Using and recycling V2O5 as high performance anode materials for sustainable lithium ion battery

Using and recycling V2O5 as high performance anode materials for sustainable lithium ion battery

Journal of Power Sources 424 (2019) 158–164 Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/lo...

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Journal of Power Sources 424 (2019) 158–164

Contents lists available at ScienceDirect

Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour

Using and recycling V2O5 as high performance anode materials for sustainable lithium ion battery

T

Lingyu Dua, Huijuan Lina, Zhongyuan Maa, Qingqing Wanga, Desheng Lia, Yu Shena, Weina Zhanga, Kun Ruia, Jixin Zhua,∗, Wei Huanga,b a

Key Laboratory of Flexible Electronics (KLOFE) & Institute of Advanced Materials (IAM), Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing Tech University (NanjingTech), 30 South Puzhu Road, Nanjing, 211816, China b Shaanxi Institute of Flexible Electronics (SIFE), Northwestern Polytechnical University (NPU), 127 West Youyi Road, Xi'an, 710072, China

H I GH L IG H T S

G R A P H I C A L A B S T R A C T

Hydrated V O nanoribbons entangled • with GO nanosheets was fabricated. Hierarchical V O ·nH [email protected] exhibits • excellent lithium storage performance. energy-saving process was in• An troduced to recycle the spent LIBs. recycled product delivers 542 • The after 600 cycles at mAh g 2

5

2

5

2

−1

200 mA g−1.

A R T I C LE I N FO

A B S T R A C T

Keywords: V2O5 Hierarchical structure Lithium ion battery Sustainable Recycling process LiV3O8

A versatile synthetic approach is demonstrated to fabricate vanadium pentoxide hierarchical structures with three-dimensional electron carriers as anode materials for lithium-ion battery. Such unique structures are favorable for providing easy access of electrolyte to the electrode during lithiation-delithiation process and also shortening the pathway of the ion and electron transport, which guarantee excellent electrochemical performance. As a consequence, high specific capacities of 960 mAh g−1 at 200 mA g−1 and 738 mAh g−1 at 500 mA g−1 after 300 cycles are achieved without obvious decay. More remarkably, it is essential to rebuild a new recycling process owing to the massive waste produced by dealing with spent lithium-ion battery. Therefore, an energy-saving and environment-friendly process is introduced to recycle the used V2O5 batteries. Through a facile annealing process, LiV3O8 is obtained and reused as sustainable anode materials for the first time. The recycled product LiV3O8 delivers excellent electrochemical performance, e.g., a high capacity of 542 mAh g−1 at 200 mA g−1 and the coulombic efficiency of over 99% after 600 cycles. This finding not only promotes the development of vanadium oxides for lithium-ion battery, but also sheds light on searching potential protocol for metal ion battery recycling.

1. Introduction The development of portable electronics and electric vehicles



requiring high energy density and environment-friendly energy storage systems has motivated the studies in new replacement energies especially the lithium-ion batteries (LIBs) in recent years [1,2]. Among

Corresponding author. E-mail address: [email protected] (J. Zhu).

https://doi.org/10.1016/j.jpowsour.2019.03.103 Received 30 August 2018; Received in revised form 23 February 2019; Accepted 25 March 2019 0378-7753/ © 2019 Elsevier B.V. All rights reserved.

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also frozen by liquid nitrogen and dried by vacuum pump to sublime the ice.

various energy storage materials, the exploration of vanadium pentoxide (V2O5) compounds has attracted tremendous attention owing to its multiple redox states, low cost, and abundant resource [3–6]. As anode material in LIBs, V2O5 offers a high theoretical capacity up to 1472 mAh g−1, which is superior to most transition metal oxides (e.g. Fe2O3, MnO2, Co3O4) [7–10]. Therefore, considerable researches have been carried out to develop V2O5-based materials as anode electrodes [11,12]. However, the limited electronic and ionic conductivity give rise to poor stability and slow kinetics largely obstruct the way of their applications as electrode materials [13,14]. Significant attention has been paid to improve the specific capacity of V2O5 via carbon or other metal oxide doping [15–18]. In spite of these extensive efforts, finding a simple route to fabricate well-performed vanadium pentoxide composites as anode material is highly desirable to meet practical usage [11,19]. Because of environment-unfriendly and expensive/complex recycling processes, scale-up production of vanadium pentoxide as electrode materials nowadays remains challenging [20–23]. In detail, the traditional recycling technologies, such as hydrometallurgical process, involved acid dissolution and chemical precipitation usually complicates the recycling process by using vast acid and base solutions and generates additional waste [24,25]. Moreover, vanadium pentoxide materials have degradation problems after cycling due to the Li insertion and phase changes. The generated toxic products from disposal of used batteries can cause severe environment pollution. Finding a green approach to solve these problems directly not only reduces the high cost but also prevents environmental pollution. Therefore, a simple, inexpensive, sustainable plus energy-saving strategy is eagerly pursued to recycle the product from the spent V2O5-based battery to satisfy the requirement of cost-efficient mass production in industry practice. Here, we report a versatile approach for synthesizing hydrated vanadium pentoxide nanoribbons with single-crystalline, simultaneously entangling with graphene oxide nanosheets (noted as V2O5·[email protected]). Constructed by intertangled V2O5 nanoribbons and GO nanosheets, the V2O5·[email protected] composites show extraordinary electrochemical performance compared with bulk V2O5. Moreover, for the first time we design a facile annealing procedure to obtain LiV3O8 as the recycled product. The recycled LiV3O8 is reused as new anode material which exhibits highly reversible specific capacity and excellent rate capability with long cycle life. These strategies prove the potential to apply the recycling process to similar electrode materials, which is believed to be an unprecedented exploration to develop the low-cost and high-performance anode material to date.

2.2. Recycling of anode materials After 300 continuous discharge/charge cycles, the coin-type cells were unassembled by hydraulic crimping machine and collected together. In general, 6 recycled coin cells could be obtained from 10 spent coin cells. The generated anode materials were gathered by washing the Cu foils with DI water and ethanol in order to remove the residual foreign materials and organic solvents. Then Cu foils were sonicated in ethanol to separate anode materials from the foils. The black collections were maintained at 500 °C for 3 h under a heating rate of 10 °C min−1 in a muffle furnace. The electrode materials were recycled for the 2nd time under the same process as the first one. 2.3. Material characterization The crystal structures of the materials were investigated on X-ray diffractometer (XRD, Scintag PAD-V) at the 2θ range of 5–70 using Cu Kα radiation. The morphologies were characterized using a fieldemission scanning electron microscopy system (FE-SEM, JEOL, JSM7600F), and the nanostructure was characterized by using a transmission electron microscopy instrument (TEM, JEOL-2100F) operating at 200 kV. Thermal gravimetric analysis (TGA, Q500) was carried out at a heating rate of 10 °C min−1 from room temperature to 600 °C in air. Raman spectroscopy was conducted on a micro-Raman spectrometer (WITec Alpha 300 M+) with excitation-beam wavelength of 488 nm. 2.4. Electrochemical measurements Electrochemical properties of the as-prepared active materials and the recycled materials were measured using the CR2032-type coin cells in an Ar-filled glove-box, where both moisture and oxygen levels were under 0.5 ppm. The working electrodes were prepared by mixing the active materials, graphene and polyvinyldifluoride (PVDF) at a weight ratio of 7:2:1 in N-methyl-2-pyrrolidone (NMP) solvent. Then the resulting slurry were uniformly pasted onto the Cu foils with a mass loading of about 1 mg cm−2 and dried overnight under vacuum. Li metal foils were used as the counter and reference electrode. The electrolyte was made of 1 M LiPF6 in ethylene carbonate (EC)/dimethyl carbonate (DMC)/ethyl methyl carbonate (EMC) (1:1:1, V/V/V). The cells were galvanostatically charged and discharged at different current densities within the range of 0.01–3.0 V on a NEWARE multi-channel battery test system. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements were performed on an electrochemical workstation (CHI 660C).

2. Experimental section 2.1. Preparation of V2O5·[email protected]

3. Results and discussion

60 mg of graphene oxide (GO) powders were dispersed into 50 mL de-ionized (DI) water and ultrasonicated at room temperature for 4 h to form a stable GO dispersion. Certain quantity of V2O5 powders (the weight ratio of V2O5 and GO is 3:1, 3:2 and 3:4) were dissolved into 16 mL DI water, then 1.25 mL H2O2 (30 wt %) was added dropwise into the mixture and reacted for 2 h to produce a transparent red solution. The above synthesized solution was added into the as-prepared GO dispersion to form a homogeneous dispersion under magnetically stirring overnight in a water bath at 55 °C. The resulting mixture was transferred into a 100 mL Teflon-lined stainless steel autoclave and maintained at 180 °C for 24 h. After cooling down naturally, the hydrated V2O5 nanoribbons interpenetrating into the GO nanosheets (V2O5·[email protected]) were obtained by centrifuging the mixture, which were then washed with ethanol and DI water several times and then frozen by liquid nitrogen and dried by a cryodesiccation process to sublimate the ice. In order to illustrate the impact of GO on the electrochemical performance of V2O5·[email protected], layered V2O5 nanosheets with water molecules were also prepared with the absence of GO and

The fabrication process and energy storage characteristics of the V2O5·[email protected] are systematically illustrated in Fig. 1. First, bulk V2O5 was dissolved in a mixture of hydrogen peroxide and de-ionized water. Second, V2O5 was separated into ultra-thin ribbons and then dispersed along graphene oxide through a hydrothermal reaction. Finally, the obtained viscous solution is treated by vacuum freeze-drying process. Thus, vanadium pentoxide in hierarchical structure with 3D electron carriers are obtained, consisting of V2O5 nanoribbons entangled with GO nanosheets with pore structures. Such unique architectures can (1) provide extensive channels for fast transport of lithium ions and electrons, (2) enhance the electrical conductivity of the electrode, (3) accommodate volume change and increase the electrochemical reaction sites and, (4) avoid aggregation and fracture of V2O5. In addition, the water molecules intercalated in V2O5 interlayers could effectively improve the electrochemical performance of V2O5-based materials owing to the expanded interlayer space [26–29]. 159

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Fig. 1. Schematic illustration for the synthesis of the V2O5·[email protected] composites. Fig. 2. Characterization of as-synthesized V2O5•[email protected] with the weight ratio of V2O5 and GO is 3:2. (a–c) SEM images, (d) TEM image, (e–f) high-resolution TEM images, inset in (f) shows the SAED pattern and (g) corresponding elemental mapping of the obtained products, indicating the homogeneous dispersion of V, O, and C in the composites.

dispersive X-ray (EDX) and elemental mapping analysis. As shown in Fig. 2g, the V, O, and C atoms are homogeneously distributed in the materials which match well with the SEM images. Such interpenetrating architectures favor for the good compatibility with organic electrolytes and offer short lithium ion pathways as well as improve the electrical conductivity due to the introduction of graphene oxide nanosheets. The counterparts layered V2O5·1.6H2O nanosheets and V2O5·[email protected] materials (RV2O5:GO = 3:1 and RV2O5:GO = 3:4) were also investigated by SEM as shown in Fig. S1 and Fig. S2. It can be see that the ultra-thin V2O5 nanosheets are uniformly stacked in the layered V2O5·1.6H2O nanosheets (Fig. S1). The approximate similar thickness of the layered V2O5 nanosheets and V2O5 nanoribbons in the hierarchical structure indicates that the layered V2O5 are separated into smaller pieces during the hydrothermal process and interpenetrated with GO nanosheets in the produced V2O5·[email protected] composites. The weight ratio of V2O5 and GO also affects the hierarchical structure of the products. In V2O5·[email protected] composites with the weight ratio of V2O5 and GO is 3:1, lots of V2O5 nanoribbons stack together on few graphene oxide networks due to the low concentration of GO. When the weight ratio of V2O5 and GO reaches 3:4, the V2O5 nanoribbons are buried in the layered GO nanosheets (Fig. S2). Therefore, the appropriate weight ratio of V2O5 and GO is 3:2, which is exquisitely designed to form the unique hierarchical structure. The subsequent discussion is mainly based on the V2O5·[email protected] composites with RV2O5:GO = 3:2. To obtain deep insight into the structure of the V2O5·[email protected] and the layered V2O5·1.6H2O nanosheets, XRD patterns and Raman analysis were performed as well. As illustrated in Fig. 3a, the major peak of the

The morphology and structure of the as-prepared V2O5·[email protected] were observed by field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM). When the weight ratio of V2O5 and GO is 3:2 (Fig. 2a–c), the V2O5 nanoribbons with thickness less than 5 nm are interspersed among the GO nanosheets, forming a tightly interweaved structure as if they are mixed as a whole. The pore size ranging from several micrometers to tens of micrometers is derived from the removal of water in the procedure of the freezedrying process. The porous structure is proposed to facilitate the diffusion of lithium ions from electrolyte to the surface and interstices of V2O5 nanoribbons during the lithium ion insertion and extraction processes. As displayed in the TEM image in Fig. 2d, ultrathin V2O5 nanoribbons with 200–800 nm in width and tens of micrometers in length are closely integrated into the GO nanosheets, forming a connected 3D network and providing continuous pathway for lithium ions. The typical high-resolution TEM images (Fig. 2e–f) further disclose that these ribbons are single crystalline and the lattice fringes spacing is 2.0 Å, consistent with the selected area electron diffraction (SAED) pattern (inset of Fig. 2f). The lattice fringes spacing is much bigger than the (001) planes of the V2O5·1.6H2O nanosheets (1.2 Å). The expanded V2O5 intercalating space is in good accordance with the XRD pattern mentioned later which shifts to a lower angle, indicating there is more than 1.6 water in each molecule. The expanded layer structure caused by the water molecule can host more lithium ions and facilitate the ion diffusion. Furthermore, the GO nanosheets interpenetrated with the V2O5 are discontinuous (Fig. 2e), which are favorable for buffering the volume change and relieving aggregation of the V2O5. The compositions of as-prepared V2O5·[email protected] were demonstrated by energy 160

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Fig. 3. (a) XRD patterns, (b) Raman spectra of the V2O5·[email protected] composites and the layered V2O5·1.6H2O nanosheets.

V2O5·[email protected] situates at 2θ = 6.2° with a relatively low intensity. This peak along with the other smaller experimental peaks which locate at 12.4°, 18.6°, 24.9°, 30.8°, 37.8°, 44.4°, 50.4°, and 61.2° are assigned to the (001), (002), (003), (004), (005), (006), (007), (008), and (010) planes. Due to the presence of interlayer water, the corresponding peaks strongly shift to relatively lower peak positions as compared with the standard database pattern [27]. The graphene oxide transfer to the reduction state through the hydrothermal reaction and some distinguished peaks occur [30,31]. The marked peak at 25.7° belongs to the reduced graphene oxide matrix [32]. Particularly, the well-defined XRD pattern suggests that the counterpart without GO could be perfectly ascribed to the V2O5·1.6H2O crystal structure (JCPDS no. 40–1296). The Raman spectra shows five well-resolved peaks at 152, 294, 417, 531, 697, and 1002 cm−1 for both the V2O5·[email protected] architectures and the layered V2O5·1.6H2O nanosheets as observed in Fig. 3b, which are well-indexed to the perfect structural integrity of the V2O5 [33]. It is worth noting that the characteristic peaks at 1379 (D band) and 1611 cm−1 (G band) are respectively detected in the V2O5·[email protected] composites, which further demonstrates the presence of GO in the as-prepared material [34,35]. Thermogravimetric analysis (TGA) was conducted to reveal the component of the composites (Fig. S3). As the TGA profiles depict, the first mass loss of the V2O5·[email protected] composites and the layered V2O5·1.6H2O nanosheets both occur at below 300 °C corresponding to the desorption of absorbed water and bound water molecules (about 14 wt%). Another mass loss of V2O5·[email protected] composites at 300–400 °C is generally attributed to the burning of GO (17.6 wt%) [36]. The different weight ratio between V2O5·[email protected] and the previous precursor is resulted from the oxidization of GO by the high valence state of V2O5 and some unreacted materials [37,38]. The more inclined slope of V2O5·[email protected] verifies that the number of water in each V2O5·[email protected] molecular is bigger than 1.6 as well, which is in accord with the former XRD and HRTEM results. The electrochemical behaviors of the V2O5·[email protected] anodes were systematically carried out by galvanostatic discharge/charge and cyclic voltammetry (CV) measurements. To the best of our knowledge, this is the unprecedented achievement showing such excellent electrochemical performance of V2O5-based materials (Table S1). As displayed in Fig. 4, a remarkable initial discharge and charge capacity of 1170 mAh g−1 and 692 mAh g−1 are achieved at 200 mA g−1, respectively. The capacity gradually increases with cycling owing to the activation process during the initial 20 cycles and reaches 960 mAh g−1 after 300 cycles. A high capacity of 738 mAh g−1 at 500 mA g−1 is also achieved, exhibiting the superior cycling stability of V2O5·[email protected] The rate capability of V2O5·[email protected] is excellent as well. As seen in Fig. 4a, remarkable capacities of 706, 524, 419, 302, 224, 158, and 120 mAh g−1 can be retained for recycled LiV3O8 at 200, 500, 1000, 2000, 3000, 5000, and 7000 mA g−1, respectively. Moreover, the reversible discharge capacity can get back to 788 mAh g−1, even after undergoing a

Fig. 4. Electrochemical performance of the V2O5·[email protected] (RV2O5:GO = 3:2) with the potential range of 0.01–3.0 V vs Li+/Li. (a) the specific capacities of the composites at various current densities, (b) the cycling performance at a current density of 200 mA g−1 and 500 mA g−1.

large current density of 10000 mA g−1. It is noteworthy that both the specific capacities increased in the initial 20 cycles, which are attributed to the activation process of the electrode materials, the incomplete conversion reaction and the reversible formation of the polymeric Solid Electrolyte Interphase (SEI) films by electrolyte degradation [10,39]. The tendency of increasing occurred in the rate performance is not as obvious as in the long life cycles because of the change to large current. The SEM and TEM images after 300 cycles clearly show the formation of SEI layers (Fig. S4). The SEI layers not only improve the lithium storage performance with increasing capacity but also accommodate volume change during cycling [40]. For comparison, V2O5·[email protected] composites with different weight ratio and the layered V2O5·1.6H2O nanosheets were also tested under same conditions. When the weight ratio of V2O5 and GO is 3:1, only 196 mAh g−1 is achieved at 18th cycle at a current density of 500 mA g−1. Then the specific capacity increases all the way and reaches 396 mAh g−1 after 250 cycles. The exaggerated capacity increase shows the instability of the material. When V2O5:GO reaches 3:4, the electrode delivers 210 mAh g−1 at a current density of 500 mA g−1 which is relatively stable (Fig. S5). V2O5·[email protected] (RV2O5:GO = 3:2) composites outperform the counterparts for lithium storage capacity, which is in 161

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the LiV3O8 nanorods have diameters of about 170–300 nm, thickness of 60–100 nm and length of up to several micrometers. The corresponding EDX in Fig. 5c clearly shows the existence of V and O atom in the recycled products, and a hint of P element is attributed to the impurity from the electrolyte which adhered to the recycled material. XRD was performed to uncover the crystallinity and composition of the obtained material (Fig. S10a). A series of characteristic peaks at 13.8°, 23.6°, 25.9°, 28.3°, 29.2°, 30.0°, 39.5°, 40.9°, 50.8°, 62.0°, and 67.3° are observed, which can be indexed to the LiV3O8 (JCPDS no. 13–0248) [50]. Furthermore, trace of components stemed from the electrolyte and residues of SEI layers are detected [51]. The Raman spectrum (Fig. S10b) is relatively consistent with the LiV3O8, indicating the negligibility of the impurities [52,53]. It is worth noting that the recycled sample exhibits considerably high reversible capacities and good rate capability. As shown in Fig. 5d, superior capacities of 442, 408, 307, 257, 214, 165, and 127 mAh g−1 can be achieved for recycled LiV3O8 at 200, 500, 1000, 2000, 3000, 5000, and 7000 mA g−1, respectively. Moreover, after undergoing a serious high rate process, the specific capacity returns to 437 mAh g−1 with no sign of capacity decay, demonstrating excellent reversibility of the recycled LiV3O8. As displayed in Fig. 5e, the recycled LiV3O8 delivers a high initial discharge and charge capacity of 716 mAh g−1 and 449 mAh g−1, respectively. The specific capacity slowly reduces to 435 mAh g−1 during the first 13 cycles, and then exhibits an upward trend due to the activation process. After 600 cycles, the reversible capacity keeps at 542 mAh g−1 and the coulombic efficiency maintains over 99%. In addition, a remarkable specific capacity of 483 mAh g−1 can be retained at a current density of 500 mA g−1 without distinct capacity fading (Fig. S11). The capacity increases are mainly attributed to the activation process during which polymeric gel-like films by electrolyte degradation are progressive generated. The films coated around the active materials can promote the lithium storage performance [10,54,55]. The charge-discharge curves of the recycled product from the 1st cycle to the 400th cycle at a current density of 500 mA g−1 is shown in Fig. S12 to explain the capacity increase. The tendency of specific capacity is gradually increased within 100 cycles, then the capacity keeps stable and attains 483 mAh g−1 after 400 cycles. More importantly, the 2nd recycled anode material delivers desirable electrochemical performance as well. Specifically, a reversible capacity as high as 381 mAh g−1 can be retained at 200 mAh g−1 after 120 cycles without capacity fading (Fig. S13). CV studies were also conducted to illustrate the electrochemical reactions of the recycled composites as displayed in Fig. S14a, the four reduction peaks located at 2.71, 2.32, 1.90, and 0.38 V are attributed to phase transitions of Li1+xV3O8, respectively. The oxidation peaks located at 0.26, 1.15, and 2.91 V correspond to the backward transition of phases [56]. After the first cycle, the overlapping CV profiles of the subsequent cycles suggest the good reversibility and stability of the electrode material. The EIS was conducted to investigate the excellent electrochemical properties of the LiV3O8 composites after three discharge/charge cycles (Fig. S14b). The small charge-transfer resistance related to the semicircle at the high-medium frequency region elucidates a favored charge-transfer reaction for Li+. In general, the recycled LiV3O8 composite after a simple annealing process not only possesses unique structure but also exhibits excellent electrochemical performance.

consistent with the structure results. As displayed in Fig. S6, the V2O5·1.6H2O nanosheets apparently doesn't possess excellent rate capability and reversible capacity owing to its poor electric conductivity. The specific capacity only attains 300 mA h g−1 at a current rate of 200 mA g−1 after 100 cycles which is immensely lower than the V2O5·[email protected] These results indicate that the interpenetrating structure and appropriate V2O5 weight percentage in the composites are favorable for exceptional lithium storage capacity. The CV curves of the V2O5·[email protected] nanocomposites and the layered V2O5·1.6H2O nanosheets between potentials of 0.01 and 3.0 V (vs. Li/Li+) at a scan rate of 0.2 mV s−1 were revealed in Figs. S7 and S8, respectively. The first discharge cycle of V2O5·[email protected] nanocomposites is displayed in Fig. S7. Three reduction peaks at approximate 2.39, 1.63, and 0.70 V are in good agreement to Li+ intercalation process during which the lithium ions intercalate into V2O5 layers thereby forming different LixV2O5 phases. Three oxidization peaks located at about 0.16, 0.23, and 1.91 V can be associated with the Li+ deintercalation from the LixV2O5 phases [10,16,41]. Notably, the curves corresponding to the following second and third cycles overlap significantly, indicating excellent reversibility of the electrochemical reactions. It can be also clearly seen in Fig. S8, the first cycle of the layered V2O5·1.6H2O nanosheets CV curve has multiple redox peaks which is in line with the previous results [21,42]. The electrochemical impedance spectroscopy (EIS) analysis for the V2O5·[email protected] composites and the layered V2O5·1.6H2O nanosheets were shown in Fig. S9 to investigate electrode interfacial kinetics. The Nyquist plots consisted of a semicircle and an inclined line corresponds to electrochemical reaction impedance and ion diffusion impedance, respectively. The Nyquist plot is analyzed and fitted using an equivalent circuit model as shown in the inset of Fig. S9. The charge transfer resistance of V2O5·[email protected] is 188.1 Ω, fairly smaller than that of layered V2O5·1.6H2O nanosheets (248.5 Ω). The smaller resistance demonstrates that the mesoporous structure and the GO matrix in the V2O5·[email protected] composites help to accelerate electron transfer and prevent the aggregation of V2O5, thus decrease the resistance. The fitted results of electrode kinetics are well corroborated by the electrochemical performance described above. All of these excellent electrochemical performances of the V2O5·[email protected] composites are benefited from the good electronic conductivity of graphene oxide and the entangled V2O5 nanoribbon into GO nanosheets. The hierarchical structures are beneficial for accelerating electron transfer and lithium ion diffusion, shortening lithium ion diffusion pathway, as well as easily accommodating with large volume change. Lots of attention has been focused on the V2O5 and V2O5-based materials as electrode materials to pursue stable electrochemical performance or long-life cycles [43–46]. However, sustainable environmental issues are becoming the dominating factors that largely hamper their practical applications in high-energy lithium ion batteries owing to its toxic nature [17,47,48]. To the best of our knowledge, no articles were published yet exclusively against V2O5 for its recycling procedure. Herein, we notably introduced a simple and efficient approach to directly regenerate high-performance V2O5-based materials anodes. Specifically, LixV2O5 was formed during the charge-discharge process because the lithium ions inserted into the V2O5 crystal [49]. LiV3O8 can be obtained through a facile annealing process applied to the anode materials and be reused as new active electrode materials in LIBs. The calcination process is easy to achieve in practice due to the inexpensive cost and simple operation. The disappearance of GO and conductive additives through the annealing process makes the calcination possible as well. In conclusion, high phase purity of LiV3O8 is obtained through the annealing process and also exhibits high specific capacity, good cycling stability, and high rate capability as anode material. The microstructure of the recycled product LiV3O8 was investigated by SEM, as seen in Fig. 5a, the belt-like nanorods possessing almost rectangular cross section and nearly round tips are dispersed at liberty and supported by each other. A close observation (Fig. 5b) reveals that

4. Conclusion In summary, we develop a facile hydrothermal and freezing-drying method to fabricate V2O5·[email protected] composites bearing ultra-thin V2O5 nanoribbons entangled with GO nanosheets forming a hierarchical structure. When applied for LIBs as anode, it exhibits a high reversible capacity of 960 mAh g−1 at 200 mA g−1 after 300 cycles. The extraordinary high capacity and good cycling stability are contributed 162

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Fig. 5. (a, b) SEM images of the recycled product LiV3O8, (c) the EDX pictures vanadium, oxygen, and phosphorus, (d) the rate performance, and (e) the cycling performance at a current density 500 mA g−1 of the recycled product LiV3O8 composites.

from the interpenetrating network of V2O5 and GO, as well as the porous structure. Remarkably, we introduce an unprecedented recycling approach to reuse the V2O5-based materials. The recycled composites obtained by a simple annealing process also deliver a very high reversible capacity of 542 mAh g−1 at 200 mA g−1 even after 600 cycles. Our strategies of synthesizing anode composites and recycling procedure highlight the possibility to design other desired electrode materials for high-rate lithium ion batteries.

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