Simultaneous Purification and Perforation of Low-Grade Si Sources for

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Simultaneous Purification and Perforation of Low Grade Si Sources for Lithium-ion Battery Anode Yan Jin, Su Zhang, Bin Zhu, Yingling Tan, Xiaozhen Hu, Linqi Zong, and Jia Zhu Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.5b03932 • Publication Date (Web): 22 Oct 2015 Downloaded from http://pubs.acs.org on October 23, 2015

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Simultaneous Purification and Perforation of Low Grade Si Sources for Lithium-ion Battery Anode

Yan Jin,† Su Zhang,† Bin Zhu,† Yingling Tan,† Xiaozhen Hu,† Linqi Zong,† and Jia Zhu*† †

National Laboratory of Solid State Microstructures, College of Engineering and

Applied Sciences, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China

* E-mail: [email protected] (J. Z.)

ABSTRACT: Silicon is regarded as one of the most promising candidates for lithium-ion battery anodes because of its abundance and high theoretical capacity. Various silicon nanostructures have been heavily investigated to improve electrochemical performance by addressing issues related to structure fracture and unstable Solid-Electrolyte Interphase (SEI). However, to further enable wide-spread applications, scalable and cost effective processes need to be developed to produce these nanostructures at large quantity with finely controlled structures and morphologies. In this study, we develop a scalable and low cost process to produce porous silicon directly from low grade silicon through ball-milling and modified metal-assisted chemical etching. The morphology of porous silicon can be drastically changed from porous-network to nanowire-array by adjusting the component in reaction solutions. Meanwhile, this perforation process can also effectively remove

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the impurities, and therefore increase Si purity (up to 99.4%) significantly from low grade and low cost ferrosilicon (purity of 84%) sources. The electrochemical examinations indicate that these porous silicon structures with carbon treatment can deliver a stable capacity of 1287 mAh g-1 over 100 cycles at a current density of 2 A g-1. This type of purified porous silicon with finely controlled morphology, produced by a scalable and cost-effective fabrication process can also serve as promising candidates for many other energy applications, such as thermoelectrics and solar energy conversion devices.

KEYWORDS: low-grade silicon, porous, purification, ball-milling, modified metal-assisted chemical etching, lithium-ion battery anodes

With the increasing demand of portable electronics, electric vehicles and the storage of renewable energy, next generation energy storage technologies such as lithium-ion batteries (LIBs) with high energy density and long cycle life are urgently needed.1 Silicon is widely considered as one of the most promising anode materials because of its high theoretical capacity (the fully lithiated alloy Li4.4Si is 4200 mAh g-1) and abundant resource (the second-most abundant element in the earth’s crust). Unfortunately, ~300% volume change of silicon during lithiation and delithiation leads to severe particle pulverization, loss of electrical contact and unstable SEI formation, resulting in capacity fading and limited cycle life.2-6 In recent years, various silicon nanostructures such as nanowires, nanotubes, nanoparticles and porous networks, have been extensively studied, which show great potential to


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overcome the pulverization and unstable SEI problems by reducing stress and accommodating large volume expansion and contraction during electrochemical alloying.7-20 However, low cost and scalable processes are necessary to produce these nanostructures with fine controlled morphologies, in order to further enable large scale applications. Traditionally, silicon nanostructures are fabricated either from top-down (templated chemical etching) or bottom-up (CVD) method, which involves either expensive high purity silicon sources or toxic silane precursors. As an example, the price of commercial crystalline silicon powder (~325mesh) with a purity of 99.5% is ~$920 kg-1 (Alfa Aesar). Several low grade silicon sources, such as metallurgical-grade silicon (M-Si, ~98wt% Si, $1kg-1) and ferrosilicon (F-Si, ~83wt% Si, $0.6kg-1) with annual global production over six million tonnes can serve as cost effective sources to produce nanostructured silicon for lithium-ion battery.21-23 In this study, a scalable and low cost process, which involves ball-milling24-25 and modified metal-assisted chemical etching,26-34 is developed to perforate and purify these low grade silicon sources at the same time. Fig. 1a shows the schematic diagram of the fabrication processes of porous silicon and simultaneous purification effect. First, low grade silicon sources with 98% purity were ball milled for 5 hours at the speed of 500 r min-1. These ball-milled low grade Si powders, with overall dimensions of ~10 mm, were then immersed in 150 ml reaction solution containing silver nitrate (AgNO3, 20 mM), 33 ml hydrofluoric acid (HF, 5 M) and 117 ml De-ionized (DI) water for 2 hours. In most of previous metal-assisted chemical


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etching (MACE) studies, silicon wafers are used, therefore MACE etching will start only from the top surface.13, 15, 29, 33 However, in this case, as silicon powders are floating in the solution, silver atoms are expected to be deposited on all the surfaces of the M-Si powder. These silver sites and the area around them act as cathodes and anodes in the electrochemical redox reaction, respectively. The whole chemical reaction can be formulated as below: 4Ag++Si+6F-→4Ag+SiF62-

(1)

As shown in schematic of our modified MACE process (Figure S1, Supporting information), Ag particles tend to drill deep into the micron-sized silicon particle, which result in a porous structure. At the same time, impurities (such as iron, aluminum etc.,) original existed in these low grade Si sources are also removed as long as they are exposed to the acidic etchant solution.

In this modified MACE method, it is found that by adding ethanol in the reaction solution to tune dispersibility and hydrophobicity of silicon powder, porous nanostructures with different morphologies can be obtained. For example, by substituting 117 ml, 30 ml, 10 ml ethanol and an additional 1 ml H2O2 for DI water, the morphology of porous silicon can be tuned from porous-network to nanowire-array, as shown in Fig. 1b, c, d and e respectively. This change of porous morphology can be attributed to the indissolubility of AgF in ethanol. It is noted that when DI water is completely replaced with ethanol, very little AgF dissolved in limited amount of water brought by 40% HF. Therefore the electrochemical etching is


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largely prohibited, and silicon porous networks with shallow pores (~30-50 nm) are obtained, as shown in Fig. 1b. By reducing the amount of ethanol to 30 ml, silicon with larger (~100-200 nm) and deeper pores are obtained, as displayed in Fig. 1c. As ethanol is reduced further to 10 ml, etching will be more effective, electrochemical redox reaction can happen deep into the surface. Therefore, the morphology of porous silicon is dramatically changed from porous-network to nanowire-array. For 2 hours etch, these wires are ~2-5 µm long with ~50 nm diameter. However, if additional 1 ml H2O2 (30%) was then added, silicon particles with micron sized pores were obtained due to reaction between silicon with H2O2 (chemical reaction formula: Si+2H2O2+6F-+4H+→SiF62-+4H2O). It is determined based on BET measurements (Figure S6, Supporting information) that the exposed surface areas of porous silicon in Fig. 1e are 94.9 m2 g− 1 and the pore volumes are 0.126 cm3 g− 1.

X-ray Fluorescence (XRF) is used to quantitatively investigate the level of impurities in Si and evaluate the purification effect (Fig. 1f and g) after the etching processes. In the case of metallurgical silicon, three major impurities content decrease significantly (Fe 0.421% to 0.022%, Ca 0.139% to 0.019%, Al 0.308% to 0.16%), as shown in Fig. 1f. In the case of ferrosilicon, impurities are also removed very effectively (Fe 12.816% to 0.196%, Ca 2.157% to 0.0075%, Al 1.108% to 0.04068% shown in Fig. 1g). Therefore the purity of silicon increases dramatically from 83.4% to 99.4%.

Once porous silicon with different morphologies was obtained, the electrochemical performance was systematically investigated. The electrodes were composed of


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porous silicon powder, carbon black, and CMC as a binder (2:1:1, weight ratio) combined in DI water. For comparison, micro-sized 98% M-Si electrode, made by ball-milling for 5 hours at a speed of 500 r min-1 without MACE is labeled as sample A. Fig. 2a shows the long-term cycling data of these two kinds of porous silicon with modified MACE (sample B: 30 ml ethanol and sample C: 1 ml H2O2) in comparison with sample A (without MACE electrode). Sample A shows quick capacity fading and limited cycle life, because ~300% volume change of silicon during lithiation and delithiation can lead to severe particle pulverization of micron sized particles and loss of electrical contact between the active material and current collector.3,4 Porous silicon demonstrates much improved electrochemical performance, which is expected as porous structures have large void space allowing for volume expansion during electrochemical alloying. Among these porous silicon samples (electrochemical performance of samples with 10 ml and 117 ml ethanol are shown in Figure S2, Supporting information), sample C shows the best electrochemical performances because of micron sized porous structures. Sample C (1 ml H2O2) was also cycled at 420 mA g-1 for 100 cycles, as shown in Fig. 2a. A capacity of ~1000 mAh g-1 and ~80% capacity retention over 100 cycles are obtained. A cyclic voltammetry of sample C is shown in Fig. 2b. The cathodic peak at ~0.21 V and the anodic peaks at ~0.32 V and ~0.49 V are characteristic of amorphous silicon and the cathodic peak at ~0 V is characteristic of both crystalline and amorphous silicon. In the first cathodic scan, the curves appear very similar to those obtained from standard crystalline silicon,7 and they are consistent with the crystalline


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XRD pattern shown in Figure S3 (Supporting information). As only crystalline silicon exists, just one peak at ~0 V is observed. However, as the crystalline structure becomes amorphous during lithiation, two anodic peaks of amorphous silicon (at ~0.32 V and ~0.49 V) are observed in the subsequent anodic scans. The typical charge-discharge curves (Fig. 2c) obtained between 0.05 and 1.5 V at a current density of 420 mA g-1 are similar to those observed with other silicon nanostrucures.31,33 The first cycle shows the characteristic potential profile of crystalline silicon, lithiation and delithiation take place at 0.1 V and 0.42 V vs. Li/Li+, respectively. The increased capacity of the second cycle can be attributed to the electrolyte infiltrating into porous structures. In order to further improve the electrochemical performance, two kinds of carbon coating were employed to enhance the electrical conductivity of micron sized porous silicon (SEM shown in Fig. 1e and sample C in Fig. 2a). One is layered Si/ reduced graphene oxide (rGO) composite through filtration of grapheme oxide (Hummers method36) with porous silicon powder solution. Figure 3 shows the schematic and detailed characterizations of the obtained Si/rGO composite. Micrometer-sized porous silicon particles are completely enfolded by sheets of rGO (Fig. 3a). The edge-view SEM images of the multilayered composite (Fig. 3b) clearly demonstrates the layered structures of the composite, where Si particles are fully encapsulated by well-separated rGO films. It also confirms that the rGO does not restack during the reduction or the following coating process. Furthermore, the porous structures of these Si particles are well protected during the multilayer compound formation


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process, as shown in the high magnification SEM images after graphene coating (Fig. 3c). The tight connection between the Si particles and graphene indicates that the electrostatic interaction is an efficient way to encapsulate irregular Si micro particles into rGO sheet. Therefore, both the void structure of Si particles and the layered structure of Si/rGO compound can act as efficient buffer layers of the volume change, beneficial for electrochemical cycling. The other method for carbon coating is the citric acid treatment. The porous Si powders and citric acid powders were mixed in deionized water with a weight ratio of 1:2.5 and followed by a 3h ultrasonic treatment. Then the obtained porous Si powders and citric acid suspensions were dried at 110℃ in a vacuum oven and heat-treated at 800℃ for 2 h under a flowing Ar atmosphere to carbonize the citric acid, forming the carbon coated Si powders. SEM and Energy-dispersive X-ray Spectroscopy (EDS) elemental mapping (Figure S4, Supporting information) clearly confirms the presence and uniform distribution of C element, therefore the conformal carbon coating on porous silicon. 88 wt% silicon content in the composite is determined by thermal gravimetric (TG) analysis (Figure S2, Supporting information). Figure 4 shows the electrochemical performance of micron sized porous silicon after carbon treatment. Fig. 4a and 4b show the electrochemical performances of Si/rGO composite. With the reduced oxide graphene, the first discharge capacity of Si/rGO composite electrode can reach 2110 mAh g-1 at the 0.2 A g-1 rate. From the 6th cycle, the current density is increased to 0.8 A g-1, the charge capacity remained stable above 1070 mAh g-1 after 100 cycles. The initial coulombic efficiency of porous


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Si/rGO composite is 68%. The loss of first reversible capacities can be mainly attributed to the irreversible reduction of the electrolyte to form a surface passivation layer on the active particles. Besides, Li trapped on defects such as edges and/or oxygen- and hydrogen-containing surface groups of rGO is responsible for low first cycle CE. At charge/discharge current densities ranging from 0.2 A g-1 to 4 A g-1, the capacities of 2694 to 1200 mAh g-1 in the electrode were obtained (Fig. 4b). Additionally, Fig. 4c and 4d present the battery performance of citric acid carbon coated porous silicon. The initial discharge capacity can reach 1830 mAh g-1 at the 0.2 A g-1 rate. From the 6th to 100th cycle at a rate of 2 A g-1, the charge capacity remained stable above 1287 mAh g-1 after 100 cycles with over 90% capacity retain. SEM image of porous silicon powder in the electrode with SEI after 70 cycles shows that silicon powder did not break into smaller fragments during the lithiation process, but still preserved its initial porous geometry (Figure S7, Supporting information). Fig. 4d shows the capacity change of electrodes at different current densities. At 0.2 A g-1 rate, the capacity was approximately 1561 mAh g-1, when at 4 A g-1 rate, the capacity still maintained above 1150 mAh g-1. Therefore it is confirmed that these carbon layers can serve as both good electronic conductors and buffer layers for the volume change during lithiation/delithiation process. In summary, low grade silicon sources can be perforated and purified to produce high purity porous Si particles through scalable processes, which combines simple ball-milling and modified metal-assisted chemical etching processes. The morphology can be finely controlled by simply adjusting the amount of ethanol and hydrogen


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peroxide in reaction solution. The porous silicon with carbon treatment exhibit large discharge lithium storage capacity (1287 mAh g-1) over 100 cycles. The finely controlled morphology, dramatic purification effect together with scalable and cost-effective fabrication processes make purified porous silicon promising candidates for the development of next generation lithium-ion battery anodes, as well as thermoelectrics, solar energy conversion and other energy related devices.

Methods:

Fabrication processes of porous silicon: 98% metallurgical-grade silicon (M-Si) was used as received to prepare porous silicon via ball-milling and modified metal-assisted chemical etching. It was first crushed into millimeter range and then ball-milled into powder by planetary ball-milling for 5 hours at a speed of 500 r min-1. The M-Si powder was then immersed in a solution of 20 mM silver nitrate (AgNO3) and 5 M hydrofluoric acid (HF) at 50℃ for 2 hours. Then DI water was substituted by 117 ml, 30 ml,10 ml ethanol and additional 1 ml H2O2 to get porous silicon. Silver (Ag) on the surface was then removed in concentrated nitric acid for 1 hour. For carbon coating of porous silicon powder, porous silicon powders were added into the graphene oxide solution (Si:GO = 1:1, wt ratio) with ultrasonic for 1h and collected with micropore filter paper through filtration. GO/Si paper was removed carefully from the filter membrane and air-dried at 110 °C in a vacuum oven. The dried paper was cut into smaller strips and loaded into a quartz tube for reduction in a flow of 2% H2 in Ar at 100℃ for 1 h to form the rGo/Si composite.


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Material Characterizations: The morphologies and structures of the as-prepared porous silicon were characterized by scanning electron microscopy (Dual-beam FIB 235,FEI Strata) and transmission electron microscopy (JEM-200CX). XRD spectra was obtained on a Rigaku Ultima X-ray Ⅳ diffractometer using a Cu Ka 1°min-1. The weight percentage of Si and C in the carbon-coated porous silicon was determined from the weight loss curves measured under simulated air atmosphere (25% O2 + 75% N2) on a TG instrument (Netzsch STA 409PC) with a heating rate of 10 oC min-1. Nitrogen sorption isotherms were obtained using a surface area and porosity analyzer (Tristar micromeritics) at -196℃. Electrochemical testing: The prepared porous silicon was mixed with carbon black and CMC binder (2:1:1, weight ratio) to make slurry and then cast onto a thin copper foil and dried in a vacuum oven at 90℃ overnight and 110℃for 2h. Coin-type cells (2032) were fabricated inside an Ar-filled glove box using Li metal foil as counter/reference electrode, along with a celgard 2250 separator. The electrolyte employed was 1.0 M LiPF6 in 1:1 vol/vol ethylene carbonate/diethyl carbonate with 2 m% vinylene carbonate (Guotai Huarong Corporation) added to improve the cycling stability. Galvanostatic cycling was performed using a LANHE CT2001A, the galvanostatic voltage cutoffs were 0.01 and 1.5 V vs Li/Li+. The specific capacity was calculated based on the mass of active materials (contain silicon and carbon). The charge/discharge rate was calculated with respect to the theoretical capacity of silicon (4200 mAh g-1, 1C = 4200 mA g-1). The mass loading of active material (silicon and carbon in the porous silicon) was ~0.2 mg cm-2. Cyclic voltammograms were


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measured on a CHI660E workstation (CH Instruments, Shanghai) in the voltage range of 1–0.01 V under the scanning rate of 0.1 mV s-1.

Supporting Information Available Fabrication schematics of metal assisted chemical etching, Long-term cycling electrochemical performance of samples with 10 ml and 117 ml ethanol, XRD pattern of HF-treated porous silicon, SEM image and elemental mapping of carbon-coated porous silicon, TG curve of carbon-coated porous silicon, isothermal curves of the porous silicon, SEM images of porous silicon powder in the electrode with SEI after 70 cycles. This material is available free of charge via the Internet at http://pubs.acs.org.

Author Information Corresponding Author * E-mail: [email protected] (J. Z.) Notes The authors declare no competing financial interest.

Acknowledgements This work is jointly supported by the State Key Program for Basic Research of China (No. 2015CB659300), National Natural Science Foundation of China (NSFC No. 11321063 and No. 11574143), Natural Science Foundation of Jiangsu Province (No. BK20150056), the Priority Academic Program Development of Jiangsu Higher


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Education Institutions (PAPD) and the Fundamental Research Funds for the Central Universities.

REFERENCES 1.

Tarascon, J. M.; Armand, M. Nature 2001, 414, 359-367.

2.

Arico, A. S.; Bruce, P.; Scrosati, B.; Tarascon, J. M.; Van Schalkwijk, W. Nat

Mater 2005, 4, 366-377. 3.

Bruce, P. G.; Scrosati, B.; Tarascon, J. M. Angew Chem Int Edit 2008, 47,

2930-2946. 4.

Wu, H.; Cui, Y. Nano Today 2012, 7, 414-429.

5.

Su, X.; Wu, Q. L.; Li, J. C.; Xiao, X. C.; Lott, A.; Lu, W. Q.; Sheldon, B. W.;

Wu, J. Adv Energy Mater 2014, 4. 6.

Szczech, J. R.; Jin, S. Energ Environ Sci 2011, 4, 56-72.

7.

Chan, C. K.; Peng, H. L.; Liu, G.; McIlwrath, K.; Zhang, X. F.; Huggins, R. A.;

Cui, Y. Nat Nanotechnol 2008, 3, 31-35. 8.

Wu, H.; Chan, G.; Choi, J. W.; Ryu, I.; Yao, Y.; McDowell, M. T.; Lee, S. W.;

Jackson, A.; Yang, Y.; Hu, L. B.; Cui, Y. Nat Nanotechnol 2012, 7, 309-314. 9.

Ge, M. Y.; Rong, J. P.; Fang, X.; Zhou, C. W. Nano Lett 2012, 12, 2318-2323.

10. Hwang, T. H.; Lee, Y. M.; Kong, B. S.; Seo, J. S.; Choi, J. W. Nano Lett 2012, 12, 802-807. 11. Liu, N.; Lu, Z. D.; Zhao, J.; McDowell, M. T.; Lee, H. W.; Zhao, W. T.; Cui, Y. Nat Nanotechnol 2014, 9, 187-192. 12. Li, X. L.; Gu, M.; Hu, S. Y.; Kennard, R.; Yan, P. F.; Chen, X. L.; Wang, C. M.; Sailor, M. J.; Zhang, J. G.; Liu, J. Nat Commun 2014, 5. 13. Jia, H. P.; Gao, P. F.; Yang, J.; Wang, J. L.; Nuli, Y. N.; Yang, Z. Adv Energy Mater 2011, 1, 1036-1039. 14. Yao, Y.; McDowell, M. T.; Ryu, I.; Wu, H.; Liu, N. A.; Hu, L. B.; Nix, W. D.; Cui, Y. Nano Lett 2011, 11, 2949-2954. 15. Peng, K. Q.; Jie, J. S.; Zhang, W. J.; Lee, S. T. Appl Phys Lett 2008, 93 .


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

16. Jung, D. S.; Ryou, M. H.; Sung, Y. J.; Park, S. B.; Choi, J. W. P Natl Acad Sci USA 2013, 110, 12229-12234. 17. Liu, N.; Wu, H.; McDowell, M. T.; Yao, Y.; Wang, C. M.; Cui, Y. Nano Lett 2012, 12, 3315-3321. 18. Park, M. H.; Kim, M. G.; Joo, J.; Kim, K.; Kim, J.; Ahn, S.; Cui, Y.; Cho, J. Nano Lett 2009, 9, 3844-3847. 19. Kim, H.; Cho, J. Nano Lett 2008, 8, 3688-3691. 20. Kim, H.; Han, B.; Choo, J.; Cho, J. Angew Chem Int Edit 2008, 47, 10151-10154. 21. Ge, M. Y.; Lu, Y. H.; Ercius, P.; Rong, J. P.; Fang, X.; Mecklenburg, M.; Zhou, C. W. Nano Lett 2014, 14, 261-268. 22. Zhang, J.; Song, T.; Shen, X. L.; Yu, X. G.; Lee, S. T.; Sun, B. Q. Acs Nano 2014, 8, 11369-11376. 23. Li, X.; Yan, C.; Wang, J.; Graff, A.; Schweizer, S. L.; Sprafke, A.; Schmidt ,O. G.;Wehrspohn,R.B.Advanced Energy Materials2014, 5,1401556. 24. Gauthier, M.; Mazouzi, D.; Reyter, D.; Lestriez, B.; Moreau, P.; Guyomard, D.; Roue, L. Energ Environ Sci 2013, 6, 2145-2155. 25. Xu, J.; Jeon, I. Y.; Seo, J. M.; Dou, S.; Dai, L.; Baek, J. B. Advanced materials 2014, 26, 7317-23. 26. Ge, M. Y.; Rong, J. P.; Fang, X.; Zhang, A. Y.; Lu, Y. H.; Zhou, C. W. Nano Res 2013, 6, 174-181. 27. Lee, J. I.; Lee, K. T.; Cho, J.; Kim, J.; Choi, N. S.; Park, S. Angew Chem Int Edit 2012, 51, 2767-2771. 28. Peng, K. Q.; Yan, Y. J.; Gao, S. P.; Zhu, J. Adv Funct Mater 2003, 13, 127-132. 29. Peng, K. Q.; Hu, J. J.; Yan, Y. J.; Wu, Y.; Fang, H.; Xu, Y.; Lee, S. T.; Zhu, J. Adv Funct Mater 2006, 16, 387-394. 30. Peng, K. Q.; Fang, H.; Hu, J. J.; Wu, Y.; Zhu, J.; Yan, Y. J.; Lee, S. Chem-Eur J 2006, 12, 7942-7947. 31. Bang, B. M.; Kim, H.; Song, H. K.; Cho, J.; Park, S. Energ Environ Sci 2011, 4, 5013-5019.


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32. Huang, R.; Fan, X.; Shen, W. C.; Zhu, J. Appl Phys Lett 2009, 95. 33. Vlad, A.; Reddy, A. L. M.; Ajayan, A.; Singh, N.; Gohy, J. F.; Melinte, S.; Ajayan, P. M. P Natl Acad Sci USA 2012, 109, 15168-15173. 34. Bang, B. M.; Lee, J. I.; Kim, H.; Cho, J.; Park, S. Adv Energy Mater 2012, 2, 878-883. 35. Liu, X. H.; Zhong, L.; Huang, S.; Mao, S. X.; Zhu, T.; Huang, J. Y. Acs Nano 2012, 6, 1522-1531. 36. Hummers, W. S.; Offeman, R. E. J Am Chem Soc 1958, 80, 1339-1339.


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FIGURE CAPTIONS

Figure 1. a) Schematic diagram of simultaneous perforation and purification processes, b), c), d) and e) SEM images of porous silicon obtained with different reaction solutions, 117 ml, 30 ml, 10 ml ethanol and 1 ml H2O2 respectively, f) and g)


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XRF data of the M-Si and F-Si before and after the modified MACE process, respectively.


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Figure 2. Electrochemical performances of porous silicon: a) Long-term cycling of porous silicon electrodes. Sample A (without MACE), Sample B(with 30 ml ethanol) and Sample C(with 1 ml H2O2), b) Cyclic voltammetry curves of first 3 cycles of the porous silicon electrode (Sample C) in the potential window between 0.01 to 1 V at a rate of 0.1 mV s-1, c) Voltage profiles of porous silicon (Sample C) for the 1st, 50th and 100th cycles at a current density of 420 mA g-1 (corresponding to the dark curve in Fig. 2a).


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Figure 3. a) Schematics of fabrication processes of Si/rGO composite, b) Edge-view SEM images of the multilayered composite (inset shows optical images of Si/rGO composite paper), c) High resolution SEM image showing tight connection between the porous Si particles and reduced graphene oxide.


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Figure 4. Electrochemical performance of carbon-coated porous silicon: a) Charge-discharge cycling test of porous Si/rGO composite, b) Capacity retention of porous Si/rGO composite cycled at different current densities ranging from 0.2 A g-1 to 4 Ag-1, c) Charge-discharge cycling test of porous Si after citric acid carbon coating, d) Capacity retention of porous after citric acid carbon coating cycled at different current densities ranging from 0.2 A g-1 to 2 A g-1.


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Simultaneous Purification and Perforation of Low Grade Si Sources 99x60mm (300 x 300 DPI)


Simultaneous Purification and Perforation of Low-Grade Si Sources for

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