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Nanoporous Red Phosphorus on Reduced Graphene Oxide as Superior Anode for Sodium-Ion Batteries Shuai Liu,† Hui Xu,† Xiufang Bian,*,† Jinkui Feng,*,† Jie Liu,‡ Yinghui Yang,† Chao Yuan,† Yongling An,† Runhua Fan,†,§ and Lijie Ci† Downloaded via DURHAM UNIV on June 21, 2018 at 23:16:36 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

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Key Laboratory for Liquid−Solid Structural Evolution and Processing of Materials (Ministry of Education), School of Materials Science and Engineering, Shandong University, Jinan 250061, China ‡ Institute of Functional Textiles and Advanced Materials; Growing Base for State Key Laboratory of New Fiber Materials and Modern Textile, Qingdao University, Qingdao 266071, China § College of Ocean Science and Engineering, Shanghai Maritime University, Shanghai 201306, China S Supporting Information *

ABSTRACT: As a potential alternative to lithium-ion batteries, sodiumion batteries (SIBs) have attracted more and more attention due to the lower cost of sodium than lithium. Red phosphorus (RP) is an especially promising anode for SIBs with the highest theoretical capacity of 2596 mAh g−1, which faces the challenges of large volume change and low conductivity. Herein, we develop a nanoporous RP on reduced graphene oxide (NPRP@RGO) as a high-performance anode for SIBs through boiling. Its nanoporous structure could accommodate the volume change and minimize the ion diffusion length, and the high electronic conductive network built on RGO sheets facilitates the fast electron and ion transportation. As a result, NPRP@RGO exhibits a superhigh capacity (1249.7 mAh gcomposite−1 after 150 cycles at 173.26 mA gcomposite−1), superior rate capability (656.9 mAh gcomposite−1 at 3465.28 mA gcomposite−1), and ultralong cycle life at 5.12 A gRP−1 for RP-based electrodes (775.3 mAh gRP−1 after 1500 cycles). The successful synthesis of NPRP@RGO marks a significant enhanced performance for RPbased SIB anodes, providing a scalable synthesis route for nanoporous structures. KEYWORDS: nanoporous, red phosphorus, reduced graphene oxide, anode, sodium-ion battery ions.17,18 Among the promising SIB anode materials, such as alloy-based materials,9,19−21 metal oxides,22,23 and nongraphitized carbon,24,25 red phosphorus (RP), with a high theoretical specific capacity (about 2600 mAh g−1), is a great potential anode for SIBs.8 However, the RP anode for SIBs shows an exceptional capacity fading due to its low conductivity (about 10−14 S cm−1) and large volume expansion (about 300%) during repeated charge−discharge processes, which may cause large polarizations, severe pulverization of active material, poor electrical contact between RP and the conductive network, and unstable solid electrolyte interphase (SEI) films.3,26−28 To conquer these impediments, RP-C composites, such as chemically bonded RP/graphene hybrids prepared via ball milling, RP-carbon nanotubes with chemical bonding and a

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ithium-ion batteries (LIBs) with high energy density have been the key power supply for portable electronic devices and widely applied in electric vehicles.1−3 But the large-scale application of LIBs in smart grids is limited by the high cost and insufficient lithium resources.4,5 Sodium-ion batteries (SIBs) are the most promising alternatives for LIBs in large-scale energy storage applications, due to the lower cost and more abundant sodium resources.6,7 Moreover, the chemical and physical properties of sodium are similar to those of lithium.8−10 However, it is impossible to simply adopt the current strategies of LIBs to design high-performance SIBs due to the larger radius of the sodium ion (0.097 nm) than that of the lithium ion (0.068 nm).9,11,12 Reported cathode materials for SIBs have exhibited a capability comparable to their lithium-ion counterparts, and the main challenge for competitive SIBs is to design high-performance anodes.13−16 Graphite as the most widespread anode for LIBs shows a very low sodium storage capacity (30−35 mAh g−1) due to the crystalline mismatch between the graphite lattice and sodium © XXXX American Chemical Society

Received: May 30, 2018 Accepted: June 19, 2018

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DOI: 10.1021/acsnano.8b04075 ACS Nano XXXX, XXX, XXX−XXX

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Figure 1. Preparation schematics of NPRP@RGO. (i) Prepared RP mixing with GO uniformly in the solution. (ii) RP@GO is reduced to RP@RGO by N2H4·H2O. (iii) RP@RGO is immersed in residual solution after centrifugation. (iv) Heating in a vacuum drying chamber at 200 °C, the RP is assembled around gas bubbles. (v) With the bubbles growing, more and more disordered RP distributes on the surface of the gas bubbles. (vi) NPRP@RGO is produced after gas bubbles detach.

mA gRP−1 after 150 cycles, excellent rate performance (971.7 mAh gRP−1 at 5.12 A gRP−1), and good cycling performance (775.3 mAh gRP−1 after 1500 cycles at 5.12 A gRP−1) for RPbased SIB anodes. The advanced electrochemical energy storage performance of NPRP@RGO can be attributed to the nanoporous structures and the high electronic conductive network built on RGO sheets, which not only facilitate ion and electron migration but also can buffer the volume expansion efficiently.

cross-linked polymer binder,3,29 RP-multiwall carbon nanotube composites,30 RP-single-walled carbon nanotube composites,31 P@CMK-3 synthesized via a vaporization−condensation process,10 and C@P/GA prepared by vapor redistribution,32 have greatly improved the electrochemical performance of RP anodes for SIBs. However, the rate capability and cycle life of RP-based anodes for SIBs is rather poor compared with those of LIBs. The electrochemical performance of RP/carbon-based materials as anodes for SIBs is impeded by the following factors: (1) limited carbon coverage on RP and poor electrical contact due to the simple mixing of carbon and RP; (2) large volumetric change of RP during repeated sodiation− desodiation processes; (3) limited carbon loading level due to the uncontrollability of carbon layer thickness on the RP surface.32 Nanoporous structures have been considered as an ideal structural model that not only can accommodate the volume changes but also benefit efficient ion diffusion via the nanoporous channels, which can avoid pulverization during repeated sodiation−desodiation processes.9,33−36 Moreover, graphene can improve the conductivity of nanomaterials greatly and avoid nanoparticle aggregation effectively, improving the electrochemical performance of electrodes based on it.37 Hence, the nanoporous red phosphorus on reduced graphene oxide (NPRP@RGO) electrode design is considered to be an effective way to solve the aforementioned problems. However, synthesis of the red phosphorus nanomaterial via a wet-chemical method is always a great challenge, not to mention the nanoporous red phosphorus (NPRP). Zhang et al.38 reported a sublimation-induced synthesis of phosphorusbased composite nanosheets by a chemistry-based solvothermal reaction. Chang et al.39 reported the large-scale synthesis of red phosphorus nanoparticles (RPNPs) by reacting PI3 with ethylene glycol. As anodes for LIBs, the RPNP electrodes exhibit a high specific capacity, long cycling life, and excellent rate capability. Moreover, Zhou et al.40 developed a wet solvothermal method to fabricate hollow P nanospheres with porous shells via a gas-bubble-directed formation mechanism, which needs gas bubble generation during the chemical reaction. Developing an easier method to prepare the NPRP is strongly needed. Herein, we prepare NPRP@RGO via a typical redox reaction and boiling process. NPRP@RGO shows a high specific capacity (based on RP) of 1848.67 mAh gRP−1 at 256.3

RESULTS AND DISCUSSION Preparation Schematics of NPRP@RGO. Phosphorus triiodide (PI3) can be reduced by ethylene glycol with cetyltrimethylammonium bromide (CTAB) to produce red phosphorus.39 In this reaction, the reducing agent is ethylene glycol, and the phosphorus source is PI3. The surfactant we used is CTAB, which can inhibit the growth of phosphorus in the reaction solution. Beforehand, a solution of PI3 in iodobenzene (1.6 M), a solution of graphene oxide (GO) (10 mg/mL), and CTAB (0.018 M) in ethylene glycol (as shown in Figure S1 0−10 s) should be prepared. As shown in Figure S1 (16 s), the PI3 iodobenzene solution is injected into the GO and CTAB ethylene glycol solution with intense magnetic stirring. The color of the solution turns brown after 9 s (Figure S1 (25 s)), demonstrating the formation of RP. After the PI3 solution injection, the color of the solution turns from brown to black gradually (Figure S1, 40−180 s), indicating the prepared RP mixing with GO uniformly in the solution (as shown in Figure 1 (i)). Then the RP@GO is reduced to RP@RGO by N2H4·H2O (Figure 1 (ii)). After centrifugation, the RP@RGO is immersed in residual solution (Figure 1 (iii)). As indicated in Figure 1 (iv), then it is heated in the vacuum drying chamber at 200 °C, the solution mainly composed by ethylene glycol and iodobenzene is boiled, and the RP is assembled around gas bubbles. As the bubbles grow, more and more disordered RP distributes on the surface of the gas bubbles (Figure 1 (v)). Finally, as shown in Figure 1 (vi), with a simple and scalable boiling method, we successfully produce NPRP@ RGO after gas bubbles detach. In order to analyze the formation mechanism of the NPRP@RGO, as shown in Figure S2a, a TEM image of the prepared RP@RGO after centrifugation shows that the RP is immersed in residual B

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NPRP@RGO and corresponding EDS element mapping images of P (Figure 2k) and C (Figure 2l) elements further demonstrate the NPRP particles are distributed on RGO sheets. The SEAD pattern of NPRP@RGO (Figure S2i) includes two sharp polycrystalline rings decorated with multiple bright hexagons, demonstrating an overlay of crystalline RGO nanosheets in the film.41−43 As shown in Figure 3a, the X-ray diffraction (XRD) pattern of NPRP shows three broadened diffraction peaks at 12−20°, 25−40°, and 45−70° corresponding to that of commercial RP.8 NPRP@RGO exhibits four broadened characteristic peaks at 12.7−19°, 20−27°, 28−42°, and 46−70°, consistent with the characteristic peaks of NPRP and RGO. Figure 3b shows Raman spectra of commercial RP, NPRP, RGO, and NPRP@RGO composites. The Raman spectrum obtained for NPRP is similar to that of commercial RP with the presence of characteristic peaks between 300 and 550 cm−1. The RGO pattern indicates the characteristic G band (1592 cm−1) and D band (1322 cm−1).44 The characteristic peaks of NPRP@RGO composites combine that of NPRP and RGO clearly. The chemical bonding between RP and RGO sheets in NPRP@ RGO composites were investigated with X-ray photoelectron spectroscopy (XPS), as shown in Figure 3c,d. The P 2p spectrum in Figure 3c can be fitted to four Gaussian− Lorentzian peaks at 134.1, 133.2, 129.9, and 129.2 eV, corresponding to P−O, P−C, 2p3/2 P−P, and 2p1/2 P−P bonds, respectively.11,39,45 It is worthy to note that the P−C chemical bonding forms between NPRP and RGO, and it can facilitate the intimate and robust conductive contact between NPRP and RGO sheets. The C 1s spectrum in Figure 3d can be fitted to five peaks: the O−CO bond at 289 eV, the C O bond at 286.6 eV, the C−O bond at 285.3 eV, the CC/ C−C bond at 284.7 eV, and the sp2 C−P bond at 283.3 eV according to previous literature.11,46−48 It further proves the formation of C−P chemical bonding between RGO and NPRP. The Brunauer−Emmett−Teller (BET) measurements of NPRP@RGO (Figure S5) were conducted to obtain the surface area information, and the NPRP@RGO composites have a large surface area of 1192.5 m2 g−1, while the pore size distribution curves (Figure 3e) indicate that there are many micropores and mesopores in the NPRP@RGO composites. Figure 3f exhibits the thermogravimetric analysis (TGA) of the RGO and NPRP@RGO in a nitrogen atmosphere. The asprepared NPRP@RGO has an obvious weight loss at around 400 °C due to the vaporization of NPRP, and the content of NPRP is 67.6 wt %. Moreover, the RP content in NPRP@ RGO can be increased by decreasing the graphene oxide content in ethylene glycol solution under the same conditions (as shown in Figure S6). The successful synthesis of NPRP@ RGO composites may offer robust electrode integrity, fast ion and electron transport, and excellent electrochemical energy storage properties as anodes for SIBs. Sodium Storage Performance Charaterization. Figure 4a shows the cyclic voltammogram (CV) of the initial four cycles for the NPRP@RGO at a scan rate of 0.1 mV s−1 between 0.01 and 2.0 V (vs Na+/Na). There are two peaks in the first cathodic scan. The peak at around 0.86 V due to formation of a SEI film on the electrode surface3,49 disappears in the subsequent scans, indicating that the SEI formation occurs mainly during the first cycle. Moreover, the sharp cathodic peak between 0.45 and 0.01 V appears due to sodiumion insertion into NPRP@RGO to form NaxP compounds.8 The peak at around 0.71 V during the first anodic scan is

solution on RGO, corresponding to Figure 1(iii). After heating in a vacuum drying chamber at 200 °C for 10 min, the amount of residual solution decreases because of the boiling and a small number of nanopores form, as shown in TEM images of the RP@RGO (Figure S2b−d). With the boiling time increasing, more and more residual solution is evaporated, forming more and more nanopores. As indicated in TEM images (Figure S2e,f) of the RP@RGO after heating for 1 h, more nanopores form in the RP on RGO compared with that heated for 10 min. Corresponding to Figure 1 (vi), the residual solution is evaporated completely and the NPRP forms on the RGO (Figure 2f−i and Figure S2g,h) after heating in a vacuum

Figure 2. (a−c) SEM images of NPRP@RGO, EDS mapping of elemental P (d) and C (e) corresponding to (b); (f−i) TEM images of NPRP@RGO; (j) STEM of NPRP@RGO and corresponding EDS element mapping images of P (k) and C (l) elements.

drying chamber at 200 °C for 6 h. In order to further prove the NPRP@RGO formation mechanism (as shown in Figure 1), the obtained RP@RGO was collected by centrifugation after the reaction. Then it was dispersed in ethanol and stirred to remove the residual ethylene glycol and byproducts. Then the RP@RGO was collected by centrifugation without boiling. As shown in Figure S3, there is no nanoporous structure in the RP particles, indicating that the nanoporous structure is induced by boiling. Morphology and Structure Characterization of NPRP@RGO. Figure 2a−c show the SEM images of the asprepared NPRP@RGO. The RGO we used is reduced from GO (as shown in Figure S4). The SEM images (Figure 2a−c) and EDS element mapping (Figure 2d,e) indicate that NPRP particles are distributed on RGO sheets uniformly and densely. Less than 0.1 wt % iodine was found in NPRP@RGO by energy-dispersive X-ray spectroscopy (EDS) analysis. Interestingly, as shown in the TEM images of NPRP@RGO (Figure 2f−i and Figure S2g,h), the NPRP (with sizes mainly located at 20−100 nm) is distributed on RGO sheets. The scanning transmission electron microscopy (STEM) (Figure 2j) of C

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Figure 3. (a) XRD patterns of commercial RP, NPRP, RGO, and NPRP@RGO. (b) Raman spectra of commercial RP, NPRP, RGO, and NPRP@RGO. High-resolution XPS spectra of P 2p (c) and C 1s (d) for NPRP@RGO. (e) Pore size distribution curves of NPRP@RGO obtained by HK and BJH methods. (f) TGA of the RGO and NPRP@RGO in a nitrogen atmosphere.

1.28, 2.56, and 5.12 A gRP−1 for NPRP@RGO, respectively. After 50 cycles of rate testing, when the rate is restored to 2.56 and 0.512 A gRP−1, the specific capacities of NPRP@RGO return to 1350.2 and 1869.2 mAh gRP−1, respectively, demonstrating that the sodiation−desodiation processes of NPRP@RGO anodes are reversible even at a high current density. To further study the superior capacity output and cycling stability of NPRP@RGO as anode for SIBs, it was also evaluated at 5.12 A gRP−1 (3465.28 mA gcomposite−1) (Figure 4e). The capacity−voltage curves (Figure S9) of both desodiation and sodiation are well reproducible, implying its outstanding electrochemical reversibility during high-rate charge−discharge processes. The NPRP@RGO anodes retain a high reversible capacity of 775.3 mAh gRP−1 (524.1 mAh gcomposite−1) after 1500 cycles at 5.12 A gRP−1 (3465.28 mA gcomposite−1, as shown in Figure S10). Figure S11 shows the competitive electrochemical performance of NPRP@RGO compared with that of reported SIB anodes in the literature (only partial reported results over 200 cycles are listed). It is worth mentioning that the NPRP@RGO as anode for SIBs delivers an excellent cycling performance among these results and RP-based electrodes at a high current density of 5.12 A g RP −1 . The NPRP@RGO anodes (NPRP@RGO:Super P:carboxymethyl cellulose = 8:1:1 (in weight)) for SIBs also exhibit a high capacity of 505.6 mAh gcomposite−1 at 3465.28 mA gcomposite−1 after 500 cycles (Figure S12). However, as shown in Figure S13, the RP@RGO (Figure S3) without the boiling process as anode for SIBs exhibits a poor cyclic performance. It maintains only 87.8 mAh gcomposite−1 at 3465.28 mA gcomposite−1 after 150 cycles. The excellent electrochemical performance of NPRP@RGO anodes for SIBs is attributed to the structure design, as shown in Figure 5, which illustrates the sodiation schematics of NPRP@RGO as anodes for SIBs. During the sodiation process (P + 3Na+ + 3e− → Na3P), the NPRP is confined on RGO sheets by P−C chemical bonding, increasing the interface contact between the NPRP and the conductive network. The nanoporous structure of NPRP could accommodate RP volume expansion during the sodiation process, increase the

related to the desodiation process.11,50 In the following cycles, the area of the oxidation peak is almost equal to that of the reduction peak without obvious peak position shifting, implying excellent reversibility of NPRP@RGO as SIB anode. Figure 4b displays galvanostatic charge/discharge curves of the NPRP@RGO electrode at a current density of 256.3 mA gRP−1 (173.26 mA gcomposite−1) with a voltage range of 0.01−2 V. The discharge profile consists of three regions located at 0.9−0.38, 0.38−0.24, and 0.24 V vs Na+/Na (two sloping regions and one plateau, respectively), while in the charge process three slopes are located at around 0.38, 0.53, and 1.8 V and one plateau at around 0.7 V, consistent with the CV results in Figure 4a. Additionally, the capacity−voltage curves of both desodiation and sodiation are well reproducible from 1 to 150 cycles, implying the stable nanoporous structure of the NPRP@RGO and its outstanding electrochemical reversibility during sodiation−desodiation processes. It shows the first charge specific capacity of 2109.5 mAh gRP−1 with an initial Columbic efficiency of 78.5%. Figure 4c exhibits the cyclic performance of NPRP@RGO and commercial RP electrodes at 256.3 mA gRP−1 (173.26 mA gcomposite−1) within the voltage range of 0.01−2 V. The NPRP@RGO anodes reveal an excellent cycling stability, maintaining a reversible discharge capacity of 1848.67 mAh gRP−1 (1249.7 mAh gcomposite−1, as shown in Figure S7) after 150 cycles. Additionally, as shown in Figure S8, the RGO we used as anode for SIBs, exhibiting a capacity of 58.9 mAh g−1 at 173.26 mA/g. Hence, the capacity of RGO in the NPRP@RGO can be neglected. The Coulombic efficiency of NPRP@RGO approaches 99.9% after capacity loss of the initial cycles, implying its excellent reversibility, while the commercial RP anodes exhibit a poor cyclic performance (as shown in Figure 4c, RP). In addition to the high capacity and cyclic performance of NPRP@RGO electrodes, they also show a high rate capability, as shown in Figure 4d. The rate performance of NPRP@RGO anodes is investigated at various current densities from 0.256 to 5.12 A gRP−1. With current density increasing, specific capacities of 2080.2, 1876.5, 1682, 1398.7, and 971.7 mAh gRP−1 are obtained at 0.256, 0.512, D

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Figure 4. (a) CV of the initial four cycles for the NPRP@RGO at a scan rate of 0.1 mV s−1 between 0.01 and 2.0 V (vs Na+/Na). (b) Galvanostatic charge/discharge curves of the NPRP@RGO electrode at 256.3 mA/gRP (173.26 mA/gcomposite) with a voltage range of 0.01−2 V. (c) Cyclic performance of NPRP@RGO and commercial RP electrodes at 256.3 mA/gRP within the voltage range of 0.01−2 V. (d) Rate capability of NPRP@RGO electrodes from 0.256 to 5.12 A/gRP. (e) Long-term cycling performance of NPRP@RGO electrodes at 5.12 A/ gRP (3465.28 mA/gcomposite) between 0.01 and 2.0 V. Current density and specific capacity were calculated based on the mass of NPRP.

a single depressed semicircle in the high−medium frequency region (corresponding to composite impedance of sodium-ion transport through the film surface and charge transfer at the electrolyte/electrode interface) and an inclined line (related to the Na-ion diffusion inside electrodes) at low frequency.9,21,33 The charge transfer resistance of NPRP@RGO electrodes after 50 cycles is lower than those of commercial RP electrodes, indicating a rapid and efficient electron transport network of the NPRP@RGO electrodes. Figure S15 presents TEM images of NPRP@RGO anodes after 1500 cycles at 5.12 A gRP−1. The NPRP does not pulverize completely, implying the marvelous structural stability of NPRP@RGO electrodes.

Figure 5. Sodiation schematics of NPRP@RGO as anode for SIBs. NPRP@RGO can not only accommodate the volume changes efficiently but also ensure the rapid electron transport and ion diffusion.

CONCLUSIONS In summary, we have demonstrated a scalable synthesis route for NPRP@RGO by boiling. Moreover, NPRP@RGO as anode for SIBs exhibits a superhigh capacity (1249.7 mAh gcomposite−1 after 150 cycles at 173.26 mA gcomposite−1), superior rate capability (656.9 mAh gcomposite−1 at 3465.28 mA

contact area with the electrolyte, and shorten the ion transport distance. Additionally, the highly conductive network based on RGO can ensure the efficient and rapid electron and ion transport, which is illustrated by electrochemical impedance spectroscopy (EIS). As shown in Figure S14, it is composed of E

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ACS Nano gcomposite−1), and ultralong cycle life at 5.12 A gRP−1 for RPbased electrodes (775.3 mAh gRP−1 after 1500 cycles). The excellent electrochemical performance can be attributed to volume accommodation by the nanoporous structure and high electronic conductive network built on RGO sheets. The successful synthesis of NPRP@RGO provides a synthesis method for nanoporous structures, paving the way for enhancing the performance of SIBs and other electrochemical energy storage systems.

RP@RGO, and RGO as anodes for SIBs; Nyquist plots of NPRP@RGO and commercial RP electrodes; TEM images of NPRP@RGO electrodes after 1500 cycles (PDF)

AUTHOR INFORMATION Corresponding Authors

*E-mail (X. Bian): [email protected]. *E-mail (J. Feng): [email protected].

EXPERIMENTAL SECTION

ORCID

Materials Synthesis. Phosphorus triiodide (99%, Sigma-Aldrich), CTAB (99%, Aladdin), anhydrous ethylene glycol (99%, Aladdin), ethanol (99.7%, Sinopharm), iodobenzene (98%, Alfa Aesar), commercial red phosphorus powder (98.5%, Aladdin), graphene oxide (XFNANO), and hydrazine hydrate (N2H4·H2O) (80%, Aladdin) were used in sample preparation. The NPRP@RGO was prepared with a typical redox reaction. Beforehand, a solution of PI3 in iodobenzene (1.6 M) and a solution of additive (GO (10 mg/mL)) and CTAB (0.018 M) in ethylene glycol should be prepared. The PI3 iodobenzene solution was injected into the GO and CTAB ethylene glycol solution with intense magnetic stirring for 10 min. After the reaction, N2H4·H2O was added to the solution (mass ratio, N2H4· H2O:GO = 2:1) in a water bath at 95 °C for 0.5 h. After 4000 rpm centrifugation, the precipitate was heated in a vacuum drying chamber at 200 °C for 6 h. Microstructural Characterization. The microstructure of the prepared sample was characterized by scanning emission microscope (SEM, Hitachi SU-70) and high-resolution transmission electron microscope (JEOL JEM-2100). The structure and composition were characterized using XRD (Rigaku Dmax-rc diffractometer), a LabRAM HR800 spectrometer for Raman spectra, and an ESCALAB 250 for XPS (ThermoFisher Scientific). TGA was measured from 30 to 600 °C at a rate of 10 °C/min (Netzsch, STA 449F3-QMS403C). BET surface area and pore distribution plots were measured by a Micromeritics ASAP 2020. Electrochemical Measurements. The as-prepared active material was mixed with Super P (from lzy Battery Sales Department, China) and a carboxymethyl cellulose binder (Aladdin) (70:15:15 in weight) in deionized water to form a homogeneous slurry. Then it was painted on a copper foil (lzy Battery Sales Department, China) and then dried at 80 °C in a vacuum drying chamber for 10 h to form the electrodes. The areal loading mass of the active materials (RP) is about 0.3−0.4 mg cm−2. A Na sheet (homemade) was used as the counter electrode, while Celgard 2400 was used as the separator. A mixture of 1 M NaClO4 in propylene carbonate with 5% fluoroethylene carbonate additive was used as the electrolyte. All the cells (CR2016 coin-type) (lzy Battery Sales Department, China) were assembled in a glovebox with an oxygen/water content lower than 1 ppm and tested at room temperature. CV measurements were carried out with coin cells at a scan rate of 0.1 mV s−1 between 0.01 and 2.0 V (vs Na+/Na) using a CHI 660E electrochemical workstation (Shanghai, China). Galvanostatic discharge/charge cycles were conducted between 0.01 and 2.0 V (vs Na+/Na) on a NewareCT-3008 test system (Shenzhen, China). EIS was also performed on a CHI 660E electrochemical workstation with a frequency of 100 kHz to 0.01 Hz.

Shuai Liu: 0000-0002-8862-2116 Hui Xu: 0000-0003-3166-9770 Xiufang Bian: 0000-0001-6680-3891 Jinkui Feng: 0000-0002-5683-849X Yinghui Yang: 0000-0002-0849-7096 Chao Yuan: 0000-0001-7323-085X Yongling An: 0000-0002-2666-3051 Lijie Ci: 0000-0002-1759-105X Notes

The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (Grant No. 51571130), the Key Research Plan of Shandong Province (2015GGE27286), and The Young Scholars Program of Shandong University (2016WLJH03). REFERENCES (1) Tarascon, J. M.; Armand, M. Issues and Challenges Facing Rechargeable Lithium Batteries. Nature 2001, 414, 359. (2) Zhong, Y. R.; Yang, M.; Zhou, X. L.; Luo, Y. T.; Wei, J. P.; Zhou, Z. Orderly Packed Anodes for High-Power Lithium-Ion Batteries with Super-Long Cycle Life: Rational Design of MnCO3/Large-Area Graphene Composites. Adv. Mater. 2015, 27, 806−812. (3) Song, J.; Yu, Z.; Gordin, M. L.; Hu, S.; Yi, R.; Tang, D.; Walter, T.; Regula, M.; Choi, D.; Li, X.; Manivannan, A.; Wang, D. Chemically Bonded Phosphorus/Graphene Hybrid as A High Performance Anode for Sodium-Ion Batteries. Nano Lett. 2014, 14, 6329−6335. (4) Goodenough, J. B.; Park, K. S. The Li-Ion Rechargeable Battery: A Perspective. J. Am. Chem. Soc. 2013, 135, 1167−1176. (5) Qu, B. H.; Ma, C. Z.; Ji, G.; Xu, C. H.; Xu, J.; Meng, Y. S.; Wang, T. H.; Lee, J. Y. Layered SnS2-Reduced Graphene Oxide Composite A High-Capacity, High-Rate, and Long-Cycle Life Sodium-Ion Battery Anode Material. Adv. Mater. 2014, 26, 3854−3859. (6) Yabuuchi, N.; Kubota, K.; Dahbi, M.; Komaba, S. Research Development on Sodium-Ion Batteries. Chem. Rev. 2014, 114, 11636−11682. (7) Yabuuchi, N.; Komaba, S. Recent Research Progress on Ironand Manganese-Based Positive Electrode Materials for Rechargeable Sodium Batteries. Sci. Technol. Adv. Mater. 2014, 15, 043501. (8) Liu, S.; Feng, J.; Bian, X.; Liu, J.; Xu, H.; An, Y. A Controlled Red Phosphorus@Ni-P Core@Shell Nanostructure as An Ultralong Cycle-Life and Superior High-Rate Anode for Sodium-Ion Batteries. Energy Environ. Sci. 2017, 10, 1222−1233. (9) Liu, S.; Feng, J.; Bian, X.; Liu, J.; Xu, H. The MorphologyControlled Synthesis of A Nanoporous-Antimony Anode for HighPerformance Sodium-Ion Batteries. Energy Environ. Sci. 2016, 9, 1229−1236. (10) Li, W.; Yang, Z.; Li, M.; Jiang, Y.; Wei, X.; Zhong, X.; Gu, L.; Yu, Y. Amorphous Red Phosphorus Embedded in Highly Ordered Mesoporous Carbon with Superior Lithium and Sodium Storage Capacity. Nano Lett. 2016, 16, 1546−1553.

ASSOCIATED CONTENT S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsnano.8b04075. Photographs of the synthesis process for NPRP@RGO; TEM images of NPRP@RGO at different synthesis stages and RP@RGO without boiling; SEM images of GO and RGO used in this study; BET analysis and TGA of NPRP@RGO; cyclic performance of NPRP@RGO, F

DOI: 10.1021/acsnano.8b04075 ACS Nano XXXX, XXX, XXX−XXX

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DOI: 10.1021/acsnano.8b04075 ACS Nano XXXX, XXX, XXX−XXX