Preparation and electrochemical performance of micro-nanostructured nickel

Article abstract of DOI:10.1016/j.electacta.2009.05.069

Micro-nanostructured nickel has been prepared as anode materials for Li ion batteries, via a rheological phase reaction method. Ni₂C₂O₄·xH₂O (x = 2 or 2.5) as precursors are obtained from the solid-liquid rheolo

Full text of DOI:10.1016/j.electacta.2009.05.069

Electrochimica Acta 54 (2009) 6161–6165
Contents lists available at ScienceDirect
Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Preparation and electrochemical performance of micro-nanostructured nickel
∗
Xiaoyan Han, Feng Zhang, Jiangfeng Xiang, Caixian Chang, Jutang Sun
Department of Chemistry, Wuhan University, Wuhan 430072, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Micro-nanostructured nickel has been prepared as anode materials for Li ion batteries, via a rheological
phase reaction method. Ni2C2O4·xH2O (x = 2 or 2.5) as precursors are obtained from the solid–liquid
rheological mixture of (NH4)2C2O4·H2O and Ni(NO3)2. The nickel powders are prepared by thermal
decomposition of the precursors. The structural, morphological and electrochemical performance are
investigated by means of thermogravimetry (TG), differential scanning calorimetry (DSC), powder X-
ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and
typical electrochemical tests. The micro-nanostructured nickel displays an initial discharge capacity of
Received 24 March 2009
Received in revised form 11 May 2009
Accepted 16 May 2009
Available online 27 May 2009
Keywords:
Rheological phase reaction method
Micro-nanostructured nickel
Anode
−1
4
57 mAh g . It also has a remarkable cycling stability with an average capacity fade of 0.17% per cycle
−
1
from 13th to 50th cycle in 0.01–3.00 V versus Li at a constant current density of 100 mA g
.
Li ion batteries
© 2009 Elsevier Ltd. All rights reserved.
1
. Introduction
However, some of the above-mentioned methods need rigorous
reaction conditions such as high temperature or high pressure,
some need organic solvent, and some need the addition of extra
precipitator to the reaction system, which cause the safety prob-
lem, complicated manufacture equipment, high production cost,
poor quality, low production efficiency and so on. As a result, the
design and synthesis of nanosized materials is the current subject
of intense research.
Nanosized materials with novel properties present a wide
potential application in many fields [1–6]. Constructions of well-
ordered and realizations of their potential applications have
resulted in intensive research for the past few years. The demands
of superfine metal powders have increased dramatically in the
electronics, biotechnology, powder metallurgy and energy sources
fields. Micro-nanostructured nickel with unique morphology, size
and structure may exhibit superior functionality or provide new
possibilities due to the composite structure, porosity, stability and
the inherent properties of nanosized materials.
So far as we know, there are many researches on nickel including
alloy used as anode materials [7–12]. However, a well-known fact
is that the pulverization, which brings the fast capacity fade during
cycling, is the key issue to restrict metal or alloy being widely used
as the anode materials for Li ion batteries. There have been many
attempts to resolve the cracking and crumbling problems of metal
or alloy materials for Li ion batteries. Nanosized particles or com-
posite materials have been considered. Nevertheless, just reducing
the particle size or synthesizing simple composite materials can-
not effectively improve the cycleability or capacity of the anode
materials [10].
In this study, micro-nanostructured nickel was prepared via
a rheological phase reaction method. Rheological phase reaction
is a simple, economical and effective route to prepare functional
materials [19–25], which does not need complicated processes. The
◦
thermal decomposition of the precursors carried out at 300–400 C
in a self-assembly device without protective gas.
2. Experimental
2.1. Material preparation
(
NH ) C O ·H O, Ni(NO ) ·6H O and anhydrous ethanol were
4
2
2
4
2
3
2
2
all analytical-grade reagents. Solutions were prepared by use of
deionized water.
(
NH ) C O ·H O (48.87 g) was added in 5.0 M nickel nitrate
4
2
2
4
2
◦
solution [Ni(NO ) ·6H O (100 g), H O (20 mL)] at 70–90 C to form
Various methods have been used to prepare superfine nickel
powders such as mechanical milling, chemical reduction, evap-
oration, polyol process, spattering and atomize method [13–18].
3
2
2
2
a rheological body with viscoelasticity. The ropy rheological body
was fully dispersed with an appropriate amount of deionized water
added, then filtered, washed, dehydrated with anhydrous ethanol
◦
and dried at 80–90 C to yield NiC O ·2H O (Precursor A), the over-
2
4
2
all yield was 99.76%. The nickel nitrate was added in supersaturated
∗ Corresponding author. Tel.: +86 27 87218494; fax: +86 27 68754067.
E-mail address: jtsun@whu.edu.cn (J. Sun).
ammonium oxalate solution to give NiC O ·2.5H O (Precursor B),
2
4
2
the overall yield was 97.98%.
0
013-4686/$ – see front matter © 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2009.05.069

6
162
X. Han et al. / Electrochimica Acta 54 (2009) 6161–6165
Fig. 1. TG–DTG–DSC curves of Precursor A (a) and B (b) in covered Al crucible.
An appropriate amount of nickel oxalate was cased in sealed
2.3. Electrochemical measurements
vessel. The air inside expanded and let out slowly when the thermal
decomposition was carried out, which ensured the precursor was
The electrochemical experiments were examined on a Neware
cell test system at room temperature. The charge–discharge tests
were carried out with the coin-type cell (size: 2016), which con-
sisted of a working electrode and a lithium foil counter electrode
separated by a Celgard-2300 microporous membrane. The working
electrode was prepared by mixing the nickel powders, acetylene
black and polytetrafluoroethylene (PTFE) binder, in a weight ratio
of 80:15:5, compressing the mixture onto a stainless steel current
collector. A 1 M LiPF6 EC/DMC (1:1, volume ratio) was used as the
electrolyte. The cells were assembled in an argon-filled glove box
◦
saturated with self-atmosphere. The vessel was heated up to 335 C
◦
−1
◦
in air furnace with a heating rate of 5 C min , kept at 335 C for
h to give a black sample. The nickel obtained from the Precursor
A and B was marked as NiA and NiB, respectively.
6
2.2. Material characterization
The powder X-ray diffraction (XRD) patterns of the precursors
and the products were collected by a Shimadzu model XRD-6000
diffractometer with a Ni filter and Cu-K␣1 radiation (ꢀ = 1.54056 Å)
(Mikrouna, Super 1220/750, China). The cells were discharged and
charged between 0.01 and 3.0 V versus Li at a constant current
◦
◦
in the range of 10–60 (2ꢁ) and 10–120 (2ꢁ) with a scanning
−1
density of 100 mA g
.
◦
−1
rate of 4 min , respectively. The refined crystal lattice parame-
ters were calculated by the JADE5.EXE procedure (Rietveld analysis
of the powder XRD patterns using on a step-scan mode with a step
3. Results and discussion
◦
◦
of 2 in the 2ꢁ range of 20–130 ). Chemical analysis was carried
out by inductively coupled plasma atomic emission spectrometry
3.1. Thermal decomposition reaction
(
ICP-AES, model IRIS, TJA). The particle size and morphology were
observed using scanning electron microscope (SEM, Hitachi 400)
and transmission electron microscope (TEM, JEM-2010 FEF). The
thermal analysis experiments were carried out in covered Al cru-
Fig. 1 presents the TG–DTG–DSC curves of Precursor A
(6.223 mg) and B (7.620 mg). The specific temperature and mass
losses are labeled on DSC–TG curves. Analysis shows that the
molar compositions of Precursor A and B are NiC O ·2H O and
◦
cible with a Netzsch STA 449C thermal analyzer from 50 to 600 C
2
4
2
◦
−1
at a heating rate of 5 C min . The sample mass was kept about
.0–8.0 mg.
NiC O ·2.5H O, respectively. The DSC peaks closely correspond
2
4
2
6
to the weight changes observed on the TG curves. The thermal

X. Han et al. / Electrochimica Acta 54 (2009) 6161–6165
6163
Table 2
Lattice parameters of NiA and NiB.
Parameter
NiA
NiB
S. G.
Fm 3¯ m(225)
Fm 3¯ m(225)
a (Å)
V (Å )
3.5232 (1)
43.73
4
3.5245 (1)
43.78
4
3
Z
Dcalc (g cm−3)
8.9150
8.9058
indicates that the two precursors are different from each other.
Diffraction relative intensity and peak position of two XRD patterns
are different from those reported in the literature (JCPDS File Card
No. 25-0581).
XRD patterns and lattice parameters of the products are given
in Fig. 2b and Table 2. In order to get an accurate lattice param-
eters silicon element (internal standard) is added to compensate
for sample displacement error (Fig. S4 and Fig. S5, Supplemen-
tary Information). Results show that lattice parameters and the
position of main peaks of face centered cubic nickel are well consis-
tent with the standard file (JCPDS File Card No. 04-0850), proving
the sole existence of nickel particles. No sign of the formation of
oxides species could be observed in Fig. 2b. All diffraction peaks
are very sharp, which indicates that the high crystallinities of the
products.
3.3. Particle size and morphological characterization
Particle sizes and morphology changes throughout the ther-
mal decomposition are shown in Figs. 3 and 4 by SEM and TEM
observations. The particles size and morphology of the Precursor
A and B are obviously different from each other. The Precursor
B consists of monodispersed quadrate crystals with the parti-
Fig. 2. XRD patterns of oxalate nickel precursors (a) and nickel products (b).
decomposition generally proceeds in two steps: dehydration and
cle sizes of 0.6–1.0 ␮m (Fig. 3b ). The Precursor A consists of
1
decomposition of the anhydrous oxalate. The mass loss before
many irregular block crystals with the particle sizes of 0.1–0.2 ␮m
◦
2
00 C, characterized by a small endothermic peak on DSC curves, is
(
Fig. 3a ). After thermal decomposition, Precursor A changes into
1
ascribed to the dehydration of adsorptive water. XRD analysis con-
firms that the final products of thermal decomposition in Al crucible
are nickel powders, which is different from the common reports on
thermal decomposition of nickel oxalate in air [26,27]. The thermal
decomposition reaction formula of the precursors can be expressed
as follows (x = 2 or 2.5):
close-grained spherical heteromorphy with the average particle
sizes about 0.1 ␮m (Fig. 3a2 and Fig. 4a ). The product NiB with
3
the average particle sizes about 0.5 ␮m keeps the quadrate mor-
phology of the Precursor B and the single quadrate crystal still
consists of many nanospheres with the average particle sizes about
2
0 nm (Fig. 3b and Fig. 4b ). The results from SEM and TEM images
2 3
NiC O ·xH O → NiC O + xH O
(1)
(2)
agree well with the observations from the XRD and electrochemical
measurements.
2
4
2
2
4
2
NiC O → Ni + 2CO
2
4
2
But thermal decomposition behaviors of the two precursors are
different: the decomposition rate of Precursor B is twice than that
of Precursor A (shown in DTG curves).
3.4. Electrochemical characterization
Fig. 5 shows the typical discharge and charge curves of Ni and
A
−
1
NiB electrode at a constant current density of 100 mA g between
0.01 and 3.0 V. The three obvious plateaus in the first discharge
curve suggest that there are three Ni atoms and three Li atoms in
a unit cell. More detailed results of the formation and composition
of the LiNi alloy are given in Table S1, Table S3 and Fig. S2, Supple-
mentary Information. The reaction mechanism of intercalation of
Li ions can be expressed as follows:
3.2. Powder X-ray diffraction analysis
Fig. 2a shows the XRD patterns of Precursor A and B prepared
via rheological phase reaction method. The partial refined crys-
tal lattice parameters calculated by the JADE5.EXE procedure are
presented in Table 1. All characteristic diffraction peaks of two pre-
cursors are well indexed to the monoclinic phase of nickel oxalate,
with the space group P2/m (No. 10). The broken line in Fig. 2a
1.60–0.84 V
0.84–0.62 V
0.62–0.01 V
1/3Li + Ni → Li1/3Ni
1/3Li + Li1/3Ni → Li2/3Ni
1/3Li + Li2/3Ni → LiNi
(3)
(4)
(5)
Table 1
Lattice parameters of Precursor A and B.
The initial discharge capacity of NiA electrode is 376 mAh g 1
−
Parameter
Precursor A
Precursor B
and the coulombic efficiency is 55.3%. However, the initial discharge
S. G.
a (Å)
b (Å)
c (Å)
P2/m (No. 10)
7.8167 (16)
2.6607 (6)
5.9066 (11)
122.84
P2/m (No. 10)
9.8874 (40)
4.2409 (19)
6.5671 (47)
266.13
−
1
capacity of NiB electrode is 457 mAh g and the coulombic effi-
ciency is 62.4%. The low initial coulombic efficiency is attributed
to the formation of the alloy framework and the solid electrolyte
interface (SEI) film. As shown in Fig. 5, the first discharge curve is
3
V (Å )

6
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X. Han et al. / Electrochimica Acta 54 (2009) 6161–6165
Fig. 3. SEM images of Precursor A (a1) and NiA (a2), Precursor B (b1) and NiB (b2).
characterized by four plateaus. The small plateau at about 1.5 V cor-
responded to the irreversible capacity loss, which disappears in the
following cycles. The NiB electrode delivers higher initial discharge
and charge capacity of 457 and 285 mAh g , respectively. The rea-
son for the higher initial capacity of NiB electrode may be attributed
to the particle size and the microstructure. The deintercalation pro-
cess of Li ions between the layers of the anode is a diffusion process
lead to a long path for Li ions, are not advantageous to deintercala-
tion.
Fig. 6 shows the cycling performances of NiA and NiB elec-
−1
trode. The Ni electrode delivers an initial reversible capacity
A
−
1
−1
in the 50th cycle. In
of 208 mAh g
and maintains 87 mAh g
comparison, the NiB electrode delivers an initial reversible capac-
−
1
ity of 285 mAh g . In the 50th cycle, the charge capacity still
−
1
[
25]. Therefore, the larger or close-grained particles, which would
retains 143 mAh g , which is much better than NiA electrode. After
Fig. 4. TEM images of NiA (a3) and NiB (b3).

X. Han et al. / Electrochimica Acta 54 (2009) 6161–6165
6165
Fig. 5. Discharge–charge curves for the typical cycles of NiA (a) and NiB (b) over 0.01–3.0 V.
Acknowledgements
This work was supported by The National Natural Science Foun-
dation of China (No. 20771087).
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.electacta.2009.05.069.
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