Selflating synthesis of silicon nanorods from natural sepiolite for high-performance lithium-ion battery anodes

Article abstract of DOI:10.1039/c8ta00587g

Nanostructured silicon is an attractive anode material for next-generation lithium-ion batteries, but its commercialization remains a challenge owing to the energy-intensive, costly, and complex preparation of nanostructured silicon. Herein, one-dimensional (1D) silicon nanorods (SNRs) have been synthesized from natural sepiolite by a simple selflating synthesis method. The intrinsic crystal structure and chemical composition of sepiolite allow for the maintenance of 1D structures during magnesiothermic reduction without any additional templates and heat scavengers. The as-prepared SNRs showed a large specific surface area (～122 m² g^-1) and hierarchical porous structure (i.e., macro- A nd meso-pores). As anodes for lithium-ion batteries, SNRs exhibited a high reversible capacity of 1350 mA h g^-1 at 1.0 A g^-1 after 100 cycles, and 816 mA h g^-1 at 5.0 A g^-1 after 500 cycles (with a capacity retention of 98%). With a low-cost precursor and facile approach, this strategy for synthesizing 1D nanostructured Si would be promising in practical production of high-performance anode materials for lithium-ion batteries.

Full text of DOI:10.1039/c8ta00587g

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ISSN 2050-7488
PAPER
Kun Chang, Zhaorong Chang et al.
Bubble-template-assisted synthesis of hollow fullerene-like
MoS nanocages as a lithium ion battery anode material
2
rsc.li/materials-a

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DOI: 10.1039/C8TA00587G
Journal Name
ARTICLE
Self-templating synthesis of silicon nanorods from nature
sepiolite for high-performance lithium-ion battery anodes
a,b
a,*
c
c
a,b
a
Qingze Chen , Runliang Zhu , Shaohong Liu , Dingcai Wu , Haoyang Fu , Jianxi Zhu and
Hongping He
Received 00th January 20xx,
Accepted 00th January 20xx
a,b
DOI: 10.1039/x0xx00000x
Nanostructured silicon is an attractive anode material for the next-generation lithium-ion battery, but its commercialization
remains a challenge owing to the energy-intensive, costly, and complex preparation of nanostructured silicon. Herein, one-
dimensional (1D) silicon nanorods (SNRs) have been synthesized from natural sepiolite by a simple self-templating synthesis
method. The intrinsic crystal structure and chemical composition of sepiolite allow for the maintenance of 1D structures
during magnesiothermic reduction without any additional templates and heat scavengers. The as-prepared SNRs showed a
www.rsc.org/
2
−1
large specific surface area (~122 m g ) and hierarchical porous structure (i.e., macro- and mesopores). As anodes for
lithium-ion battery, SNRs exhibited a high reversible capacity of 1350 mAh g−1 at 1.0 A g−1 after 100 cycles, and 816 mAh g−1
at 5.0 A g−1 after 500 cycles (with a capacity retention of 98%). With low-cost precursor and facile approach, this strategy for
synthesizing 1D nanostructured Si would be promising in practical production of high-performance anode materials in
lithium-ion battery.
nanostructures offer the advantage of allowing the volume
expansion radially to minimize the cracking tendency, and the
small axial dimension could facilitate the lithium ion diffusion.11
As a result, 1D nanostructured Si exhibited good rate capability
and long cycling stability.
Introduction
25
30
35
40
45
50
Lithium-ion batteries (LIBs) with high power and high energy-
density have been rapidly developed nowadays to meet the
ever-increasing demands of hybrid electric vehicles, portable
electronic devices, and smart electricity storage units.1-4
Exploiting the high-performance electrode materials is the key
to fabricate the next-generation LIBs. Silicon (Si) is identified
as the most promising candidate to supersede the traditional
graphite-based anode in commercial LIBs, owing to its high
specific capacity (~3579 mAh g− based on Li15Si
discharge potential (< 0.4 V vs. Li/Li ). However, insufficient
transport properties and huge volume change of Si anode
during repeated lithium insertion/extraction resulted in the
serious capacity decay, which hindered the practical application
of Si anodes in LIBs.
To address this problem, various Si nanostructures,
including nanoparticles,13, 14 nanowires,
A variety of preparation methods have been established
accompanying with the rising demands of 1D Si nanomaterials,
5
0
5
0
such as electrochemical/electroless etching of Si wafers2 and
3-26
5
-7
chemical vapor deposition (CVD) of gaseous Si precursors2
7-29
.
These conventional methods are able to produce 1D
nanostructured Si with high-quality and controlled morphology,
but lack potential of massive production due to the expensive
precursors, harsh reaction condition, and low yield.
Electrospinning of silica followed by magnesiothermic reduction
1
1
1
2
4
alloy) and low
+
8-10
30-32
is
another
representative
approach.
However,
electrospinning process is usually based on template-assisted
synthesis method. The introduction and removal of the
template (e.g., carbon nanofibers and organic surfactants)
1
1, 12
15, 16
17, 18
nanosheets,
have been designed to improve
3
0-32
make this process very sophisticated,
further impeding the
19, 20
and porous nanostructures,
commercialization of 1D Si. Therefore, a low-cost, large-scale,
and environment-friendly strategy for synthesizing 1D
nanostructured Si is highly necessary.
the structural and cycling stability of Si anodes. Due to the
robust charge transport along the axis and flexible nature, one-
dimensional (1D) nanostructured Si is considered as an
In fact, the magical nature has already created many kinds
of 1D Si-containing materials, such as aciform wollastonite and
attractive anode material in LIBs.2
1,
22
Furthermore, 1D
33-35
fibrous sepiolite,
which inspired us to directly use these
a.CAS Key Laboratory of Mineralogy and Metallogeny, Guangdong Provincial Key
natural precursors to synthesize 1D Si. Herein, for the first time,
we have successfully prepared Si nanorods (SNRs) from natural
sepiolite by a simple self-templating synthesis method, which
could be very promising in scalable production due to the
abundant and low-cost precursor and facile approach. Owing to
the intrinsic crystal structure and chemical composition of
sepiolite, the 1D structure of SNR was maintained during
Laboratory of Mineral Physics and Material, Guangzhou Institute of
Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China. *E-mail:
zhurl@gig.ac.cn
University of Chinese Academy of Sciences, Beijing 100049, China.
Materials Science Institute, PCFM Lab and GDHPRC Lab, School of Chemistry, Sun
b.
c.
Yat-sen University, Guangzhou 510275, China.
†
Electronic Supplementary Information (ESI) available: Experimental details;
auxiliary analysis. See DOI: 10.1039/x0xx00000x
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Journal Name
magnesiothermic reduction without the addition of templates 55Si 2p X-ray photoelectron spectroscopy (XPS) spectrum was
View Article Online
DOI: 10.1039/C8TA00587G
and heat scavengers. The as-prepared SNRs exhibited a large carried out on a Thermo Fisher K-Alpha XPS instrument (Thermo
2
−1
specific surface area (~122 m g ) and hierarchical porous Fisher Scientific, UK) with a monochromatic Al-Kα X-ray source
structure (i.e., macro- and mesopores). When used as the (1468.6 eV). N adsorption-desorption isotherm of SNRs was
2
5
0
anode materials in LIBs, the SNR anodes showed prominent collected at liquid nitrogen temperature (–196°C) on an ASAP
electrochemical performance including excellent rate capability 602020 system (Micromeritics, USA). Before measurement, SNRs
−
1
−1
(
g
reversible capacity of 1350 mAh g at 1.0 A g and 478 mAh were outgassed at 200°C for 12 h under vacuum. The specific
−
1
−1
at 10 A g ), remarkable cycling stability (capacity retention surface area was evaluated by the multi-point Brunauer–
of 98% at 5.0 A g after 500 cycles), and low volume expansion Emmett–Teller (BET) equation and the total pore volume was
(~50%) of electrode after 100 cycles at 1.0 A g .
−
1
−
1
1
2
obtained from N adsorption capacity at a relative pressure of
65
0.97. The pore size distribution was calculated based on the
Barrett-Joyner-Halenda (BJH) method.
Experimental
Materials
Electrochemical measurements
The electrochemical performance of the as-prepared SNRs was
investigated in a coin-type half-cell (CR2032) which was
assembled in an argon-filled glovebox (less than 0.1 ppm of both
The pristine sepiolite (Hebei, China) was first purified by the
simple sedimentation method, dried overnight, and then 70
1
5
0
collected (purity > 98%) for the following experiments.
Magnesium (Mg) powder was of analytical grade and supplied
by Shanghai Aladdin Chemical Reagent Co., Ltd. Hydrochloric
acid (HCl, 37 wt.%) and hydrofluoric acid (HF, 40 wt.%) were
purchased from Guangzhou Chemical Reagent Factory, China.
Materials synthesis
2 2
H O and O ). The working electrode was prepared as follows:
the resulting SNRs, acetylene black (Super P), and sodium
alginate (SA, analytical grade) binder were homogeneously
mixed at a mass ratio of 6: 2: 2 in distilled water; then, the slurry
was blade-coated on a cooper foil and vacuum-dried at 60°C for
7
5
0
5
0
5
2
−
2
1
2 h. The mass loading of SNRs was around 0.7 mg cm . For
SNRs were prepared by the self-templating synthesis method
involved in magnesiothermic reduction. According to the known
coin-cell fabrication, the cast electrodes were cut into disks as
working electrodes. Lithium foils were employed as the counter
and reference electrodes, and polyethylene membranes
magnesiothermic reduction reaction (SiO
2MgO (s)), SiO
ratio of 1: 0.8. Considering the calculated chemical formula of
sepiolite (i.e., Mg (OH ·8H O) and the actual mass
2
(s) + 2Mg (g)
→
Si (s) 8
+
2
can be completely reduced by Mg in a weight
(
Celgard 2400) as separators. The electrolyte consisted of 1 M
LiPF solution in ethylene carbonate/dimethyl carbonate
EC/DMC, 1:1 v/v) and 10 wt.% fluorinated ethylene carbonate
25
30
35
6
8
Si12
O30(OH)
4
2
)
4
2
(
transfer process, we used the stoichiometric weight ratio of
sepiolite/Mg as 1: 0.6. In a typically procedure, sepiolite (1 g) 8
and Mg powders (0.6 g) were fine mixed in a mass ration of 1:
0.6 and then sealed into a stainless steel reactor in an argon-
filled glovebox. Subsequently, this reactor was placed in the
middle of tube furnace and heated to 650°C at a rate of 5°/min
and held for 5 h under a constant argon flow. After cooling down 9
to room temperature, the resultant mixtures were washed with
100 mL 1 mol/L HCl for 5 h to remove the byproducts (e.g.,
MgO), followed by leaching with 100 mL 1% HF. Finally, the
resulting silicon products SNRs were collected after rinsing
thoroughly with distilled water and vacuum-drying overnight.
Characterization
additives. The rate performance and cycling stability were
conducted at room temperature on a CT2001A multichannel
Battery Test System with a voltage window between 0.001 and
+
1
.5 V (vs. Li/Li ). The cyclic voltammetry (CV) measurements
were performed on a CHI660D electrochemical workstation
−
1
with a scan rate of 0.1 mV s in the voltage range of 0.001–1.5
+
V (vs. Li/Li ). The specific capacity in this study was evaluated
based on the mass of active materials only. The electrochemical
impedance spectroscopy was carried out with an alternating
current perturbation of 5 mV in the frequency range from 0.01
to 100 kHz. After electrochemical test, the cells were
disassembled in an argon-filled glovebox, and the working
electrodes were completely rinsed with dimethyl carbonate and
9
40
45
50
The scanning electron microscopy (SEM) images and energy dried for further characterization.
dispersive X-ray spectroscopy (EDS) results were measured by
an SU-8010 cold field emission scanning electron microscope
(
Hitachi, Japan). Transmission electron microscopy (TEM) Results and discussion
images and high-resolution TEM (HRTEM) images were
The schematic illustration demonstrated the synthetic process
from natural sepiolite to SNR (Fig. 1a). Sepiolite is a typical 2:1
type clay mineral with one octahedral (O) sheet sandwiched by
two tetrahedral (T) sheets. Unlike ideal phyllosilicates,3
sepiolite possesses a discontinuous O sheet due to the periodic
inversion of apical oxygen atoms of the tetrahedron, forming a
fibrous pattern with nanosized channels (0.37 × 1.06 nm)
recorded on an FEI Talos F200S field-emission transmission 100
electron microscope (FEI Co., USA) with selected area electron
diffraction (SAED) attachments at an acceleration voltage of 200
kV. The X-ray diffraction (XRD) patterns of the samples at
different stages were obtained on a Bruker D8 ADVANCE X-ray
6, 37
diffractometer (Bruker AXS, Germany), operating at 40 kV and 105
4
0 mA with Ni-filtered CuKα radiation (λ = 0.154 nm). Raman
3
8
running parallel to the fiber. The reduction reaction between
Mg and the external silicon-oxygen T sheets was initiated over
spectra were performed on a Renishaw 2000 confocal micro-
Raman Spectrometer (Renishaw, UK) with an air-cooled CCD
detector and an Ar-ion laser (λ = 514.5 nm). The high resolution
17
5
50°C. When the temperature reached the fusion point of Mg
2
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DOI: 10.1039/C8TA00587G
Fig. 1 (a) Schematic illustration of SNRs from natural sepiolite. (b)
SEM image of natural sepiolite showing 1D nanofiber morphology.
40
Fig. 2 Morphological characterization of SNRs. (a and b) TEM images
(
the yellow circles represent the mesopores in the nanorods), (c)
(
c) SEM image of 1D SNRs.
HRTEM image showing crystalline structure, and (d) the
corresponding SAED pattern.
(648°C), Mg atoms readily enter into the nanosized channels of
5
0
5
0
5
0
5
sepiolite and attack T sheets inside. The X-ray diffraction (XRD)
pattern of intermediates after magnesiothermic reduction
showed the presence of the characteristic reflections of Si and
MgO but disappearance of those of raw sepiolite (Fig. S1a, b,
ESI†), which suggested a complete reduction of sepiolite. Slight
addition of heat scavenger. The successful self-templating
synthesis of SNRs might be primarily attributed to three
reasons: (1) the magnesium-oxygen/hydroxide O sheet (i.e.,
brucite-like sheet) could absorb the heat via its decomposition
45
50
55
60
65
70
75
41
2 2
(Mg(OH) (s) → MgO (s) + H O (g); ΔH = 1.4 kJ/g Mg(OH)2); (2)
1
1
2
2
3
3
2
amount of Mg Si was simultaneously formed in the local Mg-
the intact trioctahedral sheets (Fig. S4a, ESI†) acted as isolation
barriers to inhibit the random bonding of newly formed Si
nanoparticles during the reaction, effectively keeping the
nanostructure of original sepiolite; and (3) the O sheet-
converted MgO with high specific heat capacity was located
within two T sheets, which then could serve as negative catalyst
rich surroundings. Subsequently, selective acid treatment was
employed to remove all of the byproducts and achieve the final
product SNRs. The XRD pattern of SNRs manifested the
formation of well-crystallized silicon phase (Fig. S1c, ESI†).
The SEM images of SNRs showed that the resulting Si
product exhibited a morphology of nanorods with rough
surface, almost maintaining the original 1D nanostructure of
sepiolite (Fig. 1b, c). The corresponding EDS result confirmed
the high purity of SNRs after acid treatment (Fig. S2, ESI†). The
TEM images of SNRs further disclosed that the fibrous texture
was composed of interconnected or overlapped Si
nanoparticles (Fig. 2a, b). Moreover, the hierarchical porous
architectures were observed, i.e., macropores built by the
stacking or aggregation of nanorods and mesopores in the
nanorods (marked by the yellow circles). The measured
interplanar spacing was ~0.31 nm in the HRTEM image,
corresponding to the (111) plane of crystalline Si (Figure 2c). The
SAED pattern further verified the high crystallinity of SNRs due
to the distinct diffraction rings that can be indexed to Si (Figure
2d), consistent with the XRD result. In addition, the EDS
mapping and spectra of TEM image strongly demonstrated the
high purity of the as-prepared SNRs (Fig. S3, ESI†).
42
to slow down the exothermic reaction.
To further verify the important role of O sheets in forming
SNRs, a control experiment using fibrous palygorskite (Fig. S5a,
b) as Si precursor was conducted under the same preparation
conditions. Compared with sepiolite, palygorskite has similar
chain-layered structure but different composition (i.e., a large
amount of Al existing in O sheets due to massive isomorphous
2
+
3+
substitution of Mg by Al ) (Fig. S4b, ESI†). Noticeably, a
severely agglomerated morphology was visible in the SEM
image of the final Si products (Fig. S5c, ESI†). Besides, a small
amount of high-temperature phase (i.e., spinel and forsterite)
appeared simultaneously in the corresponding XRD pattern (Fig.
S5d, ESI†). These results implied a higher reaction temperature
in the palygorskite system than that in the sepiolite system,
which could be ascribed to the lower endothermic capacity of
the decomposition of aluminium-oxygen/hydroxide O sheets
(
ΔH = 1.0 kJ/g Al(OH)3). Furthermore, different from the true
As reported by previous studies, massive heat generated
from magnesiothermic reduction reaction would heavily
destroy the structures of Si precursors and even fuse the
trioctahedral sepiolite, palygorskite belongs to intermediate
3
8
between di and trioctahedral clay minerals. The vacant
octahedral sites usually emerge at the edge of the ribbons in
the Mg-deficient parts (Fig. S4b, ESI†), which allows Mg atoms
to attack the aluminium-oxygen/hydroxide O sheets. As a result,
the O sheet of palygorskite could not function as an effective
39
resultant Si nanoparticles into bulk crystals. Therefore, several
studies introduced molten inorganic salt as a heat absorbent to
39, 40
scavenge the excessive heat.
Interestingly, SNRs in our work
still kept the similar nanorod structure as sepiolite without the
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Fig. 3 Characterization of SNRs. (a) Raman spectrum, (b) high
resolution Si 2p XPS spectrum, (c) N adsorption-desorption
2
isotherm, and (d) the corresponding BJH pore size distribution curve.
template to maintain the original structure.
5
0
5
0
5
0
5
The resulting SNRs from sepiolite were further analyzed by
Raman spectrum (Fig. 3a). Compared with the sharp Raman
band at ~521 cm− (resulting from the Si–Si stretching mode) of
monocrystalline Si (Fig. S6, ESI†), that of SNRs red-shifted to
1
Fig. 4 Electrochemical performances of the SNR anodes. (a) CV curves
at a scan rate of 0.1 mV s in the voltage range of 0.001–1.5 V (vs.
−
1
4
0
5
−
1
~
513 cm and widened. Besides, two broad peaks at 301 and
+
−1
Li/Li ); (b) discharge-charge curves at a current density of 0.2 A g
−
1
1
1
2
2
3
3
938 cm , corresponding to the overtones of TA(X) and TO(L),
+
between 0.001 and 1.5 V (vs. Li/Li ); (c) rate capability at various
current densities from 0.1 to 10 A g ; (d) cycling performance at
current densities of 0.2 A g for the initial three cycles and 5.0 A g
for the remaining cycles.
43
respectively, exhibited the same trends. Similar phenomena
were reported in other studies about the Si nanostructures,39, 44
which was attributed to the decreased diameters of Si. The high
resolution Si 2p XPS spectrum of SNRs showed an intense
asymmetric peak mainly composed of Si 2p1/2 and Si 2p3/2 of
pure Si at ~99.9 and ~99.3 eV (Fig. 3b),18 respectively. The three
very weak peaks at ~100.5, ~101.4, and ~103.0 eV, assigned to
−
1
−
1
−1
4
disappeared from the second cycle onwards, suggesting the
formation of stable solid electrolyte interphase (SEI) film on the
surface of SNRs due to the decomposition of electrolyte.13 The
reductive peaks (0.1 and 0.17 V) assigned to the lithiation
process and oxidative peaks (0.36 and 0.51 V) resulting from the
delithiation process gradually increased in intensity and then
SiO
amount of amorphous SiO
probably originated from the post-oxidation of Si nanocrystals
x
derivatives, suggested the presence of almost negligible
x
on the surface of SNRs, which
50
55
60
65
44
in air.
The pore structure of SNRs was investigated via N
45
coincided. The phenomenon indicated a kinetic enhancement
process of the SNR electrode before stabilization, which usually
2
adsorption-desorption isotherm (Fig. 3c, d). The obtained
isotherm of SNRs belongs to characteristic type IV, with a type
H3 hysteresis loop indicative of non-rigid slit-like pores. The
30, 46, 47
happened for the Si-based anodes.
As shown by the galvanostatic discharge-charge curves of
the SNR anode (Fig. 4b), a long and flat voltage plateau emerged
at ~0.1 V in the first discharge curve, suggesting the alloying
2
rapid increase of N adsorption capacity in high relative
pressure range implied the existence of macropores, in good
agreement with the TEM observation. Moreover, SNRs showed
a broad distribution of pore size from 2 to 100 nm, with the
most probable pore size at ~32 nm, according to the pore size
distribution plot evaluated by the BJH method. The calculated
specific surface area of SNRs based on multi-point BET equation
48
reaction between lithium and crystalline Si. The SNR anode
exhibited the first discharge/charge capacity of 2705/1635 mAh
−
1
g
with an initial Coulombic efficiency (CE) of 60.5%. The
moderate initial CE was probably associated with the large
specific surface area of SNRs which could facilitate the
4
8, 49
generation of SEI film.
Noticeably, this disadvantage could
2
−1
3
−1
was 122 m g , and the total pore volume was 0.43 cm g .
To evaluate the electrochemical performance of SNRs as
anodes in LIBs, CR2032 coin-type half cells were assembled in
an argon-filled glovebox. The CV plots of the SNR anode were
be overcome by the simple prelithiation (Fig. S7, ESI†).4
0, 50
In
the subsequent cycle, the voltage plateau was replaced by the
sloping curves, owing to the formed amorphous phase during
4
6
the first lithiation/delithiation process. Despite of the capacity
loss in the first cycle, the SNR anode rapidly reached a high CE
over 98% after several cycles. Moreover, the discharge-charge
−
1
tested at a scan rate of 0.1 mV s (Fig. 4a). A board and weak
peak at ~1.19 eV occurred in the first discharge scan then
4
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cycles. Remarkably, the SNR electrodes still exhibited good
View Article Online
DOI: 10.1039/C8TA00587G
45
50
55
cycling performance with a higher active mass loading (~1.1 mg
−
2
cm ) or a different ratio of active material, binder, and
conductive agent (7: 1.5: 1.5) (Fig. S9, ESI†).
The volume expansion of the SNR electrode during the
repeated lithium insertion/extraction was further investigated
by measuring the cross-sectional SEM images of electrodes
before and after 100 cycles at 1.0 A g− (Fig. S10, ESI†). The SNR
electrode exhibited an obviously suppressed volume expansion
1
(
~50%), compared to the conventional bulk Si (>300%),
reflecting the good interfacial stability of SNR during cycling.
The superior electrochemical performance of the SNR electrode
may result from the following several reasons: (1) the SNRs with
hierarchical porous structure could effectively accommodate
interior stress upon the uptake of lithium ions, causing a
reduced volume expansion; (2) the 1D structure composed of
interconnected Si nanoparticles contributed to shortening the
diffusion path of lithium ions and facilitating the charge
transport, which enabled the SNR anode to endure high current
density; (3) the relatively rough surface of SNRs increased the
surface area and electrochemical reaction sites, which was
Fig. 5 Nyquist plots of the SNR electrodes after 3 and 100 cycles at
−
1
5
.0 A g .
curves for the 5th and 10th cycles were almost overlapped, 60
indicating the superior reversible electrochemical process
between the SNR electrode and lithium ion. Noticeably, it took
5
0
5
0
5
0
5
0
1
0 cycles to reach a steady state in the discharge-charge curves,
while 15 cycles in CV curves (Fig. 4a and b), which may be
attributed to the different current densities. The current density 65
1
1, 56
beneficial to the lithium insertion and extraction.
Without
the sophisticated designs and surface modification, the SNR
anode in our work showed excellent rate performance and
cycling stabilization from a practical point of view, in
comparison with recently reported 1D Si-based anodes
synthesized through other methods (Table S1, ESI†).
for the oxidative peak (0.36 V) in the CV tests was calculated to
−
1
1
1
2
2
3
3
4
be ~0.4 A g , much larger than that in the discharge-charge
−
1
measurements (0.2 A g ). With the small current density, the
electrode had enough time to be activated completely, so the
electrode could be stabilized after several cycles.
7
0
The SNR electrode displayed the reversible discharge
capacities of ~1794, 1644, 1494, 1350, 1116, 841, and 478 mAh
Conclusions
−
1
−1
g
at 0.1, 0.2, 0.5, 1.0, 2.0, 5.0, and 10 A g (Fig. 4c),
respectively. The specific capacity was restored to the initial In summary, 1D silicon nanorods with hierarchical porous
−
1
value when the current density was back to 0.1 A g , structure were successfully synthesized from natural sepiolite
manifesting the efficient kinetics for lithium storage. by a simple self-templating synthesis method. Without complex
Remarkably, as the current density was abruptly switched to 1.0 75pre/post-treatment and extra additives (e.g., templates or heat
−
1
A g , the SNR electrode delivered a quite stable capacity of scavengers), the 1D structure of SNR was maintained during
−
1
~
1400 mAh g , implying a good cycling stability. The long-term magnesiothermic reduction, owing to the intrinsic crystal
cycling stability of the SNR electrode at high current density was structure and chemical composition of sepiolite. As anode
also carried out (Fig. 4d). A high capacity of ~816 mAh g− was material for LIBs, SNR exhibited outstanding electrochemical
still retained after 500 cycles at a high current density of 5.0 A 80performance in terms of excellent rate capability, remarkable
1
−
1
g , corresponding to an outstanding capacity retention of 98%. cycling stability, and low volume expansion. Our work provided
It is noteworthy that the specific capacity of the SNR electrode a facile, low-cost, and scalable strategy for synthesizing 1D
slightly increased during the first 30 cycles, consistent with the nanostructured Si from natural clay minerals, which would be
CV results. Such phenomena were not rare for various very promising in the practical production and application of
51-54
nanostructured anodes (e.g., Si and metal oxide),
which 85high-performance anode materials in LIBs.
could be ascribed to the gradual activation of active materials
at high current density, the enhanced electrolyte wetting during
cycling, and the generation/dissolution of an organic gel-like
Conflicts of interest
5
1-54
coating on the surface of electrode.
Besides, the
There are no conflicts to declare
.
electrochemical impedance spectroscopy spectra further
disclosed that the SNR electrode after 100 cycles possessed
lower charge transfer resistance and ionic diffusion resistance
than the electrode after 3 cycles, as verified by the decreased
diameter of the high-frequency semicircle and the increased
Acknowledgements
This work was financially supported by the National Natural
Science Foundation of China (41572031), the National Program
for Support of Top-notch Young Professionals, and Guangdong
Provincial Program for Support of Top-notch Young
Professionals (2014TQ01Z249).
90
55
slope of the low-frequency line (Fig. 5). These results were
further confirmed by the fitted data based on the equivalent
circuit (Fig. S8, ESI†). In addition, the SNR electrode showed a
high CE close to 100% during cycling after the first several
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
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J Po lue r an sa el od foMna ot et rai ad l js u Cs ht emm ai rs gt ri yn sA
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2 D. J. Lee, H. Lee, M.-H. Ryou, G.-B. Han, J.-N. LVeieew, JA.rtiScloenOgn,linJe.
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DOI: 10.1039/C8TA00587G
Table of contents entry:
One-dimensional silicon nanorods with hierarchical porous structure were synthesized
from natural sepiolite by a simple self-templating synthesis method.