Porous NiO architecture prepared with coordination polymer precursor as a high performance anode material for Li-ion batteries

Article abstract of DOI:10.1039/c5ra15452a

By the calcination of a coordination polymer precursor, a porous flower-like NiO architecture was conveniently synthesized. The electrode fabricated by it exhibited excellent cycling stability and high rate performance in electrochemical tests. The lithium storage could be maintained at ～1000 mA h g^-1 with a high coulombic efficiency (～95%), which is among the best reported results.

Full text of DOI:10.1039/c5ra15452a

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Porous NiO architecture prepared with coordination polymer
precursor as high performance anode material for Li‐ion batteries
†
Received 00th January 20xx,
Accepted 00th January 20xx
An Guo, Yue Li, Kun Liu and Wen‐Juan Ruan*
DOI: 10.1039/x0xx00000x
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By the calcination of coordination polymer precursor, a porous large volume shrinkage and gaseous composites (CO2, H2O, et
flower‐like NiO architecture was conveniently synthesized. The al.) release accompanied with the decomposition induce
electrode fabricated by it exhibited excellent cycling stability and porous structure to the product. Macro/nanoscale
high rate performance in electrochemical tests. The lithium coordination polymers (CPs) are ideal precursors for the
storage could maintain at ~1000 mA h g‐1 with high columbic synthesis of porous metal oxides because the limitless choice
efficiency (~95%), which is among the best of reported results.
of organic ligands and synthesis conditions makes their
morphology easy to be modulated.16‐21 Some studies indicated
that the obtained metal oxide could inherit the small size and
morphology of CP precursor.18‐21 Therefore, the thermal
decomposition with CP as precursor is a reliable method to
synthesize porous metal oxides with complicated structures,
which are difficult to be obtained with traditional direct
methods.
In this work, a porous flower‐like NiO architecture was
synthesized by the thermal decomposition of a CP precursor,
and its electrochemical properties were investigated in detail.
Experimental results indicate that this NiO product is an ideal
electrode material for LIBs.
The CP precursor was prepared by the solvothermal
reaction among H2bdc, Hina and Ni(NO3)2 in the mixed solvent
of H2O and DMF (1:1, v/v). The SEM image (Fig. 1a) shows that
the precursor is mainly composed of uniform flower‐like
architectures with diameters of 6−7 μm. The close observaꢀon
(Fig. 1b) exhibits that these architectures are constructed by
numerous smooth nanosheets. The composition of the CP
precursor was investigated with FT‐IR spectrum and elemental
analysis (EA). Fig. 2a gives the FT‐IR spectrum of the CP
precursor. The broad band in the range of 3000−3600 cm‐1
could be assigned to the O−H vibraꢀon of coordinated H2O
molecules. The carboxyl groups give intense peaks at 1578 and
1419 cm‐1 instead of the range of 1690−1730 cm‐1, indicating
that the organic ligands are completely deprotonated to
coordinate with metal ions. The intense peaks at 818 and 756
cm‐1 correspond to the bending vibraꢀons of the C−H bonds on
the benzene ring of bdc and the pyridine ring of ina,
respectively. EA gave the contents of C, H and N as 34.86, 3.51
and 3.78%, respectively. Combining EA results and the building
components determined by FT‐IR, the empirical formula of the
CP precursor is defined as Ni4O2(bdc)(ina)2(H2O)2.
Lithium ion batteries (LIBs) are becoming the most widely used
power sources for portable electronics nowadays. Transition
metal oxides are extensively explored as candidates for
reversible anode material in advanced LIBs.1‐4 Among them,
NiO shows great promise because of its high theoretical
lithium storage capacity of 718 mA h g‐1,5 which is nearly 2
times of that of the traditional graphite anode. Additionally,
the high density of NiO (6.67 g cm‐3) further enhances its
volumetric energy density. However, as other transition metal
oxides, the performance of NiO electrode is limited by its poor
electronic conductivity and the large volume variation upon
cycling.6 Inducing porous structure to the NiO electrode and
minimizing its particle size are effective ways to address these
concerns. In recent years, plenty of macro/nanoscale porous
NiO materials with various morphologies, such as fiber,7
nanotube,8 nanosheet9 and nanorod,10 have been synthesized
to improve the electrochemical performance. However, to the
best of our knowledge, the reports about the porous NiO with
hierarchically assembled structure are still rare yet.
Generally, porous materials are synthesized by a template
method.11 The removal of the template usually involves
laborious and harsh post‐treatments, which not only enhance
the cost and instrumental demand but also induce
unpredictable impurities to the product. These drawbacks
determine that the template method is not suitable for large‐
scale production. Porous materials could also be obtained by
the thermal decomposition of a suitable precursor.12‐15 The
Department of Chemistry and Key Laboratory of Advanced Energy Materials
Chemistry (Ministry of Education), Nankai University, Tianjin 300071, China. E‐
mail: wjruan@nankai.edu.cn; Tel: +86‐22‐23501717
† Electronic Supplementary Information (ESI) available: Experimental details and
the comparison with reported results. See DOI: 10.1039/x0xx00000x
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Fig. 3 PXRD pattern of the as‐prepared NiO sample.
detected in the pattern, which indicates the complete
transformation of the precursor and the phase purity of NiO
product. The broadening of the diffraction peaks suggests the
small crystalline size of the obtained NiO sample. Calculated
with the Debye‐Scherrer formula, the average crystalline size is
20 nm (based on the (200) diffraction peak), which is in
accordance with the TEM observation (discussed below).
As shown in Fig. 1c and 1d, the obtained NiO product
basically retains the flower‐like morphology of CP precursor.
The architecture size of NiO shows some degree of shrinkage
and is in the range of 3−4 μm. In contrast to the compact
structure of the precursor, the NiO product presents a porous
morphology, which is due to the large volume shrinkage
associated with ligand removal. The high magnification TEM
image reveals that the porous structure of the sample is made
up by randomly interconnected crystallines with size in the
range of 15−25 nm. The typical HRTEM laꢁce image of the NiO
sample is shown in Fig. 1f. The space between adjacent lattice
fringes is 0.243 nm, which is in good agreement with the (111)
facet of the cubic phase of NiO. The corresponding selected
area electronic diffraction (SAED, inset of Fig. 1f) shows well‐
defined diffraction rings, demonstrating the polycrystalline
nature of the sample.
Fig. 1 (a) low and (b) high magnification SEM images of CP precursor. (c) SEM, (d) low
magnification TEM, (e) high magnification TEM and (f) HRTEM lattice images of NiO
sample. Inset of (f): SAED pattern of NiO sample.
Fig. 2 (a) FT‐IR spectrum and (b) TGA curve of the CP precursor.
The decomposition process of the CP precursor was
investigated with thermogravimetric analysis (TGA, Fig. 2b).
The TGA curve presents two major stages of rapid weight loss.
o
The first stage of weight loss was in the range of 151−190 C
and could be assigned to the loss of coordinated H2O
molecules (obsd. 5.0%; calcd. 5.1%). The organic content was
o
lost in the temperature range of 352−447 C (obsd. 51.4%;
calcd. 52.9%), and the further heating of the sample caused no
remarkable weight loss. The final residue was expected to be
NiO (obsd. 43.6%; calcd. 42.0%). The accordance between
measured weight loss and the calculated value confirms the
proposed formula.
Based on its TGA curve, the CP precursor was used to
prepare NiO by a simple calcination process (heated from
room temperature to 450 oC by 2 oC min‐1 and then maintained
at 450 oC for 120 min). The PXRD pattern of the obtained NiO
sample is given in Fig. 3. All the diffraction peaks shown in the
pattern could be perfectly indexed to the cubic phase of NiO
(JCPDS card no. 47‐1049). No other impurity peaks were
Fig. 4 N2 adsorption‐desorption isotherm of the as‐prepared NiO sample. Inset: the BJH
pore‐size distribution curve.
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The surface area and pore structure of the NiO product
was studied with N2 adsorption‐desorption method (Fig. 4).The
sample gives a type IV isotherm with H3 hysteresis loop, and
its BET surface area is as high as 72.6 m2 g‐1. The pore size
distribution was calculated with Barrett‐Joyner‐Halenda (BJH)
method. This sample presents a wide pore size distribution in
the range of mesopore and large pore, and the total pore
volume is 0.85 cm3 g‐1. The large surface area and large pore
volume of NiO product show its potential as an electrode
material.
The electrochemical performance of the porous NiO
product was evaluated by cyclic voltammetry (CV) and
galvanostatic discharge‐charge measurements. The CV curves
(the initial three cycles) of the sample were tested at a scan
rate of 0.1 mV s‐1 (Fig. 5). A strong reduction peak with the
maximum at ~0.37 V was detected in the first cathodic sweep,
which is due to the initial reduction of NiO to Ni and the
simultaneous formation of amorphous Li2O (NiO + 2Li+ + 2e‐ =
Ni + Li2O) and solid electrolyte interphase (SEI) layer.22‐25 In the
subsequent cycles, the reduction peak shifted to ~1.00 V,
which could be explained by the drastic structural
rearrangement during the first lithiation process. For the
anodic scans, the oxidation peak was located at ~2.25 V, which
could be ascribed to the decomposition of Li2O and the
oxidation of Ni (Ni + Li2O = NiO + 2Li+ + 2e‐). It is noteworthy
that the CV curves almost remain the same after the second
cycle, showing the excellent cyclability of the porous NiO
product.
The discharge‐charge profiles of the electrode fabricated
by porous NiO were measured in the voltage range from 0.01
to 3.0 V at a current density of 0.5 C (1 C = 718 mA g‐1) (Fig. 6).
In the first discharge process, the potential of the electrode
underwent a lithiation caused quick decrease initially and then
gave a plateau at about 0.5 V, corresponding to the reduction
of Ni2+ to Ni. The discharge capacity was determined to be
1536.3 mA h g‐1, which is much larger than the theoretical
value of 718 mA h g‐1. Besides, the irreversible capacity loss
was 31.8% in the first cycle, which could be ascribed to the
decomposition of electrolyte and the irreversible formation of
SEI layer. Due to the structural rearrangement during the first
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DOI: 10.1039/C5RA15452A
3.0
2.5
2.0
1.5
1.0
0.5
0.0
1rt
2nd
3rd
0
200 400 600 800 1000 1200 1400 1600
Capacity(mA h g-1
)
Fig. 6 The galvanostatic discharge/charge voltage profiles of the porous NiO electrode
at a current density of 0.5 C for the initial three cycles.
lithiation process, the discharge curve of the second cycle was
remarkably different from the first one, that is, the major
potential plateau was replaced by a long sloping curve from
1.5 to 0.9 V. Then the electrode came to a steady state, so the
potential curve of the third cycle well overlapped with the
second one. The second and third discharge processes also
gave close discharge capacities of 1090.2 and 1080.5 mA h g‐1,
respectively, which is well consistent with the CV results.
Fig. 7 displays the cycle performance of the porous NiO
sample at a current density of 0.5 C. The NiO electrode
maintained a stable capacity of about 1000 mA h g‐1 in 40
cycles and exhibited good cyclic performance with high
columbic efficiency (~95%). Although a series of NiO electrode
materials have been synthesized in recent years, the examples
with the capacity maintaining above the theoretical value are
still rare (Table S1, ESI†). These experimental results indicate
that the flower‐like porous NiO architecture reported in this
work is among the best of the reported NiO materials. To
examine the high rate performance of the porous NiO
electrode, rate performance experiments were carried out (Fig.
8). The discharge capacities at 0.2, 0.5, 1, 2 and 5 C were 1100,
880, 800, 700 and 450 mA h g‐1, respectively. Notably, the
3200
2800
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90
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80
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2000
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2nd
3rd
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20
Cycle Number
30
40
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Voltage/V(vs.Li/Li)
Fig. 7 Cycle performance and columbic efficiency test of the porous NiO electrode at a
current density of 0.5 C.
Fig. 5 CV curve of the porous NiO electrode in the voltage range of 0.01−3.0 V at a scan
rate of 0.1 mV s‐1.
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Fig. 8 Rate performance of the porous NiO electrode at different current densities.
,
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Conclusions
In summary, a novel NiO material was synthesized by the
thermal decomposition of a CP precursor. The obtained NiO
product exhibits a rare porous flower‐like morphology, which
are composed by nanocrystalline constructed puffed plates.
This sample presents a high pore volume of 0.85 cm3 g‐1, and
the pore sizes distribute mainly in the range of mesopore and
large pore. Benefiting from its porous structure, this NiO
material exhibited excellent cycling stability in electrochemical
tests. At a current density of 0.5 C, the electrode fabricated by
it could maintain a stable capacity of ~1000 mA h g‐1 and a high
columbic efficiency of ~95% in 40 discharge‐charge cycles,
indicating that the NiO sample is an ideal anode material for
rechargeable LIBs. The results also suggest that the
hierarchically assembled porous structure applied in this work
is a promising morphology for the design of new electrode
materials.
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Graphical Abstract
Porous NiO architecture prepared with coordination polymer
precursor as high performance anode material for Li-ion
batteries
An Guo, Yue Li, Kun Liu and Wen-Juan Ruan*
A porous NiO architecture, which was synthesized by the calcination of coordination
polymer precursor, exhibited high Li-storage and excellent cyclability and could be
used as anode materal for Li-ion batteries.