C Hollow Nanospheres Hybrid for High-Capacity

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Urchin-like V2O3/C Hollow Nanospheres Hybrid for High-Capacity and Long-Cycle-Life Lithium Storage Peng Yu, Xu Liu, Lei Wang, Chungui Tian, Hai-Tao Yu, and Honggang Fu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b01640 • Publication Date (Web): 12 Oct 2017 Downloaded from http://pubs.acs.org on October 13, 2017

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ACS Sustainable Chemistry & Engineering

Urchin-like V2O3/C Hollow Nanospheres Hybrid for High-Capacity

and

Long-Cycle-Life

Lithium

Storage Peng Yu, Xu Liu, Lei Wang,* Chungui Tian, Haitao Yu, and Honggang Fu*. Key Laboratory of Functional Inorganic Material Chemistry, Ministry of Education of the People’s Republic of China, Heilongjiang University, Harbin, Xuefu Road, 150080, P. R. China E-mail: [email protected], [email protected], [email protected].

ABSTRACT: Vanadium oxides (VOx) show potential in Li-ion batteries (LIBs) originating from the abundance, low cost and high theoretical capacities. Although V2O3 exhibits a high theoretical capacity of 1070 mAh g -1, most of the current reported V2O3-based anodes are suffering from poor electrical conductivity and huge volume change upon cycling in practice. Herein, urchin-like V2O3/C hybrid composed of 1 D nanofibers (a length-to-diameter ratio of 4) and hollow nanospheres (a diameter of 200−300 nm) has been synthesized via a template-free solvothermal method combined with a carbothermal reduction strategy. Both of the nanofibers and hollow nanospheres are consisted of carbon-coated V2O3 nanostructures. During the solvothermal process, glucose plays as not only the carbon resource but also the structural

ACS Paragon Plus Environment

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direction agent of nanosphere structures, and the formation of 1D V 2O3 nanofibers is attributed to the epitaxial growth of V2O3 nanoparticles on the out surface of nanosheets. When applied as LIB anode, the hybrid could exhibit an ultrahigh reversible capacity of 1250 mAh g-1 at 1 A g-1 after 1000 cycles, and a capacity of 500 mAh g -1 still could be achieved even at 500 mA g-1. Moreover, the V2O3/C hybrid anode can match well with the commercial high-voltage LiMn1/3Co1/3Ni1/3O2 cathode for fabricating full cell with a specific capacity of 197.2 mAh g-1 between 2.0 and 4.7 V at 100 mA g-1, and high energy density of ca. 740 Wh kg -1 at a power rate of 375 W kg-1, which is sufficient to turn on a 3 V and 10 mW LED.

KEYWORDS: Urchin-like structure; Hollow sphere, Vanadium oxides, Anode, Li-ion battery.

Introduction

To impel the applications of portable electronic devices, hybrid electrical vehicles and electrical grids, the exploitation of advanced energy storage devices as a predominant power source is the essential prerequisite[1,2]. Lithium ion batteries (LIBs) are the prior choice because of their excellent energy density and power density, good safety and long lifespan. It is well known that the electrode materials play the decisive role on the performance of LIBs

[3].

However, the relatively low theoretical capacity (372 mAh g −1) and poor rate capability of graphite anode cannot meet the ever-increasing demand for next-generation LIBs [4,5]. In contrast, the high-capacity Si-based electrodes show limited cycling performance owing to the huge volume variation during the lithium insertion/extraction [6,7]. In the past few years, tremendous efforts have been devoted to developing novel advanced substituted electrode materials [8-10].


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Vanadium oxides (VOx), a kind of earth-abundant and inexpensive transition-metal oxide, have been extensively researched as promising candidates for LIB anodes

[11-13].

Owing to

vanadium possesses several different stable oxidation states (+3, +4 and +5), many oxides, such as V2O5, VO2, V2O3, VOOH, and so forth, have been explored as LIB electrodes. Among them, V2O5 and VO2 with high valence of V are applied as cathode material because of their high intercalation voltage, while the low valence VO x are more suitable as anode [14-17]. Particularly, V2O3 could experience an intriguing change from insulator to metal as a function of temperature [18].

In detail, it shows an relative lower electrical resistance at the normal operating temperature

of LIBs (253−333 K) compared with other transition metal oxides, such as Fe 2O3, Co3O4, MnO2, etc, which endows V2O3 with fascinating rate capability in theory[19-22]. This is attributed to the metallic behavior resulted from the 3D V–V framework in V2O3 make V 3 electrons can tour along the V–V chains. Besides, the high theoretical capacity of 1070 mAh g −1 make V2O3 as an ideal electrode material for advanced LIBs

[23].

However, most current reported V2O3-based

anodes are far from satisfactory. Like most transitional metal oxides, V 2O3 anodes also face the problems of poor cyclic stability and rate performance, which are mainly attributed to the intrinsic insufficient electron conductive ability and inevitable tremendous volume variation during Li+ insertion/extraction [24-25]. To cover the above shortages, considerable researches have been devoted to exploring hybrid nanostructures composed of inorganic nanostructures (nanospheres, nanotubes, nanofibers, nanosheets, etc) and carbon-based species (amorphous carbon, carbon spheres, carbon nanotubes, graphene, etc) for LIB anodes

[26, 27].

For instance, peapod-like V2O3 nanorods

encapsulated into carbon nanostructures were prepared via multistep hydrothermal route to reduce V2O5, which exhibit appreciable rate capability and desired long-term cycling stability.


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[28]

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As such, carbon-supported nanosheet-assembled VOx microspheres synthesized via a

solvothermal reaction could deliver high-rate and long-life performance with a specific capacity of 860 mAh g-1 at 1000 mA g-1 [23]. It is well demonstrated that these hybrid constructions could improve the electronic conductivity and the overall structural stability. Moreover, hollow nanostructures could effectively accommodate the volume changes of conversion reaction V2O3 + xLi+ +xe- = LixV2O3 during cycling to induce a large capacitance and excellent stability performance [29]. Despite the progresses, there are rare reports about the designed synthesis of V2O3@C hollow nanospheres due to the limitations of present synthetic strategies. Herein, a novel hybrid of urchin-like V2O3/C hollow nanospheres is reported by combining template-free solvothermal and carbothermal reduction strategy. During the solvothermal process, metavanadate was coordinated with glucose uniformly and then formed nanospheres precursor under the structural direction effect of glucose. Afterwards, the precursor was gradually decomposed to hollow nanospheres, accompany by the epitaxial growth of V 2O3 nanoparticles to form 1D nanofibers, so urchin-like V2O3/C hollow nanospheres could be obtained. The special hybrid offers many remarkable advantages, including the hollow nanosphere structures could provide more space to accommodate the huge volume change during the insertion and extraction of Li ion, the intimate contact between V2O3 and amorphous carbon could shorten the diffusion pathway of Li+ ions and electrons. As a result, the hybrid shows high reversible capacity, outstanding stability, and extraordinary rate capability when applied as the LIB anode. The full cell assembled by using V 2O3/C as cathode together with commercial LiMn1/3Co1/3Ni1/3O2 as cathode displays high capacity, high energy and power density.


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Experimental Section Synthesis of V2O3/C composites: For V2O3/C, 1 mmol ammonium metavanadate was dissolved in 20 mL ethanoland and 1 mmol glucose in 15 mL distilled water. Then the above two solution were mixed and magnetically stirred to form a homogeneous light-yellow solution. Afterwards, the above solution was transferred into a Teflon-lined autoclave, and then maintained at 180 °C for 24 h. After that, the resultant black precipitant was obtained by centrifugation, and then washed by deionized water and ethanol for several times, respectively. Subsequently the obtained product was dried at 80 °C overnight. Finally, the resultant black-green solid was heated under N2 atmosphere with the heating rate of 5 °C/ min and then maintained at 700°C for 2 h, leading to the formation of V2O3/C composites. For comparison, VOx rods were synthesized through the similar processes without glucose, carbon spheres were synthesized without ammonium metavanadate. Characterizations: The X-ray diffraction (XRD) patterns were collected by a Bruker D8 Advance diffractometer equipped with Cu Kα (λ = 1.5406 Å) radiation in the range 10 - 80°. Raman spectra were recorded by a Jobin Yvon HR 800 micro-Raman spectrometer at 457.9 nm. Thermogravimetric analyses (TGA) were carried out by TA Q600 in air. Scanning electron microscopy (SEM) image were recorded with a Hitachi S-4800 field emission scanning electron microscope operating at 15 kV. Transmission electron microscopy (TEM) images were recorded on a JEM-2100 electron microscope (JEOL, Japan, acceleration 200 kV). XPS analyses was performed on a VG ESCALABMK II device with a Mg Ka achromatic X-ray source (1253.6 eV). The N2 adsorption/desorption isotherms were collected on Micromeritics Tristar II. The samples were outgassed for 10 h at 150oC under vacuum before the measurements. The X-ray absorption spectroscopy data were collected on Beamline BL14W1 at the Shanghai Synchrotron


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Radiation Facility (SSRF) through transmission mode, using a Si (111) double crystal monochromator for energy selection. Meanwhile, the XAFS data for V2O3, VO2, and V2O5 were measured for comparison. Electrochemical measurements: To investigate the electrochemical performance, working electrodes were prepared via pasting the mixture containing active materials, super-P carbon black and polyvinylidene fluorides (PVDF) with the weight ratio of 8:1:1 onto copper foil using N-methyl-2-pyrrolidinone (NMP) as solvent. After drying in vacuum at 100 °C for 10 h, the electrode was punched into round with the diameter of 14 mm. The active material loading was about 1.2-1.5 mg cm-2. For half cells, CR2025 coin-type cells were assembled in an Ar filled glove box using lithium metal as the counter/reference electrode, Cellgard 2400 membrane as the separator, and 1 M LiPF6 into EC : EMC : DMC = 1 : 1 : 1 organic solutions as the electrolyte. Charge-discharge profiles for the half-cells were recorded by LAND CT2001A system (Wuhan Jinnuo Electronics, Ltd.). Cyclic Voltammetry was performed on Autolab (Metrohm, Switzerland) at a scanning rate of 0.1 mV s -1 with the range from 0.01 to 3.0 V. Electrochemical impedance spectroscopy (EIS) was carried out on Autolab with the frequency in the range of 10 kHz - 10 MHz with an AC signal of 5 mV in amplitude as the perturbation. For further investigation, cycled batteries were dissembled in the argon-filled glove box with the obtained electrode was washed with dimethyl carbonate (DMC) and ethanol mixed solvent to remove the residual salts and electrolyte on the surface. For full cell assembly, the LiMn1/3Co1/3Ni1/3O2 electrode was employed as the cathode material (Charge and discharge profile of the LiMn1/3Co1/3Ni1/3O2 electrode shown in Figure S18) with a loading mass of 1.0 - 1.2 mg cm-2, LiMn1/3Co1/3Ni1/3O2 and its charge-discharge cycles were evaluated at 1.0 A g-1 in voltage


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windows between 2.0 and 4.5 V. All the specific capacities and current densities were calculated by the total weight of the nanocomposite. Results and Discussion The morphology of the V2O3 /C and its precursor were presented in Figure 1. According to the SEM image in Figure 1a, the precursor synthesized from the solvothermal process possess a uniformly spherical shape with a diameter in the range of 200~300 nm. TEM and HRTEM images (Figure 1b and 1c) indicate that the spherical structures are solid and the surface is smooth. The element mapping of the V2O3 /C precursor were shown in Figure S1, showing that the V, O, C and N are evenly distribute in the spherical precursor. On the opposite, the uniform sphere structures with a rough surface is obtained after decomposing the precursor as can be seen from Figure 1d. It is further illustrated that the V 2O3/C nanospheres were homogeneous and uniformly dispersed as exhibited in Figure S2. TEM image reveals that the V2O3 /C nanospheres is interior hollow with a shell thickness of 30~40 nm (Figure 1e and Figure S3). The surface of the nanospheres is scattered around by lots of nanothorns, with the diameter about 10 nm and length about 35-45 nm, the length-diameter ratio of the nanothorns is approximately 4. The electron diffraction (SAED) pattern shows in Figure 1f. The inter-planar spacing of 0.46 nm is coincides with the (116) facets of rhombohedral V2O3, consistent with previous reports [23, 24, 28]. Moreover, the skeleton of shell was composed of V 2O3 and amorphous carbon. Additionally, VOx rods with 500 nm thickness and 5~10 μm length instead of sphere nanostructures was formed in the absence of ammonium metavanadate (Figure S4). Also, it should be noted that carbonaceous spheres obtained through the solvothermal reaction of glucose (Figure S5), indicating that glucose is served as the structural direction agent for the formation of spherical hybrid nanostructures. This unique structure endows the V 2O3/C hollow nanospheres hybrid a


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dramatic increase in the BET surface area (132.9 m2 g-1) (Figure S6), higher than the VOx rods (3.5 m2 g-1) and most VOx structure reported[8, 20]. This can be attributed to the overlap of the nanothorns on the surface shell of nanospheres. Most importantly, the nanothorns can increase the contact area between the electrode and electrolyte, theoretically expand and shrink freely, infiltrate due to the siphonic effect and shorten the path length for ionic and electronic transport. The crystallographic structure of the various V2O3/C composites is examined by XRD. As displayed in Figure 2a, the diffraction peaks including (012), (104), (110), (006), (113), (024), (116), (214) and (300) can be well indexed as V 2O3 (JCPDS no. 34-0187), which confirms that no impurities is formed[23, 28]. Raman spectra in Figure 2b shows that the peaks below 1000 cm-1 in the V2O3/C hybrid are attributed to vanadium oxides. Two peaks at approximately 1310 cm-1 and 1595 cm-1 can be ascribed to the disordered carbon (D-band) and the graphitic carbon (Gband), which confirms the existence of carbon component. Thermogravimetric (TG) analysis in Figure S7 indicates the carbon content in V2O3/C hollow nanospheres is about 16.9%. EDX spectrum (shown in Figure S8) shows the atom percentages of V, C and O in V 2O3/C hybrid are about 21.8, 40.1 and 38.1 %, respectively, implying that more carbon component distributes on the peripheral of the nanostructure. X-ray photoelectron spectroscopy is applied for further investigating element valence states. As shown in Figure S9, typical peaks of C1s, V2p, V3s, V3p and O1s for V2O3/C hybrid can be detected in the XPS wide spectrum. Figure 2c shows the high-resolution V2p XPS spectrum of V2O3/C hybrid, the two peaks at 516.1 and 523.5 eV attributed to V 2p 3/2 and V 2p 1/2 from V 3+, respectively. In order to further verify the valance of V in the V2O3/C hybrid, XANES analysis was performed using VO2 (IV), V2O3(III) and V2O5(V) as the standards. As exhibited in Figure 2d, the pre-edge features of V can be observed at around 5470 eV in all V-based oxide. Moreover, it can be observed that, with the increase of


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oxidation state in VOx, the absorb peak shift slightly toward higher energies

[30-31].

The valence

state of V in V2O3/C is closer to +3, which is consistent with the result from the XPS analysis. Investigation the formation mechanism of nanostructure has guiding significance for directional synthesis of nanomaterials with special structures [32]. For exploring the formation processes of the V2O3/C hollow nanospheres, the solvothermal time was firstly studied for researching the formation process of sphere structures. The corresponding XRD patterns in Figure S10 reveal the amorphous characteristics of the precursor derived from different solvothermal time. FT-IR spectra of the precursor at different solvothermal reaction time and V2O3/C hybrid were shown in Figure S11. For the precursor, the peaks located at about 2918 cm-1 is related to the stretching vibrations of -CH3 groups and the peak at 2850 cm-1is related to the -CH2- groups. After thermal treatment, both of them were disappeared due to the decomposition of carbonaceous component during the calcination. Moreover, the absorption peaks between 800-600 cm-1 in all the precursors correspond to the stretch vibrations of V(V)=O. It could disappear after calcination and a new peak at 982 cm-1 ascribed to the symmetric stretching vibration of V(III)=O for the V2O3/C hybrid can be detected[33]. It indicates that the precursor was transformed to V2O3 through a carbon thermal reduction progress. Based on the above analysis, the overall reaction equation for the formation processes of V 2O3/C hybrid can be concluded as Equation (1) and (2): 2 NH4+ + 3VO3-= V3O8- + 2 NH3 + H2O

(1)

4 V3O8- + 2 (C6H12O6)n = (12n-7) C + 7 CO2+ 6 V2O3 + 12n H2O

(2)

It can be obviously observed that the initial bulk structures were gradually transferred to nanospheres with the lengthen of solvothermal reaction time as the evidences of SEM images in Figure S12, because of glucose can easily hydrolyze and polymerize to carbonaceous


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microspheres under the solvothermal reaction condition

[34-36].

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Moreover, the VOx nanorods but

not hollow nanospheres could be obtained in the absence of glucose, further indicating the structural direction role of glucose in the formation of V 2O3/C hollow sphere nanostructures. Besides, to investigate the effect of the glucose usage amount on the formation of spherical nanostructures, the samples derived from different dosages of glucose by a solvothermal reaction were also synthesized for comparison (SEM images show in Figure S13). It can be observed that the sample composed both lamellar and spherical nanostructures when using small amount of glucose, and homogeneous spherical structures formed gradually with the increase of glucose amount. When the amount of glucose is up to 10 mmol or more, the resultant sample exhibits a larger and inhomogeneous nanospheres. It is demonstrated that the moderate usage amount of glucose is play vital role for the formation of spherical structures. The precursor treated with different thermal treatment time was also studied. As it is shown in Figure S14, the surface of sphere is rough and a few V 2O3 nanoparticles can be observed obviously after calcination for 30 min. More importantly, a relatively smaller cavity volume in the nanospheres can be seen clearly. Then the cavity volume is gradually enlarged and the V 2O3 nanoparticles on the surface of spheres are epitaxial growth to form nanofibers, resulting in the formation of urchin-like V2O3/C hollow nanospheres hybrid. To sum up, the formation mechanism of V2O3/C hollow nanospheres could be illustrated in Scheme 1. Initially, vanadiumglucose spherical precursor is formed during the solvothermal reaction. Subsequently, the inner part of the sphere gradually isolated and apart to form a york-shell structure during the carbothermal reduction progress. Ultimately, the inner part of the sphere gradually dissolved and diffused to the surface of the spherical structure, urchin-like hollow nanospheres were obtained.


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The charge and discharge profiles of V2O3 /C for the initial 5 cycles (current density of 100 mA g-1) are exhibited in Figure 3a. The V2O3 /C shows an initial discharge capacity of 1420 mAh g-1 and charge capacity of 1306 mAh g-1 with the coulombic efficiency of 91.9 %. The loss of capacity is mainly caused by the solid electrolyte interface (SEI) during the initial cycle[26]. The rate performance of V2O3/C electrode and VOx are explored at different current densities ranging up from 100 mA g-1 to as high as10000 mA g-1. As it is shown in Figure 3b, the V2O3/C electrode delivers higher capacity than that of VOx at every current density. The capacity of V2O3/C hollow nanospheres is 634 mAh g-1(1 A g-1), approximately 5 times higher than that of VOx nanorods (121 mAh g -1), and 1.7 times higher than that of the graphite (372 mAh g -1). Moreover, even at a current density as high as 5000 mA g-1, the capacity of V2O3/C electrode can still maintain 483 mAh g-1, however, the specific capacity of the VOx electrode rapidly decline to about 230 mAh g -1. Remarkably, after testing the rate performance, 94.5% of the original capacity is recovered (1218 mAh g-1) when coming back to 100 mA g-1, while the recovery ratio of VOx is merely 66.3%. The excellent structural and cycle stability of V2O3/C hydrids indicates the fast kinetics for the intercalation-deintercalation of LIB. For comparison, V2O3/C hybrids synthesized from different amount of glucose ( V 2O3/C-1: 0.5 mmol and V2O3/C -2: 2 mmol) were also applied as the anode of the LIB shown in Figure S15, the V2O3/C-1 and V2O3/C-2 exhibit lower capacity than V2O3/C, which may due to the structural incompleteness. The EIS of V2O3/C electrode as well as VOx rods are shown in Figure 3c. Apparently, the cycled battery has a higher charge-transfer resistance (Rct) than that of the sell at open current voltage (OCV). The CV profiles of the hollow nanospheres were acquired in the potential ranging from 0.01 to 3.0 V at a scanning rate of 0.2 mV s-1. The electrochemical insertion/deinsertion mechanism of V2O3 can be described as follows:


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V2O3 + xLi+ +xe- = LixV2O3

(3)

LixV2O3+ (6-x) Li+ + (6-x)e- = 2V + 3Li2O

(4)

Three peaks clearly appeared at voltage potentials of 0.6, 1.3 and 1.7 V in the initial cathodic cycle and disappeared in the following two cycles, which could be ascribed to the irreversible reaction related to electrolyte decomposition, the initial reduction of V2O3 to metallic vanadium and the formation of SEI layer. The broad peak at 1.25 V can be attributed to the oxidation of metallic vanadium. Then for the subsequent two cycles, the CV curves can almost be overlap, which indicates the good reversibility of the V2O3/C electrode during the electrochemical process. The cycling performance of the V2O3/C electrode were displayed in Figure 3d. Notablely, when cycling at 1000 mAh g-1 for 1000 cycles, the V2O3/C electrode shows an increase of capacity from 900 to 1250 mAh g -1, which could be ascribed that during the long cycles the unique hollow structure makes it better contact with the electrolyte, furthermore enhances the transmission rate of lithium ion, which can also be found in many metal oxide anode materials and hollow structures[37-42]. In order to explore and characterize the structure and morphology variation of the electrode, the battery was dissembled inside the glove box after the cycling finished. The SEM image of the V2O3 /C electrode after 1000 cycles is shown in Figure S16. Although the nanospheres turned to be a little more nonuniform, the spherical structure was seen to be retained after continuous charge and discharge cycles, morover, such good structural stability can guarantee the prolonged cycling stability. Schematic illustration of the lithiation / delithiation process for V2O3 /C were deduced and shown in Figure 3f with the contrast with VOx nanorods shown in Figure S17. During the lithiation and delithiation progress, the VOx nanorods may suffer from the collapse of the structure and self-aggregation, which may induce poor cycle performance. While for the V 2O3 /C hollow spheres, the Li+ can embed into


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peripheral lamellar structures of the V2O3 hollow nanosphere, which are connected to the hollow spherical shell. The crossing and overlapped lamellar structure can buffer the volume variation during the consecutive lithiation/delithiation process. Meanwhile, the void formed from the overlapping lamellar structure are beneficial for the infiltrating of the electrolyte and the fast transfer of lithium ion and electron. For another, part of the Li+ can embed directly into the shell (containing V2O3 and amorphous carbon). Then, two kinds of Li+ can form reflux along the hollow spherical shell, which will not collapse the structure of hollow sphere due to the stable amorphous carbon in the shell. To demonstrate this electrode material’s suitability for practical applications was

assembled

using

V2O3/C

as

anode

electrode

and

commercial

[43-44],

full cell

high-voltage

LiMn1/3Co1/3Ni1/3O2 as cathode. The cell performance was examined at charge/discharge current density of 100 mA g-1 at a voltage range of 2.0-4.7 V as shown in Figure 4b. The cell exhibits an excellent performance of 197.2 mAh g -1, and a high capacity of 106 mAh g -1 remained after 50 cycles, as it is shown in Figure 4c. 3V, 10 mW blue light emitting diode (LED) can be lighted on to maintain 12 h (Figure 4d). Given that the initial capacity of 198 mAh g-1, the energy density of the V2O3 /C electrode is as high as 740 Wh kg -1 with a power rate of 375 W kg-1, which is higher that of common intercalation compounds such as LiFePO 4 (580 Wh kg-1) and LiMn2O4 (590 Wh kg-1). All the results demonstrate that our urchin-like V2O3/C hollow nanospheres can be promising high-performance lithium anodes. The electrochemical properties of our V 2O3/C nanostructure and various reported V2O3-based materials in lithium ion batteries are compared and shown in Table S1. Our synthesis method has obvious advantages, as most reported methods are relatively harsh, involving environmentally unfriendly organic solvents. Moreover, most reaction temperature is higher than


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200 oC, which is unsuitable for mass production. In addition, most reported V2O3 material is large in size, and there is no much control in the structure. The above results show that the outstanding performance of the urchin-like V2O3/C hollow nanospheres can be attributed to its structural virtue. Firstly, the unique structure of the hollow nanosphere with nanothorns on the surface can hinder the harmful self-aggregation and relieve the stress coming from volume variation during the electrochemical processes. Secondly, the amorphous carbon on the surface of the nanostructure contributes to better electrical conductivity and is beneficial to maintain the structure integrity, which is advantageous for the transport of lithium ion and electron. Third, the thorns on the surface of the nanosphere enlarge the active surface area, provide more lithium ion storage sites, make it better contact with the electrolyte, furthermore guarantees the transmission rate of lithium ion. Conclusions In summary, V2O3/C hybrid composed of nanofibers and hollow nanospheres has been successfully synthesized. Glucose could play the role of carbon resource, reducing agent for carbothermal reaction and structural direction role for the formation of hollow spheres. The amorphous carbon shell is beneficial for the structural stability and conductivity of the entire nanostructure, contributing to low charge transfer resistance and high electronic transport. Meanwhile, the hollow sphere nanostructure of V2O3/C hybrid is responsible for accommodation the volume variation during the insertion and extraction of Li ion. As for LIB anodes, V2O3/C hybrid shows high reversible capacity, outstanding cycling stability and extraordinary rate capability owing to the advantages of the special nanostructures. Moreover, the full cell assembled using V2O3/C as anode and commercial LiMn1/3Co1/3Ni1/3O2 cathode exhibits excellent cycling performance and high capacity, indicating its great potential application as


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electrode for LIBs. Our simple and robust synthetic strategy can be extended for the preparation of other metal oxide hollow sphere structure as the electrode materials for high-performance LIBs. Supporting Information. SEM images, FT-IR curve, Raman, TG, N2 adsorption-desorption isotherms and so on. This material is available free of charge via the Internet at http://pubs.acs.org. Corresponding Author *E-mail address: [email protected], [email protected]; [email protected]. ACKNOWLEDGMENT This work is supported by the National Natural Science Foundation of China (21631004, 21771059, 21371053, 21401048, 51672073), the Natural Science Foundation of Heilongjiang Province (B2017008), the University Nursing Program for Young Scholars with Creative Talents in Heilongjiang Province (UNPYSCT-2016016), the Project for Foshan Innovation Group (2014IT100062), the Harbin science and technology innovation talents research Foundation (2015RAQXJ057).

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Figure Caption Figure 1. (a) SEM and (b,c) TEM images of the V2O3 /C precursor; (d) SEM, (e) TEM and (f) HRTEM images V2O3 /C (the inset SAED pattern). Figure 2. (a) XRD patterns of V2O3 /C hybrid; (b) Raman spectra of as synthesized V 2O3 /C composites; (c) high-resolution V2p XPS spectrum of V2O3 /C hybrid; (d) V K-edge XANES of V2O3/C hybrid, and corresponding reference V2O3, VO2, and V2O5. Scheme 1. Schematic illustration of the facile synthesis of the V 2O3/C hollow nanospheres hybrid. Schematic illustration of the facile synthesis of the V 2O3/C hollow nanospheres hybrid. (Ⅰ and Ⅱ represent the solvothermal reaction, during which the vanadium - glucose spherical precursor were obtained; Ⅲ to Ⅴ are the carbothermal reduction progress, during which the inner part of the sphere gradually dissolved to form a urchin-like hollow nanosphere structure) Figure 3. (a) Charge and discharge profile of the V 2O3/C hybrid electrode for the first five cycle at a current density of 100 mA g-1; (b) Rate performance of the VOx nanorods and V2O3/C nanosphere electrode from 100 to 10000 mA g-1; (c) EIS measurements of the V2O3/C hybrid electrode and VOx rods electrode at open current voltage;(d) Cycling performance of the V2O3/C hybrid electrode at a current density of 1000 mA g-1 for 1000 cycles and the corresponding Coulombic efficiency; (e) Cyclic voltammograms curves curves of as prepared V 2O3/C hubrid electrode for the 1st, 2nd and 3th cycle at a scanning rate of 0.1 mV s-1; (f) Schematic illustration of the lithiation / delithiation process for the V2O3/C hybrid electrode Figure 4. a) Schematic illustration of the full-battery based on the V2O3 /C anode and commercial LiMn1/3Co1/3Ni1/3O2 cathode; b) Voltage profile of the full-battery cycled between


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2.0 and 4.7 V at a rate of 100 mA g-1; c) rate performance of the as assembled full cell; d) Photograph of a single LED being powered by coin cell battery.


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Figure 1. (a) SEM and (b,c) TEM images of the V2O3 /C precursor; (d) SEM, (e) TEM and (f) HRTEM images V2O3 /C (the inset SAED pattern).


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Figure 2. (a) XRD patterns of V2O3 /C hybrid; (b) Raman spectra of as synthesized V 2O3 /C composites; (c) high-resolution V2p XPS spectrum of V2O3 /C hybrid; (d) V K-edge XANES of V2O3/C hybrid, and corresponding reference V2O3, VO2, and V2O5.


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Scheme 1. Schematic illustration of the facile synthesis of the V 2O3/C hollow nanospheres hybrid. Schematic illustration of the facile synthesis of the V 2O3/C hollow nanospheres hybrid.( Ⅰ and Ⅱ represent the solvothermal reaction, during which the vanadium - glucose spherical precursor were obtained; Ⅲ to Ⅴ are the carbothermal reduction progress, during which the inner part of the sphere gradually dissolved to form a urchin-like hollow nanosphere structure)


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Figure 3. (a) Charge and discharge profile of the V 2O3/C hybrid electrode for the first five cycle at a current density of 100 mA g-1; (b) Rate performance of the VOx nanorods and V2O3/C nanosphere electrode from 100 to 10000 mA g-1; (c) EIS measurements of the V2O3/C hybrid electrode and VOx rods electrode at open current voltage;(d) Cycling performance of the V2O3/C hybrid electrode at a current density of 1000 mA g-1 for 1000 cycles and the corresponding Coulombic efficiency; (e) Cyclic voltammograms curves curves of as prepared V 2O3/C hubrid electrode for the 1st, 2nd and 3th cycle at a scanning rate of 0.1 mV s-1; (f) Schematic illustration of the lithiation / delithiation process for the V2O3/C hybrid electrode.


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Figure 4. a) Schematic illustration of the full-battery based on the V2O3 /C anode and commercial LiMn1/3Co1/3Ni1/3O2 cathode; b) Voltage profile of the full-battery cycled between 2.0 and 4.7 V at a rate of 100 mA g-1; c) rate performance of the as assembled full cell; d) Photograph of a single LED being powered by coin cell battery.


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Insert Table of Contents Graphic and Synopsis Here

V2O3/C hollow nanospheres hybrid with novel urchin-like structure are synthesized through temple-free strategy. The unique structure endows the V2O3/C with large specific area, good electro-conductivity and excellent structural stability. When applied as the anode material of LIB, it delivers high reversible capacity, outstanding cycling stability and excellent rate performance, which is promising for practical application of LIBs.


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C Hollow Nanospheres Hybrid for High-Capacity

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