Carbon Nanohybrids with Ultrasmall

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Facile Scalable Synthesis of TiO2/Carbon Nanohybrids with UltraSmall TiO2 Nanoparticles Homogeneously Embedded in Carbon Matrix Xiaoyan Wang, Jianqiang Meng, Meimei Wang, Ying Xiao, Rui Liu, Yonggao Xia, Yuan Yao, Ezzeldin Metwalli, Qian Zhang, Bao Qiu, Zhaoping Liu, Jing Pan, Ling-Dong Sun, Chun-Hua Yan, Peter Muller-Buschbaum, and Ya-Jun Cheng ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.5b07784 • Publication Date (Web): 14 Oct 2015 Downloaded from http://pubs.acs.org on October 17, 2015

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ACS Applied Materials & Interfaces

Facile Scalable Synthesis of TiO2/Carbon Nanohybrids with Ultra-Small TiO2 Nanoparticles Homogeneously Embedded in Carbon Matrix Xiaoyan Wang1, 2, Jian-Qiang Meng1*, Meimei Wang2,3, Ying Xiao2, Rui Liu4, Yonggao Xia2, Yuan Yao5, Ezzeldin Metwalli5, Qian Zhang2, Bao Qiu2, Zhaoping Liu2, Jing Pan3, Ling-Dong Sun4, Chun-Hua Yan4, Peter Müller-Buschbaum5,and Ya-Jun Cheng2* 1.

State Key Laboratory of Separation Membranes and Membrane Processes,Tianjin

Polytechnic University, Tianjin 300387, P. R. China 2.

Ningbo Institute of Materials Technology and Engineering, Chinese Academy of

Sciences, 1219 Zhongguan West Rd, Zhenhai District, Ningbo, Zhejiang Province 315201, P. R. China 3.

Faculty of Materials Science and Chemical Engineering, Ningbo University,

Ningbo, Zhejiang Province 315211, P. R. China 4.

Beijing National Laboratory for Molecular Sciences, State Key Laboratory of

Rare Earth Materials Chemistry and Applications & PKU-HKU Joint Lab on Rare Earth Materials and Bioinorganic Chemistry, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, P. R. China 5.

Physik-Department,

Lehrstuhl

für

Funktionelle

Materialien,

Technische

Universität München, James-Franck-Str. 1, 85748 Garching, Germany *corresponding author: Email: [email protected], [email protected]. 1

ACS Paragon Plus Environment


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Abstract A facile scalable synthesis of TiO2/C nanohybrids inspired by polymeric dental restorative materials has been developed, which creates ultra-small TiO2 nanoparticles homogeneously embedded in the carbon matrix. The average size of the nanoparticles is tuned between about 1 nm and 5 nm with the carbon content systematically increased from 0 % to 65 %. Imaging analysis and scattering technique have been applied to investigate the morphology of the TiO2 nanoparticles. The composition, nature of carbon matrix, crystallinity, and tap density of the TiO2/C nanohybrids have been studied. The application of the TiO2/C nanohybrids as lithium-ion battery anode is demonstrated. Unusual discharge/charge profiles have been exhibited, where characteristic discharge/charge plateaus of crystalline TiO2 are significantly diminished. The tap density, cyclic capacities, and rate performance at high current densities (10 C, 20 C) of the TiO2/C nanohybrid anodes have been effectively improved compared to the bare carbon anode and the TiO2/C nanohybrids with larger particle size.

Keywords Titania/Carbon Nanohybrids; Ultra Small Nanoparticles; Photo Polymerization; Dental Methacrylate Resin; Lithium-Ion Battery Anode

2


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Introduction Nanostructured titanium dioxide (TiO2) has attracted considerable attention due to its versatile applications in photocatalysis, lithium-ion battery, dye-sensitized solar cell, and gas sensing1-9. The morphology and the surface functionality both play a crucial role in the distinct properties of the TiO22,

6-7, 10-11

. As a consequence,

nanoscale TiO2 with rich morphologies has been intensively investigated6-7,

11-23

.

Surface modification of TiO2 with carbon has proven to be an effective strategy to improve the electrochemical performance24-30. Among the different morphologies, TiO2 nanoparticles with ultra-small size are particularly interesting2, 11, 16, 31-35. Such small size scale not only creates high specific surface area to achieve exceptional performance, but also provides a good model system to study fundamental electrochemical mechanism. However, so far the synthesis of ultra-small TiO2 nanoparticles (for example, with size below 5 nm) remains a big challenge due to difficulties in controlling properly the reaction kinetics31. It is even more difficult to further reduce the particle size down to 1 nm or 2 nm, where the synthesis and structure-property correlation of the TiO2 nanoparticles with such small size had been rarely investigated. Even though the primary particle size may be controlled in the range of a few nanometers, severe particle agglomeration is often observed due to the high surface energy, which is disadvantageous36. Moreover, most studies are focusing on crystalline TiO2, whereas amorphous or poorly crystallized TiO2 have received relatively little attention29, 37-49. Nevertheless, from reported work it comes clear that amorphous or poorly crystallized TiO2 can exhibit unusual electrochemical 3



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performance as photo catalyst and lithium-ion battery anode29,

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37-49

. Finally, most

synthetic methods for nanostructured TiO2 are difficult to scale up and make use of a huge amount of water and/or organic solvent3, 10, 12, 14, 17, 19, 50-54. As a result, tedious, costly, and environmentally unfriendly solvent disposal processes become mandatory for such synthesis routes. Therefore, it is very interesting to develop a more sustainable and facile scalable strategy to synthesize ultra-small TiO2 nanoparticles with controlled crystallinity and surface carbon modification. Difunctional methacrylates have been widely used in aesthetic dentistry as resin matrix to manufacture dental restorative composites55-56. Typical dental resin monomers exploited are bisphenol A glycidyl dimethacrylate (Bis-GMA) and triethylene glycol dimethacrylate (TEGDMA). Photo polymerization initiated by blue light illumination is applied during operation, where a cross-linked methacrylate network is formed to repair damaged teeth. Inspired by the concept of polymeric dental restorative composite, a new strategy to synthesize TiO2/carbon nanohybrids has been reported previously by our group31. In this approach, the difunctional methacrylate monomers (Bis-GMA and TEGDMA) have been used as carbon source and reaction medium to replace conventional solvents as well. Titanium tetraisopropoxide (TTIP) has been used as the precursor of TiO2, which is dissolved in the resin mixture. Through the fast, green, and energy saving photo polymerization process, the methacrylate monomers have been instantly solidified and the Titania species have been homogeneously integrated into the cross-linked methacrylate network at molecular level. As a result, the solvent disposal 4


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process is totally circumvented. The fast phase change process triggered by photo polymerization allows a precise structure replication from solution to solid. By calcination in argon, TiO2 nanoparticles have been formed in situ and are homogeneously embedded in the in situ formed carbon matrix. The in situ carbonization process significantly inhibits the growth and aggregation of TiO2 nanoparticles, leading to the formation of poorly crystallized TiO2 nanoparticles with the size of around 4 nm - 6 nm. Due to this particular feature, characteristic discharge/charge plateaus of TiO2 are significantly diminished; while the tap density, gravimetric and volumetric capacities, cyclic and rate performance of the TiO2/C nanohybrids have been effectively improved. Despite the success of this approach, a further size reduction of the TiO2 nanoparticles is meaningful to explore the structure-property correlation of the TiO2/C nanohybrids with the TiO2 particles reaching its size limit. The reduction of the TiO2 nanoparticle size tends to modify the discharge/charge patterns of the electrode by lowering the characteristic discharge/charge potential of the crystalline TiO241, 43, 47-49. It helps to increase the overall energy density output of the full lithium-ion battery. Besides, the reduction of particle size also helps to stabilize the electrode structure during the repeated discharge/charge processes because the small particle size generates less stress during lithium interaction57-59. Furthermore, the reduction of particle size will suppress the crystallization process of TiO2, leading to unusual electrochemical performance. For this purpose, compared to the previously reported results, only Bis-GMA and TEGDMA are used in the present investigation. No 5



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additional thermoplastic additives such as mono functional methacrylate monomer (hydroxyl ethyl methacrylate, HEMA), concentrated HCl, and Pluronic block copolymer of F127 are used except TTIP and photo initiator of I819 (Scheme 1). On the one hand, the concentrated HCl promotes hydrolysis/condensation of TTIP, leading to increased particle size. On the other hand, the thermoplastic additives enhance melting process of the thermosetting methacrylate polymers during high temperature calcination, inducing particle growth and aggregation. Therefore, in the novel approach the use of only thermosetting difunctional methacrylate monomers (Bis-GMA and TEGDMA) offers a possibility to further reduce the particle size of TiO2.

Experimental Section Materials Titanium tetraisopropoxide (TTIP, Aladdin Reagent Co., Ltd, China), Bisphenol A glycidyl dimethacrylate (Bis-GMA, Esstech, Inc., USA), Triethylene glycol dimethacrylate (TEGDMA, Esstech, Inc., USA), and Phenyl bis (2, 4, 6-trimethyl benzoyl)phosphine oxide (IrgacureI-819, Sigma-Aldrich) were all used as received without further purification.

Sample Preparation and Characterization The typical sample preparation procedure is similar to our previous reported work31. Details are as following. I-819 (2 % mass fraction) was dissolved in a resin mixture of Bis-GMA/TEGDMA (4:6 by mass) to obtain a visible light active B/T solution. Various amounts of TTIP (from 0 g to 8.0 g) were added to 4.0 g B/T 6


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solution and stirred for about 5 minutes. The solution was poured into a silicone rubber mold (1 cm × 4.5 cm × 0.4 cm) which was then clamped between two glass slides. The photo polymerization was conducted in a visible light-curing unit (Luxomat D, blue light 9 W, range of emission: 350 nm - 500 nm) for 2 minutes each side. Next, the samples were kept at 60 °C for 24 hours before the polymerized solids were released from the moulds. The solid composites were cut into small particulate powders with an approximate diameter in the range of 0.1 mm – 1 mm by a mixer. Calcination in argon was carried out at 800 °C for 4 hours in tube furnace with a ramp rate of 5 K/min starting from room temperature, followed by natural cooling to room temperature. The TiO2/C nanohybrids obtained were further ball milled with a planetary ball miller (FRITSCH- pulverisette 7, Germany) for 4 hours with the speed of 400 rpm. The jar made of agate had a volume of 7 ml (18 mm in diameter and 28 mm in height). Beads made of agate with various sizes in the range between 2 mm and 4 mm were used. The rough mass of the sample powder to be ball milled was in the range 100 mg - 200 mg. The volume ratio of the beads and the sample powders over the jar was around 2/3. No additional solvent was used as milling medium. A pause of 5 minutes was set after each 15 minutes of ball milling. After 2 hours of ball milling, the whole powder was poured out and ground manually, followed by restart of additional two hours ball milling. No significant heat generation was observed and the jar was not warm after ball milling. Field emission scanning electron microscopy (FESEM) images were obtained with Hitachi S4800 scanning electron microscope (Tokyo, Japan) at an accelerating 7



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voltage of 4 kV. The sample powder was put on a conductive tape and sputtered with gold before imaging. Energy dispersive x-ray spectroscopy (EDX) images were recorded with FEI QUANTA 250 FEG (America FEI) at an accelerating voltage of 15 kV. Transmission Electron Microscopy (TEM) data were collected by putting a drop of aqueous suspension containing the spheres on a carbon-supported copper grid and measured with a JEOL JEM-2100F TEM operated at 200 kV. The crystallographic phases of the TiO2 powders and TiO2/C composites were investigated by X-ray diffraction (XRD) (Bruker AXS D8 Advance, λ=1.541 Å, 2.2 kW) with a 2θ ranged from 5 ° to 90 °. The content of carbon of the TiO2/C composites was studied by Thermo Gravimetric Analyzer (TGA, Mettler Toledo, Switzerland) with the temperature range from 50 °C to 800 °C with the ramp rate of 20 K/min in air. The Raman data were collected on a Renishaw (in Via-reflex) with a wavelength of 532nm. Small-angle x-ray scattering (SAXS) measurements were performed on a Ganesha 300XLSAXS-WAXS system (SAXS LAB ApS, Copenhagen/Denmark). The X-ray radiation was produced at 50 kV / 0.6 mA from a Cu anode with a wavelength of 0.154 nm. A sample-to-detector distance of 1051 mm was chosen. The sample powder was put into a glass capillary which functioned as a holder and allowed x-ray transmission experiments.

Electrochemical Measurement 8


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2032-type coin cells composed of a cylindrical pad with 20 mm in diameter and 3.2 mm in height were fabricated using Lithium foil as the counter electrode. A slurry mixture was prepared by dispersing active material, Super P and poly (vinylidene fluoride) (PVDF) (mass ratio: 8:1:1) in N-methyl Pyrrolidone (NMP). The electrodes were prepared by spreading the slurry mixture on a piece of copper foil, followed by drying at 80 °C in vacuum for 12 h. The copper foil was pressed, cut into appropriate dimension, and then dried in over at 80 °C further for 4 hours. Lithium foil was used as the counter electrode. Electrolyte (Dongguan shanshan battery material Co., LTD) was used by dissolving 1.0 M LiPF6 in a mixture of ethylene carbonate (EC) and diethyl carbonate (DMC) (1:2 v/v). The rate performance and cycle performance of the assembled cells were tested using a multichannel Land Battery Test System. The rate performance was measured at the current density sequence of 0.1 C, 0.2 C, 0.5 C, 1.0 C, 2.0 C, 5.0 C, 10 C, 20 C, and 0.1 C in the voltage range between 3.0 V and 0.005 V (vs. Li/Li+) (five cycles each current density, 1 C = 335 mAh/g). The cyclic measurement was carried out at a current density of 0.2 C in the voltage range of 3.0 V – 0.005 V (Vs. Li/Li+) for 50 rounds. The specific capacity was calculated on the basis of only the active material. The discharge process was meant to the lithiation process; while the charge process was referred to the de-lithiation process. CHI 1040B potentiostat/galvanostat analyzer (Shanghai Chenhua instrument Co., Ltd) was used to carry out cyclic voltammetry test at a scanning rate of 0.01 mV/s with the voltage range between 0.005 V and 3 V. 9



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Results and Discussions The TEM images in Figure 1 present the morphologies of TiO2 within the TiO2/C nanohybrids for different compositions. The mass ratio of TTIP over the total mass of the B/T methacrylate monomers (MTTIP) is systematically varied from 0 to 2.0. According to the TEM images, the average sizes of the TiO2 nanoparticles increases with increasing amount of MTTIP. In more detail, the measured average sizes are 1 nm, 1 nm, 2 nm, 4 nm, and 5 nm in case of MTTIP being 0.125, 0.25, 0.50, 1.0, and 2.0. The SAED patterns indicate that crystalline TiO2 has been formed. The SAED results are consistent with the HRTEM images (Figure 2), where domains of TiO2 crystallites are embedded in the amorphous matrix. From the HRTEM images with the MTTIP values up to 1.0, crystalline planes of (101) and (200) orientation are observed (Figure 2b to 2e). In contrast, in case of MTTIP being 2.0, besides the (101) crystalline plane of the anatase phase, the (101) crystalline plane of the rutile phase is also observed (Figure 2f). The coexistence of both anatase and rutile phases within the TiO2/C nanohybrid prepared with high MTTIP values was observed in our previous work as well. The excessive amount of TTIP within the methacrylate network may change the local structure of the Titania species, leading to the formation of the additional rutile phase. Unlike TEM and HRTEM, the SEM images only show featureless particles with broad size distribution (Figure 3). Compared to bare carbon, the particles composed of the TiO2/C nanohybrids do not show obvious structure difference. It is hard to uncover structure details by SEM because the TiO2 nanoparticles are very small and 10


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the nanoparticles are very well embedded in the carbon matrix. Furthermore, the EDX images show that both, Titanium and oxygen species, are homogeneously embedded in the carbon matrix (Figure 4). One has to note that the resolution of EDX is lower than the actual size of the TiO2 nanoparticles. However, it is reasonable to say that the TiO2 are well dispersed in the micrometer scale. As a complementary method, the average characteristic size distribution over a large size area is characterized by small angle x-ray scattering (SAXS)31. As visible in Figure 5, no obvious characteristic structure is measured by SAXS in case of the bare carbon sample (black points). In contrast, distinct peaks appear in the SAXS data when TiO2 nanoparticles are introduced into the carbon matrix. According to the applied fitting model, the TiO2/C nanohybrid prepared with a MTTIP value of 0.125 exhibits a characteristic size of 8.2 Å, which agrees with the results from the imaging analysis. With further increasing amount MTTIP to 0.25, 0.50, 1.0, and 2.0, the characteristic sizes derived from fitting the SAXS data are 9.7 Å, 13.5 Å, 17.9 Å and 18.3 Å, respectively. In general, the values obtained from SAXS fitting are consistent with the real space analysis. Moreover, the analysis of the SAXS data suggests that the ultra-small TiO2 nanoparticles are homogeneously embedded in the carbon matrix over the area of a few square millimeters. In this respect the SAXS complement the rather local information of the imaging analysis performed with TEM, HRTEM, SEM, and EDX. The TiO2 contents within the TiO2/C nanohybrids have been measured by TGA (Figure 6a). With MTTIP systematically varied from 0.125 to 2.0, the TiO2 content is gradually increased from 21 % to 65 %. The carbon yields against the total mass of 11



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the B/T resin monomers are around 12 %, which do not change significantly with respect to different MTTIP values. Considering that decent amount of carbon exists in the nanohybrid, a continuous carbon network is expected. Both, D band (1350 cm-1) and G band (1600 cm-1), are observed in Raman spectroscopy, which indicates the existence of both, ordered and disordered carbon in the carbon matrix (Figure 6b)60. The integrative intensity ratio of the D band over the G band (ID / IG) of the TiO2/C nanohybrids prepared with the MTTIP of 0.125 is increased compared to the bare carbon sample (1.53 vs. 1.23). It suggests that the formation of disordered carbon is increased due to enhanced cross-linking via coordination between the Titania and methacrylate network60. Furthermore, in general, the value of ID / IG increases with increased MTTIP (from 1.53 to 2.35) due to enhanced degree of cross-linking. No clear graphene like structure is observed by TEM. However, based on the Raman spectroscopy, a local graphitic layer structure may exist in the carbon matrix. The crystallization behavior of the TiO2/C nanohybrids with different TiO2 contents is characterized by XRD (Figure 6c). The measured XRD profile confirms the nature of amorphous carbon in the carbon matrix (black line). In case of MTTIP being 0.125 only a weak major (101) peak of the anatase phase appears, whereas other Bragg peaks are barely visible. The absence of other Bragg peaks is not only due to the small amount of TiO2 within the nanohybrid, but originates also from the ultra-small size feature of the TiO2 nanoparticles (around 1 nm). With further increasing MTTIP to 0.25, the diffraction peaks become more pronounced in the XRD profiles, which still indicate the formation of pure anatase phase. When the MTTIP are extended to 0.50, 1.0, and 12


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2.0, besides the major peak of the (101) crystalline plane, other diffraction peaks become distinct. Particularly, the Full-Width at Half-maximum (HWFM) of the (101) peaks continue to be narrowed with increasing MTTIP, indicating size enlargement of the (101) crystallites within the TiO2 nanoparticles. According to the Debye-Scherrer equation the sizes of the (101) crystallites are calculated to be 0.5 nm, 0.6 nm, 2.6 nm, 3.8 nm, and 5.3 nm with the MTTIP increased from 0.125 to 2.0. The calculated values are generally consistent with the sizes measured by TEM and SAXS. The slight difference may be due to the sensitivity of the XRD and TEM to the averaged large crystal size, while SAXS is sensitive to the overall average particle size. It is worth pointing out that an additional phase of rutile is also observed by XRD with the MTTIP of 2.0, which agrees with the HRTEM result. Finally, the tap densities of the TiO2/C nanohybrids are also measured (Figure 6d). The tap densities increase exponentially with increasing MTTIP. Regarding the bare carbon sample, the tap density is only 0.53 g/cm3. While with the MTTIP of 2.0 (TiO2 content: 65 %), the tap density is doubled to 1.06 g/cm3, which is good to achieve reasonable volumetric capacity for practical application in lithium-ion battery61. Compared to our previous work, the particle size of TiO2 is significantly reduced to even below 1 nm31. It is believed that it has reached a size limit for the TiO2 nanoparticles using the current synthetic technique. This size reduction is due to the fact that only difunctional methacrylate monomers of Bis-GMA and TEGDMA are used. TTIP is homogeneously dissolved in the B/T resin solution and form coordination

bonds

with

Bis-GMA

and

TEGDMA.

The

additional 13



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hydrolysis/condensation process of TTIP is significantly hindered. As a result, only molecular Titania species exist in the resin solution and they are bound to the cross-linked methacrylate network upon photo polymerization. Due to lack of thermoplastic additives within the cross-linked methacrylate network, no significant polymer melting process happens during calcination. As a result, the molecular Titania species fixed to the methacrylate resin can only locally be converted to TiO2. The simultaneous carbonization process of the thermosetting methacrylates further effectively inhibits the growth and aggregation of the TiO2 nanoparticles. The discharge/charge curves of the TiO2/C nanohybrids prepared with different MTTIP are exhibited in Figure 7 with the applied current density of 0.2 C (1 C = 335 mAg-1). The corresponding TiO2 contents are 0 %, 21 %, 32 %, 42 %, 50 %, and 65 % from Figure 7a to 7f. Several general trends can be summarized by comparing all of the discharge/charge curves. Trend 1: The characteristic lithiation/delithiation plateau of crystalline TiO2 is significantly diminished, where the discharge/charge curves exhibit very similar pattern to the bare carbon anode16, 62. Only when the TiO2 content reaches 50 %, turning points located at around 1.7 V /2.1 V come to appear. Very weak plateaus are observed with the TiO2 content further increased to 65 %. The absence of plateau may be good for the TiO2 anode because the characteristic lithiation/delithiation potential of the crystalline TiO2 are very high (1.7 V /2.1 V), leading to reduced energy density output for practical applications in full lithium-ion battery63. The change of the discharge/charge behavior of the TiO2/C nanohybrid anodes is consistent with our previous work31. Two reasons may be responsible for 14


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this pattern modification. First, the TiO2 within the TiO2/C nanohybrids are fairly poorly crystallized or amorphous. The crystallization of TiO2 significantly modifies the discharge/charge patterns of the TiO2, which originates from the formation of LixTiO2 phase upon lithium intercalation. It is reported that amorphous or poorly crystallized TiO2 leads to a narrowed plateau because the formation of a stable lithiated TiO2 phase is rather limited40-46. Second, the homogeneous dispersion of the ultra-small TiO2 nanoparticles within the carbon matrix may also contribute to the weakened plateaus because the lithium intercalation of TiO2 is kinetically smeared by the lithium intercalation process of the carbon matrix31. Trend 2: After the first cycle, the capacities are increased gradually along with increasing cycles, probably due to electrochemical activation process of the anode. From Figure 7 it can be seen that the pattern of the 20th cycle is almost identical to that of the 50th cycle, indicating stabilization of the lithiation/delithiation processes. Trend 3: Compared to the bare carbon anode, the initial discharge capacities of the TiO2/C nanohybrid anodes are increased from 320 mAhg-1 to around 400 mAhg-1, and even to 500 mAhg-1. Considering the “hard carbon” nature of the carbon matrix, the theoretical capacity of TiO2 may not be as high as the carbon matrix8-9, 36, 63-64. Therefore, the increasing initial discharge capacity of the TiO2/C nanohybrid suggests that the introduction of the titania species into the methacrylate network may change the microstructures of the carbon matrix to achieve improved initial capacity. Trend 4: Particularly, with the TiO2 content of 21 % (MTTIP: 0.125), the discharge/charge capacities after 50 cycles are increased to around 315 mAhg-1 compared to the bare carbon anode (280 mAhg-1). 15



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However, with further increasing TiO2 content, the capacities decrease slightly to the level comparable to that of the bare carbon sample. The results suggest that an excessive amount of TiO2 within the TiO2/C nanohybrids may lower the overall capacities because the theoretical capacity of TiO2 may not be as high as the carbon matrix formed by the pyrolysis of the cross-linked methacrylate polymers. Furthermore, it has been found that the increasing amount of TTIP generates a higher ratio of ID/IG. The more disordered carbon leads to poorer capacity retention. Compared to our previous research work, the initial capacities are decreased. Nevertheless, the capacities after 50 cycles are improved, indicating a good capacity retain. The lack of thermoplastic additives as plasticizer decreases the overall cross-linking degree of the difunctional methacrylates, leading to the formation of less amount of disordered carbon. That is the main reason responsible for relatively lower initial capacities and better capacity retain capability. Besides, the further reduced TiO2 nanoparticle size may also contribute to the structure stabilization of the TiO2/C nanohybrid anodes during repeated discharge/charge processes because they generate less stress upon lithiation/delithiation than larger particles. Even though the measurement protocol is not exactly identical with the reported results, the performance of the TiO2/C nanohybrids is well comparable to the previously reported work31, 41, 43, 47-49. The details of the cyclic performance of the TiO2/C nanohybrids are shown in Figure 8. In the first few cycles, the capacities are gradually increased. With less TiO2 content (up to 32 %, Figure 8c), the capacities are not stabilized until around 10th cycle. However, with increased TiO2 content, the capacities are stable from 16


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around 5th cycle (more than 42 %, Figure 8d). The results prove that higher TiO2 content contributes to better cyclic stability. The Coulombic efficiencies of all of the samples after 10th cycle are close to 100 %, indicating good cyclic stability. The cyclic voltammetry (CV) curves of the TiO2/C nanohybrids are shown in Figure 9. The peaks in the first cycle indicate the formation of solid electrolyte interface (SEI). While the patterns of the second cycle and the third cycle are quite similar, indicating that there is no significant change in the electrochemical reaction processes31. No clear peaks of TiO2 can be observed with the TiO2 content of 21 % and 32 %. However, with the TiO2 content of more than 42 %, the characteristic peaks of TiO2 come to appear (1. 7 V and 2.1 V) (Figure 8d). The CV results agree well with the discharge/charge curves presented in Figure 7. The rate performance of the TiO2/C nanohybrids is exhibited in Figure 10. With the current density up to 2 C, the capacities of the TiO2/C nanohybrids do not change significantly compared to the bare carbon anode. However, with the current density increased to 10 C and 20 C, in generally, the TiO2/C nanohybrids exhibit better performance than the bare carbon anode. Particularly, the sample with 32 % of TiO2 (MTTIP:0.25) possesses the capacity of 78 mAhg-1 (10 C) and 35 mAhg-1 (20 C) respectively, which is significantly improved compared to the capacity of the bare carbon (38 mAhg-1 for 10 C and 9 mAhg-1 for 20 C). Compared to our previous results, the rate performance at high current densities is also improved. Because ultra-small TiO2 nanoparticles with the average size of only around 1 nm are homogeneously embedded in the carbon matrix, the intrinsic inferior electron 17



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conductivity of bulk TiO2 may not lower down the electron conductivity of the 1 nm sized TiO2. Furthermore, because decent amount of TiO2 is homogeneously embedded in the carbon matrix, the 1 nm sized TiO2 also helps to stabilize the structure of the carbon matrix by absorbing stress generated from repeated discharge/charge processes. After discharge/charge at 20 C, the capacities of the TiO2/C nanohybrids can almost be fully recovered, indicating a good cyclic stability of the nanohybrids.

Conclusions TiO2/C nanohybrids have been synthesized in a sustainable and facile scalable way, where ultra-small TiO2 nanoparticles with the size ranging from around 1 nm to 5 nm are homogeneously embedded in the carbon matrix. The TiO2 contents are systematically increased from 0 % to 65 % by adjusting the mass ratio of TTIP over the total mass of the B/T resin monomers (MTTIP increased from 0 to 2.0). Poorly crystallized TiO2 of anatase phase are observed with the TiO2/C nanohybrids prepared with the MTTIP less than 1.0. However, with the MTTIP of 2.0, an additional phase of rutile appears which may be due to local structure change with excessive amount of TTIP. The tap densities of the TiO2/C nanohybrids increase exponentially with respect to MTTIP, which is doubled to 1.06 gcm-3 compared to bare carbon. The application of the TiO2/C nanohybrids as lithium-ion battery anode has been investigated. The characteristic discharge/charge plateaus of crystalline TiO2 are significantly diminished regarding the TiO2/C nanohybrid anode due to poor crystallization, ultra-small size feature, and homogeneous dispersion of the TiO2 nanoparticles within the carbon matrix. Furthermore, it is found that the TiO2/C nanohybrid anodes exhibit 18


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better or comparable cycled capacities to the bare carbon anode. This result indicates that the introduction of the Titania species may modify the microstructure of the carbon matrix, leading to improved capacities. The TiO2/C nanohybrids possess better rate performance than the bare carbon anode at high current densities. Particularly, the capacities of the TiO2/C nanohybrid with 32 % of TiO2 are more than doubled compared to the bare carbon anode at 10 C and 20 C. The enhanced electrochemical performance of the TiO2/C nanohybrids originates from the ultra-small size feature and homogeneous dispersion of the TiO2 nanoparticles within the carbon matrix. Compared to our previous research work, further reduction TiO2 nanoparticle size down to around 1 nm effectively improves the cyclic capacity retain capability and rate performance of the TiO2/C nanohybrids.

Acknowledgement This research is funded by the Natural Science Foundation of China (51103172), the Zhejiang Nonprofit Technology Applied Research Program (2013C33190), the Program for Ningbo Innovative Research Team (2009B21008), the open project of the Beijing National Laboratory for Molecular Science (20140138), and Ningbo Key Laboratory of Polymer Materials. Y.Y. acknowledges the China Scholarship Council (CSC) and P.M-B acknowledges the funding by TUM.Solar in the frame of the Bavarian

Collaborative

Research

Project

“Solar

technologies

go

Hybrid"

(SolTec).Donation of the dental resins from Esstech, Inc., USA, is greatly appreciated.

19



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Reference 1.

Chen, X. B.; Li, C.; Gratzel, M.; Kostecki, R.; Mao, S. S., Nanomaterials for renewable energy

production and storage. Chem. Soc. Rev. 2012, 41 (23), 7909-7937. 2.

Froschl, T.; Hormann, U.; Kubiak, P.; Kucerova, G.; Pfanzelt, M.; Weiss, C. K.; Behm, R. J.; Husing,

N.; Kaiser, U.; Landfester, K.; Wohlfahrt-Mehrens, M., High surface area crystalline titanium dioxide: potential and limits in electrochemical energy storage and catalysis. Chem. Soc. Rev. 2012, 41 (15), 5313-5360. 3.

Hu, J.; Chen, M.; Fang, X. S.; Wu, L. W., Fabrication and application of inorganic hollow spheres.

Chem. Soc. Rev. 2011, 40 (11), 5472-5491. 4.

Lang, X. J.; Chen, X. D.; Zhao, J. C., Heterogeneous visible light photocatalysis for selective organic

transformations. Chem. Soc. Rev. 2014, 43 (1), 473-486. 5.

Qu, Y. Q.; Duan, X. F., Progress, challenge and perspective of heterogeneous photocatalysts. Chem.

Soc. Rev. 2013, 42 (7), 2568-2580. 6.

Rawolle, M.; Niedermeier, M. A.; Kaune, G.; Perlich, J.; Lellig, P.; Memesa, M.; Cheng, Y. J.;

Gutmann, J. S.; Muller-Buschbaum, P., Fabrication and characterization of nanostructured titania films with integrated function from inorganic-organic hybrid materials. Chem. Soc. Rev. 2012, 41 (15), 5131-5142. 7.

Ren, Y.; Ma, Z.; Bruce, P. G., Ordered mesoporous metal oxides: synthesis and applications. Chem.

Soc. Rev. 2012, 41 (14), 4909-4927. 8.

Wang, H. L.; Dai, H. J., Strongly coupled inorganic-nano-carbon hybrid materials for energy

storage. Chem. Soc. Rev. 2013, 42 (7), 3088-3113. 9.

Zhang, Q. F.; Uchaker, E.; Candelaria, S. L.; Cao, G. Z., Nanomaterials for energy conversion and

storage. Chem. Soc. Rev. 2013, 42 (7), 3127-3171. 10. Lai, X. Y.; Halpert, J. E.; Wang, D., Recent advances in micro-/nano-structured hollow spheres for energy applications: From simple to complex systems. Energy Environ. Sci. 2012, 5 (2), 5604-5618. 11. Wagemaker, M.; Mulder, F. M., Properties and Promises of Nanosized Insertion Materials for Li-Ion Batteries. Acc. Chem. Res. 2013, 46 (5), 1206-1215. 12. Chen, J. S.; Liang, Y. N.; Li, Y. M.; Yan, Q. Y.; Hu, X., H2O-EG-Assisted Synthesis of Uniform Urchinlike Rutile TiO2 with Superior Lithium Storage Properties. ACS Appl. Mater. Interfaces 2013, 5 (20), 9998-10003. 13. Wang, X. D.; Cao, L.; Chen, D. H.; Caruso, R. A., Engineering of Monodisperse Mesoporous Titania Beads for Photocatalytic Applications. ACS Appl. Mater. Interfaces 2013, 5 (19), 9421-9428. 14. Chen, D. H.; Caruso, R. A., Recent Progress in the Synthesis of Spherical Titania Nanostructures and Their Applications. Adv. Funct. Mater. 2013, 23 (11), 1356-1374. 15. Chen, Z. H.; Belharouak, I.; Sun, Y. K.; Amine, K., Titanium-Based Anode Materials for Safe Lithium-Ion Batteries. Adv. Funct. Mater. 2013, 23 (8), 959-969. 16. Ren, Y.; Liu, Z.; Pourpoint, F.; Armstrong, A. R.; Grey, C. P.; Bruce, P. G., Nanoparticulate TiO2(B): An Anode for Lithium-Ion Batteries. Angew. Chem., Int. Ed. 2012, 51 (9), 2164-2167. 17. Liu, Y. D.; Goebl, J.; Yin, Y. D., Templated synthesis of nanostructured materials. Chem. Soc. Rev. 2013, 42 (7), 2610-2653. 18. Li, W.; Wu, Z. X.; Wang, J. X.; Elzatahry, A. A.; Zhao, D. Y., A Perspective on Mesoporous TiO2 Materials. Chem. Mater. 2014, 26 (1), 287-298. 19. Shchukin, D. G.; Caruso, R. A., Template synthesis and photocatalytic properties of porous metal 20


Page 21 of 35

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


oxide spheres formed by nanoparticle infiltration. Chem. Mater. 2004, 16 (11), 2287-2292. 20. Cheng, Y. J.; Muller-Buschbaum, P.; Gutmann, J. S., Ultrathin anatase TiO2 films with stable vesicle morphology templated by PMMA-b-PEO. Small 2007, 3 (8), 1379-1382. 21. Rawolle, M.; Ruderer, M. A.; Prams, S. M.; Zhong, Q.; Magerl, D.; Perlich, J.; Roth, S. V.; Lellig, P.; Gutmann, J. S.; Mueller-Buschbaum, P., Nanostructuring of Titania Thin Films by a Combination of Microfluidics and Block-Copolymer-Based Sol-Gel Templating. Small 2011, 7 (7), 884-891. 22. Orilall, M. C.; Wiesner, U., Block copolymer based composition and morphology control in nanostructured hybrid materials for energy conversion and storage: solar cells, batteries, and fuel cells. Chem. Soc. Rev. 2011, 40 (2), 520-535. 23. Cheng, Y. J.; Gutmann, J. S., Morphology phase diagram of ultrathin anatase TiO2 films templated by a single PS-b-PEO block copolymer. J. Am. Chem. Soc. 2006, 128 (14), 4658-4674. 24. Lee, K. T.; Jeong, S.; Cho, J., Roles of Surface Chemistry on Safety and Electrochemistry in Lithium Ion Batteries. Acc. Chem. Res. 2013, 46 (5), 1161-1170. 25. Xin, S.; Guo, Y. G.; Wan, L. J., Nanocarbon Networks for Advanced Rechargeable Lithium Batteries. Acc. Chem. Res. 2012, 45 (10), 1759-1769. 26. Shen, L. F.; Uchaker, E.; Yuan, C. Z.; Nie, P.; Zhang, M.; Zhang, X. G.; Cao, G. Z., Three-Dimensional Coherent Titania-Mesoporous Carbon Nanocomposite and Its Lithium-Ion Storage Properties. ACS Appl. Mater. Interfaces 2012, 4 (6), 2985-2992. 27. Wang, W. S.; Sa, Q. N.; Chen, J. H.; Wang, Y.; Jung, H. J.; Yin, Y. D., Porous TiO2/C Nanocomposite Shells As a High-Performance Anode Material for Lithium-Ion Batteries. ACS Appl. Mater. Interfaces 2013, 5 (14), 6478-6483. 28. Tan, L. L.; Chai, S. P.; Mohamed, A. R., Synthesis and Applications of Graphene-Based TiO2 Photocatalysts. ChemSusChem 2012, 5 (10), 1868-1882. 29. Zhou, Y.; Lee, J.; Lee, C. W.; Wu, M.; Yoon, S., Crystallinity-Controlled Titanium Oxide-Carbon Nanocomposites with Enhanced Lithium Storage Performance. ChemSusChem 2012, 5 (12), 2376-2382. 30. Zhang, C. L.; Zhang, Q. Y.; Kang, S. F.; Li, X., A novel route for the facile synthesis of hierarchically porous TiO2/graphitic carbon microspheres for lithium ion batteries. J. Mater. Chem. A 2014, 2 (8), 2801-2806. 31. Xiao, Y.; Wang, X.; Xia, Y.; Yao, Y.; Metwalli, E.; Zhang, Q.; Liu, R.; Qiu, B.; Rasool, M.; Liu, Z.; Meng, J.-Q.; Sun, L.-D.; Yan, C.-H.; Muller-Buschbaum, P.; Cheng, Y.-J., Green Facile Scalable Synthesis of Titania/Carbon Nanocomposites: New Use of Old Dental Resins. ACS Appl. Mater. Interfaces 2014, 6, 18461-18468. 32. Hu, Y. S.; Kienle, L.; Guo, Y. G.; Maier, J., High lithium electroactivity of nanometer-sized rutile TiO2. Adv. Mater. 2006, 18 (11), 1421-+. 33. Sasidharan, M.; Nakashima, K.; Gunawardhana, N.; Yokoi, T.; Inoue, M.; Yusa, S.; Yoshio, M.; Tatsumi, T., Novel titania hollow nanospheres of size 28 +/- 1 nm using soft-templates and their application for lithium-ion rechargeable batteries. Chem. Commun. 2011, 47 (24), 6921-6923. 34. Dar, M. I.; Chandiran, A. K.; Gratzel, M.; Nazeeruddin, M. K.; Shivashankar, S. A., Controlled synthesis of TiO2 nanoparticles and nanospheres using a microwave assisted approach for their application in dye-sensitized solar cells. J. Mater. Chem. A 2014, 2 (6), 1662-1667. 35. Lee, K. T.; Cho, J., Roles of nanosize in lithium reactive nanomaterials for lithium ion batteries. Nano Today 2011, 6 (1), 28-41. 36. Bruce, P. G.; Scrosati, B.; Tarascon, J. M., Nanomaterials for rechargeable lithium batteries. Angew. 21



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

Page 22 of 35

Chem., Int. Ed. 2008, 47 (16), 2930-2946. 37. Xiao, Y.; Hu, C. W.; Cao, M. H., Compositing Amorphous TiO2 with N-Doped Carbon as High-Rate Anode Materials for Lithium-Ion Batteries. Chem. - Asian J. 2014, 9 (1), 351-356. 38. Guan, D. S.; Cai, C. A.; Wang, Y., Amorphous and Crystalline TiO2 Nanotube Arrays for Enhanced Li-Ion Intercalation Properties. Journal of Nanoscience and Nanotechnology 2011, 11 (4), 3641-3650. 39. Yildirim, H.; Greeley, J. P.; Sankaranarayanan, S., Concentration-Dependent Ordering of Lithiated Amorphous TiO2. J. Phys. Chem. C 2013, 117 (8), 3834-3845. 40. Xiong, H.; Slater, M. D.; Balasubramanian, M.; Johnson, C. S.; Rajh, T., Amorphous TiO2 Nanotube Anode for Rechargeable Sodium Ion Batteries. J. Phys. Chem. Lett. 2011, 2 (20), 2560-2565. 41. Hibino, M.; Abe, K.; Mochizuki, M.; Miyayama, M., Amorphous titanium oxide electrode for high-rate discharge and charge. J. Power Sources 2004, 126 (1-2), 139-143. 42. Joyce, C. D.; McIntyre, T.; Simmons, S.; LaDuca, H.; Breitzer, J. G.; Lopez, C. M.; Jansen, A. N.; Vaughey, J. T., Synthesis and electrochemical evaluation of an amorphous titanium dioxide derived from a solid state precursor. J. Power Sources 2010, 195 (7), 2064-2068. 43. Menendez, R.; Alvarez, P.; Botas, C.; Nacimiento, F.; Alcantara, R.; Tirado, J. L.; Ortiz, G. F., Self-organized amorphous titania nanotubes with deposited graphene film like a new heterostructured electrode for lithium ion batteries. J. Power Sources 2014, 248, 886-893. 44. Borghols, W. J. H.; Lutzenkirchen-Hecht, D.; Haake, U.; Chan, W.; Lafont, U.; Kelder, E. M.; van Eck, E. R. H.; Kentgens, A. P. M.; Mulder, F. M.; Wagemaker, M., Lithium Storage in Amorphous TiO2 Nanoparticles. J. Electrochem. Soc. 2010, 157 (5), A582-A588. 45. Ban, C. M.; Xie, M.; Sun, X.; Travis, J. J.; Wang, G. K.; Sun, H. T.; Dillon, A. C.; Lian, J.; George, S. M., Atomic layer deposition of amorphous TiO2 on graphene as an anode for Li-ion batteries. Nanotechnology 2013, 24 (42). 46. Fang, H. T.; Liu, M.; Wang, D. W.; Sun, T.; Guan, D. S.; Li, F.; Zhou, J. G.; Sham, T. K.; Cheng, H. M., Comparison of the rate capability of nanostructured amorphous and anatase TiO2 for lithium insertion using anodic TiO2 nanotube arrays. Nanotechnology 2009, 20 (22). 47. Bi, Z.; Paranthaman, M. P.; Menchhofer, P. A.; Dehoff, R. R.; Bridges, C. A.; Chi, M.; Guo, B.; Sun, X.-G.; Dai, S., Self-organized amorphous TiO2 nanotube arrays on porous Ti foam for rechargeable lithium and sodium ion batteries. J. Power Sources 2013, 222, 461-466. 48. Borghols, W. J. H.; Luetzenkirchen-Hecht, D.; Haake, U.; Chan, W.; Lafont, U.; Kelder, E. M.; van Eck, E. R. H.; Kentgens, A. P. M.; Mulder, F. M.; Wagemaker, M., Lithium Storage in Amorphous TiO2 Nanoparticles. J. Electrochem. Soc. 2010, 157 (5), A582-A588. 49. Xiao, Y.; Hu, C.; Cao, M., Compositing Amorphous TiO2 with N-Doped Carbon as High-Rate Anode Materials for Lithium-Ion Batteries. Chem. - Asian J. 2014, 9 (1), 351-356. 50. Lee, K. H.; Song, S. W., One-Step Hydrothermal Synthesis of Mesoporous Anatase TiO2 Microsphere and Interfacial Control for Enhanced Lithium Storage Performance. ACS Appl. Mater. Interfaces 2011, 3 (9), 3697-3703. 51. Meyer, U.; Larsson, A.; Hentze, H. P.; Caruso, R. A., Templating of porous polymeric beads to form porous silica and titania spheres. Adv. Mater. 2002, 14 (23), 1768-1772. 52. Wu, H. B.; Hng, H. H.; Lou, X. W., Direct Synthesis of Anatase TiO2 Nanowires with Enhanced Photocatalytic Activity. Adv. Mater. 2012, 24 (19), 2567-2571. 53. Huang, C. H.; Gu, D.; Zhao, D. Y.; Doong, R. A., Direct Synthesis of Controllable Microstructures of Thermally Stable and Ordered Mesoporous Crystalline Titanium Oxides and Carbide/Carbon Composites. Chem. Mater. 2010, 22 (5), 1760-1767. 22


Page 23 of 35

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


54. Schuth, F., Encapsulation Strategies in Energy Conversion Materials. Chem. Mater. 2014, 26 (1), 423-434. 55. Cheng, Y. J.; Antonucci, J. M.; Hudson, S. D.; Lin, N. J.; Zhang, X. R.; Lin-Gibson, S., Controlled In Situ Nanocavitation in Polymeric Materials. Adv. Mater. 2011, 23 (3), 409-413. 56. Leprince, J. G.; Palin, W. M.; Hadis, M. A.; Devaux, J.; Leloup, G., Progress in dimethacrylate-based dental composite technology and curing efficiency. Dent. Mater. 2013, 29 (2), 139-156. 57. Liu, H.; Cao, K.; Xu, X.; Jiao, L.; Wang, Y.; Yuan, H., Ultrasmall TiO2 Nanoparticles in Situ Growth on Graphene Hybrid as Superior Anode Material for Sodium/Lithium Ion Batteries. ACS Appl. Mater. Interfaces 2015, 7 (21), 11239-11245. 58. Qin, G.; Zhang, H.; Wang, C., Ultrasmall TiO2 nanoparticles embedded in nitrogen doped porous graphene for high rate and long life lithium ion batteries. J. Power Sources 2014, 272, 491-500. 59. Sondergaard, M.; Shen, Y.; Mamakhel, A.; Marinaro, M.; Wohlfahrt-Mehrens, M.; Wonsyld, K.; Dahl, S.; Iversen, B. B., TiO2 Nanoparticles for Li-Ion Battery Anodes: Mitigation of Growth and Irreversible Capacity Using LiOH and NaOH. Chem. Mater. 2015, 27 (1), 119-126. 60. Wilamowsk, M.; Pradeep, V. S.; Graczyk-Zajac, M.; Riedel, R.; Soraru, G. D., Tailoring of SiOC composition as a way to better performing anodes for Li-ion batteries. Solid State Ionics 2014, 260, 94-100. 61. Su, Z.; Zhu, Y. X.; Wu, Z. Z.; Peng, X. Y.; Gao, C. L.; Xi, K.; Lai, C.; Kumar, R. V., Introduction of 'lattice-voids' in high tap density TiO2-B nanowires for enhanced high-rate and high volumetric capacity lithium storage. RSC Adv. 2014, 4 (44), 22989-22994. 62. Goriparti, S.; Miele, E.; De Angelis, F.; Di Fabrizio, E.; Zaccaria, R. P.; Capiglia, C., Review on recent progress of nanostructured anode materials for Li-ion batteries. J. Power Sources 2014, 257, 421-443. 63. Marom, R.; Amalraj, S. F.; Leifer, N.; Jacob, D.; Aurbach, D., A review of advanced and practical lithium battery materials. J. Mater. Chem. 2011, 21 (27), 9938-9954. 64. Jiang, J.; Li, Y. Y.; Liu, J. P.; Huang, X. T.; Yuan, C. Z.; Lou, X. W., Recent Advances in Metal Oxide-based Electrode Architecture Design for Electrochemical Energy Storage. Adv. Mater. 2012, 24 (38), 5166-5180.

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Scheme 1. Synthesis of the TiO2/C nanohybrids using dental methacrylate monomers as solvent and carbon source via photo polymerization.

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Figure 1. TEM images of the TiO2/C nanohybrids prepared with different mass ratios of TTIP over the total mass of the B/T methacrylate resin monomers (MTTIP). From a to f: 0, 0.125, 0.25, 0.50, 1.0, and 2.0. Inset: SAED pattern of each sample.

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Figure 3. SEM images of the TiO2/C nanohybrids prepared with different mass ratios of TTIP over the total mass of the B/T methacrylate resin monomers (MTTIP). From a to f: 0, 0.125, 0.25, 0.50, 1.0, and 2.0. Inset: low magnification SEM images of each sample.

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Figure 4. EDX images of the TiO2/C nanohybrids prepared with the mass ratio of TTIP over the total mass of the B/T methacrylate resin monomers (MTTIP) of 1.0, SEM image (a), element map of Ti (b), and element map of O (c).

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Figure 5. Experimental SAXS data (symbols) and related fitting (lines) of the SAXS curves of the TiO2/C nanohybrids prepared with different mass ratios of TTIP over the total mass of the B/T methacrylate resin monomers (MTTIP). Black: 0, red: 0.125, blue: 0.25, dark cyan: 0.50, magenta: 1.0, and dark yellow: 2.0.

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Figure 6. TGA (a), Raman (b), XRD (c), and tap density (d) of the TiO2/C nanohybrids prepared with different mass ratios of TTIP over the total mass of the B/T methacrylate resin monomers (MTTIP). Black: 0, red: 0.125, blue: 0.25, dark cyan: 0.50, magenta: 1.0, and dark yellow: 2.0. Image c: black diffraction peak index number: anatase, red diffraction peak index number: rutile. Image d: Symbol: experiment, line: fitted curve.

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Figure 7. Charge /discharge curves (0.2 C, 1 C = 335 mAg-1) of the TiO2/C nanohybrids prepared with different mass ratios of TTIP over the total mass of the B/T methacrylate resin monomers (MTTIP). From a to f: 0, 0.125, 0.25, 0.50, 1.0, and 2.0.

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Figure 8. Cyclic stability (0.2 C, 1 C = 335 mAg-1) of the TiO2/C nanohybrids prepared with different mass ratios of TTIP over the total mass of the B/T methacrylate resin monomers (MTTIP). From a to f: 0, 0.125, 0.25, 0.50, 1.0, and 2.0.

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Figure 9. Cyclic voltammetry profiles of the TiO2/C nanohybrids prepared with different mass ratios of TTIP over the total mass of the B/T methacrylate resin monomers (MTTIP). From a to f: 0, 0.125, 0.25, 0.50, 1.0, and 2.0.

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Figure 10. Rate performance (1 C = 335 mAg-1) of the TiO2/C nanohybrids prepared with different mass ratios of TTIP over the total mass of the B/T methacrylate resin monomers (MTTIP). From a to f: 0, 0.125, 0.25, 0.50, 1.0, and 2.0.

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Table of Content TiO2/C nanohybrids with ultra-small TiO2 nanoparticles down to around 1 nm have been synthesized in a facile scalable way by using difunctional dental methacrylate monomers as solvent and carbon source, coupled with photo polymerization process, which exhibits unusual electrochemical performance as lithium-ion battery anode.

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Carbon Nanohybrids with Ultrasmall

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