ARTICLE pubs.acs.org/JPCC Synthesis, Growth Mechanism, and Electrochemical Properties of Hollow Mesoporous Carbon Spheres with Controlled Diameter Xuecheng Chen,*,† Krzysztof Kierzek,‡ Zhiwei Jiang,§ Hongmin Chen,^ Tao Tang,§ Malgorzata Wojtoniszak,† Ryszard J. Kalenczuk,† Paul K. Chu,*,^ and Ewa Borowiak-Palen† † Institute of Chemical and Environment Engineering, West Pomeranian University of Technology, Szczecinul. Pulaskiego 10, 70-322 Szczecin, Poland ‡ Department of Polymer and Carbonaceous Materials, Wroclaw University of Technology, ul. Gdanska 7/9, 50344 Wroclaw, Poland § Changchun Institute of Applied Chemistry, Chinese Academy of Science, Changchun, China ^ Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, China ABSTRACT: Hollow mesoporous carbon spheres with controllable diameters have been fabricated from core shell structured mesoporous silica sphere templates using chemical vapor deposition (CVD). By controlling the thickness of the silica shell, hollow carbon spheres with different diameters are obtained. The use of ethylene as the carbon precursor produces mesoporous graphitic hollow carbon spheres. The hollow carbon spheres have a relatively large degree of graphitization together with good meso-structural order and high specific surface area of 771 m2/g. The mechanism governing the formation of the hollow spheres is studied, and the importance of the surfactant (CTAB) is also clarified. CTAB accelerates the carbon deposition process, thus improving the product yield. These hollow carbon spheres that have good electrochemical properties are suitable for lithium ion batteries. ’ INTRODUCTION Future nanotechnology hinges on the ability to synthesize new nanomaterials possessing distinct structural and functional features.1,2 Among them, hollow nanospheres are unique and have attracted much research and industrial interest due to their special shape, low density, and large fraction of voids. Hollow nanospheres possess “tunable” void volume, excellent flow performance, and large surface area. The large internal volume provides a storage space or an artificial reaction “cell” that can serve many functions,3,4 and much can be learned from mesoporous nanostructures. Mesoporous carbon has been a big research topic because of its remarkable properties such as high specific surface area, large pore volume, low density, thermal conductivity, electrical conductivity, good chemical and mechanical stability, and great application potential to catalysts, electrodes, batteries, sensors, adsorbents in separation processes, gas storage materials, and templates for fabricating nanostructures. Furthermore, hollow carbon spheres with mesoporous shells possess more advantages in mass diffusion and transport than conventional mesoporous materials due to their larger pore, cavity volume, and spherical morphology.5 13 Several approaches have been developed to prepare hollow mesoporous carbon spheres. These hollow mesoporous carbon spheres are generally fabricated using sacrificial templates because this method allows control of the pore structure and morphology of the resulting carbon materials. There are two common ways to synthesize hollow mesoporous carbon spheres. r 2011 American Chemical Society In the first technique, hard mesoporous templates are infiltrated with carbon precursors and then carbonized at a high temperature under nonoxidizing conditions to etch the templates and generate porous carbon. Hollow mesoporous aluminosilicate spheres and hard silica core/mesoporous silica shell spheres have been used as the templates to produce hollow mesoporous carbon spheres.14 24 Here, the carbon precursors are usually sucrose, furfuryl alcohol, and phenol formaldehyde resin, all of which are easy to carbonize under an inert gas.25 29 In 2002, Yoon and co-workers reported the fabrication of hollow carbon spheres with a mesoporous wall, and aluminum must be incorporated into the silicate framework before introduction of the carbon source. Since then, this method has been widely adopted.30 In 2006, Kleitz et. al used a spherical core shell structure (SiO2@ZrO2) as the template and furfuryl alcohol as the carbon source to produce the porous hollow carbon structure.31[ The second method is chemical vapor nanocasting in which the carbon source is usually styrene, acetonitrile, or benzene. All three are relatively easy to carbonize under an inert gas at a higher temperature.32 36 However, by using the CVD nanocasting method, only carbon spheres with large mean diameters (>500 nm) can be obtained. Synthesis of small carbon spheres (<300 nm) is still challenging. To the best of our Received: June 4, 2011 Revised: July 25, 2011 Published: July 27, 2011 17717 dx.doi.org/10.1021/jp205257u | J. Phys. Chem. C 2011, 115, 17717–17724 The Journal of Physical Chemistry C knowledge, there has been no report on the use of ethylene as the carbon source in the nanocasting technique. This is probably because ethylene is hard to carbonize in the silica channels and most of the carbon products appear on the surface of particles or in the form of amorphous carbon. Other methods such as synthesis of hollow graphitic carbon mesoporous nanospheres by chlorination of ferrocene at a high temperature have been investigated.37 Zhu produced core shell carbon nanoparticles composed of mesoporous cores and microporous shells,38 and Ji synthesized hollow carbon spheres by self-assembly of carbon nanotubes.39 In addition, oxidized fullerenes were also used to assemble hollow porous carbon nanospheres.40] Unfortunately, none of these methods allow one to precisely control the shell thickness, core diameter, and overall morphology of the resulting hollow carbon spheres with a mesoporous wall. Ordered mesoporous carbon materials with a graphitic wall structure have been studied by several research groups41 45 for the purpose of adjusting conductivity, stability, and porosity in order to satisfy conditions in various applications such as fuel cells, double-layer capacitors, and Li ion batteries.46 Carbon materials with a well-developed pore structure have an amorphous pore-wall structure instead of graphitic crystallinity. It has been shown that MCM-41 type silica has small pore (1.5 5 nm) structures. Because the MCM-41 type silica has 1-D channels, they are not interconnected. When carbon forms in the channels of the MCM-41 silica, the carbon structure produces a hexagonal arrangement of 1-D carbon rods after the silica support is removed. Hence, replication of the MCM-41 silica with carbon leads to the formation of carbon fibers that do not retain the 2-D hexagonal arrangement. Consequently, synthesis of MCM-41 type hollow carbon spheres is still challenging.47 In this paper, we present a simple and controllable nanocasting CVD method to form well-ordered hollow carbon spheres consisting of a graphitic mesoporous wall with a predesigned thickness. Different from the previously reported methods, after obtaining the silica template with the surfactant inside, only one CVD process is needed to produce the carbon-filled silica spheres. There is also no need to remove the surfactant and fill with carbon sources. This novel method employs mesoporous silica spheres as the template and ethylene as the carbon source. More importantly, the CTAB trapped in the silica channels accelerates carbon deposition during CVD, resulting in more carbon filled in the silica channels, and after HF treatment, hollow mesoporous carbon spheres with a graphitic wall are produced. ’ EXPERIMENTAL SECTION 1. Synthesis of SiO2@m-SiO2 Spheres. SiO2 nanospheres were prepared by a modified St€ober sol gel process.48 Tetraethyl orthosilicate (TEOS) (1.5 mL) was added to a mixture of ethanol (50 mL) and concentrated ammonia (28 wt %, 2.5 mL). After stirring for 24 h, the products were separated by filtration, washed with ethanol and water, and redispersed in a solution containing cetyltrimethylammonium bromide (CTAB), deionized water, concentrated ammonia (28 wt %), and ethanol. The solution was stirred for 60 min, and TEOS was added dropwise while stirring. The solution was stirred for 6 more hours, and afterward, the products were filtered, washed with ethanol and water several times, and dried in air at 100 C for 24 h (SiO2@m-SiO2_CTAB). The structure directing agent (CTAB) could be removed using heat treatment at 600 C for 5 h in air (SiO2@m-SiO2). In a typical synthesis, SiO2@m-SiO2 ARTICLE (shell: 70 nm) and 100 mg of silica spheres were added to H2O (30 mL), CTAB (170 mg) surfactant, and EtOH (13 mL) and sonicated. After stirring for 30 min, ammonium (0.45 mL) and TEOS (0.3 mL) were added and stirred at ambient temperature overnight. 2. Synthesis of SiO2@m-SiO2_C Spheres and Hollow Carbon Spheres. The dried SiO2@m-SiO2_CTAB spheres were used as the template to prepare the hollow mesoporous carbon spheres using CVD. The dried SiO2@m-SiO2_CTAB spheres were placed in an alumina boat and placed in a tube furnace. Argon was bled in at a flow rate of 100 sccm, and the temperature was raised to 800 C. Ethylene was introduced at a flow rate of 20 sccm, and the sample was processed for 3 h under ethylene and argon. Afterward, the furnace was cooled to room temperature in Ar, and the resulting SiO2@m-SiO2_C spheres were thoroughly washed with hydrofluoric acid to remove the silica. 3. Electrochemical Measurement. The electrochemical experiments were carried out using 2032 coin-type cells. The working electrodes were prepared by mixing the samples (hollow carbon spheres, carbon black (Super-P), and poly(vinyl difluoride) (PVDF) at a weight ratio of 80:10:10) and pasting onto Cu foils (99.6%, Goodfellow). A lithium foil (Aldrich) was used as the counter electrode. The electrolyte consisted of a solution of 1 M LiPF6 in ethylene carbonate (EC)/dimethyl carbonate (DMC) (1:1 by volume) obtained from Ube Industries Ltd. The cells were assembled in an argon-filled glovebox under less than 1 ppm moisture and oxygen. The electrochemical performance was evaluated in the voltage range of 0.01 3.00 V. Electrochemical impedance spectral measurements were carried out in the frequency range from 100 kHz to 10mHz on a PARSTRAT 2273 electrochemical workstation. Fitting of the impedance spectra to the typical Randles equivalent circuit was performed using the Zview code. 4. Characterization. X-ray diffraction (XRD) was conducted on a Philips diffractometer using Cu KR radiation. The morphology of the samples was examined by field emission scanning electron microscopy (FE-SEM, S4800, Hitachi). Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HR-TEM) were performed on the FEI Tecnai F30 transmission electron microscope with a field emission gun operating at 200 kV to examine the dimensions and structural details of the core shell nanoparticles. The elemental compositions were determined by energy-dispersive X-ray spectrometry (EDS) under the HR-TEM mode. The N2 adsorption/ desorption isotherms were acquired at liquid nitrogen temperature (77 K) using a Micromeritics ASAP 2010 M instrument, and the specific surface area was calculated by the Brunauer Emmett Teller (BET) method. The pore size distribution was determined using the Barret Joner Halenda (BJH) method. Raman scattering was conducted on a Renishaw micro-Raman spectrometer (λ = 514 nm). Thermogravimetric analysis (TGA) was carried out on 10 mg samples using the DTA-Q600 SDT TA Instrument at a heating rate of 10 C/min from room temperature to 900 C under air. ’ RESULTS AND DISCUSSION The sol gel synthesis approach is illustrated in Scheme 1. In conjunction with the use of a surfactant template of cetyltrimethylammonium bromide (CTAB), the mesostructured CTAB/silica composite was deposited on the silica nanospheres to produce inside of well-dispersed mesoporous silica nanospheres. The 17718 dx.doi.org/10.1021/jp205257u |J. Phys. Chem. C 2011, 115, 17717–17724 The Journal of Physical Chemistry C ARTICLE Scheme 1. Schematic Illustration of the Formation of Mesoporous Hollow Carbon Nanospheres Figure 2. SEM images of the mesoporous hollow carbon spheres. Figure 1. Powder X-ray diffraction patterns of the SiO2@m-SiO2_ CTAB core shell structured spheres (black line), SiO2@m-SiO2_C (red line), and hollow carbon spheres (green line). mesoporous silica spheres with CTAB trapped inside were placed in a horizontal quartz reactor, and after CVD and etching the silica template by HF, MCM-41 type hollow mesoporous carbon spheres were obtained. The powder XRD patterns acquired from the SiO2@m-SiO2_ CTAB, SiO2@m-SiO2_C before and after HF treatment are depicted in Figure 1. After CVD, the SiO2@m-SiO2_C shows a strong broad peak from 20 30 arising from silica and graphitic carbon (black line and red line, correspondingly). This indicates deposition of graphitic carbon on the SiO2@m-SiO2 spheres. After the HF treatment for 24 h, the broad peak (20 30) disappears, and two strong peaks emerge at 25.1 and 43, showing that the silica has been completely removed from the SiO2@m-SiO2_C and only the graphitic carbon structure (green line) remains in the sample. These two peaks appear at the same reciprocal spacings as 002 and 101 graphite reflections, respectively. A hierarchical structure can be obtained using a combination of sol gel and CVD deposition. Figure 2 depicts the representative SEM images of the hollow mesoporous carbon spheres. The spheres are nearly uniform, and the size of the spheres is about 270 nm. Some broken spheres are also observed, indicating that the spheres are hollow. Most spheres are single, although some agglomeration is visible. Prior to inspection of the morphology of the mesoporous silica spheres used as the template (SiO2@m-SiO2) by TEM, the mesoporous silica spheres after the sol gel process are heated in Figure 3. (a,b) TEM images of the mesoporous core shell structured silica spheres. air at 550 C for 5 h. This heat treatment removes the CTAB template completely, giving rise to a uniform mesoporous silica shell. As shown in Figure 3 for a typical core shell structure with a silica sphere core, an ordered mesoporous silica phase with cylindrical channels in the outer layer can be clearly observed. The mesopore channels are also found to be perpendicular to the silica core surface (Figure 3b), and the thickness of the silica shell is about 70 nm. Figure 4a shows the TEM image of the carbon silica spheres after CVD, and some carbon blocks are observed on the surface of these spheres. After HF etching, these nanospheres have hollow cores, as shown in Figure 4b. The diameter of the hollow carbon sphere is around 220 nm, and the thickness of the shell is around 20 nm. It contains confined pores, as shown by the highmagnification TEM images shown in Figures 4c. The EDS spectrum acquired from the hollow mesoporous carbon spheres (inset in Figure 4d) only shows a strong carbon signal, indicating the presence of a carbon component, but silica has been completely removed. The Cu signal in the spectrum originates from the TEM grid. 17719 dx.doi.org/10.1021/jp205257u |J. Phys. Chem. C 2011, 115, 17717–17724 The Journal of Physical Chemistry C ARTICLE Figure 4. TEM images. (a) Mesoporous silica spheres/carbon, (b) low-resolution image of the mesoporous hollow carbon spheres, (c) high-resolution image of the graphitic mesoporous hollow carbon spheres, and (d) high-resolution image of the graphitic mesoporous hollow carbon sphere wall structure. Figure 5. (a) Raman spectra of the carbon silica spheres (black line) and mesoporous hollow carbon spheres (red line) and (b) TGA profile of the mesoporous carbon hollow spheres. The bonding, order, and crystallinity of the materials are studied by Raman spectroscopy (Figure 5a). Figure 5a reveals disordered graphitic materials, as suggested by the two Raman modes. The black line arises from the carbon silica spheres, and the red line is representative of the hollow mesoporous carbon spheres. The peak at 1593 cm 1 (G-band) corresponds to an E2g mode of hexagonal graphite and is related to the vibration of sp2hybridized carbon atoms in a graphite layer. This means that the hollow carbon spheres are composed of graphitic carbon, and it is consistent with the TEM and XRD results. The D-band at about 1359 cm 1 is associated with the vibration of carbon atoms with dangling bonds in the plane termination of disordered graphite. TGA measurements (Figure 5b) provide information about the carbon content as well as the quality of the carbon spheres because the oxidation temperature affects the wall defects. Ideal graphite starts to oxidize at above 600 C, whereas the hollow carbon spheres are oxidized at above 500 C. The hollow carbon spheres begin to decompose at 585 C in air. As the temperature is further increased, the weight loss increases rapidly until all of the carbon spheres are exhausted at about 700 C. The ash content of the hollow carbon spheres after combustion at 900 C is 0% w/w, thus implying that the produced hollow carbon spheres have high purity. Controllable Synthesis of Different Diameters of Mesoporous Hollow Carbon Spheres. In order to control the diameter and wall thickness of the hollow carbon spheres, three kinds of core shell silica spheres with controllable mesoporous silica shells were prepared (Figure 6). By varying the mass ratios 17720 dx.doi.org/10.1021/jp205257u |J. Phys. Chem. C 2011, 115, 17717–17724 The Journal of Physical Chemistry C ARTICLE Figure 6. Controllable synthesis of core shell structured silica spheres and corresponding mesoporous hollow carbon spheres. (a,d) Silica spheres with a 20 nm mesoporous silica shell and corresponding hollow carbon spheres. (b,e) Silica spheres with a 50 nm mesoporous silica shell and corresponding hollow carbon spheres. (c,f) Silica spheres with a 70 nm mesoporous silica shell and corresponding hollow carbon spheres. Figure 7. N2 adsorption/desorption isotherms of the mesoporous hollow carbon spheres with a shell thickness of 70 nm. of the silica spheres to CTAB/TEOS, different diameters of core shell silica spheres and hollow carbon spheres with variable wall thicknesses can be fabricated controllably. The TEM images in Figure 6 show monodispersed spherical particles with a uniform size and smooth surface. By increasing the silica spheres to the CTAB/TEOS ratio, the thickness of the porous shell increases from 20 to 70 nm. These three kinds of core shell silica spheres are shown in Figure 6a c. After complete removal of silica, mesoporous hollow carbon spheres with different diameters are obtained, as shown in Figure 6d f. The hollow mesoporous carbon spheres (shell thickness: 70 nm) exhibit a characteristic type IV isotherm, indicating the presence of mesoporosity (Figure 7). The corresponding mesopore size distribution calculated using the BJH method from the adsorption branch reveals uniform pores centered at approximately 1.8, 2.47, 3.3, and 7 nm, as shown in the inset of Figure 7. It can be attributed to the cavity in the hollow carbon. Another Figure 8. (a) SiO2@m-SiO2 after CVD. (b) SiO2@m-SiO2_CTAB after CVD. (c) SiO2 @m-SiO2_CTAB heated to 800 C for 3 h in Ar. feature noticeable from the isotherm is the steep increase in N2 uptake at a relative pressure (P/P0) of below 0.1. This indicates the presence of micropores in the carbon shell. From Figure 7, it should be noted that the total surface area and pore volume were calculated to be 771 m2/g and 0.599 cm3/g, respectively. An increase of the carbon shell thickness from 20 to 70 nm led to an increase of the total surface area from 323 to 771 m2/g. Growth Mechanism of Hollow Carbon Spheres. Figure 8a and b shows the different silica supports after the same CVD process, and Figure 8c presents the SiO2 @m-SiO2_CTAB heated at 800 C for 3 h in Ar. During CVD, the time was set at 3 h and the temperature at 800 C. The carbon source was C2H4, and the flow rate was 20 sccm. For the sample presented in Figure 8a, the CTAB was first removed by heating in air, and then, SiO2@m-SiO2 was put into the furnace to deposit carbon. 17721 dx.doi.org/10.1021/jp205257u |J. Phys. Chem. C 2011, 115, 17717–17724 The Journal of Physical Chemistry C After CVD, a gray color appeared, indicating that a tiny amount of carbon had been deposited on the silica spheres. However, if the CTAB was not removed, the sample appeared black after CVD, implying the deposition of a lot of carbon on the silica spheres. On the basis of the difference, it can be concluded that the CTAB accelerated the reaction, enabling more carbon to deposit on the surface of the silica spheres. In order to study what happens to CTAB during CVD, the SiO2@m-SiO2_CTAB was also heated in Ar at 800 C for 3 h without introducing C2H4. In this case, the sample appeared gray with some scattered areas showing a black color. This shows that under Ar and at a high temperature, some CTAB is carbonized in the form of small Figure 9. TEM images of (a,b) SiO2@m-SiO2, (c,d) SiO2@m-SiO2_ CTAB heated in Ar at 800 C for 2 h, and (e,f) SiO2@m-SiO2 after CVD. ARTICLE graphitic islands on the sphere surface. These tiny islands may be used as the active seeds for the growth of carbon when C2H4 is introduced. On the SiO2@m-SiO2 sample, no carbon seeds were formed in the channel prior to C2H4 introduction. This increased the carbon deposition rate on the SiO2@m-SiO2_CTAB with respect to SiO2@m-SiO2. Hence, it can be concluded that CTAB accelerates the CVD process, leading to enhancement of carbon deposition. In order to corroborate the mechanism, different TEM images were acquired from the silica spheres deposited with carbon. Figure 9a and b depicts the TEM images of the core shell silica spheres. The surface of the silica spheres is very smooth, and the channels are clear. With regard to SiO2@m-SiO2_CTAB, heating in Ar for 3 h produces a small amount of carbon in the channels and on the surface of the silica spheres (Figure 9c and d, as indicated by arrows). Furthermore, the core shell structure is not very clear, implying that the channels in the mesoporous silica are blocked by carbon. The experimental evidence proves that CTAB is carbonized during the heat treatment in Ar, forming the active carbon seeds (graphitic islands). After CVD, some carbon blocks appear on SiO2@m-SiO2, but most of them are deposited on the surface of the silica spheres instead of in the channels (Figure 9e and f). The core shell structure is also visible, further proving that carbon is not deposited in the channels of the silica spheres. These TEM images confirm the existence of carbon seeds, which accelerate carbon deposition. Figure 10a shows the STEM image of the SiO2@m-SiO2_CTAB sphere after heating in Ar. The EDS map in Figure 10b shows that carbon exists in the mesoporous layer of the silica around the silica sphere (red color). This indicates that CTAB has been converted into carbon after the heat treatment in Ar. The silica elemental map in Figure 10c shows that they are just distributed in the center of the sphere (orange color). Galvanostatic discharging (Li insertion) charging (Li extraction) experiments are carried out to evaluate the electrochemical performance of the hollow carbon spheres. Surprisingly, the first charge capacity as high as 1908 mA h g 1 at a rate of C/5 is observed (Figure 11a). This is more than five times higher than the theoretical capacity of graphite (372 mA h g 1). It is worth noting that when the carbon shell increased from 20 to 70 nm, the first charge capacity also increased from 1070 to 1948 mA h g 1 at a rate of C/5. It means that the carbon shell thickness influences the charge capacity significantly. This is probably due to the exterior mesoporous shells with perpendicular nanochannels and interior graphitic solid shells that are responsible for such an excellent capability pertaining to Li insertion and extraction. This suggests the existence of other lithium storage mechanisms for the hollow carbon spheres in addition to the classical graphite intercalation compound mechanism.46 A large Figure 10. (a) STEM image and elemental mapping showing the distribution of carbon (red, b) and silica (orange, c) on the SiO2@m-SiO2_CTAB sphere heated in Ar at 800 C for 3 h. 17722 dx.doi.org/10.1021/jp205257u |J. Phys. Chem. C 2011, 115, 17717–17724 The Journal of Physical Chemistry C ARTICLE Figure 11. (a) First charging (Li insertion) and discharging (Li extraction) curves of the hollow carbon spheres (20 nm, black line; 70 nm, red line) and (b) performance of the hollow carbon sphere electrodes at rates of 1/5, 1/2, 1, 5, and 10 C (shell thickness: 70 nm). irreversible capacity of about 1489 mA h g 1 is also observed from the hollow carbon sphere electrode during the first discharging and charging processes (Figure 11b). After the fifth cycle, the Coulombic efficiency is above 98%. In fact, the low initial Coulombic efficiency is a common phenomenon for porous carbonaceous electrodes in lithium ion batteries.49,50 It can be attributed to the large specific surface area and irreversible lithium insertion into the special positions such as in the vicinity of residual H atoms in the carbonaceous materials. This can result in the decomposition of electrolyte and formation of the solid/ electrolyte interphase (SEI) films at the electrode/electrolyte interface.46,49 54 The perpendicular nanochannels in mesoporous shells present in hollow carbon structures are responsible for such an excellent high-rate capability for Li insertion and extraction. However, these hollow features also exhibit drawbacks. Owing to the large surface area, volumetric properties are less favorable than gravimetric ones; in addition, the irreversible capacity increases, and the morphological stability may also suffer in the long run. In order to reduce the irreversible capacity and improve the initial Coulombic efficiency, an inner or outer graphitic solid layer in/on these hollow carbon spheres would be helpful. These additional solid graphitic carbon shells could keep the structure stability when Li insertion and extraction would occur.55 Some further modifications such as introduction of highly gravimetric and volumetric-capacity metals (SnO2 and Sn) into the cores of hollow carbon spheres are also possible to reduce the irreversible capacity and improve the initial Coulombic efficiency. These investigations are currently in progress. The performance of the hollow carbon spheres is presented in Figure 11b. The reversible capacity is stable at 268 mA h g 1 after 60 cycles at a rate of C/5. After increasing the discharge/ charge rates to 1 and 5 C, the reversible capacity is maintained at 189 and 145 mA h g 1, respectively, which are lower than that of graphite. In addition, the high-rate cycling performance of the hollow carbon spheres is noteworthy. For example, after 60 cycles, the retention of the reversible capacity at 10 C is nearly 100%. This is in big contrast to the performance of traditional carbonaceous materials tending to be continuous and progressive. It is believed that the hollow carbon spheres that have exterior mesoporous shells with perpendicular nanochannels are responsible for the excellent capability for Li insertion. However, owing to larger irreversible capacity, introducing highly gravimetric and volumetric-capacity materials (Sn and SnO2) into the cores and pores of hollow spheres may improve the reversible capacity further. ’ CONCLUSIONS Hollow carbon nanospheres with controllable mesoporous wall thickness have been synthesized using core shell structured silica spheres as the template by CVD using ethylene as the carbon feedstock. The hollow carbon spheres exhibit a high level of graphitization especially at a CVD temperature of 800 C. The hollow carbon spheres also exhibit good meso-structural ordering and have a large surface area (771 m2/g). The presence of CTAB accelerates the CVD reaction, leading to higher carbon yields. The electrochemical properties of the hollow carbon spheres show that the materials are suitable for lithium ion batteries due to the excellent high-rate capability. ’ AUTHOR INFORMATION Corresponding Author *E-mail: xchen@zut.edu.pl (X.C.); paul.chu@cityu.edu.hk (P.K.C.). ’ ACKNOWLEDGMENT The work was supported by the Foundation for Polish Science within Focus with Contract F4/2010 and the City University of Hong Kong Strategic Research Grant (SRG) No. 7008009. ’ REFERENCES (1) Burda, C.; Chen, X. B.; Narayanan, R.; El-Sayed, M. A. Chem. Rev. 2005, 105, 1025–1102. (2) White, R. J.; Luque, R.; Budarin, V. L.; Clark, J. H.; Maquarrie, D. J. Chem. Soc. Rev. 2009, 38, 481–494. (3) Meier, W. Chem. Soc. Rev. 2000, 29, 295–303. (4) Caruso, F. Chem.—Eur. J. 2000, 6, 413–419. (5) Liang, C. D.; Li, Z. J.; Dai, S. Angew. Chem., Int. Ed. 2008, 47, 3696–3717. 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