Carbon coated mesoporous Si anode prepared by a partial magnesiothermic reduction for lithium-ion batteries

Article abstract of DOI:10.1016/j.jallcom.2017.05.057

Owing to its high theoretical capacity, Si based anode materials have been regarded as the most promising alternative anode materials for lithium-ion batteries. Unfortunately, the commercial application of Si based anode materials has been greatly hindered, due to the large volume change of Si materials during their lithiation/delithiation process, which results in severe pulverization, loss of electrical contact and rapid capacity fading. To address these issues, we reported a partial magnesiothermic reduction method by adjusting the proportion of added Mg powder to convert SiO₂ into Si/SiO₂ and subsequently to coat such a composite with a carbon layer. After removing unreacted SiO₂ using HF, carbon-coated mesoporous Si (p-Si@C) can be obtained. The internal pores could accommodate the volume changes of Si and the carbon coating layer could effectively stabilize the interface during cycling. With this design, the as-prepared p-Si@C shows superior electrochemical performance compared with bare Si. When the p-Si@C electrode evaluated at a rate of 0.5?A?g^?1, a reversible capacity of 1146?mAh g^?1 could still be maintained after 100 cycles.

Full text of DOI:10.1016/j.jallcom.2017.05.057

Accepted Manuscript
Carbon coated mesoporous Si anode prepared by a partial magnesiothermic
reduction for lithium-ion batteries
Lili Wu, Haochen Zhou, Juan Yang, Xiangyang Zhou, Yongpeng Ren, Yang Nie,
Song Chen
PII:
S0925-8388(17)31641-9
10.1016/j.jallcom.2017.05.057
JALCOM 41787
DOI:
Reference:
To appear in: Journal of Alloys and Compounds
Received Date: 27 March 2017
Revised Date: 3 May 2017
Accepted Date: 6 May 2017
Please cite this article as: L. Wu, H. Zhou, J. Yang, X. Zhou, Y. Ren, Y. Nie, S. Chen, Carbon coated
mesoporous Si anode prepared by a partial magnesiothermic reduction for lithium-ion batteries, Journal
of Alloys and Compounds (2017), doi: 10.1016/j.jallcom.2017.05.057.
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ACCEPTED MANUSCRIPT
Carbon Coated Mesoporous Si Anode Prepared by a Partial
Magnesiothermic Reduction for Lithium-Ion Batteries
Lili Wua, 1, Haochen Zhoub, 1, Juan Yanga, *, Xiangyang Zhoua, Yongpeng
Rena, Yang Niea and Song Chena
a School of Metallurgy and Environment, Central South University, Changsha, China
b School of Aerospace Engineering, Tsinghua University, Beijing, China
1 These authors contributed equally to this work.
*Corresponding Author: j-yang@csu.edu.cn
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Abstract
Owing to its high theoretical capacity, Si based anode materials have been regarded as
the most promising alternative anode materials for lithium-ion batteries. Unfortunately,
the commercial application of Si based anode materials has been greatly hindered, due
to the large volume change of Si materials during their lithiation/delithiation process,
which results in severe pulverization, loss of electrical contact and rapid capacity
fading. To address these issues, we reported a partial magnesiothermic reduction
method by adjusting the proportion of added Mg powder to convert SiO2 into Si/SiO2
and subsequently to coat such a composite with a carbon layer. After removing
unreacted SiO2 using HF, carbon-coated mesoporous Si (p-Si@C) can be obtained.
The internal pores could accommodate the volume changes of Si and the carbon
coating layer could effectively stabilize the interface during cycling. With this design,
the as-prepared p-Si@C shows superior electrochemical performance compared with
bare Si. When the p-Si@C electrode evaluated at a rate of 0.5 A g-1, a reversible
capacity of 1146 mAh g-1 could still be maintained after 100 cycles.
Keywords: Mesoporous silicon; Carbon coating; Partial magnesiothermic reduction;
Lithium-ion battery
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1. Introduction
The ever-increasing demands for high-performance rechargeable batteries for use in
various consumer electronics, electric vehicles and energy storage power stations,
have stimulated tremendous research focus on developing lithium ion batteries (LIBs)
with high energy density and long cycle life.[1-3] To date, the low theoretical capacity
of commercialized graphite anode cannot meet the demands of high performance
LIBs.[4, 5] Silicon (Si) has been widely regarded as one of the most promising anodes
for high-performance LIBs because of its high theoretical capacity (3579 mAh g-1),
which is 10 times higher than that of graphite.[6-8] However, Si anodes would face
the crush of active material and rupture of the solid−electrolyte interface (SEI) layer,
due to the huge volume changes during cycling.[9-11]
These critical problems could be alleviated by combining conductive coatings
layers and designing nano-sized construction. Yolk-shell structure with void space has
been regarded as an effective method to address these problems, because the void
space can effectively alleviate the stress strain caused by volume changes.[12-14]
Typically, to produce void space for Si@void@C anodes, SiO2 has been used as a
sacrificial layer, produced between the Si core and the carbon coating layer, and then
etched with HF. The formation of a SiO2 sacrificial layer can be achieved by
hydrolysis of TEOS or partial oxidation of Si.[13, 15, 16] Even with the improved
cycling performance for yolk-shell Si-based anodes, practical application of such a
designed anode at a low-cost remains a severe challenge.[17-20] First, most
procedures involving these nano-Si particles are expensive and require complicated
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synthesis processes, such as chemical vapor deposition (CVD). Second, the formation
of void space requires an additional sacrificial SiO2 layer, which increases the
difficulty and cost of the synthesis process.
Recently, magnesiothermic reduction of SiO2 has been regarded as an effective
method to obtain nano-Si.[21, 22] To get a high reduction yield, the added Mg powder
was usually excessive (the theoretical mass ratio SiO2:Mg=1:0.8). However, the
excessive Mg powder would lead to the formation of Mg2Si, which could react
violently with HCl to produce combustible gas, causing interference in subsequent
treatment processes. Considering the reduction degree of SiO2 can be controlled by
adjusting the proportion of added Mg powder.[23, 24] Here, we present a partial
magnesiothermic reduction method to convert SiO2 into Si/SiO2 and subsequently to
coat such a composite with a carbon layer. After removing unreacted SiO2 by the use
of HF, carbon coated mesoporous Si can be obtained. The internal pores could
accommodate the volume changes of Si and the carbon coating layer could effectively
stabilize the interface during cycling. As a result, the as-prepared p-Si@C sample as
an anode exhibits a reversible capacity of 1146 mAh g-1 at 0.5 A g-1 after 100 cycles
and a capacity around 560 mAh g-1 at 10 A g-1.
2. Experimental
2.1 Preparation of the materials
The SiO2 nanoparticles were prepared using a modified Stöber method reported
before.[25, 26] Then the as-prepared SiO2 nanoparticles were mixed with Mg powder,
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NaCl with a mass ratio of 1:0.7:10 and sealed into an argon gas filled stainless
autoclave. After heated to 650 °C for 6 h, the resulting powder was immersed into 1M
HCl solution for 6 h to remove MgO. After that, the obtained Si/SiO2 and phenolic
resin (mass ratio=1:1) were mixed in ethanol and stirred at 80 °C until the solution
was dried. The obtained precursor was calcined at 800 °C for 2 h under argon
atmosphere. Finally, the resulting powder was immersed into 5wt% HF for 30 min to
remove the residual SiO2.
2.2 Characterization
The crystal structure of the samples was characterized on Rigaku-TTRIII. Scanning
electron microscopy (SEM), transmission electron microscopy (TEM) and energy
dispersive X-ray (EDX) mapping were performed using a Nova NanoSEM230 and a
JEOL JEM-2100F. Nitrogen adsorption and desorption (Quantachrome Nova Win 2)
was used to determine the Brunauer-Emmett-Teller (BET) surface areas and pore size
distributions of the samples. X-ray photoelectron spectroscopy (XPS,
ThermoFisher-VG Scientific) was used to analyze the surface element of samples.
Thermogravimetric analysis (TGA, SDTQ600) was used to estimate the weight
percentage of Si and C in p-Si@C.
2.3 Electrochemical characterization
The obtained samples were mixed with carbon black and sodium alginate (mass
ratio=8:1:1) using water as solvent to form a slurry and then coated on the Cu foil and
dried in an oven at 60°C. The working electrodes were obtained by cutting electrode
into disks (mass loading of the active material is around 0.5 mg cm-2). Coin cells were
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fabricated in an Ar filled glovebox with lithium foil and Celgard 2400 separator. The
used electrolyte was 1M LiPF6 in 1:1 v/v ethylene carbonate/diethyl carbonate with
10wt% fluoroethylene carbonate additives. The electrochemical performance of these
coin cells were conducted on battery-testing instruments (LAND-CT2001A). All the
cells were tested between 0.01-1.2 V.
3. Results and discussion
Fig.1 shows the preparation procedure for the mesoporous Si with carbon coating
(p-Si@C). Typically, SiO2 nanoparticles synthesized via the modified Stöber method
were uniformly mixed with Mg powders with the mass ratio of 1:0.7. Then the mixed
powders were heated to 650 °C in an argon-filled reactor. During the heating process,
SiO2 was partially converted into Si (SiO2(s) + 2Mg(g) → Si(s) + 2MgO(s)), and the
reaction temperature is much lower than the traditional carbothermic reduction of
silica (over 2000 °C). Usually, to get a high reduction yield, the added Mg powder for
magnesiothermic reduction was used in excess. However, excessive Mg powder
would lead to the formation of Mg2Si, which would cause interference in subsequent
treatment processes. Therefore, the partial magnesiothermic reduction method could
not only avoid the formation of Mg2Si, but also reserve void space. After removing
MgO, the composite of Si/SiO2 can be obtained. In addition, according to the mass
ratio of silica and Mg, we can infer that the content of Si in Si/SiO2 sample is around
75wt% and the content of SiO2 in Si/SiO2 sample is around 25wt%. After that, the
phenolic resin was used as carbon resources to wrap the as-formed Si/SiO2, and
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core-shell Si/SiO2@C can be obtained. After etching the residual SiO2 from
Si/SiO2@C, void space was formed inside the Si core.
To compare the structure morphology clearly, SEM and TEM images of SiO2,
Si/SiO2, bare Si and p-Si@C are displayed in Fig.2. The as-prepared SiO2
nanoparticles have spherical structures with a diameter around 200 nm (Fig. 2a and e).
After partial magnesiothermic reduction and following HCl etching, most of the
Si/SiO2 maintained the original morphology. According to the TEM image, the
Si/SiO2 sphere consisted of many interconnected nanoparticles with particle size
around 10-20 nm, which is a common phenomenon for magnesiothermic reduction in
the literature.[27-29] For bare Si (Fig. 2c and g), after etching residual SiO2 from
Si/SiO2 composite, the porous structure of bare Si became more apparent, which can
be even observed from the SEM image. Fig 2d and h exhibit the mesoporous Si
wrapped with carbon layer, and the p-Si@C has a much smoother surface compared
with the bare Si. According to the high-resolution TEM (HRTEM) acquired from the
edges of p-Si@C, the lattice fringe of 0.31 nm can be ascribed to the (111) crystal
plane. As a result of removing SiO2 from the composite, void spaces were generated
inside the Si core and covered with the carbon layer. In addition, EDX mapping was
performed to characterize the element distribution of Si and C as shown in Fig. 2j–l.
Besides the uniform distribution of the Si core in the carbon layer, it can be easily
founded that many pores with diameter around 20 nm are uniformly distributed in the
Si core. The internal pores and wrapped carbon layer are believed to be effective in
accommodating the volume change, easing the stress strain and improving the cycling
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stability.
X-ray diffraction (XRD) patterns of these samples are provided in Fig. 3a. Five
distinct peaks located at 28.4°, 47.3°, 56.1°, 69.1° and 76.4° can be indexed to the
cubic phase of Si (JCPDS No. 77-2111). After carbon coating, a weak peak at around
22° can be ascribed to the amorphous carbon layer.[30] X-ray photoelectron
spectroscopy (XPS, Fig. 3b) result could also demonstrate the existence of carbon
outside the Si core. As we know, XPS can only detect the surface elements (~5 nm),
the enhanced C1s peak and reduced Si signal of p-Si@C can be attributed to the
carbon coating layer. While the oxygen signal detected from XPS result can be
attributed to the SiOx layer outside the Si nanoparticles, which have been commonly
recognized in previous report.[31, 32] To further evaluate the mesoporous structures
of Si/SiO2, bare Si and p-Si@C, nitrogen adsorption-desorption measurements were
carried out. The nitrogen adsorption curves of all samples are displayed in Fig. 3c,
and each shows typical type IV isotherms, indicating the mesoporous character of
these samples. The BET surface area of p-Si@C (573 m2g-1) is much higher than that
of bare Si and Si/SiO2 (383 and 108 m2g-1, respectively), which can be ascribed to the
amorphous carbon layer and inter porous Si core. Moreover, the distribution of pore
size of these samples was calculated based on the Barret–Joyner–Halenda (BJH)
method as shown in Fig. 3d. Each samples shows peak centered around 3 nm, which
could be attributed to the pores between interconnected nanoparticles of Si spheres as
we mentioned above. However, after remove the residual SiO2, broad peaks at around
20 nm can be observed for bare Si and p-Si@C samples. This result indicates that HF
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etching of SiO2 is an effective method to obtain mesoporous Si, and the pore
diameters can be consistent with the speculation of EDX analysis.
To investigate p-Si@C sample as an anode material for LIBs, thermogravimetric
analysis (TGA) measurement was carried out to determine the weight percentage of Si
in the sample. As shown in Fig. 4a, the weight percentage of Si in the p-Si@C sample
was determined to be around 49.4%. As anode materials for LIBs, the as-prepared
bare Si and p-Si@C samples were tested within a voltage window between 0.01 and
1.2 V. Fig. 4b shows the discharge-charge curves of p-Si@C electrode at typical
cycles tested at a current density of 0.5 A g-1. During the initial discharge cycle, a
distinct plateau profile below 0.1 V can be ascribed to Si lithiation process.[33] The
first discharge and charge capacities of p-Si@C electrode are 1854 and 1287 mAh g-1
respectively, with an initial columbic efficiency of 69.4%. The irreversible capacity
loss of p-Si@C electrode during the first cycle could be attributed not only to the
formation of SEI layers, but also to the irreversible lithiation of SiOx layer and carbon
layer.[34-36] In the subsequent cycles, the capacity of p-Si@C electrode decreased
slowly and the voltage profiles are almost identical, indicating a stable
electrochemical behavior of p-Si@C electrode.
Fig. 4c shows the cycling stability of bare Si and p-Si@C electrodes evaluated at a
rate of 0.5 A g-1. It is clear that the p-Si@C electrode has a much stable cycling
performance. And when cycling up to 100 cycles, the p-Si@C electrode maintains a
reversible capacity of 1146 mAh g-1 (89.1% of its initial reversible capacity), which is
almost 3 times higher than graphite anode. While the capacity of bare Si electrode
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decreased rapidly from 2147 to 732 mAh g-1, with capacity retention of 34.1%. To
clearly understand the outstanding cycling performance of p-Si@C electrode, TEM
measurement was performed to observe the morphology of p-Si@C electrode after
100 cycles. As shown in Fig. 4d, the composite could still maintain its sphere
structure, which indicates that the well-organized structure could effectively alleviate
the volume change and prevent the pulverization of active material. The cycling
stability of p-Si@C electrode could be ascribed to the mesoporous Si core inside the
carbon layer, which could provide void space for the expanded lithiated Si material.
The rate performance of these samples was also performed as shown in Fig. 4e.
When the discharge/charge current density increased from 0.2 to 10 A g-1, the
reversible capacities of bare Si electrode decreased rapidly. While the p-Si@C
electrode delivers reversible capacities of 1470, 1320, 1200, 1000, 780 and 560 mAh
g-1 at 0.2, 0.5, 1, 2, 5, 10 A g-1, respectively. Significantly, the carbon coating layer has
a positive effect on the rate performance of electrode, which could be attributed to the
enhanced electron transfer through the carbon network. Moreover, once the current
density was returned back to 0.2 A g-1, the capacity of p-Si@C electrode could
recover back to 1410 mAh g-1, corresponding to approximately 96% of the reversible
capacity at the initial rate of 0.2 A g-1. This result manifests that the p-Si@C sample
has an excellent rate performance and reversibility.
In addition, to further evaluate the high-rate electrochemical performance of
p-Si@C electrode, the cycling performance at 2 A g-1 after the activation process
(cycled at 0.5 A g-1 for the initial 20 cycles) has been provided in Fig. 4f. The coin cell
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shows a reversible capacity of 1035.1 mAh g-1 at the beginning of 2 A g-1. During the
first 100 cycles, the reversible capacity decreased rapidly to 817.2 mAh g-1 and then
increased slightly to 872.5 mAh g-1. This phenomenon can be considered a
concentration polarization, which indicates that the rate of Li-ion migration is slower
than that of electron and electrochemical reaction of Li-ions is in short supply.[10, 12,
37, 38] After cycling up to 500 cycles, the reversible capacity could still reached 600
mAh g-1, which is much higher than the theoretical capacity of graphite. We ascribed
this excellent electrochemical performance to the existence of mesoporous inside the
Si core, which in turn relieve the stress–strain during the volume change. Additionally,
the carbon coating layer also contributed to the fast electron transfer and stabilization
of SEI films.
4. Conclusions
In this study, we designed a carbon coated mesoporous Si structure using a partial
magnesiothermic reduction method to convert SiO2 into mesoporous Si. Etching of
SiO2 provided the Si core sufficient void space for the volume change. In addition, the
carbon coating layer could provide fast electron diffusion and maintain the structure
stability of the p-Si@C, thus leading to outstanding electrochemical performance for
LIBs. As a result, the as-prepared p-Si@C sample as an anode exhibits a reversible
capacity of 1146 mAh g-1 at 0.5 A g-1 after 100 cycles and a capacity around 560 mAh
g-1 at 10 A g-1.
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Acknowledgements
We acknowledge support from the National Nature Science Foundation of China
(Grant no. 51204209 and 51274240) and the Project of Innovation-driven Plan in
Central South University.
References
[1] A.S. Arico, P. Bruce, B. Scrosati, J.-M. Tarascon, W. van Schalkwijk,
Nanostructured materials for advanced energy conversion and storage devices, Nat
Mater, 4 (2005) 366-377.
[2] M. Armand, J.M. Tarascon, Building better batteries, Nature, 451 (2008) 652-657.
[3] B. Dunn, H. Kamath, J.-M. Tarascon, Electrical Energy Storage for the Grid: A
Battery of Choices, Science, 334 (2011) 928-935.
[4] H. Tang, J. Zhang, Y.J. Zhang, Q.Q. Xiong, Y.Y. Tong, Y. Li, X.L. Wang, C.D. Gu,
J.P. Tu, Porous reduced graphene oxide sheet wrapped silicon composite fabricated by
steam etching for lithium-ion battery application, Journal of Power Sources, 286
(2015) 431-437.
[5] L. Wu, J. Yang, X. Zhou, M. Zhang, Y. Ren, Y. Nie, Silicon nanoparticles
embedded in a porous carbon matrix as a high-performance anode for lithium-ion
batteries, Journal of Materials Chemistry A, 4 (2016) 11381-11387.
[6] M.N. Obrovac, L. Christensen, D.B. Le, J.R. Dahn, Alloy Design for Lithium-Ion
Battery Anodes, Journal of The Electrochemical Society, 154 (2007) A849-A855.
[7] M.-H. Park, M.G. Kim, J. Joo, K. Kim, J. Kim, S. Ahn, Y. Cui, J. Cho, Silicon
12

ACCEPTED MANUSCRIPT
Nanotube Battery Anodes, Nano Letters, 9 (2009) 3844-3847.
[8] X. Su, Q. Wu, J. Li, X. Xiao, A. Lott, W. Lu, B.W. Sheldon, J. Wu, Silicon-Based
Nanomaterials for Lithium-Ion Batteries: A Review, Advanced Energy Materials, 4
(2014) 1300882-n/a.
[9] M.N. Obrovac, L. Christensen, Structural Changes in Silicon Anodes during
Lithium Insertion/Extraction, Electrochemical and Solid-State Letters, 7 (2004)
A93-A96.
[10] Z. Lu, N. Liu, H.-W. Lee, J. Zhao, W. Li, Y. Li, Y. Cui, Nonfilling Carbon
Coating of Porous Silicon Micrometer-Sized Particles for High-Performance Lithium
Battery Anodes, ACS Nano, 9 (2015) 2540-2547.
[11] M.T. McDowell, S.W. Lee, W.D. Nix, Y. Cui, 25th Anniversary Article:
Understanding the Lithiation of Silicon and Other Alloying Anodes for Lithium-Ion
Batteries, Advanced Materials, 25 (2013) 4966-4985.
[12] N. Liu, H. Wu, M.T. McDowell, Y. Yao, C. Wang, Y. Cui, A Yolk-Shell Design
for Stabilized and Scalable Li-Ion Battery Alloy Anodes, Nano Letters, 12 (2012)
3315-3321.
[13] X. Li, P. Meduri, X. Chen, W. Qi, M.H. Engelhard, W. Xu, F. Ding, J. Xiao, W.
Wang, C. Wang, J.-G. Zhang, J. Liu, Hollow core-shell structured porous Si-C
nanocomposites for Li-ion battery anodes, Journal of Materials Chemistry, 22 (2012)
11014-11017.
[14] X. Huang, J. Yang, S. Mao, J. Chang, P.B. Hallac, C.R. Fell, B. Metz, J. Jiang,
P.T. Hurley, J. Chen, Controllable Synthesis of Hollow Si Anode for Long-Cycle-Life
13

ACCEPTED MANUSCRIPT
Lithium-Ion Batteries, Advanced Materials, 26 (2014) 4326-4332.
[15] A. Esmanski, G.A. Ozin, Silicon Inverse-Opal-Based Macroporous Materials as
Negative Electrodes for Lithium Ion Batteries, Advanced Functional Materials, 19
(2009) 1999-2010.
[16] Y. Park, N.-S. Choi, S. Park, S.H. Woo, S. Sim, B.Y. Jang, S.M. Oh, S. Park, J.
Cho, K.T. Lee, Si-Encapsulating Hollow Carbon Electrodes via Electroless Etching
for Lithium-Ion Batteries, Advanced Energy Materials, 3 (2013) 206-212.
[17] K. Evanoff, A. Magasinski, J. Yang, G. Yushin, Nanosilicon-Coated Graphene
Granules as Anodes for Li-Ion Batteries, Advanced Energy Materials, 1 (2011)
495-498.
[18] Y. Xu, Q. Liu, Y. Zhu, Y. Liu, A. Langrock, M.R. Zachariah, C. Wang, Uniform
Nano-Sn/C Composite Anodes for Lithium Ion Batteries, Nano Letters, 13 (2013)
470-474.
[19] J. Wang, X. Meng, X. Fan, W. Zhang, H. Zhang, C. Wang, Scalable Synthesis of
Defect Abundant Si Nanorods for High-Performance Li-Ion Battery Anodes, ACS
Nano, 9 (2015) 6576-6586.
[20] L. Wu, J. Yang, X. Zhou, J. Tang, Y. Ren, Y. Nie, Enhanced Electrochemical
Performance of Heterogeneous Si/MoSi2 Anodes Prepared by a Magnesiothermic
Reduction, ACS Applied Materials & Interfaces, 8 (2016) 16862-16868.
[21] M.-P. Liu, C.-H. Li, H.-B. Du, X.-Z. You, Facile preparation of silicon hollow
spheres and their use in electrochemical capacitive energy storage, Chemical
Communications, 48 (2012) 4950-4952.
14

ACCEPTED MANUSCRIPT
[22] X. Zhou, L. Wu, J. Yang, J. Tang, L. Xi, B. Wang, Synthesis of nano-sized silicon
from natural halloysite clay and its high performance as anode for lithium-ion
batteries, Journal of Power Sources, 324 (2016) 33-40.
[23] Y. Yu, L. Gu, C. Zhu, S. Tsukimoto, P.A. van Aken, J. Maier, Reversible Storage
of Lithium in Silver-Coated Three-Dimensional Macroporous Silicon, Advanced
Materials, 22 (2010) 2247-2250.
[24] D. Chen, X. Mei, G. Ji, M. Lu, J. Xie, J. Lu, J.Y. Lee, Reversible Lithium-Ion
Storage in Silver-Treated Nanoscale Hollow Porous Silicon Particles, Angewandte
Chemie International Edition, 51 (2012) 2409-2413.
[25] W. Stöber, A. Fink, E. Bohn, Controlled growth of monodisperse silica spheres in
the micron size range, Journal of Colloid and Interface Science, 26 (1968) 62-69.
[26] W. Wang, Z. Favors, R. Ionescu, R. Ye, H.H. Bay, M. Ozkan, C.S. Ozkan,
Monodisperse Porous Silicon Spheres as Anode Materials for Lithium Ion Batteries,
Scientific Reports, 5 (2015) 8781.
[27] D.J. Lee, H. Lee, M.-H. Ryou, G.-B. Han, J.-N. Lee, J. Song, J. Choi, K.Y. Cho,
Y.M. Lee, J.-K. Park, Electrospun Three-Dimensional Mesoporous Silicon Nanofibers
as an Anode Material for High-Performance Lithium Secondary Batteries, ACS
Applied Materials & Interfaces, 5 (2013) 12005-12010.
[28] S. Fang, L. Shen, Z. Tong, H. Zheng, F. Zhang, X. Zhang, Si nanoparticles
encapsulated in elastic hollow carbon fibres for Li-ion battery anodes with high
structural stability, Nanoscale, 7 (2015) 7409-7414.
[29] T. Bok, S. Choi, J. Lee, S. Park, Effective strategies for improving the
15

ACCEPTED MANUSCRIPT
electrochemical properties of highly porous Si foam anodes in lithium-ion batteries,
Journal of Materials Chemistry A, 2 (2014) 14195-14200.
[30] W. Luo, Y. Wang, S. Chou, Y. Xu, W. Li, B. Kong, S.X. Dou, H.K. Liu, J. Yang,
Critical thickness of phenolic resin-based carbon interfacial layer for improving long
cycling stability of silicon nanoparticle anodes, Nano Energy, 27 (2016) 255-264.
[31] H. Kim, M. Seo, M.-H. Park, J. Cho, A Critical Size of Silicon Nano-Anodes for
Lithium Rechargeable Batteries, Angewandte Chemie International Edition, 49 (2010)
2146-2149.
[32] Y. Chen, Y. Hu, J. Shao, Z. Shen, R. Chen, X. Zhang, X. He, Y. Song, X. Xing,
Pyrolytic carbon-coated silicon/carbon nanofiber composite anodes for
high-performance lithium-ion batteries, Journal of Power Sources, 298 (2015)
130-137.
[33] Z. Wang, C. Xu, P. Tammela, J. Huo, M. Stromme, K. Edstrom, T. Gustafsson, L.
Nyholm, Flexible freestanding Cladophora nanocellulose paper based Si anodes for
lithium-ion batteries, Journal of Materials Chemistry A, 3 (2015) 14109-14115.
[34] M. Nie, D.P. Abraham, Y. Chen, A. Bose, B.L. Lucht, Silicon Solid Electrolyte
Interphase (SEI) of Lithium Ion Battery Characterized by Microscopy and
Spectroscopy, The Journal of Physical Chemistry C, 117 (2013) 13403-13412.
[35] X. Han, H. Chen, J. Liu, H. Liu, P. Wang, K. Huang, C. Li, S. Chen, Y. Yang, A
Peanut Shell Inspired Scalable Synthesis of Three-Dimensional Carbon Coated
Porous Silicon Particles as an Anode for Lithium-Ion Batteries, Electrochimica Acta,
156 (2015) 11-19.
16

ACCEPTED MANUSCRIPT
[36] L. Wu, J. Yang, J. Tang, Y. Ren, Y. Nie, X. Zhou, Three-dimensional graphene
nanosheets loaded with Si nanoparticles by in situ reduction of SiO2 for lithium ion
batteries, Electrochimica Acta, 190 (2016) 628-635.
[37] Z.-L. Xu, Y. Gang, M.A. Garakani, S. Abouali, J.-Q. Huang, J.-K. Kim,
Carbon-coated mesoporous silicon microsphere anodes with greatly reduced volume
expansion, Journal of Materials Chemistry A, 4 (2016) 6098-6106.
[38] D. Lin, Z. Lu, P.-C. Hsu, H.R. Lee, N. Liu, J. Zhao, H. Wang, C. Liu, Y. Cui, A
high tap density secondary silicon particle anode fabricated by scalable mechanical
pressing for lithium-ion batteries, Energy & Environmental Science, 8 (2015)
2371-2376.
17

ACCEPTED MANUSCRIPT
Figure Captions:
Fig. 1. Schematic illustration of the synthesis processes of the bare Si and p-Si@C.
Fig. 2. SEM and TEM images of (a and e) SiO2, (b and f) Si/SiO2, (c and g) bare Si
and (d and h) p-Si@C. Corresponding (i) HRTEM image and (j-l) EDX mapping of
carbon and silicon distribution in the p-Si@C sample.
Fig. 3. (a) XRD patterns of the bare Si and p-Si@C samples. (b) Survey XPS spectra
of the bare Si and p-Si@C samples. (c) Nitrogen adsorption-desorption curves and (d)
pore size distribution of Si/SiO2, bare Si and p-Si@C samples.
Fig. 4. (a) TGA curves of the p-Si@C sample measured at a heating rate of 10 °C
min-1 in air. (b) Voltage profiles of p-Si@C electrode at typical cycles tested at a
current density of 0.5 A g-1. (c) Cycling stability of the as-prepared bare Si and
p-Si@C electrodes. (d) TEM image of p-Si@C electrode after 100 cycles. (e) Rate
performance of the bare Si and p-Si@C electrodes. (f) Electrochemical performance
of p-Si@C electrode at a current density of 2 A g-1.
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Fig. 1. Schematic illustration of the synthesis processes of the bare Si and p-Si@C.
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Fig. 2. SEM and TEM images of (a and e) SiO2, (b and f) Si/SiO2, (c and g) bare Si
and (d and h) p-Si@C. Corresponding (i) HRTEM image and (j-l) EDX mapping of
carbon and silicon distribution in the p-Si@C sample.
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Fig. 3. (a) XRD patterns of the bare Si and p-Si@C samples. (b) Survey XPS spectra
of the bare Si and p-Si@C samples. (c) Nitrogen adsorption-desorption curves and (d)
pore size distribution of Si/SiO2, bare Si and p-Si@C samples.
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Fig. 4. (a) TGA curves of the p-Si@C sample measured at a heating rate of 10 °C
min-1 in air. (b) Voltage profiles of p-Si@C electrode at typical cycles tested at a
current density of 0.5 A g-1. (c) Cycling stability of the as-prepared bare Si and
p-Si@C electrodes. (d) TEM image of p-Si@C electrode after 100 cycles. (e) Rate
performance of the bare Si and p-Si@C electrodes. (f) Electrochemical performance
of p-Si@C electrode at a current density of 2 A g-1.
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Highlights
ꢀ A Partial Magnesiothermic Reduction Method is used to obtain mesoporous Si.
ꢀ The internal pores could accommodate the volume changes of Si.
ꢀ The carbon coating layer could effectively stabilize the interface during cycling.