheres as Anode Materials for Lithium-ion
Batteries
Fangcai Zheng,a, b∗ Shihao Xu, Zhichen Yin , Yuanguang Zhang and Lu Lu
a
a
a
**
a
Anhui Provincial Laboratory of Optoelectronic and Magnetism Functional Materials,
School of Chemistry and Engineering, Anqing Normal University, Anqing 246011,
PR China
b
High Magnetic Field Laboratory, Hefei Institute of Physical Science, Chinese
Academy of Science, Hefei 230031, PR China
ABSTRACT
In this article, we report a facile and scalable route for the fabrication of Mn O3
2
hollow microspheres by direct pyrolysis of Mnꢀbased metalꢀorganic frameworks at
o
o
4
50 C with a hating rate of 10 C/min in air. The effect of the heating rate on the
morphology of the final samples has been also investigated. When evaluated as an
anode material for LIBs, these Mn
2
O
3
microspheres exhibited a reversible and stable
ꢀ
1
ꢀ1
capacity of 582 mAh g after 60 cycles at a current density of 100 mA g . The
2 3
improved capacity and excellent cycling stability of the asꢀprepared Mn O
microspheres could be attributed to the porously hollow structures, which can reduce
diffusion length for lithium ions and electrons, and also can enhance structural
integrity for buffering the volume expansion during the discharge/charge processes.
Key Words: MOFs; Mn O ; Hollow structures; Lithiumꢀion batteries.
2
3
Introduction
2 2 3 3 4
Recently, manganese oxides (such as MnO, MnO , Mn O and Mn O ) are believed to
be the most promising alternative anode materials for LIBs because of their
earthꢀabundance, low cost, high specific theoretical capacity, and environmental
1
ꢀ9
benignity. Furthermore, these Mnꢀbased oxides exhibit higher output voltage and
higher energy density due to their low operating voltages (1.3ꢀ1.5 V for lithium
**
∗
zfcai@mail.ustc.edu.cn lulu19861117@126.com
1

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1
0
ꢀ1
extraction). Among them, Mn
considered to be potential anode materials for LIBs. However, it has demonstrated
that the Mn electrode exhibited poor cycling stability during the discharge/charge
processes. The Mn electrode easily suffers from the volume expansion,
2 3
O has a high capacity of 1018 mAh g and thus is
11
2
O
3
1
2
2
O
3
aggregation, and intrinsically low electrical conductivity during the discharge/charge
processes, resulting in rapid capacity fading. As a consequence, several strategies
2 3
have been used to solve the aforementioned problems for the Mn O electrode. The
mostly used one is to synthesize Mn with porous and hollow structures, in which
2 3
O
vacant space provided by the structure can effectively accommodate the volume
change and structural stain, shorten the diffusion path of lithium ions and electrons,
and enlarge the contact area between the active materials and electrolyte during the
13ꢀ16
discharge/charge processes.
However, the synthesis of Mn O hollow structures
2 3
usually involves tedious and complicated steps, expensive sacrificial templates, or
1
2
timeꢀconsuming solvothermal reactions in autoclaves. Thus, it is desirable to
develop simple, scalable and economic approaches to synthesize Mn O with hollow
2
3
structures as anode materials for highꢀperformance LIBs.
Metalꢀorganic frameworks (MOFs) have attracted extensive research interest
17ꢀ19
because of their diverse architectures and high surface area.
It has been
demonstrated that MOFs can be used as promising templates or precursors to fabricate
2
1ꢀ24
porous nanostructured materials via thermolysis.
obtained Fe microboxes through direct calcination of prussian blue Fe
in air. Additionally, MOFs containing organic linkers can be also used as templates
For example Lou et al. has
2
O
3
4
6 3
[Fe(CN) ]
25
26
or precursors to develop a new class of porous functional materials. For example,
Cho et al. has used MOFs as a sacrificial template to fabricate several hollow and
multiꢀballꢀinꢀball hybrid metal oxides by taking advantage of their unique reactivity
27
and thermal behavior. Yan and coꢀworkers synthesized hollow silica nanocages
28
using nanoscale MOFs as a template. It was reported that the polyhedronꢀlike and
29, 30
nanobarꢀlike Mn
2
O
3
have been fabricated with using MOFs as a template.
Despite
the progress achieved to date, research on the facile and scalable synthesis of hollow
3
1, 32
inorganic functional materials from MOFs is still in its very early stage.
Moreover,
2

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2 3
there has been rare success in fabricating Mn O hollow microspheres with
hierarchical structures due to additional difficulties from the lack of a proper MOF
precursor. It is hence highly desirable to develop novel synthesis protocols and
2 3
concepts to prepare Mn O hollow microspheres with hierarchical structures through
direct decomposition of rationally designed MOFs precursors.
2 3
In this article, we report a facile and scalable route for the fabrication of Mn O
hollow microspheres by direct pyrolysis of Mnꢀbased metalꢀorganic frameworks
o
o
(
denoted as MnꢀBTC) at 450 C with a hating rate of 10 C/min in air. Moreover, a
large number of O and C atoms uniformly dispersed in the MnꢀBTC crystal structure
can be also oxidized into gaseous molecules and escaped from the structure during the
annealing process, which finally leads to porous structure. Furthermore, the effect of
the heating rate on the morphology of the final samples has been also investigated.
Combining the advantage of hollow hierarchical structures and nanopores within their
structures, the asꢀprepared Mn
lithiumꢀstorage performance.
Experimental Section
2
O
3
hollow microspheres exhibited improved
Material preparation
All chemicals are of analytical grade, and were used without any further
purification. Firstly, Mn(CH COO)·4H O (49 mg) and PVP (Kꢀ30, 0.3 g) were
dissolved in the mixed solution of C OH and H O (5/5 ml) system under agitated
stirring to give a transparent solution. Secondly, the mixed solution of C OH/H
5/5 ml) containing trimesic acid (90 mg) was added to the above solution slowly and
3
2
2
H
5
2
H
2 5
2
O
(
regularly with a syringe (10 ml). After 10 min, the resulting solution was incubated at
room temperature without any interruption for 24 h. The resulting white precipitates
were collected by centrifugation, washed with ethanol threel times, and finally dried
o
in an oven at 60 C. The resulted samples with different morphologies were
o
successfully obtained by thermal decomposition of MnꢀBTC precursors at 450 C for
2
h with different heating rates in air.
Material characterization
The powder Xꢀray diffraction (XRD) patterns of all samples were recorded with
3

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a Xꢀray diffractometer (Japan Rigaku D/MAXꢀγA) equipped with CuꢀKα radiation (λ
1.54178 Å). Field emission scanning electron microscopy (FEꢀSEM) images were
=
collected on a JEOL JSMꢀ6700 M scanning electron microscope. Transmission
electron microscopy (TEM) images were taken on Hitachi Hꢀ800 transmission
electron microscope using an accelerating voltage of 200 kV, and highꢀresolution
transmission electron microscope (HRTEM) (JEOLꢀ2011) was operated at an
acceleration voltage of 200 kV. The specific surface area was evaluated at 77 K
(Micromeritics ASAP 2020) using the BrunauerꢀEmmettꢀTeller (BET) method, while
the pore volume and pore size were calculated according to the
BarrettꢀJoynerꢀHalenda (BJH) formula applied to the adsorption branch. XPS
measurements were performed on a VGESCALAB MKII Xꢀray photoelectron
spectrometer with an MgKa excitation source (1253.6 eV). Thermogravimetric
analysis (TGA) was carried out using a Shimadzuꢀ50 thermoanalyser under air flow.
Electrochemical measurements
The electrochemical performance of the Mn O hollow microspheres was
2
3
6
examined by using CR 2032 coinꢀtype cells versus Li with 1 M LiPF in the ethylene
carbonate and diethyl carbonate (EC/DEC = 1:1, v/v) as the electrolyte. To prepare a
working electrode, the asꢀprepared samples (80 wt%), conductive material (acetylene
black, 10 wt%), and binder (polyvinylidene fluoride (PVDF), 10 wt%) were mixed in
NMP, and the slurry was then pasted onto the surface of a copper foil current collector.
2
The loading mass of an electrode is approximately 1 mg (1 mg/cm ). The cells were
assembled in an argonꢀfilled glove box with both the moisture and the oxygen content
bellow 1 ppm (Mikrouna, Super (1220/750/900)). The Liꢀstorage performance was
measured by a galvanostatic dischargeꢀcharge method in the voltage range between
0
.01 and 3.0 V on a battery test system (Neware CTꢀ3008W).
Results and discussion
4

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2 3
Figure 1. Schematic illustration for the formation of Mn O hollow microspheres.
2 3
The strategy for the synthesis of Mn O hollow microspheres with hierarchical
structures is schematically depicted in Figure 1. First, an improved method was
explored for synthesizing highly uniform MnꢀBTC microspheres at room temperature.
A subsequent thermal annealing process was then used to transform of the MnꢀBTC
2 3
precursor into Mn O hollow microspheres. Compared with the wildly used solutionꢀ
or templateꢀbased methods for creating hollow structures, the present solidꢀstate
approach provides a more facile route for the largeꢀscale synthesis of hierarchically
hollow microspheres.
Figure 2. (a, b) FESEM and (c, d) TEM images of MnꢀBTC precursors prepared at
room temperature.
As shown in Figure 2a, it can be clearly observed that the precursor is composed
of a great deal of microspheres with an average size of approximately 2 µm and
exhibits rough surface. A close inspection (as shown in Figure 1b) reveals that the
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microspheres are in fact assembled by smallꢀsize polyhedrons without serious
aggregation. As shown in Figure 3, Xꢀray power diffraction (XRD) was also used to
characterize the structure of the precursor, and the results confirmed the successful
33
synthesis of the targeted MnꢀBTC, according to the results reported by Lin’s group.
In addition, the precursor was further characterized by thermogravimetric analysis
(TG) in air. As shown in Figure 3b, the first step of weight loss started from room
o
temperature to 200 C, which can be attributed to the removal of physisorbed moisture
o
or solvent molecules. A steep weight loss at 420 C corresponds to the decomposition
of the host frameworks (MnꢀBTC). In order to ensure calcination of the MnꢀBTC
o
precursor completely, a temperature of 450 C is chosen as the calcination
temperature for the complete conversion of the MnꢀBTC precursor to Mn
Additionally, various heating rates was also applied to obtain the final samples with
different morphologies and structures, hereinafter designated as Mn ꢀ2R,
ꢀ2R” denotes a sample heated
2 3
O .
2
O
3
Mn
2
O
3
ꢀ5R, and Mn
2
O
3
2 3
ꢀ10R, respectively(e.g., “Mn O
o
o
at 450 C in air with a heating rate of 2 C/min).
Figure 3. (a) XRD pattern and (b) thermogravimetric analysis (TGA) curves of
MnꢀBTC precursors.
The structure of the calcinated samples was further analyzed by XRD, and the
results are shown in Figure 4. All of the peaks of the three samples can be indexed as
the cubic Mn O (JCPDS card no. 41ꢀ1442, lattice constant α = 9.409 Å). Therefore, it
2
3
2 3
can be concluded that the MnꢀBTC precursor was completely transformed into Mn O .
However, the crystallinity of the asꢀprepared samples was improved with decreasing
the heating rate. In order to get more information about the purity and chemical
composition, the Mn
2
O
3
ꢀ10R was Xꢀray photoelectron spectroscopy (XPS). The
6

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results confirm the coꢀexistence of Mn and O in the structure, indicating high purity
of the asꢀprepared sample. Figure 5 exhibits highꢀresolution XPS spectrum of Mn 2p.
The Mn 2p orbital region exhibits the binding energies of Mn 2p1/2 and Mn 2p3/2
3
4
peaks at 653.1 and 641.2 eV, respectively. The splitting energy of 1.9 eV between
3
5
Mn 2p1/2 and Mn 2p3/2 is consistent with that of Mn O . As shown in Figure S2b, the
2
3
O 1s peaks at 529.6 and 531.0 eV can be attributed to the crystal lattice oxygen
36
2 3
(OMnꢀOꢀMn) and surface hydroxyl groups (OHꢀO) in the Mn O , respectively.
2 3
Figure 4. XRD patterns of asꢀprepared Mn O samples obtained at different
calcinated temperatures.
Figure 5. (a) Mn 2p and (b) O 1s XPS spectra of the asꢀprepared Mn O ꢀ10R.
2
3
2 3
The conversion of the MnꢀBTC precursor to Mn O was further investigated by
FESEM and TEM, respectively. Figure 6a,b exhibit FESEM images at different
magnifications of Mn O ꢀ10R. It can be clearly observed that Mn O ꢀ10R exhibits the
2
3
2
3
pristine spherical shape with a porously hollow structure, and the surface of
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Mn
2 3
O ꢀ10R becomes rough, which can be attributed to the release of gaseous
molecules (e.g. CO , H O) from the decomposition of MnꢀBTC during the calcination
2
2
2 3
process. Figure 4c shows a typical TEM image of Mn O ꢀ10R, and the sharp contrast
between the centers and edges of spherical particles demonstrates a hollow structure
for Mn O ꢀ10R. The hollow structure is mainly generated by heterogeneous
2
3
contraction because of nonꢀequilibrium heat treatment. The MnꢀBTC precursor is not
homogeneously heated during the heating process. Therefore, it exits a temperature
gradient (△T) along the radial direction, resulting in the formation of a shell at the
37
surface of the asꢀprepared precursor. This shell is relatively rigid and can prevent the
further contraction of the microspheres. At the same time, two forces of opposite
2 3
directions exert at the interface of MnꢀBTC core and Mn O shell. The contraction
force (F ) facilitates the inward shrinkage of the core, while the adhesion force (F )
c
a
induces the outward contraction. Moreover, a large amount of gaseous molecules (e. g.
CO , H O) released from the decomposition of MnꢀBTC core can also decrease F
Therefore, with a large △T and numerous gaseous molecules released, F would
2
2
c
.
a
29, 34
exceed F
formation of Mn
Mn under various heating rates. At a low heating rate of 5 and 2 C min , the
c
, resulting in hollow and porous structure of the asꢀprepared Mn
2 3
O .
The
2
O
3
was investigated in detail by carrying out the decomposition of
o
ꢀ1
2
O
3
resulted sample show a broken hollow structure (SEM and TEM, Figure 7) with an
improved crystallinity (XRD, Figure 4). In addition, a representative highꢀresolution
2 3
TEM (HRTEM) image of Mn O ꢀ10R is shown in Figure 4d, the measured interplanar
distance of a randomly selected single nanocrystal is 0.27 nm, which is in good
agreement with the (222) plane of Mn
2
3
O , thus confirming the XRD analysis.
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Figure 6. (a, b) FESEM images at different magnifications, (c) TEM image, and (d)
HRTEM image of Mn ꢀ10R.
2
O
3
2 3
Figure 7. (a, b) SEM and TEM images of Mn O ꢀ5R and (c, d) SEM and TEM
images of Mn ꢀ2R.
2
O
3
To further investigate the specific surface area and the porous characteristic of
the asꢀobtained samples, nitrogen adsorptionꢀdesorption isotherms were measured at
7
7K (Figure 8). The all isotherm profiles of the samples can be categorized as type
curves with a H3 hysteresis loop at the relative pressure of 0.8ꢀ1.0, thus implying
Ⅱ
the existence of a large number of mesopores in the samples. Pore characteristics of
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the asꢀobtained samples are shown in Table 1. It is noted that the special surface area
2
ꢀ1
2
ꢀ1
of Mn O ꢀ10R (38.5 m g ) is higher than other two samples (24.9 m g for
2
3
2 3 2 3
Mn O ꢀ2R and 34.2 for Mn O ꢀ5R) obtained at relatively lower heating rates. In
addition, the pore size distribution curve (the inset in Figure 8) obtained using
BarrettꢀJoynerꢀHalenda (BJH) method reveals the pore size with a relatively wide
distribution, which is consistent with the hollow structure observed by TEM. Based
on previous reports, the porous structure might facilitate the fast transfer of lithium
ions and electrons because the nanopores and interconnections provide a more
38
favorable path for penetration and transportion of electrolytes. Therefore, it is
2 3
further suggested that the asꢀprepared Mn O ꢀ10R might be an excellent anode
material for LIBs.
Figure 8. Nitrogen adsorptionꢀdesorption isotherms and the corresponding pore size
distribution (inset) of the resulted samples.
Table 1. Summary of textural parameters obtained from nitrogen adsorption analysis.
Total pore
volumes
Average
pore size
(nm)
S
BET
Sample
ꢀ2
ꢀ1
(
m g )
3
ꢀ1
(
cm g )
0.1113
0.1689
0.1541
Mn
Mn
2
2
O
O
3
3
ꢀ2R
ꢀ5R
24.9
34.2
38.5
17.9
19.8
16.0
Mn
2
O
3
ꢀ10R
10

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To study the performance and differentiation of the asꢀprepared Mn
2
O
3
samples
as anode materials of LIBs, the lithiumꢀstorage properties were investigated using the
standard Mn /Li halfꢀbattery configuration. Figure 9a shows representative cyclic
voltammetry (CV) curves of the Mn ꢀ10R electrode for the initial three cycles at a
2
O
3
2
O
3
ꢀ1
scan rate of 0.1 mV s in the voltage range of 0.0ꢀ3.0 V vs. Li. In the first cycle, the
two reduction peaks centered at approximately 1.2 and 0.9 V could be associated with
3
+
2+
the reduction of Mn to Mn and an irreversible reaction related to the lithium ion
7
insertion of the conductive agent acetylene black, respectively. Another main peak
2
+
centered at approximately 0.2 V can be attributed to the further reduction of Mn to
0
Mn along with the formation of Li
2
O and the formation of a solid electrolyte
39, 40
interface (SEI) film.
For the first anodic process, one broad peak locates at
0
2+ 11
approximately 1.2 V, indicating the oxidation of Mn to Mn . From the second
cycle onwards, a shifting of the peak position is observed for the cathodic process,
and the intensity of the peak drops significantly in the subsequent cycles relative to
that in the first one, indicating the occurrence of some irreversible reactions with the
1
1, 39, 40
decomposition of SEI film.
Based on above analysis and previous reports, the
microspheres are believed to proceed as
lithium storage mechanism of the Mn
2 3
O
41, 42
follows:
+
ꢀ
2
2
2
Li + 3 Mn
2
O
3
+ 2 e → 2 Mn
3
O
4
+ Li
2
O
(1)
+
ꢀ
Li + Mn
3
O
4
+ 2 e → 3 MnO + Li
2
O
(2)
+
ꢀ
Li + MnO + 2 e → Mn + Li O
(3)
2
+
ꢀ
Mn + x Li
2
O ↔ 2x Li + MnO
x
+ 2x e (1.0 < x <1.5) (4)
Figure 9b shows the charge/discharge profiles of the Mn
2
O
3
ꢀ10R microspheres
ꢀ1
ꢀ2
as anode materials for LIBs at a current density of 100 mA g (0.08 mA cm ) in a
potential window between 0.01 and 3.0 V. The general features of the
charge/discharge profiles are consistent with other reported Mn
2
O
3
ꢀbased anodes that
In the first discharge profile, the voltage drops from 3.0 V
to a voltage plateau at approximately 1.6 V, which can be attributed to the reduction of
7, 42
undergo redox reactions.
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Mn
approximately 0.4 V with the formation of a new plateau. This can be associated to
the reduction of Mn to MnO expressed by Equation (2). Lastly, the slow voltage
drops to 0.01 V, expressed by Equation (3), indicating the complete reduction from
2 3 3 4
O to Mn O expressed by Equation (1). The voltage then further decreases to
3
O
4
2
+
0
Mn to Mn . The initial discharge and charge capacities are found to be 3404 and
ꢀ1
1
559 mAh g , respectively, leading to an initial coulombic efficiency of
approximately 46 %. The relative low initial coulombic efficiency can be attributed to
the formation of SEI film, the decomposition of electrolyte, and the reduction of
43
adsorbed impurities on Mn
2 3
O surface. This phenomenon also matches well with the
CV results that the cathodic peaks are present in the first scan while absent afterward.
Figure 9. (a) Cyclic voltammetry measurements on Mn
cycles. The voltage range was from 0.0 to 3.0 V at a scan rate of 0.1 mV s . (b)
Dischargeꢀcharge curves of Mn ꢀ10R. The cell was test for 60 cycles between 0.1
2 3
O ꢀ10R during the first three
ꢀ1
2
O
3
ꢀ1
ꢀ2
mV and 3.0 V under a current density of 100 mA g (0.08 mA cm ). (c) Cycleꢀlife
performance of Mn O ꢀ10R. (d) Rate capability test for the Mn O ꢀ10R at various
2
3
2
3
ꢀ1
current densities (100ꢀ1600 mA g ).
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2 3
To evaluate the cycling stability, the Mn O ꢀ10R were charged and discharged at
ꢀ1
+
a current density of 100 mA g over the voltage range of 0.01 ꢀ 3.0 V vs Li/Li , and
the cycling performance is exhibited in Figure 9c. After 60 cycles, the discharge
ꢀ1
capacity is retained at 582 mAh g . Moreover, from the 15th cycle onwards, the
Mn O ꢀ10R sample shows the fascinating cycling stability with the coulombic
2
3
efficiency over 97 %. Figure 9d exhibits the rate performance of the Mn
2 3
O ꢀ10R
sample by cycling the cell at various current densities. As the current density
ꢀ1
increased from 100 to 200, 400, 600, 800 and 1000 mA g , the capacity decreased
ꢀ1
only from 611, 393, 290, 232, 195 to 160 mAh g , respectively. When the current
ꢀ1
ꢀ1
density was reduced from 1000 to 100 mA g , a capacity of 513 mAh g can be
recovered, which has a trend to increase. Therefore, the asꢀprepared Mn ꢀ10R
2
O
3
sample exhibits an excellent electrochemical performance as an anode material for
LIBs.
Figure 10. (a) Cycleꢀlife performance of Mn
2
O
3
ꢀ5R and Mn
density of 100 mA g (0.08 mA cm ), respectively. (b) The TEM image of
Mn ꢀ10R after charge/discharge processes.
2 3
O ꢀ2R at a current
ꢀ1
ꢀ2
2
O
3
In a control experiment, other two sample obtained at different conditions
ꢀ2R and Mn ꢀ5R) were also investigated as anode materials for LIBs. As
shown in figure 10a, both of them exhibit excellent cycling stability. However,
(Mn
2
O
3
2 3
O
ꢀ1
compared with the capacity of the Mn
2
O
3
ꢀ10R, the lower capacities (369 mAh g for
ꢀ1
Mn O ꢀ2R and 417 mAh g for Mn O ꢀ5R) are retained at a current density of 100
2
3
2
3
ꢀ1
mA g after 60 cycles. Therefore, it is considered that the electrochemical
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performance of Mn
2
O
3
ꢀ2R and Mn
2
O
3
2 3
ꢀ5R is not as good as that of Mn O ꢀ10R
o
o
synthesized at 450 C with a heating rate of 10 C/min. In addition, as shown in figure
1
2 3
0b, the electrode materials (Mn O ꢀ5R) was investigated by TEM and the hollow
microsphere structure can be well retained after charge/discharge processes. The
excellent electrochemical performance of the Mn O ꢀ10R can be explained by its
2
3
unique hollow structure with a variety features. Specifically, the void space within the
hollow microsphere and the hierarchically porous shells provide abound channels and
sites for efficient electrolyte penetration and enhance the contact area between the
electrode and electrolyte. Meanwhile, such hierarchically hollow structures could also
efficiently buffer the large volume changes induced by lithium insertion/extraction.
4
. Conclusions
In summary, we have developed a facile and scalable strategy to synthesize
2 3
Mn O hollow microspheres with hierarchically porous shell structures, which
contains the fabrication of MnꢀBTC spherical template and subsequent oneꢀstep
thermal annealing the template at moderate temperature in air. The effects of the
heating rate on the morphology of the final samples have been also investigated and
the resulted hollow microspheres may undergo a nonꢀequilibrium interꢀdiffusion
process. The resulted unique structure can facilitate the transport of lithium ions and
electrons, and can also alleviate the volume changes during the discharge/charge
2 3
processes, which ensure the improved electrochemical performance of the Mn O
electrode. When evaluated as anode materials for LIBs, the resulting Mn
2
O
3
electrode
ꢀ1
ꢀ1
exhibited a capacity of 582 mAh g after 60 cycles at a current density of 100 mA g .
Furthermore, since MOFs can be synthesized with various compositions and
morphologies, the MOFsꢀderived strategy can be extended to design and synthesis of
other porously hollow metal oxides for applications in highꢀperformance LIBs,
supercapacitors, catalysts, and adsorbents in many scientific disciplines.
Acknowledgments
This work was supported by the National Natural Science Foundation (NSFC,
2
1601003, 21371009), Anhui Provincial Natural Foundation (No. 1608085QB34), the
14

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DOI: 10.1039/C6RA19334J
Scientific Research Foundation of Anqing Normal University (044ꢀ150002021) and
Natural Science Research Key Project of Anhui Provincial Department of Education
(
KJ2016A860).
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