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Surface-assembled highly flexible Na3(VOPO4)2F nanocube cathode for high-rate binder-free Na-ion batteries
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Bohua Denga, Ning Yuea, Haoyang Donga, Qiuyue Guia, Liang Xiaoa, Jinping Liua, b, c, *
Chinese Chemical Letters | 2021, 32(2) : 826 - 829
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Chinese Chemical Letters | 2021, 32(2): 826-829
• Communication •
Surface-assembled highly flexible Na3(VOPO4)2F nanocube cathode for high-rate binder-free Na-ion batteries
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Bohua Denga, Ning Yuea, Haoyang Donga, Qiuyue Guia, Liang Xiaoa, Jinping Liua, b, c, *
Affiliations
  • a School of Chemistry, Chemical Engineering and Life Science, Wuhan University of Technology, Wuhan 430070, China
  • b State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China
  • c Key Laboratory for Photonic and Electronic Bandgap Materials, Ministry of Education, School of Physics and Electronic Engineering, Harbin Normal University, Harbin 150025, China
Published: 2021-02-15 doi: 10.1016/j.cclet.2020.04.054
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Flexible Na-ion storage cathodes are still very few due to the challenge in achieving both reliable mechanical flexibility and excellent electrochemical performances. Herein, a new type of flexible Na3(VOPO4)2F cathode with nanocubes tightly assembled on carbon cloth is fabricated by a facile solvothermal method for the first time. The cathode is able to exhibit superior rate capability and stable cycling performance up to 1000 cycles, due to the surface-assembling of crystalline nanocubes on carbon fibers. In addition, it shows good mechanical flexibility, nearly no capacity decay is observed after continuous bending of 500 times. With this novel cathode and a directly-grown Na2Ti2O5 anode, a fully binder-free Na-ion battery is assembled. It can deliver a high working voltage and increased gravimetric energy/power densities (maximum values: 220.2 Wh/kg; 5674.7 W/kg), and can power a LED indicator at bending angles from 0° to 180°.

Flexible cathode  /  Na3(VOPO4)2F  /  Nanocube  /  Surface-assembling  /  Sodium-ion battery
Bohua Deng, Ning Yue, Haoyang Dong, Qiuyue Gui, Liang Xiao, Jinping Liu. Surface-assembled highly flexible Na3(VOPO4)2F nanocube cathode for high-rate binder-free Na-ion batteries[J]. Chinese Chemical Letters, 2021 , 32 (2) : 826 -829 . DOI: 10.1016/j.cclet.2020.04.054
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Flexible energy-storage systems have attracted increasing research interest for the development of flexible electronic devices such as wearable electronics, roll-up displays and bendable phones [1-3]. Lots of efforts have been dedicated to flexible Li-ion batteries (LIBs) due to their high working voltage, high energy density and cycling stability. However, the commercial expansion of LIBs is limited by the ever-increasing cost and shortage of lithium salts and costly transition metal oxides. Therefore, considerable academic attentions have been transferred to flexible sodium ion batteries (SIBs), due to the natural abundance (and low cost) of Na resources as well as similar energy-storage mechanisms between LIBs and SIBs [3-12]. It is noticed that previous investigations for flexible Na-ion storage have been mainly concentrated on anode materials, and those for cathode materials are very few due to the challenge in attaining both reliable flexibility and satisfied electrochemical performances [7, 9].
The energy-storage performances upon mechanical deformation of flexible SIBs and other devices depend strictly on the electrode selection and fabrication [1, 2, 7]. Direct growth of active materials on flexible and conductive substrates has been demonstrated to be effective strategies to enhanced mechanical and electrochemical performances due to the binder-free configuration [10, 13]. Additionally, high-potential cathode materials show advantages in achieving high voltage and consequently increased energy density [14]. For practical SIBs, Na3(VO1−xPO4)2F1+2x materials including Na3(VOPO4)2F (NVOPF) are very attractive due to their high potential (ca. 3.8V in average), high energy density (≈ 500 Wh/kg) and small volume change upon Na-ion intercalation/extraction (< 3%) [15-22]. Nevertheless, previous reports on flexible Na3(VO1−xPO4)2F1+2x electrodes are very few [23, 24], and the current approach to high-rate performance is very complicated (needing two hydrothermal steps with VO2 template/seed layer) [24]. Therefore, the design and facile synthesis of flexible and high-rate Na3(VO1-xPO4)2F1+2x cathodes are still very desirable for flexible SIBs.
Herein, we report a novel binder-free configuration for NVOPF nanocube cathodes directly assembled on flexible carbon cloth (2.0–2.5 mg/cm2). It exhibits superior high-rate capability (≈ 90% and 86% of the 1 C capacity retained at 10 and 20 C, respectively) and excellent cycling stability (≈ 88% capacity retention after 1000 cycles at 5 C). Moreover, this NVOPF cathode demonstrates good flexibility (nearly no capacity decay after continuous bending for 500 times). With this cathode and a flexible Na2Ti2O5 anode, model flexible SIBs were assembled, which show increased gravimetric energy/power density compared with previously reported SIBs, and a maximum energy density of ca. 220.2 Wh/kg can be achieved.
The NVOPF cathode was directly grown on carbon cloth by a modified solvothermal method: first, a suspension of 4 m mol NH4H2PO4, 6 m mol NaF, 2 m mol V2O5 and 0.4 m mol H2C2O4·2H2O in a mixture of 10 mL distilled water and 40 ml ethylene glycol was obtained by stirring; then, one piece of carbon cloth (2.5 cm×2.5 cm, WOS1009 commercially supplied by Cetech Co., Ltd., Taiwan) was placed in the suspension, which was transferred into a Teflon-lined reactor (100 mL, sealed by a stainless-steel autoclave) and heated at 180 ℃ for 6 h. After solvothermal reaction, the carbon cloth was picked up, and cleaned with distilled water and absolute alcohol successively. The carbon cloth (the precursor) was annealed at 600 ℃ for 5 h in Ar atmosphere. The mass loading of NVOPF materials on the carbon cloth was estimated to be about 2.0–2.5 mg/cm2 by the comparison of mass change of carbon cloth before and after reaction. The NTO nanowire array anode was prepared by a simple hydrothermal method. In brief, a pretreated and cleaned Ti foil was placed into a solution of 75 mL 1 mol/L NaOH in a Teflon-lined reactor (100 mL) and heated at 220 ℃ for 24 h. After hydrothermal process, the Ti foil (50 μm) was picked up and cleaned (similar to that of NVOPF), and then annealed at 450 ℃ for 2 h in an atmosphere of Ar/H2 (95:5 in volume). The mass loading of NTO was estimated to be about 0.6−0.8 mg/cm2.
The surface morphology and crystalline structure of the as-prepared electrode materials were characterized with SEM (Hitachi S-4800, Japan), TEM (JEM-2010FEF, 200 kV) and XRD (Bruker D-8 Advance, Cu Kα), respectively. The surface chemistry of NVOPF materials was examined with XPS (Escalab 250-Xi, U. S. A.). The electrochemical performances of the as-prepared flexible NVOPF cathode and NTO anode were characterized with coin cells or soft packages, which were assembled in an Ar-filled glove box. In the half cells, a sodium metal foil was used as the counter electrode. The electrolytes used for cell preparation are an ester-based electrolyte with 1 mol/L NaClO4 in ethylene carbonate (EC), propylene carbonate (PC) and fluoroethylene carbonate (FEC) (1:1:0.05 in volume), or an ether-based electrolyte with 1 mol/L NaPF6 in diglyme, which are commercially supplied. A glass microfiber filter (Whatman) was used as the separator. The model flexible batteries in soft packages were hot-sealed in a PE polymer bag of ca. 6.25 cm2 (2.5 cm×2.5 cm), with about 8 mg NVOPF (on 4 cm2 carbon cloth for cathode) and 3.2 mg NTO (on 5 cm2 Ti foil for anode) in one cell. Galvanostatic testing was carried out with a Land-CT2001A battery testing system (Wuhan Jinnuo, China) at room temperature. The gravimetric energy/power densities (E and P) of the model SIBs were calculated using and P = E/Δt, where I is the constant current density (A/g), V(t) is the working voltage at t, dt is time differential, t1 and t2 (s) are the start and end time of the discharge curve, and Δt is the total discharging time. It is noted that the mass used for calculation is based on the active electrode materials. Cyclic voltammetry (CV) was examined with a CHI660E electrochemical workstation (CH Instruments).
The SEM morphologies show that nanocubes of ca. 300 nm in average size are tightly and uniformly decorated on the carbon fibers (Figs. 1a and b). The elemental mapping of an individual fiber indicates the presence and uniform distribution of Na, V, P and F elements from NVOPF (Fig. 1c). Based on the characteristic XRD diffraction peaks (Fig. 1d), the nanocubes can be indexed to a well-crystallized phase of tetragonal space group (P42/mnm, PDF#89-8485) [16]. Furthermore, the TEM images and selected area electron diffraction (SAED) pattern of NVOPF nanocubes suggest that the particles are highly crystalline, which is beneficial to the facile charge-transfer between carbon fibers and nanocubes (Figs. 1e-g). Moreover, the lattice spacing of ca. 0.522 nm is in good agreement with the (002) plane of P42/mnm phase of NVOPF.
The successful growth of NVOPF materials on carbon fibers is further confirmed by the Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) (Fig. 2). According to previous literature [20, 21], the intense and broad band between 1000 and 1200 cm−1 (Fig. 2a) can be assigned to the asymmetric stretching vibration from PO43− tetrahedrons, and the two peaks at 557 cm−1 and 667 cm−1 can be ascribed to the P-O symmetric stretching and bending vibrations, respectively. Moreover, the characteristic V-O and V-F vibrations from Na3(VO1-xPO4)2F1+2x compounds can be observed at 912 cm−1 and 945 cm−1, respectively. The presence of V4+ and F- from NVOPF (Fig. 2b) is also confirmed by the XPS spectra. The V 2p absorption peaks (2p1/2, 2p3/2) at the binding energy of about 517.2 and 524.3 eV can be attributed to V4+ compounds (Fig. 2c), and the absorption peak at about 685 eV (Fig. 2d) indicates the presence of F [21].
The Na-ion storage performances of the flexible NVOPF electrode were examined by galvanostatic testing. Fig. 3a shows the typical charge/discharge profiles of the initial two cycles at 0.2 C between 2.5 V and 4.3 V, consistent with Na3(VOPO4)2F materials in previous reports [16, 21]. Two potential plateaus at about 3.61 and 4.02 V (vs. Na+/Na), as well as a reversible capacity of ca. 124 mAh/g are observed. The NVOPF cathode was also tested at various C rates (Fig. S1a in Supporting information), and about 90% (112.6 mAh/g) and 86% (106.71 mAh/g) of the 1 C capacity are retained at 10 and 20 C, respectively (Fig. 3b). By comparing with the excellent performances of other reported NVOPF materials (Table S1 in Supporting information) [22, 24-27], this high-rate performance is superior based on a mass loading > 2.0 mg/cm2. Furthermore, the NVOPF cathode exhibits excellent cycling stability, and ≈ 88% of the discharge capacity is retained after 1000 cycles while cycled at 5 C (Fig. 3c).
The NVOPF electrode was further characterized by cyclic voltammetry. The CV profiles at various sweeping rates are presented in Fig. 3d, two redox couples can be seen at about 3.65 and 4.10 V (corresponding to the two voltage plateaus in the charge/discharge processes). The Ip of the redox peaks at ca. 3.6 and 4.0 V are plotted against ʋ1/2, and the data in scattered dots are well fitted by a linear dependence of Ip on ʋ1/2 (Fig. S1b in Supporting information). Therefore, the Na-ion intercalation processes at both 3.6 and 4.0 V are attributed to be diffusion-controlled [21]. This implies that the superior high-rate performance of flexible NVOPF cathode is mainly attributed to the nano-scaled Na-ion diffusion path and enhanced electronic transport owing to the surface-assembling of crystalline nanocubes on carbon fibers [28].
To demonstrate the advantages of the flexible NVOPF cathode, model SIB was assembled by combining it with a flexible Na2Ti2O5 anode (Fig. 4a). NTO anode materials (including Na2Ti2O5 or Na2Ti3O7) show merits including high practical capacity (ca. 250 mAh/g), low potential (down to 0.2 V vs. Na+/Na) and natural abundance. Moreover, flexible NTO anodes can be constructed with nanostructured NTO on Ti foil by facile hydrothermal methods [29, 30]. Recently, superior rate performance and cycling stability could be attained with Na2Ti2O5 nanosheet-array anodes by replacing the ester-based electrolytes with ether-based electrolytes [31]. Accordingly, a Na2Ti2O5 nano-array anode is selected to pair with the flexible NVOPF cathode in the lab-made flexible SIBs.
The NTO anode is constructed with nanowires of ca. 100 nm in diameter uniformly grown on the Ti foil (Fig. S2a in Supporting information), which can be assigned to an orthorhombic phase (H2Ti2O5, PDF#47-0124) based on the powder XRD characterization (Fig. S2b in Supporting information) [29]. As a reference, the NTO anode was galvanostatic tested in an ether-based electrolyte (1 mol/L NaPF6 in diglyme). It delivers a high coulombic efficiency of ca. 80% in the initial cycle and a reversible capacity of ca. 220 mAh/g while cycled at 0.2 C between 2.5 V and 0.2 V (Fig. S2c in Supporting information). Moreover, it exhibits excellent rate performance (≈81% and 69% of the 1 C capacity retained at 10 and 20 C, respectively) and cycling stability (ca. 97% of the reversible capacity maintained after 2000 cycles at 5 C) (Figs. S2d-f in Supporting information). The NVOPF film cathode was also examined in the ether-based electrolyte, and Na-ion storage performances comparable to those in the ester-based electrolyte are observed (Fig. S3 in Supporting information). Therefore, flexible SIBs were assembled with the ether-based electrolyte for optimized energy-storage performances.
The electrochemical behaviors of the flexible SIBs were characterized between 1.5 V and 4.1 V. As for a typical battery, the mass ratio of the NTO to NVOPF is about 1:2.5 and the initial coulombic efficiency is ca. 62%. Due to the combination of high-potential NVOPF and low-potential NTO electrodes, the high-voltage plateau with a medium voltage of ca. 3.6 V (contributing nearly half of the reversible capacity) is observed at 0.2 C (Fig. 4b), outperforming most SIB systems in previous reports [21, 24, 32-35]. Moreover, our SIB can also exhibit excellent rate performance and good cycling stability. The SIB was tested at various rates (Fig. 4b), ca. 73% and 69% of the 1 C discharge capacity are retained at 10 C and 20 C, respectively (Fig. 4c). While cycled at 5 C, capacity retention of ca. 86% is obtained after 500 cycles. Meanwhile, the good flexibility of this NVOPF cathode was manifested by continuously bending for 500 times (Fig. S1c in Supporting information), and nearly no capacity loss is observed for the SIB assembled with bending-treated electrode (Fig. 4e). In addition, a model flexible SIB in soft package was assembled, and used to power a LED indicator at different bending angles (Fig. 4d inset). The good flexibility can be attributed to the strong adhesion of NVOPF nanocubes to the flexible carbon cloth.
The flexible SIB can also exhibit increased gravimetric energy and power densities due to its high voltage and the fully binder-free configuration. The Ragone plot for gravimetric energy density versus power density is presented in Fig. 4f, in which the data of previously reported SIB devices are also included for comparison [21, 30-33]. Generally, our flexible SIB delivers high gravimetric energy density which outperforms most SIB devices in previous works at similar power density. A maximum gravimetric energy density of ca. 220.2 Wh/kg can be achieved at 75.3 W/kg, which is larger than that of Sb@TiO2−x //Na3V2(PO4)3-C (151 Wh/kg at 21 W/kg) [32], VO2 NS//NVOPF Array (ca. 215 Wh/kg at 305 W/kg) [24], P2-Na0.66[Li0.22Ti0.78]O2//Na3V2(PO4)3/C (ca. 83 Wh/kg at 35 W/kg) [33], Sb//P2-Na2/3Ni1/3Mn2/3O2 (ca. 130 Wh/kg at 120 W/kg) [34] and so on [35]. Moreover, a gravimetric energy density as high as 107 Wh/kg can be reached at a high power density of 5674.7 W/kg (30 C), which is much larger than that of previously reported flexible SIB devices [24].
In summary, a novel flexible cathode with NVOPF nanocubes directly grown on carbon cloth was prepared by a facile solvothermal method. This cathode shows superior high-rate performance, excellent cycling stability and good mechanical performance. Flexible SIB assembled with this cathode and a flexible NTO anode delivers high working voltage and increased energy/power density, and it can power a LED indicator at bending angles from 0° to 180°. Our study presents a new and facile approach to fabricate flexible Na3(VO1-xPO4)2F1+2x positive electrodes, which may be extendable to other cathodes for future LIBs and SIBs.
Declaration of competing interest
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The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
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This work was supported by the National Natural Science Foundation of China (Nos. 51972257, 51672205 and 21673169) and the National Key R&D Program of China (No. 2016YFA0202602).
Appendix A. Supplementary data
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Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.cclet.2020.04.054.
References
Less
[1]
X.F. Wang, X.H. Lu, B. Liu, et al., Adv. Mater. 26 (2014) 4763-4782.
[2]
H.F. Li, Z.J. Tang, Z.X. Liu, C.Y. Zhi, Joule 3 (2019) 1-7.
[3]
R. Wang, Q.R. Wang, M.J. Yao, et al., Rare Met. 37 (2018) 536-542.
[4]
N. Yabuuchi, K. Kubota, M. Dahbi, S. Komaba, Chem. Rev. 114 (2014) 11636-11682.
[5]
X.D. Xiang, K. Zhang, J. Chen, Adv. Mater. 27 (2015) 5343-5364.
[6]
Y.Y. Huang, Y.H. Zheng, X. Li, et al., ACS Energy Lett. 3 (2018) 1604-1612.
[7]
H.G. Wang, W. Li, D.P. Liu, et al., Adv. Mater. 29 (2017) 1703012.
[8]
Y. Sun, X. Liang, H.F. Xiang, Y. Yu, Chin. Chem. Lett. 28 (2017) 2251-2253.
[9]
M.H. Wu, Y.P. Gao, Y. Hu, B. Zhao, H.J. Zhang, Chin. Chem. Lett. 31 (2020) 897-902.
[10]
T. Jin, Q.Q. Han, L.F. Jiao, Adv. Mater. (2019) 1806304.
[11]
K. Xu, Energy Environ. Mater. 2 (2019) 229-233.
[12]
D.L. Cheng, L.C. Yang, M. Zhu, Rare Met. 37 (2018) 167-180.
[13]
J. Jiang, Y.Y. Li, J.P. Liu, et al., Adv. Mater. 24 (2012) 5166-5180.
[14]
Y. You, A. Manthiram, Adv. Energy Mater. 8 (2017) 1701785.
[15]
M.H. Peng, D.T. Zhang, X.Y. Wang, et al., Chem. Commun. 55 (2019) 3979-3982.
[16]
Y.U. Park, D.H. Seo, H. Kim, et al., Adv. Funct. Mater. 24 (2014) 4603-4614.
[17]
N. Sharma, P. Serras, V. Palomares, et al., Chem. Mater. 26 (2014) 3391-3402.
[18]
M. Bianchini, F. Fauth, N. Brisset, et al., Chem. Mater. 27 (2015) 3009-3020.
[19]
J.M. Zhao, L.Q. Mu, Y.R. Qi, et al., Chem. Commun. 51 (2015) 7160-7163.
[20]
Y.R. Qi, L.Q. Mu, J.M. Zhao, et al., Angew. Chem. Int. Ed. 54 (2015) 9911-9916.
[21]
J.Z. Guo, P.F. Wang, X.L. Wu, et al., Adv. Mater. 29 (2017) 1701968.
[22]
C.B. Zhu, C. Wu, C.C. Chen, et al., Chem. Mater. 29 (2017) 5207-5215.
[23]
Z.F. Mao, R. Wang, B.B. He, Y.S. Gong, H.W. Wang, Small 15 (2019) 1902466.
[24]
D.L. Chao, C.H.M. Lai, P. Liang, et al., Adv. Energy Mater. 8 (2018) 1800058.
[25]
Y.S. Cai, X.X. Cao, Z.G. Luo, et al., Adv. Sci. 5 (2018) 1800680.
[26]
Z.B. Zhang, Z.H. Chen, Z.X. Mai, et al., Small 15 (2019) 1900356.
[27]
H.M. Yi, L. Lin, M.X. Ling, et al., ACS Energy Lett. 4 (2019) 1565-1571.
[28]
B.H. Deng, H.Y. Dong, T.Y. Lei, et al., Sci. China Mater. 63 (2020) 492-504.
[29]
L.F. Que, F.D. Yu, K.W. He, Z.B. Wang, D.M. Gu, Chem. Mater. 29 (2017) 9133-9141.
[30]
S.D. Fu, J.F. Ni, Y. Xu, Q. Zhang, L. Li, Nano Lett. 16 (2016) 4544-4551.
[31]
Q.Y. Gui, D.L. Ba, Z.S. Zhao, et al., Small Methods 3 (2019) 1800371.
[32]
N.N. Wang, Z.C. Bai, Y.T. Qian, J. Yang, Adv. Mater. 28 (2016) 4126-4133.
[33]
Y.S. Wang, X.Q. Yu, S.Y. Xu, et al., Nat. Commun. 4 (2013) 1-8.
[34]
L.Y. Liang, Y. Xu, C.L. Wang, et al., Energy Environ. Sci. 8 (2015) 2954-2962.
[35]
J. Ding, H. Zhou, H.L. Zhang, et al., Energy Environ. Sci. 10 (2017) 153-165.
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Year 2021 volume 32 Issue 2
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doi: 10.1016/j.cclet.2020.04.054
  • Receive Date：2020-04-07
  • Online Date：2026-01-04
  • Published：2021-02-15
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  • Received：2020-04-07
  • Revised：2020-04-25
  • Accepted：2020-04-28
Affiliations
    a School of Chemistry, Chemical Engineering and Life Science, Wuhan University of Technology, Wuhan 430070, China
    b State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China
    c Key Laboratory for Photonic and Electronic Bandgap Materials, Ministry of Education, School of Physics and Electronic Engineering, Harbin Normal University, Harbin 150025, China
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表12种不同金属材料的力学参数
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小菇科 Mycenaceae 2 12 5.74 丝盖伞属 Inocybe 5 2.39
多孔菌科 Polyporaceae 8 14 6.70 蜡蘑属 Laccaria 5 2.39
红菇科 Russulaceae 3 23 11.00 小皮伞属 Marasmius 6 2.87
小菇属 Mycena 11 5.26
光柄菇属 Pluteus 5 2.39
红菇属 Russula 17 8.13
栓菌属 Trametes 5 2.39
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