- Email: [email protected]
graphene microsphere as a potential anode material for lithium-ion batteries
Ceramics International xxx (xxxx) xxx–xxx
Contents lists available at ScienceDirect
Ceramics International journal homepage: www.elsevier.com/locate/ceramint
VPO4@C/graphene microsphere as a potential anode material for lithiumion batteries ⁎
Lin-bo Tang, Bin Xiao, Chang-sheng An, Hui Li, Zhen-jiang He, Jun-chao Zheng School of Metallurgy and Environment, Central South University, Lushan Road (south), Changsha, Hunan 410083, PR China
A R T I C LE I N FO
A B S T R A C T
Keywords: Lithium ion battery Anode material Graphene Vanadium phosphate
Three-dimensional PO4-based polyanionic structures composed of interconnected MO6 octahedra and PO4 tetrahedra, such as VPO4, are potential anode materials for Li-ion batteries given their excellent cyclic stability. However, the application of VPO4 as an anode material has been limited by its low conductivity and drastic volume expansion. Herein, VPO4@C/graphene microspheres are designed and synthesised. P covalently bridges VPO4 and graphene through P–C bonding and acts as a buffer layer to maintain structural stability during continuous charge–discharge cycling. Graphene and C improve the electrical conductivity of VPO4 and reduce volume expansion during charge–discharge cycling. When applied as a Li-ion battery anode, the VPO4@C/ graphene microspheres can achieve a specific capacity of 432.8 mA h g−1 after 100 cycles under the current densities of 100 mA g−1. This performance is superior to that of commercial graphite. The VPO4 @C/graphene microspheres provide a good rate performance with a capacity of 562.1, 494, 424.2 and 356 mAh g−1 under 200, 400, 1000 and 2, 000 mA g−1, respectively. Furthermore, the VPO4@C/graphene microspheres achieve high tap density of > 1.2 g cm−3, which is higher than that of other nanomaterials (< 1.0 g cm−3) and is compatible with commercially available anode materials. Thus, VPO4@C/graphene microspheres are a promising anode material for Li-ion batteries.
1. Introduction
that can prevent lattice disturbance when the battery is charged or discharged [26–34]. The large volume of PO43- can provide space that decreases the extent of volume expansion [35–40]. When used as an anode material for Li-ion batteries, VPO4 can provide considerably better electronic conductivity than other alternatives and can reduce Liion polarization because of its three-dimensional structural frame [25]. The theoretical capacity of VPO4 is 550 mA h g−1. The Li-ion storage mechanism of anodic VPO4 can be represented by the following conversion reaction [30]:
With the development of science and technology, electronic products have become indispensable parts of people's daily lives [1–5]. However, the fabrication and use of electronic products are associated with environmental degradation and resource depletion. Thus, environmentally friendly and energy-efficient electronic products must be developed [6–12]. Rechargeable Li-ion batteries are clean, effective and recyclable next-generation power sources [13–17]. Therefore, the discovery of novel materials that can be used to fabricate Li-ion batteries has become a crucial research topic [15,18–22]. The anode is a key component of Li-ion batteries. Graphite-type C is widely used as a commercial anode material for Li-ion batteries. Although graphite is cost-effective and environmentally friendly, the theoretical capacity of graphite is only 372 mA h g−1 [23]. In addition, the energy density of graphite continues to limit the large-scale application of Li-ion batteries [24,25]. Given these limitations, high-performance anode materials for Li-ion batteries must be developed. Vanadium(V) is highly chemically active, and its valence states range from V to V5+. As a polyvalence element, V can transfer high numbers of electrons. The phosphate ion(PO43−) has a stable tetrahedral structure
⁎
VPO4 + 3Li+ + 3e−⟷V + Li3 PO4 VPO4 composites have been synthesised through numerous methods, such as sol-gel, freeze-drying and hydrothermal methods. Zhang synthesised core–shell VPO4/C composites through the sol-gel method [19]. Cao designed a nanostructured hollow sphere [29], and our group synthesised VPO4/C nanosheets via a one-step hydrothermal method [30]. However, these strategies are complex and yield nanonscale VPO4 anodic materials, which are incompatible with the current manufacturing process of commercial electrode materials. Microspheric structure has better processability and demonstrates less particle aggregation than Nanostructure [41].
Corresponding author. E-mail address: [email protected] (J.-c. Zheng).
https://doi.org/10.1016/j.ceramint.2018.05.056 Received 3 May 2018; Received in revised form 8 May 2018; Accepted 8 May 2018 0272-8842/ © 2018 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Please cite this article as: Tang, L.-b., Ceramics International (2018), https://doi.org/10.1016/j.ceramint.2018.05.056
Ceramics International xxx (xxxx) xxx–xxx
L.-b. Tang et al.
microscopy (TEM) (JEM-3000, FJEOL). Fourier transform infrared (FTIR) spectra was performed via using pressed KBr pellets on an IRAffinity-1 FTIR spectrometer (SHIMADZU). X-ray photoelectron spectroscopy (XPS, VG ESCALAB MK II) was performed with Al Ka radiation as the X-ray source. Laser Raman measurements were carried out in the range of 100–2000 cm−1 using a Jobin Yvon LabRam (HR800 Raman) spectrometer with a laser wavelength of 632.8 nm, and carbon content of the materials was examined via C-S analysis (CS-444). In addition, after 100 cycles at the current density of 0.1 A g−1, open the coin cells and wash the anode pole pieces with dimethyl carbonate (DEC) for several minutes and then dried in oven at 60 °C. The obtained battery pole pieces were observed through SEM.
Two-dimensional graphene provides several advantages, such as high specific surface area and excellent electrical conductivity. Graphene is widely used to improve the performance of functional materials [42]. For example, doping graphene with heteroatoms increases chemical activity and helps maintain material structural integrity [43]. Chemically stable covalent bonds provide excellent mechanical integrity and electrical connections between two different materials. In this work, we used a simple in situ method to synthesise VPO4 @C/graphene microspheres, which comprise microsized VPO4 coated with hydrolytic C and wrapped with doped graphene. P covalently bridges VPO4 microspheres, hydrolytic C and graphene. Moreover, we studied the structure, morphology and electrochemical performance of VPO4 @C/graphene microspheres in detail. In this structure, hydrolytic C and graphene function as conductive additives that provide electron transfer pathways and enhance electrical conductivity and as buffers that accommodate VPO4 volume expansion, adsorb stress and maintain electrode structural integrity during cycling.
2.3. Electrochemical measurements The electrochemical characterizations of obtained materials were tested using coin-type cell (CR2025). The electrode total loadings were typically in the range of 2–2.5 mg cm−2. The active materials (the prepared materials), conductive acetylene black and polyvinylidene fluoride (PVDF) binder were grinded with the weight ratio of 8:1:1. NMethyl pyrrolidone (NMP) was added to make solution as-resultant slurry. The above mixed materials were uniformly pasted on copper foil and dried in a vacuum oven at 120 °C for 12 h. Then, cut pole pieces into the disks and dried in a vacuum oven at 60 °C for 12 h. The tested coin cell contains electrolyte which was concluded in an ethylene carbonate (EC)/dimethyl carbonate (DMC)/diethyl carbonate (DEC) mixture (1:1:1,v/v/v) and 1 M LiPF6, the electrode and a lithium foil electrode separated using a porous polypropylene film. Charge-discharge and cycling performances of the coin cells were tested through a multichannel battery testing system (LAND) in the potential range 0.01–3 V (vs Li+/Li) at constant temperature at 25 °C. Cyclic voltammograms (CV) were used through a CHI-660D electrochemical work station at 0.1 mV/s at constant temperature at 25 °C. The electrochemical impedance spectra (EIS) detection was used through a frequency range between 0.01 Hz to 100 kHZ.
2. Experimental 2.1. Material synthesis 2.1.1. Synthesis of VPO4 @C/GO VPO4 @C/graphene was synthesised via a simple process, as illustrated in Scheme 1. Firstly, Graphene oxide was prepared from graphite (Sino Chem.) using a modified Hummer's method [41]. Secondly, 2 mmol V2O5 and 40 mg GO were added in a mixture of 60 mL deionized water and 20 mL polyethylene glycol (PEG). Then, stirred the solution and 8 mmol of C2H6O6 (Oxalic acid dihydrate) were added to dissolve V2O5, and V2O5 can react with C2H6O6 to form chelate. Then, 4 mmol of NH4H2PO4 was added in the above solution when the yellow liquid turned blue and stirred for 0.5 h. The mixture was added in a Teflon-lined autoclave (100 mL). The autoclave was sealed and put in an oven at 280 °C for 20 h. Cooled the solution to room temperature naturally and washed with distilled water and alcohol for several times. Vanadium phosphate precursors were obtained after the filtration products dried at 60 °C for 24 h. Finally, the obtained vanadium phosphate precursor was annealed at 350 °C for 4 h then at 750 °C for 10 h under argon atmosphere with a heating rate of 5 °C/min to form the product (VPO4 @C/graphene). Besides, VPO4 @C was synthesised through the same solvothermal reaction as mentioned above. The pristine VPO4 without carbon was prepared through the same reaction except the oxalic acid dihydrate addition, and it can be synthesised through the reaction as follows:
3. Results and discussion Fig. 1 shows the XRD patterns of VPO4, VPO4 @C and VPO4 @C/ graphene that were first sintered at 350 °C for 4 h and then at 750 °C for 10 h. The peaks in the patterns mainly correspond to the orthorhombic phase of VPO4 (space group Cmcm (63), a = 5.23 Å, b = 7.77 Å, c = 6.29 Å; PDF# 76-2023). In the XRD pattern of VPO4 @C/rGO, the peak at 25.9° corresponds to graphene peaks. As revealed through C–S analysis, the residual C content of VPO4 @C and VPO4 @C/graphene is approximately 5.3 wt% (hydrolytic C) and 6.7 wt% (hydrolytic C and graphene), respectively. Except for the weak peak at 25.9°, the other weak peaks at 22°, 24° and 31° are indexed as VO(PO3)2 phases (PDF# 84-48 and PDF# 77-995). The incomplete reduction of V5+ in impurities may decrease the capacity of electrode materials. Nevertheless, the impurities exert negligible effects on electrochemical performance given their low contents. The SEM images of the synthesised materials are shown in Fig. 2. The synthesised composites are all spherical micrometre-sized particles with the diameters of approximately 3–5 µm. Compared with that of pure VPO4 (Fig. 2a), the growth of VPO4 particles (Fig. 2b) is effectively
V2 O5 + 3C2 H6 O6 ⟶2VOC2 O4 + 5H2 O + 2CO2 2VOC2 O4 + 2NH4 H2 PO4 ⟶2VPO4 + 3CO2 + CO + 2NH3 + 3H2 O 2.2. Materials characterization Crystalline phase analyses and structures of the samples were characterized by the X-ray diffraction (XRD) (Rigaku Rint-2000, Cu Ka radiation) at room temperature in the 2θ range from 10° to 80°. The morphology of the products was observed by scanning electron microscopy (SEM) (JSM-7001, FFESEM, JEOL) and transmission electron
Scheme 1. The synthesis process of VPO4 @C/GO.
2
Ceramics International xxx (xxxx) xxx–xxx
L.-b. Tang et al.
resolution V2p XPS spectrum can be simply divided into two peaks located at 525.8 and 517 eV, which correspond to V2p1/2 and V2p2/3, respectively. V4+ can be observed at 523.8 and 517 eV, and the V3+ of VPO4 can be observed at 523.2 and 516.8 eV. These XPS results indicate that V3+ and V4+ coexist in the samples, it is accordance with the XRD results. The XPS spectra of P2p in the VPO4 samples are shown in Fig. 4c. Two peaks are located at the binding energy of 134.2 and 133.3 eV. The 134.2 eV peak can be assigned to the P–O, and the other is attributed to P–C. The presence of the P–C bond indicates that hydrolytic C, graphene and VPO4 are connected through P–C bonding. This stable contact between VPO4 and C can attenuate volume expansion and maintain material structural integrity during the charge–discharge cycle [28]. Meanwhile, the O 1 s peaks located at 533.4 and 531.2 eV are assigned to C–O and P = O peaks, respectively (Fig. 4b). The five C peaks located at 288.8, 286.7 and 285 eV correspond to O˭C–O, C–O, C–C and C˭C (Fig. 4f). The Fourier transform infrared (FTIR) spectra of VPO4 powder is shown in Fig. 4e. The small peak at 633 cm−1 is assigned to V3+–O2−, and the characteristic absorption peak at approximately 673 cm−1 is assigned to the P–C bond, which bridges VPO4 and C materials; these results correspond with the results of XPS analysis [42]. In addition, a sharp increase in the peak at approximately 1800 cm−1 corresponds to the O˭C bond. The broad peaks at approximately 500 cm−1–700 cm−1 are attributed to PO4 and P–O stretching vibrations. A sharp strong peak at 1400 cm−1 is assigned to the C˭O stretching vibration. The two weak peaks at 950 and 1100 cm−1 shown in Fig. 4f are consistent with the PO4 and P–O peaks, respectively. The results of Raman spectroscopy (Fig. 4f) also show two strong peaks at 1341 and 1590 cm−1 that correspond to the characteristic D and G bands of C materials, respectively. This result further confirms the existence of C in VPO4 @C/graphene. Notably, the C materials act as a rigid support that prevents the agglomeration of VPO4 particles and facilitates fast electron transfer. The electrochemical performance of the VPO4 anode material in the range of 0.01 and 3.0 V was tested by using a galvanostatic chargedischarge cycler, as shown in Fig. 5a, b. The discharge capacity of the VPO4 @C/graphene anode is 1074 mAh·g−1 after the first cycle and 395.3 mA h g−1 after 100 cycles. By contrast, the discharge capacities of
Fig. 1. XRD patterns of VPO4, VPO4 @C and VPO4 @C/graphene.
prevented by the hydrolytic C. Interestingly, the graphene formed a C network with a structure similar to that of a bird's nest, and VPO4 microspheres resemble eggs in the graphene nest (Fig. 2c–e). This unique structure improves the electrical conductivity of VPO4, relieves volume expansion and prevents material breakage during charging and discharging. The TEM images show that the VPO4 microspheres are wellwrapped by graphene and coated by the hydrolytic C (Fig. 3a). The synthesised VPO4 has excellent crystallinity with an interplanar spacing of approximately 0.45 nm that corresponds to the (110) plane of VPO4 (Fig. 3b). Furthermore, the tap density of the VPO4 @C/graphene composite (> 1.2 g cm−3) is higher than that of other nanomaterials (< 1.0 g cm−3) and is comparable with that of current commercial anode materials. X-ray photoelectron spectroscopy (XPS) was performed to determine the individual elemental valence states of the materials. The wide XPS spectra of the materials (Fig. 4[a, b, c, d]) indicates the absence of impure elements. Only C, O, V and P are presented. The high-
Fig. 2. SEM of VPO4 (a), VPO4 @C (b), VPO4 @C/graphene (c,d,e) (GO=30, 40, 50 mg). 3
Ceramics International xxx (xxxx) xxx–xxx
L.-b. Tang et al.
Fig. 3. The TEM images of VPO4 @C/graphene.
VPO4 and VPO4 @C are 500.6 and 1035.2 mA h g−1 after the first cycle, respectively, and are only 103.7 and 127.7 mA h g−1 after 100 cycles, respectively. These results indicate that VPO4 @C/graphene delivers a considerably higher specific capacity and more stable cycling performance than VPO4 and VPO4 @C. The rate performance of VPO4 @C/ graphene is also superior to that of pure VPO4 and VPO4 @C, as shown Fig. 5c, d. VPO4 @C/graphene can deliver capacities of 962.3, 562.1, 494, 424.2 and 356 mAh·g−1 under the current density of 100, 200, 400, 1000 and 2000 mA g−1, respectively. As the current density recovers to 100 mA g−1, the capacity of VPO4 @C/graphene remains at 442.5 mA h g−1. The above results indicate that graphene and hydrolytic C can effectively improve the electrochemical performance of VPO4 composites. The cyclic voltammetry (CV) curves of anodic VPO4 @C/graphene obtained at a scan rate of 0.1 mV/s and potential window of 0.01–3 V are shown in Fig. 6a. The curves are typical CV curves of VPO4 composites (Fig. 6a). The curve for the first cycle is visibly different from those for subsequent cycles and shows a broad cathodic peak appeared at approximately 0.1 V. This peak resulted from the formation of a solid electrolyte interface and the side reaction of Li-ion with the O-
containing groups of graphene [43]. And the cathodic peak at 0.1 V is attributed to the formation of SEI Layer. It means the formation of stability SEI films leads to the peaks at 0.1 V fading away in the following cycles. After subsequent cycles, the cathodic peak at 0.6 V and the anodic peak at 1.1 V may be attributed to the reaction as follows: VPO4 + 3Li+↔V+Li3PO4[29]. In addition, the subsequent sweeps are in good agreement, indicating the good stability of electrode materials. Overall, these results are consistent with the previously reported data for VPO4 materials [44]. The electrochemical impedance spectrum profiles of VPO4 @C/graphene, VPO4 and VPO4 @C are shown in Fig. 6b The curves all exhibit a semicircle in the high-frequency region that corresponds to charge–transfer resistance at the cathode/electrolyte interface. Moreover, the curves exhibit a straight line in the lowfrequency region that corresponds to Li-ion diffusion into the bulk electrode material [45,46]. The impedance spectra were fitted by using the equivalent electrical circuit model, as shown in inset of Fig. 6b, where Rs represents solution resistance and Rct represents charge–transfer resistance. Rs and Rct are associated with the electrical conductivity of materials and electron transfer rate, respectively. The fitted parameters of VPO4, VPO4 @C and VPO4 @C/graphene anode derived
Fig. 4. XPS of VPO4 @C/graphene: (a) V, (b) O, (c) P, (d) C, (e) Raman spectrum of VPO4 @C/graphene, (f) FITR of VPO4 @C/graphene. 4
Ceramics International xxx (xxxx) xxx–xxx
L.-b. Tang et al.
Fig. 5. Electrochemical performance: (a) discharge−charge curves at 0.1 A g−1 for VPO4 @C/graphene electrode and (b) cycling performance of all the VPO4 electrodes at 0.1 A g−1; (c) discharge/charge curves of pure VPO4 @C/graphene at different density; (d) rate performances of all the VPO4; (e) CVs of VPO4 @C/ graphene at a scan rate of 0.1 mV s−1 and; (f) EIS of all the VPO4 electrodes.
from the equivalent circuit are shown in Table 1. The Rs values of VPO4, VPO4 @C and VPO4 @C/graphene anodes are almost equal, indicating that the Rs of all electrodes remain constant. However, the three materials present drastically different Rct values. Specifically, the VPO4 @C/graphene electrode has the lowest Rct value (49.57 Ω) among the three samples. The Lithium ion diffusion coefficient could be calculated through the following equation:
Table 1 Typical fitting parameters of VPO4, VPO4 @C and VPO4 @C /GO samples. Samples
Rs/ Ω
Rct/ Ω
DLi+/cm2·s−1
VPO4 VPO4 @C VPO4 @C/GO
8.677 7.608 11.66
428.3 69.31 49.57
1.3 × 10–21 2.73 × 10–21 8.2 × 10–21
Fig. 6. CVs of VPO4 @C/graphene at a scan rate of 0.1 mV s−1 (a); (b) EIS of all the VPO4 electrodes;(c) plot of ω−1/2 versus Z`, calculated from EIS Curves. 5
Ceramics International xxx (xxxx) xxx–xxx
L.-b. Tang et al.
Fig. 7. SEM images of the pole pieces of VPO4, VPO4 @C and VPO4 @C/graphene (a, b and c) and pole pieces of VPO4, VPO4 @C and VPO4 @C/graphene (d, e and f) samples after 100 cycles.
DLi+ =
R2T 2
After 100 cycles, the VPO4 @C/graphene anode achieves a discharge capacity of 432.8 mA h g−1. These results indicate that the VPO4 @C/ graphene anode performs better than commercial graphite anodes. Furthermore, VPO4 @C/graphene exhibits excellent capacity, rate and cycle performances. Therefore, VPO4 @C/graphene is an outstanding candidate anode material for Li-ion batteries.
2A2 n4F 4c 2σ 2
And the diffusion coefficient of Lithium ion is proportional to the numerical of σ. The plot of ω−1/2 versus Z` calculated from EIS Curves are shown in Fig. 6c. The value size of δ can be calculated by the formula “Z`=Rs+Rct+ σω−1/2”. From Table 1, the diffusion coefficient of VPO4, VPO4 @C and VPO4 @C/graphene anodes are 1.3 × 10–21, 2.73 × 10–21 and 8.2 × 10–21 cm2 s−1, respectively, suggesting that VPO4 @C/graphene electrode could be more conducive to the migration of Lithium ion. This result indicates that the VPO4 @C/graphene anode accelerates the kinetics of Li-ion intercalation/deintercalation because the hydrolytic C and graphene provide a space network structure that facilitates electron transportation. Therefore, the addition of graphene and C improves the Li-ion intercalation/deintercalation of VPO4-based anode materials. To elucidate the influence of the C materials on the VPO4-based electrode, SEM images of the pole pieces of VPO4, VPO4 @C and VPO4 @C/graphene samples after 100 cycles were obtained. The images are shown in Fig. 7. Some cracks appear in all of the pole pieces of samples due to the volume change of active materials. However, the cracks in VPO4 and VPO4 @C (Fig. 7d, e) are drastically larger than those in VPO4 @C/graphene. This crack pattern indicates that the VPO4 @C/ graphene sample is the most stable material during charge–discharge cycles. Moreover, the VPO4 @C/graphene microspheres remain completely spherical (Fig. 7f). Therefore, the addition of hydrolytic C and graphene to VPO4 inhibits the fragmentation of VPO4 microspheres and the degradation of VPO4 pole pieces.
Acknowledgements This study was supported by National Natural Science Foundation of China (Grant No. 51572300) and the Innovation-Driven Project of Central South University (NO. 2016CX021). References [1] G. Niu, S. Singh, S.W. Holland, M. Pecht, Health monitoring of electronic products based on Mahalanobis distance and Weibull decision metrics, Microelectron. Reliab. 51 (2011) 279–284. [2] T. Assavapokee, W. Wongthatsanekorn, Reverse production system infrastructure design for electronic products in the state of Texas, Comput. Ind. Eng. 62 (2012) 129–140. [3] R. Laurenti, R. Sinha, J. Singh, B. Frostell, Some pervasive challenges to sustainability by design of electronic products-a conceptual discussion, J. Clean. Prod. 108 (2015) 281–288. [4] K. Xiao, Q. Tang, Z. Liu, A. Hu, S. Zhang, W. Deng, X. Chen, 3D interconnected mesoporous Si/SiO2 coated with CVD derived carbon as an advanced anode material of Li-ion batteries, Ceram. Int. 44 (2018) 3548–3555. [5] Z. Feng, C. Kim, A. Vijh, M. Armand, K.H. Bevan, K. Zaghib, Unravelling the role of Li2S2 in lithium-sulfur batteries: a first principles study of its energetic and electronic properties, J. Power Sources 272 (2014) 518–521. [6] A. Kumar, M. Holuszko, Electronic waste and existing processing routes: a Canadian perspective, Resources 5 (2016) 35. [7] P. Guchhait, M.K. Maiti, M. Maiti, An EOQ model of deteriorating item in imprecise environment with dynamic deterioration and credit linked demand, Appl. Math. Model. 39 (2015) 6553–6567. [8] D.H. Yang, G.P. Li, T.H. Yi, H.N. Li, A performance-based service life design method for reinforced concrete structures under chloride environment, Constr. Build. Mater. 124 (2016) 453–461. [9] F. Tittarelli, G. Moriconi, A. Bonazza, Atmospheric deterioration of cement plaster in a building exposed to a urban environment, J. Cult. Herit. 9 (2008) 203–206. [10] D. Doughty, J.D. Fuentes, R. Sakai, X.M. Hu, K. Sanchez, Nocturnal isoprene declines in a semi-urban environment, J. Atmos. Chem. 72 (2013) 215–234.
4. Conclusion VPO4 microspheres, hydrolytic C and graphene are covalently bridged through P–C bonding. P–C acts as a buffer layer that maintains structural stability during continuous charge–discharge cycles. Under the current density of 100 mA g−1 between 3.0 and 0.01 V, the VPO4 @C/graphene anode delivers a discharge capacity of 1074.6 mA h g−1. 6
Ceramics International xxx (xxxx) xxx–xxx
L.-b. Tang et al. [11] H. Cui, T. Feng, H. Yang, X. Bao, W. Tang, J. Fu, Experimental study of carbon fiber reinforced alkali-activated slag composites with micro-encapsulated PCM for energy storage, Constr. Build. Mater. 161 (2018) 442–451. [12] L. Sun, L. Hammarström, B. Åkermark, S. Styring, Towards artificial photosynthesis: ruthenium-manganese chemistry for energy production, Chem. Soc. Rev. 30 (2001) 36–49. [13] X. Liang, C. Hart, Q. Pang, A. Garsuch, T. Weiss, L.F. Nazar, A highly efficient polysulfide mediator for lithium-sulfur batteries, Nat. Commun. 6 (2015) 5682. [14] C.X. Zhou, P.B. Wang, J.C. zheng, C.Y. Xia, B. Zhang, X.M. Xi, K.S. Xiao, D.Q. Liao, L.S. Yang, X.Q. Chen, S.B. Qin, Cyclic performance of Li-rich layered material Li1.1Ni0.35Mn0.65O2 synthesized through a two-step calcination method, Electrochim. Acta 252 (2017) 286–294. [15] J.B. Goodenough, Electrochemical energy storage in a sustainable modern society, Energy Environ. Sci. 7 (2014) 14–18. [16] K.F. Chiu, S.H. Su, H.J. Leu, C.H. Hsia, Titanium oxynitride thin films as highcapacity and high-rate anode materials for lithium-ion batteries, Thin Solid Films 596 (2015) 29–33. [17] Z.J. He, L.B. Tang, J.L. Wang, C.S. An, B. Xiao, J.C. Zheng, Synthesis and characterization of a sulfur/TiO2 composite for Li-S battery, Ionics (2018), http://dx. doi.org/10.1007/s11581-018-2570-y. [18] G. Ma, Z. Wen, M. Wu, C. Shen, Q. Wang, J. Jin, X. Wu, A lithium anode protection guided highly-stable lithium-sulfur battery, Chem. Commun. 50 (2014) 14209–14212. [19] Y. Zhang, X.J. Zhang, Q. Tang, D.H. Wu, Z. Zhou, Core-shell VPO4/C anode materials for Li ion batteries: computational investigation and sol-gel synthesis, J. Alloy. Compd. 522 (2012) 167–171. [20] C. Chae, J. Kim, J.Y. Kim, S. Ji, S.S. Lee, Y. Kang, Y. Choi, J. Suk, S. Jeong, Roomtemperature, ambient-pressure chemical synthesis of amine-functionalized hierarchical carbon-sulfur composites for lithium-sulfur battery cathodes, ACS Appl. Mater. Interfaces 10 (2018) 4767–4775. [21] J. Liu, Y. Zhao, X. Li, C. Wang, Y. Zeng, G. Yue, Q. Chen, CuCr2O4@rGO Nanocomposites as high-performance cathode catalyst for rechargeable lithiumoxygen batteries, Nano-Micro Lett. 10 (2017). [22] K.M. Horax, S. Bao, M. Wang, Y. Li, Analysis of graphene-like activated carbon derived from rice straw for application in supercapacitor, Chin. Chem. Lett. 28 (2017) 2290–2294. [23] X. Kong, Y. Huang, Q. Liu, Two-dimensional boron-doped graphyne nanosheet: a new metal-free catalyst for oxygen evolution reaction, Carbon 123 (2017) 558–564. [24] M.H. Kwon, H.S. Shin, C.N. Chu, Fabrication of a super-hydrophobic surface on metal using laser ablation and electrodeposition, Appl. Surf. Sci. 288 (2014) 222–228. [25] X. Huang, J. Zhang, W. Rao, T. Sang, B. Song, C. Wong, Tunable electromagnetic properties and enhanced microwave absorption ability of flaky graphite/cobalt zinc ferrite composites, J. Alloy. Compd. 662 (2016) 409–414. [26] L. Wu, Y. Hu, X.P. Zhang, J.Q. Liu, X. Zhu, S.K. Zhong, Synthesis of carbon-coated Na2MnPO4F hollow spheres as a potential cathode material for Na-ion batteries, J. Power Sources 374 (2018) 40–47. [27] X. Bin, B. Zhang, L.B. Tang, C.S. An, J.C. Zheng, Nano-micro structure VO2/CNTs composite as a potential anode material for lithium ion batteries, Ceram. Int. (2018), http://dx.doi.org/10.1016/j.ceramint.2018.04.133. [28] L. Wu, S.N. Shi, X.P. Zhang, Y. Yang, J.Q. Liu, S.B. Tang, S.K. Zhong, Room-temperature pre-reduction of spinning solution for the synthesis of Na3V2(PO4)3/C nanofibers as high-performance cathode materials for Na-ion batteries, Electrochim. Acta 274 (2018) 233–241 (X).
[29] D. Zhao, T. Meng, J. Qin, W. Wang, Z. Yin, M. Cao, Rational construction of multivoids-assembled hybrid nanospheres based on VPO4 encapsulated in porous carbon with superior lithium storage performance, ACS Appl. Mater. Interfaces 9 (2017) 1437–1445. [30] J.C. Zheng, Y.D. Han, B. Zhang, C. Shen, L. Ming, X. Ou, J.F. Zhang, Electrochemical properties of VPO4/C nanosheets and microspheres as anode materials for lithiumion batteries, ACS Appl. Mater. Interfaces 6 (2014) 6223–6226. [31] X. Nan, C. Liu, K. Wang, W. Ma, C. Zhang, H. Fu, Z. Li, G. Cao, Amorphous VPO4/C with the enhanced performances as an anode for lithium ion batteries, J. Mater. 2 (2016) 350–357. [32] X. Liang, X. Ou, H. Dai, F. Zheng, Q. Pan, P. Liu, X. Xiong, M. Liu, C. Yang, Exploration of VPO4 as a new anode material for sodium-ion batteries, Chem. Commun. 53 (2017) 12696–12699. [33] J.C. Zheng, Y.D. Han, L.B. Tang, B. Zhang, Investigation of phase structure change and electrochemical performance in LiVP2O7-Li3V2(PO4)3-LiVPO4F system, Electrochim. Acta 198 (2016) 195–202. [34] M.S. Whittingham, Ultimate limits to intercalation reactions for lithium batteries, Chem. Rev. 114 (2014) 11414–11443. [35] C. Zhu, K. Song, P.A. van Aken, J. Maier, Y. Yu, Carbon-coated Na3V2(PO4)3 embedded in porous carbon matrix: an ultrafast Na-storage cathode with the potential of outperforming Li cathodes, Nano Lett. 14 (2014) 2175–2180. [36] Q. Wei, Q. An, D. Chen, L. Mai, S. Chen, Y. Zhao, K.M. Hercule, L. Xu, A. MinhasKhan, Q. Zhang, One-Pot synthesized bicontinuous hierarchical Li3V2(PO4)3/C mesoporous nanowires for high-rate and ultralong-life lithium-ion batteries, Nano Lett. 14 (2014) 1042–1048. [37] X. Rui, W. Sun, C. Wu, Y. Yu, Q. Yan, An advanced sodium-ion battery composed of carbon Coated Na3V2(PO4)3 in a porous graphene network, Adv. Mater. 27 (2015) 6670–6676. [38] J.C. Zheng, Y.D. Han, D. Sun, B. Zhang, E.J. Cairns, In situ-formed LiVOPO4@V2O5 core-shell nanospheres as a cathode material for lithium-ion cells, Energy Storage Mater. 7 (2017) 48–55. [39] F. Wu, G. Yushin, Conversion cathodes for rechargeable lithium and lithium-ion batteries, Energy Environ. Sci. 10 (2017) 435–459. [40] N. Nitta, F. Wu, J.T. Lee, G. Yushin, Li-ion battery materials: present and future, Mater. Today 18 (2015) 252–264. [41] A.D.C. Permana, A. Nugroho, K.Y. Chung, W. Chang, J. Kim, Template-free synthesis of hierarchical porous anatase TiO2 microspheres with carbon coating and their electrochemical properties, Chem. Eng. J. 241 (2014) 216–227. [42] J. Chen, B. Yao, C. Li, G. Shi, An improved Hummers method for eco-friendly synthesis of graphene oxide, Carbon 64 (2013) 225–229. [43] X.K. Kong, Q.W. Chen, Improved performance of graphene doped with pyridinic N for Li-ion battery: a density functional theory model, Phys. Chem. Chem. Phys.: PCCP 15 (2013) 12982–12987. [44] L. Zhang, K. Zhao, R. Yu, M. Yan, W. Xu, Y. Dong, W. Ren, X. Xu, C. Tang, L. Mai, Phosphorus enhanced intermolecular interactions of SnO2 and graphene as an ultrastable lithium battery anode, Small 13 (2017) 1603973. [45] J.C. Zheng, B.Y. Yang, X.W. Wang, B. Zhang, H. Tong, W.J. Yu, J.F. Zhang, Comparative investigation of Na2FeP2O7 sodium insertion material synthesized by using different sodium sources, ACS Sustain. Chem. Eng. (2018), http://dx.doi.org/ 10.1021/acssuschemeng.7b04516. [46] H. Chen, B. Zhang, X. Wang, P. Dong, H. Tong*, J.C. Zheng, W. Yu, J. Zhang, CNTDecorated Na3V2(PO4)3 microspheres as a high-rate and cycle-stable cathode material for sodium ion batteries, ACS Appl. Mater. Interfaces 10 (4) (2018) (3590359).
7
Contents lists available at ScienceDirect
Ceramics International journal homepage: www.elsevier.com/locate/ceramint
VPO4@C/graphene microsphere as a potential anode material for lithiumion batteries ⁎
Lin-bo Tang, Bin Xiao, Chang-sheng An, Hui Li, Zhen-jiang He, Jun-chao Zheng School of Metallurgy and Environment, Central South University, Lushan Road (south), Changsha, Hunan 410083, PR China
A R T I C LE I N FO
A B S T R A C T
Keywords: Lithium ion battery Anode material Graphene Vanadium phosphate
Three-dimensional PO4-based polyanionic structures composed of interconnected MO6 octahedra and PO4 tetrahedra, such as VPO4, are potential anode materials for Li-ion batteries given their excellent cyclic stability. However, the application of VPO4 as an anode material has been limited by its low conductivity and drastic volume expansion. Herein, VPO4@C/graphene microspheres are designed and synthesised. P covalently bridges VPO4 and graphene through P–C bonding and acts as a buffer layer to maintain structural stability during continuous charge–discharge cycling. Graphene and C improve the electrical conductivity of VPO4 and reduce volume expansion during charge–discharge cycling. When applied as a Li-ion battery anode, the VPO4@C/ graphene microspheres can achieve a specific capacity of 432.8 mA h g−1 after 100 cycles under the current densities of 100 mA g−1. This performance is superior to that of commercial graphite. The VPO4 @C/graphene microspheres provide a good rate performance with a capacity of 562.1, 494, 424.2 and 356 mAh g−1 under 200, 400, 1000 and 2, 000 mA g−1, respectively. Furthermore, the VPO4@C/graphene microspheres achieve high tap density of > 1.2 g cm−3, which is higher than that of other nanomaterials (< 1.0 g cm−3) and is compatible with commercially available anode materials. Thus, VPO4@C/graphene microspheres are a promising anode material for Li-ion batteries.
1. Introduction
that can prevent lattice disturbance when the battery is charged or discharged [26–34]. The large volume of PO43- can provide space that decreases the extent of volume expansion [35–40]. When used as an anode material for Li-ion batteries, VPO4 can provide considerably better electronic conductivity than other alternatives and can reduce Liion polarization because of its three-dimensional structural frame [25]. The theoretical capacity of VPO4 is 550 mA h g−1. The Li-ion storage mechanism of anodic VPO4 can be represented by the following conversion reaction [30]:
With the development of science and technology, electronic products have become indispensable parts of people's daily lives [1–5]. However, the fabrication and use of electronic products are associated with environmental degradation and resource depletion. Thus, environmentally friendly and energy-efficient electronic products must be developed [6–12]. Rechargeable Li-ion batteries are clean, effective and recyclable next-generation power sources [13–17]. Therefore, the discovery of novel materials that can be used to fabricate Li-ion batteries has become a crucial research topic [15,18–22]. The anode is a key component of Li-ion batteries. Graphite-type C is widely used as a commercial anode material for Li-ion batteries. Although graphite is cost-effective and environmentally friendly, the theoretical capacity of graphite is only 372 mA h g−1 [23]. In addition, the energy density of graphite continues to limit the large-scale application of Li-ion batteries [24,25]. Given these limitations, high-performance anode materials for Li-ion batteries must be developed. Vanadium(V) is highly chemically active, and its valence states range from V to V5+. As a polyvalence element, V can transfer high numbers of electrons. The phosphate ion(PO43−) has a stable tetrahedral structure
⁎
VPO4 + 3Li+ + 3e−⟷V + Li3 PO4 VPO4 composites have been synthesised through numerous methods, such as sol-gel, freeze-drying and hydrothermal methods. Zhang synthesised core–shell VPO4/C composites through the sol-gel method [19]. Cao designed a nanostructured hollow sphere [29], and our group synthesised VPO4/C nanosheets via a one-step hydrothermal method [30]. However, these strategies are complex and yield nanonscale VPO4 anodic materials, which are incompatible with the current manufacturing process of commercial electrode materials. Microspheric structure has better processability and demonstrates less particle aggregation than Nanostructure [41].
Corresponding author. E-mail address: [email protected] (J.-c. Zheng).
https://doi.org/10.1016/j.ceramint.2018.05.056 Received 3 May 2018; Received in revised form 8 May 2018; Accepted 8 May 2018 0272-8842/ © 2018 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Please cite this article as: Tang, L.-b., Ceramics International (2018), https://doi.org/10.1016/j.ceramint.2018.05.056
Ceramics International xxx (xxxx) xxx–xxx
L.-b. Tang et al.
microscopy (TEM) (JEM-3000, FJEOL). Fourier transform infrared (FTIR) spectra was performed via using pressed KBr pellets on an IRAffinity-1 FTIR spectrometer (SHIMADZU). X-ray photoelectron spectroscopy (XPS, VG ESCALAB MK II) was performed with Al Ka radiation as the X-ray source. Laser Raman measurements were carried out in the range of 100–2000 cm−1 using a Jobin Yvon LabRam (HR800 Raman) spectrometer with a laser wavelength of 632.8 nm, and carbon content of the materials was examined via C-S analysis (CS-444). In addition, after 100 cycles at the current density of 0.1 A g−1, open the coin cells and wash the anode pole pieces with dimethyl carbonate (DEC) for several minutes and then dried in oven at 60 °C. The obtained battery pole pieces were observed through SEM.
Two-dimensional graphene provides several advantages, such as high specific surface area and excellent electrical conductivity. Graphene is widely used to improve the performance of functional materials [42]. For example, doping graphene with heteroatoms increases chemical activity and helps maintain material structural integrity [43]. Chemically stable covalent bonds provide excellent mechanical integrity and electrical connections between two different materials. In this work, we used a simple in situ method to synthesise VPO4 @C/graphene microspheres, which comprise microsized VPO4 coated with hydrolytic C and wrapped with doped graphene. P covalently bridges VPO4 microspheres, hydrolytic C and graphene. Moreover, we studied the structure, morphology and electrochemical performance of VPO4 @C/graphene microspheres in detail. In this structure, hydrolytic C and graphene function as conductive additives that provide electron transfer pathways and enhance electrical conductivity and as buffers that accommodate VPO4 volume expansion, adsorb stress and maintain electrode structural integrity during cycling.
2.3. Electrochemical measurements The electrochemical characterizations of obtained materials were tested using coin-type cell (CR2025). The electrode total loadings were typically in the range of 2–2.5 mg cm−2. The active materials (the prepared materials), conductive acetylene black and polyvinylidene fluoride (PVDF) binder were grinded with the weight ratio of 8:1:1. NMethyl pyrrolidone (NMP) was added to make solution as-resultant slurry. The above mixed materials were uniformly pasted on copper foil and dried in a vacuum oven at 120 °C for 12 h. Then, cut pole pieces into the disks and dried in a vacuum oven at 60 °C for 12 h. The tested coin cell contains electrolyte which was concluded in an ethylene carbonate (EC)/dimethyl carbonate (DMC)/diethyl carbonate (DEC) mixture (1:1:1,v/v/v) and 1 M LiPF6, the electrode and a lithium foil electrode separated using a porous polypropylene film. Charge-discharge and cycling performances of the coin cells were tested through a multichannel battery testing system (LAND) in the potential range 0.01–3 V (vs Li+/Li) at constant temperature at 25 °C. Cyclic voltammograms (CV) were used through a CHI-660D electrochemical work station at 0.1 mV/s at constant temperature at 25 °C. The electrochemical impedance spectra (EIS) detection was used through a frequency range between 0.01 Hz to 100 kHZ.
2. Experimental 2.1. Material synthesis 2.1.1. Synthesis of VPO4 @C/GO VPO4 @C/graphene was synthesised via a simple process, as illustrated in Scheme 1. Firstly, Graphene oxide was prepared from graphite (Sino Chem.) using a modified Hummer's method [41]. Secondly, 2 mmol V2O5 and 40 mg GO were added in a mixture of 60 mL deionized water and 20 mL polyethylene glycol (PEG). Then, stirred the solution and 8 mmol of C2H6O6 (Oxalic acid dihydrate) were added to dissolve V2O5, and V2O5 can react with C2H6O6 to form chelate. Then, 4 mmol of NH4H2PO4 was added in the above solution when the yellow liquid turned blue and stirred for 0.5 h. The mixture was added in a Teflon-lined autoclave (100 mL). The autoclave was sealed and put in an oven at 280 °C for 20 h. Cooled the solution to room temperature naturally and washed with distilled water and alcohol for several times. Vanadium phosphate precursors were obtained after the filtration products dried at 60 °C for 24 h. Finally, the obtained vanadium phosphate precursor was annealed at 350 °C for 4 h then at 750 °C for 10 h under argon atmosphere with a heating rate of 5 °C/min to form the product (VPO4 @C/graphene). Besides, VPO4 @C was synthesised through the same solvothermal reaction as mentioned above. The pristine VPO4 without carbon was prepared through the same reaction except the oxalic acid dihydrate addition, and it can be synthesised through the reaction as follows:
3. Results and discussion Fig. 1 shows the XRD patterns of VPO4, VPO4 @C and VPO4 @C/ graphene that were first sintered at 350 °C for 4 h and then at 750 °C for 10 h. The peaks in the patterns mainly correspond to the orthorhombic phase of VPO4 (space group Cmcm (63), a = 5.23 Å, b = 7.77 Å, c = 6.29 Å; PDF# 76-2023). In the XRD pattern of VPO4 @C/rGO, the peak at 25.9° corresponds to graphene peaks. As revealed through C–S analysis, the residual C content of VPO4 @C and VPO4 @C/graphene is approximately 5.3 wt% (hydrolytic C) and 6.7 wt% (hydrolytic C and graphene), respectively. Except for the weak peak at 25.9°, the other weak peaks at 22°, 24° and 31° are indexed as VO(PO3)2 phases (PDF# 84-48 and PDF# 77-995). The incomplete reduction of V5+ in impurities may decrease the capacity of electrode materials. Nevertheless, the impurities exert negligible effects on electrochemical performance given their low contents. The SEM images of the synthesised materials are shown in Fig. 2. The synthesised composites are all spherical micrometre-sized particles with the diameters of approximately 3–5 µm. Compared with that of pure VPO4 (Fig. 2a), the growth of VPO4 particles (Fig. 2b) is effectively
V2 O5 + 3C2 H6 O6 ⟶2VOC2 O4 + 5H2 O + 2CO2 2VOC2 O4 + 2NH4 H2 PO4 ⟶2VPO4 + 3CO2 + CO + 2NH3 + 3H2 O 2.2. Materials characterization Crystalline phase analyses and structures of the samples were characterized by the X-ray diffraction (XRD) (Rigaku Rint-2000, Cu Ka radiation) at room temperature in the 2θ range from 10° to 80°. The morphology of the products was observed by scanning electron microscopy (SEM) (JSM-7001, FFESEM, JEOL) and transmission electron
Scheme 1. The synthesis process of VPO4 @C/GO.
2
Ceramics International xxx (xxxx) xxx–xxx
L.-b. Tang et al.
resolution V2p XPS spectrum can be simply divided into two peaks located at 525.8 and 517 eV, which correspond to V2p1/2 and V2p2/3, respectively. V4+ can be observed at 523.8 and 517 eV, and the V3+ of VPO4 can be observed at 523.2 and 516.8 eV. These XPS results indicate that V3+ and V4+ coexist in the samples, it is accordance with the XRD results. The XPS spectra of P2p in the VPO4 samples are shown in Fig. 4c. Two peaks are located at the binding energy of 134.2 and 133.3 eV. The 134.2 eV peak can be assigned to the P–O, and the other is attributed to P–C. The presence of the P–C bond indicates that hydrolytic C, graphene and VPO4 are connected through P–C bonding. This stable contact between VPO4 and C can attenuate volume expansion and maintain material structural integrity during the charge–discharge cycle [28]. Meanwhile, the O 1 s peaks located at 533.4 and 531.2 eV are assigned to C–O and P = O peaks, respectively (Fig. 4b). The five C peaks located at 288.8, 286.7 and 285 eV correspond to O˭C–O, C–O, C–C and C˭C (Fig. 4f). The Fourier transform infrared (FTIR) spectra of VPO4 powder is shown in Fig. 4e. The small peak at 633 cm−1 is assigned to V3+–O2−, and the characteristic absorption peak at approximately 673 cm−1 is assigned to the P–C bond, which bridges VPO4 and C materials; these results correspond with the results of XPS analysis [42]. In addition, a sharp increase in the peak at approximately 1800 cm−1 corresponds to the O˭C bond. The broad peaks at approximately 500 cm−1–700 cm−1 are attributed to PO4 and P–O stretching vibrations. A sharp strong peak at 1400 cm−1 is assigned to the C˭O stretching vibration. The two weak peaks at 950 and 1100 cm−1 shown in Fig. 4f are consistent with the PO4 and P–O peaks, respectively. The results of Raman spectroscopy (Fig. 4f) also show two strong peaks at 1341 and 1590 cm−1 that correspond to the characteristic D and G bands of C materials, respectively. This result further confirms the existence of C in VPO4 @C/graphene. Notably, the C materials act as a rigid support that prevents the agglomeration of VPO4 particles and facilitates fast electron transfer. The electrochemical performance of the VPO4 anode material in the range of 0.01 and 3.0 V was tested by using a galvanostatic chargedischarge cycler, as shown in Fig. 5a, b. The discharge capacity of the VPO4 @C/graphene anode is 1074 mAh·g−1 after the first cycle and 395.3 mA h g−1 after 100 cycles. By contrast, the discharge capacities of
Fig. 1. XRD patterns of VPO4, VPO4 @C and VPO4 @C/graphene.
prevented by the hydrolytic C. Interestingly, the graphene formed a C network with a structure similar to that of a bird's nest, and VPO4 microspheres resemble eggs in the graphene nest (Fig. 2c–e). This unique structure improves the electrical conductivity of VPO4, relieves volume expansion and prevents material breakage during charging and discharging. The TEM images show that the VPO4 microspheres are wellwrapped by graphene and coated by the hydrolytic C (Fig. 3a). The synthesised VPO4 has excellent crystallinity with an interplanar spacing of approximately 0.45 nm that corresponds to the (110) plane of VPO4 (Fig. 3b). Furthermore, the tap density of the VPO4 @C/graphene composite (> 1.2 g cm−3) is higher than that of other nanomaterials (< 1.0 g cm−3) and is comparable with that of current commercial anode materials. X-ray photoelectron spectroscopy (XPS) was performed to determine the individual elemental valence states of the materials. The wide XPS spectra of the materials (Fig. 4[a, b, c, d]) indicates the absence of impure elements. Only C, O, V and P are presented. The high-
Fig. 2. SEM of VPO4 (a), VPO4 @C (b), VPO4 @C/graphene (c,d,e) (GO=30, 40, 50 mg). 3
Ceramics International xxx (xxxx) xxx–xxx
L.-b. Tang et al.
Fig. 3. The TEM images of VPO4 @C/graphene.
VPO4 and VPO4 @C are 500.6 and 1035.2 mA h g−1 after the first cycle, respectively, and are only 103.7 and 127.7 mA h g−1 after 100 cycles, respectively. These results indicate that VPO4 @C/graphene delivers a considerably higher specific capacity and more stable cycling performance than VPO4 and VPO4 @C. The rate performance of VPO4 @C/ graphene is also superior to that of pure VPO4 and VPO4 @C, as shown Fig. 5c, d. VPO4 @C/graphene can deliver capacities of 962.3, 562.1, 494, 424.2 and 356 mAh·g−1 under the current density of 100, 200, 400, 1000 and 2000 mA g−1, respectively. As the current density recovers to 100 mA g−1, the capacity of VPO4 @C/graphene remains at 442.5 mA h g−1. The above results indicate that graphene and hydrolytic C can effectively improve the electrochemical performance of VPO4 composites. The cyclic voltammetry (CV) curves of anodic VPO4 @C/graphene obtained at a scan rate of 0.1 mV/s and potential window of 0.01–3 V are shown in Fig. 6a. The curves are typical CV curves of VPO4 composites (Fig. 6a). The curve for the first cycle is visibly different from those for subsequent cycles and shows a broad cathodic peak appeared at approximately 0.1 V. This peak resulted from the formation of a solid electrolyte interface and the side reaction of Li-ion with the O-
containing groups of graphene [43]. And the cathodic peak at 0.1 V is attributed to the formation of SEI Layer. It means the formation of stability SEI films leads to the peaks at 0.1 V fading away in the following cycles. After subsequent cycles, the cathodic peak at 0.6 V and the anodic peak at 1.1 V may be attributed to the reaction as follows: VPO4 + 3Li+↔V+Li3PO4[29]. In addition, the subsequent sweeps are in good agreement, indicating the good stability of electrode materials. Overall, these results are consistent with the previously reported data for VPO4 materials [44]. The electrochemical impedance spectrum profiles of VPO4 @C/graphene, VPO4 and VPO4 @C are shown in Fig. 6b The curves all exhibit a semicircle in the high-frequency region that corresponds to charge–transfer resistance at the cathode/electrolyte interface. Moreover, the curves exhibit a straight line in the lowfrequency region that corresponds to Li-ion diffusion into the bulk electrode material [45,46]. The impedance spectra were fitted by using the equivalent electrical circuit model, as shown in inset of Fig. 6b, where Rs represents solution resistance and Rct represents charge–transfer resistance. Rs and Rct are associated with the electrical conductivity of materials and electron transfer rate, respectively. The fitted parameters of VPO4, VPO4 @C and VPO4 @C/graphene anode derived
Fig. 4. XPS of VPO4 @C/graphene: (a) V, (b) O, (c) P, (d) C, (e) Raman spectrum of VPO4 @C/graphene, (f) FITR of VPO4 @C/graphene. 4
Ceramics International xxx (xxxx) xxx–xxx
L.-b. Tang et al.
Fig. 5. Electrochemical performance: (a) discharge−charge curves at 0.1 A g−1 for VPO4 @C/graphene electrode and (b) cycling performance of all the VPO4 electrodes at 0.1 A g−1; (c) discharge/charge curves of pure VPO4 @C/graphene at different density; (d) rate performances of all the VPO4; (e) CVs of VPO4 @C/ graphene at a scan rate of 0.1 mV s−1 and; (f) EIS of all the VPO4 electrodes.
from the equivalent circuit are shown in Table 1. The Rs values of VPO4, VPO4 @C and VPO4 @C/graphene anodes are almost equal, indicating that the Rs of all electrodes remain constant. However, the three materials present drastically different Rct values. Specifically, the VPO4 @C/graphene electrode has the lowest Rct value (49.57 Ω) among the three samples. The Lithium ion diffusion coefficient could be calculated through the following equation:
Table 1 Typical fitting parameters of VPO4, VPO4 @C and VPO4 @C /GO samples. Samples
Rs/ Ω
Rct/ Ω
DLi+/cm2·s−1
VPO4 VPO4 @C VPO4 @C/GO
8.677 7.608 11.66
428.3 69.31 49.57
1.3 × 10–21 2.73 × 10–21 8.2 × 10–21
Fig. 6. CVs of VPO4 @C/graphene at a scan rate of 0.1 mV s−1 (a); (b) EIS of all the VPO4 electrodes;(c) plot of ω−1/2 versus Z`, calculated from EIS Curves. 5
Ceramics International xxx (xxxx) xxx–xxx
L.-b. Tang et al.
Fig. 7. SEM images of the pole pieces of VPO4, VPO4 @C and VPO4 @C/graphene (a, b and c) and pole pieces of VPO4, VPO4 @C and VPO4 @C/graphene (d, e and f) samples after 100 cycles.
DLi+ =
R2T 2
After 100 cycles, the VPO4 @C/graphene anode achieves a discharge capacity of 432.8 mA h g−1. These results indicate that the VPO4 @C/ graphene anode performs better than commercial graphite anodes. Furthermore, VPO4 @C/graphene exhibits excellent capacity, rate and cycle performances. Therefore, VPO4 @C/graphene is an outstanding candidate anode material for Li-ion batteries.
2A2 n4F 4c 2σ 2
And the diffusion coefficient of Lithium ion is proportional to the numerical of σ. The plot of ω−1/2 versus Z` calculated from EIS Curves are shown in Fig. 6c. The value size of δ can be calculated by the formula “Z`=Rs+Rct+ σω−1/2”. From Table 1, the diffusion coefficient of VPO4, VPO4 @C and VPO4 @C/graphene anodes are 1.3 × 10–21, 2.73 × 10–21 and 8.2 × 10–21 cm2 s−1, respectively, suggesting that VPO4 @C/graphene electrode could be more conducive to the migration of Lithium ion. This result indicates that the VPO4 @C/graphene anode accelerates the kinetics of Li-ion intercalation/deintercalation because the hydrolytic C and graphene provide a space network structure that facilitates electron transportation. Therefore, the addition of graphene and C improves the Li-ion intercalation/deintercalation of VPO4-based anode materials. To elucidate the influence of the C materials on the VPO4-based electrode, SEM images of the pole pieces of VPO4, VPO4 @C and VPO4 @C/graphene samples after 100 cycles were obtained. The images are shown in Fig. 7. Some cracks appear in all of the pole pieces of samples due to the volume change of active materials. However, the cracks in VPO4 and VPO4 @C (Fig. 7d, e) are drastically larger than those in VPO4 @C/graphene. This crack pattern indicates that the VPO4 @C/ graphene sample is the most stable material during charge–discharge cycles. Moreover, the VPO4 @C/graphene microspheres remain completely spherical (Fig. 7f). Therefore, the addition of hydrolytic C and graphene to VPO4 inhibits the fragmentation of VPO4 microspheres and the degradation of VPO4 pole pieces.
Acknowledgements This study was supported by National Natural Science Foundation of China (Grant No. 51572300) and the Innovation-Driven Project of Central South University (NO. 2016CX021). References [1] G. Niu, S. Singh, S.W. Holland, M. Pecht, Health monitoring of electronic products based on Mahalanobis distance and Weibull decision metrics, Microelectron. Reliab. 51 (2011) 279–284. [2] T. Assavapokee, W. Wongthatsanekorn, Reverse production system infrastructure design for electronic products in the state of Texas, Comput. Ind. Eng. 62 (2012) 129–140. [3] R. Laurenti, R. Sinha, J. Singh, B. Frostell, Some pervasive challenges to sustainability by design of electronic products-a conceptual discussion, J. Clean. Prod. 108 (2015) 281–288. [4] K. Xiao, Q. Tang, Z. Liu, A. Hu, S. Zhang, W. Deng, X. Chen, 3D interconnected mesoporous Si/SiO2 coated with CVD derived carbon as an advanced anode material of Li-ion batteries, Ceram. Int. 44 (2018) 3548–3555. [5] Z. Feng, C. Kim, A. Vijh, M. Armand, K.H. Bevan, K. Zaghib, Unravelling the role of Li2S2 in lithium-sulfur batteries: a first principles study of its energetic and electronic properties, J. Power Sources 272 (2014) 518–521. [6] A. Kumar, M. Holuszko, Electronic waste and existing processing routes: a Canadian perspective, Resources 5 (2016) 35. [7] P. Guchhait, M.K. Maiti, M. Maiti, An EOQ model of deteriorating item in imprecise environment with dynamic deterioration and credit linked demand, Appl. Math. Model. 39 (2015) 6553–6567. [8] D.H. Yang, G.P. Li, T.H. Yi, H.N. Li, A performance-based service life design method for reinforced concrete structures under chloride environment, Constr. Build. Mater. 124 (2016) 453–461. [9] F. Tittarelli, G. Moriconi, A. Bonazza, Atmospheric deterioration of cement plaster in a building exposed to a urban environment, J. Cult. Herit. 9 (2008) 203–206. [10] D. Doughty, J.D. Fuentes, R. Sakai, X.M. Hu, K. Sanchez, Nocturnal isoprene declines in a semi-urban environment, J. Atmos. Chem. 72 (2013) 215–234.
4. Conclusion VPO4 microspheres, hydrolytic C and graphene are covalently bridged through P–C bonding. P–C acts as a buffer layer that maintains structural stability during continuous charge–discharge cycles. Under the current density of 100 mA g−1 between 3.0 and 0.01 V, the VPO4 @C/graphene anode delivers a discharge capacity of 1074.6 mA h g−1. 6
Ceramics International xxx (xxxx) xxx–xxx
L.-b. Tang et al. [11] H. Cui, T. Feng, H. Yang, X. Bao, W. Tang, J. Fu, Experimental study of carbon fiber reinforced alkali-activated slag composites with micro-encapsulated PCM for energy storage, Constr. Build. Mater. 161 (2018) 442–451. [12] L. Sun, L. Hammarström, B. Åkermark, S. Styring, Towards artificial photosynthesis: ruthenium-manganese chemistry for energy production, Chem. Soc. Rev. 30 (2001) 36–49. [13] X. Liang, C. Hart, Q. Pang, A. Garsuch, T. Weiss, L.F. Nazar, A highly efficient polysulfide mediator for lithium-sulfur batteries, Nat. Commun. 6 (2015) 5682. [14] C.X. Zhou, P.B. Wang, J.C. zheng, C.Y. Xia, B. Zhang, X.M. Xi, K.S. Xiao, D.Q. Liao, L.S. Yang, X.Q. Chen, S.B. Qin, Cyclic performance of Li-rich layered material Li1.1Ni0.35Mn0.65O2 synthesized through a two-step calcination method, Electrochim. Acta 252 (2017) 286–294. [15] J.B. Goodenough, Electrochemical energy storage in a sustainable modern society, Energy Environ. Sci. 7 (2014) 14–18. [16] K.F. Chiu, S.H. Su, H.J. Leu, C.H. Hsia, Titanium oxynitride thin films as highcapacity and high-rate anode materials for lithium-ion batteries, Thin Solid Films 596 (2015) 29–33. [17] Z.J. He, L.B. Tang, J.L. Wang, C.S. An, B. Xiao, J.C. Zheng, Synthesis and characterization of a sulfur/TiO2 composite for Li-S battery, Ionics (2018), http://dx. doi.org/10.1007/s11581-018-2570-y. [18] G. Ma, Z. Wen, M. Wu, C. Shen, Q. Wang, J. Jin, X. Wu, A lithium anode protection guided highly-stable lithium-sulfur battery, Chem. Commun. 50 (2014) 14209–14212. [19] Y. Zhang, X.J. Zhang, Q. Tang, D.H. Wu, Z. Zhou, Core-shell VPO4/C anode materials for Li ion batteries: computational investigation and sol-gel synthesis, J. Alloy. Compd. 522 (2012) 167–171. [20] C. Chae, J. Kim, J.Y. Kim, S. Ji, S.S. Lee, Y. Kang, Y. Choi, J. Suk, S. Jeong, Roomtemperature, ambient-pressure chemical synthesis of amine-functionalized hierarchical carbon-sulfur composites for lithium-sulfur battery cathodes, ACS Appl. Mater. Interfaces 10 (2018) 4767–4775. [21] J. Liu, Y. Zhao, X. Li, C. Wang, Y. Zeng, G. Yue, Q. Chen, CuCr2O4@rGO Nanocomposites as high-performance cathode catalyst for rechargeable lithiumoxygen batteries, Nano-Micro Lett. 10 (2017). [22] K.M. Horax, S. Bao, M. Wang, Y. Li, Analysis of graphene-like activated carbon derived from rice straw for application in supercapacitor, Chin. Chem. Lett. 28 (2017) 2290–2294. [23] X. Kong, Y. Huang, Q. Liu, Two-dimensional boron-doped graphyne nanosheet: a new metal-free catalyst for oxygen evolution reaction, Carbon 123 (2017) 558–564. [24] M.H. Kwon, H.S. Shin, C.N. Chu, Fabrication of a super-hydrophobic surface on metal using laser ablation and electrodeposition, Appl. Surf. Sci. 288 (2014) 222–228. [25] X. Huang, J. Zhang, W. Rao, T. Sang, B. Song, C. Wong, Tunable electromagnetic properties and enhanced microwave absorption ability of flaky graphite/cobalt zinc ferrite composites, J. Alloy. Compd. 662 (2016) 409–414. [26] L. Wu, Y. Hu, X.P. Zhang, J.Q. Liu, X. Zhu, S.K. Zhong, Synthesis of carbon-coated Na2MnPO4F hollow spheres as a potential cathode material for Na-ion batteries, J. Power Sources 374 (2018) 40–47. [27] X. Bin, B. Zhang, L.B. Tang, C.S. An, J.C. Zheng, Nano-micro structure VO2/CNTs composite as a potential anode material for lithium ion batteries, Ceram. Int. (2018), http://dx.doi.org/10.1016/j.ceramint.2018.04.133. [28] L. Wu, S.N. Shi, X.P. Zhang, Y. Yang, J.Q. Liu, S.B. Tang, S.K. Zhong, Room-temperature pre-reduction of spinning solution for the synthesis of Na3V2(PO4)3/C nanofibers as high-performance cathode materials for Na-ion batteries, Electrochim. Acta 274 (2018) 233–241 (X).
[29] D. Zhao, T. Meng, J. Qin, W. Wang, Z. Yin, M. Cao, Rational construction of multivoids-assembled hybrid nanospheres based on VPO4 encapsulated in porous carbon with superior lithium storage performance, ACS Appl. Mater. Interfaces 9 (2017) 1437–1445. [30] J.C. Zheng, Y.D. Han, B. Zhang, C. Shen, L. Ming, X. Ou, J.F. Zhang, Electrochemical properties of VPO4/C nanosheets and microspheres as anode materials for lithiumion batteries, ACS Appl. Mater. Interfaces 6 (2014) 6223–6226. [31] X. Nan, C. Liu, K. Wang, W. Ma, C. Zhang, H. Fu, Z. Li, G. Cao, Amorphous VPO4/C with the enhanced performances as an anode for lithium ion batteries, J. Mater. 2 (2016) 350–357. [32] X. Liang, X. Ou, H. Dai, F. Zheng, Q. Pan, P. Liu, X. Xiong, M. Liu, C. Yang, Exploration of VPO4 as a new anode material for sodium-ion batteries, Chem. Commun. 53 (2017) 12696–12699. [33] J.C. Zheng, Y.D. Han, L.B. Tang, B. Zhang, Investigation of phase structure change and electrochemical performance in LiVP2O7-Li3V2(PO4)3-LiVPO4F system, Electrochim. Acta 198 (2016) 195–202. [34] M.S. Whittingham, Ultimate limits to intercalation reactions for lithium batteries, Chem. Rev. 114 (2014) 11414–11443. [35] C. Zhu, K. Song, P.A. van Aken, J. Maier, Y. Yu, Carbon-coated Na3V2(PO4)3 embedded in porous carbon matrix: an ultrafast Na-storage cathode with the potential of outperforming Li cathodes, Nano Lett. 14 (2014) 2175–2180. [36] Q. Wei, Q. An, D. Chen, L. Mai, S. Chen, Y. Zhao, K.M. Hercule, L. Xu, A. MinhasKhan, Q. Zhang, One-Pot synthesized bicontinuous hierarchical Li3V2(PO4)3/C mesoporous nanowires for high-rate and ultralong-life lithium-ion batteries, Nano Lett. 14 (2014) 1042–1048. [37] X. Rui, W. Sun, C. Wu, Y. Yu, Q. Yan, An advanced sodium-ion battery composed of carbon Coated Na3V2(PO4)3 in a porous graphene network, Adv. Mater. 27 (2015) 6670–6676. [38] J.C. Zheng, Y.D. Han, D. Sun, B. Zhang, E.J. Cairns, In situ-formed LiVOPO4@V2O5 core-shell nanospheres as a cathode material for lithium-ion cells, Energy Storage Mater. 7 (2017) 48–55. [39] F. Wu, G. Yushin, Conversion cathodes for rechargeable lithium and lithium-ion batteries, Energy Environ. Sci. 10 (2017) 435–459. [40] N. Nitta, F. Wu, J.T. Lee, G. Yushin, Li-ion battery materials: present and future, Mater. Today 18 (2015) 252–264. [41] A.D.C. Permana, A. Nugroho, K.Y. Chung, W. Chang, J. Kim, Template-free synthesis of hierarchical porous anatase TiO2 microspheres with carbon coating and their electrochemical properties, Chem. Eng. J. 241 (2014) 216–227. [42] J. Chen, B. Yao, C. Li, G. Shi, An improved Hummers method for eco-friendly synthesis of graphene oxide, Carbon 64 (2013) 225–229. [43] X.K. Kong, Q.W. Chen, Improved performance of graphene doped with pyridinic N for Li-ion battery: a density functional theory model, Phys. Chem. Chem. Phys.: PCCP 15 (2013) 12982–12987. [44] L. Zhang, K. Zhao, R. Yu, M. Yan, W. Xu, Y. Dong, W. Ren, X. Xu, C. Tang, L. Mai, Phosphorus enhanced intermolecular interactions of SnO2 and graphene as an ultrastable lithium battery anode, Small 13 (2017) 1603973. [45] J.C. Zheng, B.Y. Yang, X.W. Wang, B. Zhang, H. Tong, W.J. Yu, J.F. Zhang, Comparative investigation of Na2FeP2O7 sodium insertion material synthesized by using different sodium sources, ACS Sustain. Chem. Eng. (2018), http://dx.doi.org/ 10.1021/acssuschemeng.7b04516. [46] H. Chen, B. Zhang, X. Wang, P. Dong, H. Tong*, J.C. Zheng, W. Yu, J. Zhang, CNTDecorated Na3V2(PO4)3 microspheres as a high-rate and cycle-stable cathode material for sodium ion batteries, ACS Appl. Mater. Interfaces 10 (4) (2018) (3590359).
7